Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem

Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank

Ultraviolet-B radiation enhancement does not affect marine trophic levels during a winter-spring bloom

Elevated UV-B radiation levels (∼100% above ambient) generally failed to produce significantly different effects at different trophic levels in well-mixed mesocosms during the winter spring bloom period. Although not significantly different, several consistent trends were noted. Phytoplankton abundance, measured as total cell counts, and biomass, measured as in vivo fluorescence, tended to be reduced in UV-B enhanced treatments. Effects were significantly different for fluorescence (p \u3c 0.05) during the bloom event but not abundance (p = 0.29) and not over the entire experiment. There was a tendency for the ratio of nanoplankton to microplankton biomass to be lower in UV-B enhanced systems (p = 0.16). Total copepod abundance (adults, copepodites and nauplii) and abundance of the dominant species, Acartia hudsonica (Giesbrecht), also tended to be lower in the treatment mesocosms. Significant differences (p \u3c 0.05) in copepod abundance between controls and treatments were observed in the adult stage prior to and during the bloom event. Survival of winter flounder (Pleuronectes americanus [Walbaum]) eggs incubated at 0.1 and 0.5 m depths was significantly lower in UV-B elevated mesocosms (p \u3c 0.05) while no significant differences were observed at greater depths (p = 0.55). Survival and growth of winter flounder larvae added to the mesocosms during the final three weeks of the experiment did not vary significantly between controls and treatment mesocosms

Spatiotemporal patterns in early life stage winter flounder Pseudopleuronectes americanus highlight phenology changes and habitat dependencies

Decadal changes in the life history events of marine species are becoming increasingly important to identify under a warming climate, yet many long-term monitoring programs do not collect data at the spatiotemporal resolution needed to describe them. Such data are vital for understanding the southern New England/Mid-Atlantic winter flounder Pseudopleuronectes americanus stock, a species hypothesized to be adversely impacted by warming waters via increased temporal overlap between its early life stages and predators. To provide insight into winter flounder early life history dynamics and context for resiliency of the stock, we examined ichthyoplankton data collected from 2 monitoring programs within Narragansett Bay, Rhode Island, USA: one spatially comprehensive dataset across the bay proper (2001−2008, 2016−2017), and the other a longer time series centered in one of the sub-estuaries of the bay (Mount Hope Bay, 1972−2017). By leveraging these datasets together, we conducted a spatiotemporal synthesis of early life stage winter flounder by evaluating changes in larval phenology, decadal coherence in larval spatial patterns, and correspondence between larvae and their subsequent life stage. We identified changes in larval phenology via earlier seasonal peaks in density through time. Results also indicated stable larval spatial patterns during a period of larval decline, as well as spatial coherence between larval and young-of-the-year stages. Using winter flounder as a model species, our results highlight the importance of high-resolution spatiotemporal ichthyoplankton sampling to identify changes in phenology and site fidelity for marine fishes