Physiological effects of marine natural organic matter and metals in early life stages of the North Pacific native marine mussel Mytilus trossulus; a comparison with the invasive Mytilus galloprovincialis

The role of seawater NOM in reducing metal toxicity for marine organisms is not well understood. We investigated the effects of five different marine NOMs (two autochthonous, one allochthonous, two of mixed origin, at 8 mg C/L), three metals (6 μg Cu/L; 20 μg Pb/L; 25 μg Zn/L), and combinations between them, to early life stages of Mytilus trossulus (a North Pacific native) in 48-h tests. Endpoints were whole body Ca2++Mg2+-ATPase activity, carbonic anhydrase (CA) activity and lipid peroxidation. Comparisons were made with previously reported tests (identical conditions) on the invasive M. galloprovincialis. Unexposed M. trossulus had lower Ca2++Mg2+-ATPase but similar baseline CA activity and lipid peroxidation to unexposed M. galloprovincialis. NOMs alone induced increased enzyme activities, and increased lipid peroxidation, but the latter did not occur with NOMs of mixed origin in M. trossulus. There was no clear difference in the sensitivity to various NOMs between species. In M. trossulus, all three metals by themselves caused increases in lipid peroxidation, as did many metal-NOM combinations. The origin of the NOMs influenced the nature of the responses to NOM-metal combinations in both species, but no clear relationship to NOM chemistry was apparent. Overall, M. trossulus was more sensitive to metals and NOM-metal combinations, with a greater number of significant responses (27 versus 22 treatment endpoints, out of a total of 72) and a greater proportion of negative effects (81% versus 50%) than in M. galloprovincialis. Therefore, marine NOMs by themselves, as well as metals by themselves and NOM-metal combinations, can induce both positive and negative physiological responses. Lipid peroxidation appears to be a particularly common negative response. In future studies, NOM quality and mussel species should be considered since native M. trossulus and invasive M. galloprovincialis exhibited markedly different responses after exposure to the same environmental conditions.