The photosynthetic resilience of Porites furcata to salinity disturbance

Manzello, Derek; Lirman, Diego

Benthic habitats of Biscayne Bay, a shallow lagoon adjacent to the city of Miami, Florida, contain a limited number of coral species that represent a subset of the species found at nearby reefs of the Florida Reef Tract. The physical characteristics of this basin (i.e., variable salinity and temperature, high sedimentation) make it a marginal environment for coral growth(Lirman et al. 2003). Salinity fields of Biscayne Bay are influenced by freshwater inputs from canal, surface, and groundwater sources that create a nearshore environment with low mean salinity and high salinity fluctuation. For example, salinity fell to levels below 25 ppt in this area for 188 days in 1998 and 156 days in 1999 (Lirman et al. 2003). Siderastrea radians and Porites furcata are the most abundant coral species found in this near-shore environment(Lirman et al. 2003), suggesting their high tolerance to low and variable salinity. In this study, we test the hypothesis that a high physiological tolerance for salinity fluctuations enables P. furcata to occupy these marginal environments. Osmotic stress has long been recognized as a limiting physical parameter for marine organisms, as emphasized by the negative correlation observed between marine species and salinity levels in estuarine environments (Wells 1961). Changes in salinity are known to pose a significant metabolic drain on marine organisms, and disrupt normal cellular electrochemical processes, enzyme kinetics, and nerve conduction(Vernberg and Vernberg 1972). In corals, sudden changes in salinity are known to negatively impact reproduction (Richmond 1993), photosynthesis and respiration (Muthiga and Szmant 1987; Moberg et al. 1997; Nystrom et al. 1997; Porter et al. 1999), and survivorship (Marcus and Thourhaug 1981; Coles 1992; Krupp et al. 1998). Corals are considered to be stenohaline, with a limited ability to adapt to or survive salinity changes (Wells 1957; reviewed by Coles and Jokiel 1992). Mortality in corals is predicted to occur at salinities lower than 25 ppt (Edmondson 1928) or higher than 45 ppt (Jokiel et al. 1974). However, other studies suggest that corals can tolerate both low (17.5–28 ppt; Vaughn 1919; Edmondson 1928) and high salinities (38.5–52.5 ppt; Edmondson 1928; Wells 1957). In this study, we evaluate the photosynthetic response of P. furcata to sub-optimal salinity levels (20–45 ppt) in a series of exposure experiments of different duration (2 to 24 h).

The photosynthetic resilience of Porites furcata to salinity disturbance

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