Comparison of Fish Assemblages and Water Quality in Two Marinas in the British Virgin Islands
Eutrophication is a widespread problem in tropical marine environments that leads to the increase of nutrients in a water body, usually nitrate and phosphate, and is usually associated with the discharge of untreated sewage, intensive farming or fertilizer-enriched agricultural runoff (Wu 1999). Common symptoms are increased N and P levels, increased macroalgal production in shallow areas, reduced dissolved oxygen, loss of seagrass and coral habitats and changes in the fish community (Hallock and Schlager 1986, Granelli et al. 1990, Valiela 1995, Hemminga and Duarte 2000). Direct chemical testing to establish pollution levels can be difficult because of sharp pollution gradients, rapid dilution effects, changing tides and currents, variable pollutant concentrations, varying pollution activities, unavailability of water quality test kits, a prohibitive range of pollutants to test for and high testing costs (Resh et al. 1995). Many of these problems can be countered with bioassessment methods that use biotic indicators to assess ecosystem integrity (Karr 1981, Noss 1990, Wright et al. 1993, Chessman 1995). Biotic indicators of pollution have several advantages over chemical methods: they are broad-ranged, detect many forms of pollution, reflect pollution history and indicate overall health of the system.
Animal bioindicators should be: 1) sufficiently sensitive to disturbance, 2) widely distributed, 3) capable of living in a wide range of conditions, 4) relatively independent of sample size, 5) easy and cost effective to study, 6) able to differentiate between natural and man-made disturbance, and 7) relevant to ecologically significant phenomena (Noss 1990). Fish meet many of these criteria and have been included in several freshwater bioassessment protocols, sometimes referred to as biological integrity indices (Larkin and Northcote 1969, Karr 1981, Karr 1990, Hughes et al. 1998). Marine fish have been widely used as indicators of coral cover and overfishing (Bell and Galzin 1984, Findley and Findley 1985, Roberts 1995, Russ and Alcala 1998), but few studies have successfully used marine fish assemblages as indicators of pollution. One reason is that it is difficult to determine the direct effects of pollution on marine fish assemblages because natural experiments are usually confounded by habitat alteration due to dredging, siltation and pollution. This study aims to assess the potential of marine fishes as bioindicators using artificial reefs as habitat controls in 2 marinas with different pollution levels.
Gratwicke, B. and M. R. Speight.
Comparison of Fish Assemblages and Water Quality in Two Marinas in the British Virgin Islands.
Gulf and Caribbean Research
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