Net Tows Research Articles

Mathematical modelling and analysis of plastic waste pollution and its impact on the ocean surface

Plastic contamination is universal all through the marine condition, yet gauges of the worldwide plenitude and weight of coasting plastics have needed information, especially from the Southern Hemisphere and remote areas. Here we report a gauge of the all-out number of plastic particles and their weight gliding on the planet's seas from 24 endeavours (2007–2013) over every one of the five subtropical gyres, coastal Australia, Bay of Bengal and the Mediterranean Sea directing surface net tows (N = 680) and visual review transects of huge plastic flotsam and debris (N = 891). Utilizing an oceanographic model of coasting trash dispersal adjusted by our information, and rectifying for wind-driven vertical blending, we gauge at least 5.25 trillion particles weighing 268,940 tons. When looking at between four size classes, two micro plastic <4.75 mm and meso and micro plastic >4.75 mm, a huge loss of micro plastics is seen from the ocean surface contrasted with anticipated paces of discontinuity, recommending there are systems at play that expel <4.75 mm plastic particles from the sea surface. The focus on the life cycle assessment and the brief overview of the plastic waste management over the ocean surfaces with the various mathematical models has been studied. The impact of the ocean pollution is also being analysed.

Krill spatial distribution in the Spanish Mediterranean Sea in summer time

Abstract We documented krill distribution in the Spanish Mediterranean Sea for the first time using acoustic methods, highlighting the method’s suitability to study marine communities restricted to specific areas with patchy aggregation behavior. The 2009–2017 acoustic time series analysis revealed that krill distribution, mainly located on the continental shelf edge, was driven by the presence of fronts and submarine canyons. On the other hand, areas of persistent krill distribution included from Cape La Nao to the eastern part of Almeria Bay, although an interannual northwards increase of krill presence had been detected in 2015–2017 likely related to the position of the Balearic front. We provide information on the aggregation characteristics and biological parameters of three krill species, Nyctiphanes couchii, Nematoscelis megalops and Meganyctiphanes norvegica. N. couchii and N. megalops formed patchy pelagic aggregations in the neritic and oceanic zone, respectively, and they were the most common species in the net tows. By contrast, M. norvegica formed a large demersal aggregation on the continental shelf edge and was only found in 2017; nevertheless, its 861-kg catch represented a unique milestone in the Mediterranean. Finally, krill species shared distribution area with Maurolicus muelleri; thus, coexistence between them are also described.

Modeled spatial-temporal distribution of productivity, chlorophyll, iron and nitrate on the northern Gulf of Alaska shelf relative to field observations

The northern Gulf of Alaska (GOA) shelf is dynamic spatially and temporally. With two major current systems and numerous eddies and meanders, interpretation of field data from ship-based observations at specific times and locations is complicated. We used the Regional Ocean Modeling System (ROMS) with an embedded nutrient-phytoplankton-zooplankton (GOANPZ) model to aid in understanding spatial-temporal patterns of productivity, chlorophyll concentration and biomass over the GOA shelf between 132oW and 160oW from 2000 to 2013. Carbon chlorophyll ratios in the model were varied in response to light to alter production-irradiance curves by season to conform to field measurements. Simulations reveal regions of high productivity in March–May on the southeast Alaskan Shelf, and the western inner shelf between Prince William Sound (PWS) and the Shumagin Islands, but with lower productivity on the outer shelf between PWS and western Kodiak. The model produced regions of elevated productivity on the outer shelf of the western GOA during summer and fall. This pattern is driven by circulation affecting the distribution of iron on the western shelf. Simulated productivity on the shelf between 2000 and 2006 was elevated relative to 2007–2013, apparently due to changes in the simulated iron concentration. Correlations indicate that simulated production on the western GOA shelf during March–May can explain up to 65% of the variance in the mean biomass of large copepods from net tows during spring. Simulations suggest that detailed temporal-spatial data on iron concentration and the processes affecting iron are crucial to understanding interannual spatial-temporal differences in magnitudes of production and biomass at lower trophic levels on the GOA shelf.

Assemblage structure, vertical distributions and stable-isotope compositions of anguilliform leptocephali in the Gulf of Mexico.

