Plankton Net Tows Research Articles

New observations of Papulifères, putative ciliate cysts, from the plankton of the Chukchi Sea (Western Arctic Ocean) in August of 2023

We recently documented the existence of 26 different forms of Papulifères, presumptive ciliate cysts, from plankton net tow material of the Chukchi Sea gathered in 2015, 2021, and 2022. The forms appeared to be rare, found in only 7 of the 308 samples taken in annual August surveys from 2010 to 2022. Thus, we were surprised to find them relatively common and widespread in samples gathered in August of 2023. We found 18 different Papulifére forms, 8 of which appear to be new forms, in samples from 19 of the 36 stations sampled. They were found in localities ranging from 70.5°N to 80°N. Here we report on these Papulifére forms found in 2023, providing information on morphologies and geographical distributions. With this report we have expanded the catalogue of observed Papulifére, and photographed, forms of the Chukchi Sea to a grand total of 34 of morphologically distinct forms. However, we continue to urge caution in assigning a ciliate identity to any given Papulifére form in the absence of corroborating data.

Revealing zooplankton diversity in the midnight zone

Zooplankton diversity in the deep “midnight zone” (>1000 m), where sunlight does not reach, remains largely unknown. Uncovering such diversity has been challenging because of the major difficulties in sampling deep pelagic fauna and identifying many (unknown) species that belong to these complex swimmer assemblages. In this study, we evaluated zooplankton diversity using two taxonomic marker genes: mitochondrial cytochrome oxidase subunit 1 (COI) and nuclear 18S ribosomal RNA (18S). We collected samples from plankton net tows, ranging from the surface to a depth of 5000 m above the Atacama Trench in the Southeast Pacific. Our study aimed to assess the zooplankton diversity among layers from the upper 1000 m to the ultra-deep abyssopelagic zone to test the hypothesis of decreasing diversity with depth resulting from limited carbon sources. The results showed unique, highly vertically structured communities within the five depth strata sampled, with maximal species richness observed in the upper bathypelagic layer (1000–2000 m). The high species richness of zooplankton (>750 OTUS) at these depths was higher than that found in the upper 1000 m. The vertical diversity trend exhibited a pattern similar to the well-known vertical pattern described for the benthic system. However, a large part of this diversity was either unknown (>50%) or could not be assigned to any known species in current genetic diversity databases. DNA analysis showed that the Calanoid copepods, mostly represented by Subeucalanus monachus, the Euphausiacea, Euphausia mucronata, and the halocypridade, Paraconchoecia dasyophthalma, dominated the community. Water column temperature, dissolved oxygen, particulate carbon, and nitrogen appeared to be related to the observed vertical diversity pattern. Our findings revealed rich and little-known zooplankton diversity in the deep sea, emphasizing the importance of further exploration of this ecosystem to conserve and protect its unique biota.

Conventional net tow versus environmental DNA for metabarcoding-based analysis of plankton-environment interactions in polluted aquatic ecosystems

Human societal development has caused rapid degradation of freshwater ecosystems, resulting in significant biodiversity decline globally. The conservation of aquatic ecosystems, particularly the management of biodiversity in urban areas, has become an increasingly significant issue for ensuring the sustainability of these ecosystems. The restoration of degraded aquatic ecosystems relies on a comprehensive understanding of the interactions between biological communities and multiple stressors derived from human activities. Environmental DNA (eDNA)-based methods have emerged as effective tools for dissecting complex community-environment interactions. Nevertheless, potential causes for technical disparities and conclusions drawn from conventional sampling versus eDNA-based methods remain inadequately evaluated. In this study, we conducted a comprehensive survey of plankton communities along the environmental gradient of the North Canal River in Northern China to assess causes and consequences for any disparities between conventional plankton net tow and eDNA sampling for metabarcoding-based analysis of plankton-environment interactions. Our findings demonstrated that eDNA-metabarcoding was effective for characterizing both biodiversity and geographical distribution. Both methods exhibited general consistency in elucidating community structure and identifying the key environmental factors influencing geographical distribution of both zooplankton and phytoplankton. As we explored lower taxonomic ranks, we found inconsistent patterns at certain levels (e.g., phylum or order) within some taxa (e.g., Bacillariophyta and Rotifera), even substantial variability for several taxonomic groups (e.g., Euglenozoa and Apicomplexa). The varied environmental prevalence and persistence of eDNA, biological and ecological characteristics of diverse taxa in plankton, and sampling efficiency of both methods likely contributed to the observed disparities. Given its higher biodiversity recovery capacity, efficiency, sampling convenience, and capability to identify influential factors driving the geographical distribution of biodiversity, eDNA-based metabarcoding is recommended for studying plankton-environment interactions, particularly in studies involving a large number of samples at extended geographical scales.

