Competition and interaction between Neosarmatium smithi (Crustacea: Grapsidae) and Terebralia palustris (Mollusca: Gastropoda) in a Kenyan mangrove

 In a Kenyan mangrove, we studied the interactions between the gastropod Terebralia palustris and the crab Neosarmatium smithi when foraging on decaying mangrove leaves. Interactions are considerable on account of their wide overlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves) and activity window (diurnal low water). The snails find a leaf by a systematic transecting of the platform and eat the leaf after crawling on to it, usually en masse. The crabs rarely venture beyond 80 cm from their burrows, and once they find a leaf they quickly drag it back into their burrow, probably to reduce the strong intra-specific competition. A crab is able to drag a leaf away even if a number of snails are already feeding on it, by strongly pulling the leaf away or by pushing the snails off the leaf. The success of the “thief ” depends on both the crab's size and the number of snails on the leaf. Received: 25 July 1999 / Accepted: 27 April 2000     

Ontogenetic change in the radula of Conus magus (Gastropoda)

Specimens of the Indo-Pacific piscivorous gastropod Conus magus Linnaeus, 1758 were either collected by SCUBA in the field in Palau (1983–1984) or raised in the laboratory from egg capsules. C. magus captures adult fish with a specially modified radula tooth. Radula morphology was analyzed in a size range of individuals from 4.1 to 43.7 mm shell length, which encompassed early postmetamorphic juveniles to adults. Post-metamorphic C. magus juveniles are too small to consume fish, and all individuals below 9 mm possess a juvenile radula tooth totally different from that of the adult and resembling that of some vermivorous Conus species. The only food remains found in the digestive tracts of juveniles were the setae of syllid polychaetes. All individuals above 10.5 mm possessed adult teeth and had only fish remains in the gut. Two specimens, 10.1 and 9.2 mm in shell length, had intermediate-type radula teeth.     

Use of Stress‐Hormone Levels and Habitat Selection to Assess Functional Connectivity of a Landscape for an Amphibian

Abstract: The influence of landscape matrix on functional connectivity has been clearly established. Now methods to assess the effects of different land uses on species’ movements are needed because current methods are often biased. The use of physiological parameters as indicators of the level of resistance to animal movement associated with different land uses (i.e., matrix resistance) could provide estimates of energetic costs and risks to animals migrating through the matrix. To assess whether corticosterone levels indicate matrix resistance, we conducted experiments on substrate choice and measured levels of corticosterone before and after exposure of toads (Bufo bufo) to 3 common substrates (ploughed soil, meadow, and forest litter). We expected matrix resistance and hormone levels to increase from forest litter (habitat of the toad) to meadows to ploughed soil. Adult toads had higher corticosterone levels on ploughed soil than on forest litter or meadow substrates. Hormone levels did not differ between forest litter and meadow. Toads avoided moving onto ploughed soil. Corticosterone levels in juvenile toads were not related to substrate type; however, hormone levels decreased as humidity increased. Juveniles, unlike adults, did not avoid moving over ploughed soil. The difference in responses between adult and juvenile toads may have been due to differences in experimental design (for juveniles, entire body used to measure corticosterone concentration; for adults, saliva alone); differences in the scale of sensory perception of the substrate (juveniles are much smaller than adults); or differences in cognitive processes between adult and juvenile toads. Adults probably had experience with different substrate types, whereas juveniles first emerging from the water probably did not. As a consequence, arable lands could act as ecological traps for juvenile toads.     

