Date

Spring 2023

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Rapid changes in environmental climate trends have influenced the temperature and salinity of marine ecosystems across the globe. This ongoing shift is predicted to have implications for the reproductive success of species that are integral to both the generation and identity of their ecosystem; namely, foundation species. Coastal marine foundation species, such as macroalgae, are expected to experience drastic environmental changes. Of particular interest to central Californian shores is the foundation species Fucus distichus (Family Fucaceae). This alga serves as a community builder residing in the upper intertidal throughout the Northern Hemisphere. While F. distichus residing within San Francisco Bay (SFB) have been determined to be genetically well-mixed, populations within the Bay are currently declining, so a better understanding of what affects their reproductive success is needed. This research explored how the reproductive success of F. distichus in SFB and along nearby open coast is influenced by habitat (i.e., sites that vary in their location and salinity), temperature, and the interaction between these factors to better understand how the reproductive success of coastal marine foundation species may respond to predicted future climate regimes.

Samples of F. distichus were collected from three habitat types (i.e., Outer Coast, Inner Coast Full-Salinity, and Inner Coast Low-Salinity) with three haphazardly-selected replicate fields per habitat over the course of 7 sampling cycles. Randomly-selected receptacles from the F. distichus samples were processed according to standardized protocols. They were then randomly sorted and incubated in two different temperature treatments that resemble current (12°C) and predicted (15°C) environmental conditions in SFB and nearby open coastline. For each cycle, the total number of eggs and embryos released by each receptacle (defined as reproductive output) along with the fertilization success of embryos was observed after 96 hours. The resulting data were analyzed using a series of three-way ANOVAs that investigated the effects of temperature, habitat type, and sampling cycle, and their multi-way interactions.

Both reproductive output and fertilization success were determined to have significant three-way interactions between the three factors analyzed. Reproductive output primarily was driven by a relationship between temperature and habitat, whereas fertilization success was primarily influenced by relationships involving sample cycle. In general, receptacles in the 15°C group experienced greater reproductive output and fertilization success than those in the 12°C group. Additionally, individuals from more saline habitat types experienced higher reproductive output and fertilization success than those from fresher conditions. These findings align with previous hypotheses that F. distichus may respond favorably to warmer future conditions. Future research should add more F. distichus populations or survey related genera to determine how predicted environmental conditions may influence reproductive success of coastal marine foundation species.

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