Bibliographical Synthesis of Biological Features of The Major Oyster Predators

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2.5 Bibliographical Synthesis of Biological Features of The Major Oyster Predators

Even after many decades of study, predation remains one of the major hurdles to successful field marine culture of mollusks in many areas of the world. In the table 1 below, we have some of oyster’s predators. Table 1. Oyster’s Predators of Crassostrea gigas Predator Place Reference Gastropod, Ocinebrellus inornatus Pacific-coast of North America in 1924 Washington State, Coast of the British Columbia 1931, Oregon 1930-1934, California 1941 and France in 1997. • Pigeot. et.al., 2000 • Miossec et. al., 2009 Gastropod, Whelk, Macron trochlea San Quintin Bay, Mexico • Rodriguez, 2009 Gastopod, The veined whelk Rapana venosa • Miossec et.al., 2009 Gastropod,Ocenebra erinacea Fal, Helford River, England • Spencer, 1990 Star fish or ‘’five fingers’’ Astrerias rubens • Spencer, 1990 Crustacea, Red rock crab Cancer productus and green crab Carcinus maenas • Miossec et.al., 2009 Toad fish Tetractenos spp . In Salamander bay, Port Stephen estuary, New South Wales Australia • Anderson and Connell, 1999 • Connell, and Anderson, 1999 Fish, Sparus aurata France • Marteil, 1976 Parasites, The copepod Mytilicola spp., boring sponges Cliona spp., and sea worms Polydora spp. • Miossec. et.al., 2009 Flatworm, Pseudostylochus ostreophagus Alaska • Prince William Sound Regional Citizens “The Advisory Council”, 2004 • Miossec. et. al., 2009 11 Ocinebrillus inornatus Rapana venosa http : elrinconmarinosgasteropodos 2. iespana . es Thaididae . htm , 2011 Ocenebra erinacea Cancer productus en.wikipedia.org, 2011 Carcinus maenas http : www . glaucus . org . uk c - maenas . htm , 2011 Asterias rubens Tetractenos spp. http : www . scuba - equipment - usa . com marine FEB 05 , 2011 Figure 3. The images oyster’s predators of Crassostrea gigas 12 Table 2. Oyster’s Predators of Crassostrea virginica Predator Place Reference Gastropod, oyster drill, Stramonita haemastoma Kool 1987 In United state • Brown, 1997 Gastropod, oyster drills Urosalpinx cinerea, and veined rapa whelks Rapana venosa • Harding, et.al., 2007 Crustacea, Blue Crabs, Callinectes sapidus Virginia, USA • Eggleston, 1990a • Eggleston, 1990b Mud Crabs Panopeus herbstii and Blue Crabs Callinectus sapidus Mud crabs Rhithropanopeus harrisii, Eurypanopeus depressus, Dyspanopeus sayi, and Panopeus herbstii, the blue crab Callinectes sapidus, and two sizes of polyclad Xatworms Stylochus ellipticus and Euplana gracilis Chesapeake bay • Bisker and Castagna, 1987 • Newel, et.al., 2007 Flatworm, Stylochus ellipticus Connecticut • Landers and Rhodes, 1970 Stramonita haemastoma http : www . flickr . com photos goldenpixel 2548646586 , 2011 Urosalpinx cinerea Callinectes sapidus http : www . jaxshells . org bcrab . htm , 2011 Panopeus herbstii http : www . sms . si . edu irlfieldguide Panope _ herbst . htm , 2011 Rhithropanopeus harrisii Keith D.E- Tarleton State University, 2011 Eurypanopeus depressus Keith D.E- Tarleton State University, 2011 Dyspanopeus sayi http:www.msn.ve.it, 2011 Euplana gracilis http:www.cryptosula.nlintroduced20 Platyhelminthes.html , 2011 Figure 4. The images oyster’s predators of Crassostrea virginica 13 Table 3.Oyster’s Predators of Ostrea edulis Predator Place Reference Gastropod, Murex erinacous In the Golf du Morbihan, France • Arin and Arin., 1976 Star fish or ‘’five fingers’’ Astrerias rubens L. In Scotland • Shelmerdine and Leslie, 2009 Crustacea, • Green Crab, Carcinus maenas • Velvet swimming Crab, Necora puber • In Morbihan, district in the southwestern part of Brittany • In Scotland • In Scotland • Arin and Arin, 1976 • Shelmerdine and Leslie, 2009 • Shelmerdine, and Leslie, 2009 Fish, Myliobatis Aquila and the fish locally called “guele pavée” Pagrus pagrus The Golf du Morbihan, France • Arin and Arin, 1976 The parasitic protozoans, Marteilia refringens and Bonamia ostreae North America, the Netherland, Spain, Denmark, England Ireland and France • Baud, et.al., 1997 • Kroeck, and Montes, 2005 • Culloty and Mulcahy, 1996 Fungus, Ostracoblabe implexa. The Golf du Morbihan, France • Arin and Arin, 1976 Necora puber http : www . marlin . ac . uk taxonomyidentification . php ? speciesID =3858 , 2011 Myliobatis aquila http:www.flmnh.ufl.edufishorganizationsssgdaythree.htm, 2011 Pagrus pagrus