Ocypodid Crabs Research Articles

Growth characteristics and population dynamics of Macrophthalmus japonicus with decreasing microphytobenthos biomass in muddy estuarine tidal flat

The present study evaluated the population dynamics, growth, and biomass production of the ocypodid crab Macrophthalmus japonicus in muddy estuarine tidal flat through monthly surveys over a 10-year period. The mean annual biomass was 4.71–11.51 (7.9±2.5) g dry·m−2, and secondary production was 2.1–19.3 g dry·m−2·year−1 (11.3±5.3 g dry·m−2·year−1) and 1.59–6.16 (3.71±1.55) g C·m−2·year−1. Two to three cohorts of M. japonicus were observed in each year, with the population density of 10–61 individuals·m−2. New recruitment was noted around August in the summer of each year, with an estimated lifespan of 2–3 years. The production/biomass ratio was 0.46–2.02 (1.38±0.44). The population density of M. japonicus showed stable seasonal variations, while annual growth, production, and biomass decreased over the years. M. japonicus growth was associated with microphytobenthos biomass. In particular, long-term field investigations revealed the association between M. japonicus and microphytobenthos, suggesting that the feeding pressure of M. japonicus affected microphytobenthos biomass. Our findings will contribute to the better understanding of the growth characteristics and population dynamics of M. japonicus as well as the interactions between prey and predators in benthic tidal flat ecosystems, providing fundamental information for estimating material cycles.

Ingestion and translocation of microplastics in tissues of deposit-feeding crabs (Grapsoidea, Ocypodoidea) in Kochi estuary, Japan

Estuaries contain some of the highest concentrations of accumulated microplastics (MPs) that can be ingested by abundant deposit-feeding crabs. We investigate MPs in gill, hepatopancreatic, and gastrointestinal tissues of seven intertidal crab species in Kokubu River, Kochi, Japan. By applying a reliable method that considers limits of detection and quantification, we report MPs in 63 of 116 crabs (>50%), with a mean of 3.2 MPs individual−1. Concentrations are greatest in gastrointestinal tracts (62.15%), suggesting that feeding is the main route for MP uptake. PET is the dominant polymer (44%), and fragments are the dominant shape (50%–77%). A greater MPs burden g−1 body weight is reported for deposit-feeding small ocypodid crabs than for larger herbivorous/omnivorous grapsoid crabs. Factors possibly influencing MP uptake by crabs include feeding habit, crab size, and ambient MP composition.

Estimating the amount of food ingested by the ocypodid crab Macrophthalmus japonicus via feeding pellets

This study aimed to estimate the amount of food ingested by the ocypodid crab Macrophthalmus japonicus using the number of feeding pellets produced. The amount of food ingested by the ocypodid crab has not been confirmed because of its characteristic of producing pseudofeces, such as feeding pellets. We measured the gut content turnover rate, rate of feeding pellets, actual number of feeding pellets produced, and crab behavior using a video recorder during emersion at the Katsuura River muddy tidal flat, Japan. The pellet production rate increased with increasing soil temperatures. M. japonicus did not constantly feed during emersion, and the feeding percentage did not increase, even during longer emergence times. The number of feeding pellets had a significant positive correlation with emergence time and soil temperature. Neither the production rate nor the number of feeding pellets produced was influenced by crab size. The amount of food ingested by M. japonicus was estimated based on soil temperature, carapace width, and emersion time. The amount of food ingested by M.japonicus could be estimated using three simple on-field parameters. This study contributes to a better understanding of the material cycle in tidal flat ecosystems and provides important parameters for estimating the amount of food ingested by ocypodid crabs in tidal flats.

The diet of Florida Box Turtles (Terrapene bauri) in a coastal ecosystem in southwestern Florida

North American Box Turtles are opportunistic generalists with omnivorous tendencies, but diets of box turtles are known to vary by population, region, and season. Relatively few studies have examined the diet of Florida Box Turtles (Terrapene bauri). By analyzing fecal samples and direct observations of feeding, we describe the diet of Florida Box Turtles in a coastal area in southern Florida. Fecal samples of turtles in this population contained four functional groups of plants and algae, 11 categories of animals, plus miscellaneous unidentifiable and mineral matter. Frequencies of occurrence differed significantly between wet and dry seasons but not between sexes. Seeds of the invasive Beach Cabbage (Scaevola taccada) were among the most frequently detected plant items, whereas Coffee Bean Snails (Melampus coffea) and ocypodid crabs were the most frequently encountered animal items.

