Biodiversity along onshore-offshore gradients in tropical coastal shelf areas
Coral reef areas may differ in species richness due to their variation in habitat diversity. Species-poor areas usually lack clear environmental gradients, such as those related to increasing distance from river outlets (onshore–offshore or alongshore). Oceanic island groups without large rivers may for instance lack brackish water, gently declining reef slopes, or variation in exposure to wave action along their coastlines.
Shelf-based reef systems present a large variety of environmental gradients, from inshore to oceanic conditions. Together with fringing reefs, they have variation in salinity, nutrients, and turbidity in common. In addition, they show much more variation in depth ranges and wave exposure (depending on increasing shelf depth), and temperature (cold-water upwelling near barrier reefs). Cross-shelf reef systems contain much habitat diversity along gradients perpendicular to the coastline, whereas fringing reefs show along-shore variation related to distance from rive-outlets, The total reef surface area along such gradients results in an increasing habitat heterogeneity, which reflects a species–area relationship.
Selected references
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Friday, February 6, 2009