OCCURRENCE OF SHALLOW WATER BENTHIC FORAMINIFERA ON AN EASTERN INDIAN OCEAN REEF: MENTAWAI ISLANDS, WEST SUMATRA, INDONESIA

Relationships between community composition and environmental variables must be recognized in order to interpret changing patterns in marine biodiversity. Foraminifera are widely utilized as bioindicators of short and long-term environmental change due to their abundance, diversity, and robust geologic record. The Coral Triangle region contains highly diverse foraminiferal assemblages, however, studies from the Eastern Indian Ocean are scarce. This study discusses the occurrence and distribution of shallow water benthic foraminifera from Pulau Karangmanjat (P. Karangmanjat), Mentawai Islands, Indonesia. P. Karangmanjat hosts an array of coastal environments, is relatively secluded from local anthropogenic stressors, and its modern sedimentary record is void of evidence of uplift or tsunami deposition, making it an ideal site for foraminiferal analysis.

A total of 21 species of foraminifera were identified from 13 shallow water sites characterizing a range of habitat and hydrodynamic conditions. Amphistegina spp. were abundant in shallow, low energy lagoons and near seagrass beds, and were absent from reefs exposed to strong, continual wave action. Neorotalia calcar, Pararotalia stellata, and Calcarina spp. were abundant at all sites representing 40-95% of total foraminiferal composition. Sites with strong macro-algal cover were composed of >80% N. calcar and related species. Reef crest and reef flat environments showed highest overall foraminiferal density as well as high percent composition of N. calcar. Abundance of N. calcar and related species may be indicative of a shift from a coral to macro-algal regime. This is likely a repercussion of coral mass mortality following recent IOD events and/or the result of local pressures exerted on this ecosystem. If the latter is true, the magnitude of a macro-algal regime is likely to intensify toward greater population densities, resulting in reduced biodiversity. This study provides the first dataset of shallow water foraminiferal assemblages for the region as well as baseline data for monitoring of spatial and temporal environmental trends utilizing benthic foraminifera. Further analysis of foraminiferal assemblages within this region of the Coral Triangle will aid in defining spatial patterns of marine biodiversity in the present, past and future.