WO2006012670A1

WO2006012670A1 - Habitat structure for aquatic animals

Info

Publication number: WO2006012670A1
Application number: PCT/AU2005/000573
Authority: WO
Inventors: John Scheirs
Original assignee: Tristano Pty Ltd
Priority date: 2004-08-06
Filing date: 2005-04-22
Publication date: 2006-02-09

Abstract

A habitat structure (10) for an aquatic animal, the structure (10) being defined by one or more walls (40) which extend wholly or partially around an inner cavity, wherein the structure (10) has at least one opening (60) into the inner cavity and wherein the structure (10) is made from a biodegradable polymer.

Description

HABITAT STRUCTURE FOR AQUATIC ANIMALS

Field of the Invention

The present invention relates generally to a habitat structure to be used in an aquatic environment by an aquatic animal. The structure provides an environment within, on and/or around which the aquatic animal may reside, breed and/or be reared.

Background of the Invention

Wild stocks of many commercially important aquatic animals such as fish and shellfish have diminished considerably over the last few decades. The ever-increasing demand for these animals as a source of food for humans has clearly been a significant contributing factor to their population decline. However, the loss of natural habitat for aquatic animals in natural water bodies such as oceans, rivers and lakes has exacerbated the problem. In particular, breeding and juvenile rearing grounds such as grass beds and reef structures for the animals are increasingly being degraded through overuse by humans. These sensitive ecosystems are not only being damaged by overuse, but are also suffering from storm damage and pollution.

Attempts have been made to address the problems of overfishing and the loss of natural habitat by providing artificial environments within which the aquatic animals can reside, breed and/or be reared.

One approach at providing such an artificial environment has been to breed and rear the animals using a variety of aquaculture techniques. A common aquaculture technique has been to breed and rear to maturity certain commercial species of aquatic animals in purpose built tanks as part of an aquatic farm. However, such farms are generally very labour intensive and it is often difficult to control and maintain adequate water quality within which to breed and rear the animals.

An increasingly popular alternative to the above technique has been to utilise the tank based aquatic farms for the sole purpose of breeding and producing juvenile aquatic animals. The juvenile animals are then transferred to a natural water system such as the ocean where the animals are matured in a controlled environment and subsequently harvested. This technique has the advantage of being able to utilise the natural water system to control and maintain the quality of the water within which the animals reach maturity. The controlled environment in which the animals are matured is typically provided in the form of an enclosure or support structure.

For example, scallop (phylum: Mollusca, class: Bivalvia, order: Ostreoida, families: Pectinidae, Entoliidae, Propeamussiidae) aquaculture can be effected by breeding the animals in a hatchery, or through the capture of wild seed. The animals may be reared in a tank based aquatic farm until they are of sufficient size for release to a bottom habitat in a natural water system, or alternatively they can be suspended in surface waters of a natural water system during the grow-out stage, for example by using a technique called ear- hanging. Ear-hanging of scallops has been practiced for a number of years and is performed by drilling a small hole in the base of the shell from which the scallop is fastened to a buoyed line. Similar suspension techniques involving suspended cages enclosing the scallops, or suspended ropes with the shell of juvenile scallops cemented thereon, are also known.

Bottom culture of the animals is no different to what occurs in the wild and requires many square kilometres of suitable bottom habitat. This technique of scallop aquaculture is often not feasible because security of the stock is difficult to enforce, and suitable bottom habitat of sufficient area for commercial farming is often difficult to find.

The advantages of suspending juvenile shellfish such as scallops in natural waterways for the final grow-out period has been recognised for some time. By this technique enhanced growth rates and lower mortality rates are generally observed. The suspended shellfish are typically positioned within a few metres of the surface where they can receive better nutrition and be less subject to attack by parasites and other disease-causing organisms compared with bottom culture.

Suspension rearing techniques are advantageously suited to many shellfish, such as most bi-valves and sea urchins (phylum Echinodermata, class Echinoidea, order Cidaroidea). However, harvesting the animals from the enclosure or support structures, and the maintenance of these structures, can be particularly labour intensive. Where labour costs are high, such a farming technique can be rendered uneconomic.

As a further example, gastropods such as abalone (phylum Mollusca, class Gastropoda, family Haliotidae) can also be raised to a juvenile size in a tank based aquatic farm and transferred to the ocean to be matured in a controlled environment and subsequently harvested. Given that gastropods are generally not particularly mobile, the nature of the controlled environment in this case is generally provided in the form of a surface upon which the gastropods can cling as they forage for food. Numerous structures have been developed to facilitate the growth of juvenile abalone in this manner. US 4,320,717 discloses a structure for growing sea life which uses multiple habitat modules vertically stacked on a support which rests on the sea floor. The disclosure appears to relate to an undersea captive habitat for growing abalone in segregated modules.

US 6,044,798 also discloses a modular structure for cultivating marine animals caged within rearing units submerged in a body of water. Each rearing unit comprises a perforated wall container suspended from a row member by a suspension assembly so as to hang above the water floor. The modular structure is said to be particularly useful for growing juvenile abalone in captivity. However, as discussed above in relation to the rearing of bi-valves, harvesting the gastropods from such structures, and the maintenance of the structures, can be particularly labour intensive and has the potential to render the farming technique uneconomic.

An alternative gastropod rearing technique involves seeding the juvenile gastropods at a location in a natural water body which has suitable surface structure that provides sites upon which the gastropods can cling and forage for food. Such a location may be a natural rocky outcrop or even artificial surfaces provided on an otherwise barren water floor. In this case, the juvenile gastropods would typically be seeded by dropping the animals overboard from a boat positioned above the desired location. This approach has the advantage of not requiring complicated structures which require maintenance, with the gastropods being harvested in the conventional manner using a diver. However, the technique is subject to the disadvantage of a high mortality rate during seeding or deployment of the juvenile gastropods. In particular, the gastropods are often devoured by predatory animals before they can locate themselves in a secure position.

Another approach at providing artificial environments within which aquatic animals can reside, breed and/or be reared has been to provide artificial reef structures to areas in natural water bodies that are devoid of natural reef structures or where the reef structures have been damaged.

