The subtidal distribution of macroalgae on the coral reefs of the Chagos Archipelago: a preliminary study

This is the first quantitative investigation of the subtidal distribution of erect benthic macroalgae on three northern atolls of the Chagos Archipelago; Salomon, Peros Banhos and the Great Chagos Bank. The Line Intercept Transect technique was used to estimate macroalgal abundance, in terms of percent cover, on both the outer and lagoon reefs. The transects were replicated at shallow (5 m), intermediate (15 m) and deep (25 m) depths. On the outer reefs the abundance of erect macroalgae increased with depth, except for _turf? and microalgal assemblages which were most abundant in the shallower areas. The benthic cover, averaged over all depths, was c. 4 %. In contrast, the depth distribution on the lagoon reefs appeared unimodal, where maximum abundance occurred at intermediate depths and the average percent cover was three to four times greater than the outer reefs. This difference was primarily due to Halimeda spp., especially H. copiosa. Halimeda was the most abundant genus throughout the Archipelago, and Boodlea, Caulerpa and Dictyosphaeria were also relatively common. Despite the reputed species richness of the Chagos reefs, the algal diversity is relatively low compared to those reported from benthic habitats at similar latitudes. This is attributed to the few studies that have examined the benthic algae of the Archipelago, rather than any geographical effects. Four previously unrecorded taxa are reported. The recorded abundance and distribution patterns are comparatively similar to those detailed by other studies and their regulation by biological and environmental factors such as herbivory, light penetration and wave exposure is discussed.
Jolliffe A , Basson P .
marine algae, biogeography, grazing, Chlorophyta, Rhodophyta, Phaeophyta, Cyanophyta, benthic ecology, macro algae