Effects of suspended sediment and burial on scleractinian corals from west central Florida patch reefs

The distribution and abundance of eight species of endemic scleractinian corals were determined for patch reefs off west central Florida in the depth range of7-18 m. Phyllangia americana and Cladocora arbuscula were the most abundant species encountered. Five of the eight species censussed were absent from the shallowest reef(7 m). Seven species of corals were exposed to increasing levels of suspended sediment in the laboratory and seven species were subjected to prolonged burial in sediment. Survival rates were not affected by IO-day exposures to suspended sediment concentrations of49, 10 I, 165, or 199 mg' liter-'. Combined mean growth rates for six species were significantly different between control and experimental treatments at 165 mg' liter I suspended sediment. Coral burial experiments produced survival LT 50 values of7 days for Scolymia lacera, 7.2 days for lsophyllia sinuosa, 10days forManicina aereolata, 13.6 days for Siderastrea radians, 15 days for C. arbuscula, 16.2 days for Stepha nocoenia michelinii. and 15+ days for Solenastrea hyades. The results of these experiments indicate that the species tested are among the most resistant corals in the Caribbean region to the effects of suspended sediment and physical burial. These findings are consistent with the fact that west central Florida patch reefs are exposed to more severe environmental conditions, such as high turbidity and low light penetration (in addition to a broader range of temperatures) than more tropical reefs to the south. Since most vigorous coral reef development occurs in transparent tropical waters, it has become axiomatic that low levels of turbidity and suspended sediments are essential for optimal hermatypic coral growth and survival. High turbidity and sedimentation rates may depress coral growth and survival due to I) attenuation of light available to symbiotic zooxanthellae (Rogers, 1979), 2) redirection of energy expenditures for clearance of settling sediments (Dallmeyer et aI., 1982; Abdel-Salam and Porter, 1988), or 3) actual smothering of coral tissue (Rogers, 1983). However, tolerance of corals to high sediment loads may vary considerably among species, with some corals being fairly resistant to low light levels and/or sedimentation effects (Edmondson, 1929; Dodge and Vaisnys, 1977; Lasker, 1980; Rogers, 1983; Hodgson, 1990). Sensitivity to these effects depends on sediment clearing ability, calyx and colony morphology, orientation of growth, and the types of sediment involved (Hubbard and Pocock, 1972; Bak and Elgershuizen, 1976; Dodge and Szmant-Froelich, 1985). Rogers (1990), in a review of the effects of sedimentation on corals, suggested that reefs with high sediment loads may have lower diversity, percent cover, and growth rates of coral species, small colony sizes (or large colonies in areas in which recruitment is limited by siltation), an upward shift in depth zonation, and a predominance of resistant growth forms or species. In general, field observations have confirmed a relationship between suspended sediment levels and coral distributions in a variety of geographic locations including: Palau (Motoda, 1939), Australia (Mayer, 1918; Marshall and Orr, 1931); Fanning Island (Roy and Smith, 1971), Guam (Randall and Birkeland, 1978), Hawaii (Edmondson, 1928), Costa Rica (Cortes, 1990), Florida (Hubbard and Pocock, 1972), Jamaica (Dodge et aI., 1974), Puerto Rico (Loya, 1976; Acevedo and Morelock, 1988), and the Virgin Islands (Rogers, 1983; Hubbard et aI., 1987). In many cases, the same species or