Search

Observations made on Heron Island reef flat during the 1970s-1990s highlighted the importance of rapid change in hydrodynamics and accommodation space for coral development. Between the 1940s and the 1990s, the minimum reef-flat top water level varied by some tens of centimetres, successively down then up, in rapid response to local engineering works. Coral growth followed sea-level variations and was quantified here for several coral communities using horizontal two-dimensional above water remotely sensed observations. This required seven high spatial resolution aerial photographs and Quickbird satellite images spanning 35 years: 1972, 1979, 1990, 1992, 2002, 2006 and 2007. The coral growth dynamics followed four regimes corresponding to artificially induced changes in sea levels: 1972-1979 (lowest growth rate): no detectable coral development, due to high tidal currents and minimum mean low-tide water level; 1979-1991 (higher growth rate): horizontal coral development promoted by calmer hydrodynamic conditions; 1991-2001(lower growth rate): vertical coral development, induced by increased local sea level by similar to 12 cm due to construction of new bund walls; 2001-2007 (highest growth rate): horizontal coral development after that vertical growth had become limited by sea level. This unique time-series displays a succession of ecological stage comprising a 'catch-up' dynamic in response to a rapid local sea-level rise in spite of the occurrences of the most severe bleaching events on record (1998, 2002) and the decreasing calcification rates reported in massive corals in the northern part of the Great Barrier Reef.

International audience; Regeneration of a reef flat ten years after the impact of the cyclone Firinga (Reunion, SW Indian ocean) 0. aim', P. Chabanet', T. Done', C. Tourrand' and Y. Letourneur' ABSTRACT Changes in composition of corals, algae and fishes at St-Leu, La Reunion, appear to be successional in character, the presence and abundance of each group facilitating the presence and abundance of others by changing the local community structure and resource base. This was shown in a study following Cyclone Firinga in 1989. Before the cyclone, large colonies of Acropora nturicata, dominated the coral zone. forming with Porites lobota. Po~~otia divaricate and large tables of Acropora cytherea, a coral community of 30-40% coverage with relatively low diversity. Immediately after the cyclone, only 2 coral species survived. but the growth rate of living coral later exceeded its previous maximum due to the low tendency for competition for space, reaching more than 6% per year. By 2000. the coral richness on St-Leu (51 species) was comparable to that recorded 20 years earlier. For fish. total species richness and the mean species number 1 census slightly increased between 1993 and 2000, but there were important differences among sites and times that were mainly due to change in individual numbers inside the territories of the damselfish Slegastes trigricans, which in turn were linked to the changing coral and algal cover. Variations in fish density were related to variation of benthic cover ,including corallivorous Chaetodontidae. that useful as bioindicators of coral reef health.

The article highlights a workshop held in Key West, Florida in November 1993 attended by a group of 35 international scientists where topics of ecosystem function and biodiversity on coral reefs were discussed.