A comparison of spatially explicit and classic regression modelling of live coral cover using hyperspectral remote-sensing data in the Al Wajh lagoon, Red Sea

Live coral is a key component of the Al Wajh marine reserve in the Red Sea. The management of this reserve is dependent on a sound understanding of the existing spatial distribution of live coral cover and the environmental factors influencing live coral at the landscape scale. This study uses remote-sensing techniques to develop ordinary least squares and spatially lagged autoregressive explanatory models of the distribution of live coral cover inside the Al Wajh lagoon, Saudi Arabia. Live coral was modelled as a response to environmental controls such as water depth, the concentration of suspended sediment in the water column and exposure to incident waves. Airborne hyperspectral data were used to derive information on live coral cover as a response (dependent) variable at the landscape scale using linear spectral unmixing. Environmental controls (explanatory variables) were derived from a physics-based inversion of the remote-sensing dataset and validated against field-collected data. For spatial regression, cases referred to geographical locations that were explicitly drawn on in the modelling process to make use of the spatially dependent nature of coral cover controls. The transition from the ordinary least squares model to the spatially lagged model was accompanied by a marked growth in explanatory power (R 2 = 0.26 to 0.76). The theoretical implication that follows is that neighbourhood context interactions play an important role in determining live coral cover. This provides a persuasive case for building geographical considerations into studies of coral distribution

Localized outbreaks of Acanthaster planci at an isolated and unpopulated reef atoll in the Chagos Archipelago

Outbreaks of the crown-of-thorns starfish (COTS), Acanthaster planci, have occurred at many locations throughout the Indo-Pacific and are a major contributor to widespread coral loss and reef degradation. The causes of outbreaks remain controversial, but are commonly attributed to anthropogenically elevated nutrients and/or over-fishing. If so, it seems unlikely that outbreaks would occur in reef systems that are largely isolated from anthropogenic disturbances. However, high densities of COTS were recently observed on reefs in the Chagos Archipelago, a remote group of atolls and banks within the central Indian Ocean, which experience very limited anthropogenic influence. Aggregations of COTS were first noticed at Eagle Island in 2012, which, although unquantified, appeared to be at outbreak levels, and very high densities (1624 km�2) were subsequently recorded at Danger Island in 2013. While these islands are uninhabited by humans, it is possible that nutrient inputs result from upwelling zones around the Archipelago, or high densities of breeding seabirds. Among islands within the Great Chagos Bank, densities of the red-footed booby Sula sula ranged from 8 to 7888 individuals km�2, with associated guano input ranging from 96 to 25,381 kg island�1 year�1. However, Danger and Eagle Islands where high COTS densities were recorded, had both high and low levels of guano production, respectively, which suggests that outbreaks may not be directly linked to guano nutrient enrichment. Other factors which might be responsible for intermittent COTS outbreaks should be considered in isolated reef systems such as the Chagos Archipelago