Coral Reefs Essay -- Environment, Global Degradation

Coral reefs have been undergoing global degradation due to increasing natural and anthropogenic impacts for at least the last half-century. The intensity and frequency of stressors, including global climate change, have rapidly increased in number over recent years (Hughes & Connell 1999; Hoegh-Guldberg et al. 2007; Pandolfi et al. 2011). Frequent disturbances such as hurricanes/cyclones, predation outbreaks, diseases and mass bleaching events eat-away at the percent of living coral cover and without recovery, the available space is colonized by sponges, soft corals, and macroalgae. These alternative organisms are often competitive dominants in less than ideal conditions (Norstrà ¶m et al. 2009). The transition is termed a phase-shift from a coral-dominated landscape to one that is dominated by other benthic organisms. Phase-shifts are also often associated with low-herbivory (from disease and/or overfishing) and nutrient enrichment (from run-off and coastal eutrophication)(see Re lative Dominance Model in Littler et al. 2006; 2009). The resilience of particular coral species to recover and/or resist disturbance and subsequent phase-shifts may be indicative of which coral reefs are more or less imperiled. Macroalgae are frequently the competitive dominant driving phase-shifts, thus â€Å"coral-macroalgal phase-shifts† is widely used to describe unusually low-levels of coral cover and a persistent state of high macroalgal cover. There have been a number of studies and reviews describing the negative effects of macroalgae and phase-shifts on coral reefs (Done 1992; Hughes & Connell 1999; Hughes et al. 2003; Hughes et al. 2007; McCook et al. 2001; McManus & Polsenberg 2004; Birrell et al. 2008; Bruno et al. 2009). Potential competitive... ...(SML) microbial samples were collected in Belize, the Florida Keys, and St. Thomas U.S.V.I. along interaction gradients between two ubiquitous Caribbean corals (Montastraea faveolata and Porites astreoides), and their interaction with foliose brown macroalgae (Dictyota menstrualis), and calcareous green macroalgae (Halimeda opuntia). These macroalgae were chosen because they are known to reduce coral growth rates, increase coral tissue mortality, and produce potent allelochemicals that are active against coral reef microorganisms (Ballantine et al. 1987; Lirman 2001; Beach et al. 2003; Rashar & Hay 2010; Morrow et al. 2011). We show that macroalgae can shift M. faveolata microbial assemblages more readily than P. astreoides. We also found that coral microbial assemablages of both species were less stable in Florida than at Belize or St. Thomas sampling sites.