Date of Award

Spring 4-7-2020

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Dr. Nathalie Reyns

Committee Member

Dr. Jesus Pineda

Committee Member

Dr. Jennifer Prairie

Abstract

Most benthic organisms living in the intertidal zone have planktonic larvae that reside temporarily in the water column before settling in their adult habitats. Larvae aggregate in offshore larval pools, and transport horizontally and vertically in the water to remain in the nearshore and during their pelagic life. While some horizontal transport of larvae can be attributed to advection, behavioral responses, like vertical swimming and buoyancy control, allow larvae to position themselves at depths where flow direction can be exploited. Thus, knowledge on how vertical larval distribution relates to physical processes can be fundamental to better understand larval transport. These larvae must then return to shore to successfully metamorphose and complete their life cycle. Recent work at our study site in Bird Rock (La Jolla), California, USA suggests that late-stage barnacle larvae (cyprids) accumulate at a mid-depth in a shallow (4m) station when offshore waters are stratified. However, it remains unknown how the water column structure (e.g., temperature) varies at this site, and the consequences to the vertical distribution and abundance of larvae. This study conducted repeated hourly larval collections at 1m-depth intervals at a 4m-deep station ~300m from shore. Sampling was conducted over 5, 24-hour cruises during the summers of 2017 and 2018. Larval vertical distributions were characterized and compared to hydrographic (thermal stratification, thermocline depth) and hydrodynamic (currents) variables collected at three stations (4m, 5m and 8m depths). Vertical distribution patterns of barnacle cyprids showed that they remained closer to the bottom during the day and migrated slightly shallower at night, despite varied physical conditions between cruises. Additionally, our results showed that higher thermal stratification allowed the thermocline to penetrate closer to shore, and more larvae to accumulate at 4m-deep. This study supports previous work suggesting that thermal stratification is a key factor in nearshore accumulation and suggests that larval behavior can be better exercised when thermal stratification is high, all of which have important implications on barnacle settlement and recruitment to the intertidal.

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