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Abstract AN OVERVIEW OF SYMBIONT-BLEACHING IN EPIPHYTIC FORAMINIFERANS Susan L. Richardson Sorites dominicensis is a disk-shaped foraminiferan that
lives attached to phytal substrates in tropical to subtropical,
shallow-water habitats. This species harbors dinoflagellate endosymbionts
(Symbiodinium sp.) that are closely related to the zooxanthellae
in corals and other cnidarians. Symbiont bleaching has been observed
in field populations of S. dominicensis collected from
turtle grass (Thalassia testudinum) meadows in the Florida
Keys, the Indian River Lagoon, Florida, and Belize. The degree of
bleaching for each specimen is assessed using a relative scale:
healthy, pale, mottled, or white. Healthy individuals possess a
distinct yellowish-brown coloration to their cytoplasm. Pale individuals
possess a light, yellowish coloration to their cytoplasm. In both
healthy and pale individuals, cytoplasmic coloration is evenly distributed
throughout the foraminiferal test. Mottled specimens possess large
patches of white cytoplasm interspersed with regions of healthy
cytoplasm. Individuals are recorded as being totally bleached if
they possess completely white tests. Field studies involve surveying
several hundred individuals (~500) from each population, or collecting
site, and recording the incidence of bleaching. Bleaching rates
vary from 0.3-19%, with the lowest rates of bleaching to date observed
in populations living in the tannin-stained waters of Boston Bay,
within the mangrove islands of Twin Cays in Belize (7/07). The highest
rates of bleaching to date were observed in the same population,
a few days later after a period of intense rainfall. High rates
of bleaching (18%) were observed in July 2005, in populations living
on the reef flat off Carrie Bow Cay, a site that experiences subaerial
exposure during extreme low spring tides, and water temperatures
as high as 40 ºC. Other environmental factors that appear to
trigger bleaching in foraminiferans include: increased irradiance,
exposure to UV and blue wavelengths of light, freshwater influx,
and periodic disturbance by hurricanes.
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