Trade-Offs Between Risks of Predation and Starvation In Larvae Make the Shelf Break an Optimal Spawning Location For Atlantic Bluefin Tuna

Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions

Trade-offs between risk of predation and starvation in larvae make the shelf break an optimal spawning location for Atlantic Bluefin tuna

Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions.Postprin

Habitats and Biota of the Gulf of Mexico: Before the Deepwater Horizon Oil Spill: Volume 1: Water Quality, Sediments, Sediment Contaminants, Oil and Gas Seeps, Coastal Habitats, Offshore Plankton and Benthos, and Shellfish

environmental management; marine; freshwater science

Habitats and Biota of the Gulf of Mexico: Before the Deepwater Horizon Oil Spill: Volume 1: Water Quality, Sediments, Sediment Contaminants, Oil and Gas Seeps, Coastal Habitats, Offshore Plankton and Benthos, and Shellfish

environmental management; marine; freshwater science

Temporal distribution of cold-water corals in the northwest Atlantic through the Late Quaternary : footprint of intermediate water mass circulation

Over the last two decades, extensive geological investigations on cold-water coral (CWC) areas of the northeastern Atlantic revealed that the temporal occurrence of framework-forming CWC presents a climate-dependent pattern. The pattern follows the glacial-interglacial changes of the surface ocean conditions and intermediate-depth water masses. Over geological time scales, CWC can form substantial seabed features, called CWC mounds that may serve as archives for assessing their long-term development. Several CWC mound areas have been described in the northwestern Atlantic, where the presence of living reef-like structures advocates for favorable conditions for CWC at present. A limited number of ages of fossil CWC collected from various sites in the northwestern Atlantic further suggests that conditions were also favorable during the last glacial. However, the less of a handful of available ages emphasizes the need for a thorough investigation of the temporal pattern of CWC occurrence in this area. This study was designed (1) to identify the periods of sustained CWC growth in two coral mound areas of the northwestern Atlantic (the Campeche CWC Province, southern Gulf of Mexico, and the Cape Lookout CWC area, off North Carolina) and (2) to detect the environmental factors influencing their long-term development. The temporal occurrence of CWC was established by using U-series dating, while a multi-proxy approach was followed to reconstruct the present and past environmental conditions (incl. water column analyses; ROV video observation and sampling; foraminifera-based stable isotope analyses, Mg/Ca-thermometry and assemblage analyses; grain size and carbonate content analyses of sediments). The results suggest that for the last 260,000 years, pronounced coral growth at these two coral mound areas was restricted to interglacial periods, which confirms a climate influence on the CWC temporal occurrence also in these northwestern Atlantic areas. The pattern coincides with the glacial-interglacial changes of the intermediate-depth water masses, where periods favorable for CWC growth are marked by enhanced hydrodynamics that increase the food supply to the CWC. At the Campeche CWC area, such conditions result from the density gradient between the Antarctic Intermediate Water and the overlying Tropical Atlantic Central Water, whereas at the Cape Lookout CWC area, coral growth is steered by the Gulf Stream presence. Although similar occurrence patterns were found in the two studied areas, they differ from the few ages previously reported for the NE Gulf of Mexico and the East Florida Strait CWC mound areas, where CWC occur today but obviously also occurred under glacial conditions. Therefore, it is necessary to conduct further research in order to better constrain the general pattern of CWC occurrence in coral mound areas of the northwestern Atlantic and its possible connection to the intermediate-depth circulation

An Overview of Marine Biodiversity in United States Waters

Marine biodiversity of the United States (U.S.) is extensively documented, but data assembled by the United States National Committee for the Census of Marine Life demonstrate that even the most complete taxonomic inventories are based on records scattered in space and time. The best-known taxa are those of commercial importance. Body size is directly correlated with knowledge of a species, and knowledge also diminishes with distance from shore and depth. Measures of biodiversity other than species diversity, such as ecosystem and genetic diversity, are poorly documented. Threats to marine biodiversity in the U.S. are the same as those for most of the world: overexploitation of living resources; reduced water quality; coastal development; shipping; invasive species; rising temperature and concentrations of carbon dioxide in the surface ocean, and other changes that may be consequences of global change, including shifting currents; increased number and size of hypoxic or anoxic areas; and increased number and duration of harmful algal blooms. More information must be obtained through field and laboratory research and monitoring that involve innovative sampling techniques (such as genetics and acoustics), but data that already exist must be made accessible. And all data must have a temporal component so trends can be identified. As data are compiled, techniques must be developed to make certain that scales are compatible, to combine and reconcile data collected for various purposes with disparate gear, and to automate taxonomic changes. Information on biotic and abiotic elements of the environment must be interactively linked. Impediments to assembling existing data and collecting new data on marine biodiversity include logistical problems as well as shortages in finances and taxonomic expertise

Iterative spatial leave-oneout cross-validation and gap-filling based data augmentation for supervised learning applications in marine remote sensing

