Fish species as indicators of freshwater inflow within a subtropical estuary in the Gulf of Mexico
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2017 Elsevier Ltd As anthropogenic pressures on fresh water continues, a balance must be achieved to ensure estuaries receive sufficient riverine inputs to sustain ecosystem health. With increased demand on freshwater resources upstream, salinities in the coastal systems may increase, providing an opportunity for encroachment or invasion by species with a higher salt tolerance. These events compromise ecosystem function, integrity and sustainability, particularly of native estuarine habitats. Estuarine dependent teleost fish species may be considered appropriate bioindicators of abiotic stressors. While estuarine fish have a wide tolerance of many environmental conditions, each species has its own tolerance range and/or sensitivity, and at specific phases during their life cycle. A statistical analysis was conducted to better understand the relationship of Ictalurus furcatus (blue catfish), Brevoortia patronus (Gulf menhaden) and Lagodon rhomboides (pinfish) to abiotic parameters associated with freshwater inflows (i.e. salinity, nutrients, turbidity, etc). Data for this study were collected in Galveston Bay, Texas (USA) by various state agencies and spanned 124 seasons between 1979 and 2010. Distance based linear models were run to determine correlations between the selected indicator species and water quality parameters known to be related to freshwater inflows. These relationships were visualized with Spearman vectors overlain on principal coordinates analysis plots. Blue catfish and Gulf menhaden displayed a significant inverse correlation with salinity and significant positive correlation with NO3 +NO2 (M), DIN:DIP and turbidity (NTU). During periods of drought, blue catfish were found closest to the river mouth, where salinity was lowest when considering other locations within Galveston Bay. Gulf menhaden maintain a wider distribution across the Bay as they have a wider salinity range tolerance. Pinfish display a significant positive correlation with salinity and temperature within Galveston Bay; as bioindicators this species is expected to be more tolerant to higher salinities. These relationships support the potential use of these species as beneficial indicators of changing estuarine conditions, namely freshwater inflows. Further study is essential to determine if these and/or other species can be applied to other bays along the Texas coast as well as other sub-tropical estuarine systems in which they are found.
