Plankton Net Tows Research Articles

Particulate carbon and nitrogen fluxes and compositions in the central equatorial Pacific

Mass, carbon, and nitrogen fluxes and carbon and nitrogen compositions were determined for particulate samples from plankton net tows, shallow floating sediment traps, intermediate and deep moored sediment traps, and sediment cores collected along 140°W in the central equatorial Pacific Ocean during the US JGOFS EqPac program. Mass, particulate organic carbon (POC), and particulate inorganic carbon (PIC) fluxes measured by the floating sediment traps during the Survey I (El Niño) and Survey II (non-El Niño) cruises follow essentially the same pattern as primary production: high near the equator and decreasing poleward. POC fluxes caught in free-floating traps were compared with alternative estimates of export fluxes, including 234Th models, new production, and other sediment trap studies, resulting in widely differing estimates. Applying 234Th corrections to the trap-based fluxes yielded more consistent results relative to primary production and new production. Despite factors of five differences in measured fluxes between different trap types, POC : 234Th ratios of trap material were generally within a factor of two and provided a robust means of converting modeled 234Th export fluxes to POC export fluxes. All measured fluxes decrease with depth. Trap compositional data suggest that mineral “ballasting” may be a prerequisite for POC settling. POC remineralization is most pronounced in the epipelagic zone and at the sediment–water interface, with two orders of magnitude loss at each level. Despite seawater supersaturation with respect to calcium carbonate in the upper ocean, 80% of PIC is dissolved in the epipelagic zone. Given the time-scale differences of processes throughout the water column, the contrasting environments, and the fact that only 0.01% of primary production is buried, sedimentary organic carbon accumulation rates along the transect are remarkably well correlated to primary production in the overlying surface waters. POC to particulate total nitrogen (PTN) ratios for all samples are close to Redfield values, indicating that POC and PTN are non-selectively remineralized. This constancy is somewhat surprising given conventional wisdom and previous equatorial Pacific results suggesting that particulate nitrogen is lost preferentially to organic carbon.

Methods for estimating decapod larval supply and settlement: importance of larval behavior and development stage

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 209:257-273 (2001) - doi:10.3354/meps209257 Methods for estimating decapod larval supply and settlement: importance of larval behavior and development stage Per-Olav Moksnes*, Håkan Wennhage Göteborg University, Kristineberg Marine Research Station, 45034 Fiskebäckskil, Sweden *E-mail: p.moksnes@kmf.gu.se ABSTRACT: In marine benthic organisms with a pelagic larval phase, assessment of recruitment regulation necessitates accurate estimates of larval supply and initial settlement densities. We assessed 2 commonly used methods for estimating decapod larval supply, plankton net tows and artificial settlement substrates (ASS), together with a new technique using passive-migration traps. The aim was to evaluate how these methods estimate larval supply and settlement of 3 common decapod species (the shore crab Carcinus maenas L., the brown shrimp Crangon crangon L. and the grass shrimps Palaemon spp.) in a microtidal nursery area on the Swedish west coast, and to assess how these estimates relate to the juvenile recruitment of these species. Discrete plankton net tows outside the shallow nursery area collected a higher proportion of larvae at an early development stage, compared to the other methods, and produced only a snapshot of the variable water-column abundance of shore crab and grass shrimp larvae that correlated poorly with numbers collected with ASS at the same location. Artificial settlement substrates appeared to produce good, integrated relative estimates of shore crab larval supply and settlement. The number of larvae collected from ASS correlated significantly with larval abundance estimated by passive-migration traps in shallow nursery areas, and reflected changes in shore crab settlement densities in caged mussel habitats. We did not detect any effect of predation on ASS placed in nursery areas. However, a large proportion (an estimated 83%) of shore crab postlarvae appeared to emigrate from ASS immersed for periods longer than 12 h, possibly during the night. All grass shrimp larvae appeared to emigrate from the collectors within 24 h, suggesting that ASS immersed longer than 12 h do not produce useful integrated estimates of larval supply for this species. These results demonstrate the importance of assessing postlarval emigration patterns from ASS to optimize immersion and collection time, and to avoid confounded estimates of larval abundance and settlement. A new method using replicated passive migration traps that fished continuously in opposite directions (on-shore and off-shore) gave promising integrated estimates of net fluxes (total number immigrating minus number emigrating per unit time) of both pelagic postlarvae and early benthic juvenile stages of crabs and shrimp. The majority of the brown shrimp recruits were young juveniles, demonstrating the importance of incorporating juvenile migration in recruitment studies of motile benthic species. High numbers of shore crab and grass shrimp larvae were found to emigrate from the bay, indicating that many decapod postlarvae found in nursery areas may be transitional. The emigrating larvae were on average in an earlier development stage than those migrating to the bay. These short-term experiments demonstrate the importance of assessing larval development stage and migratory behavior when estimating larval supply and settlement for recruitment studies. KEY WORDS: Larval supply · Settlement · Juvenile migration · Development stage · Sampling problems Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 209. Online publication date: January 05, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Preparing Diatoms for EM

