Musculista Senhousia Research Articles

<i>Sanyuania cuneata</i> Zhao & Whatley, 1992 (Ostracoda, Cytheroidea, Cytherideidae) from Japan: morphology, distribution and environmental significance

Abstract. Sanyuania cuneata Zhao & Whatley, 1992 was reported initially from Late Pleistocene core samples from the northern part of the Yellow Sea and Recent sediments collected from supra tidal pools (17 practical salinity unit (psu)) in Xiangshangang Bay, East China Sea (Zhao & Whatley, 1992). Later, specimens were discovered, but not identified, in Lake Nakaumi, Shimane Prefecture, SW Japan (Fig. 1) (as Cytheridae gen. et. sp. indet. by Tanaka et al. (1998) and Sanyuania sp. by Seto et al. (1999)). Further examination of these Japanese specimens has clarified that they are conspecific with the Chinese specimens. This has provided an opportunity to review the distribution (Fig. 1) and potential environmental significance of Sanyuania cuneata and, for the first time, to describe its appendages (Fig. 2).Specimens figured herein were recovered from Lake Nakaumi (35°26′ 50″ N, 133°07′50″ E) at a depth of 0.3–6.0 m and salinity of 8–17 psu on 9 September 1998. The surface of the sediment was covered by the byssus of the mussel Musculista senhousia (Benson, 1842).Sanyuania cuneata is probably endemic to the East China Sea and the southwestern part of the Sea of Japan and is a potentially useful palaeoenvironmental indicator of brackish (steno-haline) environments in the area. By using the oxygen isotopic data from planktonic foraminifers and the estimated value of salinity flowing into the Japan Sea, Matsui et al. (1998) approximated that the salinity of the surface water of Japan Sea declined to about 20 psu during the Last Glacial Maximum . . .

Changes in the shelf macrobenthic community over large temporal and spatial scales in the Bohai Sea, China

Over the past 20 years, the Bohai Sea has been subjected to a considerable human impact through over-fishing and pollution. Together with the influence of the Yellow River cut-off, the ecosystem experienced a dramatic change. In order to integrate available information to detect any change in macrobenthic community structure and diversity over space and time, data collected during the 1980s and the 1990s from 3 regions of the Bohai Sea (Laizhou Bay, 16 stations, 37–38°N, 119–120.5°E; central Bohai Sea, 25 stations, 38–39°N, 119–121°E; eastern Bohai Bay, 12 stations, 38–39°N, 118.5–119°E) were reanalyzed in a comparative way by means of a variety of statistical techniques. A considerable change in community structure between the 1980s and the 1990s and over the geographical regions at both the species and family level were revealed. After 10 years, there was a considerable increase in abundance of small polychaetes, bivalves and crustaceans but decreased number of echinoderms. Once abundant in Laizhou Bay in the 1980s, a large echinoderm Echinocardium cordatum and a small mussel Musculista senhousia almost disappeared from the surveying area in the 1990s. Coupled with the increased abundance was the increased species richness in general whereas evenness was getting lower in central Bohai Sea and Bohai Bay but increased in Laizhou Bay. K-dominance plot showed the same trend as evenness J′. After 10 years, the macrobenthic diversity in the Bohai Sea as a whole was slightly reduced and a diversity ranking of central Bohai Sea > Laizhou Bay > eastern Bohai Bay over space was also suggested. Sediment granulometry and organic content were the two major agents behind the observed changes.

Seasonal patterns of pore-water nutrients, benthic chlorophyll a and sedimentary AVS in a macrobenthos-rich tidal flat

