An archive of data gathered by the U.S. Navy shows that the oceans’ waters have warmed up over the past few decades. At least some of the current rise of global sea level is due to the thermal expansion of water—warmer waters are less dense due to an expansion of their volume with temperature. In some budgets, warmer water accounts for half of the rise in sea level in recent years.
Several studies indicate that the waters in the Gulf of Maine are warming faster than most of the world’s oceans. Beyond the general trend of global warming, other factors seem to be involved in this region, including the position of the northward flowing, warm waters of the Gulf Stream. Coastal waters in this region were also warm in the early 1950s, though the recent temperatures are the highest on record.
Even skeptical fishermen are taking note of the changes. The lobster fishery of Downeast Maine is of huge importance to its economy. Given the demise of the cod, herring and sardine fisheries, those who make their living from the sea don’t want to see the collapse of yet another of the ocean’s bounties. Warmer seawater temperatures are believed to be responsible for the lack of recovery of Atlantic cod populations, despite a ban on fishing off the coast of Maine.
There is some evidence that the demise of cod has allowed the lobster population to explode, since cod feed on young lobster. Right now, lobster landings in Maine are at their highest levels, but the loss of lobster in southern New England and Long Island Sound is widely attributed to warming ocean waters in those regions. It could happen in Maine too.
No doubt, the creatures of the world’s oceans are distributed according to physical parameters, including temperature, so changing temperatures should change their distributions. However, the science that links successful lobster recruitment to water temperature looks equivocal. One study in 2015 attributed a 31% drop in lobster reproduction between 2008 and 2013 to warmer temperatures. Other work suggests that warmer temperatures stimulate lobster recruitment. More experimental work is needed; the correlation between warmer temperatures and fewer lobsters is suggestive but not definitive. At best, it gives us an early warning signal.
When we think of the impacts of rising CO2 in the atmosphere, we normally think of changes in our climate and the land we live on. But, big changes are likely beneath the ocean’s surface, which will be much harder to see.
References
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Boudreau, S.A., S.C. Anderson and B. Worm. 2015. Top-down and bottom-up forces interact at thermal range extremes in American lobster. Journal of Animal Ecology 84: 840-850.
Fernandez, I.J., C.V. Schmitt, S.D. Birkel, E. Stancioff, A.J. Pershing, J.T. Kelley, J.A. Runge, G.L. Jacobson, and P.A. Mayewski. 2015. Maine’s Climate Future: 2015 Update. University of Maine, Orono, 24pp.
Frank, K.T., B. Petrie, J.S. Choi, and W.C. Leggett. 2005. Trophic cascades in a formerly cod-dominated ecosystem. Science 308: 1621-1623
Koopman, H.N., A.J. Westgate, and Z.A. Siders. 2015. Declining fecundity and factors affecting embryo quality in the American lobster (Homarus americanus) from the Bay of Fundy. Canadian Journal of Fisheries and Aquatic Science 72: 352-363.
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Lindegren, M., O. Ostman, and A. Gardmark. 2011. Interacting trophic forcing and the population dynamics of herring. Ecology 92: 1407-1413.
Pershing, A.J., M.A. Alexander, C.M. Hernandez, L.A. Kerr, A. Le Bris, K.E. Mills, J.A. Nye, N.R. Record, H.A. Seanmell, J.D. Scott, G.D. Sherwood and A.C. Thomas. 2015. Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery. Science 350: 809-812.
Steneck, R.S. and R.A. Wahle. 2013. American lobster dynamics in a brave new ocean. Canadian Journal of Fisheries and Aquatic Sciences 70: 1612-24.
