Particulate dimethylsulfoniopropionate at DYNAPROC station

In the framework of the projects DYFAMED and PICASSO, diel variations of particulate dimethylsulfoniopropionate (DMSPp) and of its size fraction higher than 10 µm (DMSPp>10 µm) were studied in surface waters of the central Ligurian Sea in May 1990 and May 1995, and in the harbour of the city of Barcelona (Spain) in July 1998. Time series performed in stratified and nitrate depleted surface waters of the Ligurian Sea revealed that DMSPp>10 µm was undergoing diurnal variations. DMSPp-containing particles in the size range higher than 10 µm also markedly affected the DMSPp-to-chlorophyll (chl) a ratio of surface waters on a daily basis. The ratios were 35% to 72% lower at dawn than at dusk. The fact that the diadinoxanthin (DD)-to-chl a ratio of surface phytoplanktonic populations did not exhibit diurnal cycles suggests that physiological adaptation of cellular DMSP and chl a to the light conditions was not a likely process to account for the diurnal changes of the DMSPp-to-chl a ratio. It is suggested that such diurnal variability resulted from changes in plankton composition due to vertical migrations of DMSP-containing organisms larger than 10 µm. We have demonstrated from samples collected in the harbour of the city of Barcelona that DMSP-containing dinoflagellates are active diel migrants. However, the results obtained in the open sea in May 1990 suggest that dinoflagellates and also ciliates contribute to the pool of DMSPp in the size range larger than 10 µm. The results of May 1995 are ambiguous as to the role of dinoflagellates because, in the absence of specific cell counts, DMSPp>10 µm and the pigment peridinin, which is usually present in dinoflagellates (but peridinin-free dinoflagellates exist) showed very different vertical and temporal patterns.

Ingestion rate and egg production of copepods collected in the Turkish Strait during Bilim 2 cruise in April 2008

The copepod Ingestion on ciliates, phytoplankton and the copepod production dataset is based on samples taken during April 2008 in Dardanelles Straits, Marmara Sea and Bosporus Straits at the third priority stations. These experiments were set up according to DoW of Sesame project. Copepods for the experiments were obtained with slow non-quantitative tows from the upper 50 m layer of the water column using 200 µm mesh size nets fitted with a large non-filtering cod end. For the grazing experiments we used the following copepod species: Centropages typicus and Acartia clausi according to the relevant reference (Bamstedt et al. 2000). Copepod clearance rates on ciliates were calculated according to Frost equations (Frost 1972). Ingestion rates were calculated by multiplying clearance rates by the initial standing stocks (Bamstedt et al. 2000). Egg production rates of the dominant calanoid copepods were determined by incubation of fertilised females (eggs/female/day) collected in the 0-20m layer. Copepod egg production was measured for the copepods Centropages typicus and Acartia clausi. On board experiments for the estimation of copepod egg production were taken place. For the estimation of copepod production (mg/m**2/day), lengths (copepods and eggs) were converted to body carbon (Hopcroft et al., 1998) and production was estimated from biomass and weight-specific egg production rates, by assuming that those rates are representative for juvenile specific growth rates (Berggreen et al., 1988).