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

The p75 Neurotrophin Receptor Mediates Neuronal Apoptosis and Is Essential for Naturally Occurring Sympathetic Neuron Death

Abstract. To determine whether the p75 neurotrophin receptor (p75NTR) plays a role in naturally occurring neuronal death, we examined neonatal sympathetic neurons that express both the TrkA tyrosine kinase receptor and p75NTR. When sympathetic neuron survival is maintained with low quantities of NGF or KCl, the neurotrophin brain-derived neurotrophic factor (BDNF), which does not activate Trk receptors on sympathetic neurons, causes neuronal apoptosis and increased phosphorylation of c-jun. Function-blocking antibody studies indicate that this apoptosis is due to BDNF-mediated activation of p75NTR. To determine the physiological relevance of these culture findings, we examined sympathetic neurons in BDNF−/− and p75NTR−/− mice. In BDNF−/− mice, sympathetic neuron number is increased relative to BDNF+/+ littermates, and in p75NTR−/− mice, the normal period of sympathetic neuron death does not occur, with neuronal attrition occurring later in life. This deficit in apoptosis is intrinsic to sympathetic neurons, since cultured p75NTR−/− neurons die more slowly than do their wild-type counterparts. Together, these data indicate that p75NTR can signal to mediate apoptosis, and that this mechanism is essential for naturally occurring sympathetic neuron death

Effects of ultraviolet-B enhancement on marine trophic levels in a stratified coastal system

We examined the effects of enhanced UV-B radiation (relative to ambient) on marine trophic levels inhabiting a stratified coastal ecosystem, using living models (13000 liter marine enclosures) of a temperate estuarine water column. The experiment was carried out in June and July 1994 on a plankton community drawn from lower Narragansett Bay, Rhode Island, USA. The effects of altered UV-B radiation (elevated 50% over ambient, tenfold DNA-weighted) on three trophic strata: the primary producers (photosynthetic algae), primary herbivores (copepods), and fish eggs and larvae (Anchoa mitchilli Cuvier and Valenciennes) were examined. The goal was to determine if UV-B-induced alterations at the base of the food chain had impacts on other elements of the trophic web. Phytoplankton abundance (P = 0.02) and biomass (P = 0.007) were significantly reduced in UV-B-enhanced treatments, above but not below the thermocline (2.25 m), during the second week of the study. Copepod nauplii were significantly less abundant in UV-B-enhanced mesocosms than in control treatments during the third and fourth weeks of the study (P = 0.01). A portion of the impact on nauplii may be a result of alterations at the base of the food web. The greater mortality of nauplii in UV-B-enhanced systems did not translate to reduced abundance of copepodite (P = 0.83) or adult (P = 0.29) copepods. No significant effects were observed for microzooplankton (P = 0.15). Neither the mortality rates nor the growth rates of larval anchovy were significantly affected by the experimental increase in UV-B (P \u3e 0.05). Despite the tenfold increase in biologically damaging UV-B, effects were not seen at higher trophic levels, most likely because of the rapid extinction of UV-B in the highly colored coastal water

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