Fate of cyanobacterial toxins in the pelagic food web: transfer to copepods or to faecal pellets?

Abstract

Toxic cyanobacterial blooms are a common phenomenon in the Baltic Sea. The fate of the toxin in the food web is largely unknown. We studied the effect of algal diets on production of pellets and toxin content of the calanoid copepod Eurytemora affinis in the northern Baltic Sea. Fieldcollected copepods were fed with (1) cultured toxic cyanobacteria Nodularia spumigena; (2) cultured non-toxic flagellates Brachiomonas submarina; and (3) a natural phytoplankton assemblage. Natural phytoplankton was dominated by non-toxic cyanobacteria Aphanizomenon flos-aquae, but also remnants of toxic N. spumigena were found. Pellet production was highest on cultured B. submarina, second highest on N. spumigena and lowest on natural phytoplankton. Because pellets were produced on cultured N. spumigena, this shows that toxic cyanobacteria are consumed if no other food is available. The toxin content of E. affinis was highest in copepods fed with cultured N. spumigena, but toxin was also found in lower concentrations in animals fed with natural phytoplankton. Results indicate that an accumulation of toxins mainly occurs during a growing phase of cyanobacterial blooms. The toxin concentration in the pellets was approximately 6 to 12 times lower than in the copepods. We suggest that a large part of the ingested toxin accumulates in copepod tissues, although some is egested with pellets. This may lead to transport and, possibly, accumulation of cyanobacterial toxin in higher pelagic trophic levels in the Baltic Sea. KEY WORDS: Cyanobacterial toxin · Nodularia spumigena · Toxin transfer · Copepods · Faecal pelletsResale or republication not permitted without written consent of the publisher

Feeding, reproduction and toxin accumulation by the copepods Acartia bifilosa and Eurytemora affinis in the presence of the toxic cyanobacterium Nodularia spumigena

“…Values found in E. affi-nis were in the same range as previously observed for this species , Lehtiniemi et al 2002.…”

“…Addition of B. submarina to <100 µm FW increased the C (carbon) and N (nitrogen) contents of Eurytemora affinis eggs even when no increase was detected in the females (Koski 1999). Furthermore, we have observed that the pellet production rate by E. affinis feeding on B. submarina, which corresponded to rates of other copepods feeding on good food, was significantly higher than on natural community or N. spumigena diets (Lehtiniemi et al 2002).…”

“…The PP1 assay gave values up to 5 times higher than those detected by the ELISA, which has also been observed before , Lehtiniemi et al 2002. Protein phosphatases can be inhibited by a series of different compounds (An & Carmichael 1994, Honkanen et al 1994, while in general, the antibodies in the ELISA tend to recognise and cross-react only with microcystins, nodularins and closely related molecules.…”

“…216 000 Nodularia spumigena cells (average 24 h ingestion rate for E. affinis in the Gulf of Finland) with a toxin content of 0.13 pg cell -1 (measured by HPLC), the amount of toxin ingested in our study during 24 h should equal 28 ng copepod -1 . In another study performed during the same cruise, the content of nodularin equivalents in the pellets produced by Eurytemora affinis, feeding on the same Nodularia spumigena strain as in the present experiment, was quantified (Lehtiniemi et al 2002). During this study, E. affinis females produced 10.38 ± 5.90 pellets during 24 h (in a food suspension containing 876 µg C l -1 of N. spumigena).…”

Accumulation of nodularin in sediments, mussels, and fish from the Gulf of Gdańsk, southern Baltic Sea

“…N. spumigena cells can also be ingested by herbivorous zooplankton. This was definitely proved in experiments with radiolabeled NOD and by detection of the toxin in faecal pellets produced by the organisms (Lehtiniemi et al, 2002;Karjalainen et al, 2003Karjalainen et al, , 2005. Zooplankton is presumed to be an important vector in toxin transfer to higher trophic levels.…”