Offshore artificial reefs have long been used to attract aquatic life to a particular area by providing shelter, protection and a surface for the aquatic life to utilise. As various encrusting organisms such as corals, barnacles, sponges cover the artificial reef, small animals take up residence. As these animals become abundant, larger animals are attracted and feed upon the smaller animals, yet larger animals are then attracted and so on until a complete reef ecosystem is created. At that point, the artificial reef can be considered to be functioning as a natural reef.

Through their ability to promote the growth of aquatic life, artificial reefs may be strategically located to provide enhanced fishing grounds for commercial fisheries or sports anglers, to provide scuba divers with new nature observation posts, and to generally increase the population of commercially important marine animals.

Artificial reefs have been traditionally made from rock, concrete or steel, usually in the form of surplus or scrap materials such as disused automobiles and ships, whitegoods and demolition materials. However, the manner in which artificial reefs have traditionally been made is increasingly being considered by governments as a form of dumping, and the regulatory requirements as to what may be used to construct an artificial reef is becoming increasingly stringent. Furthermore, conventional artificial reef materials are also generally very heavy, making their transport and installation difficult and costly.

In the light of the problems mentioned above associated with providing artificial environments within, on and/or around which aquatic animals may reside, breed and/or be reared, there remains an opportunity to develop a habitat structure for aquatic animals which may be of a simple design, can be used in a variety of applications, can be cost effective, and importantly, can present minimal if any detrimental environmental impact on the surrounding aquatic environment.

Summary of the Invention

The present invention provides the use of a biodegradable polymer in an aquatic environment, wherein the biodegradable polymer is provided in the form of a habitat structure for an aquatic animal.

The invention also provides a habitat structure for an aquatic animal, the structure being defined by one or more walls which extend wholly or partially around an inner cavity, wherein the structure has at least one opening into the inner cavity, and wherein the structure is made from a biodegradable polymer.

In a preferred embodiment of the invention, the structure is used in an aquatic environment to promote growth of aquatic animals within, on and/or around the structure, wherein the at least one opening allows for the aquatic animals to enter into and exit from the inner cavity.

In a further preferred embodiment of the invention, the structure is used for deploying an aquatic animal into an aquatic environment, wherein the inner cavity provides a chamber in which the aquatic animal can reside prior to deployment, and wherein the at least one opening allows for the aquatic animal to exit from the inner cavity after deployment.

In another preferred embodiment of the invention, the structure is used for rearing an aquatic animal in an aquatic environment, wherein the inner cavity provides a chamber in which the aquatic animal can be reared, and wherein the at least one opening is of a dimension which (i) allows nutrients for the aquatic animal to enter into the inner cavity, (ii) allows waste products from the aquatic animal to exit from the inner cavity, and (iii) prevents the aquatic animal from exiting the inner cavity.

It has now been found that a habitat structure made from a biodegradable polymer can be used for various applications in an aquatic environment to provide a site within, on and/or around which aquatic animals may reside, breed and/or be reared. The structure provides for numerous advantages in that it can be light weight and therefore readily transported to its particular application site, it can be provided in an array of shapes and sizes to suit a variety of applications, it can be provided in a modular form if required, it can be manufactured in a relatively inexpensive manner, it is generally assimilated in the aquatic environment more readily than conventional habitat structures, and, by virtue of it being biodegradable, environmental concerns are alleviated.

Conventional habitat structures have to date been made from materials that are renowned for their durability in an aquatic environment. For example, the structures designed to operate in the aforementioned juvenile scallop and abalone grow-out techniques are made from durable materials such as non-biodegradable plastics and metal in order to prolong the longevity of the equipment. However, by designing the structures with longevity in mind, the materials used for the construction will often be expensive, and owing to the expense of the equipment operators will spend considerable time and effort maintaining it.

Similarly, the mind set in providing artificial reef structures has to date been to use materials having considerable durability in an aquatic environment. In this case, the materials used are often so foreign to the aquatic environment (eg. car bodies, car tyres etc.) that the durability of the materials is in fact required in order to provide sufficient time for the aquatic animals to assimilate with it.

The present invention provides a paradigm shift in the manner in which habitat structures for aquatic animals are designed. In particular, by being made from a biodegradable polymer the habitat structures in accordance with the invention are designed to breakdown into relatively inert materials such as carbon dioxide and water, thereby advantageously leaving behind no physical form of the structure that was initially in place. For example, in the case of rearing juvenile bi-valves such as scallops using the aforementioned suspension technique, the structure in accordance with the invention may be designed such that the timing of its breakdown coincides with the maturing of the scallops. In this case, the scallops are released to the water floor to be harvested using conventional bottom harvesting techniques. This technique advantageously requires no maintenance of the structure, harvesting can be performed using conventional techniques, and the structures present minimal if any detrimental environmental impact on the surrounding aquatic environment.

With regard to rearing juvenile gastropods such as abalone to maturity, the structure in accordance with the invention can advantageously be used as a deployment device for deploying the animals to a site in an aquatic environment having suitable surfaces upon which the animals can cling and forage for food. In this case, the structures containing the animals can be simply dropped overboard from a boat positioned above a suitable site where the animals can be left to mature. The structures provide a temporary protective habitat for the animals during the transition from the surface to the water floor, and also for a period of time in which the animals acclimatise to their new surroundings. The animals will instinctively, under the cover of darkness, exit from the deployment structure to seek out a secure location where they can cling and forage for food. The structure therefore considerably reduces the mortality rate during seeding of such animals, and when vacated simply breaks down resulting in substantially no negative environmental impact to the surrounding aquatic environment.

Structures in accordance with the invention have been found to be particularly compatible with aquatic life forms within the aquatic environment in which they are used. In particular, as an artificial reef in a marine environment, the structures have been found to promote aquatic life more rapidly than some foreign materials used for conventional artificial reefs. The structures can advantageously be quite rapidly encrusted with organisms such as corals, barnacles, sponges and seaweeds, to thereby afford a permanent natural reef structure when the internal biodegradable structure ultimately breaks down. In those cases where the structure breaks down before sufficient encrustation has occurred to form a permanent natural reef structure, the structure nevertheless provides a habitat for sufficient time in order to promote aquatic life. Due to the limited environmental impact of the structures, they can in this case be simply replaced with new structures at an appropriate time to maintain the environment for the aquatic animals to reside, breed and/or be reared. Brief Description of the Drawings

Preferred embodiments of the invention will now be illustrated by way of example only with reference to the accompanying drawings.

