Date Thesis Awarded

4-2019

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Dr. Jonathan Allen

Committee Members

Dr. Mark J. Brush

Dr. Randolph Chambers

Abstract

Common eelgrass, Zostera marina, is the most widespread marine plant on earth and plays a crucial role in supporting commercial fisheries, marine nutrient cycling, and marine biodiversity. Despite their importance, eelgrass and other seagrasses are in decline at a rate matching or exceeding other highly threatened habitats such as coral reefs. At my study site, Casco Bay Maine, eelgrass meadows experienced a 50% decline between 2012 and 2013. The decline and failure of eelgrass restoration has been attributed to the invasive green crab Carcinus maenas, but there are potentially other species that could contribute to restoration failures such as the native eastern mud snail, Tritia obsoleta. Currently, mud snails are considered to have a beneficial effect on eelgrass growth by grazing epiphytes. However, a critical aspect of mud snail biology has not been considered: mud snails preferentially lay high densities of egg capsules on eelgrass to avoid benthic predation. I found that a single layer of mud snail egg capsules can reduce available surface irradiance by 67%, and at environmentally observed densities of 10 layers, 98% of surface irradiance is blocked. With 98% surface irradiance blocked eelgrass, is in a negative carbon balance and could experience an increase in mortality. When the benefits of mud snails as eelgrass epiphyte grazers and the potential negative effects of their light blocking egg capsules are combined, I found that there was a net negative effect on eelgrass growth, although the effect was not significant. I found support for the strong laying preference of mud snails for eelgrass throughout the mating season. In total, I found that mud snail egg capsules have the potential to profoundly affect the light reaching eelgrass and their June mating season should be avoided in future restoration efforts.

Available for download on Saturday, May 01, 2021

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