Alexander T. Lowe

Pacific geoduck (Panopea generosa) resilience to natural pH variation

Pacific geoduck aquaculture is a growing industry, however little is known about how geoduck respond to varying environmental conditions, or how production might be impacted by low pH associated with ocean acidification. Ocean acidification research is increasingly incorporating multiple environmental drivers and natural pH variability into biological response studies for more complete understanding of the effects of projected ocean conditions. In this study, eelgrass habitats and environmental heterogeneity across four estuarine bays were leveraged to examine low pH effects on geoduck under different natural regimes, using proteomics to assess physiology. Juvenile geoduck were deployed in eelgrass and adjacent unvegetated habitats for 30 days while pH, temperature, dissolved oxygen, and salinity were monitored. Across the four bays pH was lower in unvegetated habitats compared to eelgrass habitats, however this did not impact geoduck growth, survival, or proteomic expression patterns. However, across all sites temperature and dissolved oxygen corresponded to growth and protein expression patterns. Specifically, three protein abundance levels (trifunctional-enzyme β-subunit, puromycin-sensitive aminopeptidase, and heat shock protein 90-α) and shell growth positively correlated with dissolved oxygen variability and inversely correlated with mean temperature. These results demonstrate that geoduck are resilient to low pH in a natural setting, and other abiotic factors (i.e. temperature, dissolved oxygen variability) may have a greater influence on geoduck physiology. In addition this study contributes to the understanding of how eelgrass patches influences water chemistry.

Gut content, fatty acid, and stable isotope analyses reveal dietary sources of macroalgal-associated amphipods along the western Antarctic Peninsula

Shallow water subtidal marine communities along the western Antarctic Peninsula are characterized by dense beds of macroalgae and strikingly dense assemblages of associated amphipods. However, direct grazing by amphipods on the dominant macroalgae is unlikely as most of these algae elaborate secondary metabolites known to be herbivore feeding deterrents. What resources, then, support this vast macroalgal-associated amphipod assemblage? We addressed this question by analyzing the gut contents, fatty acids, and stable isotopic ratios of 15 different amphipod species associated with the macrophyte community. The δ15N and δ13C stable isotope values revealed that most of the abundant species of amphipods are primary consumers whose ultimate carbon source is derived from some combination of brown macroalgae, epiphytic diatoms, and endo/epiphytic filamentous algae. Gut contents revealed that a large percentage of the amphipod diets are comprised of diatoms and macroalgal tissues, both filamentous and multiseriate. Fatty acid analysis corroborated our conclusions based on stable isotope and gut content data, demonstrating the importance of diatoms to assimilated material, but also highlighting the rich diversity of diets within the macroalgal-associated amphipod assemblage. Our findings suggest that amphipods routinely clean their host macrophytes of potentially harmful epiphytes, including both diatoms and emergent filaments from brown algal endophytes. Some prominent species of amphipods may also derive a small percentage of their carbon from palatable and, in one case, unpalatable, chemically defended red algae. These results, combined with previous studies showing that the amphipods gain refuge from predators by associating with unpalatable macroalgae, support the hypothesis that amphipods along the western Antarctic Peninsula are living in mutualism with their macrophyte hosts rather than consuming the host directly.