A Biological Assessment of Oyster Restoration Mats throughout the Indian River Lagoon: Changes in Community Composition and Filtration Capacity of Living Docks
Gilligan, Morgan Katherine
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Like many estuaries worldwide, the Indian River Lagoon (IRL), has seen a decline in resources and overall water quality due to human activities. There is a growing interest in implementing ecological engineering methods to restore water quality. One such method is the construction and deployment of oyster restoration mats on dock pilings, known as the Living Docks program. This community driven program was founded at Florida Tech with the goal of promoting the growth of filter feeding benthic organisms to improve local water quality. Since 2013, twelve docks have been deployed in the central IRL, spanning from Cape Canaveral (28º 22’59’’N, 80º 36’32’’ W) to Sebastian (27º 49’26’’N, 80º 29’ 25’’ W), Florida. To date, a thorough biological assessment has not been performed on the docks. The goal of this thesis was 1) to compare community composition during two seasons as denoted by changes in temperature, and 2) to determine the filtration rates of several Living Dock communities during the different temperature periods. Nine of the twelve docks were biologically assessed for temporal changes during a warmer period (25.9-30.5 ºC) and a cooler period (15.1-23.5 ºC). Ten percent of the nine docks were analyzed along with six randomly selected shells per mat. The back of each analyzed mat was assessed for organism growth and their ability to cement the mat to the piling. Results indicate the most biodiverse community was present during the 15.1-23.5 ºC (cool) assessment at Melbourne Beach Pier, Beach Woods, Lighthouse Cove, and Sebastian. Organisms such as barnacles, biofilm, encrusting bryozoans, and sponge had the greatest change due to temperature across both assessment periods. Cementation for all analyzed mats experienced an increase from the warm (25.9-30.5 ºC) to the cool (15.1-23.5 ºC) assessment period. A1A, Beach Woods, and Crab E Bills had the highest cementation from organisms such as barnacles, sponge, and encrusting bryozoan. Filtration capacities of Living Dock communities were assessed during the same warm and cool period for four locations: IAP, A1A Condo Association Lighthouse Cove, and Crab E Bills. Five oyster shells covered with benthic organisms were randomly selected and removed from each location. Shells were placed in tanks and changes in water quality as a function of total suspended solids and chlorophyll a were monitored over a 48-hour period. The IAP dock without the presence of oysters and A1A with young oysters (<5 cm at 6 months old) had the greatest reduction for chlorophyll a and total suspended solids (TSS) reduction. Lighthouse Cove and Sebastian had some of the largest oysters present but had lower filtration rates. Based off these results filtration rates are not just dependent on large oysters but reliant on a diverse community. Sessile benthic communities provide many ecosystem functions, such as water filtration and habitat structure for mobile organisms. The Living Docks program provides a structure for benthic organisms, and the established community will vary both spatially and temporally depending on location within the IRL. Oysters, while important filter feeders, are not the only benthic organisms which will have an impact on water quality including the reduction of harmful algal cells and suspended particulates. Future research may consider how climate change and other human induced problems may impact benthic communities and their ecosystem functions.