Coral core records, combined with measurements of coral community structure, were used to assess the long-term impact of multiple environmental stressors on reef assemblages along an environmental gradient. Multiple proxies (luminescent lines, Ba/Ca, d 15 N) that reflect different environmental conditions (freshwater discharge, sediment delivery to the nearshore, nutrient availability and transformations) were measured in Porites coral cores collected from nearshore reefs at increasing distance from the intensively agricultural region of Mackay (Queensland, Australia). The corals provide a record (1968-2002) of the frequency and intensity of exposure to terrestrial runoff and fertilizer-derived nitrogen and were used to assess how the present-day coral community composition may have been influenced by flood-related disturbance. Reefs closest to the mainland (5-32 km offshore) were characterized by low hard coral cover (B10%), with no significant differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 lmol mol-1 ; mean ± SD) in the most inshore corals (Round Top Island; 5 km offshore) indicated chronic, sub-annual exposure to freshwater and resuspended terrestrial sediment that may have historically prevented reef formation. By contrast, corals from Keswick Island (32 km offshore) indicated episodic, high-magnitude exposure to Pioneer River discharge during extreme flood events (e.g., 1974, 1991), with strongly luminescent lines and substantially enriched coral skeletal d 15 N (12-14%). The reef assemblages at Keswick and St. Bees islands were categorically different from all other locations, with high fleshy macroalgal cover (80.1 ± 7.2% and 62.7 ± 7.1%, respective mean ± SE) overgrowing dead reef matrix. Coral records from Scawfell Island (51 km offshore) indicated little exposure to Pioneer catchment influence: all locations from Scawfell and further offshore had total hard and soft coral cover comparable to largely undisturbed nearshore to middle shelf reefs of the southern Great Barrier Reef.

A ciliate associated with the coral disease brown band (BrB) was identified as a new species belonging to the class Oligohymenophorea, subclass Scuticociliatia. The ciliates were characterized by the presence of large numbers of intracellular dinoflagellates and displayed an elongated, tube-shaped body structure. They had uniform ciliature, except for three distinct cilia in the caudal region, and were typically 200 to 400 m in length and 20 to 50 m in width.

Increasing episodes of mass coral bleaching and a growing number of reports of coral disease epizootics have led to an expanding research field investigating the microbial ecology of reef building corals. Corals reside in a complex ecosystem and form intimate symbiotic relationships with eukaryotic dinoflagellates (commonly called zooxanthellae), which have been well studied. Less understood is the complex interactions that corals form with Bacteria, Archaea and viruses, all of which play an important functional role in coral health. Understanding how the coral animal and its symbiotic partners (eukaryotic, bacterial, archeal and viral) are influenced by environmental perturbations such as global climate change, rising sea surface temperatures and increasing anthropogenic inputs into the ecosystem such as nutrients, is the driving factor behind this expanding microbial discipline.