http:www.naturamediterraneo.com, 2011 Figure 5. The images oysters predators of Ostrea edulis Figure 6. Ocenebra erinacea 14 2.5.1 Gastropod 1. Ocenebra erinacea Classification Biota : Animalia Kingdom : Mollusca Phylum : Gastropoda Class : Caenogastropoda Subclass : Neogastropoda Order : Muricoidea Superfamily : Muricidae Family : Ocenebrinae Subfamily : Ocenebra Ocenebra erinacea is present all along the European coast, north, south and west of British Islands, Ireland, south of the North Sea to the south of Spain, Madeira and Azores Grangeré, 2002. Hayward and Ryland 1995 recorded O. erinacea is on rocky shores, silty crevices and beneath stones from the lowest to 150 m; intertidal range increased in summer, distributed from the Azores and Mediterranean to south and west coasts of British Isles and becoming rare in north. It size up to 50x25 mm. This species is found easily in the middle of oyster bed or clam Barthelemy, 1991. O. erinacea distributed in the intertidal zone which is exposed to low water spring tides . It is usually found on hard substrate , when it is in a sandy area , it is half embedded . It is also found but in smaller amounts on deep water offshore in the bottoms driven by strong currents Grangeré, 2002 . It moves slowly on muddy , sandy or rock and moves closer to the shore to spawn Beaudesson, 1992. I n France O. erinacea known as the oyster drill , is gray , its shell is thick , rough , and strong ribs , the shell measures on average 3 to 4 cm , 5 cm sometimes . The siphon canal is short and firm ; the labrum is thick and the ornaments just like 15 the rest of the shell. In the retracted position , a lid closes tightly the opening of the shell . The animal may move slowly crawling over a flat part of the foot pedal sole . Usually living at the limit of the low-tide , it has good resistance to prolonged emersion Marteil. et al, 1976 . At the reproduction level, almost inactive in winter, the oyster drill begins his sexual activity from a temperature of 10 o C , correspond to the Brittany coast to the period from March to April . The sexes are separate Barthelemy, 1991. The water temperature probably plays an important role in the reproduction of Ocenebra erinacea. At the beginning of egg laying in 1977 and 1978 it was 9 o C, it also reported a temperature of 9 o C at the beginning of spawning. Muricids gastropods are known to lay eggs enclosed in capsules firmly bonded to substrates . Of these capsules can emerge either planktonic larvae or juveniles with a morphology and behavior similar to those of adults Sauriau, 2002 . The oyster drill need a hard substrate to lay the egg capsule . It is on the rocks in the intertidal zone . There are also lying on shells . In deep water , the egg capsules are laid on empty shells scallops, slipper limpets, oysters Papineau, 1978. Figure 7. Capsule of Oyster Drill Mazurié, 2010 16 O. erinacea has a single spawning peak in spring. During that time, it deposits most of its capsules Garcia-Meunier, 2004. The larvae have planktonic phase extremely short, on average 2-3 days and a maximum of 5 days. The hatched larva has a morphology comprising a shell and velum an organ which allow this species to swim in open water and only in consequence of the loss of the velum it becomes benthic Sauriau, 2002. The oyster drill have proliferation. Barthelemy 1991 said that spawning may take several days; each female can deposit 30 to 40 capsules, each capsule containing 10 to 160 eggs. The females have a negative geotropism and tend to up out of 1 to 2 meters before lying. Its activity decreases gradually in autumn Beaudesson, 1992. In this species, females are slightly larger than males . The predatory activity of O . erinacea is independent of production . It increases continuously from March until the summer , and then decreased in autumn Grangeré, 2002 . On the other hand, the smaller prey seemed to be more attractive to borers, that is to say that they place with the small predator prey. They observed that the first attacks were quickly place on small prey 4 days while on large prey they had to wait 14 days before observing predatory behavior. Behavior of the predators shows that both species behave differently. Indeed, the species O. erinacea has mainly attacked the oysters that present in the water intake Grangeré, 2002. 