Figure 1 shows a habitat structure in accordance with a preferred embodiment of the invention in the form of an artificial reef for use in an aquatic environment to promote growth of aquatic animals within, on and/or around the structure.

Figure 2 shows a habitat structure in accordance with a preferred embodiment of the invention in the form of a deployment structure for seeding aquatic animals.

Figure 3 shows a habitat structure in accordance with a preferred embodiment of the invention in the form of a mesh envelope for rearing aquatic animals.

Detailed Description of Aspects of the Invention

The present invention provides a habitat structure for an aquatic animal. By an "aquatic animal" it is meant an animal which respires predominantly under water. The phrase is intended to include, but not be limited to, gastropods such as abalone, bi-valves such as scallop, mussel, oyster and clam, fish, crustaceans such as lobster, crab and prawn, and echinoidea such as sea urchins. The habitat structure can advantageously be used to assist in the breeding and/or rearing of most commercially important aquatic animals. The nature of the aquatic animals extend to both fresh and sea water varieties, and hence the structures can be used in both a marine and a fresh water environment.

By providing a "habitat structure" for the aquatic animals, it is meant that the structure provides a site within, on and/or around which the aquatic animals may reside, breed and/or be reared. Depending on the application of the structure, the habitation of the aquatic animals may be temporary or more permanent. The structures can be advantageously designed to suit the habitat requirements of various aquatic animals, and as such will generally also be designed to afford protection to the target animal from predatory animals that commonly prey on them. The "inner cavity" of the structure is in effect is a hollow or vacant space within the structure where an aquatic animal may reside. The size of the cavity may vary depending upon the intended application of the structure, one or more cavities may be present in the structure, and the cavities may be of a size which can accommodate one or more of the aquatic animals.

The structure is defined by one or more walls which extend wholly or partially around the inner cavity. By extending "wholly" around the inner cavity it is meant that the one or more walls extends substantially 360° around the inner cavity. For example, a hollow sphere may be considered to have a single wall extending wholly around the inner cavity, or an elongate hollow tube profile open at both ends, depending upon the cross-sectional shape thereof and the manner in which it is manufactured, may be considered to have one wall extending wholly around the inner cavity. By this arrangement, the inner cavity may be considered to be substantially defined by the one or more walls of the structure.

By the one or more walls extending "partially" around the inner cavity it is meant that the wall(s) extend less than 360° around the inner cavity. For example, an elongate U-shaped profile may be considered to have one wall which extends partially around the inner cavity.

Where the structure is defined by one or more walls which extend partially around the inner cavity, when in use the portion of the cavity around which the wall(s) do not extend may be covered by a separate surface in order to form an enclosed cavity. For example, the portion of the cavity around which the wall(s) do not extend in the aforementioned U- shaped profile may be positioned such that it is against the water floor, or mounted such that it is against an inclined surface such as underwater rock face. By this arrangement, the inner cavity may be considered to be defined by the one or more walls of the structure in conjunction with another surface.

The shape, size and number of walls which define the structure will vary depending upon the intended application of the structure, and will be discussed in more detail below.

The structure has at least one opening into the inner cavity. The at least one opening may be provided by virtue of the one or more walls only extending partially around the inner cavity. Alternatively, where the one or more walls extend wholly around the inner cavity, the nature of the shape of the structure may inherently provide for the at least one openings into the inner cavity. For example, a hollow tube profile open at both ends may be considered to have one wall extending wholly around the inner cavity and two openings into the inner cavity.

The at least one opening can also be provided in the one or more walls which extend wholly or partially around the inner cavity.

By providing an opening into the cavity an aquatic animal outside of the structure can enter the cavity through the opening, or an animal within the cavity can exit the structure through the opening. The opening will also provide means by which water can flow into and out of the cavity, potentially bringing with it nutrients for the aquatic animal. Exiting water can also take with it waste products produced by the animal.

The structure may have a plurality of openings into the inner cavity. The one or more walls may also have a plurality of openings therethrough which lead into the inner cavity, and for certain applications the wall(s) may be provided in the form of a mesh or net type arrangement. The wall(s) of the structure are preferably self-supporting or rigid.

The size of the at least one opening will vary depending upon the intended application of the structure. For example, in some applications it may be desirable to allow the aquatic animal to enter and exit the inner cavity at will, whereas in other applications it may be desirable to prevent the aquatic animal from exiting the inner cavity while still allowing nutrients to enter into the cavity and waste products from the aquatic animal to exit from the inner cavity. In the latter case, a mesh or net type wall structure can be particularly effective. Where a plurality of openings are provided into the cavity, the openings do not necessarily need to be of the same size or shape.

The one or more walls which extend wholly or partially around the inner cavity will vary in thickness depending upon the intended application of the structure. However, a particular advantage of the structure in accordance with the invention is that it can be manufactured in a relatively light weight form. Being made from a polymer material, the structure will clearly be lighter than other similar structures made from materials such as concrete or steel. The weight of the structures can be further reduced by manufacturing relatively thin-walled structures. Accordingly, the thickness of the one or more walls will typically be in the range of 1 to 10 mm.

In accordance with the invention, the structure is made from a biodegradable polymer. By "biodegradable" it is meant that the polymer will break down in water to form water and carbon dioxide as degradation products. The mechanism of biodegradation will typically be by hydrolysis in the first instance, followed by a biological process. From a practical point of view, the break down of the polymer will typically first result in the structure loosing its physical and mechanical properties resulting in its disintegration (ie fragmentation), and then ultimate biodegradation of the polymer. The time frame within which break down of the polymer affects the integrity of the structure (ie catastrophic loss of its physical and mechanical properties) will vary depending upon its intended application, but will generally range from about 1 week to about 36 months. Once the structure has disintegrated, ultimate biodegradation of the polymer will generally take from about 4 to 10 months.

