Figure 1.
Coral bleaching, algal overgrowth of corals and coral recovery.
A) Bleached corals in the Keppel Islands, Great Barrier Reef, during the mass bleaching event in January 2006. The fleshy brown seaweed Lobophora variegata grows at the base of the branches of Acropora spp. corals. B) L. variegata is released from space competition by coral mortality and overgrows coral skeletons as well as some coral tissue, causing an unprecedented algal bloom. C) Seaweed bloom on North Keppel Island after coral bleaching. The reef has lost its structural complexity and has experienced little coral recovery. D) Recovered reef on Barren Island, showing high coral cover and low cover of seaweeds.
Figure 2.
Coral – algal dynamics in response to the 2006 warming-induced coral bleaching event.
Data from the reef slopes of four islands in the Keppel Islands, southern Great Barrier Reef. % cover data are means (n = 10) ±SE, except for Feb 2006 (n = 25–26). CCA: Crustose calcareous algae.
Table 1.
Two-way analyses of variance for the effects of sampling date and site on % cover of corals, brown seaweed Lobophora variegata, algal turfs and crustose calcareous algae (CCA).
Figure 3.
Coral recovery following algal overgrowth.
Branches of Acropora corals died after bleaching and were subsequently colonized by a variety of benthic algae. Remnant coral tissue at the base of the coral colonies regrew upward and deposited new skeleton along the old dead coral branch, overgrowing A) algal turfs (arrows), B) fleshy seaweed Lobophora variegata, and C) crustose coralline algae. D) Coral tissue has all but completely overgrown the colonizing algae. E) Thin section of coral showing benthic algae sandwiched between old coral skeleton and a thin layer of new skeleton. Examination using a compound microscope showed that coral tissue overgrew a range of algal types.
Figure 4.
Calcification rates of Acropora millepora at North Keppel Island and Davies Reef (an offshore reef). Data are means±SE (n = 12 for North Keppel Island and 8 for Davies Reef), and show unusually high growth rates in the Keppel Islands.
Table 2.
Kruskal-Wallis one-way analyses of variance for the effects of sampling date on density of coral recruits of four islands.
Figure 5.
Seasonality in Lobophora variegata on Goold Island, inshore central GBR.
Abundance of L. variegata consistently shows strong declines during the austral summer. Data are means±SE of 5 replicate quadrats.
Figure 6.
Herbivore density data from the study sites; data are square root transformed, means+/−SE of 5 transects per site.