2. Ocinebrellus inornatus The muricid gastropod, Ocinebrellus inornatus, was formely identified as a new oyster drill sampled in 1997 by Sauriau the bay of Marennes- Oleron, on the French Atlantic coast. This species normally dwell along the coasts of Korea and Figure 8. Ocinebrellus inornatus 17 South Japan. It was introduced along the Pacific coasts of North America in 1924 Washington State. It was also present on the coasts of Colombia 1931, Oregon 1930-1934 and California 1941 Pigeot, 2000. In 2007, this gastropod was found in Netherland Faasse and Ligthart, 2009. Like the European oyster drill Ocenebra erinacea, Ocinebrellus inornatus is a carnivorous species preferentially feeding on bivalves and which may cause serious damage on cultivated oysters. Ocinebrellus inornatus differs from Ocenebra erinacea by shell ornamentation. The last whorl of O. inornatus presents only three to four varices at the surface of its otherwise smooth shell, whereas the local species displays five to seven small varices at the finely laminate surface of the shell. Also, the thin outer lip is less crenated in O. inornatus than in O. erinacea. In France, O. inornatus lives in the same sites as O. erinacea, with preferences for mediolittoral rocky shores in the middle of the bay of Marennes-Oléron. At low tide, the adults live beneath flat stones. Their density reaches ten to twelve individuals per linear meter. At exceptionally favorable sites, as many as 800 individuals of O. inornatus were found per square meter Pigeot, 2000. The reproductive cycle of Ocinebrellus inornatus does not include any planktonic larval stage. Similar to Ocenebra erinacea, females produce 30–40 egg capsules each containing 10–15 larvae, which are benthic at hatching Pigeot, 2000. This species possesses two peaks of spawning of smaller amplitude : first, in spring and second, in autumn . The development of the capsules is approximately three weeks Garcia-Meunier, 2004 . Numerous females oyster drills were observed during the breeding period, in autumn and winter. They live in the same habitat as adults, but preferentially in silty crevices of the stone. Adults of Ocinebrellus inornatus feed on the oyster Crassostrea gigas by perforating its valve. In the bay of Marennes-Oléron, O. inornatus seem very well fitted to its new environment and reached larger shell sizes total shell height: h ≈ 60 mm than in its native area h≈ 33 mm Pigeot, 18 2000. Sexual dimorphism was noted for females O. inornatus Garcia-Meunier, 2004. Sauriau 2002 showed that the development of embryos in their capsule during the entire period of their development : the shell appears in the 5 th week of development and hatched 7 th week in laboratory conditions , the juvenile has a shell which the peristome has good shape but with the incomplete apex . The embryo does not have a velum, an organ body which characterizes the planktonic larvae phase . The larva hatches so that the capsule cannot swim but has all the characteristics of a future adult . Therefore a direct development and the hatching larva lead a benthic life phase . 3. Comparison Ocenebra erinacea and Ocinebrillus inornatus Grangeré 2002 showed the O. erinacea had a higher pressure of predation in the invasive species O. inornata. In fact, O. erinacea showed a clear preference on the smaller oysters 20g, instead of average 50g and large 80g. Even though behavior of the predators shows that both species behave differently, the species O. inornata attacked on above and below the water intake in the same proportions, so it seems that this species has a more opportunistic behavior. O. erinacea moves closer to the shore to spawn and its predation activity decreases gradually in autumn Beaudesson, 1992. It has a single spawning peak in spring, during that time, it deposits most of its capsules and O. inornatus possesses two peaks of spawning of smaller amplitude : first, in spring and second, in autumn Garcia-Meunier, 2004 . Figure 9. Urosalpinx cinerea 19 4. Urosalpinx cinerea Classification: Kingdom : Animalia Phylum : Mollusca Class : Gastropoda Order : Neogastropoda Family : Muricidae Common Name : Atlantic Oyster Drill, American Tingle, American Whelk Tingle The American whelk tingle, drill or borer, Urosalpinx cinerea, was first recorded in this country United State on the oyster beds of the river Black-water, Essex. In America, Urosalpinx occurs in very large numbers from Cape Cod to Florida, and was carried more recently oysters to San Francisco. Urosalpinx