Relative importance of benthic microalgae,phytoplankton, and mangroves as sources of nutrition for penaeid prawns and other coastal invertebrates from Malaysia

Carbon, sulfur, and nitrogen stable isotope ratio techniques were used in 1989 and 1990 to evaluate the relative importance of algae and of mangrove detritus in the nutrition of two penaeid prawn species on the west coast of Peninsular Malaysia. Mangrove detritus was found to contribute to the nutrition of juvenile Penaeus merguiensis de Man living within tidal creeks, but not to adult P. merguiensis and juvenile and adult Parapenaeopsis sculptilis (Heller) captured offshore. Results from radiotracer feeding studies, with refractory ¹⁴C mangrove lignocellulose as the food source, indicated that juvenile P. merguiensis from tidal creeks assimilated mangrove carbon with an efficiency of 13.4%. This did not differ significantly (P=0.05) from the assimilation efficiencies of juvenile and adult P. sculptilis living offshore (10.0 and 10.9%, respectively); these values were significantly higher (P<0.001) than for adult P. merguiensis (2.1%). Thus, the differential contribution of mangrove material to the nutrition of prawns in the tidal creeks and offshore was not related to differences in the prawn's ability to utilize detritus. Instead, our analysis of C stable isotopes in sediments indicated that mangrove detritus was generally more abundant within the tidal creeks than offshore. Juvenile prawns in the tidal creeks may also utilize mangrove material indirectly by feeding on small detritivorous invertebrates. Stable isotope analyses suggest that benthic microalgae constitute the other major dietary component for prawns living in tidal creeks. Prawns offshore were utilizing mainly phytoplankton-based material.     

Feeding ecology of the mangrove crab <Emphasis Type="Italic">Ucides cordatus</Emphasis> (Ocypodidae): food choice,food quality and assimilation efficiency

Food preferences, consumption rates and dietary assimilation related to food quality were investigated for the large semi-terrestrial and litter-consuming mangrove crab Ucides cordatus cordatus (Ocypodidae, L. 1763) in northern Brazil. Stomach contents were composed of mangrove leaves (61.2%), unidentified plant material and detritus (28.0%), roots (4.9%), sediment (3.3%), bark (2.5%), and animal material (0.1%). U. cordatus prefers Rhizophora mangle over Avicennia germinans leaves despite a higher nitrogen content, lower carbon to nitrogen (C/N) ratio and lower tannin content of the latter. Also, assimilation rates for senescent R. mangle leaves (C: 79.3%, N: 45.4%) were higher than for A. germinans leaves (C: 40.6%, N: 9.1%). Faeces composition indicates that A. germinans leaves were more difficult to masticate and digest mechanically. The leaf-ageing hypothesis, according to which crabs let leaves age in burrows to gain a more palatable and nutritive food, was rejected for U. cordatus since N content, C/N ratio and the abundance of microorganisms did not differ significantly between senescent leaves and leaves taken from burrows. The low microbial biomass on leaf surfaces and in the sediment indicates its minor importance for the nutrition of U. cordatus. It is concluded that high ingestion and assimilation rates of a R. mangle diet together with the consumption of algae allow for a high intake of C, N, and energy. The data suggest that the digestibility of mangrove leaves by U. cordatus is not hampered by tannins. This may have provided a competitive advantage over other leaf-consuming invertebrates unable to digest mangrove litter with high tannin concentrations. Due to the large stock biomass of U. cordatus in the study area, a great amount of finely fragmented faeces is produced (about 7.1 ton dry matter ha⁻¹ year⁻¹ in a R. mangle forest) which is enriched in C, N and bacterial biomass compared to the sediment. The decomposition of mangrove litter, and thus nutrient and energy transfer into the sediment, is greatly enhanced due to litter processing by U. cordatus.     

Movements of <Emphasis Type="Italic">Ilyanassa obsoleta</Emphasis> (Gastropoda) on an intertidal sandflat

