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Sedimentation can play an important role in shaping tropical and temperate benthic marine communities. Here, I quantified sedimentation rates on a hard-bottom reef in the South Atlantic Bight (SAB) off the coast of Georgia, USA and assessed its effects on a conspicuous member of the benthic community: the scleractinian coral, Oculina arbuscula. I addressed the predictions that: 1) inorganic and organic sedimentation rates vary in relation to wind speed and wave height in the SAB, 2) the ability of juvenile O. arbuscula to shed sediment depends on skeletal morphology, and 3) inorganic sedimentation reduces growth and survival of encrusting O. arbuscula juveniles more than those with a branching morphology. The first prediction was tested by quantifying sedimentation rates from July 2008-October 2010 at J-Y Reef, a hard bottom reef at 18-20 m depth ~32 km off the coast of Sapelo Island, GA. Collected sediments were divided into inorganic and organic fractions and compared with wave height and wind speed from the region. Results showed that organic material comprised ~3% of total sediment. Inorganic sediments consistently exceeded 50 mg cm-2 day-1 and were positively correlated with wave height and wind speed. The second prediction was investigated by documenting passive and active sediment shedding abilities in juvenile O. arbuscula with morphologies ranging from encrusting to branching. Laboratory experiments showed that juveniles with greater branching morphology exhibited better passive sediment shedding ability under both low (30 mg cm-2) and high (100 mg cm-2) sediment regimes. However, this morphological advantage was nullified when active sediment shedding mechanisms were included. The third prediction was tested by investigating the relationship between inorganic sedimentation and growth and survival of O. arbuscula juveniles settled on artificial recruitment tiles. Mortality of coral recruits was positively correlated with sedimentation. Juveniles with a branching morphology survived best under sediment stress. Collectively, these results provide evidence that sedimentation can affect the population structure of O. arbuscula via mortality at the juvenile stage and that developing a branched morphology early in life provides a selective advantage for countering the negative impacts imposed by the high sediment loads present on Georgia offshore reefs.

Sessile organisms employing inducible defenses may receive protection from consumers while simultaneously minimizing the metabolic costs of maintaining these defenses. To investigate if reef sponges in the South Atlantic Bight employ inducible chemical defenses, I tested two predictions with Ircinia campana, I. felix, and Aplysina fulva. First, concentrations of antipredator compounds should covary with the abundance of sponge predators. Second, higher compound concentrations should be more effective at deterring predators. Secondary metabolite concentrations in two (I. campana and I. felix) of the sponge species showed temporal variation, which is consistent with the inducible defense hypothesis. Interestingly, higher concentrations of these compounds did not deter feeding by fish or urchins. In contrast, A. fulva, showed no significant temporal variation in the concentration of secondary metabolites, but had deterrent effects on fish predators even at low concentrations. Combined, these results do not support an antipredator strategy based on inducible chemical defenses.

The allocation of chemical defenses to regions most at risk to predator attack may provide adequate protection at minimal metabolic cost. This study examined chemical defense allocation within three sponge species from a temperate reef by investigating the predictions that: concentrations of chemical defenses are 1) higher in the outer 2 mm of the sponge tissue, 2) positively correlated with tissue nutritional quality, 3) negatively correlated with sponge structural components, and 4) varied enough to have differential effects on predator deterrence. The concentrations of chemical defenses varied within Ircinia felix and Aplysina fulva, but were equal throughout I. campana. There were, however, no consistent positive or negative correlations between chemical defenses and nutritional quality or structural components and no clear correlation between chemical defense concentration and predator deterrence. Together, these results suggest the need for a reevaluation of currently accepted ideas regarding chemical defense allocation within sessile prey.

The interaction between predation and anti-predator defenses of prey is important in shaping community structure in all ecosystems. This study examined the relationship between sponge predation and the distribution of sponge anti-predator defenses on temperate reefs in the South Atlantic Bight. Significant differences in the distribution of sponge species, sponge densities, and densities of sponge predators were documented across two adjacent reef habitats. Significant differences also occurred in the distribution of sponge chemical and structural defenses with chemical deterrence significantly greater in sponges associated with the habitat having higher predation intensity. Structural defenses, although effective in some instances, appear to be inadequate against spongivorous predators thereby restricting the distribution of sponge species lacking chemical defenses to habitats with lower predation intensity. These results, when compared to published data from tropical studies, also indicate that predation pressure and the production of anti-predator defenses may be inversely correlated with latitude.