67 research outputs found
Physics-informed laboratory estimation of Sargassum windage
A recent Maxey--Riley theory for \sarg raft motion, which models a raft as a
network of elastically interacting finite-size, buoyant particles, predicts the
carrying flow velocity to be given by the weighted sum of the water and air
velocities . The theory provides a
closed formula for parameter , referred to as \emph{windage}, depending
on water-to-particle-density ratio or buoyancy (). From a series of
laboratory experiments in an air--water stream flume facility under controlled
conditions, we estimate ranging from 0.02 to 0.96\pct. On average, our
windage estimates can be up to 9 times smaller than considered in conventional
\emph{Sargassum} raft transport modeling, wherein it is customary to add a
fraction of to chosen in an ad-hoc piecemeal manner.
Using the formula provided by the Maxey--Riley theory, we estimate
ranging from 1.00 to 1.49. This is consistent with direct
measurements, ranging from 0.9 to 1.25, which provide support for our
estimation
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Fine-scale planktonic habitat partitioning at a shelf-slope front revealed by a high-resolution imaging system
Ocean fronts represent productive regions of the ocean, but predator-prey interactions within these features are
poorly understood partially due to the coarse-scale and biases of net-based sampling methods. We used the In
Situ Ichthyoplankton Imaging System (ISIIS) to sample across a front near the Georges Bank shelf edge on two
separate sampling days in August 2010. Salinity characterized the transition from shelf to slope water, with
isopycnals sloping vertically, seaward, and shoaling at the thermocline. A frontal feature defined by the
convergence of isopycnals and a surface temperature gradient was sampled inshore of the shallowest zone of
the shelf-slope front. Zooplankton and larval fishes were abundant on the shelf side of the front and displayed
taxon-dependent depth distributions but were rare in the slope waters. Supervised automated particle counting
showed small particles with high solidity, verified to be zooplankton (copepods and appendicularians), aggregating
near surface above the front. Salps were most abundant in zones of intermediate chlorophyll-a fluorescence,
distinctly separate from high abundances of other grazers and found almost exclusively in colonial form (97.5%).
Distributions of gelatinous zooplankton differed among taxa but tended to follow isopycnals. Fine-scale sampling
revealed distinct habitat partitioning of various planktonic taxa, resulting from a balance of physical and biological
drivers in relation to the front.Keywords: Shelf edge, Georges Bank, Fronts, Gelatinous, Zooplankton, Larval fishes, Diatom aggregates, Predatorâprey, Salp
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Larval fishes utilize Batesian mimicry as a survival strategy in the plankton
Marine teleost fishes often experience over 99% mortality in the early life stages (eggs and larvae), yet larval survival is essential to population sustainability. Marine fish larvae from a wide range of families display elaborate, delicate features that bear little resemblance to adult forms and hinder their swimming escape ability by increasing drag. Here, we systematically examine the criteria needed for Batesian mimicry to evolve as a survival strategy and present new evidence from in situ imaging technology and simulation modelling to support the hypothesis that many larval morphological features (particularly long, delicate fin rays) and behaviors evolved at least in part through Batesian mimicry of less palatable or noxious gelatinous zooplankton. Many of these organisms (e.g. hydromedusae, ctenophores, and siphonophores) are much more abundant than previously recognized. The high predation mortality during the larval phase provides strong potential for selection in favor of maintaining complex and metabolically costly features that mimic gelatinous zooplankton, provided that larger fishes, as selective visual predators, can occasionally be fooled. We conclude that recent advances in our understanding of mimicry combined with information obtained from plankton imaging supports the hypothesis that Batesian mimicry is a widespread survival strategy for larval fishes, which could have broad implications for fish population dynamics. However, further research is needed in the areas of predator cognition and larval fish behavior in the presence of different predators and models to elucidate the circumstances in which the larval fish mimicry hypothesis may apply.This is the publisherâs final pdf. The published article is copyrighted by the author(s) and published by Inter-Research. The published article can be found at: http://www.int-res.com/journals/meps/meps-home/Keywords: Survival, Plankton, Larval fish, Batesian mimicry, Recruitment, Gelatinous zooplankto
Ocean convergence and the dispersion of flotsam
Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than âŒ10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of âŒ200 surface drifters covering âŒ20 Ă 20 km2 converged into a 60 Ă 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 sâ1 and 0.01 msâ1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material
Ocean convergence and the dispersion of flotsam
Floating oil, plastics, and marine organisms are continually redistributed by ocean surface currents. Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change. Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than âŒ10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of âŒ200 surface drifters covering âŒ20 Ă 20 km2 converged into a 60 Ă 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing. As predicted, the convergence occurred at density fronts and with cyclonic vorticity. A zipperlike structure may play an important role. Cyclonic vorticity and vertical velocity reached 0.001 sâ1 and 0.01 msâ1, respectively, which is much larger than usually inferred. This suggests a paradigm in which nearby objects form submesoscale clusters, and these clusters then spread apart. Together, these effects set both the overall extent and the finescale texture of a patch of floating material. Material concentrated at submesoscale convergences can create unique communities of organisms, amplify impacts of toxic material, and create opportunities to more efficiently recover such material
CALYPSO 2019 Cruise Report: field campaign in the Mediterranean
This cruise aimed to identify transport pathways from the surface into the interior ocean during the late winter in the AlborĂĄn sea between the Strait of Gibraltar (5°40âW) and the prime meridian. Theory and previous observations indicated that these pathways likely originated at strong fronts, such as the one that separates salty Mediterranean water and the fresher water in
owing from the Atlantic. Our goal was to map such pathways and quantify their transport. Since the outcropping isopycnals at the front extend to the deepest depths during the late winter, we planned the cruise at the end of the Spring, prior to the onset of
thermal stratification of the surface mixed layer.Funding was provided by the Office of Naval Research under Contract No. N000141613130
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In situ ichthyoplankton imaging system (ISIIS): system design and preliminary results
Over the last two decades, there has been an accelerating advancement of acoustic and optical plankton samplers, opening many opportunities for fineâscale studies of plankton distribution. To date, however, the imaging systems have been limited in the volume of water being sampled, thereby restricting their utility to quantifying highly abundant, small zooplankton like copepods, but not relatively rarer, larger ichthyoâ and other mesoâzooplankton (e.g., larval decapods, salps, pteropods, ctenophores, etc.). Here we describe an imaging system, In situ ichthyoplankton imaging system (ISIIS), that is capable of In situ (i.e., noninvasive) sampling of sufficiently large volumes of water at very high resolution, allowing quantitative measurement of these rare plankton, while at the same time also recording the smaller more abundant taxa. Capitalizing on stateâofâtheâart digital line scan cameras and highâthroughput computer data transfer and storage, combined with shadow photographic lighting techniques, we have designed and built a towed system capable of imaging at 68âmicron pixel resolution, yet with up to a 20âcm depth of field (with a 14âcm field of view). This system is coupled with various environmental sensors (e.g., CTD, fluorometer), enabling the evaluation of fineâscale, taxonâspecific distributions in relation to environmental conditions. Field testing demonstrated highâresolution imagery of plankters, while quantitatively imaging >70 L sâ1 continuously for a 78âmin trial
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