Abstract Diatoms make for beautiful specimens for both transmission and scanning electron microscopy. As well, they are studied by many people, and there is always a need for good diatom preparations for EM. I find that the diatoms in diatomaceous earth are usually broken, and like to prepare my own from fresh specimens. The materials needed for this are a plankton net, some potassium dichromate, and 30% hydrogen peroxide. Once the diatoms are collected (plankton net tows from shoreline, or wherever), they can be cleaned using the chemicals.

Zooplankton production in Lake Ontario: a multistrata approach

We present evidence that estimates of annual zooplankton production in Lake Ontario based on stratified plankton net tows are preferable to those based on single, integrated tows through the whole water column. Samples were collected roughly every 2 weeks during 1993 and 1994 at a deep midlake station and at a shallower nearshore station. Stratified net tows were taken through each of the epilimnion, metalimnion, and hypolimnion and the mean temperatures of these strata used in production calculations. Integrated net tows were taken through the whole water column and the mean temperature of the column used in production calculations. Production estimates based on stratified samples were consistently higher (up to 310%) than those based on integrated samples. We show that higher stratified estimates are partly due to higher plankton net filtering efficiency over the shorter stratified hauls and partly due to the lower mean temperatures used in integrated hauls. Our analyses provide a basis for approximating the error in integrated production estimates caused by temperature stratification, water column depth, and plankton net efficiency.

Larval distribution of Ophiothrix fragilis (Echinodermata: Ophiuroidea) in a macrotidal area, the Dover Strait (eastern English Channel, France)

Seasonal and spatial variations in the distribution and abundance of Ophiothrix fragilis larvae (2-arm to 8-arm stages) were determined from a series of plankton net tows in the Dover Strait in 1995 and 1996. Ophioplutei appeared in the plankton between June and September. Larval population was constituted by ophioplutei from different spatio–temporal origins. A major fraction of the ophioplutei observed in the Dover Strait might come from a population localized southward.

The influence of shelf vicinity on the distribution of planktic foraminifera south of Puerto Rico

The effects of water masses and depth on the distribution of planktic foraminifera across the island slope of southwestern Puerto Rico were studied in Holocene surface sediments. Samples from the depth range of 432–4700 m covered 0.5–95 km distance from the shelfbreak. Shallower samples in this region are altered by winnowing. Plankton net tows through the upper 120 m of the water column sampled the living planktic foraminiferal population in the same area. They contained shallow water benthic foraminifera that were probably brought into suspension on the shelf and transported seawards with the shelf outflow water, illustrating the exchange of water and suspended particles from the shelf to the slope. The grain size spectrum of the sediment samples shows no depth-related trend. The sand fraction (>63 μm) consists of foraminifera, pteropoda and, on the upper slope, of reef detritus. The bulk carbonate content varies from 51 to 73%. The abundance of planktic foraminifera per gram sediment increases with depth, while the number of benthic foraminifera decreases with water depth. The composition of the benthic assemblage shows an increase of the ratio of agglutinated versus calcareous perforate forms. The planktic foraminiferal assemblage (>150 μm) is dominated by Globigerinoides ruber and shows no obvious trend over the sampled depth range. The plankton/benthos ratio increases with depth from 0.63 to 0.99 as a result of opposite trends in accumulation rates of benthic and planktic foraminifera. Accumulation rates of planktic foraminifera increase with distance from the shelfbreak and with water depth from 10,000 to 30,000 specimens cm-2 ka, indicating the influence of ecological and/or depositional processes on their distribution. It is suggested that the tests of planktic foraminifera are displaced in a seaward direction by lateral advection. Therefore, their place of deposition does not lie directly underneath the place of production.

Precision of different methods used for estimating the abundance of the nitrogen-fixing marine cyanobacterium, Trichodesmium Ehrenberg.

