Short-term hypoxia modulates Rapana venosa (Muricidae) prey preference in Adriatic lagoons

We studied the effect of short-term hypoxia on predation by the non-native rapa whelk (Rapana venosa) on the three most common bivalve prey in northern Adriatic lagoons: the non-native ark shell (Scapharca inaequivalvis) and Manila clam (Tapes philippinarum), and the native cockle Cerastoderma glaucum. In mesocosm experiments, bivalves were offered to predator as single prey, and as multiple choice of prey. Bivalve prey showed behavioral responses when exposed to short-term hypoxia. Under normoxia, prey were consumed in almost equal numbers when offered separately, but when choice was offered to the predator R. venosa showed a marked preference for S. inaequivalvis. Short-term hypoxia increased the vulnerability of T. philippinarum, and, consequently, rapa whelks modified their predatory behavior and switched their preference to T. philippinarum. We hypothesize this to be a case of environmentally-mediated, non-reciprocal indirect interaction between the two non-native prey species, whose causes are based upon differences in specific traits of prey. Hypoxia may facilitate the coexistence of the two non-native bivalves via predator switching. The native cockle seems the net loser of the game.     

Distribution Patterns and Size–Age Composition in Aggregations of the Gastropod Mollusk Nucella heyseana in Peter the Great Bay, Sea of Japan

Gastropods Nucella heyseana were collected from 1999 to 2001 from different habitats in Vostok Bay (Sea of Japan). The spatial distribution, the seasonal and interannual dynamics, and the composition of aggregations of this mollusk were analyzed. In Vostok Bay, N. heyseana inhabits biotopes that are typical of this species and other members of the genus and sometimes forms aggregations with an unusually high density and biomass (up to 1690 spec/m² and 3680 g/m²), thus exceeding 10–40 times the greatest values reported elsewhere for populations of the southern Kuril Islands and Pos'eta Bay (Sea of Japan). N. heyseana is a typical polyphagous predator, and its diet includes numerous species of the associated fauna of bivalve and gastropod mollusks (more than 30 species). The abundance, composition, and stability of local aggregations of N. heyseana are largely dependent on the abundance dynamics of its prey (primarily the most common species, such as Mytilus trossulus, Ruditapes philippinarum, Protothaca euglypta, and Littorina spp.). The opinion on the low density of N. heyseana in southern Primorye (Golikov, Kussakin, 1978) is probably based on a lack of information about the intertidal fauna of this region compared to the South Kuril Islands.     

Mollusks of the Utlyuk Liman (Sea of Azov): A Review of Species Composition with Remarks on Distribution and Ecology

Summarized data on the fauna composition, distribution, and ecology of gastropod and bivalve mollusks of the Utlyuk Liman in the northwestern part of the Sea of Azov is presented. The total number of mollusk species identified was 63; 43 species belonged to the class Gastropoda, and 20 species, to the class Bivalvia. The distribution of mollusks in the liman has extremely irregular character, whereas the distribution of species along the marine shore of Biryuchii Ostrov spit is more homogeneous. Euryhaline Mediterranean species represent the core of liman malacofauna; some taxa of the Ponto-Caspian zoogeographical complex (Dreissena polymorpha and species of the genus Theodoxus) and invader species from distant sea basins (Mya arenaria and Anadara inaequivalvis) were also identified.     

Immunohistochemical localization and radioenzymatic measurements of serotonin (5-hydroxytryptamine) in hearts of Aplysia and several bivalve mollusks

Summary Serotonin immunoreactivity was localized in hearts of the opisthobranch gastropod, Aplysia californica (sca hare) and several species of bivalve mollusks, the heterodonts, Mercenaria mercenaria (quahog or cherry stone clam), Protothaca staminea (little neck clam), and the pteriomorphs, Hinnites multirugosus (rock scallop), Crassostrea virginica (eastern oyster), Mytilus edulis (eastern mussel), and Geukensia demissa (ribbed mussel). In addition, serotonin was assayed in the ventricles, auricles and heart-associated tissues in A. californica, M. mercenaria, H. multirugosus, and G. demissa with a sensitive radioenzymatic assay. Serotonin concentrations and the density of innervation were significantly higher in members of the subclass Heterodonta compared to the subclass Pteriomorpha. Serotonin immunoreactivity was observed in all species surveyed except G. demissa, which also contained relatively low concentrations of serotonin. Varicose fibers presumably corresponding to release sites were localized in the ventricles, auricles, and the auricular-ventricular valves. We hypothesize that in the species where serotonin-immunoreactive fibers are present, serotonin serves to modulate cardiac myogenic activity. The significance of the observed distribution and concentration of serotonin to the physiological effects of serotonin on cardiac function in these species is discussed.     

