Seasonal and site-specific differences in biofouling communities on Pacific oyster Mariculture farms

Abstract

Artificial substrates are ideal for the settlement of biofouling communities. Oyster cages used in mariculture are known to provide substrate for a diversity of epibiotic organisms to settle and grow. While oyster farmers regularly clean their cages of these epibionts, diverse biofouling communities can still develop and contribute to the composition of the overall ecosystem surrounding mariculture farms. Colonization by biofouling organisms, including algae and animals, can be sudden and have rapid development. Biofouling on cages can have deleterious impacts on the farmed oysters, ultimately increasing operational expenses and decreasing farmer profits. Identifying seasonal and spatial patterns in biofouling community composition and their relationship to environmental conditions is essential for effectively addressing the impact these organisms pose. Here, we examined changes in taxonomic composition of biofouling communities over time at multiple oyster mariculture farms in the Gulf of Alaska with the intent of answering our overarching research question: Does composition of biofouling communities vary seasonally and spatially? To address this question, we took bi-monthly photographs of oyster cages from March to September of 2023 at three farms in Kachemak Bay and one sampling was done in September 2023 in Prince William Sound to assess seasonal and spatial differences in biofouling community composition. A subset of photographs taken at all sites in September were paired with scrape collections for biomass to compare surveying methods. Though there were notable differences in taxonomic resolution between the two sampling methods, both resulted in similar diversity measurements and spatial patterns of composition. Diatom mats and red filamentous algae were predominant contributors to biofouling. Additionally, the spatial differences in community variability and composition were stronger than seasonal differences, and salinity was found to best correlate with patterns in biofouling communities. Altogether, these findings have practical implications for monitoring impacts of biofouling on mariculture, as the methodological approach can be catered to specific research goals or resource constraints.