has entirely replaced the native rough tingle, Ocenebra erinacea, it has spread and multiplied by cold winters Handcock, 1954. Hayward and Ryland 1995 recorded that U. cinerea on the oyster, from lower intertidal to 12 m, hibernating in mud at 7 o C or less, and it size up to 40 x 20 mm. The oyster drill U. cinerea, a carnivorous gastropod native to the East coast of the North America, is an important predator of oysters and has been inadvertently introduced with Crassostrea virginica in Great Britain Pratt, 1974. It is also exists in France, in the Arcachon basin and was discovered in Brest on oyster beds Marteil, 1976. Urosalpinx drilled Balanus balanoides, B. eburneus, Crassostrea virginica, Crepidula fornicata, C. plana, Mercenaria mercenaria, Modiolus demissus, Mya arenia, Mytilus edulis, Spisula solidissima, and Yoldia limitula Pratt, 1974. Marteil 1976 showed that although Urosalpinx looks like Ocenebra erinacea, it is differentiated by the presence of a siphon canal open and long, a 20 labrum less thick and ornamented. Its size is also smaller and rarely exceeds 3 cm. The size and shape of the egg cases are different from those of Ocenebra, the shorter incubation period 8-9 weeks against 12 to 13. Cole 1942 observed that females of Urosalpinx grow more quickly than males and reach a larger size. Urosalpinx reaches a much greater average size in Britain than in its natural habitat on the Atlantic coast of the U.S.A. Urosalpinx has no free-swimming larval stage, the eggs being deposited in capsules from which fully formed young tingles emerge. Spawning begins when the water temperature in its seasonal rise reaches 12° C. Adult females may deposit an average of 25 egg capsules at a single laying, but it is possible that further capsules are deposited later in the season. The bulk of the spawn is deposited in May and June on British beds, but a few freshly laid capsules may sometimes be found in August and September. The average period of incubation is about eight weeks. Young tingles usually begin to emerge early in July. The average number of young emerging from each capsule is 11–74 Cole, 1942. Gera 2009 found that historically, U. cinerea was a pest to the oyster industry in the Chesapeake Bay; a single U. cinerea may consume in excess of 20 to 200 oysters in a season, depending on size water temperature 19 o C to 28 o C; size range of oysters not noted. Manzi 1970 showed that the initiation and rate of egg capsule deposition appear to be greatly influenced by temperature, although other factors, such as food, availability of suitable substratum, and population density, may be contributory regulators of spawning intensity. Gera 2009 observed that the copulation occurs year round and egg capsule deposition occurs as water temperatures rise above 20 o C in May through early November, with a brief pause in egg capsule deposition observed in August. Each U. cinerea egg mass contains 1 to 22 egg capsules. Incubation U. cinerea of embryos ranges from 18 days at 23 o C to 29 o C to 78 days at 15 o C to 30 o C. Sexual maturity is reached within the first 1 to 2 years of life 15 mm SL. The lifespan may range in excess of 10 years. 21 5. Rapana venosa Rapana whelk, Rapana venosa, is a native mollusk to the Sea of Japan, Yellow sea, Eastern China sea and the gulf of Bohai Seyhan et al., 2003. Chandler et al 2008 observed that in the 1940s, Rapana venosa were discovered in the Black Sea. Additionally, in 1997 R. venosa were discovered in the Bay of Quiberon Joly et al., 2002, in Chesapeake Bay USA in 1998, in the Rio de la Plata between Uruguay and Argentina in 2000, and Kerckhof et al. 2006 showed that the veined whelk R. venosa, was first recorded in July 2005 in the Dutch part of the North Sea, and in September 2005 in the central southern North Sea the wider Thames estuary. It may exceed 160 mm in length Harding et al. 2007 Figure 10. Rapana venosa http:www.gastropods.com1Shell_1631.shtml, 2011 22 Seyhan et al 2003 observed that feeding behavior of Rapana have been studied previously. Rapana prefer hard sand bottom habitats but will also invade hard substrate where food is abundant. They mainly feed on bivalve mollusks, but the preference of their prey depends on the diversity of the available prey items. For example preferred prey can vary from hard clams to oyster, soft clam and mussel Mytillus edulis. On average of 50 g Rapana in the Eastern