Diaz-Pulido et al., 2007:

"Macroalgae have critical and complex roles on coral reefs of the GBR, including making significant contributions to primary production, nitrogen fixation, construction and cementation of reef framework, facilitation of coral settlement, and creation of habitats for other reef species. Macroalgal colonisation and abundance have also been recognised as causes – or, more importantly, consequences – of coral reef degradation.

The distribution and abundance of macroalgae on coral reefs are determined by the resources they require (i.e. light, carbon dioxide, mineral nutrients, substrate), the effects of environmental factors (e.g. temperature, salinity, water movement), individual rates of recruitment, mortality and dispersal, and biological interactions such as competition and herbivory. All these aspects and their interactions are of particular importance under climate change scenarios since they are all likely to be altered (see Figure 7.1). For instance, sea temperatures govern global biogeographic distributions of seaweeds and therefore any temperature change is expected to affect distribution ranges and seasonality of reef algae. Increased resources such as carbon dioxide (CO2) and nutrients may enhance growth rates but the accumulation of biomass will largely depend on interactions with herbivores."

Figure 7.1: General model of the impacts of global climate change on macroalgae of the Great Barrier Reef and likely outcomes