Field and laboratory observations on predation and prey selectivity of the scyphomedusa Chrysaora cf. caliparea in Southeast Indian waters

Chrysaora cf. caliparea, one of the most abundant medusae species in India, seems to be an important predator in the coastal waters of Bay of Bengal. The ability of Chrysaora cf. caliparea to feed at maximum rate in high prey concentrations implies that this jellyfish can efficiently exploit dense prey patches, at least for a short period. This study presents preliminary information regarding digestion and feeding rate upon copepods in a warm water environment. The ingestion rate of the average-sized medusae Chrysaora cf. caliparea is well balanced in nature, which in turn implies that this jellyfish is tuned for optimal utilization of available prey resources. Comparison with earlier research indicates that prey escape speed is one important factor governing which prey will be captured. A full understanding of predation mechanics awaits further investigation of both predator and prey behavior. However, because of the scarcity of long-term quantitative population data most insights have to be made indirectly. Nevertheless, low abundance of Chrysaora cf. caliparea in the water column during summer (May 2007) and the overall annual abundance seem not to considerably affect the zooplankton population, especially copepods. The present work contributes to the knowledge of prey-predator relationship of the forgotten fauna in Indian waters, which is especially crucial for understanding the process of ecological recovery of coastal water environment.     

The frequency and effect of shark-inflicted bite injuries to the reef manta ray Manta alfredi

Shark bite injuries on reef manta rays Manta alfredi off the coast of Inhambane, Mozambique, were examined over a three-year period (2003–2006). The frequency and seasonality of attacks, the rate of wound healing, and the possible identities of attackers were explored. This study presents the first examination of bite wounds on manta rays in the wild and the role sharks may play in the natural mortality of this species. The reported incidence of shark-inflicted injuries is high with over three-quarters of the sampled population affected. In total, 571 bite injuries were observed on 283 identified individuals. The number of bite injuries varied from one to seven, with a mean of 1.54 bite wounds. There was no significant difference in the frequency of bite injuries in male and female rays. The majority (96%) of the observed bite wounds were healed. Fresh wounds occurred throughout the year, with no obvious seasonality. The bull shark Carcharhinus leucas and tiger shark Galeocerdo cuvier are suggested as the primary mediators of attacks, although up to 11 other shark species are listed as potential attackers. The majority of the bite marks (96%) occurred to the most posterior region of the body, specifically the posterior edges of the pectoral and pelvic fins, with many injuries likely having a negative impact on the reproductive abilities and fitness of the rays.     

Sources and threats of chronic tissue loss on coral reefs in the Lakshadweep Islands,Indian Ocean

Tissue degradation and resulting mortality are major threats to coral reefs around the world. Information on interactions of the major environmental factors that mediate tissue loss and mortality in coral reefs is of great importance. It is essential to understand the prevailing reef health conditions and to develop appropriate management actions. In the present study, a series of benthic surveys conducted in the Lakshadweep Islands revealed the interaction of major biological factors in causing tissue loss and mortality. Hierarchical regression analysis revealed interactions of various environmental scenarios. Tissue loss was prevalent in islands with high cover of massive corals (m = 20.91) and low in islands dominated by branching corals (m = 0.61). Hierarchical regression analysis revealed black band disease (β = .59; p < .001) and algal interactions (β = .48; p < .001) to be major factors responsible for coral mortality caused by tissue loss in the region.     

Seedling recruitment in a semi-arid steppe: The role of microsite and post-dispersal seed predation

Grasslands dominated by Stipa tenacissima are important ecosystems in the arid and semiarid climates of western Mediterranean, where they have originated by degradation of open dry forests and shrublands. At present, although the level of exploitation in these ecosystems is very low, succession processes seem to have stopped. In this study, we explore the role of microsite and post-dispersal seed predation on the seedling emergence of two species from advanced successional stages (Rhamnus lycioides, Quercus coccifera), three species from degraded stages (Cistus clusii, Helianthemum violaceum, Anthyllis terniflora), and of the dominant species (Stipa tenacissima). Seeds of these species were sown in plots divided into two microsites: (i) under tussocks of S. tenacissima and (ii) in the bare soil between tussocks. Soil moisture was significantly higher in the tussock microsites. The interaction observed between microsite and time, reflected the slower drying process under tussocks. Seed predation was in general high and differed significantly between species but not between microsites. Q. coccifera was especially affected by predation. The only germination detected in gap areas was that of H. violaceum. The results pointed to a direct facilitative effect of tussock grass on the germination in R. lycioides (20.4±8.0%) and S. tenacissima (41.3±5.7%) while the corresponding figures for bare ground were 0%. These results suggest that the recovery of potential vegetation in this ecosystem is not possible or, at least, is very slow because the residual shrub patches do not generate a sufficient number of seeds able to disperse to favorable germination microsites. S. tenacissima may act as facilitator of seedling recruitment if there is a supply of diaspores.     

