Tolerances and responses of seagrasses to hydrogen sulfide and implications to ecology and restoration
Dooley, Frederick D
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Predicting an individual or species response to climate change, ecosystem disruptions or any environmental change is highly problematic and often requires assumptions. Currently Zostera marina (eelgrass) and other seagrasses have undergone extensive changes within their ecosystems much of which has effected there population size and fecundity. In the Pacific Northwest (PNW) changes have occurred within the ecosystems since the industrial revolution, and correspondingly reductions in the meadows have been observed. Many of these changes are anthropogenic in nature. Bio-matter accumulation, increases in temperature and prevalence of disease are only a few of many factors influencing survival. In the late 1990's and early 2000's Westcott bay, a typical eelgrass habitat, abruptly went extinct. Many hypotheses were developed in hopes of explaining the disappearance, and restoration efforts tried yet failed to re-establish a viable population in the bay. In 2007 I started evaluating Z. marina response to different environmental conditions and as I transitioned into my graduate career I used these and other experiments to explain in part the reductions and extinctions observed. Here, I report on the tolerances of seagrasses found in the PNW to hydrogen sulfide (H2S), its physiological interactions, and implication to restoration and seed banking. Additionally, I report on the concentrations of H2S/sulfide found in embayments throughout the San Juan archipelago and surrounding areas within the Salish Sea (PNW). Based on laboratory experiments I found that eelgrass is highly vulnerable to low concentrations of H2S (LD50 = 334μM). More specifically it was determined that the H2S decreased photosynthetic output and inhibited photosystem II. No reduction in respiration was detected until ~10mM. This is also the case with Phyllospadix scouleri, however based on its physiology and adaptions for a rockier habitat the lethal limit was significantly lower (LD50 = 86μM). Field observations indicate that concentrations vary dramatically based on site location, sediment type and biomatter accumulation, but is highly correlated with eelgrass presence (or absence). And in cases when there are no shoots found concentrations are higher than those observed to be lethal. Sites experiencing high concentrations of sulfide(s) may be a candidate for restoration: capping. In populations which are undergoing reductions seed storage may be necessary, however it is highly problematic, and I report that seed viability decreases with each year of storage and plantation may not be passable after 2 years.
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