Graduation Year

2019

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Pamela Hallock Muller, Ph.D.

Committee Member

Susan Bell, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Keywords

Archaias angulatus, bioindicator, Distribution, Miliolida, refugia

Abstract

Florida’s Springs Coast, located in the northeast Gulf of Mexico, includes an extensive system of salt marshes that discharge millions of liters of fresh water into coastal waters daily. The chemical properties of the spring waters include high alkalinity and high calcium concentrations due to the Paleogene limestone lithology of this region of Florida. Benthic foraminifers, which are recognized as ecologically important bioindicators, occur abundantly on the shallow shelf off the Springs Coast. Based on the prevalence of the benthic foraminifer Archaias angulatus in the seagrass beds along this shallow shelf, a previous study proposed that the Springs Coast provides favorable conditions for such “subtropical” calcifying organisms, despite existing literature indicating that salinities and winter temperatures are suboptimal for such species. Thus, a motivation for my study was to provide insight into the hypothesis that, during times of ocean acidification, limestone lithofacies may provide suitable water chemistry and physical habitat to provide refuges for calcifying organisms.

Selected environmental parameters and sediments from 41 sites at depths <8 m were sampled in September 2013, during routine seagrass monitoring by researchers from the Florida Fish and Wildlife Research Institute. The 152 benthic foraminiferal species identified included 71 porcelaneous, 67 hyaline, and 14 agglutinated species. Overall, 74% of the specimens identified were porcelaneous and most of the remainder were hyaline; agglutinates composed <1% of those counted. Species dominance in samples revealed an apparent distribution reversal compared to previous reports from Gulf of Mexico coastal habitats. Smaller miliolids, notably Quinqueloculina spp., dominated in samples from most of the inshore brackish sites. In contrast, at the more offshore sites characterized by normal marine salinities, hyaline taxa such as Haynesina spp. were much more abundant. We postulate that these unusual distributions are associated with the calcium and carbonate chemistry of the brackish waters. The salinity threshold for small miliolids appeared to be lowered by the carbonate saturation state (Ω).

Although 152 species were identified, only 13 species accounted for 56% of the specimens counted. The high diversity coupled with low abundances of most species may indicate the influence of foraminiferal propagule dispersal. The seasonal range of environmental conditions and the diversity of habitats available within the seagrass may allow a diverse array of propagules to recruit and grow at suitable times during the year, while not necessarily establishing sustained populations.

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