Suitable biodegradable polymers include, but are not limited to, aliphatic or aliphatic-co- aromatic polyesters such as poly(hydroxy butyrate) (PHB), poly(hydroxy valerate) (PHV), poly(lactic acid) (PLA), poly(butylene succinate) (PBS), poly(butylene succinate/adipate) (PBSA), polyester carbonate or poly(butylene succinate/carbonate) (PEC), poly(ethylene succinate) (PES), poly(butylene adipate/terephthalate) (PBAT), poly(tetramethylene adipate/terephthalate) (PTMAT), cellulose acetate, cellulose acetate/butyrate, polybutylene adipate (PBA), and polylactic acid (PLA), polycapralactone, polyvinyl alcohol, starch materials such as corn starch, potato starch, tapioca starch, and high-amylose starch in a gelatinous or thermoplastic form, or combinations thereof.

Particularly preferred aliphatic-co-aromatic polyester resins are sold under trade name Ecoflex® by BASF, and Mater-bi® by Novamont. Ecoflex® is a statistical aliphatic- aromatic copolyester based on 1 ,4-butanediol and the dicarbonic acids, adipic acid and terephthalic acid and is strictly known as poly(tetramethylene adipate-co-terephthalate). Mater-bi® is a proprietary polyester resin which is believed to have an aliphatic-co- aromatic polyester composition. A preferred grade of a Mater-bi® resin is Mater-bi® YIOlU.

The aliphatic-co-aromatic polyester resins are preferably synthesised from butanediol, adipic acid and terephthalic acid and contain approximately 30 to 55 mol% terephthalic acid based on the total mol% of acid.

A particularly preferred aliphatic polyester resin is sold under the trade name Bionelle® by Showa Highpolymer Co., Ltd., Tokyo, Japan. Bionelle® is a poly(butylene succinate/adipate) based on the ester of succinic acid/adipic acid and 1,4-butanediol. Preferred grades of Bionelle® resin are sold commercially as BIONELLE 1000 and BIONELLE 3000 series resin.

Blending the thermoplastic or gelatinous starch materials with the aliphatic or aliphatic-co- aromatic polyesters can increase biodegradability and reduce cost. The ratio of starch to polyester is balanced to achieve a favourable compromise between moldability, cost, mechanical properties, water resistance and the rate of biodegradation. Typically the ratio of starch material to polyester ranges from about 5:95 to about 70:30 weight percent based on the total mass of the structure.

The biodegradable polymer may include a biodegradable fibre in order to provide reinforcement to the structure. The biodegradable fibre is preferably a natural fibre such as coconut, elephant grass, straw, cotton, flax, jute, sisal or bamboo fibre, used alone or in combination. The fibres used will typically have a length of about 1 mm to about 4 mm and a diameter of about 80 μm to about 600 μm.

The fibres may be present in the biodegradable polymer in an amount ranging from 0 to about 50 weight percent. Preferably, the biodegradable polymer comprises 5 to 30 weight percent, more preferably 10 to 20 weight percent of the fibres.

The biodegradable fibres used are also preferably hydrophilic, or in other words capable of absorbing or being swollen with water. For convenience this hydrophilic property of the fibres will hereinafter be referred to as "water- wicking". It has been found that by combining water-wicking biodegradable fibres in the biodegradable polymer, the disintegration/biodegradation time of the structures can be advantageously tailored to suit a variety of different applications. Without wishing to be limited by theory, it is believed that structures made from a biodegradable polymer including the water-wicking fibres present surfaces with entrapped fibres protruding therefrom. Through capillary action, these fibres can draw water into the polymer matrix of the wall to thereby accelerate the degradation of the structure. By varying the amount of water-wicking fibre in the biodegradable polymer, and the thickness of the wall, it has been found that the time taken for degradation of the structure to occur in an aquatic environment can be tailored in a particularly effective manner.

In order to attain consistent degradation times, and also consistent physical and mechanical properties of the structure, the fibres are preferably dispersed substantially uniformly throughout the biodegradable polymer matrix.

Other factors that affect the rate of disintegration/biodegradation of the structures include the composition of the polymer, the temperature of the aquatic environment within which it is located and the thickness of the wall(s) which forms the structure. In general, the rate of biodegradation has been found to be proportional with the square of the wall thickness of the structure. Without wishing to be limited by theory, it is also believed that the rate of disintegration/biodegradation increases substantially linearly with weight percent of fibre present in the structures.

The biodegradable polymer may also include filler materials. In this case, the filler materials are preferably biodegradable, or of a type that would be considered inert from an environmental impact point of view. Filler materials include, but are not limited to, starch materials such as corn starch, potato starch, tapioca starch, high-amylose starch in particulate form, calcium based mineral fillers such as calcium carbonate, calcium hydroxyapatite, aragonite such as crushed oyster shells, or combinations thereof.

Use of the aforementioned calcium based mineral fillers in the structure is believed to be particularly advantageous in that such materials may be extracted from the structure and metabolised by numerous aquatic organisms. The calcium content of the structures therefore attracts certain aquatic life forms and consequently assists in the assimilation of the structure within the aquatic environment.

Filler materials may be present in the biodegradable polymer in an amount ranging from 0 to about 50 weight percent. Preferably, the biodegradable polymer comprises 5 to 30 weight percent, more preferably 10 to 20 weight percent of filler.

The structure in accordance with the invention can be advantageously manufactured using conventional polymer processing techniques known in the art. Suitable polymer processing techniques include, but are not limited to, extrusion, roto-moulding, injection moulding thermoforming and vacuum forming. Where the structures are made up from more than one structural panel/wall, the panels may be connected to each other by any suitable means such as ultrasonic welding, adhesive means, binding etc. The panels can also be advantageously formed with interlocking means to enable them to be readily connected to each other. For example, snap-lock or complementary engaging threaded portions may be provided on the panels. By such techniques, the structure can be formed into a diverse array of shapes and sizes. For example, the biodegradable polymer may be extruded to provide for a hollow tubular structure, or flat thin-walled panels may be prepared by an injection moulding technique to be subsequently assembled so as to provide for a structure with one or more walls that extend wholly or partially around an inner cavity.