Filter no more: A modified plankton sampler for rapid in‐water eDNA capture

Abstract The combination of an efficient sampling method and high‐throughput analysis of environmental DNA (eDNA) can be a powerful approach for characterising biodiversity across aquatic ecosystems. Plankton net tows are one of the oldest, simplest, and least expensive methods for seston and eDNA collection, but require laborious filtration steps which often lead to clogging and/or the introduction of contaminants. In this study, we used a cruising speed net (CSN) device enabling the collection of seston‐derived eDNA at 5 knots speed combined with a novel modified cod‐end with 20 μm nylon mesh inserts enabling eDNA capture while towing. We compared the performance of the CSN sampling protocol with the original conventional filtration of water sample versus the modified cod‐end. Samples were collected in parallel horizontal tows along New Zealand's North‐Eastern coastline. Concentrated water was filtered on conventional 5 μm cellulose acetate membranes, while the 20 μm nylon mesh inserts were immediately isolated post‐towing. Metabarcoding of bacterial 16S rRNA, eukaryotic nuclear 18S rRNA and mitochondrial COI genes, revealed no significant difference in alpha diversity between filtration techniques. In terms of community composition, a clear and significant shift could be observed between sampling sites and environments. Significant differences could be detected between filtration methods for 16S and COI markers, likely driven by fine‐scale differences at more turbid sheltered sites. Nonetheless, each technique could detect shifts in communities between sites and environments with similar sensitivity. Our results demonstrate the promising potential of the modified cod‐end to enable practical and cost‐effective isolation of eDNA‐derived biodiversity data from any vessel types (at ≤5 knots) across a large range of aquatic ecosystems and biogeographic scales.

Interannual summer biodiversity changes in ichthyoplankton assemblages of the Strait of Sicily (Central Mediterranean) over the period 2001–2016

Interannual fluctuations in the structure and the composition of ichthyoplankton assemblages in the pelagic waters of the Strait of Sicily (SoS, Central Mediterranean) were investigated, trying to relate them to the observed variability in oceanographic conditions. Plankton data used in this study were from 16 summer surveys carried out in the SoS every year from 2001 to 2016, using oblique bongo plankton net (0–100 m) tows. Out of more than 12,000 fish larvae collected in the sampling stations included in the analysis, 9,519 of them were identified and regularly classified in 15 orders and 49 families. Ichthyoplankton assemblages, defined at the family level due to the uniform availability of this information along the time series, showed a decreasing trend over time in total larval abundance, along with taxonomic (family) richness and Shannon index (α diversity), more pronounced in the shelf area and in the slope area, respectively. Conversely, the relatively high levels of yearly compositional changes observed in the larval assemblage from both shelf and slope areas, as estimated by the Jaccard dissimilarity index (β diversity), did not show any significant linear trend. In addition, a biodiversity hotspot (both in terms of family richness and Shannon index) was evidenced in the frontal structure characterizing the southeastern part of the study area. Generalized additive models were used to evaluate the effect of oceanographic conditions on the temporal and spatial patterns of ichthyoplankton biodiversity. Results evidenced the role of salinity, surface temperature, and surface currents in modulating biodiversity indices, especially in the shelf area. Finally, the relevance of local frontal oceanographic structures in sustaining high biodiversity levels is postulated.

