The influence of mariculture farms on epibenthic fish, invertebrate, macroinfauna, and seaweed assemblages

Brian Ulaski collecting biofouling data at Bootleggers Cove Farm in Kachemak Bay.

PROJECT

The influence of mariculture farms on epibenthic fish, invertebrate, macroinfauna, and seaweed assemblages

Mariculture Research and Restoration Consortium: Mariculture with Biological Communities, Benthic Component

Background

The Mariculture Development Plan for Alaska suggests that research is needed to continue to develop mariculture in the state, including studies that will quantitatively document environmental impacts of mariculture. While some aspects of this environmental influence have been studied elsewhere in the world, their findings are inconsistent and therefore cannot be applied to Alaska waters without local studies. The Benthic Component of Mariculture ReCon will examine the relationship between mariculture farms and various biological community components along with various static and dynamic environmental characteristics.

The overarching objectives of the Benthic Component are to determine if the suspended culture techniques used in mariculture in Alaska have influenced the associated biological communities at established farm sites that have been working for numerous years. We will also explore the short-term impacts of farm implementation on associated biological communities.  Key to this component will be determining if oyster and seaweed farms influence the associated biological community in similar ways (i.e., similar patterns of change between established and new farms regardless of farmed species). These biological community data will be correlated with environmental data being collected by our component, other components within the project, and partner farmers to find associations between species and environmental characteristics. Lastly, we will work with farmers to determine what fouling organisms are associated with mariculture farm infrastructure and how similar those fouling communities are to naturally occurring benthic communities.

Methods

The benthic team will conduct surveys at farms in Kodiak, Prince William Sound, and Kachemak Bay. Epibenthic invertebrates and seaweeds will be sampled in six randomly placed 50 x 50 cm2 quadrats along three 30 m transects. In each quadrat, epibenthic mobile invertebrates and kelp will be identified and collected for biomass and abundance, and percent cover of sessile organisms will be estimated. Also along the 30 m transect, all large and rare organisms (e.g., sea stars, sea cucumbers) and benthic fish will be identified and counted within 2 m of the line. Macroinfauna will also be sampled at each sub-site, using three replicate 4’ diameter PVC cores randomly placed (manually pushed into the substrate to approximately 15 cm depth) along each transect. Each core will be sieved over 2 mm and all organisms identified to larger taxonomic levels and counted. Biofouling organisms on the farming cages will be sampled using photographs and settling cages.

What We Are learning

The benthic team completed their first field season in 2023. So far, approximately 130 benthic cores have been collected to assess infaunal communities, over 250 quadrats sampled for epibenthic invertebrates and seaweeds, and around 240 photographs of biofouling communities taken. Much of our analytical efforts so far have focused on the biofouling component. Analysis of photographs for percent cover revealed a total of 16 taxonomic groups contributing to the biofouling communities, with bare substrate on the cages accounting for a relatively high proportion of the cover (Figure 1). Overall, across all sampled sites and months, biofouling communities were predominantly composed of diatoms, a variety of red filamentous algae, and brown algae that included kelps. All other taxa on average accounted for 3% or less of the biofouling communities. Less common sessile biofoulers included tube worms, tunicates, hydroids, sponges, mussels, bryozoans, barnacles, and green algae. Mobile biofoulers included filter-feeders, such as anemones and sea cucumbers, and scavengers or predators, such as nudibranchs, sea stars, and crabs. Initial investigations revealed significant variability in the biofouling communities across the different farms, which had a stronger effect than season (Figure 2). This could be due to the irregular cage cleaning schedules across the farms. The benthic team recently deployed biofouling settlement cages at the oyster farms to control for cleaning since they will not be cleaned.