An Ecological Imbalance Induced by a Non-Native Species: The Manila Clam in the Venice Lagoon

Among the 19 non-native species of marine invertebrates which have invaded the Venice Lagoon and have established populations, Ruditapes philippinarum, deliberately introduced in 1983, is surely the most successful species. According to the hypothesis that alien species invasion could be favoured by an altered ecological, chemical or physical state of the system induced by anthropogenic disturbance, R. philippinarum turned out to be ‘the right species at the right moment’. By comparing historical data (1968, 1985, 1990) with 1999 data, changes in macrobenthic community, in particular bivalve molluscs, of the lagoon induced by R. philippinarum introduction and subsequent clam exploiting activity were assessed. It has been possible to describe a sharp reduction, both in terms of distribution area and density, of all other filter feeder bivalves. Moreover, by using the clearance rate of the most abundant bivalve species in 1990 and 1999 (Cerastoderma glaucum and R. philippinarum, respectively), it was possible to estimate that the filtration capacity, expressed as l h⁻¹ m⁻², has more than doubled. This has altered the functioning of the ecosystem, resulting in a stronger benthic–pelagic coupling. In this context, R. philippinarum attains control of the system. Considering all this, it is possible to state that the Venice Lagoon ecosystem has entered into a new state, probably more resistant but less resilient, with implications for future management choices.     

Invasion of the North American Atlantic Coast by a Large Predatory Asian Mollusc

The large Asian gastropod mollusc Rapana venosa Valenciennes 1846 (Neogastropoda, formerly Muricidae, currently Thaididae) is reported for eastern North America in the lower Chesapeake Bay and James River, Virginia, USA. This record represents a transoceanic range expansion for this carnivorous species. This species has previously been introduced to the Black Sea, Adriatic Sea, and Aegean Sea. Ballast water transport of larval stages from the eastern Mediterranean or Black Sea is the suspected vector of introduction into the Chesapeake Bay; 650 adult specimens in the size range 68–165mm shell length (SL) have been collected from hard sand bottom in depths ranging from 5 to 20m at salinities of 18–28ppt. The absence of small individuals from local collections is probably related to bias in collection methods. Age of the specimens could not be determined. R. venosa is probably capable of reproducing in the Chesapeake Bay. Egg cases of R. venosa were collected from Hampton Roads, a section of the James River, in August 1998, and hatched over a 21-day period under laboratory conditions to release viable bilobed veliger larvae. Four lobed larvae developed 4 days post-hatching and apparent morphological metamorphic competency was observed 14–17 days post-hatching. Despite the provision of live substrates and/or metamorphic inducers no metamorphosis to a crawling form was observed for larvae cultured on the monospecific diet. In work performed during 1999 settlement was observed for larvae cultured on a diet of mixed flagellates and diatoms and subsequently exposed to local epifaunal species. Salinity tolerance tests were performed on larvae at 1–6 days post-hatching. No deleterious effects were observed at salinities as low as 10ppt with limited survival to 7ppt at 6 days post-hatch. Current distribution is considered in context with larval salinity tolerance tests and literature describing native Asian and introduced populations to assess potential for establishment and further range extension both within the Chesapeake Bay and along the Atlantic coast of North America. Establishment within the Bay mainstem to the Rappahannock River with minor incursions into the mouths of the southerly subestuaries is considered feasible. A projected breeding range on the Atlantic seaboard extending from Cape Cod to Cape Hatteras is considered as tenable. Potential impact of R. venosa on commercially valuable shellfish stocks throughout the projected range is cause for serious concern. Boring by the polychaete Polydora websteri is more prevalent in the younger whorls of the shell, and absent in shell laid down later in life. This pattern suggests that juvenile animals may prefer hard substrates and not adopt an infaunal lifestyle until a size in excess of 50mmSL, or after reaching maturity.     

Genetically monomorphic invasive populations of the rapa whelk,Rapana venosa

Rapana venosa is a predatory marine gastropod native to the coastal waters of China, Korea, and Japan. Since the 1940s, R. venosa has been transported around the globe and introduced populations now exist in the Black Sea, the Mediterranean Sea, the Adriatic and Aegean seas, off the coasts of France and the Netherlands, in Chesapeake Bay, Virginia, USA, and in the Rio de la Plata between Uruguay and Argentina. This study surveyed variation in two mitochondrial gene regions to investigate the invasion pathways of R. venosa, identify likely sources for introduced populations, and evaluate current hypotheses of potential transportation vectors. Sequence data were obtained for the mitochondrial cytochrome c oxidase I and NADH dehydrogenase subunit 2 gene regions of 178 individuals from eight native locations and 106 individuals from 12 introduced locations. Collections from within the native range displayed very high levels of genetic variation while collections from all introduced populations showed a complete lack of genetic diversity; a single haplotype was common to all introduced individuals. This finding is consistent with the hypothesis that R. venosa was initially introduced into the Black Sea, and this Black Sea population then served as a source for the other secondary invasions by various introduction vectors including ballast water transport. Although non‐native R. venosa populations currently appear to be thriving in their new environments, the lack of genetic variability raises questions regarding the evolutionary persistence of these populations.     