The gastropod Ilyanassa obsoleta (Say) is native to the east coast of North America where it is locally abundant on sandflats, mudflats, and in saltmarsh creeks. The local disturbances created by snails and their movements affect soft-sediment community composition. Movements of individually marked snails were followed on an intertidal sandflat on Cape Henlopen, Delaware, U.S.A. In June 1991, 1,200 snails that had tested as trematode-uninfected were released and over 5 months 554 were sighted 971 times. Mean daily net distance moved was 1.7 m, but snails often moved 10–20 m day⁻¹ and one snail was 180 m distant after 130 days. Net dispersal of the released population was attained in ≈10 days, by which time, a typical distance from release was 15–20 m. Snails were not found crossing sandbars and most moved away from shore into a tidal gully. In June 1993, 500 snails, both uninfected and trematode-infected, were released at the same position and over 6 months, 350 snails were sighted 949 times. Sandbars were again barriers to movement, but their changed positions allowed wider dispersal. Net dispersal was complete in ≈20 days by which time a typical distance from release was 30–40 m. Mean daily net distance moved was 2.2 m, but within 10 days snails had moved 50–100 m. In both years, following initial dispersal, snails (infected or not) took up random directions from move to move. Infected and uninfected snails dispersed equal distances, but had different mean final dispersal directions. Dispersal of I. obsoleta individuals was extensive and affected by shifting sandbar positions and parasitism. Recognizing this will be important in appreciating the ecological dynamics of this gastropod and in determining its effects on soft-bottom communities.Electronic Supplementary Material Supplementary material is available for this article at     

Reproductive patterns of three intertidal salt-marsh gammaridean amphipods

Among three sympatric species of epibenthic amphipods found at different tide marks at Jamaica Bay, New York (USA), the length of time juveniles spend with the mother increases and the number of juveniles per brood decreases as tidal height increases. Each brood has two developmental periods: (1) the embryonic period, from ovulation to hatching; (2) the juvenile period, from hatching to emergence from the marsupium. Gammarus palustris, found at the high-tide mark, has a mean juvenile period of 1.7 days and a mean brood size of 12.4 offspring; G. mucronatus, found at mean-tide mark, has a mean juvenile period of 0.8 days and a mean brood size of 27.4 offspring; Melita nitida, found at low-tide mark, has a mean juvenile period of 0.5 days and a mean brood size of 30.0 offspring. Further, the range of days that a juvenile may emerge is widest for G. palustris (0 to 8 days after hatching) and narrowest for M. nitida (0 to 2 days).This work was submitted in partial fulfillment of the requirements for the Ph.D. at the City University of New York.     

The role of the amphipod <Emphasis Type="Italic">Gammarus locusta</Emphasis> as a grazer on macroalgae in Swedish seagrass meadows

Mesograzers are thought to play a critical role in seagrass beds by preventing overgrowth of ephemeral algae. On the Swedish west coast, eelgrass Zostera marina has decreased in recent decades as a result of eutrophication and increased growth of macroalgal mats (mainly filamentous Ulva spp. and Ectocarpales), with no indication of grazer control of the algae. The aim of this study was to investigate the ability of the amphipod Gammarus locusta to control algal blooms during nutrient-enriched and ambient conditions, using a combination of laboratory, field and model studies. Laboratory experiments demonstrated that juvenile and adult G. locusta could consume both Ulva spp. and Ectocarpales, but that consumption of Ulva spp. was significantly higher. Cannibalism was common in individual treatments involving multiple size-classes of G. locusta, but only large, male gammarids consumed smaller juveniles in the presence of Ulva spp. as an alternative food source. However, no negative effects of cannibalism were found on total grazing impact. A model using size-specific grazing rates and growth rates of G. locusta and of Ulva spp. suggests that approximately 62 young juvenile, or 27 adult G. locusta are needed per gram DW of Ulva spp. to control the algal growth during ambient nutrient conditions, and approximately 2.6 times as many gammarids during enhanced nutrient conditions. On the Swedish west coast, densities and mean sizes of G. locusta in eelgrass beds are below these critical values, suggesting that the gammarids will not be able to control the growth of the filamentous macroalgae. However, in the field cage experiment, immigration of juveniles and reproduction of encaged adult G. locusta resulted in unexpectedly high densities of G. locusta (>4,000 individual m⁻²), and very low biomass of Ulva spp. in both ambient and nutrient-enriched treatments. Although the high numbers of juveniles in all cages precluded any significant treatment effects, this suggests that in the absent of predators, the population of G. locusta can grow significantly and control the biomass of Ulva spp. Furthermore, low grazing of Ectocarpales in the laboratory and high biomass of these filamentous brown algae in the field indicate a preference for the more palatable green algae Ulva spp. This study indicates that the high grazing capacity of G. locusta, in combination with high reproduction and growth rates, would allow the amphipod to play a key role in Z. marina ecosystems by controlling destructive blooms of filamentous green algae. However, high predation pressure appears to prevent large populations of G. locusta in eelgrass beds on the Swedish west coast today.     

