Seasonal Occurrence of Gastropterids (Gastropoda: Cephalaspidea) and Their Habitat Selection in a Subtropical Back-reef on Okinawajima Island (Ryukyu Archipelago, Japan) (original) (raw)
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Habitat preferences of coral-associated wentletrap snails (Gastropoda: Epitoniidae)
Contributions to Zoology, 2013
Examination of about 60,000 scleractinian corals of the families Dendrophylliidae, Euphylliidae and Fungiidae for the presence of associated wentletrap snails (Gastropoda: Epitoniidae) revealed various ectoparasitic life history strategies. Twenty Indo-Pacific wentletrap species were found, which were either host-specific or generalist. Most species were associated with mushroom corals, especially free-living species belonging to the Fungiidae. Snails showed different preferences with regard to their position relative to mushroom corals, the host's size and its substrate. No preferences for depth were found. Infestation rates of mushroom corals in multi-species assemblages were negatively correlated with coral densities, which indicates that epitoniid veliger larvae may actively look for preferential hosts. Indirect proof was found that burrowing shrimps remove any epitoniid that is on or underneath the mushroom coral under which they have their burrow. Fishes like wrasses and damselfishes were seen to eat the snails the moment their host corals were overturned, which suggests that the host corals may provide the snails with protection against predators.
Intertidal coarse woody debris: A spatial subsidy as shelter or feeding habitat for gastropods?
Estuarine, Coastal and …, 2006
Coarse woody debris (CWD) in the intertidal region of rocky shores serves as a potential source of nutrients as well as habitat or refugia from predation, ecologically linking the adjacent marine and terrestrial habitats. In a series of field and laboratory experiments, the affinity of slow-moving motile intertidal gastropods to CWD either as food source or as shelter that increases habitat complexity was tested. In intertidal pools, CWD did not increase colonization by Littorina spp., while it did so in supratidal pools. Habitat complexity, brought about by algal cover and barnacles, was apparently sufficient in intertidal pools without woody debris, while the increase in habitat complexity by CWD increased the attractiveness of supratidal pools with little natural complexity to Littorina spp. Overall, however, comparison of pools containing woody debris and those containing artificial shelter provided evidence for CWD, and/or its biofilm, serving as food source rather than refugium per se. Similarly, Tegula funebralis chose CWD as food source rather than as shelter as indicated by comparison of autoclaved and unmanipulated woody debris. Further, both unfed and fed snails from a site where CWD was present significantly preferred CWD over macroalgae. Among snails from a site without woody debris, fed individuals showed no preference, while unfed snails significantly preferred macroalgae. From this, experience appears to be a factor that mediates the role of CWD. Overall, however, CWD appears to provide supplementary food to snails in the inter- and supratidal zone.
Refuge function of marine algae complicates selection in an intertidal snail
Oecologia, 2005
Species with restricted gene flow often show trait-shifts from one type of environment to another. In those rock-dwelling marine gastropods that lack larval dispersal, size generally decreases in wave-exposed habitats reducing risk of dislodgement, while increases in less exposed habitats to resist crab-crushing. In Littorina fabalis, however, snails of moderately exposed shores are generally much larger (11-14 mm) than snails of sheltered shores (5-8 mm). Observations from the White Sea (where crabs are not present) indicate that in the absence of crabs snails are small (6-7 mm) in both habitats. We assumed that the optimal size for L. fabalis in the absence of crabs is less than 8 mm, and thus that increased size in moderately exposed habitats in areas with crabs might be a response to crab predation. In a crab-rich area (Sweden) we showed that crab predation is an important mortality factor for this snail species in both sheltered and moderately exposed habitats. In sheltered habitats, snails were relatively more protected from crab-predation when dwelling on their habitual substrate, fucoid algae, than if experimentally tethered to rocks below the algae. This showed that algae function as snail refuges. Snail dislodgement increased, however, with wave exposure but tethering snails in moderately exposed habitats showed that large snails survived equally well on rocks under the algae as in the canopy of the algae. Thus in sheltered habitats a small snail size is favored, probably due to life-history reasons, while increased risk of being dislodged from the algae refuges promotes a large size in moderately exposed habitats. This study shows an example of selection of a trait depends on complex interactions of different factors (lifehistory optimization, crab predation, wave induced dislodgement and algal refuges).
Substratum-dependent predator-prey dynamics: patch reefs as refuges from gastropod predation
Journal of Experimental Marine Biology and Ecology, 1989
The impact of the gastropod predator Cassis tuberosa (Linnaeus ) on the local distribution of the sea urchin Diadema antiOanml Philippi was investigated. Artificial reefs stocked with Diadema were established 5 m otTthe fringing reef of St John, US Virgin Islands. Cassis preyed upon 17% of the urchins after 30 days. All predation by Cassis occurred on sand rather than on artificial reefs or a nearby fringing reef. Arenas containing a single Diadema and Cassis were set up with sand, flat rock and piled rock habitats. This resulted in urchin mortality of70, 40 and 10% for the three treatment groups, respectively. The results suggest that Diadema distribution and foraging may be restricted to reef habitats by predation pressure. The risks of mortality from predation may outweigh the costs of remaining in high-density food-timited conditions.