Tintinnid ciliates (marine microzooplankton) of the Ross Sea

For the Ross Sea, the only Marine Protected Area in Antarctica, available data on the tintinnid ciliates of the marine microzooplankton are mostly limited to nearshore waters near Terra Nova Bay or the vicinity of the McMurdo Sound. Here, we report results from a geographically extensive sampling across the Ross Sea conducted in December 2020. Material from plankton net tows (20 µm mesh), made at 38 stations spanning over 30° of latitude, was examined. We found 11 tintinnid species of varying commonality or rarity, many showing considerable morphological variability that is here documented. We found four forms that had not been previously reported from the Ross Sea. Based on our findings and previous reports, we assembled a species accumulation curve showing the growth in the inventory of tintinnid species recorded from the Ross Sea as a function of sampling effort and time since 1983. Extrapolation of the species accumulation curve, derived from sampling over the last 37 years, indicates that continued sampling will likely provide new species records, suggesting that the Ross Sea is under-sampled at present. This complicates efforts to detect temporal changes in species compositions, at least with regard to tintinnid ciliates. Comparing species accumulation curves for the Ross Sea and the relatively well-studied Weddell Sea, it appears that the Ross Sea may be more species-rich.

The neglected contributions of William Beebe to the natural history of the deep-sea

Abstract William Beebe (1877–1962) was a very popular 20th century naturalist and an early proponent of studying all organisms in a habitat. Beebe’s deep-sea work began with his Arcturus Oceanographic Expedition in 1925 with sampling closely modelled on the Michael Sars deep-sea expedition. Dissatisfied with ship-based sampling of stations for a few days at best, he established a field laboratory in Bermuda to do intensive deep-water sampling. From 1929 to 1934, plankton net tows were carried out at the same site, over several months each year, totalling over 1500 net tows in deep waters. Here, the sampling efforts and results are reviewed from both the Arcturus Expedition and the Bermuda station. Study of the deep-sea samples yielded 43 scientific articles, published from 1926 to 1952, on a large variety of taxa. Beebe is still a popular figure connected in the public view with deep-sea exploration from his famous Bathysphere dives at the Bermuda site. However, his name rarely, if ever, appears in academic reviews of deep-sea biology or deep-sea expeditions. This study is an attempt to draw attention to Beebe’s considerable scientific deep-sea work and provide some speculation as to why his contributions might be neglected.

A note on the differences found between examining whole water vs. phytoplankton net (52 μm mesh) samples to characterize abundance and community composition of tintinnid ciliates (marine microzooplankton)

AbstractMost tintinnid species have a shortest linear dimension < 50 μm. Hence, a priori, nets of mesh sizes ≥ 50 μm will likely under‐sample most tintinnid species. However, studies often appear (23 since 2015) using sampling with nets of meshes sizes ≥ 50 μm, reporting both tintinnid concentrations, and community composition. How biased are results from using coarse mesh nets? We provide a comparison of whole water vs. net sampling based on fortuitous, that is, unplanned, parallel sampling. Pairs of samples from a standard monitoring station in the Bay of Villefranche (N.W. Mediterranean Sea) taken on 44 dates from 2013 to 2018 were compared. Tintinnids were enumerated in settled material from a water column sample, an integration of six discrete depth samples between 5 and 70 m, prepared for analysis of phytoplankton composition and in material from a plankton net (52 μm mesh) tow from 70 to 0 m, taken the same day. Despite the large confidence limits due to low raw cell counts from whole water samples, cell concentration estimates were about an order of magnitude higher than those from plankton net samples and frequently biomass estimates as well. Community composition also differed. The most common species in whole water samples were small (diameter ≤ 20 μm), and some common forms were absent, or nearly, from the net samples. We show that, while valuable for collecting larger and rarer species, coarse net samples do not yield robust estimations of overall concentrations, nor allow identification of the dominant tintinnid species.

