Assessing the impact of boat propeller scars on fish and shrimp utilizing seagrass beds

We investigated the relationship between damage from boat propeller scarring in seagrass (Thalassia testudinum) beds and the abundance of three faunal taxa commonly associated with seagrass vegetation in Charlotte Harbor and Tampa Bay, Florida. We chose sites with no damage (reference sites) to compare to those with propeller scarring within each of the two geographic locations. Thirty 141‐m² sites in both Charlotte Harbor and Tampa Bay, representing a gradient of scarring from 6% to 31% of the total area, were sampled in spring and winter 1996 along with reference sites to evaluate effects of propeller damage on abundance of the pinfish, Lagodon rhomboides, and the pipefish, Syngnathus scovelli. Additionally, 60 sites in both Charlotte Harbor and Tampa Bay representing areas with up to 50% scarring and comparison reference sites were sampled in spring 1997 to investigate whether propeller scar damage impacted epibenthic shrimp abundance and community structure in seagrass. Our results indicated no significant difference in pinfish density in scarred vs. reference areas; fish abundances were remarkably similar between sites regardless of the differing amount of vegetation removal. Patterns of pinfish abundance between damaged and reference sites were consistent over seasons (spring vs. winter) and between geographic locations (Charlotte Harbor vs. Tampa Bay). Pipefish abundance was significantly higher in scarred vs. reference seagrass beds in Charlotte Harbor in spring. Moreover, total shrimp densities were not significantly different between propeller‐damaged and reference sites at either geographic location. Hippolyte zostericola was the most abundant of the eight most dominant shrimp species in both scarred and reference sites at both locations but comprised a higher relative proportion of the shrimp community in scarred sites in Tampa Bay. While our study targeted some of the highest reported levels of scarring within Tampa Bay and Charlotte Harbor, negative impacts on fish and shrimp abundance were not detected. Higher levels of scarring that lead to degeneration of seagrass bed stability may need to be present before nekton are affected.