Black Sea marine ecosystem consume 0.17-0.30 g mussel in a day. Savini et al. 2006 also showed an average consumption of about 1 bivalve prey per day or 1.2 g wet weight per day. Predation was species and size selective towards small specimens of Indo-Pacific invasive clam. Anadara inaequivalvis; consumption of the two commercial species was lower. R. venosa are highly fecund and their eggs hatch as planktonic veliger larvae that can be carried in ballast water, characteristics that make them effective invasive species. R. venosa are dioecious and adult females lay large mats of egg cases from April through September. Each egg case contains approximately 100 to 3000 eggs, and a female can lay up to 500 egg cases in each mat. Additionally, females may produce over 10 different egg mats per year Chandler et al, 2008. Harding et al. 2007 observed that the number of embryos observed in egg cases produced by Chesapeake Bay Rapana whelks ranged from 123 embryos in a 7.4 mm high egg case to 3,673 embryos in a 33.5 mm high egg case. Rapa whelk fecundity number of embryos female −1 yr −1 increased with female size. Figure 11. Asterias rubens 23 2.5.2 Echinoderm 1. Asterias rubbens Classification: Domain : Eukaryota Kingdom : Animalia Subkingdom : Bilateria Branch : Deuterostomia Infrakingdom : Coelomopora Phylum : Echinodermata Subphylum : Eleutherozoa Infraphylum : Asterozoa Class : Stelleroidea Subclass : Asteroidea Superorder : Forcipulatacea Order : Forcipulatida Family : Asteriidae Asterias rubens, widespread across the English Channel and the Atlantic coast, is a well known predator of bivalves, particularly mussels from natural beds or livestock Barthelemy, 1991. Karhan et al., 2007 observed that three specimens of Atlantic starfish, Asterias rubens are here reported as the first record from the Black Sea, after being first reported from the Bosphorus Strait in 1996. Typically found in edge of various beds of shells, the bottom sandy-muddy, but also in the rocks Barthelemy, 1991. The five arms of the body ends in a point and carry a median row of spines, the size does not exceed 20 cm. The dorsal surface is uniform pigmented purplish red; the underside is white or yellowish Marteil et al., 1976. The behavior of Asteria rubens feeding on selection of common infaunal bivalves was investigated on a sand bottom in aquaria, a seasonal preference for Abra alba and Spisula substruncata was noted Allen, 1983. Saier 2001, observed that A. rubens feeds opportunistically on a variety of items including slipper limpets, Crepidula fornicata, oysters, infaunal bivalves such as Spisula and even dead fish. However, Handcock 1955 showed that alhought Asterias 24 occasionally ate spat and adult oyster, but almost always exhibited a preference for mussels and, in the absence of these, for Crepidula, and sometimes even for Urosalpinx. Asterias rubens are migrating because of lack of food Gallagher et al. 2008, to changes in the abundance and distribution of the slipper limpet Crepidula fornicata, to aggregate and spawn in the spring April to May when seawater temperatures are increasing. Increasing seawater temperature has been shown to be important in controlling spawning asteroids. Bennet-Clark 1976 recorded large invasion of Asterias onto beds of mussels just above low-water mark in Morecambe Bay England; starfish densities were up to 200-450 animals m -2 , and the swarm, at one time, covered 2.25 ha of ground, and may have cleared up to 4000 t of first-year mussel between June and September. Synder and French 2006 observed at Moose Point Park in Maine, United State, there were high abundant of Asterias which have link sea star aggregation to prey abundance. They also showed that longer distance Asterias migration also been linked with food abundance and these migration may be from areas of low mussel cover to high mussel cover or from deep water to shallow mussel beds during the summer, when conditions were warm. Marteil et al. 1976 also showed that temperature and salinity affect the activity, reproduction and distribution of A. rubens. It is less active in the winter and moves toward the coast in the spring. The migrations are influenced by foraging and salinity. In estuaries and coastal Atlantic, its distribution is followed by the distribution of water salinity15-20‰. The temperature also determines the phenomenon of reproduction. It begins at about 15°C, it means that on the Atlantic coast in April-May or June, depending on the year. Barker and Nichols 1983 observed that intertidal A. rubens had a clearly defined reproductive cycle with spring-early summer spawning. It has planktotrophic pelagic life of Figure 12. Asterias feeding behavior 25 approximately 90 days for A. rubens. Growth of juvenile starfish was followed for 17 months. Juvenile starfish feed carnivorously at the completion of metamorphosis. Early growth is rapid; however, there is a reduction in the growth rate during winter months. 