Spatial and temporal variations in the population structure of the soft-shell clam Mya arenaria in the Pomeranian Bay (southern Baltic Sea)

The population structure of Mya arenaria has been investigated in the sublittoral zone of the Pomeranian Bay (southern Baltic Sea). Box-corer samples were collected during a 1.5-year period in 1993/94 to follow changes in size and age structure of the clam populations in different parts of the study area. Large spatial differences in population structure were found between the sheltered southwest of the Bay and the shallow and exposed Oder Bank in the centre. The stock of the Oder Bank consisted of two different clam types. A slow-growing cohort was assumed to be autochtonous on the Oder Bank, whereas a fast-growing one was assumed to have immigrated from the surrounding area. The contribution of the two cohorts to the total density varied seasonally. Because of bedload transport of clams, the contribution to the reduction of the clam stock by wintering sea ducks could not be quantified. In the southwest of the Pomeranian Bay erosion was of minor importance. High mortality rates during the first two years of life were assumed to be caused by predation. Mortality rates of older cohorts remained stable until old age. Variations in cohort strength were related to interannual differences in the reproductive success. A mild winter presumably lowers the reproductive success in the subsequent summer. Severe oxygen depletion in summer 1994 caused a strong reduction in the clam stock at stations deeper than 10 m.     

Food Deprivation in the Muricid Drill Ocinebrina edwardsi (Mollusca: Prosobranchia): Histomorphological and Behaviour Research

Abstract. After a starvation period the predation rate in specimens of Ocinebrina edwardsi is less than in animals which feed normally. The closer the prey predator contact during the starvation period, the higher the level of predation when the snails are allowed to resume feeding. The reduction in predation after a long or short fast is obviously the result of changes in the structure and function of the ABO. In the secreting cells of normally fed animals the following enzymatic activities can be distinguished: acid and alkaline phosphatases, carbonic anhydrase and ATPase. Carbonic anhydrase and acid phosphatase activities are not present in starved individuals. Only after the animals have resumed feeding for 10 days does the ABO completely recover its enzymatic functions.     

Energy budgets and predation impact of dominant epibenthic carnivores on a shallow soft bottom community at the Swedish west coast

The energy flow through the epibenthic community on a shallow soft bottom in Gullmar Fjord, Sweden, is evaluated. The interaction between the dominant epibenthic predators: brown shrimp Crangon crangon L., juvenile plaice Pleuronectes platessa L. and sand goby Pomatoschistus minutus (Pallas), and their food supply is examined, and the fate of the biomass produced within the shallow water ecosystem is described. A steady state model is presented which describes the amounts, pathways and annual rates of energy flowing through the shallow water community. Field and laboratory studies are performed in order to validate the consumption rates of the fish and shrimp species. The brown shrimp occupies a key position in this ecosystem. It represents food, consisting of newly settled juveniles, both to its conspecifics and to other epibenthic species in shallow water. Sixty to eighty per cent of the annual production of shrimps in shallow water is consumed by the epibenthic predators. The brown shrimp constitutes a main predator on other epibenthic species and, by providing such feedback loops, the shrimp constitutes a highly significant regulator of epibenthic carnivores in shallow water. A loss from the benthic community will occur due to predation, maximally amounting to 24–34% of the annual production, which is a high value compared to similar areas. A dynamic simulation is also performed in order to calculate the seasonal change of energy in the epibenthic community in shallow water. Based on mortality calculations, the total output from the shallow nursery should amount to 0·6 g m⁻² year⁻¹ (dry wt).