Community Research and Development Information Service - CORDIS

ERC

INCORALS Report Summary

Project ID: 311179
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Final Report Summary - INCORALS (Influence of nutrient starvation on corals' susceptibility to bleaching)

The limestone skeletons of warm water corals, deposited in symbiosis with their algal symbionts, form the 3-dimensional framework of reefs that provides home to ~25 % of all marine biodiversity. Reefs sustain diverse artisanal fisheries and ornamental trade and represent an essential source for food, providing up to 50% of protein needs in some countries. They form underwater architectures that protect many coastlines from wave energy and erosion. Reef organisms represent a source for potential drugs, biotechnological tools and biomimetic designs. Finally, reefs are an important source for recreation and they are integral to the cultural identity of numerous nations.
Coral reefs are in decline at a global scale. They are threatened by overfishing, maritime construction, coastal pollution and the introduction of invasive species. Episodes of unusually hot sea water temperatures are occurring with increasing frequency, resulting in the breakdown of the vital symbiosis between corals and their microalgal partners that manifests as coral bleaching. If the corals are not able to restore this symbiosis, they become vulnerable to starvation and disease and die.
Using the experimental coral mesocosm facility of the Coral Reef Laboratory at the University of Southampton and monitoring coral reefs in several parts of the world, INCORALS researchers have discovered that an increased supply of dissolved nitrogen (N) compounds in combination with a restricted availability of phosphate (P) can induce phosphate starvation of the coral’s symbiotic algae. This condition is associated with a reduction of photosynthetic efficiency of the microalgae and can be further diagnosed by the use of biomarkers that have been established by the INCORALS project. Phosphate starvation increases the susceptibility of corals to temperature and light-induced bleaching. Primary effects of experimentally increased nitrate-to-phosphate ratios included a significantly increased mortality rate of corals exposed to elevated temperatures. Using mass spectrometry analyses of the coral’s algal symbionts, INCORALS demonstrated that the lipid composition of photosynthetic membranes, key to the heat stress tolerance of corals, is dependent on the nutrient environment. These insights allowed to establish mechanistic links between the nutrient availability in the water column and the heat stress tolerance of the corals.
INCORALS researchers have introduced the novel concept that phytoplankton blooms, initiated by the availability of excess nutrients, can have secondary effects such as the exhaustion of nutrients vital for the thermo-tolerance of corals at a later point in space or time. Therefore, paradoxically, the initial addition of nutrients to the water column might result in nutrient starvation of the corals at a later stage. In reef environments, these direct negative effects on the coral physiology will add to a range of indirect effects of nutrient enrichment that affect ecosystem functioning for instance through enhanced pressure from bioeroders and macroalgal competition.
The improved understanding of the effects of nutrient pollution on coral bleaching gained during this project forms a knowledge-base for the management of nutrients in coastal waters as a strategy to support reef resilience under the pressure of ocean warming. The key findings of INCORALS highlight the need to reduce and ideally avoid anthropogenic introduction of nutrients in coastal waters. Specifically, the imbalanced enrichment with either nitrogen or phosphorus should be prevented. The results of INCORALS demonstrate the potential to mitigate some impacts of global climate change on coral reefs at the regional scale by maintaining the best possible water quality.

Reported by

UNIVERSITY OF SOUTHAMPTON
United Kingdom
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