In August 2007, October 2008 and September-October 2010, 241 Tucker trawl and plankton net tows were conducted at the surface to depths of 1377 m at six locations in the northern and eastern Gulf of Mexico (GOM) to document leptocephalus diversity and determine how assemblage structure, larval size, abundance and isotopic signatures differ across the region and with depth. Overall, 2696 leptocephali representing 59 distinct taxa from 10 families were collected. Five families accounted for 96% of the total catch with Congridae and Ophichthidae being the most abundant. The top four most abundant species composed 59% of the total catch and included: Ariosoma balearicum, Paraconger caudilimbatus, Rhynchoconger flavus and Ophichthus gomesii. Four anguilliform species not previously documented in the GOM as adults or leptocephali were collected in this study, including Monopenchelys acuta, Quassiremus ascensionis, Saurenchelys stylura and one leptocephalus only known from its larval stage, Leptocephalus proboscideus. Leptocephalus catches were significantly greater at night than during the day. Catches at night were concentrated in the upper 200 m of the water column and significantly declined with increasing depth. Leptocephali abundances and assemblages were significantly different between sites on the upper continental slope (c. 500 m depth) and sites on the middle to lower continental slope (c. 1500-2300 m). Sites on the lower continental slope had a mixture of deep-sea demersal, bathypelagic and coastal species, whereas upper-slope sites contained several numerically dominant species (e.g., A. balearicum, P. caudilimbatus) that probably spawn over the continental shelf and upper slope of the GOM. Standard lengths of the four dominant species differed between sites and years, indicating heterochronic reproduction and potential larval source pools within and outside of the GOM. Stable-isotope analyses (δ13 C and δ15 N) conducted on 185 specimens from six families revealed that leptocephali had a wide range of isotopic values at the family and size-class levels. Species in the families Muraenidae, Congridae and Ophichthidae had similar δ15 N values compared with the broad range of δ15 N values seen in the deep-sea families Nemichthyidae, Nettastomatidae and Synaphobranchidae. Stable-isotope values were variably related to length, with δ15 N values being positively size correlated in ophichthids and δ13 C values being negatively size correlated in A. balearicum and P. caudilimbatus. Results suggest that leptocephali feed in various water depths and masses, and on different components of POM, which could lead to niche partitioning. Ecological aspects of these important members of the plankton community provide insight into larval connectivity in the GOM as well as the early life history of Anguilliformes.

Vibrio parahaemolyticus risk assessment in the Pacific Northwest: it's not what's in the water.

The Gram-negative bacterium Vibrio parahaemolyticus (Vp) is a major cause of illness associated with the consumption of raw or undercooked seafood, primarily oysters. This species is a natural member of the bacterial community in brackish waters and is bioaccumulated by oysters through filter feeding. Only a subset of strains is thought to be pathogenic. Currently known virulence markers include the gene for the thermostable direct hemolysin (tdh). In this work we analyzed water and oysters for total Vp and strains encoding tdh from 26 oyster-growing areas of the Puget Sound and Pacific coast of Washington state in 2007 and 2008. In addition, possible plankton-associated Vp were assessed from net tow samples. The density of both total and tdh+ Vp in the water column were considerably higher in 2008 than 2007. However, the concentrations of both total and tdh+ Vp in the oyster tissue was similar for both years. A high proportion of Vp strains in the water column was found to be tdh+ in both 2007 and 2008; however, tdh+ strains were detected at much lower levels in oysters. The data show that analysis of Vp density in the oysters is a better risk assessment tool than density in the overlying water column.

Food web constraints on larval growth in subtropical coral reef and pelagic fishes

Prey availability and predation pressure are thought to be key constraints on larval growth, especially in low-productivity, subtropical environments. Yet, measuring their effects on larval fishes has been challenging, given the dynamic biophysical drivers of plankton distributions and small scales of interactions. We integrated fine-scale net tows (10s of meters) within situimaging to explore how predator-prey interactions influence larval fish growth in the Straits of Florida. Otolith-derived recent growth was analyzed for 3 ecologically important fishes: 2 coral reef labrids (Thalassoma bifasciatumandXyrichtys novacula) and 1 tuna (Katsuwonus pelamis), with differing mean growth rates (labrids 0.25 mm d-1,K. pelamis0.44 mm d-1) and prey (labrids-copepods; tuna-appendicularians). We used generalized additive models to examine the interactive effect of background density and frequency of elevated (&gt;2 SD above background) prey and predators on recent (last 3 d) larval growth. For all taxa, recent growth increased with prey background density. Recent growth of labrids was also higher when copepod densities were more often elevated (14% of transect &gt;20 ind. m-3) above otherwise low background densities (2 ind. m-3). Predators (chaetognaths and hydromedusae) had a growth-selective effect: stronger selection in transects with high-density predator patches, although the direction of the effect was species-specific. The effect of temperature was taxa-specific: growth increased with temperature for the labrids and peaked at an optimum (28°C) for the rapidly growing tuna. Integration of these fine-scale sampling methods improves our understanding of the variable influence of prey and predators on larval growth and, consequently, larval survival.

