Date

Spring 2022

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The surf zone is an important and highly dynamic ecosystem situated at the land-sea interface; however, this habitat is relatively understudied in California. Beaches and surf zones are among the most intensely used coastal resources by humans (e.g., recreation, fishing, development). The dual threats of habitat modification and climate change can alter these ecosystems, affecting the composition and abundance of species that reside there. In addition, oceanographic conditions such as upwelling, water temperature, and storm-generated waves have a predictable seasonality that may drive shifts in surf zone species assemblages throughout the year. This study investigated the factors influencing spatial and temporal changes in surf zone communities at four beaches in central California from July 2020 to June 2021. I evaluated seasonal trends, the effects of marine protected areas (MPA), and associations with environmental conditions for these communities. Each site was sampled eleven times, roughly once a month, during the sampling window using replicated (n = 6 per sampling day) horizontal baited remote underwater video stations (BRUVS). The MaxN statistic (i.e., the maximum number of individuals of the same species observed in a single frame of the video), was used to estimate abundance for fish and invertebrates on each sampling day, while the relative abundance of drift algae was extracted from still frames using percent cover estimation techniques. Environmental data were obtained from in situ observations on the day of sampling (e.g., water temperature, salinity, wind speed, and wave height and period) or weather stations (e.g., wind and wave direction). The abundance and community composition of fish and invertebrates were analyzed separately due to differences in relative abundance and behavior. Surf zone fish assemblages exhibited marked seasonality. Species like the barred, calico, and walleye surfperch and leopard shark were far more common in the winter and spring and the speckled sanddab was more common in the summer. Other species like the silver surfperch, thornback ray, dwarf perch, and black-and-yellow rockfish were common throughout the year. There were no impacts of seasonality on invertebrate assemblages, but the system was dominated by benthic species including the purple dwarf olive snail, Pacific sand crab, slender crab, and red rock crab species. Protection inside MPAs had a significant impact on the community structure of surf zone fish. Species such as the reef perch, black perch, kelp rockfish, black-and-yellow rockfish, striped surfperch, rainbow surfperch, señorita, cabezon, and pile perch were observed more commonly within MPAs while species such as the thornback ray, grass rockfish, barred surfperch, and walleye surfperch were more common at reference sites. No effects of MPA status on the invertebrate species diversity or assemblage were detected. Significant environmental variables affecting both fish and invertebrate species included wave height and visibility, with the former being the dominant driver of surf zone assemblage structure. Fish species like the barred, calico, and walleye surfperch, leopard sharks, and invertebrate species like the Dungeness crab, purple dwarf olive snail, and Pacific sand crab were more common during larger wave seasons, while most other species were more abundant on calmer days and seasons. Future studies should continue monitoring the surf zone to gather additional years of sampling and further investigate the predator-prey interactions of surf zone species. This study is one of the first to evaluate temporal trends in the structure of surf zone assemblages in California. The seasonal trends identified and positive responses to MPAs provide key insights into surf zone dynamics and can be used to help inform management and fishing regulations for this ecosystem.

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