First reports of protists in land crabs of the family Gecarcinidae (Crustacea: Decapoda: Brachyura) suggest a relatively widespread phenomenon

ABSTRACT Eccrinales are protists of the class Mesomycetozoea exclusively found in the digestive tract of marine, freshwater and terrestrial arthropods. Isopods are the only terrestrial crustaceans from which eccrinids have been reported. Among brachyuran crabs, eccrinids were exclusively reported in grapsid and ocypodid crabs, with a percentage of occurrence ranging from 5% to 100% in the respective species. The eccrinid Enteromyces callianassae Lichtwardt, 1961 has been found in the guts of various decapod crustacean species in marine habitats and intertidal mud or sand flats in Chile, France, Japan and the USA. Semi-terrestrial species of Leptuca and Minuca were the most terrestrial crabs in which E. callianassae has been observed. Here we report the presence of E. callianassae in stomachs of the land crab Gecarcinus lateralis. These are the first observations of protists in gecarcinid crabs, which are regarded as the most terrestrial brachyuran crabs. The presence of E. callianassae in 11% of 74 examined stomachs from males and females of G. lateralis from three locations in Costa Rica suggests that the occurence of E. callianassae in these crabs is a relatively widespread phenomenon. Considering that these highly terrestrial crabs are important herbivores on island and continental landscapes, the presence of eccrinids in the stomachs of these crabs may have important implications for the carbon cycling in coastal ecosystems.

Population structure and use of space by ghost crabs (Brachyura: Ocypodidae) on an equatorial, macrotidal sandy beach

Ocypodid crabs are important components of sandy beach ecosystems and potential indicators of environmental stress. This is the first study about Ocypode quadrata population on an equatorial, macrotidal, high-energy dissipative beach, located in the Amazon coast. The steady temperature and marked hydrological seasons in this region, along with a wide supralittoral extension, provide exceptional conditions for assessing the effect of rainfall on population structure and across shore distribution. Additionally, von Bertalanffy growth parameters were estimated in order to compare with other studied populations of this crab at higher latitudes (subtropical beaches). Burrow abundance had marked differences between the two hydrological seasons in the Amazon coast, with higher values related to higher rainfall. A bimodal burrow zonation was observed, with a significant relationship between burrow abundance and depth, which shows that burrows are generally less abundant and deeper under drier conditions. Growth parameters were similar to those on some subtropical areas, as opposed to some global, expected ecological trends. Large beach width and local climate were important factors to identify clear population trends, which implies that moisture affects the use of the space by these individuals.

Testing behavior model for Ocypode cursor (Linnaeus, 1758) living on Iztuzu Beach

Current study was carried out between May 2014 and May 2015 on Iztuzu Beach (Mugla, Turkey). Carapace width, the depth they were caught in their burrows and distance of their burrows from the sea parameters of 244 Ocypode cursor individuals were recorded. A hypothesis derived from the observations during the fieldworks was tested statistically based on the data. According to the hypothesis of study, caught crabs with larger carapace widths (> 20 mm) intent to escape from their burrows while they are still close to the sand surface during the digging activity of researcher. But smaller ghost crabs (< 20 mm) shows tendency to hide in the deeper portions of their burrows. Statistical analysis showed that there is a negative correlation between caught depth and carapace width, and gender factor has an important role in this hypothesis (r = -0.69 for females and r = -0.70 for males; p < 0.05). It was found that distance of burrows from the sea had no effect on the behavior model. Caught depth parameter was collected first time by this study for the ocypodid crabs.

Feeding behavior of the ocypodid crab Macrophthalmus japonicus and its effects on oxygen-penetration depth and organic-matter removal in intertidal sediments

