The processes influencing larval fish survival in the low-latitude open ocean are poorly understood, especially with regard to feeding. As part of a large-scale study that included two years of monthly sampling in the Straits of Florida (SOF), the objectives of this dissertation were to elucidate the larval fish feeding behaviors and strategies of 1) istiophorid billfishes, 2) tunas, and 3) coral reef fishes, while also 4) characterizing the feeding environment, synthesizing the dominant trophic pathways to fish larvae, and reviewing the literature for evidence of latitudinal distinctions in larval fish trophodynamics. Larval billfishes exhibited highly selective feeding, and their diets were numerically dominated (90%) by two genera of crustaceans, Farranula copepods and Evadne cladocerans. These prey were consumed throughout early larval ontogeny, from first-feeding through piscivorous lengths (> 5 mm), until piscivory became exclusive near 12 mm. High feeding incidence (0.94) and rapid digestion (~3.5 hrs) suggests frequent and successful feeding by billfish larvae. For tunas, nearly all larvae examined (>98%) contained prey. Thunnus spp. exhibited a mixed diet, while skipjack, little tunny, and Auxis spp. nearly exclusively consumed appendicularians. All four tuna taxa co-occurred in the western SOF where prey was more abundant, while in the central and eastern SOF (where prey availability was lower), only Thunnus spp. and skipjack were present. Additionally, these two taxa exhibited significantly different vertical distributions. Estimates of predatory impact indicated the potential for depletion of resources in the absence of the spatial and dietary niches of larval tunas. Coral reef fish families examined included Serranidae, Lutjanidae, Mullidae, Pomacentridae, Labridae, Scaridae, and Acanthuridae. Feeding incidences were high (0.94 to 1.0) for all taxa except scarids (0.04), and diets were narrow and predator-specific. Cluster analysis yielded clear groupings based on the selective feeding exhibited by the taxa, while within taxa, canonical correspondence analysis illustrated the change in diet with a variety of variables. The physical and biological environment varied markedly across the SOF, largely influenced by the Florida Current. Characteristics examined included thermocline depth, fluorescence, and abundances of total plankton and copepod nauplii. The feeding ecologies of the 21 taxa of fish larvae in this work were synthesized into qualitative and quantitative webs that illustrate the variable trophodynamic strategies of larvae in the SOF and the levels of community reliance upon zooplankton prey types. A review of 170 investigations on larval fish feeding revealed notable distinctions between high- and low-latitude regions, highlighting the substantial variability across environments in the role of larval fishes within the planktonic food web.

The ecological impact of past extinction events is one of the central issues in paleobiology. In face of present environmental changes, a better understanding of past extinctions will enable us to identify the magnitude of biodiversity crises and their underlying processes. The Late Neogene was a time of extraordinary climatic reorganization, including Northern Hemisphere glaciation, the rise of the Central American Isthmus, and associated changes in environmental conditions. Therefore, the Late Neogene extinctions of marine molluscs of South Florida present an ideal platform to examine the interaction between environmental changes and biotic response. In the present study, three different aspects of the Late Neogene extinctions are examined: temporal diversity patterns, selectivity patterns, and the impacts of these extinction events on ecological interactions. In the first part of this study, the diversity pattern of marine bivalves of Florida during the Late Neogene. Using bulk samples enables to take account of varying sampling intensity and underlying relative abundance distributions in diversity estimation. Comparison of sample-standardized diversity analyses shows that both richness and evenness of marine bivalve community declined at the Tamiami - Caloosahatchee transition, which coincides with the proposed first phase of the Late Neogene extinctions at the end of the Pliocene. Although magnitude of biodiversity loss was severe during these late Neogene extinction events, extinction risk was non-randomly distributed across taxa. Selectivity analyses, a combination of both commonly used non-parametric tests and logistic regressions, suggest that abundance or local population size was positively related with survivorship during the late Neogene. As other biological or ecological traits can influence this observed relation between abundance and extinction vulnerability, multivariate approach is used to control for these traits. Even after effects of geographic range and feeding mode is considered, the positive relation between abundance and survivorship, which supports predictions from biological studies, is evident in case of these Late Neogene extinction events. While present analyses show that the increase in relative abundance of Chione is a major factor in driving changes in community compositions, interactions between Chione and its' drilling predators also varied during the Late Neogene. This study suggests that identification of predators is a critical part of evaluation of prey-predator interactions. When drill hole traces of two predatory gastropod groups, muricids and naticids, are differentiated based on a revised site selectivity criteria, temporal trend of prey size selectivity differs from previous reports. Both groups exhibit some changes in predatory behavior during phases of the Late Neogene extinctions, suggesting that previous hypothesis of prey turnover at the Caloosahatchee - Bermont transition cannot explain the observed temporal trends of prey size selectivity in the present study.

Blue Catfish Ictalurus furcatus are native to tributaries of the Mississippi River but are now invasive in several Atlantic slope drainages. This includes subestuaries of the Chesapeake Bay, where their feeding ecology and potential impact on native species was largely unknown. We collected stomach contents from 16,110 Blue Catfish at 698 sites in three large subestuaries of the Chesapeake Bay (James, York, Rappahannock rivers). Cumulative prey curves revealed that sample size was sufficient for diet description, though 1,000 – 1500 stomachs were needed per river. Blue Catfish are opportunistic generalists that feed on a broad array of plant and animal material. Logistic regression models reveal that Blue Catfish undergo significant ontogenetic diet shifts to piscivory at larger sizes (P<0.01) though the lengths at which these shifts occur varies by river system (500 – 900 mm total length; TL). Over 60% of Blue Catfish stomachs contained other invasive species, primarily Hydrilla verticillata and Asian clams Corbicula fluminea. Canonical Correspondence Analysis (CCA) revealed that salinity and season explained the most variation in Blue Catfish diet, while Generalized Additive Models (GAMs) demonstrated that there is considerable spatiotemporal and length-based variation in predation of species of concern. Species of concern include American Shad, American Eel, and river herring, which are imperiled, and blue crab, which support valuable fisheries in Chesapeake Bay. Predation of American Shad, American Eel, and river herring was rare (max predicted occurrence in Blue Catfish diets = 8%), while blue crab was much more common in the diet (max predicted occurrence =28%). Predation of American Shad and river herring peaks in freshwater areas in April, while predation of blue crab peaks in brackish areas in October. Predation of all species of concern is highest for large catfish (500 – 1000 mm TL). Field and laboratory-based estimates of consumption rate revealed that Blue Catfish feed at similar rates as Channel Catfish Ictalurus punctatus, and daily ration is estimated to be 2-5% bodyweight per day during warm temperatures, while peak feeding (maximum daily ration) can approach 10% bodyweight per day. While consumption of imperiled species is rare, Blue Catfish could still have negative impacts on these species due to dense catfish populations. / Ph. D.