In some applications, it may be desirable to promote growth of coralline algae upon the surfaces of the structure. In this case, it has been found that the structure can be coated with coralline algae spores before it is installed in its intended application, to thereby accelerate coralline encrustation. Inoculation of the structures with coralline algae spores is discussed in more detail below.

In a preferred embodiment of the invention, the habitat structure is used in an aquatic environment for promoting the growth of aquatic animals within, on and/or around the structure. For convenience, a structure of this type will hereinafter be referred to as an "artificial reef structure". The artificial reef structure may be provided in a diverse array of geometric forms. For example, the structure may be in the form of a hollow spherical, pyramidal, hexagonal, octagonal, or cuboid shape with at least one opening into the inner cavity. These individual structures can be manufactured such that they can interlock with each other to enable the construction of extensive and complex expanded structures. The individual artificial reef structure shapes referred to above will generally be constructed in their own right from one or more wall panels. For example, a cuboid type structure might be constructed from six separate interlocking wall panels, or a pyramidal shaped structure might be constructed from five separate interlocking wall panels. Alternatively, the cuboid and pyramidal structures may be constructed from 5 and 4 interlocking panels, respectively, with a separate surface being used take the place of the sixth and fifth walls, respectively.

As an artificial reef structure, the habitat structure in accordance with the invention preferably has a wall thickness of from about 2 mm to about 10 mm, more preferably from about 2 mm to about 8 mm, most preferably from about 2 mm to about 4 mm.

The artificial reef structures will be generally designed to maximise both internal and external surface areas, and the inner cavity of the structure might also be provided with one or more inner walls, with the inner walls preferably having one or more openings therein. For example, a structure having a cuboid shape may be provided with a series of perforated internal walls to thereby form a segregated inner cavity.

In order to provide sufficient water circulation through the structure, and to provide entry points into and exit points out of the inner cavity for multiple aquatic animals, the structure is preferably provided with a plurality of openings into the inner cavity, and also in the one or more inner walls if present.

The artificial reef structure may be of a lower density than the body of water in which it is to be installed. In this case, the structure can be weighted or tethered in order to position it in the desired location. For example, if the structure were to be located on the water floor, it can be provided with ballast such as a concrete base. In this case, the structure could be transported to the desired location by boat and dropped overboard where it would come to rest on the water floor in an upright position. Although an artificial reef structure comprising concrete ballast will inherently have a non-biodegradable component associated with it, the overall structure nevertheless provides for significantly less non¬ biodegradable materials than conventional artificial reef structures.

The artificial reef structures that are intended to reside on the water floor are preferably designed such that they extend to about one metre from the water floor. Aquatic animal productivity in this benthic zone is typically limited by the amount of solid surface area available for encrustation by aquatic organisms and flora. Accordingly, the structures can be particularly effective at promoting aquatic life when located at sites where the water floor comprises loose sand or mud. By providing the structure with a height extending about 1 metre from the water floor, animals that are not adapted to live on an unstable sand or mud surfaces can colonise the solid surface of the structure at a height from the water floor that best suits their habitat needs.

The artificial reef structures are preferably deployed in locations on the water floor where prevailing currents are rich in drift seaweed. Drift seaweed is a main source of food for many aquatic animals.

By virtue of being made from a biodegradable polymer, the artificial reef structures will inevitably break down. Preferably, the artificial reef structures are manufactured such that they maintain their structural integrity for about 6 to about 36 months, more preferably for about 12 to about 36 months, within the aquatic environment in which they are located.

Upon being located in the desired aquatic environment, the artificial reef structures will serve as a substrate upon which a diverse array of marine organism may colonise. In particular, it has been found that the structures in accordance with the invention are particularly compatible within the aquatic environment and they become encrusted quite rapidly with life forms such as coralline algae, polyps, photosynthetic plants and microfauna/flora. Through such encrustation, the biodegradable reef structure can serve as a temporary scaffold upon which a more permanent natural reef structure can form. Accordingly, when the artificial reef structure ultimately breaks down the natural reef structure remains in its place. In this case, where a ballast has been used to weight the artificial reef structure, the ballast can advantageously serve as an anchor point for the natural reef structure.

A preferred form of encrustation results from coralline algae which secrete a rigid calcareous skeleton over the artificial reef structure. Coralline algae can lay down their calcareous secretion at a rate of about 1 to 2 mm per year, and over a period of about 2 to 3 years these calcified layers will be sufficient to provide the encrusted structure with its own structural integrity absent that provided by the original artificial reef structure. In order to accelerate encrustation by coralline algae, it is preferable to coat the artificial reef structure with coralline algae spores prior to its installation in the desired aquatic environment. In this case, the coated structures are preferably installed in late spring in order to take advantage of the superior growing conditions for the algae over the summer months.

Through use of this coating technique it has been found that a coherent cover of coralline algae can be formed over the artificial reef structure in as little as two weeks. As a result of this encrustation, herbivorous aquatic animals such as butterfly fish, sea urchins, sea cucumbers, brittle stars and numerous species of molluscs are attracted to the structure in order to feed on the algae. Under these conditions, crustaceans such as amphipods, decapods and copepods, which multiply rapidly, are also enticed to the structure providing a valuable food source for fish, corals, sponges and other filter feeders, the net result of which promotes the formation of a new ecosystem.

Coating the artificial reef structures with coralline algae spores prior to installation can be achieved by submersing the structure, or components thereof, in water comprising coralline algae spores and subjecting the water to bright light in order to promote rapid growth of the spores on the surfaces of the structure. The coralline algae spores may be obtained by any suitable means. It has been found that an adequate source of the spores can be obtained by scrubbing a coralline rock with an abrasive pad in order to turn the coralline growth layer into dust. The coralline rock can then be scrubbed with a bristled brush in the water in order to release an adequate spore starter culture. Nutrients such as CaribSea™ aragonite (sold by CaribSea, Inc., Miami, Florida, USA), SeaChem™ organic reef calcium (sold by Seachem Laboratories, Inc, Covington, GA 30014 USA), and Coral Vital™ (sold by Marc Weiss Co., Ft. Lauderdale Florida 33312 USA) can be introduced in the water to accelerate coralline growth. Other additives such as trace elements and buffering solutions can also be added to the starter culture. The bright light can be provided by any light source, but it is preferable that fluorescent lights are used. The coating process will usually be performed over about 1 to 2 days.

