Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

https://science.sciencemag.org/content/sci/315/5820/1846.full.pdf

Cascading effects of the loss of apex predatory sharks from a coastal ocean.

Supporting Online Material for Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Ninety-eight percent of recently surveyed papers in fisheries and aquatic sciences that did not reject some null hypothesis (H0) failed to report β, the probability of making a type II error (not r...

Statistical Power Analysis can Improve Fisheries Research and Management

Suspended particles are instrumental in controlling the reactivity, transport and biological impacts of substances in aquatic environments, and provide a crucial link for chemical constituents between the water column, bed sediment and food chain. This article reviews the role of suspended particles in the chemical and biological cycling of trace constituents (trace metals, organo-metallic compounds and hydrophobic organic micropollutants; HOMs) in estuaries, with particular emphasis on the effects of and changes to particle reactivity and composition.

The partitioning (or distribution coefficient,KD ) and bioavailability of chemical constituents, and assimilation efficiency (AE) of such by bivalve suspension feeders, are identified as key parameters requiring definition for accurate biogeochemical modelling, and the discussion centres around the determination of and controls on these parameters. Particle-water interactions encompass a variety of physical, biological, electrostatic and hydrophobic effects, and are largely dependent on the character and concentration of suspended particles and salinity. The salinity-dependence results from the competing and complexing effects of seawater ions for trace metals, and the compression of water in the presence of dissolved seawater ions and consequent salting out of neutral solute (HOMs, organo-metallic compounds and some trace metal complexes). The extent of biological solubilization of chemical constituents from suspended particles is dependent on the nature of chemical components of the gastro-intestinal environment and their interactions with ingested particles, and the physiological (e.g. gut passage time) and chemical (e.g. redox conditions and pH) constraints imposed on these interactions. Generally, chemicals that associate with fine, organic-rich particles (or, for some HOMs, fine inorganic particles), and desorb at pH 5–6 and/or complex with digestive enzymes or surfactants are most readily solubilized in the gut. The extent of assimilation of solubilized chemical is then determined by its ability to pass the gut lining and partition into cytosolic material.

In practice, KD and AE are determined experimentally by means of radiotracers added to contained suspensions or mesocosms, while operational measurement of bioavailability relies on in vitro chemical or biological (enzymatic) extraction of particles. What is lacking, however, and is identified as an ultimate goal of future research, is the ability to predict these parameters from theoretical principles and thermodynamic constants. Since many of the inherent interactions and mechanisms are controlled by particle composition and reactivity, a more immediate objective would be better characterization of the biogeochemical properties of suspended particles themselves. This includes chemical resolution of the bulk organic matter, definition of the abundance and synergistic effects of component sorbent phases, and determination of the effects of particle-seawater ion interactions on the reactivity of the particle surface.

Suspended Particles: Their Role in Estuarine Biogeochemical Cycles

The Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Interagency Task Force, jointly convened by the U.S. Global Change Research Program (USGCRP) and the National Ocean Council (NOC), began its work in August 2015. The Task Force has focused its efforts on three primary tasks: 1) updating scenarios of global mean sea level (GMSL) rise, 2) integrating the global scenarios with regional factors contributing to sea level change for the entire U.S. coastline, and 3) incorporating these regionally appropriate scenarios within coastal risk management tools and capabilities deployed by individual agencies in support of the needs of specific stakeholder groups and user communities. This technical report focuses on the first two of these tasks and reports on the production of gridded relative sea level (RSL, which includes both ocean-level change and vertical land motion) projections for the United States associated with an updated set of GMSL scenarios. In addition to supporting the longer-term Task Force effort, this new product will be an important input into the USGCRP Sustained Assessment process and upcoming Fourth National Climate Assessment (NCA4) due in 2018. This report also serves as a key technical input into the in-progress USGCRP Climate Science Special Report (CSSR).

/pdf/global-and-regional-sea-level-rise-scenarios-for-the-united-1wbg6h5din.pdf

Global and Regional Sea Level Rise Scenarios for the United States

Recent studies have demonstrated that short-term and small-scale variation in seston availability can have significant effects on individual and population characteristics of benthic suspension feeders. To provide a better understanding of in situseston dynamics 1–2 cm above the substrate surface we measured hourly variation in seston quantity and composition (total C and N, chlorophyll a, bacteria, energy content, and particle size spectra) over a tidal cycle. Mean seston concentration was significantly lower in water collected during ebb tide than in water sampled during flood tide (37·1 vs.78·1 mg 1−1). The range of seston concentrations observed in a single tide was almost as great as the range of seston concentrations measured at this site over an entire year in other studies. Particles 2–20 μm in diameter comprised most (>80%) of the volume of the seston throughout the entire tidal cycle. The organic portion of the seston remained fairly constant when tidal velocities increased during flood tide; the seston was not ‘diluted’ by inorganic particles. In general, mean seston concentration for the entire tide (57·1 mg l−1) was greater in our study than has been reported in the majority of comparable studies. This may be a consequence of our sampling much closer to the substrate surface. The patterns of variation in seston concentration and quality were not predictable solely from measurements of physical factors responsible for particle suspension (e.g. current speeds, wind speeds).