Variability of swept area by sea-surface tows of a neuston net: Balance of resistance, clogging, and over-inflow effects

Variability of swept area by horizontal tows of a neuston net at the sea surface was examined based on a data set of flow-meter revolutions from larval surveys for Pacific saury off the Pacific coast of Japan in winter during 2003 to 2016 (total of 1566 tows). The swept area rate was defined as the realized swept area by the actual net tow relative to the theoretical value of the swept area calculated from the towing speed, towing duration, and frame width without any resistance of the net. Despite the high variability at the individual tow level, the median value of the swept area rate (0.996) closely approximated the theoretical value of 1.0. Thus, over large scales, the swept area rate was on a balance of resistance effect of net and cod-end, clogging effect of collected organisms, and over-inflow effect of complex hydrodynamics at the sea surface. For the data divided into three areas (inshore, Kuroshio axis, and offshore areas) and three periods (2003–2007, 2008–2012, and 2013–2016), the median values also approximated 1.0. No significant difference was found in the swept area rate among the areas and periods. Therefore, we speculate that the variability of swept area rate could be attributed to small-scale transient variability of ocean conditions rather than large-scale variability related to the current system or climate variability. The information presented here are anticipated to be a reference for research projects and monitoring surveys in various regions.

Using eDNA, sediment subfossils, and zooplankton nets to detect invasive spiny water flea (Bythotrephes longimanus)

In light of the ongoing spread and adverse impacts of invasive species, there is an urgent need to develop more effective monitoring and management strategies. Such efforts are constrained by our limited capacity to efficiently detect invasive species. Here, we present the case of Bythotrephes longimanus (spiny water flea) invasion into Wisconsin lakes. Detecting Bythotrephes has proven to be challenging due to its capacity to persist at low densities and its highly seasonal population dynamics. We use Bythotrephes to explore detection using three monitoring methods: zooplankton net tows, environmental DNA (eDNA), and sampling of Bythotrephes tail spine subfossils in sediments. Detection probabilities were highly seasonal for both the net tow and eDNA sampling methods—though detections occurred one to two weeks earlier in net tows—and seasonal targeting substantially improved detection by both methods. Conversely, Bythotrephes spine subfossils were found in all 10 lakes with confirmed Bythotrephes populations and in all five samples taken from each lake, except for a single lake where four of the five samples had subfossils. This method was insensitive to seasonally varying population densities as sediments integrate over variation in population densities. In this case, detection and abundance estimation were well covered by sediments and zooplankton nets, respectively, and eDNA provided little additional benefit to surveillance. Our work highlights the importance of choosing methods that address both species life history and monitoring objectives when designing surveillance programs.

The first snapshot study on horizontal distribution and identification of five peritrich ciliates (Genus Vorticella Linnaeus and Zoothamnium Bory de St. Vincent) from the eastern Indian Ocean

Epipont peritrich ciliates are one of the most sessilie protists that attached to the substrate of zooplankton communities especially copepods and crustaceans. Peritrich ciliates can be solitary or colonial form found from the coastal zones and embayment around the world. Present research report is the first snapshot study of the peritrich ciliates and the horizontal distribution in open waters from surface to 200 m depth in the eastern Indian Ocean. Recently, five peritrich ciliates, e.g., Vorticella oceanica, Zoothamnium alternans, Z. alrasheidi, Z. pelagicum, and Z. marinum were collected from plankton net tow samples during the cruise from April 10 to May 13, 2014. The characteristics of the peritrich ciliate were determined according to the shape of the zooids, the ciliary structure and the stalks. The morphometric shape, sizes and characters also explained by examination under light/scanning electron microscopy. Vorticella oceanica and Z. pelagicum showed their association with host such as diatom (i.e, Chaetoceros coarctatus) and copepod (Oithona brevicornis) including some individuals around the dinoflagellate species (Ceraitum tripose). The distribution of these sessilid ciliates was dominated by the V. oceanica, Z. pelagicum and Z. marinum at the southeast zone while the large colonies of Z. alrasheidi observed at the Bay of Bengal. This distribution can be influenced by substrate availability like diatom (Ch. coarctatus) and copepods (O. brevicornis).