Monthly field investigations were carried out at controlled low-tide in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between January 1995 and April 1996. We assessed the spatial and temporal distribution of pore-water nutrient [NH4+-N, (NO3− + NO2−)-N, PO43−-P and Si(OH)4-Si], chlorophyll a (chl a) and acid-volatile sulphide (AVS) concentrations in the uppermost 0–10 cm sediment horizon, and evaluated their relationships with macrobenthic assemblages. Monthly hydrological data, nutrient and chl a concentrations in low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. All different pore-water nutrients showed a 10 to > 30-fold variability between different layers and periods. NH4+-N, PO43−-P and Si(OH)4-Si concentrations were lowest in winter, progressively increased throughout spring and summer, and were highest between September and October, with a major increase at intermediate (4–8 cm) layers. In contrast, (NO3− + NO2−)-N concentrations, correlated positively with chl a, peaked in winter and sharply decreased with depth in all different seasons and in most occasions. Depth-integrated NH4+-N, PO43−-P and Si(OH)4-Si pools were correlated positively with biogenic nutrient flux calculated from the nutrient excretion rates of dominant bivalves Ruditapes philippinarum and Musculista senhousia. These relationships indicated rapid removal pathways of P, Si and N (i.e., every 0.1, 0.24 and 0.34 day, respectively), implying highly dynamic sediments. Based on the mass balance P = F + I, biogenic production (P) vs. diffusive flux (F) estimates suggested a predominant contribution of animal bioirrigation (I) to the upward flux of nutrients. AVS concentrations, correlated negatively with both (NO3− + NO2−)-N and chl a, showed a progressive increase from late summer throughout winter, subsequent to that of NH4+-N, PO43−-P and Si(OH)4-Si. The results indicate that in our study area the spatial and temporal distribution of pore-water nutrients, chl a and AVS in sediments are strongly interlinked and suggest that the metabolic processes (e.g., excretion, bio-deposition) and behavioural activities (e.g., particle mixing, bioirrigation) of abundant macrobenthos play an important role in the year-round biogeochemical processes occurring on this flat.

Effects of native predators and eelgrass habitat structure on the introduced Asian mussel Musculista senhousia (Benson in Cantor) in southern California

The ability of predators to control the abundance of non-native species has been little explored in marine systems. Native predators may be used to control non-native species or may confer invasion resistance to communities if predation rates on invaders are density-dependent. We studied the response of southern California native predators to the density of Musculista senhousia (Benson in Cantor, 1842), a small, fast growing mussel that has been introduced from Japan to several coastlines worldwide. We performed field experiments to determine if M. senhousia proportional mortality is density-dependent and if eelgrass Zostera marina L. habitat structure influenced mussel density-dependent mortality. We also evaluated the effect of seagrass habitat structure on the aggregative and functional responses of the predatory gastropod Pteropurpura festiva (Hinds, 1844) to Asian mussel density. In the summer of 2002, P. festiva aggregated in plots with high mussel density and was responsible for nearly all predation on M. senhousia. However, M. senhousia proportional mortality was inversely density-dependent at all levels of eelgrass above-ground and below-ground habitat structure. Asian mussel proportional mortality also was inversely density-dependent and was not influenced by eelgrass habitat structure in the spring of 2004 when wading birds were the chief predator of mussels. In contrast to results for mussel proportional mortality, the aggregative and functional responses of P. festiva varied with seagrass habitat structure. P. festiva density increased with Asian mussel density in plots with low simulated habitat structure, but the relationship between P. festiva density and Asian mussel density was parabolic at zero, intermediate and high levels of habitat structure. In field enclosures, P. festiva exhibited a Type I (linear) functional response to Asian mussel density at low levels of eelgrass structure, and a Type II (hyperbolic) functional response to mussel density at high levels of eelgrass structure. Our results and those of others suggest that the degree to which local benthic communities in southern California are resistant to Asian mussel invasion depends on habitat structure, mussel settlement rates, and the density and diversity of predators.

The infaunal community in experimentally seeded low and high density Manila clam (Tapes philippinarum) beds in a Po River Delta lagoon (Italy)

Abstract The Sacca di Goro is a shallow, brackish, eutrophic coastal lagoon in the southernmost part of the Po River Delta (northern Adriatic Sea, Italy). It is heavily exploited for rearing the Manila clam (Tapes philippinarum), mean annual production since 1986 being 10 000 t. Commercial cultivation of bivalves can exert severe impact on a local environment, especially on the invertebrate community, reducing species richness and abundance. An in situ experiment was conducted from March 2003 to February 2004 to examine the effect of clam cultivation on the macrobenthic community. Replicated sites within an area licensed for clam farming were seeded with low (500 m−2) and high (1500 m−2) clam densities; the surrounding unseeded areas were used as a control. There were only weak effects of clam presence and density on macrobenthic community abundance and functional group composition. The main determinants regulating the macrobenthic community were seasonal variations in other biota, particularly proliferation of the invasive mussel, Musculista senhousia, in August, which in turn caused a significant increase in the biomass of surface deposit-feeders and the subsequent development of Ulva rigida beds in September.