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.

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).

Comparison of morphological and next generation DNA sequencing methods for assessing zooplankton assemblages

Morphological taxonomic methods are currently insufficient to satisfy the rising demand for taxonomic information and rapid sample turnover required to support conservation and resource management efforts. Next generation DNA sequencing (NGS) is capable of rapidly producing taxonomic assessments for a broad diversity of organisms present in environmental samples. To achieve taxonomic coverage of similar breadth, multiple morphologists who tend to specialize by taxonomic group would be required. Unfortunately, both morphological and molecular approaches are subject to various methodological biases. Accurate assessment (both taxonomic composition and abundances) of marine zooplankton assemblages is a critical component of effective ecosystem-based conservation and resource management efforts. To address this need and determine the extent of agreement between methods, morphological data was compared to 454 NGS results for zooplankton assemblages collected in plankton net tows from northern Monterey Bay, California. Results indicate areas of agreement between data sets, but also characterize biases specific to each method. Morphological analyses provided life history stage and biomass information for many zooplankton taxa. The NGS data included 313bp from the 3′ end of the mitochondrial cytochrome-c-oxidase subunit-I (COI; 3234 OTUs) region and 365bp from the 5′ end of the large subunit of the nuclear ribosomal RNA (28S; 1669 OTUs). Results of NGS analysis corroborated the presence of 40 of the 61 morphologically identified genera and species. For some organisms, NGS provided finer taxonomic resolution where morphological data or knowledge was limited. Correlations between biomass and NGS percent sequence abundances were significant for some, but not all taxa, and were gene-specific in some cases (i.e., COI—Diplostraca, Polychaeta, Callianassidae, Clausocalanidae, Oncaeidae, Podonidae, Evadne, Neotrypaea, Oncaea, Podon, Psuedocalanus; 28S—Euphausiacea, Euphausiidae, Oncaeidae, Oncaea). Despite various methodological biases, both data sets were in agreement with respect to alpha diversity indices generated for zooplankton assemblages collected at four sampling stations. These results suggest that a partnership between morphological and molecular methods represents a powerful tool, that when used appropriately, can effectively extend taxonomic assessment capabilities to better address present needs.

Development of techniques for the collection and culture of wild-caught fertilised snapper (Chrysophrys auratus) eggs for stock enhancement purposes

Restocking or stock enhancement programs have traditionally relied on captive broodstock to produce individuals for release into the wild. However, this is costly and may limit genetic diversity of the resulting progeny. If fertilised eggs could be collected from the wild and individuals reared for release, the genetic diversity of the released progeny may be improved and associated restocking/enhancement programs may become more cost-effective. Snapper (Chrysophrys auratus: Sparidae), is an iconic recreational and commercial fish species across Australia and New Zealand and has been subjected to overfishing in many locations. Enhancement programs may be useful for increasing biomass in some circumstances, but would require careful evaluation of advantages and disadvantages before commencement. This study developed and optimised egg collection methods for snapper from its wild spawning aggregations in Cockburn Sound, Western Australia, and developed effective otolith marking techniques that would enable future monitoring of released individuals. The study identified the optimum sea conditions for collecting large numbers (>100,000) of eggs using plankton nets, in addition to the need for side-scan sonar to locate spawning aggregations, the distance from aggregations at which to sample and the water depth for plankton net tows. Large numbers of eggs collected in 2014 and 2015 were subsampled and visually screened for presence of snapper eggs using known egg diameters. Real-time PCR techniques validated visual identifications of snapper eggs and larvae, limiting accidental rearing of non-target species and reducing associated costs. Trials on larvae reared from these eggs, successfully determined appropriate alizarin complexone concentrations and immersion times for producing enduring marks on post-larvae otoliths. These marks remained visible in otoliths after 12 months, potentially allowing future monitoring of fish released into the wild. Delayed disinfection of eggs to the second day after capture resulted in improved egg viability. Following optimisation of collection and culture techniques, 208,000 larvae were stocked from a single sampling occasion in 2015, of which 19% survived to 55days post hatch (dph). This survival rate is typical for snapper produced from captive broodstock. This study demonstrated that wild spawned snapper eggs can be captured and cultured in high numbers and future identification of recaptured released fish potentially conducted. An associated genetic study also demonstrated no loss of genetic diversity in cultured fish versus that of adults in the spawning aggregations. This technique has the potential to reduce both the cost of restocking/stock enhancement programs for snapper (and could be evaluated for other suitable aggregating species) and the risks of altering the genetic makeup of wild stocks.

