The focus of my thesis research is on the interplay between individual behavior, population dynamics and community-level processes within zooplankton communities in coastal Maine. The target organisms of my thesis work are marine copepods. Copepods are small (1-10 mm) crustaceans that perform the essential ecosystem function of consuming and assimilating primary production (phytoplankton) making it available to higher trophic levels such as commercially important fishes. Therefore, copepod population growth is of critical importance to marine food webs. Fertilization limitation has been suggested as a constraint on copepod population growth but field surveys describing the prevalence of fertilization limitation are lacking. During my doctoral research, I explored the in situ fertilization success of two marine copepod species, Temora longicornis and Eurytemora herdmani in coastal Maine. I collected monthly zooplankton samples and analyzed clutches from field-caught females using an egg-staining technique. My results indicate that both species exhibit fertilization limitation in nature and the factors correlated with their fertilization span population, community and ecosystem level factors. To determine a causal relationship between predator density and copepod mating success, I conducted laboratory experiments to assess the effects of a common mysid shrimp predator, Neomysis americana on Eurytemora herdmani mating success. I subjected males and females to predators or predator cues. I found that the presence of a mysid predator, or only a predator cue, reduced copulation frequency and spermatophore transfer leading to a 38-61% decrease in E. herdmani nauplii production. These results suggest that mysid predators can constrain copepod population growth through non-consumptive processes. To determine the effects that resources can impose on copepod behavior, I explored the behavioral and fitness consequences of Temora longicornis ingesting Alexandrium fundyense, a phytoplankton species that forms harmful algal blooms in coastal Maine. My results suggest that ingesting A. fundyense causes copepods to swim faster and with more directional persistence compared to control algae. Temora longicornis increased their average swimming velocity by 24%, which leads to a 24-54% increase in their theoretical encounter rate with predators. Therefore, these findings suggest behaviorally mediated copepod-algal interactions may have significant impacts on harmful algal bloom dynamics and the fate of toxins in marine food webs.

Orientador: Tânia Márcia Costa / Resumo: As características granulométricas do sedimento têm sido relatadas como um dos principais fatores determinantes na distribuição dos caranguejos nos manguezais. Os caranguejos chama-marés são importantes representantes por estarem amplamente distribuídos em diferentes frações granulométricas ao longo do estuário e várias espécies serem encontradas coexistindo em um mesmo local, competindo por alimento e espaço. Esse estudo teve como objetivo avaliar a escolha de caranguejos chama-maré por sedimentos com diferentes granulometrias, usando como organismo modelo Leptuca uruguayensis. Em laboratório, terrários com e sem escolhas foram utilizados para avaliar a escolha de caranguejos por três diferentes frações granulométricas (fina, média e grossa). Foram avaliadas a alimentação, o número de tocas escavadas em cada compartimento, se o animal mudou sua escolha ao longo do tempo e se a escolha foi influenciada pela posição em que o animal era solto. Leptuca uruguayensis escolheu o sedimento fino para se alimentar. O consumo de matéria orgânica foi maior no compartimento escolhido para escavar sua toca, do que nos demais, independente do tratamento e dos compartimentos. Os caranguejos construíram apenas uma toca por terrário e escolheram os compartimentos com frações finas para escavar suas tocas. Nossos resultados evidenciam que L. uruguayensis escolhe ativamente sedimento com frações granulométricas menores para forrageamento e escavação de suas tocas / Abstract: The sediment granulometric characteristics have been reported as one of the determining factors in the distribution of mangrove crabs. The fiddler crabs are important representatives because they are widely distributed in different granulometric fractions along the estuary and several species are found coexisting and competing for food and space. The purpose of this study was to evaluate the choice of fiddler crabs for sediments with different grain sizes using Leptuca uruguayensis as our model species. In the laboratory, terrariums with and without choices were used to evaluate the choice of crabs for three different granulometric fractions (fine, medium and coarse). We evaluated the feeding behavior, number of burrows excavated in each compartment, whether the animal changed its choice over time and whether the choice was influenced by the position in which animal was released. Leptuca uruguayensis chose finer sediments when feeding. The organic matter consumption was higher in compartments where they excavate their burrows regardless the treatment and compartments. The fiddler crabs built only one burrows per terrarium and also chose compartments with fine fractions to excavate their burrows. Our results showed that L. uruguayensis actively select sediments with smaller particle sizes when foraging and also to excavate their burrows / Mestre