Príspevok k topografickému výskumu malakofauny okresu Levice [Contribution to the topographic malacological survey in the Levice District, SW Slovakia

The paper brings new information on mollusc distribution of Levice District in southern part of Central Slovakia. The data were obtained from 14 localities, which lie mainly in the vicinity of the Ipeľ River and southern slopes of Štiavnické vrchy Mts. Together 78 mollusc species (50 land species and 28 fresh-water species) were found. From 9 localities a litter sample from 1m² was analyzed for quantitative evaluation of snail assemblages. Malacocoenoses of thermophilous forest mollusc species were determined in the area of Štiavnické vrchy Mts. foothill (localities 2, 7, 8). The species Limacus flavus, Euconulus praticola, Pisidium amnicum and Unio crassus albensis are important from the viewpoint of nature conservation and geographical distribution. Carpathian species Bythinella austriaca, Vestia turgida, Bielzia coerulans and also European forest species Merdigera obscura reach the southern boundary of their natural area of occurrence. Typical for this region are malacocoenoses of xeric biotopes, composed from species of 4–6 ecoelement – Cecilioides acicula, Cepaea vindobonensis, Granaria frumentum, Chondrula tridens, Xerolenta obvia, Truncatellina cylindrica, Cochlicopa lubricella and Monacha cartusiana. High diversity was observed by freshwater malacocoenoses. Anodonta anatina attenuata, A. cygnea solearis, Unio tumidus zelebori, Radix ampla are typical for stagnant water biotopes (abandoned ‘paleopotamon’ side arms). In slow flowing waters of the Ipeľ River beside the common species also rare species like Anisus septemgyratus and Pisidium amnicum were detected. Interesting is also the occurrence of strong population of invasive species of Asian mussel Sinanodonta woodiana, which is known to infiltrate into a number of streams all around Slovakia.

Vertical Distributions of Larvae of the Clam Ruditapes philippinarum and the Striped Horse Mussel Musculista senhousia in Eastern Ariake Bay, Southern Japan

We have examined the vertical distributions of planktonic bivalve larvae, particularly the clam Ruditapes philippinarum and the mussel Musculista senhousia which are common and abundant on tidal flats of eastern Ariake Bay, southern Japan. Submersible pumping gear was used to take samples at 2 stations every 2 hours during the spring tide over a whole tidal cycle and/or through daytime and nighttime. Water samples were pumped up from 3 to 5 depths from the surface to sea bottom. Regardless of tidal cycles, D-shaped larvae were concentrated near the surface, while umbo larvae were found at the surface to intermediate depths. On average, these larval densities were significantly higher at the station close to the shore than the offshore station, with no significant difference between daytime and nighttime and between flood and ebb tides at each station. The velocity and direction of water movement at both stations revealed remarkable difference between the surface and bottom waters. The larvae at the surface may quickly disperse and be transported elsewhere, while those in water close to the sea bottom may tend to be retained.

Does the recruitment of a non‐native mussel in native eelgrass habitat explain their disjunct adult distributions?

ABSTRACTWe studied variability in the abundance of small individuals of an invasive mussel (Musculista senhousia) across the depth distribution of a native marine angiosperm, eelgrass (Zostera marina). Adult mussels and eelgrass have a disjunct local distribution, each limiting the other in complex ways. To assess whether eelgrass also influenced the distribution of juvenile mussels, we sampled inside and outside eelgrass beds in one site in Mission Bay and two in San Diego Bay, California, USA. We sampled mussels in size classes 0.26–0.50 mm, 0.51–1.00 mm, 1.10–2.00 mm and > 2.00 mm from September 1997 to April 1999. We also monitored gonad development in larger mussels and in situ growth of mussels ≤ 2 mm tagged with the chemical marker calcein. Spatial and temporal variations in mussel abundances were high but seasonal patterns were roughly similar at San Diego Bay sites; very few mussels were found in Mission Bay. Mussels with full gonads were found year‐round in San Diego Bay, as were mussels in the smallest size class (with a large peak in fall and a smaller secondary one in spring), suggesting that many of the smallest mussels represent recruitment. The observation that most, although not all, tagged mussels increased in size provides further support for recruitment. Some of the highest numbers of mussels in the smallest size class were found inside eelgrass beds, indicating that eelgrass does not restrict and may actually enhance the distribution of very small mussels. The disjunct distribution of adult mussels and eelgrass thus is apparently established primarily postrecruitment. M. senhousia is capable of year‐round reproduction, recruitment and growth, and thus is poised to preempt space from eelgrass following any disturbance that results in eelgrass declines, such as habitat fragmentation, eutrophication, or disease.

