Estuarine bivalve metabolic response mediated by environmental drivers

Humans are rapidly modifying environmental conditions in estuaries, which are among Earth's most productive and dynamic ecosystems. Bivalve molluscs are key estuarine organisms, contributing to range of ecosystem functions and services, though human-induced environmental changes are affecting their behaviour, physiology, and fitness with implications at individual, population, community, and ecosystem levels. Understanding how estuarine bivalves respond and adapt to different environmental drivers will enable us to better predict change at multiple levels of biological organisation. In this study, we investigated the metabolites of a common and ecological important suspension-feeding bivalve in New Zealand, the cockle, Austrovenus stutchburyi. At seven of eight pre-established monitoring sites in a North Island estuary, we evaluated differences in cockle metabolite abundance, diversity, and composition, as well as relationships between cockle metabolites and environmental conditions. Our findings revealed differences in the abundance and diversity of cockle metabolites across sites, particularly in the metabolites alanine, aspartic acid, glutamic acid, glycine, proline, and succinic acid. The differences in metabolites across sites were mediated by the site-specific environmental conditions, in particular, the sediment's mud content and organic matter. Differences in metabolites were most pronounced when comparing sites close to freshwater inputs versus sites located closer to the estuary mouth. In general, Austrovenus metabolite abundance was higher at sites with less signs of stress (i.e., close to the estuary mouth) and lower in sites with with higher mud content (i.e., close to freshwater inputs), while the metabolite diversity followed an inverse pattern. The metabolic responses of cockles appeared to be linked to processes such as feeding, oxygen regulation, and energy allocation. The observed metabolic trends highlight the complex interactions between cockles and their environment and provide insights into the metabolic responses of bivalves to the rapidly changing environment.