The FoRAM Index Revisited: Uses, Challenges, and Limitations

The FoRAM Index (FI) was proposed as a foraminiferal-based indicator to distinguish whether water quality supports recruitment and proliferation of calcifying, photosynthesizing holobionts. 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 shells from small, heterotrophic taxa overwhelmingly dominate (FI ~2), environmental conditions favor autotrophic and heterotrophic organisms over calcifying symbioses. Shells of larger foraminifers that host algal symbionts raise the FI; for example, when shells of larger taxa make up \u3e25% of the foraminiferal assemblage, the FI will be \u3e4. Where 100% of the shells are those of larger taxa, FI = 10. Smaller taxa are further distinguished as “stresstolerant” or “other”. Prevalence of stress-tolerant taxa (FI \u3c2) typically indicates high biological oxygen demand, euryhaline conditions, or other stressors. Although proposed for western Atlantic-Caribbean reefs, the FI has been used as a coastal water-quality indicator in Puerto Rico, Florida, Brazil, Pacific Islands, Australia, and Greece. However, the FI may not be useful in Indonesia where large Calcarinidae thrive in mesotrophic waters. Moreover, where larger foraminifers have historically been major sediment producers, relict shells can be abundant where these taxa no longer live. The recommended depth range for collection of samples for FI analysis is approximately 3-15 m as shallower sediments may be too wave worked and deeper sediments tend to accumulate finer sediments including shells of smaller heterotrophic foraminifers