Abstract
Coral reefs in the western Atlantic and Caribbean are deteriorating primarily from disease outbreaks, increasing seawater temperatures, and stress due to land-based sources of pollutants including sediments associated with land use and dredging. Sediments affect corals in numerous ways including smothering, abrasion, shading, and inhibition of coral recruitment. Sediment delivery resulting in deposition and water quality deterioration can cause degradation at the spatial scale of corals or entire reefs. We still lack rigorous long-term studies of coral cover and community composition before, during and after major sediment stress, and evidence of recovery after watershed management actions. Here we present an overview of the effects of terrestrial sediments on corals and coral reefs, with recent advances in approaches to watershed assessment relevant to the delivery of sediments to these ecosystems. We present case studies of northeastern Caribbean watersheds to illustrate challenges and possible solutions and to draw conclusions about the current state of knowledge of sediment effects on coral reefs. With a better understanding of erosion and the pathways of sediment discharge to nearshore reefs, there is the increased potential for management interventions.
Highlights
Sediments have long been considered a primary source of stress on corals and coral reefs (e.g., Johannes, 1975; Hatcher et al, 1989; Rogers, 1990; Ginsburg, 1993; Wilkinson, 2008)
This paper focuses on terrigenous sediments delivered in runoff from discrete watersheds to nearshore waters in the U.S Virgin Islands (USVI; Rogers et al, 2008) and Puerto Rico (PR; Ballantine et al, 2008), and not on resuspension of terrigenous and carbonate sediments as described by Larcombe et al (2001) for Great Barrier Reef reefs in highly turbid environments
In terms of sediment sources, studies have shown that landslides may be key contributors in steep, wet tropical terrain and that in many cases sediment sources with a small areal footprint, such as unpaved roads and quarries, contribute a disproportionally large amount of the sediment discharged from watersheds
Summary
Sediments have long been considered a primary source of stress on corals and coral reefs (e.g., Johannes, 1975; Hatcher et al, 1989; Rogers, 1990; Ginsburg, 1993; Wilkinson, 2008). Sediment stress remains critically important in many locations and is more tractable to management than thermal stress and diseases (Spalding and Brown, 2015; Bruno and Valdivia, 2016). Sediments are a natural component of coral reefs and are generated even by undisturbed watersheds. Carbonate sediments, which can be re-suspended by waves, arise from the breakdown of calcifying reef organisms and are an important building block for reef construction, when they are cemented in place by coralline algae and abiotic processes (Hubbard, 1997). Controlled by complex processes, sediment delivery from watersheds to coastal waters
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