The influence of eelgrass habitat structure on restoration success and scallop recruitment
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Citation
Abstract
Globally, seagrass abundance has declined across all oceans due to anthropogenic impacts. The predominant seagrass species on the northeast coast of the United States is eelgrass, Zostera marina L., which is experiencing rapid declines amidst habitat loss, this species is predominantly located in one of the fastest-warming locations on the planet. Loss of Z. marina meadows disrupts biological, physical, and chemical processes in nearshore communities, and thus it is not surprising that Z. marina-associated species, such as bay scallops (Argopecten irradians), have concurrently declined. To slow Z. marina losses, restoration efforts are actively underway in bays and estuaries along the northeast coast of the United States, and research is needed to determine the most successful restoration techniques and optimize efforts. The goals of this study were a) to determine whether planting Z. marina seeds, shoots, or a combination of the two had the strongest influence on restoration success, b) to examine the influence of Z. marina habitat structure on scallop recruitment, and c) to trial a new methodology to optimize restoration success in coastal New England. To achieve these goals, Z. marina seeds and vegetative shoots were collected and replanted at a restoration site in Nantucket Harbor. Our six treatments consisted of different densities of Z. marina seeds and a set number of transplants, with one plot being just grass, one being a control, one having grass and high abundance of seeds, one having grass and low abundance of seeds, one of just a high abundance of seeds, and one having a low abundance of seeds. We found that plots with both seeds and grass together exhibited similar survival rates of mature grass when compared to the grass-only plot. The mixed plots also exhibited seedling survival, but Z. marina seeds were surprisingly most successful at establishing themselves when there was no mature grass, and when planted at low densities. Lastly, we found that bay scallops were more likely to recruit into plots containing grass and seeds over just seed or just grass. These results show the complexity of restoring Z. marina, and more broadly, seagrass ecosystems as a whole. When restoring Z. marina, it will be more beneficial to use a low seed density approach with less transplanted grass. However, this will result in fewer scallops recruiting into the environment until the shoot density increases, indicating that restoration efforts cannot fully shortcut ecological successional pathways. If the goal is seed success, then transplanted grass is not needed; if the goal is scallop recruitment, mature grass is necessary, and if the goal is creating the greatest habitat density, then incorporating transplanted grass is needed. While the planting method of vegetative shoots and low seeds was not the highest preforming method for each individual response, this treatment had the highest distribution of benefits by contained the highest amount of vegetation, contributed to seedling success, and recruiting the most scallops. The results and observations from this study may refine Z. marina restoration methods and help to improve the success of Z. marina restoration efforts in vital coastal ecosystems.
Description
2024
License
Attribution 4.0 International