A specimen of diatom-bearing foram ( Calcarina sp.) in its natural habitat. Image: Sven Uthicke.

Current discussions about coral reef decline focus mainly on global disturbances such as increasing sea temperatures and ocean acidification. However, the impacts of local and regional stressors such as land runoff continue to affect reef health, and management of local stressors will improve reef resilience.

Research by AIMS ecologists has assessed whether foraminifera (forams) can be used as biological indicators for changes in water and sediment quality on inshore reefs of the Great Barrier Reef. Forams are single-celled marine organisms with calcareous shells full of tiny holes through which slender filaments project. Biological indicators have clear advantages over directly measuring water quality to assess the effects of changes in water quality on reef health.

Foram communities differed between the four geographic regions studied in the GBR, from Cairns to Rockhampton. Within these regions, environmental variables such as sediment grain size and organic carbon and nitrogen content, and water turbidity and particulate matter, explained most of these differences.

The organisms mainly separated into assemblages dominated by species with no symbionts (heterotrophic), mainly found in sediments with high organic content and in low light availability, and assemblages of species with algal symbionts. The latter occurred mostly in sediments with low organic content and high light availability.

This pattern is also reflected in the FORAM index (a Caribbean coral reef health indicator), which is based on the ratio of heterotrophic to symbiont-bearing species. This work showed that foram composition is a good bio-indicator for environmental conditions on coral reefs, specifically those related to inputs from land runoff.

Assessments of foram composition are now part of the Reef Rescue Marine Monitoring Program, to measure long-term improvement in the condition of water quality in the inshore GBR lagoon and marine ecosystem health (inshore coral reefs and intertidal seagrasses) with the adoption of improved land management practices in the Great Barrier Reef catchment.