Primacy of seascape connectivity effects in structuring coral reef fish assemblages

Connectivity has fundamental consequences for the productivity, persistence and management of coral reefs. The area and position of adjacent mangroves and seagrass can affect the demography of reef fish populations and the composition of reefal assemblages. To date, no studies have attempted to partition the influences of these habitats on reef fish assemblages. We used an exploratory seascape approach to separate the effects of connectivity with mangroves and seagrass on reef fish in Moreton Bay, Australia. We then compared the performance of seascape connectivity and reef complexity (i.e. coral cover, rugosity and area) in structuring these assemblages. Our results suggest a hierarchy of seascape connectivity effects, with reef fish assemblages being primarily distinguished by isolation (i.e. separation distance) from mangroves and secondarily by proximity (an index incorporating habitat isolation and area) to seagrass. Importantly, measures of reef complexity were only useful in separating reef fish assemblages within levels of connectivity with mangroves and seagrass. We demonstrate that neighbouring mangroves and seagrasses can exert different effects on reef fish assemblages, with 25% of all species being primarily influenced by mangroves and a different 25% being affected by seagrass. These findings have important implications for the design of marine reserve networks. They show that position in the seascape can be of greater significance than reef area or complexity to the composition of reef fish assemblages and highlight the value of incorporating seascape connectivity into conservation planning.