Flattening of Caribbean Coral Reefs

Image: Complex coral reef structure is critical to provide habitats for marine creatures


The three-dimensional structure of a coral reef plays an important role in the abundance and diversity of its marine inhabitants: a highly complex reef provides many crevices for marine animals to shelter and feed. Reef structural complexity also influences tourism and fishing industries, and can reduce shoreline erosion through the dissipation of wave energy.


Decline in Reef Complexity

In the Caribbean, there has been a staggering decline in the complexity of coral reefs over the last 40 years. A study by Lorenzo Alvarez-Filip et al. (2009), found 75% of Caribbean reefs were in the flattest range (rugosity less than 1.5) compared to 20% in the 1970s. All sub regions in the Caribbean were affected with the rates of complexity lost similar on shallow (<6 m), mid-water (6–20 m) and deep (>20 m) reefs.


Causes of Decline

It is thought the steep decline in Caribbean reef architecture began with the outbreak of White-band disease, which killed approximately 90% of reef-forming corals Acropora palmata and Acropora cervicornis, in the late 1970s. Other ecological events such as the mass mortality of the grazing urchin Diadema antillarum (a key remover of algae from reef surfaces) created a shift to macro-algal dominant reefs, and region-wide coral bleaching episodes which have become increasingly frequent and extensive, have exposed coral systems to stressed conditions.


Concern for the future

No one knows what long-term effects flattened Caribbean coral reefs will have for the biodiversity of reefs or well being of Caribbean coastal communities. The recovery of large branching corals (i.e. Acropora spp.) and massive robust species (e.g. Montastrea spp.) would assist with the reconstruction, but if nothing is done the flattening of reefs will probably continue throughout the region and seriously compromise biodiversity and environmental services.