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope.     

Feeding of marine planktonic copepods on mixed phytoplankton

The feeding of juveniles and adults of the copepods Eucalanus pileatus, Temora stylifera and T. turbinata fed a mixture of the phytoplankton Skeletonema costatum, Leptocylindrus danicus and Rhizosolenia alata f. indica was studied at 20°C. E. pileatus nauplii, copepodids and adult females ingest similar percentages of the 3 algae in terms of carbon. Temora juveniles younger than CII ingest mainly S. costatum; at more advanced developmental stages, the ingestion rate on S. costatum remains constant whereas feeding on L. danicus and R. alata f. indica increases with increasing body weight. Feeding on high concentrations of large particles reduces the grazing pressure on small particles, thus favoring zooplankton which require small-sized food.     

Ontogenetic habitat shift,population growth,and burrowing behavior of the Indo-Pacific beach star, <Emphasis Type="Italic">Archaster typicus</Emphasis> (Echinodermata; Asteroidea)

Archaster typicus, a common sea star in Indo-Pacific regions, has been a target for the ornamental trade, even though little is known about its population biology. Spatial and temporal patterns of abundance and size structure of A. typicus were studied in the Davao Gulf, the Philippines (125°42.7′E, 7°0.6′N), from February 2008 to December 2009. Specimens of A. typicus were associated with intertidal mangrove prop roots, seagrass meadows, sandy beaches, and shoals. Among prop roots, specimens were significantly smaller and had highest densities (131 ind. m⁻²) between November and March. High organic matter in sediment and a relatively low predation rate seemed to support juvenile life among mangroves. Size and density analyses provided evidence that individuals gradually move to seagrass, sandy habitats, and shoals as they age. Specimens were significantly larger at a shoal (maximum radius R = 81 mm). New recruits were found between August and November in both 2008 and 2009. Timing of recruitment and population size frequencies confirmed a seasonal reproductive cycle. Juveniles had relatively high growth rates (2–7 mm month⁻¹) and may reach an R of 20–25 mm after 1 year. Growth rates of larger specimens (R > 30 mm) were generally <2 mm month⁻¹. The activity pattern of A. typicus was related to the tidal phase and not to time of day: Specimens moved over the sediment surface during low tides and were burrowed during high tides possibly avoiding predation. This is one of the first studies to document an ontogenetic habitat shift for sea stars and provides new biological information as a basis for management of harvested A. typicus populations.     

Relating bird host distribution and spatial heterogeneity in trematode infections in an intertidal snail—from small to large scale

Shorebird abundance and spatial distribution of larval trematodes in the New Zealand mudsnail, Zeacumantus subcarinatus, were investigated in soft-sediment intertidal bays within Otago Harbour, South Island, New Zealand. In a small-scale study, recruitment of trematodes to caged sentinel snails and the prevalence of infection in free-living snails were examined across a grid of fifteen 50×25 m plots arranged in a representative area of an intertidal bay, in relation to within-plot shorebird abundance (definitive hosts) and tidal height. In a large-scale study, natural spatial variation of larval trematodes in Z. subcarinatus was examined across 12 bays in relation to local abundance of shorebirds. Our results revealed that trematode prevalence in snails was positively correlated with bird abundance across bays (R ²=0.503, P=0.006). In contrast, despite a difference in bird abundance between tidal heights, there was no evidence that trematode prevalence reflected the spatial distribution of birds in the small-scale study, suggesting that factors related to differences in submersion time may override the differential input of trematode eggs from birds.     