Southern limit of distribution of the soft-shell clam <Emphasis Type="Italic">Mya arenaria</Emphasis> on the Atlantic East Coast

The invasive soft-shell clam Mya arenaria was recorded for the first time in the Tagus estuary, central Portugal. Propagules of the soft-shell clam were probably unintentionally introduced into the Tagus estuary through ballast water. Mya arenaria was observed in muddy sands in the upper intertidal zone. The assemblage in which the soft-shell clam was observed was composed of typical estuarine species such as the gastropod Hydrobia ulvae, the bivalve Scrobicularia plana and several polychaete species. The population density of Mya arenaria in the finding area was 40 ind m⁻² with a fresh biomass of 163.5 g FW m⁻².     

Feeding by marine fish larvae: developmental and functional responses

Synopsis The relationship between prey consumption rate and prey concentration (functional response), and its change with growth (developmental response) were examined in the laboratory for three species of marine fish larvae: bay anchovy Anchoa mitchilli (Engraulidae), sea bream Archosargus rhomboidalis (Sparidae) and lined sole Achirus lineatus (Soleidae). The major objective was to determine relative predatory abilities of the larvae by fitting feeding rate data to developmental and functional response models. Feeding success, prey capture success, attack rates, handling times and search rates were estimated. Prey consumption rates and attack rates of bay anchovy usually were highest, but at the lowest prey level (50 per liter) first-feeding sea bream larvae had the highest consumption rate. Sea bream could consume prey at near-maximum rates at prey levels lower than those required by the other species. As larvae grew, time searching per attack decreased rapidly for all species, especially at low prey levels. Handling time also decreased, but most rapidly for bay anchovy. Search rates were highest for bay anchovy and lowest for lined sole. Bay anchovy had the best apparent predation ability, but when previous results on larval growth rates, survival rates and growth efficiencies were considered, sea bream larvae were the most efficient predators and the least likely of the three species to be limited by low prey levels.     

Differential prey utilization by the generalist predator Coleomegilla maculata lengi according to prey size and species

Prey utilization by the generalist predator Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) of three sympatric lepidopterous species was quantified in relation with prey size (age) and prey species. Based on optimal foraging theory, we argued that costs associated with the utilization of small and large prey are higher than those of intermediate prey size. As a result, we expected a higher prey consumption rate on intermediate prey size leading to a convex prey consumption curve. Laboratory experiments showed that, within a given prey instar, Coleomegilla maculata lengi preyed more on Plutella xylostella (L.) compared to Artogeia rapae (L.) and Trichoplusia ni (Hübner). Generally, prey consumption rate by Coleomegilla maculata lengi on the three prey species decreased with increasing immature prey size (age). The predation efficacy of Coleomegilla maculata lengi adults and fourth instar larvae was higher compared to younger coccinellids (L2). Although, Coleomegilla maculata lengi showed a higher level of predation on smaller immature prey, we demonstrated that it is not the optimal size range for this predator. As predicted, prey weight consumption rate by Coleomegilla maculata lengi was higher at intermediate prey size leading to a convex prey utilization curve. The beneficial impact of Coleomegilla maculata lengi predation on the host plant was also estimated by using a Protection Index that considers the differential predation caused by the coccinellids and the relative importance of each pest species in terms of plant injury. Coleomegilla maculata lengi has a more significant beneficial impact when it preys on T. ni immatures.     

Isolation and characterization of microsatellite loci in the xishishe clam <Emphasis Type="Italic">Coelomactra antiquata</Emphasis> (Bivalvia: Veneroida)

The xishishe clam Coelomactra antiquata is a commercially important bivalve species, but has been suffering from severe population decline due to over-exploitation and the deterioration of environmental conditions. To investigate the genetic variation and structures of this clam, nine polymorphic microsatellites were developed. The number of alleles ranged from two to 28 per locus with the observed heterozygosity ranging from 0.083 to 0.921. This set of microsatellites will be useful for the study of the genetic structures of C. antiquata.     

