By Janet Nye
National Oceanic and Atmospheric Administration
The atmosphere and the oceans are warming. These changes are altering the physical oceanography and the ocean chemistry of the Gulf of Maine. Changes in sea surface temperature (SST) and salinity have been observed. The rate of increase of coastal SST in the Gulf of Maine is about 0.7oC over the last century. The rate of increase has accelerated in recent years and regional studies indicate that SST in this region have increased about 0.23oC from 1982-2006. The salinity of the Gulf of Maine is decreasing as a result of the melting ice caps and increased precipitation.
These changes in temperature and salinity have altered the state of the Gulf of Maine ecosystem.
In the last 20 years the position of the Gulf Stream has been consistently further north. How future changes in temperature will effect the hydrography is unknown.
The Gulf of Maine has experienced changes in thermal habitats. Thermal habitats in the 5-15oC range, which most species prefer, have decreased over the last 20 years, but the coldest and warmest habitats have been increasing.
There has also been a suggested increase in primary productivity in the region from 1958-2002 and a shift in phytoplankton species from large diatoms to small dinoflagellates. There may have also been a change in the timing of the occurrence of different phytoplankton species.
With climate change it is predicted that organisms will shift their spatial distribution in response to changes in temperature, salinity, and hydrography. In the Gulf of Maine more than half of the 36 fish stocks examined have shifted their spatial distribution to a greater depth or further north. Fish generally remain in their preferred temperature, but shift to higher latitudes or depths. Changes in oceanographic conditions may also cause organisms to shift the timing of migration and spawning. There is concern that organisms may shift events so that they are out of phase with other elements of the ecosystem such as they prey they rely on.
Zooplankton assemblages have changed from large zooplankton to small zooplankton. This has higher trophic level consequences, as less energy is transferred up the food web.
Fish and invertebrate assemblages in the Gulf of Maine have also changed. There has been a shift in dominance from more cold-water species to more warm-water species.
More detailed information is available in the theme paper. www.gulfofmaine.org/state-of-the-gulf/docs/climate-change-and-its-effects-on-ecosystems-habitats-and-biota.pdf
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