Floating plastics in Adriatic waters (Mediterranean Sea): From the macro- to the micro-scale

Macro- and microplastics abundances were determined in the Adriatic Sea following the MSFD TG10 protocol. The studied areas included populated gulfs, river outlets and offshore waters in five Adriatic countries. The use of small ships enabled us to detect small sized plastics (2.5–5 cm) and record average macroplastics densities of 251 ± 601 items km−2, one order of magnitude higher than previously considered. Results from manta net tows for microplastics revealed an average abundance of 315,009 ± 568,578 items km−2 (217 ± 575 g km−2). We found significantly higher microplastics abundances in nearshore (≤4 km) than in offshore waters (>4 km) and this trend seems to affect also the small sized macro plastic fragments (2.5–5 cm). The dominant polymers were polyethylene and polypropylene while the presence of some rare polymers and waxes used in food and dentistry indicated waste water treatment plants as potential sources of microplastics.

High-frequency observations from a deep-sea cabled observatory reveal seasonal overwintering of Neocalanus spp. in Barkley Canyon, NE Pacific: Insights into particulate organic carbon flux

Many submarine canyons are known hotspots of pelagic and benthic biodiversity and productivity. Despite a very limited knowledge of the ecology, biodiversity and ecosystem function of Canada’s West Coast canyons, Barkley Canyon is becoming a relatively well studied system, particularly after the installation of the NEPTUNE seafloor cabled observatory in 2009. Video observations of large densities of overwintering calanoid copepods (likely a combination of Neocalanus plumchrus, N. cristatus, and a small contribution of N. flemingeri) drifting near the bottom at 970 m in the axis of Barkley Canyon motivated our interest in investigating the temporal dynamics of their ontogenetic migration cycle. Particularly, since these large calanoid copepods, and especially Neocalanus plumchrus, comprise up to 50% of of the mesozooplankton biomass in the subarctic NE Pacific, being considered a keystone species in the trophodynamics of pelagic ecosystems in the region. Here we used ∼20-months (May 2013–Jan 2015) of seafloor video imagery combined with acoustic Doppler current and backscatter time-series data from the NEPTUNE observatory to identify the precise timing and seasonal and inter-annual variability in the deep ontogenetic migration of Neocalanus spp. in Barkley Canyon. A total of 33,486 still images were extracted from 1674 × 5-min segment videos, captured at two-hour intervals, and used in a computer-automated image analysis protocol designed to estimate Neocalanus spp. densities near the seafloor. The results from the entire time-series revealed close correspondence with the described developmental and reproductive cycle for Neocalanus spp., with the highest densities of copepodite-5 (C5) and adult individuals present at depth from the late fall and through the winter. The concomitant high-frequency (2 MHz) ADCP backscatter time-series nearly mirrored the patterns obtained from the video imagery, and also highlighted a clear inter-annual variability, with higher copepod densities in 2013 relative to 2014. Such inter-annual variability was also evidenced by ground-truth net tow casts from Line P and La Perouse monitoring stations in the vicinity of Barkley Canyon. The low and high-frequency ADCP (75 KHz and 2 MHz) current data demonstrated an along axis mean flow near the bottom and an up-canyon mean subsurface flow from 70 to 300 m above the seabed, suggesting a recirculation cell at this segment of the canyon. Based on this circulation pattern and on our video and backscatter data, we propose a conceptual model describing how the topographically-constrained currents along the canyon axis and the up-canyon flow may help trap the seasonally migrating biomass of Neocalaus spp. near the core of its overwintering depth at mid-canyon (∼1000 m). Based on a previously calculated 25-yr mean of carbon export flux attributed to N. plumchrus in the NE Pacific (i.e., 5 g C m2 yr−1; min. 1.44, max 8.82C m2 yr−1 – Bradford-Grieve et al., 2001), which considers respiration and mortality at the overwintering depth throughout winter after spawning, we estimated that 35–215 tons of carbon reach Barkley Canyon’s seafloor yearly over an area of approximately 24 km2. Future studies should aim to further constrain the role of submarine canyons in transporting and concentrating deep zooplankton migrating biomass, as there are at least another 230 submarine canyons in the subarctic NE Pacific, a region where zooplankton biomass is heavily dominated by deep ontogenetically migrating calanoid copepods.