This study examined the poorly understood feeding behavior of the ocypodid crab Macrophthalmus japonicus in the field to explore its effects on oxygen-penetration depth (OPD) and organic-matter removal from intertidal sediments. An in situ investigation was conducted on an upper mud flat in the mouth of the Han River estuary, on the western coast of Korea. The behavior of M. japonicus and variation in the OPD within its habitat were surveyed and contents of organic materials such as organic carbon (OC), organic nitrogen (ON) and δ15N in its feeding pellets were compared as contrasted with non-feeding sediments during the daytime ebb in summer. We continuously recorded the surface activity of the crab during two main feeding periods and during a resting period, when the crabs remain immobile on the surface. Feeding periods exceeded 1 h; crabs fed on sediments more actively during the first feeding period (45 pseudo-pellets individual−1 h−1) than during the second feeding period (19 pseudo-pellets individual−1 h−1). The feeding period duration increased as body size decreased. Adult crabs devoted more of their time to basking in sunlight to dry their bodies, whereas young crabs spent most of their time feeding. Crab feeding activity on the surface generally enhanced the OPD. Conversely, OPD decreased during basking, when most crabs were immobile. Crab feeding greatly altered sediment geochemistry in the intertidal flat. In feeding pellets, OC and ON concentrations decreased to 55% and 60%, respectively, of those in non-feeding sediments. OC and ON were removed at rates of 1.89 mmol C m−2 h−1 and 0.24 mmol N m−2 h−1, respectively. The removal rate of OC by crab feeding was three-fold higher than that of OC mineralization by diffusive oxygen uptake (average: 0.56 mmol C m−2 d−1) and was comparable with the rate of anaerobic carbon mineralization (1.74–3.83 mmol m−2 h−1) in this region. The increase in the C/N ratio (10.6%–12.5%) and decrease in δ15N (7.21‰–5.99‰) in feeding pellets compared with non-feeding sediments indicate that M. japonicus removed N more selectively to meet requirements. These results imply that in situ crab activity significantly influenced OC and ON cycles; therefore, it is necessary to consider processes such as macroinvertebrate production and consumption when evaluating the purification function of intertidal sediments.

Burrow Morphology of the Ocypodid Crab &lt;i&gt;Ocypode ceratophthalma&lt;/i&gt; at Chandipur Coast, Eastern India and its Implications

Burrow Morphology of the Ocypodid Crab &lt;i&gt;Ocypode ceratophthalma&lt;/i&gt; at Chandipur Coast, Eastern India and its Implications

Tomographic reconstructions of crab burrows from deltaic tidal flat: Contribution to palaeoecology of decapod trace fossils in coastal settings

Trace fossils play an important role in reconstructing palaeoecology and depositional environment. Their palaeoecological implications can be better understood when the trace makers are correctly identified. Neoichnology studies the burrow morphologies, behavioral ecology of modern organisms and their interaction with the environment. Neoichnology is of great significance in linking burrowing behaviors of extant organisms with interpretation of trace fossil palaeoecology. This paper reports a study on burrows produced by the ocypodid crab (Macrophthalmus japonicus De Haan) in the tidal region of the Yellow River Delta using CT scanning techniques. Our results show that M. japonicus produces abundant I-, U-, and Y-shaped burrows in a mudflat of the delta. These domicile structures are similar in morphological characteristics to the trace fossil Psilonichnus, suggesting M. japonicus as its possible additional trace maker. Our study supports the usage of Psilonichnus as a significant palaeoenvironmental indicator for coastal and shelf environments. Furthermore, this study highlights the great potential of applying CT techniques in future ichnological-related studies.

Sediment Temperature Impact on Population Structure and Dynamics of the Crab Austruca iranica Pretzmann, 1971 (Crustacea: Ocypodidae) in Subtropical Mangroves of the Persian Gulf

Ocypodid crabs inhabit intertidal sandy/muddy flats of tropical and sub-tropical mangroves. Iran has three species of the genus Austruca. In contrast to A. sindensis and A. lactea, almost nothing is known about the population dynamics and its driving factors in Austruca iranica. Thus, population ecology and reproductive biology of A. iranica were studied in relation to sediment temperature and rainfall in a sub-tropical Iranian mangrove forest over a period of 13 months. Crab density and Gonado Somatic Index (GSI) were significantly correlated with sediment temperature (r2 = 0.87, p ≤ 0.05). Reproduction was restricted to spring and summer and ovigerous females appeared when both sediment temperature and rainfall had their maximum values. Rainfall triggered crab reproduction, but did not significantly correlate with crab density. Symptotic carapace width (L∞) and growth constant (k) were 16.9 mm and 1.0 yr. −1 in females (n = 251), and 18.5 mm and 0.9 yr. −1 in males (n = 325), respectively. Size frequency distributions in both females and males had a common asymmetrical bi-modal pattern with two cohorts. Total mortality was higher in females (2.74) than in males (2.29). The overall sex ratio did not differ significantly from the expected 1:1 proportion (χ2 = 20.50, p > 0.05). Size at the onset of maturity was 10.2 mm in females. In comparison to other literature on ocypodid crab species, this study revealed that A. iranica is a relatively slow growing crab, with low fecundity and mortality rates, and with a relatively long life expectancy of about two years. The results of this research are a key for establishing a management plan to conserve the population of A. iranica along the Iranian coasts.