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.

Functional responses and scope for growth of two non‐indigenous bivalve species in the Sacca di Goro (northern Adriatic Sea, Italy)

A comparative study was carried out on the functional feeding behaviour of the infaunal Manila clam, Ruditapes philippinarum, and the epifaunal Asian date mussel, Musculista senhousia, inhabiting the Sacca di Goro lagoon, in response to changing temperature and variable quantity of food. The rates of clearance, ingestion, absorption, respiration, and energy budget (scope for growth, SFG) were measured and compared. The two non‐indigenous species show a similar trend for all parameters measured in the two seasons considered (late winter and summer). SFG followed a clear seasonal trend, reaching higher values in the warmer period (July) for M. senhousia and in the cooler period (March) for R. philippinarum. Probably, this seasonal divergence was a consequence of the two species’ different reproductive cycles.

Predatory behavior and preference of a successful invader, the mud crab Dyspanopeus sayi (Panopeidae), on its bivalve prey

Predator–prey relationships between the panopeid crab, Dyspanopeus sayi, and the mytilid, Musculista senhousia, were investigated. Through laboratory experiments, prey-handling behavior, prey size selection, predator foraging behavior and preferences for two types of prey ( M. senhousia and the Manila clam Ruditapes philippinarum) were assessed. Handling time differed significantly with respect to the three prey sizes offered (small: 15.0–20.0 mm shell length, SL; medium: 20.1–25.0 mm SL; and large: 25.1–30.0 mm SL); mud crabs were more efficient in predating medium–small than large prey. Although differences in prey profitability were not evident, D. sayi exhibited a marked reluctance to feed on larger-sized prey whilst smaller, more easily predated mussels were available. Size selection may be the result of a mechanical process in which encountered prey are attacked but rejected if they remain unbroken after a certain number of opening attempts. D. sayi exhibited inverse density-dependent foraging. A significant higher mortality of prey was evident at low prey density. Thus, at low predator density, the D. sayi– M. senhousia interaction was a destabilizing type II functional response. Interference responses affected the magnitude of predation intensity by D. sayi on M. senhousia, since as the density of foraging crabs increased, their foraging success fell. At high density (4 crabs tank −1), crabs engaged in a high amount of agonistic activity when encountering a conspecific specimen, greatly diminished prey mortality. Finally, presenting two types of prey, Manila clam juveniles were poorly predated by mud crabs, which focused their predation mostly on M. senhousia. It is hypothesized that, when more accessible prey is available, mud crabs will have a minimal predatory impact on commercial R. philippinarum juvenile stocks.

Effect of Musculista senhousia mats on clam mortality and growth: much ado about nothing?

By means of manipulative experiments, growth and mortality of the clams Tapes decussatus and Ruditapes philippinarum were assessed in the presence and absence of Musculista senhousia (Mytilidae) in its mats. The experiment was arranged as a randomized complete block design, with eight blocks of nine cages each: four blocks contained T. decussatus, and four blocks R. philippinarum. The experimental units received one of the following treatments: T. decussatus (or R. philippinarum) with no mats, with mats of M. senhousia in high density, with mats in low density. The experiment ran for 100 days. The growth of both clam species was not affected by the presence of mussel mats. Mortality was higher for T. decussatus than for R. philippinarum, but the presence of mats, both in high and low density, seemed to exert no significant effect on clam mortality. It is hypothesized that deeper-dwelling species, as the carpet-shell and the Manila clam, are much less affected than other bivalves by mussel mats.

