Case Study: Is Laying Roe Friend or Foe? Investigating the relationship between Phyllaplysia taylori and Zostera marina in False Bay, San Juan Islands, WA

Abstract

Estuarine ecosystems, similar to that of False Bay in the San Juan Islands of WA, are indispensable and therefore high priority in conservation efforts due to their highly specialized and endemic inhabitants. Anthropogenic influences on estuarine ecosystems (dredging, trawling, coastal development, eutrophication, compound effects of climate change) damage subtidal and intertidal estuaries. The eelgrass species, Zostera marina , is prevalent in both East and West Coast estuaries. Eelgrasses require approximately 24% more photosynthetic light than other angiosperms, making them more vulnerable to environmental change, such as rising sea surface temperatures (Orth et. al. 2006). This study examines the relationship between facilitative sea hare grazers, Phyllaplysia taylori , and their respective substrate of choice, Zostera marina . We investigated the abundance of P. taylori in False Bay and found a linear relationship between surface and subsurface egg mass abundance. In the field, data was collected on the characteristics of where egg masses were laid. The analyses revealed that height location on the blade was a significant factor for egg mass laying, but the epiphyte coverage surrounding the egg mass was not. Additionally, we ran a series of manipulative experiments to get a better understanding of the multivariable relationship between P. taylori and Z. marina . While P. taylori keeps the eelgrass blades relatively clean as a grazer, their eggmasses can block up to 69% of light to the eelgrass plant. Here we offer a case study of False Bay to further understand the symbiosis between Z. marina and P. taylori , which can help to inform the ecological conditions needed to support shrinking Z. marina beds.