Influence of predation by a crab on the distribution of the size-groups of three intertidal gastropods in South Australia

Two South Australian rocky intertidal platforms were sampled in April 1981 and December 1982 (Marino Rocks) and in December 1982 (Lady Bay), respectively. Three snail species, Nerita atramentosa Reeve, 1855, Bembicium nanum (Lamarck, 1822) and Austrocochlea concamerata (Wood, 1828), exhibited shore-level size-gradients, with smaller individuals occupying the higher intertidal levels. The reef crab (Ozius truncatus M.-Edwards, 1834), whose distribution overlaps that of the gastropods, is an important predator of these gastropods. The shore-level distribution of shell sizes can be explained by differential selection against smaller individuals by reef crabs. The decreased density of small snails at lower intertidal levels may be the result of either their consumption by reef crabs and/or their movement to higher shore levels where crab predation is less intense.     

Substratum relationships of some tropical Pacific intertidal gastropods

Among tropical Indo-West Pacific herbivorous intertidal gastropods, high intertidal neritids, and limpets and certain lower intertidal limpets are restricted to a narrow range of substratum types. Littorinids, planaxids, low intertidal neritids, most lower intertidal limpets, and the trochid Monodonta labio tolerate a wide variety of substrata. This pattern of substratum specialization is related to the overall adaptive strategies of the various groups: those with a large area of soft tissue in contact with the substratum (neritids and limpets) often specialize to a particular substratum, especially at high shore levels, while those in which the area of contact between animal and substratum is small do not. High intertidal neritids and limpets able to live on a wide range of substrata tend to be species of limited geographic distribution. It is concluded that, even within a tropically similar group of animals (raspers in this case) relevant dimensions of niche separation depend upon the structure of the environment as well as upon the structure of the animals themselves.     

Temperature relationships of some tropical Pacific intertidal gastropods

Tissue and environmental-temperature measurements were made using thermistors in Hawaii, Guam, Palau and Singapore in the summer of 1970. Limpets have a very limited ability to regulate body temperature, and several species possessed tissue temperatures greater than those of the substratum. Some neritids and the trochid Monodonta labio possessed tissue temperatures as much as 2.2° to 2.8°C below substratum temperature. Littorinids attached by a mucus film to the substratum were found to have relatively lower body temperatures than those attached by the foot. Among neritids there is a tendency for high intertidal species to be better temperature regulators than low intertidal species. A very important factor in the temperature regulation of intertidal snails appears to be the extent of the area of contact between the animal and the substratum, which is greatest in limpets and least (negligible) in littorinids. Evaporative cooling and light coloration of the shell play a role in certain species and groups.     

Shell-size selection by intertidal sympatric hermit crabs

This study evaluated selection for shell size by three species of tropical intertidal hermit crabs, Clibanarius antillensis, C. sclopetarius, and C. vittatus, from species of shells which are frequently used in nature. Crab size and weight were strongly and significantly related to all measured parameters of the selected shells. The strength of these relationships (r² values) depended neither on the crab nor on the shell variables taken into account. The relationships between crab size and the dimensions of the selected shells showed higher r² values than the corresponding relationships with the shells that the crabs had occupied when they were collected (0.482–0.903 in comparison to 0.091–0.652, respectively), indicating that the crabs were occupying sub-optimal shells in nature. Negative allometry was frequently found in the relationships between crab and shell variables, indicating that large crabs select and use proportionally lighter shells than do small crabs. This negative allometry was stronger for the shells used in nature (except for C. antillensis), i.e. larger crabs tended to select heavier shells in the laboratory than in nature. Different allometric relationships were also recorded among the dimensions of shells used in nature and those selected by the hermit crabs in free-access experiments: as shell length increased, the selected shells were heavier and had larger apertures than the shells used in nature. The relationships between crab size and the length and weight of the selected shells did not depend on the species of crab or species of shell, but only on crab size. Therefore, analyses using these variables can be performed without taking the species of crab or shell into account, i.e. data from different crab or shell species can be pooled. The influence of crab and/or shell species was recorded only in the models fitted for aperture length and width, variables which were more related to shell architecture than did shell length or weight. In contrast, if crab weight is used as an independent variable, different crab or shell species can be analyzed together independently of the particular shell parameter. This indicates that crab weight may be less susceptible than crab shield length to shell morphological constraints. Finally, the results indicate that the preferred size of a given shell type chosen by a given hermit crab will depend more on crab size or weight, than on the crab or shell species under consideration, i.e. crab shell-size relationships are not species specific.Communicated by P.W. Sammarco, Chauvin     

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.     