Ground-truthing the planktic foraminifer-bound nitrogen isotope paleo-proxy in the Sargasso Sea

We report the nitrogen (N) isotope ratios (δ15N) of planktic foraminifera collected from upper-ocean net tows (surface to 200 m), moored sediment traps, and core-top sediments at the Bermuda Time-series Site in the northern Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually-averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling, dinoflagellate symbiont-bearing foraminifera collected in net tows (2.3‰ on average) approximates that of shallow thermocline (∼200 m) nitrate (2.6‰), the dominant source of new N to Sargasso Sea surface waters. Deeper-dwelling foraminifer species without dinoflagellate symbionts tend to have a higher δ15N (3.6‰ on average). We observe no systematic difference between the bulk tissue and shell-bound δ15N in net tow-collected foraminifera. A decline in shell N content is observed from net tows (6.8 nmol/mg) to sediment traps (5.4 nmol/mg) and surface sediment (3.0 nmol/mg). On average, shell-bound δ15N rises from net tows (3.1‰) to sediment traps (3.7‰) but does not change further upon incorporation into the sediments (3.7‰). Together, these observations are consistent with preferential loss of shells or shell portions with lower δ15N and higher N content during sinking through the upper 500 m, followed by a non-isotope fractionating decrease in N content between sinking and burial. Time-series data from sediment traps (and to a lesser extent, surface net tows) exhibit seasonal δ15N variations, with a minimum in early spring, a maximum in late spring and a decline from summer to fall. These variations appear to arise from seasonal changes in the δ15N of total upper-ocean biomass, which are, in turn, driven by early springtime nitrate supply, subsequent nitrate drawdown, and an increase in the relative importance of ammonium recycling into the late summer and early fall. The δ15N connection between total upper ocean biomass and foraminifera indicates that foraminifer-bound δ15N records the δ15N of the annual nitrate supply in oligotrophic (e.g., subtropical) environments but will also be sensitive to the degree of nitrate consumption in high-nutrient regions and possibly to changes in upper-ocean ammonium recycling under some conditions.

First record and description of Planctoteuthis (Cephalopoda: Chiroteuthidae) paralarvae in the Gulf of California, Mexico

We report for the first time the presence of doratopsis stages of P lanctoteuthis sp. 1 (Cephalopoda: Chiroteuthidae) in the Gulf of California, Mexico, including a description of the morphological characters obtained from three of the five best-preserved specimens. The specimens were obtained from zooplankton samples collected in oblique Bongo net tows during June 2014 in the southern Gulf of California, Mexico. Chromatophore patterns on the head, chambered brachial pillar, and buccal mass, plus the presence of a structure, possibly a photophore, at the base of the eyes covered by thick, golden reflective tissue are different from those of the doratopsis stages of Planctoteuthis danae and Planctoteuthis lippula known from the Pacific Ocean. These differences suggest Planctoteuthis sp. 1 belongs to Planctoteuthis oligobessa , the only other species known from the Pacific Ocean or an unknown species. Systematic sampling covering a poorly sampled entrance zone of the Gulf of California was important in the collection of the specimens.

Evaluation of marine zooplankton community structure through environmental DNA metabarcoding.

