Article

The impact of changing climate on phenology, productivity, and benthic–pelagic coupling in Narragansett Bay

Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, United States
Estuarine Coastal and Shelf Science (Impact Factor: 2.25). 03/2009; 82(1):1-18. DOI: 10.1016/j.ecss.2008.12.016

ABSTRACT The timing and magnitude of phytoplankton blooms have changed markedly in Narragansett Bay, RI (USA) over the last half century. The traditional winter–spring bloom has decreased or, in many years, disappeared. Relatively short, often intense, diatom blooms have become common in spring, summer, and fall replacing the summer flagellate blooms of the past. The annual and summer mean abundance (cell counts) and biomass (chl a) of phytoplankton appear to have decreased based on almost 50 years of biweekly monitoring by others at a mid bay station. These changes have been related to warming of the water, especially during winter, and to increased cloudiness. A significant decline in the winter wind speed may also have played a role. The changes in the phenology of the phytoplankton and the oligotrophication of the bay appear to have decreased greatly the quantity and (perhaps) quality of the organic matter being deposited on the bottom of the bay. This decline has resulted in a very much reduced benthic metabolism as reflected in oxygen uptake, nutrient regeneration, and the magnitude and direction of the net flux of N2 gas. Based on many decades of standard weekly trawls carried out by the Graduate School of Oceanography, the winter biomass of bottom feeding epibenthic animals has also declined sharply at the mid bay station. After decades of relatively constant anthropogenic nitrogen loading (and declining phosphorus loading), the fertilization of the bay will soon be reduced during May–October due to implementation of advanced wastewater treatment. This is intended to produce an oligotrophication of the urban Providence River estuary and the Upper Bay. The anticipated decline in the productivity of the upper bay region will probably decrease summer hypoxia in that area. However, it may have unanticipated consequences for secondary production in the mid and lower bay where climate-induced oligotrophication has already much weakened the historically strong benthic–pelagic coupling.

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    • "The American lobster is not the only species to have experienced dramatic changes associated with ocean warming in southern New England (Keller et al., 1999; Nixon et al., 2004, 2009). In the wellstudied Narragansett Bay and nearby coastal waters, the winter– spring diatom bloom has all but disappeared (Keller et al., 1999; Oviatt et al., 2002; Nixon et al., 2009), eelgrass has been on the decline (Bintz et al., 2003), comb jellies have increased (Sullivan et al., 2001), the composition of the groundfish assemblage has changed (Jeffries and Terceiro 1985; Jeffries, 2002), and the invasive green crab, Carcinus maenas, has been replaced by the equally invasive Asian shore crab, Hemigrapsis sangineus (Lohrer and Whitlatch, 2002). Of particular relevance to lobster, summer water temperatures in southern New England have exceeded a long-recognized 208C physiological threshold with historical frequency (McLeese and Wilder, 1958; Pearse and Balcom, 2005; Glenn and Pugh, 2006). "
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    • "trend . It is not clear why N 2 fixation did not respond to the post bloom deposition in spring . Fulweiler et al . ( 2013 ) proposed that the quality of organic matter plays a role in controlling N 2 fixation . It is possible that a different timing of the phytoplankton blooms alters both the quantity and quality of the deposited organic matter ( Nixon et al . , 2009 ) and we speculate that benthic diazotrophs depend on a restricted range of organic matter and / or its concentration . The positive correlation ( Pearson , ρ = 0 . 95 , p < 0 . 05 , n = 9 ) between pelagic and benthic N 2 fixation suggests that both respond in the same way to environmental factors ."
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