Graduation Year


Document Type




Degree Granting Department

Marine Science

Major Professor

Pamela Hallock


Benthic communities, Concentration ratio, coral reef, environmental indicators, FORAM Index



Foraminiferal Assemblages on Sediments and Reef Rubble

at Conch Reef, Florida USA

Christy Stephenson

Benthic foraminiferal assemblages are widely used to interpret responses of the benthic communities to environmental stresses. This study compares epibiotic foraminiferal assemblages, collected from reef rubble, with those from reef sediments. The study site, Conch Reef, is the site of the Aquarius Underwater Habitat research facility and includes protected areas used only for scientific studies. Although a number of studies have enumerated foraminiferal taxa from the Florida reef tract, no projects have focused on the assemblages that occur at Conch Reef.

Sediment and reef rubbles samples were collected via SCUBA from a depth range of 13 to 26 m during October 2008. Foraminiferal assemblages were assessed and compared between the two sample types. A total of 117 foraminiferal species, representing 72 genera, 37 families, and 8 orders were identified in 13 sediment samples and 21 rubble samples.

In the rubble samples, 70 genera were identified, including 12 symbiont-bearing genera representing 20% of the total assemblage, 12 stress-tolerant genera representing 6%, planktic foraminifers representing 1%, and 46 other smaller foraminiferal genera representing 73% of the total foraminiferal assemblage. The rubble samples were quite homogenous. The mean (+SD) Fisher alpha α diversity of genera in these samples was 12.9 + 1.4.

Sediment samples included 60 of the same genera. The 12 symbiont-bearing genera represented 41% of the total assemblage, 10 stress-tolerant genera represented 3%, planktic taxa represented 2%, and 40 other smaller foraminiferal genera represented 54% of the total assemblage. Overall, the taxonomic assemblages were very similar between the sample types, with sediment assemblages clearly representing the local and regional reef foraminiferal assemblage. The mean (+SD) Fisher alpha α for sediment samples was 11.4 + 2.3, which is not significantly different from that found for the rubble samples.

A concentration ratio comparing relative abundances in sediment vs. rubble samples revealed that shells of larger, symbiont-bearing taxa were about 2.5-5.5 times more concentrated in the sediment, indicating winnowing of smaller taxa. Shells of Siphonatera, an agglutinated miliolid, and Textularia, an agglutinated textularid, were more abundant in sediments than in rubble, indicating high preservation potential. The concentration ratio provides a new taphonomic index that reflects the size and durability of foraminiferal taxa.

The mean FORAM Index (FI) for the sediment samples (5.57 + 0.83) indicates that water quality at Conch Reef is suitable for calcifying symbioses. The most abundant symbiont-bearing genera were Amphistegina, Laevipeneroplis, Asterigerina, and Archaias.