Paracalanus quasimodo and Temora turbinata are two calanoid copepods prominent in the planktonic communities of the southeastern United States. Despite their prominence, the species and population level structure of these copepods is yet unexplored. The phylogeographic, temporal and phylogenetic structure of P. quasimodo and T. turbinata are examined in my study. Samples were collected from ten sites along the Gulf of Mexico and Florida peninsular coasts. Three sites were sampled quarterly for two years. Individuals were screened for unique ITS-1 sequences with denaturing gradient gel electrophoresis. Unique variants were sequenced at the nuclear ITS-1 and mitochondrial COI loci. Sampling sites were analyzed for pairwise community differences and for variances between geographic and temporal groupings. Genetic variants were analyzed for phylogenetic and coalescent topology. Paracalanus quasimodo is highly structured geographically with populations divided between the Gulf of Mexico, temperate Atlantic and subtropical Atlantic, in addition to isolation by distance. No significant differences were detected between the T. turbinata samples. Both P. quasimodo and T. turbinata are stable within sites over time and between sites within a sampling period, with two exceptions. The first was a pilot sample from Miami taken two years prior to the general sampling whose community showed significant differences from most of the other Miami samples. Paracalanus quasimodo had a positive correlation of Fst with time. The second was high temporal variability detected in the samples from Fort Pierce. Phylogenetically, both P. quasimodo and T. turbinata were in well supported, congeneric clades. Paracalanus quasimodo was not monophyletic, divided into two well-supported clades. Temora turbinata variants were in one clade with insignificant support for topology within the clade and very little intraspecific variation. Paracalanus quasimodo and T. turbinata populations show opposite trends. Paracalanus quasimodo occurs near shore and shows population structure mediated by hydrological features and distance, both geographic and temporal. The phylogeny shows two deeply divergent clades suggestive of cryptic speciation. In contrast, T. turbinata populations range further offshore and show little geographic or temporal structure. However, the low genetic variation detected in this region suggests a recent bottleneck event.

Blooms of the toxic dinoflagellate Karenia brevis are common on the West Florida Shelf (WFS), yet little is known of the relationships between zooplankton and K. brevis. A comprehensive analysis was undertaken to examine 1) perturbations in zooplankton community composition within K. brevis blooms 2) the contribution of zooplankton ammonium and phosphate excretion to K. brevis bloom nutrient requirements, and 3) the role of zooplankton grazing in K. brevis bloom termination. Prior to undertaking the first portion of the study, an examination of the perturbations in the normal zooplankton assemblage within K. brevis blooms, it was first necessary to define the normal zooplankton assemblage on the WFS. To this end, a seasonal analysis of abundance, biomass and community composition of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50- m isobaths. Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) stations. Considerable overlap was seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but little overlap in community composition was observed between the 5-m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (>90%) contributors to community composition. Near shore, important contributors were Parvocalanus crassirostris, Penilia avirostris, Paracalanus quasimodo, Oithona colcarva, Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, important contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus, Oithona plumifera, Oithona frigida, Oncaea mediteranea, Calaocalanus pavoninius, Oithona similis, and Gastropod larvae. Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduction in abundance of 3 key species within K. brevis blooms. One potential source of nutrients to support K. brevis blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods (Labidocera aestiva, Acartia tonsa, Temora turbinata, and Paracalanus quasimodo) were measured and prorated to a 24-hour day. These excretion rates were then extrapolated to other West Florida Shelf zooplankton, combined with available literature excretion rates for some taxa, and applied to zooplankton abundances found for K. brevis blooms on the West Florida Shelf in 1999 and 2001. Ammonium excretion rates were found to be inadequate to support all but 104 cells l-1 of K. brevis, though phosphate excretion rates were adequate to support even 106 cells l-1 of K. brevis. Grazing assessment was conducted for three common zooplankton species that were found within two K. brevis blooms, A. tonsa, P. quasimodo, and L. aestiva, using 14C labeled K. brevis cells. Grazing rates were then applied to the zooplankton community and grazing assessed. Grazing pressure was occasionally heavy, and was capable of reducing K. brevis to background concentrations at stations in the 1999 bloom and at 1 station in the 2001 bloom. Generally, however, grazing pressure proved to be insufficient to reduce K. brevis to background concentrations during the 1999 and 2001 blooms.