High capacity for a dietary specialist consumer population to cope with increasing cyanobacterial blooms

Abstract

We present a common-garden experiment to examine the amphipod Monoporeia affinis, a key deposit-feeder in the Baltic Sea, a low diversity system offering a good model for studying local adaptations. In the northern part of this system, the seasonal development of phytoplankton is characterized by a single diatom bloom (high nutritional quality), whereas in the south, the diatom bloom is followed by a cyanobacteria bloom (low nutritional quality) during summer. Therefore, the nutrient input to the benthic system differs between the sea basins. Accordingly, the amphipod populations were expected to be dietary specialists in the north and generalists in the south. We tested this hypothesis using a combination of stable isotope tracers, trophic niche analyses, and various endpoints of growth and health status. We found that when mixed with diatomes, the toxin-producing cyanobacteria, were efficiently incorporated and used for growth by both populations. However, contrary to expectations, the feeding plasticity was more pronounced in the northern population, indicating genetically-based divergence and suggesting that these animals can develop ecological adaptations to the climate-induced northward cyanobacteria expansion in this system. These findings improve our understanding regarding possible adaptations of the deposit-feeders to increasing cyanobacteria under global warming world in both limnic and marine ecosystems. It is possible that the observed effects apply to other consumers facing altered food quality due to environmental changes.

Understanding amphipod reproductive health drivers in the Baltic Sea: A Study Based on Structural Equation Modeling

“…S6). Taking into account the reported lower δ 15 N values of the amphipods in BS compared to WGB (Ledesma et al, 2022), the observed differences in the niche size can imply both a less diverse food base and lower fractionation as a result of higher nitrogen-use efficiency, which would be expected in BS, where the nitrogen availability is lower than in the more eutrophied WGB. Such mechanisms were documented in fishes (Carter et al, 1998), with a direct routing of amino acids to protein synthesis, resulting in the decrease of depleted nitrogen in urea and ammonia relative to the assimilation of nitrogen into the tissues, and a decreased tissue-diet enrichment.…”