Calcium levels in the vulvar opercula of grapsoid and ocypodoid crabs (Decapoda: Brachyura)

The derived condition in Brachyura is exhibited when mating is not linked to moulting (i.e. hard-shell mating). Grapsoid and ocypodid crabs have this type of mating wherein females become receptive and have mobile vulvae covered by operculae without moulting. The mobility of the operculae has been attributed to a decalcification process although it has never been demonstrated experimentally. We described the morphology of the vulvae (operculum and hinge) and measure calcium levels employing X-ray Energy Dispersive Spectroscopy of the intermoult immature and mature female of several different species of grapsoid crabs: Austrohelice crassa , Cyclograpsus lavauxi , Hemigrapsus crenulatus , Hemigrapsus sexdentatus (Varunidae), Guinusia chabrus (Plagusiidae), Leptograpsus variegatus (Grapsidae), and the ocypodid Hemiplax hirtipes (Macrophthalmidae). We measured calcium levels during a reproductive cycle in the case of H. sexdentatus . In all the studied species the opercula and hinge had lower calcium levels compared to the adjacent exoskeleton, and the hinge showed the lowest values of calcium (9.7 and 40.8 weight%, respectively). Immature and adult crabs showed that the distribution of calcium remains the same after the pubertal moult as it was before. Furthermore, in H. sexdentatus , hinge calcium levels do not change during the female reproductive cycle when females become receptive. It is suggested that an alternative mechanism, not related to decalcification, could be involved in promoting mobility of the hinge in receptive females of these species. We need to modify our ideas of the processes involved in female receptivity in all these crabs with an operculate vulva and hence mate attraction. Answers to these questions are the key to understanding how the linkage of mating to moulting was broken.

Mangrove rehabilitation in high erosion areas: Assessment using bioindicators

This study identifies a potentially effective rehabilitation technique for implementation in high erosion areas through the use of bioindicators. This is significant given that one third of mangroves have been cleared globally with clearing continuing at a rate of 1–2% per annum. There have been various attempts to rehabilitate degraded mangrove forests, however the success or failure of these is mostly unclear due to a lack of assessment. The two rehabilitation techniques assessed in this study were a basic fence system and another more elaborate fence technique designed by the Kien Giang Biosphere Reserve Project (KGBRP), Vietnam. The assessment was conducted by comparing vegetation and faunal communities in rehabilitation areas to those in adjacent old-growth areas. The indicators included: tree and understory plant diversity and density; forest cover and the density of crabs, mudskippers and gastropods. The results show the KGBRP rehabilitation fence technique delivered tree diversity, plant diversity, tree density and forest cover that most closely resembled old-growth areas. This suggests that the additional protection provided by the KGBRP fence was instrumental in achieving these results. In terms of total mudskipper, Boleophthalmus spp., Periophthalmodon spp. and ocypodid crab density, the KGBRP rehabilitation was most similar to the old-growth areas. This similarity is thought to be related to the comparable forest cover at these sites. The density of large crab holes was much higher in old-growth areas than in basic or KGBRP rehabilitation areas. The disparity between large crab hole density at KGBRP rehabilitation and old-growth areas, despite similar levels of forest cover, is thought to be linked to the immaturity of the KGBRP rehabilitation sites. As the KGBRP rehabilitation is most similar in terms of vegetation and faunal communities to the old-growth areas, it appears to be the most successful rehabilitation.

Potential Small- and Large-Scale Effects of Mechanical Beach Cleaning on Biological Assemblages of Exposed Sandy Beaches Receiving Low Inputs of Beach-Cast Macroalgae

Mechanical beach cleaning occurs worldwide on heavily urbanised beaches to remove litter and decomposing macroalgae from impacting tourism and recreation. This study investigated the potential small- (100 s of metres) and large-scale (kms) ecological impacts of beach cleaning in a region receiving low inputs of macroalgae with a focus on: levels of total nitrogen and nitrate; abundances of bacteria, meiofauna, macrofauna and ocypodid crabs; and assemblages of meiofauna and macrofauna. Results indicated that beach cleaning was not having an impact. Given beach cleaning occurred only weekly to twice-weekly on small sections of a few beaches, and that collected beach-cast macroalgae in the study region is relocated on the same beach for degradation, it is likely that nutrients are redistributed from surrounding areas to cleaned sites and that potential physical impacts to biota are short-term and sustainable. Impacts of beach cleaning may be evident in regions that experience more extensive beach cleaning operations or on beaches with high inputs of beach-cast macroalgae. This study also highlights the importance of comparing sites at the same location to investigate the effects of beach cleaning, as ecological differences among distant locations may incorrectly be attributed to beach cleaning but may actually be driven by differences in their physical characteristics.