Short-term variation in the quantity and quality of seston available to benthic suspension feeders

Meiofauna are eroded from sediments and transported in the water column. To examine how meiofauna respond to erosive currents, in situ current speeds were altered on an intertidal sandflat located in Bogue Sound, North Carolina, USA in July 1982. Replicates of two different weir designs were erected. One design increased measured current speed and the other, a control, did not. The depth distributions of meiofauna in each treatment and from undisturbed sediment were compared. There were few differences among treatments in depth distribution of the most abundant taxa: nematodes, turbellarians, and ciliates (>37-μm-long). However, a significant amount of sediment erosion (a mean of almost 0.5 cm in 2 h) occured in the increased flow treatment. Meiofauna responded to the loss of sediment with no discernable differences in depth distribution relative to the controls. There was some evidence that nematodes were less abundant and ciliates more abundant in the top 0.5 cm of the increased flow treatment. This may indicate that nematodes respond to fast surface current speeds by moving deeper into the sediments, while ciliates manage to remain near the surface even as sediment erodes. The entrainment of meiofauna may be passive but meiofauna clearly exert considerable behavioral influence over their susceptibility to entrainment.

Experimental variation of near-bottom current speeds and its effects on depth distribution of sand-living meiofauna

Thirteen monthly measurements of individually marked juvenile (16 mm long) and adult (60 mm long) specimens of Mercenaria mercenaria (L.) from field plots in North Carolina demonstrated similar seasonal patterns in size-adjusted monthly growth rates in shell volume: a large absolute maximum occurred in spring (April or May) with smaller relative maxima in mid summer and late autumn. The ratio of juvenile to adult size-adjusted growth rates in shell volume was nearly constant for ten months but then increased eight-fold in December and January. This growth anomaly between size classes could not be explained by examining dry weights of soma and gonads from additional marked juvenile and adult Mercenaria that were sacrificed monthly. Juveniles differed from adults by possessing negligible gonadal mass on all dates. However, knowledge of monthly changes in adult gonadal mass did not explain a significant amount of the residual variation in the regression of monthly juvenile volumetric growth on monthly adult volumetric growth. Seasonal changes in growth of adult gonadal mass and quarterly examinations of gonad histology both suggested a winter period of negligible gametogenesis followed by a spring burst of intense reproductive activity. The best explanations for the anomalously high

Seasonal allocation of resources to growth of shell, soma, and gonads in mercenaria mercenaria

Biological and physical reworking of sediments can profoundly affect the structure and functioning of benthic communities. The depth of the disturbance is an important factor that controls the types of organisms that can exist within the sediments. Large numbers of horseshoe crabs,Limulus polyphemus, spawn each spring on the sandy shores of Delaware Bay beaches. We have used this abundance peak to provide an estimate of the depth of sediment disruption caused by this species on an intertidal flat adjoining a major spawning beach. Vertical columns of marked sediment were placed in three locations of an intertidal flat. Some columns were protected with cages while others remained unprotected. Analysis of variance of the depth of disruption of the marked sediment indicated that different areas of the intertidal zone were disrupted to different depths. Caged marked sediment was disturbed to an average depth of 3.2 cm while unprotected sediment was disturbed to a mean depth of 11.1 cm. Deepest mixing occurred in a trough between sandwave crests and averaged 17.7 cm deep. These mixing depths are greater than the 1.2 cm deep disturbance produced by nonstorm wave action in the study area.

Vertical Disturbance of Sediments by Horseshoe Crabs (Limulus polyphemus) During Their Spawning Season

Sea level anomalies are intra-seasonal increases in water level forced by meteorological and oceanographic processes unrelated to storms The effects of sea level anomalies on beach morphology are unknown but important to constrain because these events have been recognized over large stretches of continental margins Here, we present beach erosion measurements along Onslow Beach, a barrier island on the US East Coast, in response to a year with frequent sea level anomalies and no major storms The anomalies enabled extensive erosion, which was similar and in most places greater than the erosion that occurred during a year with a hurricane These results highlight the importance of sea level anomalies in facilitating coastal erosion and advocate for their inclusion in beach-erosion models and management plans Sea level anomalies amplify the erosive effects of accelerated sea level rise and changes in storminess associated with global climate change

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014GL060544

Stephen R. Fegley

Papers

Short-term variation in the quantity and quality of seston available to benthic suspension feeders

Experimental variation of near-bottom current speeds and its effects on depth distribution of sand-living meiofauna

Seasonal allocation of resources to growth of shell, soma, and gonads in mercenaria mercenaria

Vertical Disturbance of Sediments by Horseshoe Crabs (Limulus polyphemus) During Their Spawning Season

Sea level anomalies exacerbate beach erosion