A preliminary evaluation of the effects of oyster cage aquaculture on seagrass colony health

Date

2021-12

Authors

Rubino, Ryan

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Abstract

Seagrass is essential habitat for many marine species and is found in shallow, low energy, coastalwaters with high light penetration. These conditions are also conducive to oyster aquaculture. As Texas develops commercial oyster farming, it is important to understand the effects on seagrass health and to determine if this activity impacts seagrass health. The goal of this study was tocharacterize the effects of a research-scale adjustable longline oyster aquaculture system on the health of adjacent seagrass colonies in Copano Bay, TX. This was accomplished by using standard seagrass health monitoring techniques, measuring relevant water quality parameters, and characterizing sediment transport at the site. Four Halodule wrightii colonies were identified at various distances from the research site: 100 m upstream (upstream), 0 m directly adjacent to system (0 m), 30 m downstream (30 m), and 60 m downstream (60 m) and monitored for 1) seagrass health (density, leaf length, max leaf length), 2) water quality parameters (turbidity, temperature, light intensity, salinity, dissolved oxygen, NH4, NO2+NO3, PO4) and 3) sediment deposition rate and grain size analysis. In general, there were only minor differences in dependent variables over the 18-week sampling period. No significant differences (P>0.1) were found for max leaf length, water quality variables or sediment grain-size analysis. Seagrass leaf length and sediment deposition rate were significantly (P<0.1) higher for the 60-m downstream colony. Both the 30- and 60-m downstream colonies had significantly (P<0.1) denser seagrass coverage. The upstream seagrass colony had the lowest density. These results suggest that differences in health indicators were either unaffected by proximity to the oyster system or beneficial as the higher sediment deposition rate (at the 60-m downstream site) did not decrease seagrass density. It can be concluded that an oyster research aquaculture system of the type and size at the project location had no major negative impact on seagrass colony health.

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Keywords

Halodule, Oyster Aquaculture, oysters, seagrass, Shellfish, Texas

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