Diver observations of community structure on a subarctic marine artificial reef in Whittier, Alaska Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/j6731514n

Presented at the Alaska Marine Science Symposium

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  • Increased coastal development poses a potential threat to nearshore habitats in Alaska, and artificial reefs (AR) are an increasingly popular tool for mitigating habitat loss. Although well studied in tropical and temperate locations, less is known about AR efficacy in high latitude locations. Since ARs are heavily influenced by ecological factors specific to their environment, these studies may not apply to sites in subarctic Alaska. An AR was deployed in Whittier in 2006 as part of a mitigation settlement for Alaska Marine Lines facility expansion. Surveys conducted the following year suggested AR assemblages resembled those of adjacent natural reefs (NR). However, long-term surveying of community composition is necessary to allow for the establishment of a climax community. With bi-monthly dive surveys conducted June-November 2016, this research surveyed the AR to assess how demersal fish, macroalgal and invertebrate assemblages have changed in the past decade. Assemblages were quantified at n=6 plots (30 structures per plot) with two types of AR structures: Fish Havens (n=3) and Reef Balls (n=3) for a total of 180 structures, and compared to former assemblages present in 2007 at both AR and NR sites. Demersal fish density was calculated from abundance estimated in-situ via 30 m transects (60 m2; n=1 per plot). Macroalgal percent cover was estimated in-situ; macroalgal and invertebrate density was calculated using abundance estimated in situ with 0.25 m2 quadrats (n≥6 per plot). Species richness was calculated as the number of species normalized per unit area. Means and standard deviations were averaged across n=6 and n=3 reef-types in 2016 and compared to 2007 data. Preliminary results indicate an increase in Sebastes spp. species present and a change in the dominant macroalgae Laminaria saccharina to Agarum clathratum. Macroalgae species present (n=10) increased compared to 2007 when only Saccharina spp. was observed (n=1). AR assemblages in 2016 appear to resemble those of NR in 2007 in terms of species composition. Multivariate analysis will further quantify changes in community composition (MANOVA across periods, reef types and years and nMDS ordination plots) and address potential environmental variability in the model.
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