2. Marthasterias glacialis The range of the sea star Marthasterias glacialis includes Iceland, the Azores and the Mediterranean Sea and extend as far south as South Africa Minchin, 1987. Marthasterias glacialis is a benthic animal living mostly on hard bottoms in the littoral. It is an important predator living on mollusks, sea urchins and many other benthic organisms which are not fast or strong enough to survive attacks of this sea star Valentinčič, 1973. Frid 1992 observed that the spiny starfish, Marthasterias glacialis, is a common predator in the sub-littoral of Atlantic coasts. A wide variety of prey consumed by Marthasterias glacialis. Small 5 cm radius individuals consumed algae, epifaunal turfs and small gastropods, while larger individuals consumed bivalves and carrion Frid, 1992. Penney and Griffiths 1984 observed that the diet of the starfish,Marthasterias glacialis, consists of a variety of mollusc species, as well as ascidians and barnacles. Starfish densities are maximal where mussels, Choromytilus meridionalis Krauss, are abundant in such areas mussels form the bulk of the diet and indicate that Marthasterias glacialis select mussels of particular sizes. The length of prey taken is an increasing function of predator arm length. Verling et al., 2003 recorded the larger M. glacialis 100mm exploited the variety of food resources Figure 13. Marthasterias glacialis 26 found most amongst shallow water boulders. These larger individuals, in particular those 200 mm chiefly fed on bivalve prey in the deeper water zones. According to Barker and Nichols 1983 M. glacialis also spawns in summer May-June in Plymouth Sound, England. Verling et al, 2003 also recorded that increased recruitment of juveniles during summer months might influence the population structure, and M. glacialis spawns during the summer months, both in Lough Hyne and other locations. A single female lays about 200 million eggs in a season. Fertilization is external and held in the seawater Khanna and Yadav, 2005. Valentinčič 1973 also observed that Marthasterias glacialis is the most rewarding animal for research and feeding behavior. The role of chemoreception in food finding is further supported by the fact that in sea stars, photoreceptors are poorly developed, on the other hand obviously needs the distance chemoreceptors to find the food. It is located on distal tube feet of animals and on sensory tentacles. 3. Comparison Asterias rubens and Marthasterias glacialis Villalabos et. al 2006 observed developmental stages of A. rubens and M. glacialis have a potentially wider depth distribution than their respective adults. Therefore, the larvae of shallow-water species A. rubens and M. glacialis could survive transport to deeper waters and may be capable of acting as colonists in the deep sea. Synder and French 2006 also showed that longer distance Asterias migration has been linked with food abundance and this migration may be from areas less mussel cover to high mussel cover or from deep water to shallow mussel beds during the summer when condition are mild. Verling et al., 2003 note that the reputation of Marthasterias glacialis is a ubiquitous asteroid and a voracious predator. It has a strong pattern of distribution with depth and a wide dietary range. M. glacialis, in common with many other asteroids is a slow-moving predator, which relies primarily upon chemoreceptor and chance encounter to locate potential prey. On the other hand Handcock 1955 observed that Asterias rubens almost always prefer feeding on 27 mussels and, in the absence of these, for Crepidula, and sometimes even for Urosalpinx. 