Upon being coated with the coralline algae spores, the artificial reef structure, or components thereof, may be transported to the desired location for installation. During transport, the coated reef structure should be kept moist to ensure the coralline algae spores do not die.

Under circumstances where the artificial reef structure is installed in the desired location and its surfaces are not sufficiently encrusted to form a self supporting natural reef structure prior to the biodegradable polymer breaking down, a replacement artificial reef structure can simply be positioned in the same location at an appropriate time in order to maintain the habitat environment for the aquatic animals.

As an artificial reef, the structure in accordance with the invention preferably comprises a calcium based filler. The presence of this filler provides a particularly attractive surface for coralline algae to grow in that they can extract the calcium from the structure in order to convert it into the desirable calcareous secretion.

The filler and the biodegradable fibre content of the artificial reef structure will generally be in the range of about 2 to about 50 weight percent, based on the total weight of the structure.

Habitat structures for aquatic animals in accordance with the invention, when used an artificial reef, are preferably made from about 30 to about 70 weight percent of biodegradable polyester resin, about 30 to about 70 weight percent of gelatinous or thermoplastic starch, about 10 to about 30 weight percent of filler, and about 10 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure. The artificial reef structure is preferably fabricated by injection moulding wall elements and then assembling these elements by clipping then together to form a cuboid shape. The side wall panels can also be readily made by thermoforming and then assembled by ultrasonic welding.

As an artificial reef, the structure in accordance with the invention is preferably provided in the form of an elongated cuboid structure having a concrete base as shown in Figure 1. In particular, from Figure 1 the artificial reef structure (10) comprises an elongated cuboid structure (20) which has a vertical height of about one metre and is made from a biodegradable polymer, and a concrete base (30) is used as ballast. The structure is defined by four side walls (40), and a top wall (50). The side walls (40) and the top wall (50) extend partially around the inner cavity (not clearly visible) of the structure, and the concrete base (30) forms the remaining wall of the cuboid shape. Each of the four side walls (40) has a plurality of openings (60) therethrough which are of different shape and size, with each side wall (40) and the top wall (50) being manufactured as separate panels and connected to each other interlocking clips or ultrasonic welding to provide for the cuboid structure (20). The cuboid structure (20) is conveniently integrated with the concrete base (30) by having simply immersing the structure (20) in the concrete which forms the ballast prior to the concrete setting.

The artificial reef structure (10) has a series of internal walls (not visible from Figure 1) which are positioned substantially parallel with one side wall (40) and have substantially the same geometric features as the side walls (40).

The artificial reef structure can also be designed to provide for a plurality of recesses and/or a plurality of open sided compartments on its surface for habitation by sea urchins, shellfish and the like. Unlike concrete based artificial reef structures, those in accordance with the invention do not leach alkaline products and therefore present a much more amenable site for the aquatic animals to reside.

In another preferred embodiment of the invention, the habitat structure is used to deploy an aquatic animal into an aquatic environment. For convenience, a structure of this type will hereinafter be referred to as a " deployment structure". Conventional broadcast seeding of juvenile aquatic animals typically results in mortality rates as high as 30 percent due to predation. The primary function of the deployment structure of the invention is to provide a means for efficiently seeding aquatic animals to a suitable site in an aquatic environment. Through use of the deployment structures, seeding mortality rates can be reduced to less than 10 percent.

The deployment structure may be provided in a diverse array of geometric forms. Generally, the structure will be provided in the form of a hollow tube profile. In this case, the structure preferably has a square or circular profile to assist stacking of the structures during transport. It is particularly preferred that the structure has a substantially square profile to provide a flat surface upon which aquatic animals such as abalone may cling. The hollow tube profile may be made by a profile extrusion process or by connecting wall panels as previously described for the artificial reef structure.

The deployment structures containing the aquatic animals within the inner cavity can be simply dropped overboard from a boat positioned above a suitable site where the animals can be left to mature. In this case, the structures will generally be designed to provide a temporary protective habitat for the animals during the transition from the surface to the water floor, and also for a period of time in which the animals acclimatise to their new surroundings. The time frame that the deployment structures will typically function as a protective habitat for the animals will therefore be relatively short compared with the aforementioned artificial reef structures. Accordingly, the deployment structure will generally be manufactured to provide for a relatively fast rate of disintegration/biodegradation.

The deployment structures will generally be manufactured such that they maintain their structural integrity for about 1 week to about 6 weeks within the aquatic environment in which they are deployed. Such a relatively fast rate of degradation can be achieved by minimising the wall thickness of the structure and maximising the filler and/or the biodegradable fibre content of the structure.

The preferred wall thickness of the deployment structure will generally be in the range of about 1 to about 2 mm. The filler and the biodegradable fibre content of the deployment structure will generally be in the range of about 2 to about 50 weight percent, based on the total weight of the structure. Preferably, the deployment structures contain low levels or no filler.

In order to provide sufficient water circulation through the structure during use and to provide multiple entry points into and exit points out of the inner cavity, the structure will generally be provided with a plurality of openings leading into the inner cavity. The openings may be designed into the structure as part of a particular polymer processing technique employed, or alternatively, they may be generated after a given polymer processing technique, for example by drilling holes through the wall(s) of the structure. In the case where a technique such as drilling is used to form the openings in the structure, it will be important to ensure that the wall thickness of the structure provides for sufficient rigidity and mechanical strength to resist cracking or splitting.

Habitat structures for aquatic animals in accordance with the invention, when used a deployment structure, are preferably made from about 30 to about 50 weight percent of biodegradable polyester resin, about 30 to about 50 weight percent of gelatinous or thermoplastic starch, about 0 to about 30 weight percent of filler, and about 2 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure.