Bloom of Trichodesmium and seasonality of other potentially toxic and harmful phytoplankton in tropical San Pedro Bay, Leyte, Philippines in 2012-13

Since 1983, San Pedro Bay in the Philippines had been reported to be the site of episodic Pyrodinium bahamense var. compressum blooms that caused paralytic shellfish poisoning in its nearby coastal communities. This bay is also subjected to numerous storms; the strongest was super typhoon Haiyan in November 8, 2013. For the first time, the seasonal dynamics of potentially toxic and harmful phytoplankton in this bay is elucidated. This is also the first record of a bloom of the cyanobacteria, Trichodesmium erythraeum that reached 70 000 colonies/L in April 2013 in this area. There were other 19 potentially toxic and harmful phytoplankton encountered during the sampling period. These consisted of a haptophyte, Phaeocystis globosa, the diatom Pseudo-nitzschia and 17 dinoflagellates. Seven of these harmful algae had densities high enough to be traced through time. Normally, diatoms abound during the dry season. But Pseudo-nitzschia increased in abundance during the wet season of 2012 and 2013. The dinoflagellates and Phaeocystis globosa behaved as expected and exhibited a relative increase in cell density during the rainy season of both years too. High nutrient availability during this season must have influenced the behavior of the phytoplankton despite differences in temperature and light intensity among seasons. Other notable but rare harmful species found only in plankton net tows during the study were Pyrodinium bahamense var. compressum, Alexandrium tamiyavanichii, Cochlodinium polykrikoides, and Noctiluca scintillans.

A Golden Moment to Keep in the Loop - Introduction to the special issue

The Chukchi Sea was sampled in August of 2011, a year of near-normal sea ice among recent years, and again in August 2012, a year of all time record low sea ice. We exploited this sampling to test the hypothesis that different sea ice conditions are associated with differences in abundances or species composition of microzooplankton through an examination of tintinnids and radiolarians. From 18 stations in 2011, and 19 stations in 2012, organisms were enumerated in plankton net tow material, and chlorophyll determinations made (total and ≤ 20 µm) from discrete depth samples. We found that the low sea ice conditions of 2012 were associated with higher chlorophyll concentrations (both total and the ≤ 20 µm size fraction), compared to 2011. However, tintinnid ciliates and radiolarians were much lower in concentration, by about an order of magnitude, compared to 2011. In both years the radiolarian assemblage was dominated by Amphiselma setosa. The species composition of the tintinnid ciliates was similar in the two years, but there were distinct differences in the relative abundances of certain species. The 2012, low sea ice assemblage, was dominated by small forms in contrast to 2011, when large species were the most abundant. We present these findings in detail and discuss possible explanations for the apparent differences in the microzooplankton communities associated with distinct sea ice conditions in the Chukchi Sea

Monitoring Spawning Activity in a Southern California Marine Protected Area Using Molecular Identification of Fish Eggs.

