[Coral-List] Szmant 2002: Great review on nutrient enrichment on coral reefs

[Eric Hochberg]

For those interested in the topic, I would suggest continuing with Marlin Atkinson's review chapter in Coral Reefs: An Ecosystem in Transition, titled simply "Biogeochemistry of Nutrients."

On 5/1/18 7:38 AM, Bruno, John wrote:

Dear listers,

Over the weekend I read, for the 3rd or 4th time, Alina Szmant’s (2002) incredible review "Nutrient Enrichment on Coral Reefs: Is It a Major Cause of Coral Reef Decline?” and wanted to share it with you.

It’s an amazing paper and a good example of how to critically evaluate evidence for a perceived impact. Very thorough and unbiased. You can download it here:  https://www.dropbox.com/s/q6j144vwzx66e2u/Szmant%202002.pdf?dl=0


Here’s the abstract:

Coral reefs are degrading worldwide at an alarming rate. Nutrient over-enrichment is considered a major cause of this decline because degraded coral reefs generally exhibit a shift from high coral cover (low algal cover) to low coral cover with an accompanying high cover and biomass of fleshy algae. Support for such claims is equivocal at best. Critical examination of both experimental laboratory and field studies of nutrient effects on corals and coral reefs, including the Elevated Nutrient on Coral Reefs Experiment (ENCORE) enrichment experiment conducted on the Great Barrier Reef, does not support the idea that the levels of nutrient enrichment documented at anthropogenically-enriched sites can affect the physiology of corals in a harmful way, or for most cases, be the sole or major cause of shifts in coral- algal abundance. Factors other than nutrient enrichment can be significant causes of coral death and affect algal cover, and include decreased abundance of grazing fishes by fishing, and of grazing sea urchins to disease; grazing preferences of remaining grazers; temperature stress that kills coral (i..e., coral bleaching) and creates more open substrate for algal colonization; sedimentation stress that can weaken adult corals and prevent coral recruitment; coral diseases that may be secondary to coral bleaching; and outbreaks of coral predators and sea urchins that may be secondary effects of overfishing. Any factor that leads to coral death or reduces levels of herbivory will leave more substrate open for algal colonization or make the effects of even low-level enrichment more severe. Factors that contribute to an imbalance between production and consumption will result in community structure changes similar to those expected from over- enrichment. Over-enrichment can be and has been the cause of localized coral reef degradation, but the case for widespread effects is not substantiated.









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