2.5.3 Crustacea, Carcinus maenas Classification: Kindom : Animalia Phylum : Arthropoda Subphylum : Crustacea Class : Malacostraca Order : Decapoda Infraorder : Brachyura Family : Portunidae Common name : European green crab, European shore crab The shore crabs or green crab, Carcinus maenas is native to Europe and northern Africa and has been introduced to the North America, Australia, parts of South America and South Africa. It is a voracious food generalist and in some locations of its introduced range it has caused the decline of other crab and bivalve species Gollasch, 2009. This crab takes a great variety of prey and is recognized to be an important predator of juvenile spat and seed mollusks in many natural and cultivated fisheries. Serious damage is caused to stocks of soft- shell clams, Mya arenaria L, in New England, USA, to American hard shell clams, Mercenaria mercenaria L. in Britain, to palourdes, Venerupis tapes spp., in Portugal, flat oysters, Ostrea edulis L, in France and to mussels, Mytilus edulis L, in Britain and the Netherlands Dare et. al., 1983. Hughes and Elner 1979 observed that shore crabs attack dogwhelks Nucella lapillus by attempting to crush the shell. Because of differences in shell morphology, sheltered shore dogwhelks tend to be opened by removal of the apex and exposed shore dogwhelks by breaking the columella. According to Crothers 1968 Carcinus maenas, is one of the best known of all intertidal animals, being common, relatively large, and easily found. The familiar external features of this crab are those of a squat, solid animal clearly Figure 14. Cancer maenas http:www.glaucus.org.ukc-maenas.htm, 2011 28 suited for walking rather than swimming. The behavior of male crab is aggressive while the female not. Their sizes are up to 86 mm and up to 70 mm carapace breadth for the male and female respectively. C. maenas is aware of its surroundings through the sense of touch mechanoreception, smelltaste chemoreception and sight photoreception. Barthelemy 1991 also noted that the green crab is a bad swimmer but good climber. It moves quickly, has a group and ability to adapt extremely quickly. At low tide, it is usually found motionless in the seaweed, in rock crevices or simply buried in the soft substrate. Green crabs are euryhaline, tolerating salinity from 4 to 52 ppt, and eurythermic, surviving in temperatures from 0 to 30 O C. The larvae are less tolerant of temperature and salinity extremes with successful development occurring at temperatures between 11 and 25 O C and salinity between 26 and 39 ppt. Females may produce up to 185,000 eggs Perry, 2011. The sexes for the female and male are separated, the female cannot be fertilized after molting, while still soft. Fertilization takes place from July to September. Embryonic development is the winter. Throughout this phase, the female carries her embryos abdominal legs’. The green crab is living up to six years Barthelemy, 1991 2.5.4 Fish, Sparus aurata Gilthead seabream FAO 2005 noted that Sparus aurata is common in the Mediterranean Sea, present along the Eastern Atlantic coasts from Great Britain to Senegal, and rare in the Black Sea. Due to its euryhaline and eurythermal habits, the species is found in both marine and brackishwater environments such as coastal lagoons and estuarine areas. Figure 15. Sparus aurata Sola et al., 2006 29 The gilthead seabream inhabits seagrass beds and sandy bottoms, commonly to depths of about 30 m, but adults may occur at 150 m depth Marteil, 1976. The gilthead seabream inhabits seagrass beds and sandy bottoms as well as the surf zone, commonly to depths of about 30 m, but adults may occur at 150 m depth Sola et al., 2006. They born in the open sea during October-December, juveniles typically migrate in early spring towards protected coastal waters, where they can find abundant trophic resources and milder temperatures. Very sensitive to low temperatures lower lethal limit is 4 °C, in late autumn they return to the open sea, where the adult fish breed FAO, 2005. It is mainly carnivorous shellfish, including mussels and oysters, accessorily herbivorous Sola et al., 2005. Marteil 1976 noted that Sparus aurata has mouth armed with teeth making them capable of crushing the shells of oysters and other bivalves Marteil, 1976. This species is a protandrous hermaphrodite. Sexual maturity develops in males at 2 years of age 20-30 cm and in females at 2-3 years 33-40 cm. Females are batch spawners that can lay 20 000-80 000 eggs every day for a period up to 4 months FAO, 2005. In the Mediterranean, they reproduce between October and December Sola et al., 2006. 30 3 Materials and Methods

3.1 Study area