Zooplankton dominate the abundance and biomass of multicellular animals in pelagic marine environments; however, traditional methods to characterize zooplankton communities are invasive and laborious. This study compares zooplankton taxonomic composition revealed through metabarcoding of the cytochrome oxidase I (COI) and 18S rRNA genes to traditional morphological identification by microscopy. Triplicates of three different sample types were collected from three coral reef sites in the Florida Keys National Marine Sanctuary: (1) 1 L surface seawater samples prefiltered through 3 μm filters and subsequently collected on 0.22 μm filters for eDNA (PF‐eDNA); (2) 1 L surface seawater samples filtered on 0.22 μm pore‐size filters (environmental DNA; eDNA), and (3) zooplankton tissue samples from 64 μm, 200 μm, and 500 μm mesh size net tows. The zooplankton tissue samples were split, with half identified morphologically and tissue DNA (T‐DNA) extracted from the other half. The COI and 18S rRNA gene metabarcoding of PF‐eDNA, eDNA, and T‐DNA samples was performed using Illumina MiSeq. Of the families detected with COI and 18S rRNA gene metabarcoding, 40% and 32%, respectively, were also identified through morphological assessments. Significant differences in taxonomic composition were observed between PF‐DNA, eDNA, and T‐DNA with both genetic markers. PF‐eDNA resulted in detection of fewer taxa than the other two sample types; thus, prefiltering is not recommended. All dominant copepod taxa (> 5% of total abundance) were detected with eDNA, T‐DNA, and morphological assessments, demonstrating that eDNA metabarcoding is a promising technique for future biodiversity assessments of pelagic zooplankton in marine systems.

Understanding imperfect detection in a San Francisco Estuary long‐term larval and juvenile fish monitoring programme

AbstractImperfect detection can present a significant challenge when monitoring for a rare and imperilled species. Here, a long‐term larval and early‐juvenile fish monitoring programme in the upper San Francisco Estuary was examined to evaluate its overall reliability in detecting various fish species, including the imperilled delta smelt, Hypomesus transpacificus McAllister, for which the programme was designed. Using occupancy modelling, detection probability of species with pelagic larval or juvenile life stages was found to be generally high (≥.95) based on the current sampling effort of three larval net tows per site. However, detection probability can vary considerably from year to year depending on the species’ level of larval production. Water temperature and turbidity were identified as important predictors of occurrence for young‐of‐year delta smelt, longfin smelt Spirinchus thaleichthys (Ayres) and striped bass Morone saxatilis (Walbaum), and there was evidence for fish size selectivity by the sampling gear in all three species. These results highlight the need to consider adaptively managing detection probability by increasing sampling effort in years when young‐of‐year delta smelt abundance is expected to be low, especially when information on the species’ occurrence at a particular region is critical.

Zooplankton Community Dynamics in a Western Mid-Atlantic Lagoonal Estuary

ABSTRACT Howson, U.A.; Buchanan, G.A., and Nickels, J.A., 2017. Zooplankton community dynamics in a western mid-Atlantic lagoonal estuary. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay-Little Egg Harbor, New Jersey. Zooplankton are an integral component of the food web in estuarine ecosystems. The most recent studies of zooplankton in Barnegat Bay, New Jersey, occurred almost 40 years ago. Since then, this coastal lagoon estuary has been affected by anthropogenic impacts that threaten its ecological integrity, including nutrient enrichment, algal blooms, alterations of freshwater inputs, and extensive development around the bay and its watershed. Assessing the zooplankton community in this ecosystem provided updated information on the status of this important component of the bay's living resources. Zooplankton samples were collected from the upper meter of the water column with horizontal surface net tows using bongo plankton nets monthly during the w...

Synergistic effects of seasonal deoxygenation and temperature truncate copepod vertical migration and distribution

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 575:57-68 (2017) - DOI: https://doi.org/10.3354/meps12205 Synergistic effects of seasonal deoxygenation and temperature truncate copepod vertical migration and distribution James J. Pierson*, Wen-Cheng L. Slater, David Elliott, Michael R. Roman Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD 21613, USA *Corresponding author: jpierson@umces.edu ABSTRACT: The vertical distribution of copepods in coastal and estuarine systems is altered by the concentration of dissolved oxygen in the water column. We studied the combined effects of temperature and dissolved oxygen on vertical distribution and migration behavior of the copepod Acartia tonsa in the Chesapeake Bay throughout the period of seasonal deoxygenation in 2010 and 2011. Vertically stratified net tows and hydrographic casts were conducted at 2 stations over diel cycles in spring, summer, and autumn. The partial pressure of dissolved oxygen ( pO2) was used as a metric for the condition of copepod habitat during each cruise instead of oxygen concentration, because partial pressure incorporates the temperature dependence of dissolved oxygen solubility, making it a more useful indication of available oxygen supply than concentration. Habitat conditions were described as having pO2 above limiting conditions, below the maximum respiratory demand but above potentially lethal conditions, or below the minimum basal respiratory demand. In general, adult males were found deeper in the water than females in most oxygen conditions. Regression tree analysis supported these findings and showed that pO2 was a key predictor of the fraction of copepodites, adult females, and adult males above the pycnocline, and for copepodites and adult females below the pycnocline. Temperature was a strong predictor of the fraction of adult males below the pycnocline, with a smaller fraction found there at higher temperatures. These findings suggest sex-specific responses to deoxygenation, potentially as a result of different oxygen demands or behavior. KEY WORDS: Copepod · Hypoxia · Diel vertical migration · Vertical distribution · Acartia tonsa · Chesapeake Bay · Estuarine Full text in pdf format Supplementary material PreviousNextCite this article as: Pierson JJ, Slater WCL, Elliott D, Roman MR (2017) Synergistic effects of seasonal deoxygenation and temperature truncate copepod vertical migration and distribution. Mar Ecol Prog Ser 575:57-68. https://doi.org/10.3354/meps12205 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 575. Online publication date: July 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Inter-annual variation in the density of anthropogenic debris in the Tasman Sea

