Effects of propeller scarring on macrofaunal use of the seagrass Thalassia testudinum

Abstract

Propeller scarring within seagrass beds is common in shallow coastal waters. Scarring has the potential to fragment seagrass beds, resulting in habitat loss, decreased productivity, and the possibility for further erosion and degradation. We conducted a study in Thalassia testudinum beds in Puerto Rico to determine whether seagrass macrofauna are affected by this disturbance. Four sampling zones (propeller scar, seagrass-scar interface, homogeneous seagrass located 5 m from the scar, and homogeneous seagrass located 10 m from the scar) were compared among 10 replicate seagrass beds. Scarring modified faunal assemblages at the scale of the propeller scar; there was significantly lower total macrofaunal abundance and fewer species in scars. When individual taxa were considered, shrimp and mollusc abundances were lower in scars compared to the other sampling zones. Resident fish abundance was not significantly different among zones. Dominant shrimp species in scars differed from seagrass zones. Crabs and molluscs responded negatively to scarring as indicated by significantly lower densities of these 2 taxa up to 5 m from scars. The extent to which these results 'scale up' remains unknown and future studies should focus on larger, more intensely scarred areas.

Response and recovery dynamics of seagrasses Thalassia testudinum and Syringodium filiforme and macroalgae in experimental motor vessel disturbances

“…oxygen, substrate). Kenworthy et al (2002) documented scars 2 to 4 cm in depth, while other estimates ranged from 3 to 12 cm (Durako et al 1992, Uhrin & Holmquist 2003. On shallow seagrass-coral banks in the middle Keys, we have observed propeller scars up to 50 cm deep and vessel hull groundings of less than 1 m to several meters deep (pers.…”

More Than Just a Spawning Location: Examining Fine Scale Space Use of Two Estuarine Fish Species at a Spawning Aggregation Site

“…Regardless of the exact mechanism, protecting the ecological functions of seagrass habitats may require additional conservation actions to consider beyond limiting fishing effort and time area closures. These conservation actions may include maintaining water quality and foodweb structure, reducing physical habitat degradation (propeller scarring Uhrin and Holmquist, 2003) as well as other ecological mitigation actions. Seagrass beds are vulnerable to numerous stressors and are declining worldwide (Waycott et al, 2009).…”

Seagrass habitat complexity does not always decrease foraging efficiencies of piscivorous fishes

“…However, such is not always the case in and around seagrass habitats (e.g. Uhrin & Holmquist 2003, Horinouchi 2007b. For example, in the temperate coastal region of Japan, larger numbers of small juvenile fishes, usually forming large shoals and/or schools, are often observed in open areas adjacent to the outer edge of seagrass habitats in spring, and fewer individuals are found within the dense seagrass (e.g.…”