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

Abstract

11The evidence regarding BMAA occurrence in the Baltic Sea is contradictory, with benthic 12 sources appearing to be more important than pelagic ones. The latter is counterintuitive 13 considering that pelagic primary producers, such as diatoms, dinoflagellates, and 14 cyanobacteria, are the only plausible source of this compound in the food webs. To elucidate 15 BMAA distribution in trophic pathways, we analyzed BMAA in the pelagic and benthic food 16 webs sampled in summer 2010 in the Northern Baltic Proper. As potential BMAA sources, 17 phytoplankton communities in early and late summer were used. As pelagic consumers, 18 zooplankton, mysids and zooplanktivorous fish (herring) were used, whereas benthic 19 invertebrates (amphipods, priapulids, polychaetes, and clams) and benthivorous fish (perch 20 and flounder) represented the benthic food chain. To establish the trophic structure of the 21 system, the stable isotope (δ 13 C and δ 15 N) composition of its components was determined. 22Contrary to the reported ubiquitous occurrence of BMAA in the Baltic food webs, only 23 phytoplankton and lower consumers (zooplankton and mysids) of the pelagic food chain 24 tested positive. Given that our analytical approaches were adequate, we conclude that no 25 measurable levels of this compound occurred in the benthic invertebrates and any of the 26 tested fish species in the study area. These findings indicate that widely assumed presence 27 and transfer of BMAA to the top consumers in the food webs of the Baltic Sea and, possibly, 28 other systems remain an open question. More controlled experiments and field observations 29 are needed to understand the transfer and possible transformation of BMAA in the food web 30 under various environmental settings. 31 Keywords: BMAA, Baltic Sea, food web, phytoplankton, pelagic and benthic food chains, 32 stable isotopes 33 34 35 62 Réveillon et al., 2015; Salomonsson et al., 2015; Réveillon et al., 2016). However, negative 63 outcomes of such surveys are also quite common (Scott et al., 2009; Niedzwiadek et al., 64 2012). Then again, most studies reporting BMAA transfer from primary producers to fish 65 have weak sampling design, suffering inconsistencies in both temporal and spatial 66 correspondence between the collected samples of sources and consumers. These 67 4 inconsistencies hamper quantitative analysis of the BMAA transfer in the food web and make 68 it difficult to trace this compound to specific producers. As a result, controversy surrounds 69 the sources and pathways of BMAA production and accumulation in aquatic ecosystems, 70 which is further complicated by inadequate analytical approaches that have been frequently 71 used in the past. 72 The evaluation and recent development of the analytical techniques strongly suggest that 73 some of the previous data may overestimate the BMAA concentrations in the environmental 74 samples (Faassen et al., 2012). Indeed, owing to the differences between the analytical 75 methods (Faassen et al., 2012), the reported concent...