Marine diatoms sustain growth of bivalves in a Mediterranean lagoon

Abstract

Carbon stable isotopes and fatty acids were measured in the suspended particulate organic matter (POM) of the Thau lagoon to study its qualitative temporal changes in relation to environmental factors and to identify the food sources of bivalves over a one-yr-cycle in relation to their growth. Reciprocally, the impact of shellfish farming on POM was also studied. Oysters and mussels were sampled and measured for biometry, stable isotopes and fatty acid composition. Water samples were collected at two sites, both inside and outside of the shellfish farming area, to determine concentrations in POM, chlorophyll a (Chl a) and stable isotopes. Carbon isotopes and fatty acids in bivalves reflected seasonal changes in food sources, which varied consistently with the environment. Seasonal changes in δ 13 Highlights ► Carbon isotopes and fatty acids in bivalves reflected seasonal dietary changes. ► Terrestrial organic matter and bacteria can contribute to the diet of bivalves. ► Mussels and oysters showed significant differences in their fatty acids. ► Periods of high growth rate in bivalves were mainly fuelled by diatoms. ► Stable isotopes allow investigating the effects of bivalve aquaculture.

β-N-methylamino-l-alanine (BMAA) and isomers: Distribution in different food web compartments of Thau lagoon, French Mediterranean Sea

“…Nevertheless, diatoms, now reported as BMAA-producers, are highly abundant in the phytoplankton community and are suggested to sustain the growth of mollusks in the important bivalve farming area of Thau lagoon (Pernet et al, 2012). This trend was also confirmed in our study (Fig.…”

“…Previous studies have shown that Chaetoceros sp. was the main diatom species in the microplankton on several occasions separated by several years, indicating that this species is regularly abundant in Thau lagoon (Pernet et al, 2012;Vaquer et al, 1996). Data from this study, as well from previous studies, thus confirmed that diatoms, in particular Chaetoceros sp., were highly abundant during the sampling period and could have been an important food source for zooplankton and mussels.…”

“…Ion ratios for the different transitions in diatom extracts were equivalent to those of standards for all samples in which BMAA was detected. The confirmation that diatoms contained BMAA is of particular importance since they contribute significantly to the diet of mussels and oysters in Thau lagoon (Dupuy et al, 2000;Pernet et al, 2012). Specifically, BMAA was found in two out of the three Chaetoceros strains (including one isolated from the French coast) and Chaetoceros sp.…”

“…Data from this study, as well from previous studies, thus confirmed that diatoms, in particular Chaetoceros sp., were highly abundant during the sampling period and could have been an important food source for zooplankton and mussels. As previously mentioned, the presence of diatoms is noteworthy since diatoms have recently been suggested to contain bound BMAA (Jiang et al, 2014a) and they sustain the growth of mollusks in Thau lagoon (Dupuy et al, 2000;Pernet et al, 2014Pernet et al, , 2012. However, the production of BMAA by microalgae from Thau lagoon has not been studied so far and the assertion of Jiang et al, 2014a saying that "BMAA production might be common among diatoms" should be confirmed.…”

“…Diatoms are dominating the micophytoplankton community and they sustain the growth of mollusks of Thau lagoon (Dupuy et al, 2000;Pernet et al, 2012). However, ciliates (including abundant tintinnid populations) and zooplankton species have also been reported in the lagoon (Dupuy et al, 2000;Lam-Hoai and Rougier, 2001) and could represent an alternative food source for the mussels.…”