How an invasive alga species (<Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>) induces changes in foraging strategies of the benthivorous fish <Emphasis Type="Italic">Mullus surmuletus</Emphasis> in coastal Mediterranean ecosystems

The foraging behaviour variability of three striped red mullet (Mullus surmuletus L. 1758) populations with respect to the vegetation cover was examined along the French Mediterranean coasts. We tested both the carrying capacity of different habitats and the hypothesis of a food segregation by the invasive alga Caulerpa taxifolia (Vahl) C. Agardh, on the functioning of benthic fish populations. The results indicated a significant site effect on M. surmuletus foraging behaviour and movements. The vegetation cover may play an important role in modifying the striped red mullet cost of foraging (sampling effort) and thus its strategy of prey capture. As long as the cover of marine phanerogams and/or macrophyte algae (Caulerpaceae) increases, the foraging budget and the distances covered in search of prey decrease significantly. Similarly, the striped red mullet increases the prospected sample periods to augment its foraging success, swimming above the bottom. These changes are related to the development of a dense superficial network of plagiotropic rhizomes and stolons, and to the reduction of space between fronds that limits the accessibility to resources and may increase intra-specific food competition. The role of C. taxifolia does not differ from that of other marine phanerogams but induces significant changes in the structure of Mullidae populations at the local level. The rapid expansion of Caulerpaceae in the Mediterranean Sea could constitute a real threat for the balance of the marine coastal biodiversity and the ecology of M. surmuletus, which is considered a flagship species for coastal Mediterranean demersal fisheries.     

Asymmetric interactions in semiaquatic insects

Summary Interspecific interactions were studied in three coexisting species of predatory semiaquatic insects: Gyrinus substriatus Steph. (Coleoptera), Gerris lacustris (L.) and Gerris argentatus Schumm. (Hemiptera). Prey capture success was observed in trials with individuals of two different species. Two prey sizes were used: fruit flies Drosophila melanogaster and Mediterranean flour moths Ephetia kuehniella (Zeller). When the two species were starved for the same period of time, G. substriatus was generally more successful at catching prey than either Gerris species, independent of prey size. However, when individuals from the formerly dominant species of the pair were less hungry (i.e. fed shortly before trials), their prey capture success decreased. Prey sharing and prey stealing were observed in trials with large prey and occurred both intra- and interspecifically. The shift in dominance with differing hunger levels and the existence of prey sharing and prey stealing may make the interspecific competition more symmetric allowing these species to coexist.     

生态因子对红螯相手蟹捕食毛蚶苗种的影响

敌害生物的捕食在控制海洋底栖生物群落的丰度和组成中起着关键性的作用。以红螯相手蟹(Sesarma haematocheir)和毛蚶(Scapharca subcrenata)为试验对象,研究了红螯相手蟹的密度、规格、性别,以及毛蚶的密度、规格、海水温度和底质条件对毛蚶苗种存活的影响。结果表明,蟹表现出了第二种类型的功能反应,高密度底播毛蚶苗种可以显著提高成活率;当毛蚶苗种壳长达到20mm以上时,蟹的摄食速率显著下降;随着蟹个体的增大,其摄食速率显著增加,毛蚶的存活率下降;当蟹的密度逐渐增加的时候,同种个体之间的干扰竞争显著提高了毛蚶存活率;雄蟹凭借强有力的螯导致了更多毛蚶苗种的死亡;海水温度较低的春季和秋季底播毛蚶苗种可以显著提高成活率;底质条件的复杂性和异质性为毛蚶的存活提供了"庇护空间",从而减少了敌害生物捕食所带来的损失。     

Polymorphic microsatellite loci for population studies of the razor clam, <Emphasis Type="Italic">Sinonovacula constricta</Emphasis>

The razor clam (Sinonovacula constricta) is an important aquacultured bivalve in China. The natural populations of this species are decreasing quickly. To facilitate studies on genetic diversity and population structure of wild populations, microsatellites were isolated from a CA enriched genomic library. Eight microsatellite loci were polymorphic in 30 individuals from Chongming in Shanghai, China. The number of alleles per polymorphic locus varied from 6 to 13 and the values of observed heterozygosity and expected heterozygosity ranged from 0.350 to 1.000 and from 0.602 to 0.902, respectively. These microsatellites are being used in studying population differentiation and genetic diversity for effective conservation and management genetic resources of S. constricta.     

Fine Spatial Structure of Atlantic Hake (<Emphasis Type="Italic">Merluccius merluccius</Emphasis>) Stocks Revealed by Variation at Microsatellite Loci

Genetic variation at 5 microsatellite loci was analyzed for European hake Merluccius merluccius sampled from 9 different regions in the Atlantic Ocean and the Mediterranean Sea. Significant genetic differentiation was found between samples, suggesting a fine subdivision of Atlantic and Mediterranean hake stocks. These results are discussed in the context of the decline of demersal fish species, probably due to overfishing.     

