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: 2.06). 03/2009; 82(1):1-18. DOI: 10.1016/j.ecss.2008.12.016


(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 N(2) gas. Based an 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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Available from: Stephen Granger, Dec 18, 2013
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    • "Estuaries are zones of connection between land and ocean, which are vulnerable to the effects of global climate change. For instance, the warming of water has resulted in the changing of the timing and magnitude of phytoplankton bloom in estuaries[1], extreme weather condition, such as cyclone event has caused flash flood, which in turn, increased the contribution of river discharge into the adjacent estuary[2], and the sea level rise due to the effect of global warming on the hydrological cycle of estuaries, causing an increased intrusion of sea water farther upstream[3]. Based on these reasons, some measures have been put in place to assess the vulnerability of the coastal zone, so that proper management in terms of sedimentation, land subsidence, land rehabilitation and reclamation can be carried out[4]. "

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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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    • "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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    ABSTRACT: Historically, southern New England has supported one of the most productive American lobster (Homarus americanus) fisheries of the northeast United States. Recently, the region has seen dramatic declines in lobster populations coincident with a trend of increasingly stressful summer warmth and shell disease. We report significant declines in the abundance, distribution, and size composition of juvenile lobsters that have accompanied the warming trend in Narragansett Bay, Rhode Island, since the first comprehensive survey of lobster nurseries conducted there in 1990. We used diver-based visual surveys and suction sampling in 1990, 2011, and 2012, supplemented by post-larval collectors in 2011 and 2012. In 1990, lobster nurseries extended from the outer coast into the mid-sections of the bay, but by 2011 and 2012 they were largely restricted to the outer coast and deeper water at the mouth of the bay. Among five new study sites selected by the lobster fishing industry for the 2011 and 2012 surveys, the deepest site on the outer coast (15-17 m depth) harboured some of the highest lobster densities in the survey. Separate fixed site hydrographic monitoring at 13 locations in the bay by the Rhode Island Division of Fish and Wildlife recorded an approximately 2.0 degrees C increase in summer surface temperatures over the period, with 2012 being the warmest on record. Additional monitoring of bottom temperatures, dissolved oxygen and pH at our sampling sites in 2011 and 2012 indicated conditions falling below physiological optima for lobsters during summer. The invasion of the Asian shore crab, Hemigrapsus sanguineus, since the 1990s may also be contributing to declines of juvenile lobster shallow zones (<5 m) in this region. Because lobster populations appear increasingly restricted to deeper and outer coastal waters of southern New England, further monitoring of settlement and nursery habitat in deep water is warranted.
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