Coral-to-Macroalgae Phase Shifts

Lab Note #18
Jan 27, 2015

Corals are the ecological engineers of coral reefs (Bozec et al. 2013), which means they create three-dimensional habitat (via calcium carbonate, or limestone, deposition - also known as the underlying coral skeleton) as they grow (Jones et al. 1994, 1997). Although corals share the benthic habitat with many other types of organims, like macroalgae (algae large enough in size to compete with coral for space on the benthic habitat), it is imperative for the reef to maintain coral in order to maintain its three-dimensional structure over time (Bozec et al. 2013). Coral reefs can experience natural and anthropogenic disturbances that include strong wave energy (Knowlton et al. 1991) and pollution from terrestrial runoff (Brown 1987; Dubinsky & Stambler 1996) which can lead to coral mortality. This means that the three-dimensional structure originally composed of a living organism changes to limestone rock, or bare substrate. This results in available free space for other benthic organims, like macroalgae, to colonize and expand their populations on the reef. This change in the community composition of the coral reef is referred to as a phase shift (Nyström et al. 2008). If the phase shift is prolonged, then coral organisms usually fail to recruit, colonize, and grow on the reef. Therefore, the reef eventually loses its three-dimensional stucture over time and can transistion into what is known as a regime shift (Nyström et al. 2008).

From Bellwood et al. (2004)

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