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Managing Wastewater in Coastal Urban Areas
substances associated with these particle discharges may also have played a role. The kelp beds recovered following significant reductions in the solids emissions (Grigg 1978, Harris 1980, Wilson et al. 1980).
Reduced light levels from excessive phytoplankton and macroalgal growth in eutrophic environments can cause coral dieback. Shading affects coral growth by decreasing the productivity of the zooxanthallae, symbiotic algae in the coral tissue, which provides much of the coral's nutrition (Smith 1981). Excess nutrients can also cause a shift in the composition of the coral community as other species outcompete corals for space. Filter-feeding species such as sponges take advantage of the high phytoplankton productivity and become dominant, displacing the corals (Pastorak and Bilyard 1985). Sedimentation of decomposing phytoplankton may have an additional detrimental impact on coral growth (Smith 1981).
Nuisance Algal Blooms
Blooms of nuisance algae are characterized by very high abundances of one overwhelmingly dominant species in the phytoplankton. These blooms often result in noticeable color and are popularly named by this color: red tides, green tides, and brown tides. As with eutrophication generally, these blooms can result in anoxic or hypoxic conditions. In addition, many nuisance blooms produce substances toxic to aquatic organisms or humans (Cosper 1991). Green tides during the 1950s heavily damaged oyster populations on Long Island (Ryther 1954, 1989), and brown tides in 1985 and 1986 greatly reduced populations of bay scallops on Long Island (Cosper et al. 1987, Bricelj and Kuenstner 1989) and of blue mussels in Narragansett Bay (Tracey et al. 1989). These shellfish starved to death since they were unable to graze on the brown-tide algae. Blooms of some dinoflagellates (red tides) can result in the accumulation of toxins in shellfish, which, when eaten by humans, cause paralytic or diarrhetic shellfish poisoning (Smayda 1989). Frequent blooms of a gold-brown dinoflagellate in Northern Europe have caused extensive fish mortality since the mid-1960s (Smayda 1989). In 1991, toxins produced by a diatom bloom concentrated in anchovy and caused the death of pelicans that fed on these fish (Work et al. undated, as cited in Smayda 1992). Recently, Burkholder et al. (1992b) discovered a new toxic dinoflagellate that releases toxins only in the presence of fish and appears to be responsible for several fish kills in estuaries in North Carolina.
Nuisance-bloom tides have been known since biblical times (Cosper 1991), but blooms of many species appear to be occurring with greater frequency throughout the world (Hallegraeff et al. 1988; Anderson 1989; Smayda 1989, 1992; Robineau et al. 1991). Red-tide blooms of toxic dinoflagellates appear to be more frequent in many parts of the world (Ander-