Wed, Aug 17, 2022: 4:45 PM-5:00 PM
513F
Background/Question/MethodsOn September 1st, 2019 hurricane Dorian hit Abaco, The Bahamas as the strongest hurricane ever to make landfall. The resulting destruction introduced large amounts of debris into coastal marine ecosystems, including seagrass beds which support several of Abaco’s economically and culturally important species. Ecological theory suggests healthier habitats should be more resilient to disturbances. However, this may not be true for seagrass beds. Seagrass beds baffle and retain sediments, potentially capturing contaminants, leading the seagrass to incorporate contaminants into their tissues, making them available to higher trophic levels. Accumulation of contaminants in the food web may increase organismal stress and ultimately impact ecosystem function. Here we ask if pre-storm seagrass density predicted post-storm seagrass bed health and if seagrass density is correlated with the persistence of contaminants in the nearshore environment. To accomplish this, we measured contaminants at multiple sites around Abaco by using oysters as natural passive samplers. Additionally, we surveyed 6 seagrass beds where pre-storm data on seagrass density existed and measured contaminant levels in the water column, sediments, and seagrass and consumer tissues at impacted sites of varying habitat quality. We also collected samples from consumers to determine contaminant load and physiological stress.
Results/ConclusionsPre-storm seagrass density did not correlate with post-storm seagrass bed health. Rather, post-storm seagrass bed health was negatively correlated with relative storm intensity. Immediately after Dorian’s passing, seagrass density was significantly lower and seagrass species composition had shifted towards early successional species at sites that experienced more intense storm conditions. Twenty-seven months after hurricane Dorian, seagrass density had still not recovered at the most impacted sites, but has begun to recover at all other sites. Twenty-one months after Dorian, contaminants were undetectable in the water column, even at sites with persisting debris (e.g., cars). However, sites differed in contaminant levels in other sample types. Sites differed in water column oxygen demand, with respiration outpacing photosynthesis at one heavily impacted site. Overall, relative storm intensity rather than pre-storm ecosystem health was the major driver of post-storm dynamics in Abaco’s seagrass beds. These results contradict many studies of hurricane impacts on seagrass beds, and may be due to the unprecedented strength and slow movement of hurricane Dorian. This highlights the need to better understand how storm-specific characteristics such as wind speed, rainfall totals, speed of movement may drive ecosystem response.
Results/ConclusionsPre-storm seagrass density did not correlate with post-storm seagrass bed health. Rather, post-storm seagrass bed health was negatively correlated with relative storm intensity. Immediately after Dorian’s passing, seagrass density was significantly lower and seagrass species composition had shifted towards early successional species at sites that experienced more intense storm conditions. Twenty-seven months after hurricane Dorian, seagrass density had still not recovered at the most impacted sites, but has begun to recover at all other sites. Twenty-one months after Dorian, contaminants were undetectable in the water column, even at sites with persisting debris (e.g., cars). However, sites differed in contaminant levels in other sample types. Sites differed in water column oxygen demand, with respiration outpacing photosynthesis at one heavily impacted site. Overall, relative storm intensity rather than pre-storm ecosystem health was the major driver of post-storm dynamics in Abaco’s seagrass beds. These results contradict many studies of hurricane impacts on seagrass beds, and may be due to the unprecedented strength and slow movement of hurricane Dorian. This highlights the need to better understand how storm-specific characteristics such as wind speed, rainfall totals, speed of movement may drive ecosystem response.