New From our friends over at the Burkepile Lab at Florida International University –
It’s been communicated many times that nutrient pollution of the oceans can affect the performance of various coral species. To date, the results have been varied…researchers find different responses, but they also apply nutrients in different amounts (total and relative (stoichimetry)). Because of these differences it’s been hard to figure out what the effects of nutrients on corals actually are. One way to clarify these issues is a literature review or a meta-analysis, a technique that compiles and analyzes the results of multiple studies at one time. Such a a study was recently accepted for publication in Ecology by a friend of the Abaco Scientist, Andy Shantz. Below is a summary I solicited from him that tells us a bit more about his findings.
Context-dependent effects of nutrient loading on the coral-algal mutualism
Communicated for Andrew Shantz, PhD candidate in the Burkepile lab and an all around decent fella.
There is a general consensus amongst coral reef scientists that excess nutrients are bad for coral reefs. The belief is that enrichment with common nutrients – such as the nitrogen and phosphorus found in animal waste and agricultural run-off – shifts the balance on reefs from corals to macroalgae that can smother and overgrow coral reefs. However, the effects of these nutrients on the coral itself is not so clear. We compiled results from previous studies of coral-nutrient dynamics to try to establish clear patterns in how nutrients impact coral growth and health.
We found that nitrogen clearly impairs coral growth, but phosphorus may actually promote calcification in corals, although potentially at the expense of skeletal strength and integrity. In an interesting twist, we found that not all nutrients are bad for corals. When nitrogen and phosphorus are from the metabolic waste of fishes that shelter around corals, the corals actually grow faster than those without access to these fish-derived nutrients. Although the difference between fish-derived nutrients and pollution remains unclear, we speculate this may be due to differences in the overall amounts delivered or the ratio of nitrogen-to-phosphorus found in fish waste.
We concluded that nitrogen impairs coral growth by disrupting the symbiotic relationship between corals and the photosynthetic algae (zooxanthellae) that live within their tissue. In nutrient poor conditions, the coral-host provides these algae with nitrogen and in turn the algae provide excess sugar produced by photosynthesis to the coral host. As nitrogen levels increase however, these algae, known as Symbiodils become energy-starved and growth rates suffer.
Shantz, A.A., & D.E. Burkepile. Context-dependent effects of nutrient loading on the coral-algal mutualism. In Press, Ecology
Link to Publisher: http://www.esajournals.org/doi/abs/10.1890/13-1407.1?af=R