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Stability in the feeding ecology of four demersal fish predators in the US Northeast Shelf Large Marine Ecosystem

Posted on Jul 31, 10 at 11:37 pm.

Evidence of species interactions are generally well understood over broad temporal and spatial scales, particularly for commercially valuable species. Yet species that are not as commercially valuable may nonetheless be ecologically important in stabilizing trophic interactions in large marine ecosystems. We examined the diets for 4 of these demersal fish species: black sea bass Centropristis striata, scup Stenotomus chrysops, Northern searobin Prionotus carolinus, and striped searobin P. evolans. We examined food habits data across size class, season, 5 yr time block, and geographic region to evaluate the major determinants of diet composition. We used multivariate statistics, specifically canonical correspondence analysis, as the primary method to explore diet determinants. Our results showed that the scup and 2 searobin species are primarily benthivorous, whereas black sea bass notably shifts towards piscivory with ontogeny. Our results also showed that the diet of these predators was mainly influenced by size class, region, and (to a lesser extent) season, whereas 5 yr time block did not notably influence diet composition, a surprising observation given the well-documented changes to benthic habitat in this ecosystem. These results suggest that these species feed opportunistically in proportion to the relative abundance of available prey given the constraints of their morphology, which implies that despite notable impacts to benthic habitat, the prey field for these understudied species has been consistent (within seasonal variation) over the past 3 decades. Stable feeding dynamics such as these may act to enhance resilience in large marine ecosystems.... ...
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How Do Polar Marine Ecosystems Respond to Rapid Climate Change?

Posted on Jul 31, 10 at 11:37 pm.

Climate change will alter marine ecosystems; however, the complexity of the food webs, combined with chronic undersampling, constrains efforts to predict their future and to optimally manage and protect marine resources. Sustained observations at the West Antarctic Peninsula show that in this region, rapid environmental change has coincided with shifts in the food web, from its base up to apex predators. New strategies will be required to gain further insight into how the marine climate system has influenced such changes and how it will do so in the future. Robotic networks, satellites, ships, and instruments mounted on animals and ice will collect data needed to improve numerical models that can then be used to study the future of polar ecosystems as climate change progresses.... ...
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The Growing Human Footprint on Coastal and Open-Ocean Biogeochemistry

Posted on Jul 31, 10 at 11:37 pm.

Climate change, rising atmospheric carbon dioxide, excess nutrient inputs, and pollution in its many forms are fundamentally altering the chemistry of the ocean, often on a global scale and, in some cases, at rates greatly exceeding those in the historical and recent geological record. Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants. Most of these perturbations, tied either directly or indirectly to human fossil fuel combustion, fertilizer use, and industrial activity, are projected to grow in coming decades, resulting in increasing negative impacts on ocean biota and marine resources.... ...
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The Great Indo-Pacific Communicator

Posted on Jul 31, 10 at 11:37 pm.

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Determinants of Myosin II Cortical Localization during Cytokinesis

Posted on Jul 31, 10 at 11:37 pm.

Myosin II is an essential component of the contractile ring that divides the cell during cytokinesis. Previous work showed that regulatory light chain (RLC) phosphorylation is required for localization of myosin at the cellular equator [1, 2]. However, the molecular mechanisms that concentrate myosin at the site of furrow formation remain unclear. By analyzing the spatiotemporal dynamics of mutant myosin subunits in Drosophila S2 cells, we show that myosin accumulates at the equator through stabilization of interactions between the cortex and myosin filaments and that the motor domain is dispensable for localization. Filament stabilization is tightly controlled by RLC phosphorylation. However, we show that regulatory mechanisms other than RLC phosphorylation contribute to myosin accumulation at three different stages: (1) turnover of thick filaments throughout the cell cycle, (2) myosin heavy chain-based control of myosin assembly at the metaphase-anaphase transition, and (3) redistribution and/or activation of myosin binding sites at the equator during anaphase. Surprisingly, the third event can occur to a degree in a Rho-independent fashion, gathering preassembled filaments to the equatorial zone via cortical flow. We conclude that multiple regulatory pathways cooperate to control myosin localization during mitosis and cytokinesis to ensure that this essential biological process is as robust as possible.... ...
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