New research reveals alternative coral reef states
- Important to prevent and reverse phase shifts.
A review of the primary and grey literature indicates that reefs dominated by corallimorpharia, soft corals, sponges and sea urchins can enter an alternative state as a result of a phase shift. However, they may differ from the archetypical coral — macroalgae shift, in the factors driving the shift. This is one of the key findings from a new article published by centre-affiliated researchers Albert V. Norström, Magnus Nyström, Jerker Lokrantz and Carl Folke. Their article, entitled Alternative states on coral reefs: beyond coral-macroalgal phase shifts, was recently published in Marine Ecology Progress Series. - Whereas coral-macroalgae and coral-urchin shifts seem to be driven by loss of top-down control through overfishing, soft coral and sponge dominance seem more associated with changes in bottom-up dynamics. Understanding the differences and similarities in mechanisms that cause and maintain this variety of alternative states will aid management aimed at preventing and reversing coral reef phase shifts, says co-author Albert V. Norström. Phase shift characterized by multiple drivers and outcomes The article, which follows up from their research on how to apply resilience theory to coral reef management, is based on four cases from Eilat (Israel), the Aldabra Atoll (Seychelles), Channel Cay (Belize) and Uva Island (Panama) as examples of phase shifts to corallimorpharian, soft coral, sponge and urchin states, respectively. The study has identified several alternative states of coral reefs which could benefit the ability to manage ecosystem changes such as coral reef degradation. - Phase shift dynamics on coral reefs seem to be characterized by multiple drivers and multiple outcomes. The occurrence of coral-macroalgae phase shifts is now widely recognized and supported by numerous robust case studies that demonstrate the often abrupt nature of the shifts, says Norström who calls for better management strategies that take into account the potential range of alternative states. - Management of coral reefs requires an understanding of the conditions under which phase shifts to different states are likely to occur, he concludes.
Source: Norström, A., Nyström, M., Lokrantz, J., Folke, C., 2009. Alternative states of coral reefs: beyond coral-macroalgal phase shifts. In Marine Ecology Progress Series, Vol. 376: 295-306, 2009.
Potential feedback mechanisms reinforcing the macroalgal, soft coral, corallimorpharian and sponge states. (1) Space opening up due to coral mortality leads to an increase in the abundance of the alternative organism. (2) Positive feedback mechanisms, which directly or indirectly reinforce the (3) alternative state are attributed to a) macroalgae, b) soft corals, ccorallimorpharia, d) sponges.
Norström, A., Nyström, M., Lokrantz, J., Folke, C., 2009. Alternative states of coral reefs: beyond coral-macroalgal phase shifts. In Marine Ecology Progress Series, Vol. 376: 295-306, 2009.