Investigating the effects of disturbed beaches on crustacean biota in Okinawa, Japan
Regional Studies in Marine Science, 2017
Subtropical Okinawa Island is known for its high marine biodiversity, yet relatively little work has been performed on examining the impacts of coastal development on its marine ecosystems. In this study, we examined three sandy disturbed beaches (including two artificial beaches) on three different sides of the island (artificial Ginowan Tropical Beach on the west coast, artificial Azama San-san Beach on the east coast, public Odo John Man Beach on the south coast) to investigate if differences exist in the environment and crustacean biota between paired disturbed and natural beaches. We conducted seasonal surveys (n=4 surveys) by placing quadrats at three paired locations (artificial/disturbed and natural beaches at each location, to collect and record the diversity of infaunal crustacean (isopods and amphipods) taxa. Amphipods and isopods are basal parts of the food chain and therefore many marine creatures' diets contain them directly or indirectly, and they have been used in many studies as bioindicators. As well, environmental parameters including sand grain size, water temperature, and seawater quality (salinity, dissolved oxygen content, particulate organic matter, turbidity, conductivity, pH, phosphate, nitrite, nitrate, ammonium levels) were obtained from each site during each survey. The results showed that while water nutrients, sand composition, and water quality were very similar between paired disturbed and natural beaches, disturbed beaches had significantly less biodiversity. These results show that despite no obvious effects on water nutrients or quality, disturbed and artificial beaches influence the infaunal crustacean biodiversity/community in the classic manner of a disturbance. Furthermore, our results indicate that amphipods may be better indicators of disturbance compared to isopods, as the numbers of isopods were too low to be used in statistically robust analyses. With increasing tourism and corresponding development of artificial beaches in Okinawa Island, it is clear more research needs to be done on this subject.
Publications of the Seto Marine Biological Laboratory. Special Publication Series., 2010
Spatial and temporal variability of intertidal rocky shore bivalves and gastropods in Sichang Island, east coast of Thailand were studied over 12 months (March 2008 to February 2009). The study area experiences mixed tides with the largest tidal range of 3.6 m above MTL during spring tides. Shores are exposed to the prevailing northeast monsoon in the winter (November to February), resulting in stronger wave action during this season than in summer (March to May) and rainy season (June to October). Transects were positioned at five different heights from mid shore to high shore (2.5 to 3.5m above MTL) dominated by rock oysters in the mid shore. At each height, abundance of bivalves and gastropods were recorded within fifteen replicate quadrats (25 x 25 cm) on a monthly basis. A total of 2 bivalves and 10 species of gastropods were identified. In the high shore, the littorinid Echinolittorina malaccana dominated. Dense beds of the bivalve Isognomon nucleus were abundant in crevices at 2.5 and 2.75 m above MTL, whilst a large number of snails (Planaxis sulcatus) were found near the midshore. Below this, the rock oyster Saccostrea cucculata was dominant, with a variety of mobile gastropods (Cellana grata, C. toreuma, Patelloidea saccharina and Siphonaria japonica). The general sequence of zonation patterns were clear over time, but the vertical extent of some mobile species varied in accordance with the monsoon effect and increasing tidal range in winter, especially on the more exposed of the two sites. The high shore littorinids, E. malaccana moved up shore and were more abundant near the supralittoral line in winter suggesting that the seasonal monsoon effect and tidal range were important factors determining the distribution of some species of mobile gastropods, allowing them to exploit higher tidal levels.
The Diversity and Ecology of Mollusks at Seogundo, Southern Jeju Island, Republic of Korea
Seogundo is a small island adjacent to the southerncoast of Jeju Island and connected to it by a boulder beach at low tide Surveys of this area were conducted from 2001 to 2009 to enumerate the mollusks there and also to examine their diversity, relative abundance, and ecological relationships. Both the boulder beach itself and several large tidepools were studied, including the coarsesand substrate and several species of seaweed and coralline algae found in the tidepools. Of the 121 species obtained or observed, there were 97 gastropods, 16 bivalves, and 8 polyplacophorans. Live specimens were obtained for about half of those species. About one third were found on rocky substrate, with the most common species being Nodilittorina radiata and Nerita japonica in the upper intertidal zone, N. radiata and Littorina brevicula in the middle intertidal, and Turbo (Lunella) coronata coreensis and Acanthopleura japonica in the lower intertidal and shallow subtidal. The seaweeds and coralline algae contained about 40% of all mollusk species. The most common mollusks in two species of brown seaweed were Ittibittum parcum, Musculus nanus, and Euplica scripta. In a species of red seaweed, Komaitrochus pulcher was the most frequent, as in the coralline algae, along with M. nanus. The coarse sand in the tidepools contained about 25% of the species, with the Cerithiidae having the largest number. A sample of beach drift contained 17 species, with Bittium aleutaceum and Rissoina (Phosinella) pura being most common. Most species, about 60%, were found in a variety of habitats, especially the marine flora; few species exhibited any habitat preferences. Biographically, Jeju Island is part of the Warm Temperate Northwest Pacific Province and the East China Sea ecoregion with a strong faunal affinity with southern Japan, eastern China, and northeastern Taiwan. Zonal-geographical groupings reveal that the fauna is mainly subtropical-low boreal, preferring moderately warm water, with a somewhat smaller number of tropical-subtropical species.
