Preliminary Observations on the Feeding Activity of Fishes during Tidal and Diel Cycles in the Loire Estuary: The Bib Trisopterus luscus L. 1758

Abstract. .Series of experimental trawls repeated over the same area during both 12 and 24 h cycles coupled with an analysis of the stomach contents of the bib demonstrated quantitative and qualitative variations in the predator's diet. The population studied feeds continuously over 24 h, the coefficient of "fullness" is relatively constant, and freshly eaten prey can be observed both during the day and at night. The proportion of brown shrimp in the food increases after high tide, especially when this occurs at night, coinciding with the shrimp's period of maximum activity. However, the overall impact of the bib on the shrimp population depends more on the abundance of the former than on variations in their individual food intake.     

Abundance and biomass of scyphomedusae, Aurelia aurita and Chrysaora melanaster, and Ctenophora, Bolinopsis mikado, with estimates of their feeding impact on zooplankton in Tokyo Bay, Japan

The abundance of a scyphomedusae, Aurelia aurita and Chrysaora melanaster, and a ctenophore, Bolinopsis mikado, in Tokyo Bay was investigated from 1995 to 1997. Aurelia aurita appeared throughout the year with a peak in abundance occurring from spring to summer. The average abundance and biomass during this period for the three successive years was 4.8, 43.8 and 3.2 ind. m⁻², and 1.02, 10.0 and 0.42 gC m⁻², respectively. The values in 1995 and 1997 were comparable with those previously reported for A. aurita abundance from 1990 to 1992. Values were very high in 1996, but the size composition of the bell diameter did not differ from other years, which suggested the absence of food limitation for A. aurita in 1996. C. melanaster was scarce over the survey period (<1.0 ind. m⁻²) while Bolinopsis mikado was more abundant during September to December, with maximum values of 172 ind. m⁻² and 0.33 gC m⁻² observed in December 1997. The weight-specific clearance rate for A. aurita on zooplankton (mainly copepods and their nauplii) was 0.16 ± 0.05 lgWW⁻¹ h⁻¹ (n = 13). Population clearance rate peaked from spring to summer, with average levels of 14.2%, 162% and 5.0% day⁻¹ obtained from spring to summer for respective years. Population clearance rates for B. mikado, calculated based on minimum carbon requirements, was 7.1% day⁻¹ in December 1997. Consequently, the trophic role of gelatinous zooplankton as predators in Tokyo Bay is important all the year round, considering the high impact of A. aurita from spring to summer and B. mikado from autumn to winter.     

The Association of Ophiothrix lineata and Callyspongia vaginalis: A Brittlestar-Sponge Cleaning Symbiosis?

Abstract. The relationship between a sponge, Callyspongia vaginalis, and an associated brittlestar, Ophiothrix lineata, was examined for mutualistic symbiotic interaction. Cinematography, feeding experiments, and analyses of stomach contents reveal that O. lineata (unlike other Ophiothrix species) is a non-selective deposit feeder. Its diet consists of detrital particles adhering to the sponge, which are too large to be utilized by the sponge as food. Thus, the brittlestar cleans the inhalent surface of the sponge as it feeds. Since siltation interferes with sponge pumping-activity, it is suggested that the cleaning behavior of O. lineata may enhance the filtration capability of C. vaginalis. In situ elapsed-time films show that brittlestars expose their arms when they feed, suggesting that they feed only at night because of a need to avoid diurnal predators. Manipulative experiments show that residence in C. vaginalis protects O. lineata from predatory fish. A comparison of the incidence of arm regeneration for brittlestars residing on C. vaginalis, and on a toxic sponge, Neofibularia nolitangere, indicates that factors other than sponge toxicity are involved in protecting sponge-dwelling brittlestars.     

Zooplankton Feeding Ecology: Contents of Fecal Pellets of the Copepod Anomalocera ornata from Continental Shelf and Slope Waters of the Gulf of Mexico

Abstract. The diet of the copepod Anomalocera ornata was examined by comparing contents of fecal pellets produced on natural diets with assemblages of available phytoplankton. Samples were collected in continental shelf and slope waters of the northern Gulf of Mexico. A wide size and taxonomic array of phytoplankters was ingested, and remains of phytoplankton taxa in fecal pellets reflected the composition of phytoplankton assemblages in the water. Absence of crustacean remains in fecal pellets suggests that A. ornata feeds primarily as an opportunistic grazer.