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.     

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     

Local and meso-scale patterns of recruitment and abundance of two intertidal crab species that compete for refuges

Interference competition for limited habitat or refuges is known to produce density-dependent mortality and generate patterns of micro-habitat distribution. While in mobile species the outcome of interference at a local scale can usually be determined from differences in body size and behavior, the population-level consequences of such interactions vary depending on rates of settlement and recruitment at a site, which are not directly correlated to local reproductive success. Previous experimental studies in central Chile demonstrated that interference competition for refuges is the primary factor driving microhabitat segregation between the predatory crabs Acanthocyclus gayi and Acanthocyclus hassleri, with the latter species monopolizing galleries inside mussel beds and excluding A. gayi to rock crevices. Between April 2001 and March 2006 we quantified monthly recruitment rates in artificial collectors at 17 sites over 900 km of the central coast of Chile. Results show that recruitment rates of A. hassleri are almost two orders of magnitude lower than those of A. gayi, and that they are tightly and positively correlated among sites across the region, suggesting that at scales of kilometers larval stages of these species are affected by similar oceanographic processes. Total crab densities per site were also positively correlated between species and strongly associated to mussel cover, with overall low crab densities at all sites where mussel cover was lower than about 60%. At all sites with mussel cover >60%, the ratio of A. gayi to A. hassleri density progressively decreased from recruits (2.6) to juveniles (0.5) to adults (0.04), overcoming initial differences in recruitment rates. The relative success of the inferior competitor at sites with low mussel cover does not appear to provide a potential mechanism favoring regional coexistence through dispersal to other sites (“mass effects”), because their densities were lower than at sites of high mussel cover. Yet, at many sites of low mussel cover the dominant competitor is virtually absent, allowing A. gayi to attain larger population sizes at the scale of the region. Thus, the factors limiting the dominant competitor from successfully utilizing other microhabitats seem to be the most critical factor in promoting both local and regional coexistence between these species.     

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.     

Heavy metal selection of phosphoglucose isomerase allozymes in marine gastropods

The effects of zinc and copper pollution on the allozymic variation of phosphoglucose isomerase (Pgi) genotypes were tested in the Mediterranean marine gastropods Monodonta turbinata and M. turbiformis in 26 laboratory tests involving 2 081 adult individuals, with 545 survivors. Our results indicate differential survivorship of electrophoretical Pgi allozyme genotypes for both pollutants. Zinc pollution selected against the allozyme genotype SS in M. turbinata, whereas no differential survivorship was observed in M. turbiformis which lacks this allozyme. Copper pollution selected against the MM genotype in both species. These results are inconsistent with the neutral theory of allozyme polymorphisms and appear to reflect the adaptive nature of some Pgi genotypes in these marine gastropods.     

Shell selection in the hermit crab Pagurus bernhardus

Three shell variables were deemed to be important in the selection of a shell by the hermit crab Pagurus bernhardus (L.). These were the weight, volume and aperture width of a shell. Each of these variables were used in multiple regressions against crab weight for 25 Littorina littorea and 25 Thais lapillus shells chosen when both shell species were together in a tank, and for a further 25 L. littorea and 25 T. lapillus when the two shell species were separate. Principal component analysis was performed on the four groups of 25 shells selected, and multiple-regression equations were calculated using the principal components as the new variables. It was found that crabs chose a shell of suitable general dimensions rather than solely on the basis of one shell variable. The advantages of using statistical techniques developed in this paper over previous approaches to shell selection are discussed.     

The seasonal selection by temperature of heterotrophic bacteria in an intertidal sediment

The seasonal selection by temperature of bacteria in an intertidal sediment was investigated, and a simplified method of demonstrating the temperature adaption of a mixed heterotrophic bacterial population was suggested. The method relied upon counting the bacteria which grew at only two separate incubation-temperatures, and compared favourably with more tedions methods which utilise replicated cultures grown at a large number of incubation temperatures. Using this technique, a temperature adaptation index was calculated for the heterotrophic bacterial population and changes in the value of this index were shown to be correlated with seasonal changes of environmental temperature.     