The shape and size of the deployment structures can be tailored to suit a particular aquatic animal that is to be deployed. For example, in the case of deploying juvenile abalone, the structure is preferably in the form of an elongate hollow tube having a square profile. The tube will generally be open at both ends and have a plurality of additional openings therein leading into the inner cavity. To charge the structures with abalone for deployment, the structures can be simply placed in a tank of water containing the juvenile abalone and the tank exposed to bright light. Abalone find bright light particularly unpleasant, and quite rapidly seek shelter and cling to the inner cavity surface of the structure. Once charged, the deployment structures can be transported to the desired location and the abalone seeded as required. The abalone will generally be seeded in relatively shallow waters that enable sunlight to penetrate to the water floor, that is, the so-called photic zones. A deployment structure for use in deploying juvenile abalone is shown in Figure 2. The deployment structure (10) is in the form of an elongate hollow tube having a square profile. The dimensions of the tube are typically in the range of about 15 to about 25 cm long, and about 15 to about 20 mm wide. The wall thickness of the tube is typically in the order of about 1 to 2 mm. In addition to having open ends (20), the tube has a plurality of openings (30) along its length leading into the inner cavity. The openings (30) shown are approximately 10 mm in diameter and are spaced along the tube length at intervals of approximately 6 to 8 cm. The openings (30) are sufficiently large enough to enable the juvenile abalone to enter into and exit from the inner cavity. Once charged, it has been found that the entry/exit points of the tube can become covered with one or more of the juvenile abalone and therefore reduce water flow through the structure. Under these circumstances, it can be useful to provide the structure with a plurality of smaller openings of about 3 mm in diameter (not shown) leading in to the inner cavity to promote water flow through the tube.

In another preferred embodiment of the invention, the habitat structure is used to rear an aquatic animal in an aquatic environment. For convenience, a structure of this type will hereinafter be referred to as a " rearing structure".

Generally, the wall(s) of the rearing structure will be in the form of a substantially rigid or self-supporting mesh or webbing. The mesh may be provided with a ribbed pattern to maximise its strength to weigh ratio. The mesh can be fashioned into a diverse array of geometric forms, but tubular mesh structures, modular tray mesh structures, or a flat hinged or envelope mesh structure has been found to being particularly suitable for most commercially important shellfish such as scallop, abalone, mussel, clam, pearl-oyster, edible-oyster and sea urchins. The mesh can be fashioned into the desired geometric form using techniques well known in the art, for example by using moulding or ultrasonic welding techniques or by using suitable binding or interlocking means to fasten relevant edges of the mesh.

In the case where the mesh is fashioned into a tubular structure, the tube will preferably have a diameter of from about 10 cm to about 50 cm, more preferably of about 20 cm, and preferably a length of from about 50 cm to about 200 cm, more preferably from about 100 cm to about 150 cm.

In the case where the mesh is fashioned into a flat hinged or envelope structure, the structure is typically about 50 to 200 cm x 50 to 200 cm in size.

In the case where the mesh is fashioned into a modular tray structure, the structure is typically about 50 to 200 cm wide, 50 to 200 cm long, and 10 to 30 cm deep. The modular tray are preferably designed to be stacked vertically on top of each other.

The size and shape of the inner cavity of the rearing structure will be dictated to a large extent by the geometric form of the structure. Where the structure is in a flat hinged or envelope form, the aquatic animals contained therein can also influence the size and shape inner cavity. For example, the inner cavity will typically expand upon placing scallops within a flat hinged or envelope rearing structure such that the wall(s) of the structure support and make contact with the scallop. In this case, the inner cavity can also expand with the growth of the aquatic animals.

The apertures in the mesh used to form the structures will be of a sufficient size to allow nutrients for the aquatic animals to enter into the inner cavity, allow waste products from the aquatic animal to exit from the inner cavity, and importantly prevent the aquatic animal from exiting the inner cavity. The size of the mesh apertures will therefore vary depending on the type aquatic animal that is to be reared, but will generally range from about 10 to about 60 mm. A mesh aperture size of about 20 mm has been found to be particularly suitable for most commercially important animals that might be reared in the structure.

The mesh strands will generally have a thickness (ie diameter) of about 1 to about 3 mm.

The filler or biodegradable fibre content of the rearing structure will generally be in the range of about 2 to about 50 weight percent, based on the total weight of the structure. Preferably, the rearing structures do not contain a filler.

Habitat structures for aquatic animals in accordance with the invention, when used a rearing structure, are preferably made from about 30 to about 50 weight percent of biodegradable polyester resin, about 30 to about 50 weight percent of gelatinous or thermoplastic starch, about 2 to about 30 weight percent of filler, and about 2 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure.

In use, the juvenile aquatic animals will be placed within the inner cavity of the rearing structure and the structure suspended by any suitable means typically within 2 meters from the surface of the water. In such nutrient rich surface waters, the aquatic animals can advantageously mature quite rapidly. The rearing structure is manufactured such that the rate of disintegration to provide catastrophic failure of the structure is timed to substantially coincide with the peak maturity of the aquatic animals. Upon failure of the structure, the aquatic animals will fall to the water floor where they can be harvested by conventional means. Accordingly, the use of a rearing structure in accordance with the invention can provide for many of the advantages associated with conventional rearing structures, but conveniently avoids the disadvantages associated with the labour intensive task of retrieving and maintaining the rearing structures.

The time frame over which the rearing structures are manufactured to maintain their integrity will vary depending upon time frame over which the aquatic animals to be reared are expected reach sufficient maturity for commercial sale. This time frame will clearly depend on the type of aquatic animal and the quality of the aquatic environment in which the animals are reared. Generally, the rearing structures are manufactured such that they maintain their integrity for about 6 to about 18 months, more preferably for about 6 to 12 months, within the aquatic environment in which they are located.

A rearing structure for use in rearing scallops is shown in Figure 3. The rearing structure (10) is in the form of mesh envelope. The structure (10) has a front mesh wall (20) and a rear mesh wall (30). The apertures of the openings in the mesh are about 1 cm x lcm, and the warp and weft elements making up the mesh have a diameter of about 2 mm. The structure is shown with a scallop (40) located in the inner cavity, with the front (20) and rear (30) mesh walls contacting the scallop to support it within the inner cavity.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

CLAIMS:

1. A habitat structure for an aquatic animal, the structure being defined by one or more walls which extend wholly or partially around an inner cavity, wherein the structure has at least one opening into the inner cavity, and wherein the structure is made from a biodegradable polymer.