Ontogeny of space use and diet of two temperate damselfish species, <Emphasis Type="Italic">Parma microlepis</Emphasis> and <Emphasis Type="Italic">Parma unifasciata</Emphasis>

Studies of reef fish herbivory have mainly focused on the impacts and behaviour of adults of tropical species. In this study, the ontogenetic shifts in home range, aggression, feeding rate, diet and gut morphology in juveniles and adults of two temperate territorial damselfishes, Parma microlepis and Parma unifasciata, were determined. Both P. microlepis and P. unifasciata juveniles under 80 mm TL exhibited no aggressive chases towards conspecifics or other species, while above 80 mm TL aggressive chase frequency increased in conjunction with an increase in home range, defended as a territory. Ontogenetic diet shifts, characterised by an increase in herbivory (P. unifasciata: juveniles: 64% plant material, adults: 95% plant material; P. microlepis: juveniles: 43% plant material, adults: 67% plant material) were observed for both species. The ratio of digestive tract length to body length, which often accompanies a switch to herbivory, increased significantly with ontogeny for both species. Compared to tropical confamilial grazers, these temperate damselfish species feeding rates were lower, and they had larger territories which were not as strongly defended (fewer aggressive chases).     

Life history of the golden ring cowry Cypraea annulus (Mollusca: gastropoda) on Okinawa Island,Japan

Two mark-recapture studies, regular population censuses, field observations, and laboratory culture were used to study the life history of the tropical marine gastropod Cypraea annulus Linnaeus, 1758 from Cape Maeda, Okinawa Island, from April 1984 to March 1986. In the field, the average rate of increase in shell length of marked juvenile snails was 1.0±0.3 mm wk^-1 (N=13), with a maximum of 1.5 mm wk^-1 (initial shell length 10.6 to 17.2 mm). In the laboratory, the maximum growth rate of juveniles was 3.0 mm wk^-1 with food ad libitum. Snails with primordial teeth on the shells grew at a rate of 0.1 to 0.5 mm wk^-1 for about 2 wk. The adults continued to grow at a similar rate for an additional 3 to 6 wk, and ceased detectable growth when some females started spawning egg masses. In the littoral zone on Okinawa Island, snails reproduced throughout the year. Egg masses brooded by three females (shell length 17.4 to 21.3 mm) in the field contained 90 000 to 133 000 ova. In the laboratory, brooding periods of three females lasted 6,8, and 9 d. The estimated average frequency of spawning was 5 egg masses female^-1 yr^-1. The mean shell length of adult females (20.3 mm) was significantly larger than that of adult males (19.6 mm). The life-history strategy of C. annulus is characterized by rapid growth, high fecundity, and repeated spawning throughout the year.     

Population ecology of the mud crab <Emphasis Type="Italic">Scylla paramamosain</Emphasis> (Estampador) in an estuarine mangrove system; a mark-recapture study

Mud crabs of the genus Scylla are commercially important mangrove residents that are extensively fished throughout their range in the Indo-West Pacific. Despite this high level of exploitation very little is known about the population dynamics of any of the Scylla species. The present study concentrated on an exploited population of Scylla paramamosain in a natural estuarine mangrove on Can Coc Island in the mouth of the Hau River, Mekong Delta, Vietnam. A total of 6,114 juvenile crabs captured on the seaward mangrove fringe were internally tagged by injection of coded microwire tags and released over a period of 29 days. Recaptures were monitored over the following 144 days. There was little migratory movement within the estuary; of 285 recaptured crabs, 93% were recovered within the island mangrove study area and only two individuals were recovered from mangroves lining the opposite mainland riverbanks. A von Bertalanffy growth function was fitted to growth increment data from recaptured crabs, with L _max = 150 mm to derive a growth constant, k = 2.39 year⁻¹. The theoretical age at which carapace width is zero (t ₀) was derived from known size at recruitment at instar 1, giving a value of −0.0095 years. Previous studies of the same population have shown that female S. paramamosain reach maturity at a mean size of 102 mm carapace width. The present study indicates that they attain this size at around 160 days from first settlement in the mangrove fringe. Abundance of juvenile crabs in the study area was estimated by the Petersen method as 1,101,500 (95% CI 4,17,300–1,785,800, representing 1,102 crabs ha⁻¹ of mangrove. Estimation of mortality from tag returns and from the age-catch curves during a period of constant recruitment were comparable (Z = 1.11 and 1.04 month⁻¹, respectively). Fishing only accounted for 14% of total mortality, suggesting that at the time exploitation was not at a critical level despite the apparent high level of fishing activity.     

