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Long-term eelgrass loss due to joint effects of shade, heat

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Analysis puts resulting economic losses at $1-2 billion in Chesapeake Bay alone

February 14 2017  Science Daily see full article here

A new study links a long-term decline in Chesapeake Bay’s eelgrass beds to both deteriorating water quality and rising summertime temperatures. It also shows that loss of the habitat and other benefits that eelgrass provides comes at a staggering ecological and economic cost…….”Declining water clarity has gradually reduced eelgrass cover during the past two decades, primarily in deeper beds where lack of light already limits growth. In shallow beds, it’s more that heat waves are stressing the plants, leading to the sharp drops we’ve seen in recent summers.”

“Not only have we lost a huge ecological resource, there have been real economic and recreational consequences….Blue crab fisheries, for example, have probably lost a year or more of catch based on the amount of eelgrass we’ve already lost. For silver perch, it’s 10-20 years. In all, we estimate the potential economic cost to citizens at $1-2 billion.”…

…mean summertime water temperature in the lower Chesapeake Bay has already increased by more than 2 degrees Fahrenheit since 1984 — from 76.8° to 79.5°F — and that the frequency of extreme warm spells with water temperatures exceeding 82° has doubled in the last decade….As global warming continues to raise the area’s water temperatures — a conservative estimate is a further 3.5° F increase by 2040 — the team predicts a further 38% decline in eelgrass cover. And if water clarity follows its current downward trajectory during the next 30 years, eelgrass would decline an additional 84%. When both declining clarity and warming are considered, say the researchers, the predicted increases in temperature and turbidity would result in a loss of 95% of Bay eelgrass — a near total eradication

…”Our analysis suggests that eelgrass could still persist in the face of moderate increases in temperature, if the water remains clear enough” adds Lefcheck. “But that will only happen if managers adopt an integrated perspective, and continue with their efforts to curb inputs into the Bay.

Jonathan S. Lefcheck, David J. Wilcox, Rebecca R. Murphy, Scott R. Marion, Robert J. Orth. Multiple stressors threaten the imperiled coastal foundation species eelgrass (Zostera marina) in Chesapeake Bay, USA. Global Change Biology, 2017; DOI: 10.1111/gcb.13623

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