Diet selection of the Chilean stone crab Homalaspis plana

Diet selection of the Chilean stone crab Homolaspis plana (Milne-Edwards, 1834) was studied using the optimal foraging theory to explain its feeding strategy. The hypothesis that H. plana prefers prey species of the highest prey (“energy”) value was experimentally tested on adult crabs during 1980–1981. Food value was defined as the ratio between caloric content and consumption time, according to energy maximization as the criterion to optimize diet selection. Diet composition of adult crabs from the littoral of Valparaíso (Chile) and ingestion under laboratory conditions were studied to determine type, size and quantity of food to be offered in experiments on prey-type preference. Porcellanid crabs, barnacles and bivalves were the most frequently occurring items in stomachs from in situ conditions. In the aquaria, daily ingestion rates were quite variable among crabs and among days. H. plana showed no size preference for molluscs (Tegula atra, Semimytilus algosus) but preferred larger sizes of porcellanids. The order of preference for prey type was S. algosus>T. atra> porcellanids. However, no differences between their energy values were found and, therefore, the optimal foraging hypothesis was rejected. By extension, the energy maximization criterion alone may not explain the diet selection of H. plana under experimental conditions.     

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     

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.     

Density-dependent habitat selection and performance by a large mobile reef fish.

Many exploited reef fish are vulnerable to overfishing because they concentrate over hard-bottom patchy habitats. How mobile reef fish use patchy habitat, and the potential consequences on demographic parameters, must be known for spatially explicit population dynamics modeling, for discriminating essential fish habitat (EFH), and for effectively planning conservation measures (e.g., marine protected areas, stock enhancement, and artificial reefs). Gag, Mycteroperca microlepis, is an ecologically and economically important warm-temperate grouper in the southeastern United States, with behavioral and life history traits conducive to large-scale field experiments. The Suwannee Regional Reef System (SRRS) was built of standard habitat units (SHUs) in 1991-1993 to manipulate and control habitat patchiness and intrinsic habitat quality, and thereby test predictions from habitat selection theory. Colonization of the SRRS by gag over the first six years showed significant interactions of SHU size, spacing, and reef age; with trajectories modeled using a quadratic function for closely spaced SHUs (25 m) and a linear model for widely spaced SHUs (225 m), with larger SHUs (16 standardized cubes) accumulating significantly more gag faster than smaller 4-cube SHUs (mean = 72.5 gag/16-cube SHU at 225-m spacing by year 6, compared to 24.2 gag/4-cube SHU for same spacing and reef age). Residency times (mean = 9.8 mo), indicative of choice and measured by ultrasonic telemetry (1995-1998), showed significant interaction of SHU size and spacing consistent with colonization trajectories. Average relative weight (W(r)) and incremental growth were greater on smaller than larger SHUs (mean W(r) = 104.2 vs. 97.7; incremental growth differed by 15%), contrary to patterns of abundance and residency. Experimental manipulation of shelter on a subset of SRRS sites (2000-2001) confirmed our hypothesis that shelter limits local densities of gag, which, in turn, regulates their growth and condition. Density-dependent habitat selection for shelter and individual growth dynamics were therefore interdependent ecological processes that help to explain how patchy reef habitat sustains gag production. Moreover, gag selected shelter at the expense of maximizing their growth. Thus, mobile reef fishes could experience density-dependent effects on growth, survival, and/or reproduction (i.e., demographic parameters) despite reduced stock sizes as a consequence of fishing.     

