Size-related selection of two intertidal gastropods by the reef crab Ozius truncatus

Reef crabs, Ozius truncatus H. Milne-Edwards 1834, and gastropods, Bembicium nanum (Lamarck, 1882) and Nerita atramentosa Reeve, 1855, were collected from a South Australian rocky intertidal platform in April 1981. Laboratory experiments were conducted to determine (1) the size of prey chosen, and (2) the energy gained by the reef crabs feeding on B. nanum and N. atramentosa. The time taken to break open and consume prey increased exponentially with prey shell height. Crabs with larger master claws had shorter handling times for a given prey size. When offered a range of prey sizes, crabs selected prey of a certain size, well below the maximum prey size that they could handle. The mean prey size selected by crabs did not concide with the size predicted to yield the maximum rate of energy gain. For example, one reef crab preferred B. nanum 5 to 8 mm in size, but the size class predicted to yield the greatest energy gain was 4 to 4.9 mm. The results of the laboratory prey-choice experiments are discussed in relation to the shore-level size gradients of B. nanum and N. atramentosa.     

Anthropogenic influences on the infestation of intertidal gastropods by seabird trematode larvae on the southern Barents Sea coast

In this study we examined how the variation in the distribution of six species of seabird trematodes was influenced by human activities along the subarctic Barents Sea coast of northern Norway. This was done by comparing the prevalence of the parasites in two species of intermediate host (Littorinasaxatilis and Littorina obtusata) on seashores near fishing industry complexes, fish farms and at control sites. In L. saxatilis there were higher prevalences at sites influenced by human activities for three out of five trematode species (Microphallus piriformes,  M. similis, Cryptocotyle lingua) which have gulls (Larus spp.) as their predominant final hosts, while in L. obtusata, only  M. similis was more common at sites with human activity. For  M. pygmaeus, a trematode which has the common eider (Somateria mollissima) as its most predominant final host, the prevalence in L.␣saxatilis tended to be higher at sites with fishing industry, but differences were not significant. No such tendency was found in L. obtusata for this trematode. The overall prevalence in L. obtusata was lower than in L.␣saxatilis. This indicates that the vulnerability to trematode infection differs between the two snail species depending on the variation in the distribution patterns in the intertidal zone. Gulls tend to concentrate in areas near fishing industry and fish farms to feed on fish offal, which leads to an increase in the transmission between hosts, and to a higher level of parasite infection, locally. Received: 4 May 1998 / Accepted: 18 October 1998     

The importance of sandflat morphology to recruitment of the intertidal snail Nassarius pauperatus during ten consecutive years at three sites in South Australia

This project was desinged to confirm the temporal consistency of inter-site differences in recruitment of an intertidal gastropod, and to test the hypothesis that these differences are accounted for by differences in shore topography. Annual recruitment of the intertidal sanil Nassarius pauperatus (Lamarck) was estimated at two sandflats in Gulf St Vincent, South Australia, over a period of 12 yr (1979 to 1990). At one sandflat the gradient was slight, the zone containing N. pauperatus was wide, and there were extensive pools of water at low tide, whilst at the other sandflat the gradient was steeper, the zone containing N. pauperatus was narrower, and there were fewer or no pools. Although recruitment at both sites varied temporally, the density of recruits was always higher at the first site. These data, together with data covering 10 yr (1981–1990) from a sandflat where the gradient of the substratum was decreasing due to accretion of sediment, suggest that shore topography is an important determinant of relative recruitment for N. pauperatus in South Australia.     

Hydrocarbon metabolism in the intertidal fiddler crab Uca pugnax

The fiddler crab Uca pugnax was examined for its ability to metabolize foreign hydrocarbons. The microsomal mixed function oxidase system was identified in U. pugnax tissues using Aldrin epoxidation rates as the assay. Rates were slow: 96 pM Dieldrin per mg microsomal protein per hour in the hepatopancreas, 438 pM mg^-1 h^-1 in the gill, and 228 pM mg^-1 h^-1 in claw-muscle microsomes. Using standard methods, no difference in rates could be detected between crabs living in clean areas and those living in environments highly contaminated with foreign hydrocarbons. In vivo rates of naphthalene oxidation were measured and used to calculate a clearance time for U. pugnax body tissues based on the aromatic hydrocarbon content of crabs collected from an oil-polluted salt marsh. Calculated clearance time was beyond the life span of the crab. It is concluded that this minimal ability of U. pugnax to metabolize foreign hydrocarbons partially accounts for its sensitivity to oil pollution in the environment.     

