Biological and chemical responses in a temporarily open/closed estuary to variable freshwater inputs
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In coastal lagoons with occasional connection to oceans, variations in physicochemical conditions and biological responses can be pronounced. To examine the influence of variable rainfall and tidal flushing, we measured, over a 4-year period, salinity, temperature and dissolved oxygen, and fish abundances, in Devereux Slough, a coastal lagoon occasionally connected to the Pacific Ocean along the California coast. We test the hypotheses that salinity is the primary influence on fish composition, and that fish density is affected by freshwater discharge and by berm breaches. During our sampled years, annual rainfall varied from 188 to 971 mm, and the sand berm separating the Slough from the ocean breached in each year except 2007, a drought period. Average yearly salinity ranged from 7.7 to 37.1 ppt. Hypoxic conditions in the near-bottom water were common each year. The best predictor of the fish composition was salinity, and an indirect correlation with fresh water discharge was responsible for much of the temporal variation in the fish assemblage. The interaction between salinity, state of the estuary mouth (open vs. closed), and precipitation significantly predicted densities of Fundulus parvipinnis (Girard 1984).
KeywordsSalinity Coastal lagoon Physicochemical conditions Fish Resource management
This research was supported by the NSF-funded Santa Barbara Coastal Long-term Ecological Research Program (Awards OCE-9982105 and OCE-0620276), the Coastal Fund, the UC Natural Reserve System and volunteer service. We thank Kevin Lafferty and Cristina Sandoval of Coal Oil Point Reserve for logistical support and advice, Tara Longwell, Darryl Yin, Michael Massoud, Alex Hurst and Kevin Le for field assistance, and Blair Goodridge and Scott Coombs with hydrological data.
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