Study: Cramer, Katie, Mary Donovan, Jeremy Jackson, Benjamin Greenstein, Chelsea Korpanty, Geoffrey Cook, and John Pandolfi. “The Transformation of Caribbean Coral Communities since Humans.” Preprint. Preprints, January 12, 2021. https://doi.org/10.22541/au.161048962.21724991/v1.

Coral Reefs in the West

For years now every so often we see another headline about the decline of the world’s coral reefs spurring articles and debates about global warming, ocean protection, fishing, and pollution. The Carribean sea hosts one of the world’s largest collections of living corals and coral ecosystems. Systematic monitoring of coral communities began in the late 1970’s; since monitoring, Carribean reefs have seen a 50-80% decline in reef-building corals. The decline of corals has resulted in the dominance of greener algae based ecosystems. The evidence does not point to one specific cause, but a multitude of stressors which include the global warming of the seas, land-based pollution, overfishing of herbivorous fish and urchins, and diseases afflicting corals and urchins. The “White Band Disease” that appeared throughout the 1980’s specifically decimated 80% of elkhorn and staghorn corals. Significant coral bleaching events have occurred predominantly since the early 1990’s until present day increasing coral disease and vulnerability.

Experiment

Data on coral species and their compositions were gathered via semi-quantitative, quantitative, and qualitative records from a variety of sources ranging from peer reviewed scientific literature, government reports, and historical literature. Data for corals starting from the 1980’s were obtained from the Global Coral Reef Monitoring Network (GCRMN) database that consists of peer reviewed literature from 1970-2011. The researchers focused the study on 14 different coral taxonomic groups that are common throughout the Carribean and persist through time since the Late Pleistocene era (131,000-12,000 years ago) to 2011. The researchers also analyzed coral data based on depth or reef zone which was divided up into “reef crest” (0-6 m.) and “midslope” (6-20 m.) reef zones. For the experiment, stress tolerances of different corals were also taken note of.

Results

The long term changes regarding Carribean reefs were divided into three main categories: declines in competitive corals by the 1960’s, increase of stress tolerant and weedy (fast growing corals that usually are first to colonize a reef) corals by the 1970’s and 1980’s, and the leveling off of these stress tolerant and weedy corals by the 1980’s and 1990’s. These trends were consistent with all 14 groups of coral. These trends were also consistent at most depths from most of the site locations.

Overall, corals declined in all locations at every depth with sensitive corals declining the most. Weedy corals increased their share of reefs relative to other species. Most significant declines in corals were 2000-2004 at the reef crest and 1985-1989 at the midslope zones. This research covers about 131,000 years of coral reef history in the Caribbean and the researchers found that coral reefs drifted from competitive Acropora corals typified by fast growth, large and structurally complex colonies, and high rates of reproduction by fragmentation and lower tolerance to human disturbances to systems dominated by stress-tolerant and weedy corals with relatively slower growth, lower-relief colony forms, and higher tolerance to human disturbances (Cramer et. al, 2021, p. 6).

What now?

Now that we have a general history about what has happened to the corals since humans have been introduced, what now? It is not like humans are going to disappear and the coral reefs are going to thrive again. The damage has been done, but there is still time and room to prepare. Some good news on the horizon is that corals are beginning to adapt to the effects of global warming and reefs are even being found at latitudes previously impossible. Because of various studies and international efforts, we now know more about corals than ever before. Educating the public about coral reefs and the importance of keeping our oceans healthy would be one of the most effective ways to spread awareness and activism for these natural monuments.

Additional References

1. Gardner TA, I. M. Cˆot´e, J. A. Gill, A. Grant, A. R. Watkinson (2003) Long-term region-wide declines in Caribbean corals. Science301, 958-960. 
2. Jackson, J. B. C., Donovan, M. K., Cramer, K. L., Lam, V. V. (2014). Status and trends of Caribbean coral reefs: 1970-2012. Global Coral Reef Monitoring Network, IUCN, Gland, Switzerland. 
3. Hughes TP, M. J. Rodrigues, D. R. Bellwood, D. Ceccarelli, O. Hoegh-Guldberg, L. McCook, N. Moltschaniwskyj, M. S. Pratchett, R. S. Steneck, B. Willis (2007) Phase shifts, herbivory, and the resilience of coral reefs to climate change. Curr. Biol. 17 , 360-365. 
4. Aronson RB, Precht WF (2001) White-band disease and the changing face of Caribbean coral reefs. Hydrobiologia 460: 25–38.
5. National Geographic Society Newsroom. “Why Weedy Species Matter on Coral Reefs,” May 16, 2017. 
6. Wild For Life. “Elkhorn and Staghorn Coral,” February 20, 2020. https://wildfor.life/species/elkhorn-and-staghorn-coral.
7. Steneck, Robert S., Peter J. Mumby, Chancey MacDonald, Douglas B. Rasher, and George Stoyle. “Attenuating Effects of Ecosystem Management on Coral Reefs.” Science Advances 4, no. 5 (May 2018): eaao5493. https://doi.org/10.1126/sciadv.aao5493.