Is there a BMAA transfer in the pelagic and benthic food webs in the Baltic Sea?

The evidence regarding BMAA occurrence in the Baltic Sea is contradictory, with benthic sources appearing to be more important than pelagic ones. The latter is counterintuitive considering that pelagic primary producers, such as diatoms, dinoflagellates, and cyanobacteria, are the only plausible source of this compound in the food webs. To elucidate BMAA distribution in trophic pathways, we analyzed BMAA in the pelagic and benthic food webs sampled in summer 2010 in the Northern Baltic Proper. As potential BMAA sources, phytoplankton communities in early and late summer were used. As pelagic consumers, zooplankton, mysids and zooplanktivorous fish (herring) were used, whereas benthic invertebrates (amphipods, priapulids, polychaetes, and clams) and benthivorous fish (perch and flounder) represented the benthic food chain. To establish the trophic structure of the system, the stable isotope (δ13C and δ15N) composition of its components was determined. Contrary to the reported ubiquitous occurrence of BMAA in the Baltic food webs, only phytoplankton and lower consumers (zooplankton and mysids) of the pelagic food chain tested positive. Given that our analytical approaches were adequate, we conclude that no measurable levels of this compound occurred in the benthic invertebrates and any of the tested fish species in the study area. These findings indicate that widely assumed presence and transfer of BMAA to the top consumers in the food webs of the Baltic Sea and, possibly, other systems remain an open question. More controlled experiments and field observations are needed to understand the transfer and possible transformation of BMAA in the food web under various environmental settings.

5. Food chains to fish

‘Food chains to fish’ considers the nature of pelagic and benthic food webs and the coupling between them. Life at the bottom of lakes in the benthic zone is mostly made up of worms, molluscs, and amphipods. In the open lake waters, three groups of zooplankton play a leading role in the transfer of carbon and energy from the base of the food web (phytoplankton and bacteria) to pelagic fish: rotifers, cladocerans, and copepods. Although certain fish species remain within specific zones of the lake, others swim between zones and access multiple habitats. The tracking of elements through the food chain can help understand the impacts of chemical pollution.