Asparagopsis armata Exudate Cocktail: The Quest for the Mechanisms of Toxic Action of an Invasive Seaweed on Marine Invertebrates

The red seaweed Asparagopsis armata exhibits a strong invasive behaviour and is included in the list of the “Worst invasive alien species threatening biodiversity in Europe”. This seaweed has been shown to produce a large diversity of halogenated compounds with effective biological effects, deeply affecting rockpool species. Therefore, the present study aimed to investigate the biochemical responses to sublethal concentrations of Asparagopsis armata exudate on two coastal organisms, the marine snail Gibbula umbilicalis and the rockpool shrimp Palaemon elegans. Antioxidant defences superoxide dismutase (SOD) and glutathione-S-transferase (GST), oxidative damage endpoints lipid peroxidation (LPO) and DNA damage, the neuronal parameter acetylcholinesterase (AChE), as well as the fatty acid profile were evaluated. Results revealed different metabolic responses between species, indicating that A. armata exudate affected the organisms through different pathways. Despite previous studies indicating that the exudate effected G. umbilicalis’ survival and behaviour, this does not seem to result from oxidative stress or addressed neurotoxicity. On the other hand, for P. elegans, an inhibition of AChE and the decrease of antioxidant capacity concomitant with the increase of LPO, suggests neurotoxicity and oxidative stress as mechanisms of exudate toxicity for this species. For fatty acids, there were different profile changes between species, also more pronounced for P. elegans with a general increase in PUFA with exudate exposure, which commonly means a defence mechanism protecting from membrane disruption. Nonetheless, the omega-3 PUFAs ARA and DPA were increased in both invertebrates, indicating a common mechanism regulation of inflammation and immunity responses to this stress. This work provides further insight on the mechanisms of invertebrate response and tolerance to an expanding coastal environmental stress as is the marine invader A. armata.