Two new species of benthopelagic Stephos (Copepoda, Calanoida, Stephidae) from Korea.

Two new species of benthopelagic copepods of the genus Stephos T. Scott, 1892, belonging to the family Stephidae G.O. Sars, 1902, are described based on specimens collected in the stagnant water flooding the burrows excavated by ocypodid crabs in two intertidal mud-flats, and from near-bottom shallow waters in Korea, respectively. They can be easily diagnosed based on the ornamentation of both the female genital double-somite and genital operculum; the morphology of the distal segment of the male right P5; the presence/absence of a tiny pointed process on the distomedial angle of second segment of female P5; and the condition (seta or spine) of the lateral armature element on the distal segment of female fifth legs, among other features. This is one of the few cases reported of calanoid copepods living as commensals of other invertebrates, and raises to six the number of members of the genus reported from Asia. This is also the first record of the family Stephidae in Korea.

Actuopaleontological characterization and molluscan biodiversity of a protected tidal flat and shallow subtidal at the northern Red Sea

Tidal flats are abundantly developed throughout the Phanerozoic but actualistic studies on subtropical‒tropical tidal flats are rare. This study of a tidal flat and shallow subtidal of a lagoon protected behind a fringing reef at the northern Red Sea is therefore aimed to contribute to the understanding of the distribution and abundance of paleontologically relevant fauna and its lebensspuren. Muddy sands to sands and beachrock are the predominating benthic habitats. Important ecosystem engineers are the oyster Saccostrea cucullata, which forms decimeter- to meter-scale bioherms in the lower intertidal, the ocypodid crab Dotilla sulcata, which reaches highest abundances on the tidal flat, some tens of meters from the low-tide line, and the callianassid decapod Paratrypaea bouvieri, which is very abundant in the subtidal. The sediment surface in the intertidal was densely covered with lebensspuren of gastropods. Quantitative and qualitative samples revealed 130 species of molluscs from 51 families. Most species found belong to the Veneridae, Lucinidae, Turridae, Cardiidae, Trochidae, and Pyramidellidae in the subtidal and to the Cerithiidae in the intertidal, but overall only 32 species were found alive (13 on the tidal flat, 28 in the subtidal). Distinct assemblages of living and dead molluscs characterized the intertidal and subtidal, which suggests that dead shells can be used to assess regional biodiversity. Numerically, the living assemblage on the tidal flat was strongly dominated by the deposit-feeding potamidid gastropod Pirenella conica, and in the subtidal by infaunal bivalves (Glycymerididae, Lucinidae, Tellinidae, and Veneridae). Predatory gastropods (Naticidae, Melongenidae, Fasciolariidae, Muricidae, and Conidae) were accessory components that were mostly present in qualitative samples in the subtidal and lower intertidal. Accordingly, frequencies of drilling predation for the total assemblage are significantly higher in the subtidal (25.7 %) than in the intertidal (1.2 %). We conclude that the preservable fauna and its lebensspuren are characteristically developed along an environmental gradient and suitable to distinguish intertidal from subtidal habitats in a potential fossil record.

Spatial distribution and population structure of fiddler crabs in an Indian Sundarban mangrove

Brachyuran crabs constitute the most abundant faunal component of mangrove ecosystems and support a wide range of ecosystem services. In the present study, seasonal variation of population density and biomass along with demographic categories and sex ratios of four species of fiddler crabs (Uca rosea, Uca triangularis, Uca dussumieri and Uca vocans) from Jhorkhali Island in the Sundarban mangrove were studied in relation to some major environmental parameters (salinity, nutrient content, soil organic carbon, dissolved oxygen, total dissolved solute, etc.) during bimonthly sampling for three consecutive years (2010-2012). Maximum population density and biomass of the ocypodid crabs were recorded during the pre-monsoonal month and minimum values during the monsoon. Different peaks in reproductive activity were observed among seasonal breeders (U. triangularis, U. dussumieri). For U. vocans, the sex ratio peaks declined during the ovigerous period. All four populations were characterized by significantly more males than females. Multiple regression analysis suggested a cumulative effect of several ecological parameters on seasonal fluctuations of the crab population. Breeding periodicity might be controlled by a combination of factors, including temperature, quality of the substratum, food availability for the adult and larval stages, and intertidal zonations.