Variances involved in estimating the abundance of the nitrogen-fixing marine cyanobacterium, Trichodesmium Ehrenberg, were evaluated by repeated sampling using bottle casts and plankton net tows at two stations in the southern East China Sea. The variance among individual samples and the variance arising from subsampling processes were separated by the method of analysis of variance, and the coefficient of variation (C.V.) of an abundance estimate based on a single subsample was calculated. For bottle-collected samples, the major source of variation came from taking subsamples from a water bottle. The C.V. of a single subsample estimate ranged from 57% to 184%. For net-collected samples, variance in abundance estimation was mainly caused by distinctive net tows, and when distributing materials in the receiving bucket into smaller containers. The C.V.s of single subsample estimates were 34% and 40%, respectively. Trichodesmium abundance estimated with bottle- and net-collected samples were further compared using data obtained from 17 stations in the East China Sea. Although a general distribution pattern was supported by both methods, the correlation coefficient between them was 0.461, not significantly different from 0.

First Record of Daphnia lumholtzi Sars in the Great Lakes

Adults of the cladoceran Daphnia lumholtzi, native to Australia, Africa, and parts of Asia, were first collected in August 1999 in Lake Erie. Individuals were collected near East Harbor State Park, Lakeside, Ohio from vertical plankton net tows. The average number of D. lumholtzi that were found (0.03/L) indicate that D. lumholtzi is beginning to establish itself in Lake Erie. The morphology of this Daphnia differs greatly from native species because of its elongated head and tail spine. This sighting is important because it acknowledges yet another exotic invader into the Great Lakes basin and it also shows that this, normally, warm water species continues to expand its range northward.

Distribution of zooplankton in the Northeast Water Polynya during summer 1992

Abstract The distribution and abundances of zooplankton in the Northeast Water (NEW) Polynya during the summer of 1992 have been determined from samples collected with Bongo (this study) and MOCNESS (earlier analysis) plankton net tows. The initial hypothesis was that the troughts of the Greenland Shelf in the region of the NEW polynya would be conduits for the infusion of zooplankton species of Arctic and North Atlantic origin on to the shelf. Analysis of MOCNESS tows indicated instead that advection of zooplankton onto the shelf in the polynya region was limited, resulting in low abundances of the large herbivores in the polynya. The distribution of zooplankton determined from the 43 Bongo tows reported here strengthen this finding. Low abundances of the large herbivorous copepods and of other primarily herbivorous zooplankton taxa were observed throughout the ice-free region, in contrast to higher abundances observed further to the east in Westwind Trough or in the south in Belgica Trough. Cluster analysis was used to identify groups of co-occurring zooplankton taxa and groups of stations with similar relative compositions of zooplankton taxa. The community composition of the Belgica Trough was distinctly different from that observed in northern regions, with high abundances of open ocean copepods ( Calanus finmarchicus and C. hyperboreus ). Two types of communities were identified in the northern regions: one typical of the eastern basin (Westwind Trough) and one typical of the western basin (Norske Trough) of the northern trough. The relationship between the different zooplankton communities and the water mass characteristics was not conclusive; however, it did appear that zooplankton populations had been advected in the upper water column into the Westwind Trough from north of the study area. The low abundances of herbivorous taxa in the ice free region supported previous estimates that meso-macro zooplankton may not be significant consumers of primary production in the polynya.

Sampling larval fishes with a nightlight lift-net in tropical inshore waters

The applicability of a nightlight lift-net for sampling ichthyoplankton assemblages was evaluated in inshore habitats off southwestern Puerto Rico. The effects of lunar periodicity, habitat, light duration, and gear type (nightlight vs. plankton tow) were investigated. Overall, 36 piscine taxa were collected with the nightlight lift-net from inshore habitats (i.e. coral reef, mangroves, seagrass bed, sand flat). Larval fishes (80.6%), particularly clupeids ( Jenkinsia spp. and Harengula spp.), were the predominant developmental stage collected. Juvenile and adult fishes accounted for 14.7% and 4.7% of the catch, respectively. Nightlight collections showed marked patterns in larval fish abundance during different lunar phases with peak catchability occurring during the new moon phase. New moon samples accounted for 65.7% of all larvae collected during the complete lunar cycle. Significant lunar effects were observed in coral reef, seagrass bed, and sand flat habitats. No lunar related trends were observed in mangrove cay or nearshore mangrove habitats. Spatial patterns in nightlight catches were present with many taxa showing significant differences in abundance among habitats sampled. During lunar periodicity trials, catches were highest in the seagrass bed and coral reef habitats. Taxonomic diversity was greatest in seagrass bed and coral reef habitats with 16 and 11 taxa, respectively. Low abundance and taxonomic diversity characterized mangrove cay and nearshore mangrove habitats; however, increases in taxonomic diversity were observed during a fall survey of nearshore mangrove habitats. Light duration experiments indicated that larval abundance increased with increasing sampling duration and maximum catch per unit time was obtained at 10 min. Longer and shorter durations resulted in lower catch per unit effort and greater coefficients of variation. Trends in species composition and development stage were detected among nightlight lift-net and plankton net-tow methods.