Genetic heterogeneity in a single year-class from a panmictic population of adult blue rockfish (<Emphasis Type="Italic">Sebastes mystinus</Emphasis>)

We used microsatellite genetic markers to investigate adult population structure and the formation of a new year-class in Sebastes mystinus (blue rockfish). Since S. mystinus may live as long as 45 years and reach reproductive age at approximately 5 years, the adult population may contain as many as eight generations of reproductive adults. We investigated whether the juveniles of the 2000 year-class and the adult population were genetically homogeneous along the California coast. We sampled approximately 100 juveniles from three sites, two sites along the Monterey Peninsula (Carmel and Monterey) in central California and one at Fort Ross in northern California, and approximately 50 adult S. mystinus from five sites throughout the population center. The adult sampling spanned approximately 700 km from the northern Channel Islands to Fort Bragg. The juveniles showed significant heterogeneity in allele frequencies among distant locations and genetic homogeneity among adjacent locations. In contrast, the adults showed genetic homogeneity over large distances (San Miguel Island to Fort Bragg), indicating little limitation of gene flow in this region. Allele frequencies of juveniles differed from adult samples and in some cases reduced genetic diversity indicative of sweepstakes recruitment (small sample of the adult reproductive potential). The genetic structure of the 2000 year-class suggests that despite a genetically homogenous adult population, settled juveniles can be genetically heterogeneous along the California coast. The results also suggest that the adults, with several year-classes, are capable of maintaining a panmictic population despite the genetic distinctiveness of individual year-classes.     

Familiarity with adults,but not relatedness,affects the growth of juvenile red-backed salamanders (<Emphasis Type="Italic">Plethodon cinereus</Emphasis>)

The relative roles of kinship and familiarity in affecting an individual’s growth and fitness are not easy to disentangle. Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also be related (in terms of kinship) to those nearby conspecifics. While some studies have inferred that kin discrimination affects fitness correlates, other studies found that familiarity alone can reduce aggressive interactions, thus increasing fitness. These studies have all focused on intra-age class pairs or groups. However, many animals interact with conspecifics from different cohorts. In many populations, adults of Plethodon cinereus territorially defend rocks and logs that retain moisture and food resources. We investigated whether juveniles of P. cinereus grew more in the presence of adults that were relatives or familiar. We collected pairs of juveniles and adults found under the same cover objects in the forest (familiar) and pairs of juveniles and adults found under different cover objects, approximately 10 m apart (unfamiliar). We determined parentage and relatedness of the adult–juvenile pairs and then placed these pairs in semi-natural mesocosms for 17 days. We found that juveniles housed with familiar adults had significantly greater increases in mass and snout–vent length than juveniles housed with unfamiliar adults in 2006 but not in 2007. Relatedness had no effect on growth. In addition, juveniles cohabitating with adults were not more likely to be their offspring. At least under certain environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the growth of juvenile salamanders.     

