Seasonal variation of in situ feeding rates by the temperate ascidian Halocynthia papillosa

Abstract

The natural diet and prey capture rate of the temperate ascidian Halocynthia papillosa were studied in the field in a Western Mediterranean population. In sltu grazing rates on dissolved organic carbon, detrital particulate organic carbon, procaryotes, pico-and nanoeucaryotes, phytoplankton and ciliates were examined through a year cycle. The natural diet of the species included detrital organic matter, heterotrophic bacteria, Prochlorococcus sp., Synechococcus sp. (cyanobactena type), protozoa and phytoplankton with a mean size range from 0.6 Z? 0.3 (heterotrophic bacteria) to 70 * 22 pm (pennate diatoms). Specific clearance rates varied seasonally and exhibited a pattern of increase with temperature increase in which temperature explained 55 % of the variance in clearance rate throughout the year. Annual variation in prey concentration did not affect specific clearance rate Ingestion rate of the species showed a marked seasonal pattern which was different for the 2 main food sources: detrital and live particles. Thus, while the highest ingestion of detrital particles was in spring, the highest values of live particle ingestion occurred during summer and fall. Overall, an H. papillosa specimen of mean size 0.25 g AFDW (ash-free dry weight) was estimated to ingest an annual mean of 1305 * 496 pg C g AFDW-' h-' and 84 + 16 pg N g AFDW" h-' Carbon from detrital origin accounted for 92 k 2 % of the total ingested carbon, while ingestion of live carbon accounted for 8 -r-2 %. However. the seasonal variation of ingested nitrogen from live particles explained 91 % of the gonadal development variance for the year, suggesting that live particles are likely to be of more significance in the diet of the species than particles from detrital origm. Feeding rates are discussed in relation to seasonal changes In food availability and production of the species (i.e. growth and reproduction). The results suggest that factors other than food availability determine the seasonal dynamics of the species.

Protein, carbohydrate, lipid concentrations and HSP 70–HSP 90 (stress protein) expression over an annual cycle: useful tools to detect feeding constraints in a benthic suspension feeder

“…Seasonal feeding studies on passive or active suspension feeders in warm temperate seas lead to the conclusion that in autumn, the carbon supply decreases (an important part probably coming directly from low quality detritus, e.g. Ribes et al 1998;Jordana et al 2001;Rossi et al 2004). It cannot be excluded, however, that a decrease in carbohydrate-lipid concentrations in P. clavata is associated with reproduction in the summer (Coma et al 1995b), although non-reproductive colonies of this species show similar seasonal trends (Rossi 2002).…”

Using flow cytometry for counting natural planktonic bacteria and understanding the structure of planktonic bacterial communities

“…Li et al (1995) and del Giorgio et al (1996) introduced blue-excitable stains for enumerating plankton bacteria. Li et al (several) sodium or potassium citrate Ribes et al 1998aRibes et al , 1998b Coulter EPICS 753 The Argus-100 (Skatron), the BioRad Bryte and the Bruker ACR 1400-Sp are essentially the same machines.…”

“…8 (lower panels). Flow cytometry has also been used to estimate the loss rates of bacteria and picoalgae to a variety of benthic animals: bivalves Shumway et al, 1985), sponges (Pile et al, 1996;Pile, 1997;Ribes et al, 1999a), ascidians (Ribes et al, 1998a) and gorgonian corals (Ribes et al, 1998b). The methods presented in this review have proven fast and reliable for the study of the interaction between benthic organisms and their planktonic food (e.g.…”

The ultimate opportunists: consumers of seston

“…Development of an in situ technique using incubation jars, together with the improvement of methods for analysing the seston fractions consumed, has enabled continuous dietary records to be made for filter feeders in their natural habitat (Ribes et al 1998a(Ribes et al ,b, 1999a(Ribes et al ,b, 2000. Because the submersible apparatus is surface-independent, it allows us to assess oxygen concentration changes and feeding rates over prolonged periods.…”

“…Particle concentration is measured in water samples taken from the jars at fixed time intervals (clearance method, Riisgård 2001). Feeding rates on specific seston fractions are calculated by comparing rates of change in concentration of these fractions between control and experimental jars (Ribes et al 1998a(Ribes et al ,b, 1999a(Ribes et al ,b, 2000.…”