Patch dynamics of coral reef macroalgae under chronic and acute disturbance

Abstract

The patch dynamics (colonisation rate, growth rate, and extinction rate) are quantified for two dominant species of macroalgae on a Caribbean forereef in Belize: Lobophora variegata (Lamouroux) and Dictyota pulchella (Hornig and Schnetter). Measurements were taken on time scales of days, weeks, months, and years during which three hurricanes occurred. All patches were followed on naturally occurring ramets of dead Montastraeaannularis. The first hurricane (Mitch) caused massive coral mortality and liberated space for algal colonisation. The cover of Lobophora increased throughout the study and herbivores did not appear to limit its cover within a 4 year time frame. In contrast, the cover of D. pulchella fluctuated greatly and showed no net increase, despite an increase in parrotfish biomass and settlement space. Variation in the overall percent cover of an alga is not indicative of the underlying patch dynamics. The steady rise in the cover of Lobophora took place despite a high turnover of patches (12–60% of patches per year). The patch dynamics of Dictyota were slower (7–20%), but a greater patch density and threefold higher lateral growth rate led to greater fluctuations in total cover. The dynamics of algal patches are size-specific such that larger patches are less likely to become extinct during hurricanes.