Temporal changes in brachyuran crab diversity along heterogeneous habitat in a mangrove ecosystem of Indian Sundarbans

The present study investigates the effect of different habitat attributes on brachyuran crab diversity in two different study sites in the Sundarban mangrove, India. The two sites differ in the level of anthropogenic intrusion and in the age of the mangrove forest. Seasonal changes in the environment and in brachyuran faunal abundance were recorded for three years. Species composition varied between the two habitats irrespective of season. The habitat heterogeneity and the recorded crab community was analysed by several univariate and multivariate statistical techniques. The newly replanted mangrove site showed lesser diversity than the natural one. Ocypodid crabs, mainly Uca rosea , dominated both study sites, whereas Uca triangularis was totally absent from the replanted site. Canonical correspondence analysis showed that the total acidity, total alkalinity, pH content of water, total dissolved solids, inorganic phosphate content of water, soil specific gravity, soil density and the physical constructions of the habitat play a crucial role in moderating the crab community structure. This study reveals that brachyuran crab diversity can be used as a potential indicator of the alterations of mangrove habitats.

Abundance and Spatio-Temporal Distributional Pattern of Dotilla Myctiroides (Milne-Edwards) on Exposed Sandy Beach of Aksa, Mumbai

The abundance and distributional pattern of Ocypodid crab, Dotilla myctiroides (Milne-Edwards) was studied on a sandy beach of Mumbai from January 2005 to December 2006. The area experiences semidiurnal tides. The beach is intermediate dissipative type and consists of medium to fine grade sand. The data were collected after fixing a transect line from high to low shore zone based on tidal heights. A mean abundance of 40 ± 4.55 ind.m−2 was found during 2005, while it was 37.82 ± 7.31 ind.m−2 during 2006. Although no significant difference (p > 0.05) in abundance was observed on seasonal scale, there was a marked variation (p < 0.05) in the vertical distribution with an obvious increasing trend in abundance from high to low shore zone. The zonal variation in the abundance was distinct in different seasons and it increased from pre- to post-monsoon with decreasing tidal heights during both the years. A significant difference (p < 0.05) in the abundance was recorded between high and mid shore zone during all the seasons while mid shore zone showed significantly higher (p < 0.05) abundance during post-monsoon season. Data on distributional pattern of different maturity stages (juvenile, immature, young adult and adult) based on carapace width were also collected. The juveniles were mostly observed in mid and low shore zone, while adults dominated mostly the high shore areas. The factors like morphodynamic state of beach and behavioural ecology of this species seemed to play important role in its high abundance and vertical distribution on the sandy beach of Aksa, Mumbai.

Burrow association of Hemicyclops (Copepoda: Poecilostomatoida) as a possible strategy for predator avoidance

We examined the potential advantage of the association of Hemicyclops species with decapod burrows in their avoidance from fish predators through gut-content analysis of fishes collected from the estuary of the Tama River, Japan, and an experiment applying model burrows. The small gobiid species Pseudogobius masago, collected from an area dominated by burrows of the ocypodid crab Macrophthalmus japonicus, showed a high frequency of Hemicyclops gomsoensis in their guts relative to the other co-occurring fish species. In the experiment, no significant difference was observed in the numbers of H. gomsoensis eaten by the goby between the treatments with and without the model burrows. Another goby, Acanthogobius flavimanus, from an area dominated by burrows of the mud shrimp Upogebia major, showed very low frequencies of H. gomsoensis in their guts, as compared with those in P. masago. They had also ingested H. spinulosus and H. ctenidis, in spite of the overwhelmingly high abundance of H. gomsoen- sis in the burrows. The number of H. gomsoensis eaten by A. flavimanus was significantly lower in the treatments with the model burrows than in the absence of burrows. Since A. flavimanus was the most dominant demersal fish in the study area, H. gomsoensis seemed to avoid predation from this potentially strong predator by inhabiting the decapod burrows. H. ctenidis and H. spinulosus seemed to avoid predation by trespassers by inhabiting the smaller burrows of polychaetes, but this strategy may be less efficient against large predators that feed on polychaetes.