Mud crab predation on ribbed mussels in salt marshes

Mud crab (Panopeus herbstii H. Milne Edwards) predation on Atlantic ribbed mussels (Geukensia demissa Dillwyn) was studied by a series of laboratory and field experiments at two sites at Morehead City, North Carolina, USA from 1987 to 1989. Tidal elevation had no effect on predation intensity, although mud crabs were active only when they were submerged. Horizontal distance from the water-marsh edge significantly affected mussel mortality in one of two winter experiments, despite the occurrence of virtually all the crabs at the marsh edge. Of the juvenile mussels attached to adult mussels, those totally buried in the sediment suffered mortality from mud crab predation at a rate not detectably different from those exposed above the surface. Juveniles attached to adult conspecifics, however, experienced significantly less mortality than those attached to oysters. Interestingly, the two groups of mussels (those attached to conspecifics and those attached to oysters) display shell morphological dimorphism. The more oblate shells of the mussels attached to oysters as compared to those attached to conspecifics might be induced by the higher predation rate. Alternatively, slimmer shells from individuals attached to conspecifics may be the result of living within physically compact mussel clumps.Please address all correspondence and requests for reprints to Dr Lin at his present address: Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, Maryland 21037, USA     

Effect of predation threat on repeatability of individual crab behavior revealed by mark-recapture

The persistence of behavioral types in situ and the drivers of persistence are central to predicting the ecological effects of intraspecific behavioral variation. We surveyed individual refuge use of mud crabs (Panopeus herbstii), a behavior related to the strength of a trait-mediated trophic cascade in oyster reefs, in the absence and presence of toadfish (Opsanus tau) predation threat. We then released these crabs into the field and using mark-recapture, measured the repeatability of this behavior in the absence and presence of threat, and how behavioral change was affected by time in the field (a month on average, up to 81 days), crab size, and sex. Because crabs exhibited some evidence of a circatidal rhythm in refuge use, we also tested how tidal height during observation influenced behavioral change. Predation threat increased refuge use, and small crabs used the refuge more than large crabs, particularly under threat. In recaptured crabs, refuge use was more repeatable under threat. Neither time in the field, crab size, crab sex, nor tidal height had any effect on behavioral change. Our results support the non-mutually exclusive hypotheses that (1) prey organisms in the presence, rather than absence, of predation threat should exhibit less behavioral variability because the fear of dying (a severe fitness consequence) should take precedence over less immediately important influences on behavior (e.g., hunger) and that (2) individual behaviors tied to fixed traits (e.g., the body size dependence of refuge use under threat in this study), rather than variable traits, should be more repeatable over time.     

Impact of epibenthic predation on estuarine intertidal harpacticoid copepod populations

The extent to which energy is transferred directly from benthic meiofauna to epibenthic predators was investigated on an intertidal sand-flat in the Exe estuary, southwest England, during 1981–1982 and compared with data obtained from an intertidal mud-flat in the Lyhner estuary, also in south-west England, between 1978 and 1981. Two species of flatfish (Pleuronectes platessa L. and Platichthys flesus L.), two species of goby [Pomatoschistus microps (Krøyer) and P. minutus (Pallas)], brown shrimp (Crangon crangon L.) and shore crabs (Carcinus maenas L.) are the most common epibenthic predators feeding on the benthic invertebrates in these locatites. Harpacticoid copepods are the only component of the meiofauna to form a significant part of the diet of early juvenile stages of these predators, particularly the invertebrates. Harpacticoids are a more important source of food for predators feeding over the sand-flat than for those feeding on the mud-flat because in the sand-flat alternative prey of suitable size, such as small annelids, are absent. Moreover, the impact of predation on the mud-flat is spread over the whole harpacticoid species spectrum whereas on the sandflat it is confined almost entirely to a single species, Asellopsis intermedia (T. Scott). Flatfish, gobies and shrimp consume daily an estimated 0.01 to 0.1% of the standing stock of A. intermedia and account for between 12 and 22% of the observed reduction in the population of this species between July and October. Therefore, only a very small proportion of total meiofauna biomass is transferred directly to higher trophic levels.     

