Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef

• Published in: Coral reefs Vol. 27; no. 4; pp. 887 - 903
• Main Authors: Jupiter, S., Roff, G., Marion, G., Henderson, M., Schrameyer, V., McCulloch, M., Hoegh-Guldberg, O.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.12.2008; Springer; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Barrier reefs; Biological and medical sciences; Biomedical and Life Sciences; Cnidaria. Ctenaria; Community composition; Community structure; Coral reefs; Environmental conditions; Environmental gradient; Environmental stress; Exposure; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; Invertebrates; Isotopes; Life Sciences; Luminescence; Marine; Marine biology; Marine ecology; Nitrogen; Nutrient availability; Oceanography; Porites; Reef formation; River discharge; River flow; Sea water ecosystems; Synecology; Australia; Oceania; Great Barrier Reef; ISEW, Australia, Queensland, Mackay; ISEW, Australia, Queensland, Great Barrier Reef; Barium; Disturbance frequency; Coral assemblage; Luminescence; Nitrogen isotope; Terrestrial environment; Coral reef; Perturbation; Nitrogen; Coelenterata; Coral; Cnidaria; Porites; Invertebrata; Isotopes; Community; Great Barrier Reef
• ISSN: 0722-4028; 1432-0975
• DOI: 10.1007/s00338-008-0422-3

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, δ 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 (≤10%), with no significant differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 μmol 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 δ 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.