PubMed, 2016
Daisuke Tanamura and Euichi Hirose (2016) Plakobranchus ocellatus is a sacoglossan sea slug that can retain functional chloroplast from its algal food. This species feed on multiple species of siphonous green algae and can survive several months without food by utilizing retained chloroplasts in its digestive gland (kleptoplasty). While the population dynamics of opisthobranchs are often influenced by the seasonal fluctuation of the abundance of food resources, the fluctuation of food availability would not be a crucial factor to restrict the occurrence of P. ocellatus. We monitored the population density of P. ocellatus for 20 months on a subtropical coral reef where the water temperature fluctuated from 17°C to 32°C, in order to examine whether the population density, distribution pattern of individuals, and size distribution of P. ocellatus are stable or seasonally change. The present results showed that P. ocellatus appeared all year round in the study site, while the population density changed seasonally. The population density decreased in cold (≤ 21°C) and hot (≥ 27°C) periods, and densities in the months of intermediate temperature range (< 21°C, > 25°C) were significantly higher than the densities in other months (Student's t-test, P < 0.0001). Accordingly, population density is probably influenced by water temperature. Morisita's Iδ indicated that the sea slugs were distributed in random patterns (13 months) or clumped patterns (7 months). Our field observations indicated that the sea slugs do not feed in daytime, and probably feed at night. Whereas P. ocellatus individuals of less than 10 mm were rarely recorded in the monitoring area, a decrease of the average body length and increase in population density in April - May suggest active recruitment of small individuals in this period.
AQUATIC SCIENCE & MANAGEMENT, 2013
Corallivorous gastropods, Drupella cornus are living in the Indo Pacific coral reefs. To assess the distribution of the snails at Bunaken National Park in Indonesia, a study has been conducted on three zones established in three main islands of the park: core, tourism, and exploitation zones. The zones represent degrees of human interventions in which the least intervention is for core zone, moderate for tourism zone and high for the exploitation zone. The results showed that degrees of human interventions are related to the density of snails where the least human intervention zone (the core zone) had low numbers of snails while the high human intervention (exploitation) zone had high numbers of snails. Three corals in the zones that were preferred by the snails were: Montipora spp., Acropora spp., and Porites spp. The numbers of snails living on the corals followed the percent of coral cover© Gastropod pemakan polip karang, Drupella cornus hidup di areal terumbu karang Indo-Pasifik...
Indirect effects of a predatory gastropod in a seagrass community
Journal of Experimental Marine Biology and Ecology, 1994
While research and theory have largely focused on the effects of direct interspecific interactions such as predation and competition, there is growing evidence for the importance of indirect interactions in regulating populations and community composition. In St. Joseph Bay, FL, USA, pen shells [Atrina rigidu (Sol.)] are preyed on by horse conchs [Pleuroploca gigunteu (Kiener)]. The shells of dead At&a are subsequently used as shelters and/or nest sites by a suite of benthic species, including crabs, octopi, and fish. By influencing the rate of new shelter availability, horse conchs may indirectly affect the distribution or reproduction of shell-occupant species. Feeding observations and an exclosure experiment indicate that Atrinu are the primary prey of large horse conchs. The abundance of occupant species is strongly correlated to Atrinu shell abundance, suggesting that shelter availability may influence population distributions. Experimental additions of new shelters mimicking freshly-killed pen shells caused an increase in the abundance of occupant species. Among these species, the blennies Hypsoblennius hentzi (Leseuer) and Chasmodes suburrue J. & G. and the clingtish Gobiesox strumosus Cope showed an increase in both abundance and frequency of egg-guarding, suggesting an important indirect effect of horse conchs on the distribution and reproductive output of these fish. Because the addition of new shells affected blennies and clingfish more strongly than other occupant species, community composition is influenced by shelter availability. In habitats where biogenic structures are prominent, such as mollusc shells in soft-sediment marine communities, this type of nontrophic indirect effect may be an important component of population and community regulation.