Utilisation of mangroves and seagrasses by fishes in the Negombo Estuary,Sri Lanka

In two years of sampling, 10 287 fishes belonging to 62 species (39 families) were collected from mangroves and seagrasses of the Negombo Estuary. Of the species collected, 70% were marine, 27% estuarine and 3% freshwater. Aplocheilus melastigma, Ambassis dayi, Etroplus suratensis, E. maculatus, Bathygobius fuscus and Arothron immaculatus constituted 90% of the catch. Sixteen species were caught only from mangroves, 6 only from seagrasses, and 40 from both. The number of species, individuals, biomass and diversity were higher in seagrasses than in mangroves. Gobies and some siganids moved to the mangrove habitat as they grew, but cichlids, triacanthids, some eleotrids and tetraodontids preferred seagrasses. The number of species and individuals caught increased at the beginning of the north-east monsoon when the rainfall was low. The number of species and individual numbers were positively correlated with salinity and dissolved oxygen and negatively correlated with water temperature. Of the 33 species examined, seagrasses formed >25% of the gut content in juvenile Lates calcarifer, Apogon thermalis, E. suratensis, E. maculatus, Siganus javus, Butis butis and Bathygobius fuscus. Mangrove litter was the main gut content of the family Syngnathidae. E. suratensis, E. maculatus and S. javus from seagrasses contained more filamentous algae than seagrasses in their stomachs. S. javus collected from mangroves also contained more seagrasses in their stomachs than mangrove litter, indicating that the association of juvenile fishes with mangroves or seagrasses may not be obligate in estuaries subject to low tidal fluctuations.     

Recruitment and ontogenetic habitat shifts of the yellow snapper (<Emphasis Type="Italic">Lutjanus argentiventris</Emphasis>) in the Gulf of California

We examined recruitment and ontogenetic habitat shifts of the yellow snapper Lutjanus argentiventris in the Gulf of California, by conducting surveys and collections in multiple mangrove sites and major marine coastal habitats from 1998 to 2007. Over 1,167 juvenile individuals were collected and 516 otoliths were aged to describe the temporal pattern of the settlement. L. argentiventris recruits in mangroves, where juveniles remain until they are approximately 100 mm in length or 300-days-old. Back-calculated settlement dates and underwater surveys indicated a major recruitment peak during September and October, around 8 days before and after the full moon. The majority of mangrove sites in the Gulf of California had a similar L. argentiventris average size at the beginning of the settlement season for the cohort of 2003; although there were significant differences in individual sizes at the end of the nursery stage. When sub-adults leave mangroves, they live in shallow rocky reefs and later become abundant in deeper rocky reefs. The density of migratory individuals (10–20 cm SL) decreased exponentially as the distance between a reef and a nearby mangrove site increased. This finding has important implications for local fishery regulations and coastal management plans.     

Effect of epibiosis on the fitness of the sandy shore snail<Emphasis Type="Italic"> Batillaria zonalis</Emphasis> in Hong Kong

Batillaria zonalis is a common snail on Hong Kong sandy shores, occupying the low-mid shore. Shells of B. zonalis (basibiont) are often fouled with the rock oyster Saccostrea cucullata and the barnacle Balanus reticulatus (epibiont). This epibiotic interaction has a negative impact on the fitness of B. zonalis in terms of impairing fecundity, mobility and metabolism of fouled individuals. During the reproductive season, fouled snails had lower Gonadosomatic Index and fewer egg-bearing individuals than non-fouled snails. Fouled snails crawled in a more tortuous pathway and with lower speed when compared with non-fouled snails. Reduction in oxygen consumption and metabolic rate in fouled snails further suggested the restriction in mobility of B. zonalis by the epibionts. Glycogen content in the foot muscle tissues and hepatopancreas of fouled and non-fouled snails was, however, similar, revealing epibiosis does not influence the energy storage of B. zonalis. Mortality of fouled and non-fouled snails was similar under laboratory conditions, suggesting epibiosis does not influence the survivorship of B. zonalis in Hong Kong. Impairment in the fitness of fouled B. zonalis indicates that epibiosis can influence the population dynamics of B. zonalis in Hong Kong.Communicated by T. Ikeda, Hakodate