Neutral carbohydrate geochemistry of particulate material in the central equatorial Pacific

Neutral carbohydrate compositions were determined for particulate samples from plankton net tows, shallow floating sediment traps, mid-depth and deep moored sediment traps, and sediment cores collected along a north-south transect in the central equatorial Pacific Ocean during the U.S. JGOFS EqPac program. Total neutral carbohydrate depth profiles and patterns along the transect follow essentially the same trends as bulk and organic carbon (OC) fluxes—attenuating with depth, high near the equator and decreasing poleward. OC-normalized total aldose (TCH 2,O) yields along the transect and with depth do not show any consitent patterns. Relative to a planktonic source, neutral carbohydrate compositions in sediment trap and sediment core samples reflect preferential loss of ribose and storage carbohydrates rich in glucose, and preferential preservation of structural carbohydrates rich in rhamnose, xylose, fucose, and mannose. There is also evidence for an intermediately labile component rich in galactose. It appears that compositional signatures of neutral carbohydrates in sediments are more dependent upon their planktonic source than on any particular diagenetic pathway. Relative to other types of organic matter, neutral carbohydrates are better preserved in calcareous oozes from 12°S to 5°N than in red clays at 9°N based on OC-normalized TCH 2O yields, due to either differing sources or sorption characteristics. Weight per cent glucose generally decreases with increased degradation of organic material in the central equatorial Pacific region. Based on weight per cent glucose, comparisons of samples between Survey I (El Niõn) and Survey II (non-El Niño) indicate that during Survey I, organic material in the epipelagic zone in the northern hemisphere may have undergone more degradation than organic material in the southern hemisphere.

Spatial and temporal distribution and recruitment of echinoderm larvae in the Ligurian Sea

Seasonal and annual variations in the distribution and abundance of echinoderm larvae (early to post-larvae of principally echinoids and ophiuroids), were determined from a series of plankton net tows taken at three stations in the Bay of Villefranche (France) and along a radial transect of 28 nautical miles (52 km), from the Bay to half-way to Corsica, between 1984 and 1988. Spatial distribution of six echinoderm species have been mapped. For the echinoids, Paracentrotus lividus and Arbacia lixula, spawning takes place twice a year and appears to be synchronous because larval cohorts were comprised of distinct age-classes both near and far from the coast. Recruitment for these species is, therefore, thought to occur at well-defined periods. In contrast, the ophiuroid species studied (Amphiura filiformis, Ophwthrix fragilis, Ophiopluteus bimaculatus and O. compressus) spawn several times per year with a relatively short period in late spring and a prolonged spawning between the end of autumn and winter. These later results are consistent with the presence of mixed size-classes of larvae either from the nearby coast or offshore. Recruitment for these ophiuroids appears to be much more variable and spread over time.

Quantification of diarrhetic shellfish toxins and identification of novel protein phosphatase inhibitors in marine phytoplankton and mussels

Liquid chromatography (LC)-linked protein phosphatase 1/2A (PP-1/PP2A) bioassay was used to quantitatively identify diarrhetic shellfish toxins in marine phytoplankton (cultured and natural assemblages) and commercially available mussels. Using this approach, multiple protein phosphatase inhibitor profiles of varying composition were found in diarrhetic mussels from Holland and Canada. Based on LC elution positions and relative activity versus PP-1 and PP-2A, at least six inhibitors distinct from known diarrhetic shellfish toxins were identified and termed mussel phosphatase inhibitor (MPI) 19,22,23,25,33 and 42. The levels of these inhibitors, in okadaic acid equivalent units, varied from 100 pg to 3350 ng per g shellfish tissue. The combined levels of PP-1/2A inhibitors in all instances superseded that of okadaic acid/dinophysistoxin-1 and may contribute to the diarrhetic shellfish toxin profile of the contaminated mussels. The efficacy of LC-protein phosphatase bioassay was established for cultured phytoplankton where picogram levels of okadaic acid could be detected from microgram extracts of Prorocentrum lima. Analyses of plankton net tows from estuarine mussel culture sites in Eastern Canada revealed a heterogeneous population of protein phosphatase inhibitors, with dinophysistoxin-1 being most prevalent. This toxin was predominant for at least 2 months in mussel populations in the immediate vicinity of plankton sampling sites. The results are consistent with a hypothetical model in which marine bacteria, cyanobacteria and dinoflagellates combine to produce a variety of protein phosphatase inhibitors effective against signal transduction pathways in higher eukaryotes.

