Effects of Propeller Scarring on Seagrass-associated Fauna

Seagrasses play a critical role in the function and structure of coastal ecosystems, and they are an important habitat for a variety of marine organisms. Damage to seagrass beds from boat propellers is significant in many areas. Recognizing the need to protect this valuable habitat, three voluntary no motor zones were established in Redfish Bay, Texas. This study was designed to test the effectiveness of these protected areas and to assess the impact of propeller scarring on nekton. To examine compliance, I made visual observations of boat activity in these areas. My data showed zero boater compliance in the voluntary no motor zones. I characterized the effects of the propeller scarring on seagrass-associated fauna by: (1) comparing measures of fish and decapod crustacean at three distinct scarring intensities to unscarred sites; and (2) characterizing the functional relationships size, mortality; growth rate to scarring intensity. I selected 10 replicate (10 x 25m quadrats) sites representing three distinct scarring intensities: reference (0%), low (5% or less), moderate (5-15%), and severe (>15%). Sites were sampled in 2003-2004 for nekton during 4 seasons (summer, fall, winter, and spring) using epibenthic sleds. Growth rates of selected fauna were examined using field enclosure experiments and otolith microstructure analysis. My results suggest that even severe (>15%) propeller scarring may not affect density patterns, mean size, or mortality of the organisms collected. Otolith microstructure analysis on pinfish (Lagodon rhomboides) indicated no difference in growth rate at various scarring intensities; however, field growth enclosure experiments with white shrimp (Litopenaeus setiferus) showed significantly lower growth in highly scarred areas than reference sites. These results suggest the need for