In order to protect the diverse ecosystems of coastal California, a series of marine protected areas (MPAs) have been established. The ability of these MPAs to preserve and potentially enhance marine resources can only be assessed if these habitats are monitored through time. This study establishes a baseline for monitoring the spawning activity of fish in the MPAs adjacent to Scripps Institution of Oceanography (La Jolla, CA, USA) by sampling fish eggs from the plankton. Using vertical plankton net tows, 266 collections were made from the Scripps Pier between 23 August 2012 and 28 August 2014; a total of 21,269 eggs were obtained. Eggs were identified using DNA barcoding: the COI or 16S rRNA gene was amplified from individual eggs and sequenced. All eggs that were successfully sequenced could be identified from a database of molecular barcodes of California fish species, resulting in species-level identification of 13,249 eggs. Additionally, a surface transport model of coastal circulation driven by current maps from high frequency radar was used to construct probability maps that estimate spawning locations that gave rise to the collected eggs. These maps indicated that currents usually come from the north but water parcels tend to be retained within the MPA; eggs sampled at the Scripps Pier have a high probability of having been spawned within the MPA. The surface transport model also suggests that although larvae have a high probability of being retained within the MPA, there is also significant spillover into nearby areas outside the MPA. This study provides an important baseline for addressing the extent to which spawning patterns of coastal California species may be affected by future changes in the ocean environment.

Amazon River water in the northeastern Caribbean Sea and its effect on larval reef fish assemblages during April 2009

AbstractDuring April to June 2009, a large bolus of Amazon River water impacted the northeastern Caribbean Sea. Shipboard observations collected near Saba Bank, the U.S. and British Virgin Islands, and the Anegada Passage showed low surface salinity (35.76 ± 0.05 Practical Salinity Unit (PSU)), elevated surface temperature (26.77 ± 0.14°C), high chlorophyll‐a (1.26 ± 0.21 mg m−3) and high dissolved oxygen (4.90 ± 0.06 mL L−1) in a 20‐ to 30‐m thick surface layer in the riverine plume. The water was ~1°C warmer, 1 PSU fresher, 0.3 mL L−1 higher in oxygen and 1.2 mg m−3 higher in chlorophyll‐a than Atlantic Ocean waters to the north, with Caribbean surface waters showing intermediate values. Plankton net tows obtained in the upper 100 m of the water column revealed larval fish assemblages within the plume that were significantly different from those of the surrounding waters and from those encountered in the area in previous years. The plume waters contained higher concentrations of mesopelagic fish larvae from the families Myctophidae and Nomeidae, which as adults typically inhabit offshore, deep water habitats. Concentrations of larvae from inshore and reef‐associated families such as Scaridae, Serranidae, Labridae and Clupeidae were lower than those found outside the plume in similar shallow areas, particularly in near‐surface waters. An event like the one observed in 2009 had not been documented in at least the past 30 yr, and yet it was followed by another similarly extreme event in 2010. The ecological implications, including any long‐term consequences of such recent extreme events, are important and merit further study.

Distribution of Surface Plastic Debris in the Eastern Pacific Ocean from an 11-Year Data Set

We present an extensive survey of floating plastic debris in the eastern North and South Pacific Oceans from more than 2500 plankton net tows conducted between 2001 and 2012. From these data we defined an accumulation zone (25 to 41 °N, 130 to 180 °W) in the North Pacific subtropical gyre that closely corresponds to centers of accumulation resulting from the convergence of ocean surface currents predicted by several oceanographic numerical models. Maximum plastic concentrations from individual surface net tows exceeded 10(6) pieces km(-2), with concentrations decreasing with increasing distance from the predicted center of accumulation. Outside the North Pacific subtropical gyre the median plastic concentration was 0 pieces km(-2). We were unable to detect a robust temporal trend in the data set, perhaps because of confounded spatial and temporal variability. Large spatiotemporal variability in plastic concentration causes order of magnitude differences in summary statistics calculated over short time periods or in limited geographic areas. Utilizing all available plankton net data collected in the eastern Pacific Ocean (17.4 °S to 61.0 °N; 85.0 to 180.0 °W) since 1999, we estimated a minimum of 21,290 t of floating microplastic.