Geographic range limitation of the intertidal gastropods Littorina sitkana and L. planaxis

Geographic ranges of marine intertidal organisms are not entirely governed by discontinuities in temperature gradients. This is especially true in the eastern north Pacific Ocean, where temperature gradation is less steep than in the western north Atlantic Ocean. The southern limit of distribution of Littorina sitkana (Philippi, 1845) and the northern limit of L. planaxis (Philippi, 1847) occur at Charleston, Oregon (Latitude 43.4°N). No discontinuity in air or water temperature can be correlated with these distributional boundaries. A third species, L. scutulata (Gould, 1849), has the widest range, overlapping with L. planaxis in the south and L. sitkana in the north (Latitude 27.5° to 58°N). L. planaxis transplanted to northern Washington survived for 4 years, grew and produced planktonic larvae. Either larval mortality or south-flowing currents during planktonic life prevent this species from dispersing northward. L. sitkana has direct development and occurs only in habitats where adults are sheltered from waves and egg masses from desiccation. Lack of suitable habitat, coupled with the presence of the predatory crab Pachygrapsus crassipes (Randall, 1839) prevent the southward establishment of L. sitkana.     

A multi-factorial experiment on heart rate variations in the intertidal crab Pachygrapsus marmoratus

A multi-factorial experiment was designed to investigate the effect of the following factors on the cardiac activity of the intertidal crab Pachygrapsus marmoratus: respiratory medium (air, water), temperature (four levels, 10, 17.5, 25, 32.5 °C), season (winter, summer) and body size (two levels, carapace ≤21 mm and carapace >21 mm). The results showed that the heart rate of P. marmoratus increased linearly with temperature and decreased when the specimens were exposed to air rather than water. Moreover, the heart rate values in summer were lower than those in winter at the corresponding temperature and body size. The summer heart rate–temperature regression line was laterally (to the right) shifted with respect to the winter line, suggesting a seasonal acclimation. Body size affected heart rate only at the acclimation temperature (17.5 °C), while no significant effect was detected at lower or higher temperatures. During the reproductive season a separate experiment was carried out to assess the effect of sex and reproductive status on heart rate. No significant difference was found among mean values of males, berried females and females without eggs. The results of the present study confirm the high physiological plasticity of this species, suggesting that P. marmoratus is a truly amphibious crab, able to deal with both water- and air-breathing during its activity. Received: 5 January 1999 / Accepted: 7 July 1999     

Interspecific variation of heavy metal concentrations in the different tissues of tropical intertidal gastropods from Malaysia

The present study aims to determine the concentrations of Cd, Cu, Fe, Ni, Pb, and Zn in the different tissues of five species of tropical intertidal gastropods from Malaysia. Each of the species have organs/tissues that highly accumulated certain metals. For Cu, the mantles of Cerithidea obtusa, Pugilina cochlidium, and Murex trapa; and the digestive caeca of Thais sp. and Chicoreus capucinus highly accumulated Cu. The shells of Chi. capucinus and M. trapa, the digestive caeca of P. cochlidium, and the digestive glands of Thais sp. and Chi. capucinus highly accumulated Cd. The tentacles and the digestive caeca of Cer. obtusa and P. cochlidium, respectively, highly accumulated Zn, the digestive glands of Thais sp., Chi. capucinus, and M. trapa also highly accumulated Zn. The shells of most of the gastropods accumulated high levels of Pb and Ni. The opercula of most of the gastropods, besides the digestive glands for Thais sp., accumulated high levels of Fe. The present study on interspecific variations of heavy metals in gastropods provided information on differences of metal distributions in the different tissues, which could be useful in proposing potential tissues as better biomonitoring tools of heavy metal bioavailabilities in the coastal waters of Peninsular Malaysia.     

Competition, predation and coexistence in a three trophic system

Simple ecological models that mostly operate with population densities using continuous variables, explain quite well the behavior of real populations. In this work we propose and discuss the continuous dynamics of a system of three species, which belongs to the well-known family of Lotka–Volterra models. In particular, the proposed model includes direct effects such as predation and competition among species, and indirect effects such as refuge. The model is proposed to explain recent studies about a group of crustacean (amphipods of genus Hyallela) found in all the plain streams and shallow lakes of the American continent. The studied system includes three compartments: algae, a strictly herbivore amphipod and an omnivore (herbivore and carnivore) one. The analysis of the model shows that there are stable extinction equilibria throughout all the parameters’ space. There are also equilibria with stable coexistence of the three species and two interesting binary equilibria: one with stable coexistence of algae and herbivore and other with coexistence between algae and omnivore amphipods. The presence of Allee effect in the algae growth and the existence of refuge for the herbivore amphipod (prey) determine a bottom-up control.     