THE SPREAD OF AN ALIEN BIVALVE (MUSCULISTA SENHOUSIA) IN THE SACCA DI GORO LAGOON (ADRIATIC SEA, ITALY)

The Asian date mussel, Musculista senhousia (Mytilidae), which is endemic in the western Pacific, appeared and became abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. The course of the invasion was documented through a macrobenthic monitoring programme at three sites in the Sacca. From 1994, when the new mussel was first collected, M. senhousia spread throughout the lagoon and, within a few years, reached densities exceeding 10,000 individuals m ‐2 . Mussel effects on biodiversity were assessed by comparing macrobenthic community structure and composition: over a 5-year period some changes in the macrobenthic community seem to be apparent, suggesting a positive effect of the mussel on the number of species and benthic richness. Considering trophic guilds, significant positive correlations were found between M. senhousia and detritivores and herbivores, while suspension feeders probably suffered competition from the mussel. Musculista senhousia was initially successful because it exploited a naturally disturbed, sparsely occupied environment. The well-dated documentation of the first collections, increasing abundance and spread of M. senhousia at our study sites provided an opportunity to observe a biological invasion of a habitat in progress.

Observations on the recruitment of Musculista senhousia (Mollusca, Bivalvia) in the Taranto seas (Eastern-Central Mediterranean Sea)

Biogeographia vol. XXV — 2004 (Printed December, 30 ”’ 2004) Marine Biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity Observations on the recruitment of Musculistrz sen/vousirz (Mollusca, Bivalvia) in the Taranto seas (Eastern—Central Mediterranean Sea) FRANCESCO MASTROTOTARO, ALFONSO MATARRESE, GIANFRANCO D’ONGHl.A Dzjmrtimenra dz‘ Zoologia, Universitiz dz’ Bari, Via Ombomz, 4, 70125 Bari (Italy) e— mail: mzzstrototzzro @bz'o[0gz'zz. zmibrz. it Key words: Mumilistrz ten/yazzrizz, Taranto seas, Mediterranean Sea, non indigenous species, recruitment. S UMMARY Juveniles and adults of 11/Ium¢lz'.rtzt sen/Jamirz were collected during four monthly benthic surveys carried out from September to December 2002 in the Mar Piccolo ofTaranto (Southern Italy). Two recruitment pulses were observed in September and December and a growth rate of about 2 mm/month was observed for the juveniles. In September and October rwo cohorts were shown in the sampled population. The present study confirms the settlement of M. mz/zaurizz in the Mar Piccolo ofTaranto. Considering the ephemeral nature ofthe mussel mats and the seasonal changes in some environmental factors in the study area, Further studies are required in order to define the dynamics of such a settlement. INTRODUCTION The presence of non indigenous species in the Mediterranean basin has increased in the recent years. The spreading of these species is often due to adult or larval transport by fouling on the hulls of ships and in ballast waters, respectively (Occhipinti Ambrogi, 2001). Furthermore, the transfer of exotic species into the Mediterranean for aquaculture purposes often causes the entrance of other non indigenous species (Rossi, 1992). \When a non indigenous species reaches a new habitat it may die immediately because it cannot withstand the new climatic conditions or it may survive

Effects of hypoxia on predator-prey interactions between juvenile Carcinus aestuarii and Musculista senhousia

The impact of hypoxia upon predator-prey interactions between juvenile Mediterranean shore crabs Carcinus aestuarii and the mytilid Musculista senhousia was investigated in laboratory and mesocosm experiments. These species are among the most abundant macrobenthic organisms in the Sacca di Goro, a lagoon in the Po River deltaic system (Adriatic Sea, Italy). The effect of normoxia and hypoxia on juvenile C. aestuarii predatory behaviour was examined in laboratory experiments; factors were prey size (small, medium and large) and oxygen level (normoxic: >6.0 mg O 2 l -1 ; moderately hypoxic: 3.0 to 1.5 mg O 2 l -1 ; severely hypoxic: 6.0 mg O 2 l -1 ; severely hypoxic: <1.5 mg O 2 l -1 ). Consumption rates of C. aestuarii were lower under hypoxia, resulting in reduced mortality rates of mussels. Predation was inversely dependent. Short-term hypoxia, therefore, reduced the ability of crabs to forage on mussels efficiently and increased mussel survival, probably reducing the transfer of bivalve prey to predatory crabs.

