Abstract
Disturbances of terrestrial origin are important determinants in the growth, carbonate production and well- being coral reefs. In this study, coral growth (density, linear extension and calcification rates) and corallite (diameter and density) variables were determined for selected species from four Kenyan protected reef lagoons, with one receiving a pulse of sediment discharge. Variable coral growth responses were observed, with some species showing higher growth rates while others exhibited low growth rates within the sediment impacted reef. Species corallite characteristics also showed variable responses, though corallite diameters were found to be larger in the sediment impacted reef with low corallite densities generally being observed in the mangrove-fringed reef. Coral bulk density was found to be poorly correlated to calcification and extension rate but calcification and extension rates were found to be highly correlated (R values 0.84 to 0.98). The variable responses observed in the current study have important implications and applications in coral reef health and management by providing information on the susceptibility of different corals species to local stressors, and together with coral distribution and composition data this information may be useful in the formulation of suitable and scientific based reef management strategies and also in predicting reef performance under future climate change scenarios. Key words: Calcification, corals, climate change, density, linear extension, sediments, terrestrial disturbances.
Highlights
No significant differences in temperature, salinity and current velocity were detected between study reefs though current velocity was found to be high in Malindi compared to the other sites (Table 1)
Chlorophyll a concentration was found to be significantly higher in Malindi and Watamu compared to Mombasa and Shimoni, phosphates and nitrates concentration did not differ between reefs
No significant differences between reefs were detected for total suspended sediments (TSS) organic content, Watamu reef exhibited low bottom sediment organic content compared to the rest of the study reefs
Summary
Changes in water quality due to modification of catchment areas through various human activities (Fabricius et al, 2011; Golbuu et al, 2011; Nakajima et al, 2013; Chen et al, 2015) are considered major factors in the degradation of coral reef worldwide. Increased human activities such as farming, coastal development and deforestation have elevated the rate of soil erosion and sediment input into rivers with subsequent increase in levels of turbidity, sediments and nutrients in coral reef areas (GESAMP, 2001; Rotmann and Thomas, 2012; D’Olivo et al 2014; Kumara et al, 2015). The number of reports on reef degradation due to land based stressors has increased (Crabbe and Carlin, 2007; Padilla-Gamiňo et al, 2012; Shantz and Burkepile, 2014; Prouty et al, 2014) with model estimates indicating that 22% of coral reefs worldwide (Bryant et al, 1998) and ~50% in countries with widespread land clearing are threatened by inland pollution and erosion
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