Distribution,abundance, and feeding of a disjunct population of lady crab in the southern Gulf of St. Lawrence,Canada

The lady crab (Ovalipes ocellatus) is one of the most common native species of swimming crab (Portunidae) of the Atlantic Coast of North America but most populations occur south of Cape Cod, Massachusetts. There is a disjunct population in Northumberland Strait (southern Gulf of St Lawrence), which was the focus of this study. Adult lady crabs were collected by trawling in water >4 m deep from May to October 1999 to 2005 to determine abundance, distribution, and diet. Lady crab occurred only in a small area (about 2,500 km²) in the central part of Northumberland Strait where bottom water temperature was >18°C during summer, and the substrate was mainly sand or sandy gravel. Male lady crab attained a maximum carapace width (CW) of 112 mm compared to 92 mm CW for females. The summer and autumn diet consisted mainly of infauna. The principal prey (each >5% of diet by weight) were: small bivalve molluscs (primarily Atlantic razor clam Siliqua costata and Macoma sp.; 43%), small rock crab (Cancer irroratus; 13%), polychaetes (11%), fish remains (9%), and small lady crab (9%). All stomachs collected during May (water temperature ≤10°C) were empty. There was little evidence of any difference in feeding intensity between 0700 h and 1900 h.     

Gymnophallid digenean Parvatrema duboisi uses Manila clam as the first and second intermediate host

To identify the metacercariae of a gymnophallid trematode in the Manila clam Ruditapes philippinarum from the Ariake Sea, experimental infection and molecular analysis were conducted. Based on the morphology of adult worms obtained from experimentally infected mice, the parasite was identified as Parvatrema duboisi. Comparison of internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) sequences for metacercariae and sporocysts from Manila clams and adult worms collected from wild wigeon Anas penelope showed minor differences ranging from 0 to 0.8%. These data strongly suggest that in the Ariake Sea, the parasite has a lifecycle using the Manila clam as the first and second intermediate hosts and wigeon as the definitive host.     

Food consumption of five deep‐sea fishes in the Balearic Basin (western Mediterranean Sea): are there daily feeding rhythms in fishes living below 1000 m?

Predation and food consumption of five deep‐sea fish species living below 1000 m depth in the western Mediterranean Sea were analysed to identify the feeding patterns and food requirements of a deep‐sea fish assemblage. A feeding rhythm was observed for Risso's smooth‐head Alepocephalus rostratus, Mediterranean grenadier Coryphaenoides mediterraeus and Mediterranean codling Lepidion lepidion. Differences in the patterns of the prey consumed suggest that feeding rhythms at such depths are linked with prey availability. The diets of those predators with feeding rhythms are based principally on active‐swimmer prey, including pelagic prey known to perform vertical migrations. The diets of Günther's grenadier Coryphaenoides guentheri and smallmouth spiny eel Polyacanthonotus rissoanus, which did not show any rhythm in their feeding patterns, are based mainly on benthic prey. Food consumption estimates were low (<1% of body wet mass day^?1). Pelagic feeding species showing diel feeding rhythms consumed more food than benthic feeding species with no feeding rhythms.     

Significance of new records of Tridacna squamosa Lamarck, 1819, in the Tuamotu and Gambier Archipelagos (French Polynesia)

The giant clam subfamily Tridacninae (family Cardiidae) is an important group of bivalve molluscs found throughout the Red Sea and Indo-Pacific, from East Africa to the Eastern Pacific biogeographic region. The Tridacna genus is currently revised with numerous cryptic species identified with molecular markers. New Tridacna records from the fringe of the known distribution areas are extremely useful to identify genetically unique species, geographic ranges, and to examine processes associated with species differentiation. While Tridacna maxima is abundant in French Polynesia (Central South Pacific Ocean) the larger fluted giant clam Tridacna squamosa was formerly reported only in the Austral Islands in the south. Following a recent survey that spanned 23 islands and atolls of the Society, Tuamotu and Gambier Archipelagos, the presence of T. squamosa between the Cook Islands and Pitcairn Islands is confirmed using both morphological and molecular information, suggesting a relic distribution across the Central Pacific Ocean. Tridacna squamosa is rare, but present throughout Tuamotu and Gambier. However, it remained undetected from the Society Islands, probably due to historical over-fishing. This species is valued by local inhabitants, and is sought after mainly as gifts and also for a limited local shell trade. The rarity of T. squamosa may call for conservation measures in the near future.