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Assessing the impacts of salinity and nutrient stress to Ruppia maritima and Zostera marina.
Citation:
Gutierrez, M., Peg Pelletier, AND Rick Mckinney. Assessing the impacts of salinity and nutrient stress to Ruppia maritima and Zostera marina. New England Estuarine Research Society (NEERS) Fall Meeting, Block Island, RI, October 20 - 22, 2016.
Impact/Purpose:
This poster summarizes researches examining potential factors that may limit growth and distribution of seagrass beds that were once found throughout the shallow areas of Narragansett Bay, R.I. but have disappeared due to infilling, pollution and disease. We tested the hypothesis that Ruppia maritima, an extremely salinity tolerant species, may also be more nutrient tolerant than Zostera marina, a species that has traditionally dominated estuarine habitats. Both species had significant structural responses to the nutrient and salinity variables, and isotopic analysis suggested that nutrients were well incorporated into the plants. Overall both species experienced diminished growth with nutrient increase, which could have important implications for the management and conservation of coastal habitats, particularly in the context of increasing impacts from urbanization.
Description:
Healthy seagrass beds were once found throughout the shallow areas of Narragansett Bay, R.I. but have disappeared due to infilling, pollution and disease. In Greenwich Bay, a highly developed embayment within Narragansett Bay, Ruppia maritima has colonized an area on the northern shore historically dominated by Zostera marina. Ruppia is extremely salinity tolerant, and may also be more nutrient tolerant than Zostera. To test this hypothesis 6-week microcosm experiments were conducted in the summers of 2014 and 2015. Microcosms were renewed daily to simulate tidal flushing and the water column was dosed with a 15N tracer for the first week of the experiments. In the 2014 microcosm experiment two salinity (20, 30 ppt) and four nutrient (0, 5, 10, 30 µM inorganic N) levels were used to test the species’ relative tolerance. This experiment yielded structurally significant results for Ruppia but no significant differences were detected for Zostera. In 2015 this experiment was performed for a second time with lower salinity (5, 30 ppt) and higher nutrients (0, 30, 100, 300, 1000 µM inorganic N) in order to determine Zostera’s tolerance to nutrient and salinity stress and confirm the previously observed Ruppia results. Both species had significant structural responses to the nutrient and salinity variables. Isotopic analysis run on above-ground tissue indicated that with increasing nutrient levels δ15N in the seagrass shoots increased, suggesting that nutrients were well incorporated into the plants. Overall both species experienced diminished growth with nutrient increase, however the 2015 structural results show that Zostera was more significantly impacted than Ruppia.