Factors limiting distribution and activity patterns of the soldier crab Dotilla myctiroides in Phuket, South Thailand

This study was carried out between January and March 1995 on the intertidal sand flats of Tang Khen Bay, Phuket, South Thailand, where the soldier crab Dotilla myctiroides (H. Milne-Edwards) occurs in densities of up to 120 m⁻². In this bay, long, ribbon-like sand waves (wavelength 40 m, height 0.4 m) are interspersed with shallow pools, running approximately parallel to the shore. During daylight low-tides, exposure of the sand waves is followed 15 to 20 min later by the emergence of the crabs which have been buried under the sediment surface during high tide. Their subsequent burrowing and feeding activity results in the production of large numbers of sand pellets on the sediment surface. Most crabs retreat down their burrows, and some also plug the burrow entrance, prior to being covered by the incoming tide. The crab burrows have a distinct distribution on the sand waves. Burrows are most dense at the top of each sand wave, and a band of unburrowed sediment adjoins the adjacent tidal pools. Crabs are most abundant between mean high-water neap-tide level and mean low-water neap-tide level, where the median particle size of the surface sediment is ∼2 . Measurements of water-table depth below the sand waves and the exposure time of the sediment indicated that, where sediment size is suitable, the main factor controlling crab distribution is the duration of daytime exposure. This observation is in contrast to those of many previous studies, which have suggested that water-table height and sediment drainage are the main factors controlling the distribution of D. myctiroides. Received: 14 January 1998 / Accepted: 6 May 1999     

Influence of subtle substrate differences on feeding by shorebirds on intertidal mudflats

Shallow-feeding shorebirds, dowitchers (Limnodromus griseus and L. scolopaceus), western sandpipers (Calidris mauri), dunlin (C. alpina) and American avocets (Recurvirostra americana), reduced the density of their prey in mudflats with little sand but not in mudflats with a moderate admixture of sand. An experiment in Upper Newport Bay, Southern California, during October and November 1979 to explain the difference in density is described. The effect of sand on shorebird feeding was compared in the field by measuring the times spent feeding in plots where sand had or had not been added, respectively. Increasing the sand content to 14% from 2% in the top centimeter decreased the time spent in treated plots by all species compared to adjacent untreated plots. The prey species were small polychaete and oligochaete worms (0.25 to 1.25 mm wide) similar in diameter to sand grains (0.5 to 1.0 mm). In plots where sand had been added, avocets fed by pecking at the surface in addition to scything, the more common method of feeding on muddy substrates. The results suggest that sand interferes with the detection and or capture of prey that are similar in diameter to small sand grains and explains the differences in the effects of predation by these birds seen on mudflats with a moderate admixture of sand compared to the effects on mudflats with little sand. Differential success in prey capture between one microhabitat and the nest (rather than a reduction in competition, as suggested by some authors) might explain the different use of such habitats.     

Habitat patchiness and predation modify the distribution of a coral-dwelling damselfish

Fish abundance is often better predicted by microhabitat variables on continuous reefs than on isolated patch reefs. Although this was suggested to stem from reduced post-recruitment relocation, this has not been shown experimentally. We found the relationship between the presence of a coral-dwelling fish, Dascyllus marginatus, and the size of its coral host to differ between corals on continuous reefs and the sparsely distributed corals on sandy bottoms. Empty transplanted corals were colonized exclusively by new recruits when on the sandy bottom, and both by new recruits and post-recruitment dispersal of adults when on the continuous reef. New recruits settled predominantly into small corals, although analyses of recruitment patterns were confounded by low recruitment in the studied years. Both tank experiments and field survey data suggest that the presence of recruits in small corals is at least partially driven by predation by the dottyback, Pseudochromis olivaceus, which lives predominantly in large corals within both habitats. Consequently, we suggest that the relationship between fish presence and coral size differs between the habitats due to coral size dependent predation on recruits and variability in the importance of direct recruitment to replenish fish populations.     

Impact of canal development on intertidal microalgal productivity: Comparative assessment of Patterson Lakes and Ralphs Bay,South East Australia

We assessed the potential impact of a proposed canal development in an estuarine sandflat at Ralphs Bay, Tasmania on intertidal microalgal productivity and species composition, by comparing it over summer and winter seasons with a well- established (30 year old) canal estate at Patterson Lakes, Victoria. Pulse amplitude modulation (PAM) fluorometry was used to generate a relative measure of photosynthetic performance, which combined with microalgal chlorophyll biomass and irradiance provides an assessment of potential primary productivity. We present a sophisticated mathematical model for calculating benthic microalgal production and the contribution to total primary production, taking into account sediment light attenuation as estimated from sediment grain size. Ralphs Bay had a total productive microalgal biomass of 44 mg chlorophyll a m⁻² which was six times higher than Patterson Lakes, while the relative productivity of Ralphs Bay was four times greater compared to Patterson Lakes where productivity was virtually absent in the subtidal zone of the canal waterway. Ralphs Bay exhibited a more or less homogeneous spatial distribution of microphytobenthos biomass but this was subject to some seasonal variation in species composition, abundance and productivity. By contrast, at Patterson Lakes biomass distribution, diversity and productivity was highly spatially variable in the canal system in both seasons. Patterson Lakes exhibited 60% lower microphytobenthos species richness than Ralphs Bay but little variation in species composition occurred between seasons in the canal estate. This suggests that the dominant diatom species in Patterson Lakes, Pinnularia yarrensis, Gyrosigma balticum and Pleurosigma salinarum, are well adapted to the disturbance regime within the canal estate. The proposed canal development at Ralphs Bay is estimated to cause a decrease in microalgal productivity by both reducing available marine substrate (66% reduction) and replacing productive intertidal phytobenthic habitat with nonproductive canal substrate. These combine to cause a decline in productivity of 92% with significant flow-on effects predicted for higher trophic levels such as migratory wading birds.     