Comparison of Zebra Mussel Veliger Laboratory Enumeration and Sampling Techniques

Zebra mussel (Dreissena polymorpha) invasion greatly impacts aquatic systems, with economic and ecological consequences. Monitoring zebra mussel density and reproductive timing are essential for effective detection, management, and control of this invasive species. Veligers, the free-floating planktonic life stage of zebra mussels, are often monitored to estimate reproductive effort and as a first indicator of zebra mussel invasion. Although many veliger monitoring methods exist and vary greatly in cost and effort, no study has compared results yielded by different sampling techniques. We compared estimated veliger densities collected with offshore vertical plankton net tows and oblique plankton net tows taken from shore from April through October 2011 in Marion Reservoir, Kansas. Secondarily, we compared enumeration results returned by an established laboratory and a laboratory that had recently begun enumerating veligers. Using ANOVA testing, we found no significant difference between sampling methods or laboratories. We recommend using oblique plankton net tows taken from shore because of their potential to reduce monitoring costs compared to other sampling techniques by reducing equipment, time, and manpower expenses.

Microzooplankton in a Warming Arctic: A Comparison of Tintinnids and Radiolarians from Summer 2011 and 2012 in the Chukchi Sea

The Chukchi Sea was sampled in August of 2011, a year of near-normal sea ice among recent years, and again in August 2012, a year of all time record low sea ice. We exploited this sampling to test the hypothesis that different sea ice conditions are associated with differences in abundances or species composition of microzooplankton through an examination of tintinnids and radiolarians. From 18 stations in 2011, and 19 stations in 2012, organisms were enumerated in plankton net tow material, and chlorophyll determinations made (total and ≤ 20 µm) from discrete depth samples. We found that the low sea ice conditions of 2012 were associated with higher chlorophyll concentrations (both total and the ≤ 20 µm size fraction), compared to 2011. However, tintinnid ciliates and radiolarians were much lower in concentration, by about an order of magnitude, compared to 2011. In both years the radiolarian assemblage was dominated by Amphiselma setosa. The species composition of the tintinnid ciliates was similar in the two years, but there were distinct differences in the relative abun- dances of certain species. The 2012, low sea ice assemblage, was dominated by small forms in contrast to 2011, when large species were the most abundant. We present these findings in detail and discuss possible explanations for the apparent differences in the microzooplankton communities associated with distinct sea ice conditions in the Chukchi Sea.

Scales of Spatial Heterogeneity of Plastic Marine Debris in the Northeast Pacific Ocean

Plastic debris has been documented in many marine ecosystems, including remote coastlines, the water column, the deep sea, and subtropical gyres. The North Pacific Subtropical Gyre (NPSG), colloquially called the “Great Pacific Garbage Patch,” has been an area of particular scientific and public concern. However, quantitative assessments of the extent and variability of plastic in the NPSG have been limited. Here, we quantify the distribution, abundance, and size of plastic in a subset of the eastern Pacific (approximately 20–40°N, 120–155°W) over multiple spatial scales. Samples were collected in Summer 2009 using surface and subsurface plankton net tows and quantitative visual observations, and Fall 2010 using surface net tows only. We documented widespread, though spatially variable, plastic pollution in this portion of the NPSG and adjacent waters. The overall median microplastic numerical concentration in Summer 2009 was 0.448 particles m−2 and in Fall 2010 was 0.021 particles m−2, but plastic concentrations were highly variable over the submesoscale (10 s of km). Size-frequency spectra were skewed towards small particles, with the most abundant particles having a cross-sectional area of approximately 0.01 cm2. Most microplastic was found on the sea surface, with the highest densities detected in low-wind conditions. The numerical majority of objects were small particles collected with nets, but the majority of debris surface area was found in large objects assessed visually. Our ability to detect high-plastic areas varied with methodology, as stations with substantial microplastic did not necessarily also contain large visually observable objects. A power analysis of our data suggests that high variability of surface microplastic will make future changes in abundance difficult to detect without substantial sampling effort. Our findings suggest that assessment and monitoring of oceanic plastic debris must account for high spatial variability, particularly in regards to the evaluation of initiatives designed to reduce marine debris.