During my PhD, I studied the nursery value for fishes (sensu Beck et al 2001) of macroalgae forest on temperate rocky reefs of the Mediterranean. Fucales (Cystoseira spp.) forest showed a higher nursery value for Labridae fish species than bush-like or bare substratum neighbouring rocky habitats. Given this, I wonder if in tropical environments, reef habitats that are being colonized by macroalgae (Turbinaria, Sargassum) may show an increased density for some juvenile fish taxa. In other words, while the shift from coral reefs to macro algae-dominated reefs has been described to reduce diversity and abundances of many organisms, I wonder if a beneficial effect may as well result from this habitat shift for fish assemblage replenishment.
Article Changes in Biodiversity and Functioning of Reef Fish Assembl...
From my observations in reefs with advanced phase-shift from corals to algae, the algae communities tend -as the ecological theory says- to grow in complexity (species diversity of assemblages) and i haven't -so far- seen reefs dominated by algae like Cystoseira. But yes given the growth form of those algae, it would make ecological sense that they could become surrogates of habitat complexity. That has been proven for octocorals and Sargassum in other non-reef environments, they act as cover and refugia for species like groupers and snappers.
Cheers from Mexico!
R
Recently Hoey and Belwood (2011) showed that dense macroalgal stands could deter herbivorous fishes.
Regarding the value of macroalgae as recruitment sites, you might want to read the work by Paddack and Sponaugle (2008) who show that in the Carribean, following the decline in coral cover, recruitment in a reef grazer actually increased in the macroalgae stands. This partly suggests that the complex habitat provided by macroalgae might be an alternative settlment zone for reef fishes.
Clearly more reaserch is needed to assess the overall contribution of macroalgae on reef fish communities.
Hoey AS, Bellwood DR (2011) Suppression of herbivory by macroalgal density: a critical feedback on coral reefs?. Ecol Lett 14:267-273.
Paddack MJ, Sponaugle S (2008) Recruitment and habitat selection of newly settled Sparisoma viride to reefs with low coral cover. Mar Ecol Prog Ser 369:205-212.
Yohannes
Macroalgae can certainly add complexity and structure to coral depauperate areas / habitats. Dense stands of macroalgae such as Sargassum have been shown to be beneficial for the recruitment of some reef fish species but not others (see Wilson et al (2010) PLoS ONE 5:e15185). As Yohannes mentioned above, I also found that many herbivorous fishes avoided areas with high densities of Sargassum, including several species that feed on the Sargassum itself (See Hoey and Bellwood 2011 Ecol Lett 14:267-273). We suggest this was related to the higher densities of predatory fish that were using the structure provided by the Sargassum. Clearly the structure provided by macroalgae can influence patterns and processes on coral reefs, but much more research is required to understand the complexities of these relationships.
Andrew
Thanks a lot for your answers, I will let you know any updates I may gather on this thematic. Cheers, Adrien
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