Abstract
Skeleton properties determine coral survival by influencing the range of hydraulic conditions colonies can withstand, selection of suitable habitat, ability to compete for space and light, repair damage and the overall fitness and ecological success of scleractinian corals. Skeletal properties of 16 coral species comprising 3 growth forms collected from Kenyan coral reef lagoons were investigated and found to vary considerably not only between species but between reefs as well, with corals exposed to both sediment and nutrients showing consistent lower skeleton density and strength but high porosity compared to those from sediment-unaffected reefs. Further, high skeletal density and strength but low porosity values were measured in branching relative to other growth forms. The present findings also suggest that the negative effects of nutrients on skeleton properties may be counteracted by high hydrodynamic energy, resulting in stronger skeletons in high hydrodynamic energy-nutrient-polluted reef habitats relative to pristine reefs. These findings have important ecological and management implications with regard to the existence, persistence, productivity and protective value of reefs, damage risks, maintenance and conservation of biological diversity with respect to future global climate change events. Consequently, appropriate watershed, reef and fisheries management options the impacts of local anthropogenic stresses (sediments, nutrients, overexploitation) would be expected to alleviate the effects of these disturbances and have the potential to minimize future large-scale coral reef damage resulting from increased and frequent global climate change events, such as increased ocean acidification (due to elevated atmospheric CO2) and sea surface temperature.
Highlights
1.1 Impacts of Disturbances on Coral ReefCoral reefs are maintained by the close balance between constructive and destructive processes (McKibben, 2012; McClanahan & Abunge, 2014)
No significant differences in temperature, salinity and phosphates were detected between reefs but chlorophyll a, current velocity and nitrates were all found to be significantly high in Malindi but low in Shimoni compared to the rest of the study reefs
Higher Total suspended sediment (TSS) and sedimentation rates were measured in Malindi and Watamu relative to the other study reefs no differences in TSS organics and trapped sediment insoluble residue were detected between reefs (Table 1)
Summary
1.1 Impacts of Disturbances on Coral ReefCoral reefs are maintained by the close balance between constructive (by carbonate-producing corals and coralline algae) and destructive (carbonate-removal by physicochemical and biological factors) processes (McKibben, 2012; McClanahan & Abunge, 2014). Apart from preventing assemblage dominance by small subsets of species, skeleton characteristics may be of significance in (i) determining boulder movements and damage during high hydrodynamic energy events (Spiske et al, 2008), (ii) explaining the differential mortality of corals (Roughael & Inglis, 1998) and (iii) understanding maintenance mechanisms of biological diversity, patchiness and changes in community composition in reefs after physical disturbance events (Yost et al, 2013). Previous studies have shed some light on the consequences of skeleton property characteristics and morphological modifications (Chamberlain, 1978; Schuhmacher & Plewka 1981a; Madin et al, 2012; Reyes-Nivia et al, 2013), importance of skeletal strength through geological time (Schumacher & Plewka, 1981b; Tomiak et al, 2013; Robinson et al, 2014) as well as changes in colony and reef framework strength (Caroselli et al, 2011; Chen et al, 2013). Few studies have been undertaken to elucidate the influence of water quality parameters on coral skeleton modifications, especially the effects of increased sediment and nutrient concentrations on coral skeleton mechanical properties
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