The non-indigenous mussel Musculista senhousia in an Adriatic lagoon: effects on benthic community over a ten year period

The Asian date mussel, Musculista senhousia (Mytilidae), is a good example of a species that has dispersed outwards from its native area through human-mediated transport, establishing sustainable populations in distant parts of the world. The date mussel, which is endemic in the Western Pacific region, appeared and became very abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. Effects of M. senhousia on macrobenthic biodiversity were assessed over a ten year time period. At the study site, the increase in abundance and spread of M. senhousia resulted in an alteration of the pre-established macrobenthic community. Changes in benthic dynamics seemed apparent, through the inhibition of epifaunal, suspension-feeding taxa (Ficopomatus enigmaticus, Mytilaster minimus), and the enhancement of detritivores (Neanthes succinea, Streblospio shrubsolii, Microdeutopus gryllotalpa). It is hypothesized that the Asian date mussel was initially successful because it exploited a naturally disturbed, sparsely occupied environment, rather than interjecting itself among and displacing existing species. Musculista senhousia acted, at least initially, as a colonizer rather than an invader.

Occurrence of Musculista senhousia (Mollusca: Bivalvia) in the Taranto seas (eastern-central Mediterranean Sea)

The first record of Musculista senhousia in the Taranto seas (eastern-central Mediterranean Sea) is reported. The species was mostly found on bottoms with pleustophytic algal felt where densities up to 3800 specimens per square metre were estimated. The sizes in the sampled population ranged from 5·16 to 30·59 mm. Two main modal components were detected around 11·67±0·67 mm and 18·00±2·38 mm.

Prey preference of Carcinus aestuarii: possible implications with the control of an invasive mytilid and Manila clam culture in a northern Adriatic lagoon

The cultivated Manila clam, Ruditapes philippinarum, and the accidentally introduced Asian date mussel, Musculista senhousia, are nowadays the most abundant bivalve species in the Sacca di Goro (northeastern Italy). M. senhousia, with its sub-surficial extended mats, creates quite a heavy economical impact to clam shellfish culture. Individual Mediterranean shore crabs Carcinus aestuarii were allowed to forage on the two bivalve species to examine the crab's preference in light of the optimal foraging theory. Crabs preferred M. senhousia over R. philippinarum: mortality was higher for the former (34.6%) than for the latter bivalve species (9.5%). It is suggested that the marked preference of C. aestuarii for Asian date mussels over Manila clams could be advantageously exploited to control or to reduce the extension of mats, especially where these create management problems to infaunal, burrowing bivalve cultures.

Abundance and Distribution of Pelagic Larvae of Bivalves and Echinoderms in Busse Lagoon (Aniva Bay, Sakhalin Island)

The taxonomic composition and numbers of pelagic larvae of bivalves in Busse Lagoon and the contiguous areas of Aniva Bay (southern Sakhalin) were studied in 2000–2001. In comparison with 1973–1974, the total density of larvae increased 2–3 times, but their taxonomic composition changed and a redistribution of dominant species occurred. Numbers of bivalve larvae increased at the expense of larvae of Musculista senhousia, Crassostrea gigas, and species of the Tellinidae. In 2000–2001, larvae of Ruditapes philippinarum, Mya arenaria, Swiftopecten swifti, and some other species were encountered in plankton very rarely or were not found at all. The drastic decrease in the larval density of some bivalve species was caused by uncontrolled and nearly total harvesting of mollusks. Larval echinoderm numbers in the lagoon were not high in 2000–2001; larvae of the sea cucumber Apostichopus japonicus and the sea urchin Strongylocentrotus intermedius predominated.

Foraging behaviour and mutual interference in the Mediterranean shore crab, Carcinus aestuarii, preying upon the immigrant mussel Musculista senhousia

Predator–prey dynamics between the Mediterranean shore crab Carcinus aestuarii and the immigrant mussel Musculista senhousia were examined in laboratory experiments to assess the effects of varying predator and prey densities upon predator foraging rates and prey survival. The factorial design involved three predator and three prey densities, with four trials per treatment combination. Functional responses were differentiated statistically by analysis of the exponent β of a general functional response model. Shore crabs displayed type II (decelerating rise to an upper asymptote) inversely density-dependent functional responses at low and moderate predator densities, while a non-traditional model was probably more appropriate at high predator density. No density-dependent refuge was observed for M. senhousia, whereas, at high predator density, mutual interference among crabs was evident and prey mortality was lowered. Mediterranean shore crab's combined functional and interference response, by affecting foraging rates, was important to the outcome of interactions between predators and the bivalve prey, and might play an important role in determining crab's predatory behaviour and dispersion, and prey persistence, in the field.