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Effect of multiple stressors on eelgrass Zostera marina L. from the Pacific Northwest, USA: Manipulation of temperature and nutrients
Citation:
KALDY, III, J. E. Effect of multiple stressors on eelgrass Zostera marina L. from the Pacific Northwest, USA: Manipulation of temperature and nutrients. Presented at 40th Benthic Ecology Meeting, Mobile, AL, March 16 - 20, 2011.
Impact/Purpose:
Estuarine eelgrass beds in the Pacific Northwest (PNW) are being exposed to a range of natural and anthropogenic stressors and climate change.
Description:
Estuarine eelgrass beds in the Pacific Northwest (PNW) are being exposed to a range of natural and anthropogenic stressors and climate change. These stresses include increased temperatures, sea level rise, and high nutrient inputs, all of which may directly affect the productivity and survival of Zostera marina. The purpose of the current study was to examine the effects of temperature and nutrient quantity of Z. marina growth and physiology. Experimental manipulations were conducted in clear acrylic chambers and spanned a range of temperature and nutrient concentrations appropriate for the PNW. Preliminary single factor range finding experiments were conducted to evaluate physiological tolerances to temperature and nitrogen concentrations (NO3 and NH4). Eelgrass exhibited a statistically significant (R2 = 0.64, P = 0.029), linear increase in specific growth with increasing NH4 concentration (range from 10 to 1000 µM); in contrast, there was no significant relationship (R2 = 0.18, P = 0.34) between specific growth rate and increasing NO3 concentration over the same concentration range. The amount of new leaf tissue, leaf growth and specific growth all exhibited strong (R2 = ≥0.8, P< 0.0001) statistically significant linear relationships with increasing water temperature (temperature range 4-25 °C). The factorial experiment used 3 temperatures (10, 18 and 25 °C) and 3 nitrate concentrations (10, 30 and 100 µM) with 3 replicate chambers per treatment combination. Most metrics (leaf elongation, growth, specific growth, wasting index) exhibited a statistically significant temperature effect indicating the importance of temperature on metabolic rates. Tissue stable is0otope ratios (especially δ15N) and C:N values generally exhibited a significant nutrient effect and in some cases a significant temperature effect. Non structural carbohydrate content of eelgrass exhibited no significant differences (P> 0.05) with respect to either temperature or nitrate concentration. The results indicate that Z marina in the PNW may be relatively insensitive to high N, but extremely sensitive to increased temperatures. The results also indicate that increased temperatures may predispose Z. marina to secondary stresses such as wasting disease, potentially impacting estuarine seagrass beds.