Feeding by the sand crab Portunus pelagicus on material discarded from prawn trawlers in Moreton Bay,Australia

A field and laboratory study in 1984–1985 using the foregut contents of crabs caught in Moreton Bay, Queensland, when trawling was underway, showed that animals discarded from trawls constituted about 33% of the diet. Portunus pelagicus can fill its foregut in about 8 min and clear it completely of tissues in about 6 h, except for fish bone which requires about 24 h. P. pelagicus used a zigzag search pattern to find food and moved towards it at a mean point-to-point speed of 290 m h^-1 (8 cm s^-1). Underwater still photography on the trawl grounds showed that P. pelagicus was the most common scavenger attracted to a bait that simulated trawl-discards, and that it was most active at dusk. Trawler-discards at periods of high food demand in summer may allow larger populations of P. pelagicus to exist than would otherwise occur.     

Differing distributions of potentially competing amphipods,copepods and gastropods among specimens of the intertidal alga Pelvetia fastigiata

Possible competitive interactions are inferred from the distributions and abundances of species within three invertebrate groups (Hyale spp., Ampithoe spp. and thallusdwelling species) among unmanipulated and experimental specimens of the brown alga Pelvetia fastigiata collected between 1974 and 1976, inclusive, at La Jolla, California, USA. During the fall, when the vagile amphipods Hyale grandicornis and H. frequens were relatively abundant, they were found mostly on specimens of P. fastigiata at upper mid-intertidal and mid-tide levels, respectively. H. grandicornis often dispersed to mid-tide levels, but the two species cooccurred on few plants. Although H. frequens infrequently occupied P. fastigiata in the spring, H. grandicornis still generally sheltered in upper mid-intertidal plants, in part, because the net reproduction rates of H. grandicornis were low when space was available. The tubiculous amphipod A. tea usually was the only Ampithoe species on P. fastigiata; however, A. lindbergii and A. pollex sometimes dispersed to and released broods on this alga, particularly during the early summer when abundances of A. tea were relatively low. Similarly, net immigration rates of other thallus-dwelling copepods were relatively high when abundances of Scutellidium lamellipes were low. Moreover, several copepods were most abundant on different specimens of small isolated plants, and thallus-dwelling gastropods on larger plants at sites with relatively low densities of S. lamellipes on P. fastigiata; such copepods and gastropods generally were not abundant on aggregated plants sheltering large numbers of S. lamellipes. Such differences suggest that competition for food or space is among the factors causing negative correlations in the densities of Ampithoe spp. and thallusdwelling species on P. fastigiata.     

The distribution of intertidal phytopsammon in an Oregon estuary

The sediments of two tidal flats in Yaquina Bay, Oregon, USA, were studied to determine the distribution and abundance of the interstitial microalgal communities. The hydrography of the bay, as well as fluetuations in various physical and chemical parameters appear to regulate the biomass and the vertical and intertidal distribution of these organisms.     

Annual occurrence,abundance and diversity of fish in a South Carolina intertidal creek

An intertidal creek in North Inlet Estuary, South Carolina, USA, was sampled monthly for 1 year to determine the occurrence, abundance and diversity of fish species. Sampling was so conducted as to reduce sampling bias to a minimum and all individuals caught were weighed and measured. A total of 16,611 individuals weighing 202.45 kg and comprising 51 species and 25 families of fish was collected. Three diversity indices were calculated for species number. Analysis of variance revealed that season had a highly significant effect on all indices and the number of species, but had no effect on the number of individuals caught.This work was supported by the Belle W. Baruch Foundation and the South Carolina State Development Board, and is Contribution No. 71 of the Belle W. Baruch Institute for Marine Biology and Coastal Research.