An increasing number of studies highlight the risk of plastic pollution in the marine environment. However, systematic longitudinal data on the distribution and abundance of plastic debris remain sparse. Here we present the results of a two-year study of plastic pollution within the Tasman Sea, contrasted with a further year of data from the same region, in order to document how the density of debris varies across years in this area. Surface net tows were collected between Hobart, Tasmania and Sydney, Australia during the spring of 2013 and 2014 and compared with a subset of data from autumn 2012 from the same region. Substantial inter-annual variation in mean plastic abundance was observed over the three year period, ranging from to 248.04–3711.64pieceskm−2, confirming the need for multiple years of sampling to fully estimate the extent of, and trends in, plastic pollution.

The dynamics of Chaoborus americanus in an Adirondack lake following the reintroduction of fish

• Cultural acidification extirpated a fish population from a Lake. • In the absence of fish, Chaoborus americanus colonized the Lake. • Fish were reintroduced into the Lake and C. americanus populations were tracked. • C. americanus exhibited a limited diel vertical migration. • C. americanus were extirpated by the naturalized fish. Acid deposition during the 20th century led to the gradual elimination of fish in Brooktrout Lake (Adirondack Mountains, New York State). Thereafter, the lake was colonized by Chaoborus americanus , a dipteran with an aquatic larval stage that typically resides in the pelagic zone in fishless lakes. During subsequent chemical recovery from acidification, the lake was stocked with Brook Trout ( Salvelinus fontinalis ). For seven years following this reintroduction we examined the re-adaptation of the food chain. The C. americanus abundance and distribution was quantified utilizing a combination of hydroacoustics, traditional vertical net tows and Schindler-Patalas trap collections. Hydroacoustic backscattering signals were repeatable and correlated (r = 0.86, p = 0.003) with C. americanus abundance. Backscattering, depth, month and year were used to develop a random forest model that predicted the C. americanus density (r 2 = 0.67, p< 0.05). The hydroacoustic signal revealed a clear but limited diurnal vertical migration of C. americanus . The signal continued in the presence of the fish population beginning with reintroduction in 2005 and extending through 2011. In 2012, the hydroacoustic signal no longer was present in the lake, suggesting that the fish had eliminated the C. americanus population, which was verified with net tows. Using novel and traditional survey methods, we demonstrate that the reintroduction of fish can alter the lake community structure significantly through the extirpation of the major component of the pelagic zone.

Widely used marine seismic survey air gun operations negatively impact zooplankton.

Zooplankton underpin the health and productivity of global marine ecosystems. Here we present evidence that suggests seismic surveys cause significant mortality to zooplankton populations. Seismic surveys are used extensively to explore for petroleum resources using intense, low-frequency, acoustic impulse signals. Experimental air gun signal exposure decreased zooplankton abundance when compared with controls, as measured by sonar (~3-4 dB drop within 15-30 min) and net tows (median 64% decrease within 1 h), and caused a two- to threefold increase in dead adult and larval zooplankton. Impacts were observed out to the maximum 1.2 km range sampled, which was more than two orders of magnitude greater than the previously assumed impact range of 10 m. Although no adult krill were present, all larval krill were killed after air gun passage. There is a significant and unacknowledged potential for ocean ecosystem function and productivity to be negatively impacted by present seismic technology.