The deep scattering layer associated with the Endeavour Ridge hydrothermal plume

We analyse surface-to-bottom profiles of temperature, salinity, light attenuation coefficient and acoustic (150 kHz) backscatter intensity collected in June 1990 in the vicinity of the central hydrothermal vent field on Endeavour Ridge in the northeast Pacific. Data from coincident deep plankton net tows corroborate earlier speculation (Thomson et al., 1991, Journal of Geophysical Research, 96, 4839-4844) that the 100 m thick acoustic scattering layer found near 1.9 km depth in this region consists of a dense concentration of macrozooplankton living near the top of the plume-contaminated bottom waters. Peak (≈10 dB) acoustic anomalies in the June 1990 backscatter layer were located near the top of the plume at depths of 1800–2000 m throughout the principal 60 km 2 study area. The scattering layer contained a high Zooplankton biomass of 21 mg m −3 and maximum species richness of 83 taxa. In all profiles, the backscatter intensity decreased to anomalously low values beneath the core of the plume. The presence of the backscatter layer 12 km to the east of the vent site is evidence for Zooplankton layering beyond the immediate confines of the ridge. We conclude that pelagic and deep-sea Zooplankton congregate near the top of the plumecontaminated bottom waters in the vicinity of the ridge to take advantage of increased concentrations of chemosynthetic bacteria, fine-grained particles and other nutrients carried vertically upward by the buoyant portions of the plume. The Zooplankton depletion below the central core of the spreading hydrothermal plume indicates that Zooplankton avoid elevated concentrations of hydrothermally-derived minerals and other chemicals inherent to the main body of the plume.

Occurrence and distribution of milkfish larvae,Chanos chanos off the western coast of Panay Island, Philippines

The occurence and distribution of milkfish larvae (∼3–17 mm TL) off western Panay Island, Philippines are reported based on 594 plankton net tows made in April and May 1980. Forty-two tows yielded 44 larvae, together with 1149 milkfish eggs by 98 tows. About 70% of the larvae of all stages came from stations less than 100 m deep and 1–2 km from land. Younger larvae up to 6 mm and about 1 week old occurred at stations of various distances from shore, while older larvae occurred only near shore. About 48% of larvae of all stages were caught by surface tows; younger larvae occurred also in deeper layers (20 and 30 m). Larval abundance increased towards May. Younger larvae tended to occur during the quarter moon periods and older ones during the full and new moon periods.

La répartition horizontale et verticale des larves de homard (Homarus americanus) autour des îles de la Madeleine, golfe du Saint-Laurent

Thirty-nine stations localized around the eastern tip of the Îles de la Madeleine, in two lagoons, and in the baie de Plaisance were sampled using plankton net tows during the summers of 1978, 1980, and 1981. The horizontal and vertical distributions of each of the four larval stages of Homarus americanus were assessed from sets of surface tows using simple neuston and meter nets (1978 and 1980) as well as a three-compartment plankton net (1981). Most of the stage I larval production takes place in the northeast and southeast regions. However, the abundance of stage IV larvae is low in the southeast and almost nil in the northeast. By contrast, the baie de Plaisance harbors very few stage I larvae, but a very high proportion of stage III and IV larvae. The periods of first appearance and maximum abundance are also out of phase for the three regions, occurring in the northeast before the southeast and the baie de Plaisance. These results suggest that the general pattern of abundance of larvae is driven by the current regime, flushing the larvae around the Pointe de l'Est and concentrating them in the baie de Plaisance following a gyre. On a smaller scale, 12 stations arranged in a 3 × 4 grid in the baie de Plaisance were sampled for 12 wk in the summer of 1980. The first three larval stages show a strongly aggregated distribution and are most frequent at the mouth of the bay. Conversely, stage IV larvae are found more frequently in the shore stations and inside the bay. There is a significant correlation between stage IV larval abundance and the distance to rocky bottoms favorable to benthic life. The vertical distribution of larvae at two stations (1981) shows that only the stage I larvae have a vertical distribution related to light intensity, being found in highest abundance in the surface layer (0–0.8 m) at dusk and dawn. Stage I larvae were uniformly distributed between 0 and 1.6 m during the day and down to 2.4 m at night. Stage II, III, and IV larvae were always found near the surface.