2. The habitat structure according to claim 1, wherein the biodegradable polymer is selected from aliphatic polyesters, aliphatic-co-aromatic polyesters, polycapralactone, polyvinyl alcohol, thermoplastic starch polymers, and combinations thereof.

3. The habitat structure according to claim 2, wherein the polyesters are selected from poly(hydroxy butyrate) (PHB), poly(hydroxy valerate) (PHV), poly(lactic acid) (PLA), poly(butylene succinate) (PBS), poly(butylene succinate/adipate) (PBSA), polyester carbonate or poly(butylene succinate/carbonate) (PEC), poly(ethylene succinate) (PES), poly(butylene adipate/terephthalate) (PBAT), poly(tetramethylene adipate/terephthalate) (PTMAT), polylactic acid (PLA), cellulose acetate, cellulose acetate/butyrate, polybutylene adipate (PBA) and combinations thereof.

4. The habitat structure according to claim 2, wherein the thermoplastic starch polymer is selected from corn starch, potato starch, tapioca starch, high-amylose starch, and combinations thereof.

5. The habitat structure according to any one of claims 1 to 4, wherein the biodegradable polymer comprises a biodegradable fibre.

6. The habitat structure according to claim 5, wherein the biodegradable fibre is present in an amount up to about 50 weight percent.

7. The habitat structure according to claims 5 or 6, wherein the biodegradable fibre is capable of absorbing or being swollen with water.

8. The habitat structure according to anyone of claims 5 to 7, wherein the biodegradable fibre is a natural fibre.

9. The habitat structure according to anyone of claims 5 to 8, wherein the biodegradable fibre has a length of about 1 mm to about 4 mm and a diameter of about 80 μm to about 600 μm.

10. The habitat structure according to anyone of claims 1 to 9, wherein the biodegradable polymer comprises a filler material.

11. The habitat structure according to claim 10, wherein the filler material is selected from starch, calcium based mineral, and combinations thereof.

12. The habitat structure according to claim 11 wherein the filler is present in an amount up to about 50 weight percent.

13. The habitat structure according to anyone of claims 1 to 12 which is in the form of an artificial reef for promoting growth of aquatic animals within, on and/or around the structure, wherein the at least one opening allows for the aquatic animals to enter into and exit from the inner cavity.

14. The habitat structure according to claim 13, wherein the one or more walls form a cuboid shape having a series of internal walls to thereby form a segregated inner cavity, said inner walls having a plurality of holes passing therethrough.

15. The habitat structure according to claim 14, wherein the external walls of the cuboid shape have a plurality of holes passing therethrough.

16. The habitat structure according to anyone of claims 13 to 15, wherein the structure is provided with concrete ballast.

17. The habitat structure according to anyone of claims 13 to 16, wherein the structure is inoculated with coralline algae spores.

18. The habitat structure according to anyone of claims 13 to 17, wherein the structure comprises about 30 to about 70 weight percent of biodegradable polyester, about 30 to about 70 weight percent of thermoplastic starch, about 10 to about 30 weight percent of filler, and about 10 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure.

19. The habit structure according to anyone of claims 13 to 18, wherein the structure maintains its structural integrity for about 6 to about 36 months within the aquatic environment.

20. The habitat structure according to anyone of claims 1 to 12 which is in the form of a deployment structure for deploying an aquatic animal into an aquatic environment, wherein the inner cavity provides a chamber in which the aquatic animal can reside prior to deployment, and wherein the at least one opening allows for the aquatic animal to exit from the inner cavity after deployment.

21. The habitat structure according to claim 20, wherein the one or more walls extend wholly around the inner cavity to provide for a hollow tube profile.

22. The habitat structure according to claim 21, wherein the hollow tube has a square profile.

23. The habitat structure according to claim 21 or 22, wherein the hollow tube is about 15 to about 25 cm long, and about 15 to about 20 mm in diameter.

24. The habitat structure according to anyone of claims 20 to 23, wherein the structure comprises about 30 to about 50 weight percent of biodegradable polyester, about 30 to about 50 weight percent of thermoplastic starch, about 2 to about 30 weight percent of filler, and about 2 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure.

25. The habit structure according to anyone of claims 20 to 24, wherein the structure maintains its structural integrity for about 1 week to about 6 weeks within the aquatic environment.

26. The habitat structure according to anyone of claims 20 to 25 when used for deploying juvenile abalone.

27. The habitat structure according to anyone of claims 1 to 12 which is in the form of a rearing structure for rearing an aquatic animal in an aquatic environment, wherein the inner cavity provides a chamber in which the aquatic animal can be reared, and wherein the at least one opening is of a dimension which (i) allows nutrients for the aquatic animal to enter into the inner cavity (ii) allows waste products from the aquatic animal to exit from the inner cavity and (iii) prevents the aquatic animal from exiting the inner cavity.

28. The habitat structure according to claim 27, wherein the one or more walls are in the form of a substantially rigid or self-supporting mesh or webbing.

29. The habitat structure according to claim 27 or 28 in the form of a tubular mesh structure, a modular tray mesh structure, or a flat hinged or envelope mesh structure.

30. The habitat structure according to anyone of claims 27 to 29, wherein the mesh has apertures ranging from about 10 mm to about 60 mm.

31. The habitat structure according to anyone of claims 27 to 30, wherein the mesh strands have a diameter of about 1 mm to about 3 mm.

32. The habitat structure according to anyone of claims 27 to 31, wherein the structure comprises about 30 to about 50 weight percent of a biodegradable polyester, about

30 to about 50 weight percent of a thermoplastic starch, about 2 to about 30 weight percent of filler, and about 2 to about 30 weight percent of biodegradable fibre, based on the total weight of the structure.

33. The habitat structure according to anyone of claims 27 to 32, wherein the structure maintains its structural integrity in the aquatic environment until the aquatic animal being reared is sufficiently mature for commercial sale.

34. The habitat structure according to anyone of claims 27 to 33 when used for rearing shellfish.

35. Use of a biodegradable polymer in an aquatic environment, wherein the biodegradable polymer is provided in the form of a habitat structure for an aquatic animal.