Exploratory observations on microhabitat selection within the intertidal zone by the Chinese mudskipper fish Periophthalmus cantonensis

The amphibious Chinese mudskipper fish Periophthalmus cantonensis liver in complex, variable, tropical intertidal mangrove forest and mudlfat habitats. Within these macrohabitats, an array of microhabitats are available to this species which spends most of its time out of water. It is subjected to, and tolerates, wide ranges of salinity and temperature. It is primarily diurnally active and uses dark, usually water-filled burrows in the mud as refuges and breeding places. Individuals of P. cantonensis were captured at night from intertidal mudflats of mangrove forests in the northeastern New Territories, Hong Kong in 1971 and 1972. Using choice experiments in the laboratory, we determined behavioural preferences of this fish for five combinations of abiotic environmental variables relevant to its selections of microhabitats. P. cantonensis usually preferred being out of water, resting on damp mud, to being in direct contact with water of any salinity. In salinity-choice experiments it showed no preference for any particular salinity, but avoided exposure to fresh water. Offered choices between various water temperatures it displayed a strong preference for higher temperatures (30° to 35°C), even though these temperatures were close to those known to cause distress or death. In light-dark choice experiments in very shallow water P. cantonensis preferred darkness to light. Experiments combining watertemperature differences with light-dark choices showed that these two factors interact in complex ways. We discuss implications of these results for understanding of behavioural selection of microhabitats by this fish.     

Prey selection by resident common bottlenose dolphins (tursiops truncatus) in Sarasota Bay, Florida

Prey selection was investigated in wild, resident common bottlenose dolphins, Tursiops truncatus, during the summer months in Sarasota Bay, Florida, USA. Stomach content analyses of 15 dolphins with extensive sighting histories and well-documented distributions were used to determine prey use. Prey availability was assessed by purse seine surveys. We compared the relative abundances of prey available to estimates of prey use at closely matching spatial and temporal scales. G-tests determined that dolphins in this study significantly selected for prey at the species, family, and soniferous/non-soniferous prey levels (G _adj  = 753.98–1,775.93, df = 1–21, p ≤ 0.01). While comprising only 6.3% of the total available prey, soniferous fishes accounted for 51.9% of the total prey consumed. Manly’s standardized forage ratios and 95% Bonferroni confidence intervals determined significant positive selection for soniferous prey and against non-soniferous prey (β^S = 0.9461 vs. β^NS = 0.0539). Dolphins selected against Gerridae, Clupeidae, and Sparidae (β ≤ 0.0014), as well as against all the species within those families (β ≤ 0.0190). It is likely that passive listening for soniferous prey provides an ecological or energetic advantage to cetaceans utilizing this specific foraging technique.     

Population-related toxicity responses to two butyltin compounds by zoeae of the mud crab Rhithropanopeus harrisii

We exposed zoeae of the mud crab Rhithropanopeus harrisii to either bis(tri-n-butyltin) oxide (TBT) or di-n-butyltin dichloride (DBT). Experiments were repeated with zoeae from females collected from the Petaluma River, California in June–August 1983 and 1984 or from Sykes Creek, Florida (USA) in February 1985. Using probit analysis, we calculated LC₅₀ values for exposure lasting the duration of zoeal development. Tributyltin was 54 to 65 times more toxic than dibutyltin, the lower value characterizing the response of Florida zoeae. Increases in duration of zoeal development and reduction of dry weights of megalops, both sublethal responses, were dose-dependent for the two populations. However, zoeae from Florida consistently had shorter duration of zoeal development and higher megalopal weights at metamorphosis, indicating less sensitivity to an identical exposure to either organotin compound. The results of these experiments show that dibutyltin, a putative degradation product of tributyltin, is less toxic than the parent compound. In addition, early life-history stages of two populations may have significantly different responses to xenobiotic stress which, in the case of brachyuran larvae, is evident in a differential reduction of survival and growth and an increase in duration of zoeal development.     

Competitive interactions and substratum preferences of two intertidal isopods

The intertidal isopods Gnorimosphaeroma oregonensis oregonensis (Dana) and Exosphaeroma amplicauda (Stimpson) are shown to have differing preferences for substratum particle-size categories. In field sampling, 80.9% of the total number of G. oregonensis oregonensis taken were present on substrata falling within a ?-4.2 to-3.8 diameter size-range, while 60.0% of E. amplicauda occupied the range ?-2.5 to-2.1. These relationships changed upon laboratory manipulation of density ratios, and suggest competitive interaction: when E. amplicauda is tested alone, the resultant preference assumes a greater niche breadth and overlap to that of the field. Introduction of G. oregonensis oregonensis produces a displacement of E. amplicauda, the degree being dependent upon their relative numerical strength. With an experimental ratio of 3:1 (G. oregonensis:E. amplicauda) there is a simulation of field densities, and the laboratory results approximate more closely the overlap in nature.