Oreaster reticulatus was studied in eight populations inhabiting shallow-water grassbeds and/or sand bottoms off Carriacou and Union Island in the Grenadines, and off St. Croix in the U.S. Virgin Islands (Caribbean). The sea star is fundamentally an omnivorous, microphagous substratum grazer: grassblades and/or surface sediments are accumulated beneath the disc by tube feet, and associated micro-organisms and detritus are ingested and digested by extraoral eversion of the cardiac stomach. Substratum grazing involves minimal foraging effort; however, the low concentration of particulate food resources necessitates frequent feeding. O. reticulatus also has a limited capacity for herbivory and can hydrolyze soluble algal cell contents. Opportunistic predation and scavenging of macrofauna may provide an important nutritional supplement, although capturable prey or carrion are generally unavailable or inaccessible to the sea star. Marked differences in individual size, storage and reproductive capacity among neighboring populations of O. reticulatus are attributed to differences in the quality and/or quantity of food resources. Intraspecific competition may limit productivity, particularly in isolated sand patches containing dense and extremely aggregated populations.

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I studied the behaviour and ecology of social organization in a Caribbean surgeonfish, the blue tang (Acanthurus coeruleus). In chapter 1,1 identify and describe the social modes exhibited by adult blue tangs and include the first description of adult territoriality in this species. Adults in the population were either territorial or nonterritorial. Non-territorial fish formed schools and wandered, while territorial fish never schooled but sometimes wandered from their territory. In chapter 2,1 explore potential determinants of the variation in the social organization in an attempt to explain the coexistence of the territorial and non-territorial modes. I examine the distribution of territorial, schooling and wandering tangs in relation to life history stage, habitat, time of day, competitor density, food abundance and population density. Life history stage, density of competitor damselfishes and conspecific population density appear to be key determinants of this social organization.

Foraminiferal faunas across the early to middle Eocene transition (EMET) were studied from three locations in the western Caribbean: Calle G section in Cuba, ODP site 998 B the Cayman Rise, and ODP site 999 B the Colombian basin. There were three primary objectives of this project 1) to observe changes in physical and biological paleoceanographic parameters in the Western Caribbean, more directly in the Cayman Ridge and the Colombian Basin, by the use of planktonic foraminifera data, 2) determine the cause of an oxygen isotope anomaly seen in Cuba by Fluegeman (2007) and that is expected to be present in the Western Caribbean, and 3) determine if the anomaly is a local or a more widespread regional event. The Calle G section in northwestern Cuba consists of early to middle Eocene age foraminiferal chalks. The planktonic foraminiferal fauna at this section is characterized by subbotinids and acarininids but does not contain morozovellids. Oxygen isotopes were obtained across the EMET from the planktonic foraminiferan Acarinina collactea. The resultant curve shows widely fluctuating values during the early portion of the EMET with more stable values occurring in the middle Eocene. The foraminiferal paleoecologic index tau curve at the Calle G section produced is similar to the oxygen isotope curve. ODP site 998 B, Cayman Rise, contains a series of foraminiferal limestones across the EMET. Unlike the Calle G section, this interval contains an abundant planktonic foraminifera fauna including Morozovella. The Morozovella:Acarinina ratio studied at ODP site 998 shows high, fluctuating values in the early part of the EMET with low, stable values during the middle Eocene.ODP site 999 B in the Colombian Basin consists of a series of foraminiferal chalks throughout the EMET. Similar to ODP site 998 this location also has an abundant assemblage of planktonic foraminifera including Morozovella. Evidence supporting turbidities have been observed at this locale as layers of shell hash and large benthic foraminifera. The Morozovella:Acarinina ratio studied at ODP site 999 is similar to that of ODP site 998 showing a high fluctuating values in the early part of the EMET with low, stable values in the middle Eocene. The presence of fluctuating values of oxygen isotopes, tau, and the Morozovella:Acarinina ratio followed by stable values across the EMET may be related to a change in circulation patterns through the Caribbean caused by a developing oceanic gateway. The widely fluctuating oxygen isotope values in the latest Ypresian may also be related to an influx of freshwater in the North Atlantic associated with the coeval Azolla event in the Arctic Ocean. / Department of Geological Sciences

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