In marine remote sensing, supervised learning can link variables measured in-situ near the ocean surface to variables that can be measured from space. However, the in-situ data used for training and validating such empirical satellite algorithms are often spatially auto-correlated and clustered, giving rise to various statistical challenges such as overfitting to spatial structures. Furthermore, co-located in-situ and satellite measurements are rare in the oceans because of the cost of data collection from research vessels and frequent cloud cover. We propose two methods to mitigate these challenges. The first method builds on spatial leave-one-out cross-validation (SLOOCV), an approach designed to provide sound error estimates when data are spatially auto-correlated by enforcing a minimum separation distance between training and test observations. However, estimating this distance may be impossible with sparse and spatially clustered data. We hence propose to iterate and integrate error estimates over a range of separation distances (iSLOOCV). To address the often-small size of labeled data sets based on marine in-situ data, we tested if increasing the number of observations for algorithm training by means of cloud-filling algorithms for marine satellite data improved predictions. The potential of these two methods is demonstrated by developing empirical algorithms for mapping the proportions of seven diagnostic pigments (DPs) that serve as proxies for phytoplankton community composition in the northern Gulf of Mexico. We estimated the prediction accuracy of 13 algorithms with iSLOOCV, using various sets of satellite data products as input, and found adequate algorithms for 4 of the 7 DPs. Random forests combining ocean color and environmental variables as input had the lowest prediction errors overall. Correlations between predictions and observations estimated by iSLOOCV ranged from 0.69 to 0.85 and mean absolute errors from 0.02 to 0.13. Daily maps and longer-term composites of these DPs were broadly consistent with previously published results. Overall, errors increased when extrapolating over larger distances, highlighting how iSLOOCV can illuminate changes in algorithm performance based on sub-regional data coverage. Generating larger training sets by prior gap-filling substantially improved all error measures for 3 of the 7 DPs, with mixed results for the others. Therefore, data augmentation by gap-filling of satellite data should not be used as a default approach but can be a useful tool when supervised learning applications are suspected to be limited by the size of the training set

Laboratory experiments reveal intrinsic self-sustained oscillations in ocean relevant rotating fluid flows

Several ocean Western Boundary Currents (WBCs) encounter a lateral gap along their path. Examples are the Kuroshio Current penetrating into the South China Sea through the Luzon Strait and the Gulf of Mexico Loop Current leaping from the Yucatan peninsula to Florida as part of the Gulf Stream system. Here, we present results on WBC relevant flows, generated in the world’s largest rotating platform, where the Earth’s sphericity necessary to support WBCs is realized by an equivalent topographic effect. The fluid is put in motion by a pump system, which produces a current that is stationary far from the gap. When the jet reaches the gap entrance, time-dependent patterns with complex spatial structures appear, with the jet leaking, leaping or looping through the gap. The occurrence of these intrinsic self-sustained periodic or aperiodic oscillations depending on current intensity is well known in nonlinear dynamical systems theory and occurs in many real systems. It has been observed here for the first time in real rotating fluid flows and is thought to be highly relevant to explain low-frequency variability in ocean WBCs

Investigating the Effects of a Southward Flow in the Southeastern Florida Shelf Using Robotic Instruments

We deployed a Slocum G3 glider fitted with an acoustic Doppler current profiler (ADCP), a Conductivity-Temperature-Depth sensor (CTD), optics sensor channels, and a propeller on the Southeastern Florida shelf. The ADCP and CTD provide continuous measurements of Northern and Eastern current velocity components, salinity, temperature, and density, throughout the water column in a high-current environment. The optics sensor channels are able to provide measurements of chlorophyll concentrations, colored dissolved organic matter (CDOM), and backscatter particle counts. Additionally, for one of the glider deployments, we deployed a Wirewalker wave-powered profiling platform system also fitted with an ADCP and a CTD in the vicinity of the glider’s area for intercalibration of the devices. As the glider’s velocity profiles are analyzed through time and space we saw evidence of an intermittent southward flow (SWF) opposite to the overlying northward Florida Current (FC) that was previously described by Soloviev et al. (2017). Meandering and strength of this SWF was influenced by the presence or absence of the Gulf Stream close to the shore, persisting in time spans of at least a few hours. Although specific mechanisms that influence the SWF’s behavior are still unknown, our results show that its attachment to the shore along the continental slope was associated with the presence of eddy features in some sort of coupled system with possible implications on turbulent mixing. CTD results show that the SWF appears as either an undercurrent or a countercurrent depending on the strength of the water column stratification. Optical channel results show that the SWF assists in the southwards transport of particulate matter and biological material at depth, with possible implications on nutrient transport and biological activity. Richardson number results for analysis of turbulent flow were inconclusive as to how much turbulence is actually created by the SWF, but it does show evidence of increased turbulent activity at the interface between the SWF and the FC during some deployments. Analysis of the relationship between the northern component of velocity and the eastern component revealed a possible mechanism that would provide the optimal conditions for upwelling events to take place. 23 deployments have been done so far, with more planned for the future. More research is needed to accurately assess the effect the SWF has on velocities and transport of pollution and biological material along and across the shelf against the FC