THE FORAM INDEX: A SINGLE-METRIC INDICATOR OF COASTAL AND REEF WATER QUALITY

The FoRAM Index (FI) was proposed in 2003 as a single-metric indicator of whether water quality can support recruitment and proliferation of calcifying, photosynthesizing holobionts, including reef-building corals. The rationale for a non-coral indicator was based on observations that adult coral colonies tolerate environmental conditions that no longer support recruitment as revealed by failure of coral populations to recover after mortality events. The FoRAM Index utilizes assemblages of foraminiferal shells in sediment samples. Where all shells are from small, heterotrophic taxa (FI < 2), that indicates that nutrient dynamics favor autotrophic and heterotrophic organisms over calcifying symbioses. Shells of larger foraminifers that host algal symbionts raise the FI; at >25% larger taxa, FI>4; at 100% larger taxa, FI=10. Smaller taxa are further distinguished as “stress-tolerant” or “other”. Prevalence of stress-tolerant taxa (FI<2) typically indicates high biological oxygen demand or other stressors. Although proposed for western Atlantic-Caribbean reefs, the FI has now been used as a coastal water-quality indicator in Puerto Rico, Florida, Brazil, Pacific Islands, Australia, and Greece. The FI has been incorporated into methods used to monitor water quality along the Great Barrier Reef of Australia. However, where larger foraminifers have historically been major sediment producers, relict shells can be abundant where these taxa no longer live, so care must be taken in interpreting samples. Another shortcoming is that identification to genus is time consuming. Because symbiont-bearing Amphistegina are easy to identify and are reliably sensitive to nutrification, while Ammonia are ubiquitous stress-tolerant forms, a modified index, based on proportions of Amphistegina, Ammonia, and all other taxa, might be as useful as the currently defined FI in many applications.