Hernández-Delgado 2023. Long-Term Persistence of Propeller and Anchor Damage to Seagrass Canopy and Demersal Biodiversity in Puerto Rico

Hernández-Delgado, Edwin A. 2023. “Long-Term Persistence of Propeller and Anchor Damage to Seagrass Canopy and Demersal Biodiversity in Puerto Rico.” Open Journal of Ecology 13(10):671–710. doi: 10.4236/oje.2023.1310042.

Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas; 2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas; 3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis; 4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa; and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.

Figure 1. Study site at Mata de la Gata Island, La Parguera Natural Reserve, Puerto Rico. Red polygon = scoured channel during 1996 (1784 m2); Yellow polygon = scoured channel during 2011 (2388 m2). SC = scoured channel; ES = eastern scoured edge (5 m); EH = eastern healthy (15 m); WS = western scoured edge (5 m); WH = western healthy (15 m). Aerial image source: Google Earth.

Thanks for sharing this one @dwilcox
Will be reading this one on the plane to CERF! We have a similar problem at a few spots on the northern Gulf Coast where folks like to anchor up. Even with signs, they still seem to run through the seagrass beds. We keep trying to restore the prop scars with birdstakes (which works really well!), but it’s like a game of “whack a mole”. We heal one, and find two more :slightly_frowning_face: