Plankton Net Research Articles

Temporal distribution and early development of Moenkausia cf. gracilima (Lucena & Soares, 2016) (Osteichthyes, Characidae) in the upper Paraná River, Brazil

Abstract Aim: To analyze temporal distribution of larvae and juveniles and the early development and of Moenkhausia cf. gracilima. Methods Samples were taken quarterly in twenty-five sites in the upper Paraná River floodplain between August 2013 and May 2015. The samples were taken under the water surface at night using 0.5 mm mesh plankton nets. In the laboratory, samples were sorted, identified and separated into larval (preflexion, flexion and postflexion) and juvenile periods. Results A total of 248 individuals was collected, mainly in the Saraiva Lagoon, suggesting that the entire life cycle of this species occurs in this environment. The reproductive period takes place between December and April, since the postflexion larvae were found until May. However, the occurrence of juveniles between February and May indicates probable batch spawning. Among the 95 individuals used for ontogenic description, 82 were larvae and 13 juveniles. Larvae may be characterized by irregular pigmentation in the upper region of the head, mouth, and body, increasing throughout development; upper lobe of the caudal fin more pigmented than the lower lobe, only visible in postflexion larvae; terminal mouth; anal opening located anterior to the median region of the body and total number of myomers ranging from 34 to 40 (15 to 20 pre and 16 to 23 postanal), while juveniles have characteristics similar to adults. The total number of fin rays is: P. 11-16, V. 7-11, D, 9-11 and A. 21-23. Conclusions According to the distribution of developmental periods it is possible to conclude that this species reproduces in the summer, preferably in lagoons. Growth analysis indicated important alterations in larval morphology (metamorphosis) that may be associated with the ecomorphological characteristics of the species. The morphological separation of larvae of M. cf. gracilima from other larvae of small characids, especially at preflexion and flexion stages may be complicated by the overlap of traits, suggesting the use of other variables, mainly morphometric, for the separation of the species.

Horizontal and vertical distribution of sea lice larvae (Lepeophtheirus salmonis) in and around salmon farms in the Bay of Fundy, Canada.

The sea louse, Lepeophtheirus salmonis, is parasitic to salmonid species in the Northern Hemisphere and has become a widespread biological and economic problem for the salmon farming industry. A better understanding is needed of their spatial distribution and early life history to disrupt the life cycle of the sea louse. In this study, sea lice larval densities within salmon farms, between salmon farms and reference sites, and at various depths were quantified using both plankton pumps and plankton nets. Farm sites exhibited significantly higher densities than reference sites; however, these densities dropped an order of magnitude at a distance of 100m from the cages. The majority of the larvae captured in the study were nauplii (93%), and densities ranged from 0 to 10 larvae/m3 . Free-swimming sea lice larvae were found to exhibit a diel cycle where nauplii larvae were in deeper waters (10-17m) during the day and in surface waters (1-6m) during the night. The results of this study suggest that the early life-history stages of sea lice originate from and may remain close to active salmon farms, creating a self-sustaining population.

Phytoplankton diversity of floodplain lakes of the Majuli River Island of the Brahmaputra river basin, Assam, northeast India

Phytoplankton of three floodplain lakes (beels) of the Majuli River Island of upper Assam, northeast India (NEI), sampled during September 2010–August 2012, revealed rich diversity (108 species) with Ghotonga > Holmari ≥ Bhereki beels; richness of Chlorophyta and of Cosmarium > Staurastrum > Euastrum in particular. The monthly richness and community similarities affirmed heterogeneity in phytoplankton composition. Phytoplankton comprised between 59.5±12.5, 57.1±12.3 and 48.6±13.5% of net plankton abundance of Bhereki, Holmari and Ghotonga beels, respectively. Bacillariophyta > Chlorophyta showed quantitative importance in Bhereki while Chlorophyta > Bacillariophyta recorded importance in Holmari and Ghotonga beels. Cyanophyta showed sub-dominance and Dinophyta > Euglenophyta showed low densities in the three beels. Phytoplankton richness and abundance followed oscillating monthly variations; ANOVA registered insignificant richness variations amongst beels. The results are characterized certain monthly and annual variations but mean values depicted high species diversity, low dominance and high equitability. Individual and cumulative influence ( vide CCA) yielded limited insight on the role of seventeen abiotic factors on phytoplankton in Holmari and Bhereki beels.

Low Abundance of Plastic Fragments in the Surface Waters of the Red Sea

The floating plastic debris along the Arabian coast of the Red Sea was sampled by using surface-trawling plankton nets. A total of 120 sampling sites were spread out over the near-shore waters along 1,500 km of coastline during seven cruises performed during 2016 and 2017. Plastic debris, dominated by millimeter-sized pieces, was constituted mostly of fragments of rigid objects (73%) followed by pieces of films (17%), fishing lines (6%) and foam (4%). These fragments were mainly made up by polyethylene (69%) and polypropylene (21%). Fibres, likely released from synthetic textiles, were ubiquitous and abundant, although were analyzed independently due to the risk of including non-plastic fibres and airborne contamination of samples in spite of the precautions taken. The plastic concentrations (excluding possible plastic fibres) contrasts with those found in other semi-closed seas such as the neighboring Mediterranean. They were relatively low all over Red Sea (< 50,000 items km-2; mean ± SD = 3,546 ± 8,154 plastic item km-2, 1.1 ± 3.0 g km-2) showing no clear spatial relationship with the distribution of coastal population. Results suggests a low plastic waste input from land as the most plausible explanation for this relative shortage of plastic in the surface waters of the Red Sea; however, the additional intervention of particular processes of surface plastic removal by fish or the filtering activity of the extensive coral reefs along the coastline cannot be discarded. In addition, our study highlights the relevance of determining specific regional conversion rates of mismanaged plastic waste to marine debris, accounting for the role of near-shore activities (e.g. beach tourism, recreational navigation), in order to estimate plastic waste inputs into the ocean.

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...

Keanekaragaman, Kelimpahan, dan Sebaran Kopepoda (Krustasea) di Perairan Bakau Segara Anakan, Cilacap

&lt;strong&gt;Diversity, Abundance, and Distribution of Copepods (Crustacea) in the Mangrove Area of Segara Anakan, Cilacap.&lt;/strong&gt; Observations on the diversity of Copepods, its abundance, and its distribution in three mangrove and estuarine locations in Segara Anakan Lagoon, Cilacap, were conducted in May (dry season) and November (rainy season) 2009. This study aims to determine the relationship of diversity and abundance of Copepods with some environmental factors that affect its distribution in the dry and rainy seasons. Copepod samples were taken from Kutawaru waters, Dermaga Sleko, and Ciperet using vertical and horizontal plankton nets, day and night. They were then preserved, deposited, and identified in MZB LIPI. There were 36 species of Copepods from 18 genera and 20 families, including 10 new records. The highest species diversity of Copepods was recorded in November, while the lowest was in May. The average abundance in May was higher than in November. The diversity and abundance in Ciperet in both dry and rainy seasons were always higher than the other two sites. Acartia erythraea, A. sinjiensis and Pseudodiaptomus annandalei were found to dominate the waters especially during the dry season in May. The community composition of Copepods occupying the waters was determined by salinity, while its activity and development were determined by temperature. &lt;br /&gt;

Microphytoplankton biomass and trophic state of the Estuarine Region of São Francisco River (northeastern Brazil)

One of the most serious problems that affect estuaries is the excessive enrichment of nutrients, especially nitrogen and phosphorus compounds that result in increased productivity. Studies to evaluate the trophic conditions of the São Francisco River estuary were conducted at four stations in the rainy (July/ 2006 ) and dry (January/2007) season in neap and spring tides, during high tide and low tide. Microphytoplankton was collected using plankton nets with mesh size of 45mm and the samples for analysis of nutrients and Phytoplankton biomass (chlorophyll a) were obtained from the sub-surface layer with wide-mouthed plastic bottles. The waters of this ecosystem showed salinities ranging from an oligohaline to a limnetic regime, alkaline pH and water clarity ranging between 1.00m and 2.60m. The concentrations of dissolved nutrients varied considerably, being highest during the dry season period. The Microphytoplankton was composed of 176 taxa, mainly distributed among the Chlorophyta, Charophyta and Bacillariophyta. Phytoplankton biomass (chlorophyll a) showed no significant differences between seasons, tides and tidal regimes, however the density (Cel.L-1) was significantly higher in the dry season. Values of a TSI showed oligotrophic conditions in the four stations and in the two periods analyzed. In the dry season there was a higher cell density and increased levels of dissolved nutrients with the exception of nitrate that was considered higher in the rainy season. The Microphytoplankton species are characteristic of waters of low to moderate trophic level and the TSI indicated a predominance of oligotrophic conditions in the two seasons in the study area.Keywords: chlorophyll a, estuary, hydrology, phytoplankton, seasonality

Associations between lobster phyllosoma and gelatinous zooplankton in relation to oceanographic properties in the northern Gulf of Mexico

AbstractLobster phyllosoma are known to associate with large cnidarian medusae; however, direct quantitative observations are difficult because gelatinous zooplankton are extremely fragile, and the phyllosoma easily detach from their host when sampled by plankton nets. We provide the first large scale quantitative information of the distribution of this association using an in situ imaging system, with synoptic measurements of water column properties. All phyllosoma were identified as slipper lobsters (Scyllarus chacei) and were associated with previously unreported “hosts” such as small hydromedusae, doliolids, and siphonophores in the northern Gulf of Mexico. Along the shelf, phyllosoma were more likely to be present at greater depths and higher salinities. Approximately 30% of the 347 lobster phyllosoma imaged were attached to at least one gelatinous organism, and salinity and depth were positively related to the probability of attachment on 30 October, but did not show a significant relationship for the other days of sampling. Many of the phyllosoma were larger than the gelatinous organisms to which they were attached, and some gelatinous zooplankton showed damage likely from feeding by the phyllosoma. In this coastal environment, gelatinous zooplankton tended to be more abundant in the same offshore region where phyllosoma occurred, so these gelatinous “hosts” may provide a steady food supply in the more oligotrophic waters on the outer shelf. Similar complex interactions among zooplankton may influence the life histories of other species, hindering our ability to forecast ecosystem level processes until the population level consequences of species interactions are fully understood.

Diversity and Abundance of Marine Plankton and Benthos of Maruthankerny, Off Jaffna, Sri Lanka

The distribution of plankton and macrobenthos along the coasts from the Northern and North-Eastern to South-Eastern is virtually unknown. Therefore, present study was carried out to determine the species composition, abundance and distribution of marine plankton and benthos off Jaffna, Sri Lanka to enhance the knowledge on biodiversity of this coastal environments. Field survey was conducted during February 2016. Benthic samples with triplicate were collected from selected 18 locations at Maruthankerny, Jaffna using a Peterson grab and immediately fix using 10% formalin. The benthic samples were subjected to wet sieving through 500 μm mesh sieve to separate the benthic fauna from the substrate. The organisms retain in the sieve were collected and preserved in 70% alcohol and identified up to the lowest possible taxonomic level. Vertical hauls of zooplankton and phytoplankton were collected from 12 locations using plankton nets with mesh sizes of 100 μm and 10 μm respectively. The zooplankton and phytoplankton samples were immediately fixed with 5% formalin and Lugol’s solution respectively. In the laboratory, one milliliter of each sample was placed on the Sedgewick rafter counting chamber and organisms were identified and enumerated using a binocular microscope. Twenty six (26) species of polychaetes, 9 species of crustaceans, 15 species of gastropods, 12 species of bivalves and 2 species of echinodermates were recorded in benthic samples. The most abundant group of macrobenthos was polychaetes, which contributed for 45.25% of total macrobenthic community, followed by mollusks (35.51%). The phytoplankton analysis showed that abundance varied from 279 to 866 No./L with a mean of 554±201 No./L. A total of 92 taxa were reported from the area. Sixty eight (68) taxa were identified as diatoms, while 24 taxa were belonged to dinoflagellates. Diatoms accounted for 93.97% of the total phytoplankton population at the area followed by dinoflagellates (6.03%). Most dominant phytoplankton taxa was Chaetoceros sp. which contributed 33.70% of the total population followed by Bacteriastrum (16.24%). Species richness of phytoplankton in the area varied from 48-68 with a mean 55.83±5.70. Zooplankton abundance varied from 36 to 385 indivi. L-1 with a mean of 91.57±46.02 indivi. L-1 in the study area. Most dominant group was copepods, which comprised 52.87% followed by crustacean larvae (nauplii, 9.89%). Most common zooplankton species were Calanus sp. (10.01%), Oithona sp. (6.89%), Paracalanus sp. (4.19%) and Oithona aculata (3.97%). Keywords: Phytoplankton, Zooplankton, Macrobenthos, Jaffna, Sri Lanka

The light at the end of the funnel?: Using light-based traps for the detection and collection of a nearshore aquatic, invasive invertebrate, Hemimysis anomala

Abstract Early detection of aquatic, non-native species can be challenging due to low densities, multiple life stages, and unpredictable conditions. This has led to calls for novel approaches to improve detection as well as facilitate control and eradication of emerging invaders. We explored if subaquatic traps that utilize the behavioral response of organisms to preferred light conditions could effectively capture Hemimysis anomala , an invertebrate that is expanding its range in aquatic systems throughout Europe and North America. Light-based traps provided a reliable alternative to monitoring with plankton nets and traps, as this invertebrate seeks refuge in crevices that are inaccessible to most sampling gear. In the field (Seneca Lake, NY USA), light-based traps of two designs—bucket and funnel traps—were highly effective at capturing Hemimysis , with limited non-target catch. Trap collections were representative of the juvenile-dominated population surveyed by concurrent net tows. In the laboratory, funnel traps were more successful than bucket traps at capturing Hemimysis . Funnel traps attracted 25 to > 80% of organisms introduced into aquaria. Once introduced into the trap, approximately 80% of organisms were retained, with no systematic difference in the demographic characteristics between organisms that remained and those that escaped. Light-based traps are a promising monitoring strategy across a range of densities (7 to nearly 1000 Hemimysis /m 3 based on our laboratory and field studies) for this rapidly expanding Ponto-Caspian invader that has the potential to impact recipient communities. As the behavior and life cycle of many aquatic species are tied to light intensity, the traps we describe for Hemimysis may be applied to the early detection of other species for which light preferences are known.

Sampling sufficiency for estimating zooplankton diversity in neotropical floodplain lakes

AbstractThis study focuses on determining how many samples are needed to effectively assess the species richness of a community. Zooplankton samples at 40 sampling sites distributed among four lakes in the floodplain of the middle Araguaia River (Central‐West region of Brazil) were evaluated to determine the effect of the accumulation of collecting points by lake on species richness estimates. The results indicated the zooplankton community has high spatial heterogeneity. Thus, using a single sampling unit per lake would not be sufficient to accurately estimate their diversity (i.e. the zooplankton composition in these cases would be represented mainly by abundant species). Sampling designs that include a minimum of seven sampling sites in each lake are needed to record 70% of the total species richness. It is recommended, therefore, that researchers use a larger number of sampling sites per lake or, alternatively, that the water obtained and filtered through plankton nets is extracted from a wide area and in different lake compartments, rather than from a single site.

Temporal variability of larval drift of tropical amphidromous gobies along a watershed in Réunion Island

Freshwater gobies of tropical islands are amphidromous: adults reproduce in rivers and larvae passively drift down to the sea immediately after hatching. Describing the phenology of this larval drift is essential to understanding the population dynamics of amphidromous gobies and to developing ecologically based recommendations for managing the watersheds. The larval drift patterns of two amphidromous gobies of Réunion Island, Sicyopterus lagocephalus and Cotylopus acutipinnis, were studied on a monthly basis for 1 year using plankton nets at two sites on the Mât River, located 20 km and 7 km from the river mouth. Genetic analyses showed that larval assemblages were dominated at 90% by S. lagocephalus, although the proportion of C. acutipinnis increased during early summer. Our findings highlighted a marked larval drift peak in full austral summer. The diel larval drift dynamic was described using periodic linear models. A diel pattern was only observed downstream, peaking a few hours after sunset. Finally, this study presents a new approach that improves standard methods for sampling and analyzing larval drift of amphidromous species.

Faunistic Survey of Freshwater Microcrustacean Zooplankton of Luzon, Visayas, and Mindanao Islands: New Locality Records and Updated Species Accounts

This paper updates the taxonomy and distribution of microcrustacean zooplankton belonging to Cladocera and Copepoda from selected freshwater bodies of Luzon Island, Panay Island and South Cotabato, Mindanao Island in the Philippines whose zooplankton fauna have remained undocumented to date. A total of 31 sampling sites were visited including 11 ponds, 5 lakes, 12 rivers, 1 man-made dam, and 2 streams. Zooplankton samples were collected using 80mesh size plankton nets, and processed and identified in the laboratory. Morphological characteristics were examined under light compound, dissecting, and phase-contrast microscopes for taxonomic identification. Results showed that 13 species were present from the different sampling sites with 7 cladocerana and 6 copepods. Further analyses revealed new locality records for Mesocyclops ogunnus in Lake Taal and Arctodiaptomus dorsalis in Lake Lahit. All species from Lake Holon are new locality records. Results from this study contributed much needed information to make a thorough analysis on the distribution of microcrustacean zooplankton taxa in the Philippines as well as provide the first accounts of microcrustacean zooplankton from Panay Island.

Fish larval supply to and within a lagoonal estuary: multiple sources for Barnegat Bay, New Jersey

We evaluated spatial variation in fish larval supply to a temperate, lagoon type estuary (Barnegat Bay, New Jersey) by determining species composition, size, and stage into inlets (n = 2), thoroughfares between adjacent estuaries (n = 3), and within the estuary (n = 4) in seasonal, synoptic sampling on night time flood tides during 2010–2014. Larval supply, as sampled with identical plankton nets (1 m diameter, 1 mm mesh) was dominated by post-flexion stage individuals (most 5–10 but reaching 70+ mm) from species spawned in the Atlantic Ocean from a variety of sources (e.g., Sargasso Sea, outer and inner continental shelf) and in the bay. While abundance for individual species varied among locations and years, in general, the larval composition was similar across inlets, thoroughfares, and within the bay within the same seasons. Homogenization across locations was likely the result of the tidal exchanges between the ocean, the estuary, and the adjacent locations. These exchanges provide numerous, redundant sources of larvae to this estuarine nursery. The similarity in larval supply among inlets, thoroughfares, and within the estuary indicates that the longer term study location behind Little Egg Inlet is representative for this, and probably other, estuaries along the New Jersey shore.

Algunos poliquetos holoplanctónicos (Annelida: Polychaeta) del Parque Nacional Isla del Coco, Costa Rica

Los poliquetos holoplanctónicos no han sido estudiados en las aguas oceánicas adyacentes al Parque Isla del Coco. Se estudiaron estas formas pelágicas a partir del análisis de muestras de zooplancton recolectadas en esta área protegida. Las muestras fueron obtenidas mediante redes de plancton estándar (0.2-0.5mm de malla, 0.49m de diámetro de boca) en arrastres horizontales y verticales en la isla oceánica Isla del Coco, Costa Rica, en el Pacífico Tropical Oriental. Los poliquetos pelágicos de esta zona fueron analizados taxonómicamente. El material obtenido incluye representantes de seis especies y cinco familias: Alciopidae, Lopadorhynchidae, Tomopteridae, Polynoidae y Typhloscolecidae. Se presentan diagnosis breves, sinonimias, análisis morfológicos comparativos, ilustraciones taxonómicas y la distribución conocida de las especies recolectadas en el plancton de Isla del Coco. El registro de Drieschia pellucida Moore es el primero en el Pacífico Tropical Oriental; nuestro espécimen muestra algunas diferencias respecto a la descripción original. El resto de las especies han sido encontradas previamente en aguas del Pacífico Tropical Oriental y en el Domo de Costa Rica, pero son los primeros registros para esta área protegida.

Two new methods for sampling zooplankton and larval assemblages in tropical reef ecosystems

Sampling mobile zooplankton on reefs is a major challenge, mainly due to the problems faced when towing plankton nets inside complex reef mosaics. This study presents two new systems that permit precise point sampling of micro- and mesozooplankton and larvae of invertebrates and fish: the Channel Midwater Neuston Net (CMNN) and the Reef Edge Net (REN). Both are moored systems that are equipped with 64- and 300-μm mesh nets. The CMNN system was designed for continuous sampling in tidal channels between reef patches. It samples at three precise depth layers (epineuston: 0m to 0.075m, hyponeuston: 0.075m to 0.225m, 1m layer: 0.925m to 1.075m depth). The REN system allows sampling at precise, adjustable depths at given distances from the reef edge. The objective of the REN is to collect organisms that are washed from reef tops and reef edges with the ebb flow. The performance of these two new systems was evaluated and compared with results obtained by using common Ring nets in horizontal subsurface tows. Fieldwork was performed at two reef patches of the Tamandaré reef system (Brazil) in November 2015. The CMNN and REN showed similar performance in comparison with Ring net tows, capturing microzooplankton communities as well as veliger, polychaete, decapod and barnacle larvae in similar abundances. For the mesozooplankton, the REN presented a similar performance to the Ring net tows, efficiently capturing decapod crustacean and fish larvae as well as fish eggs. The CMNN showed lower abundance of decapod larvae and fish eggs but showed a good performance for the quantification of fish larvae. The two new passive nets showed a high effectiveness in collecting larvae and advantages over tows with Ring nets since they stay for several hours continuously capturing larval aggregations during spawning events. This high capturing efficiency is probably related to the avoidance of sample reflux in the long nets that sink and close at slack tide for the CMNN, and due to the long, trap-like design with funnel-shaped internal “anti-reflux” nets, for the REN. Navigation safety and easy handling are further advantages of these moored systems, as compared to towing plankton nets at nighttime between reefs. CMNN and REN may become useful tools for the study of zooplankton and larval ecology and for integrated long-term studies in marine protected areas and reefs under multiple human impacts.

Abundance of Phytoplankton In The Coastal Waters of South Sumatera

Phytoplankton in the ocean has an important role in forming the base of food chain, responsible in primary production. Its abundance and number of phytoplankton species will indirectly affect the level of water’s fertility. This study aimed to determine the presence of phytoplankton as bio-indicators of water quality in terms of abundance, diversity index, uniformity index, and saprobic coefficient in coastal waters of South Sumatera. The study was conducted on May 2013 - February 2014, at ten stations during high and low tides. Phytoplankton samples were taken vertically using plankton nets, cone-shaped with a diameter of 30 cm, length 100 cm and mesh size 30 μm. The study found 41 genera of phytoplankton, consisted of family Bacillariophyceae (26 genera), Dinophyceae (7 genera) Cyanophyceae (7 genera) and Chlorophyceae (1 genus). The highest number of genera was recorded while low tides in November (24 genera), and the lowest was on May while high tides (16 genera). The highest abundance of phytoplankton was recorded in August during high tides (2,68 x 107 cell.m-3), and the lowest was in May during high tides (6,59 x 105cell.m-3). The diversity index (H'), the uniformity index (E), and the dominance index (D) ranged between 0,64–3; 0,15–0,71 and 0,15–0,83 respectively. Keywords: phytoplankton, abundance, diversity index, South Sumatera coast.

Factors controlling the depth habitat of planktonic foraminifera in the subtropical eastern North Atlantic

Abstract. Planktonic foraminifera preserved in marine sediments archive the physical and chemical conditions under which they built their shells. To interpret the paleoceanographic information contained in fossil foraminifera, the recorded proxy signals have to be attributed to the habitat and life cycle characteristics of individual species. Much of our knowledge on habitat depth is based on indirect methods, which reconstruct the depth at which the largest portion of the shell has been calcified. However, habitat depth can be best studied by direct observations in stratified plankton nets. Here we present a synthesis of living planktonic foraminifera abundance data in vertically resolved plankton net hauls taken in the eastern North Atlantic during 12 oceanographic campaigns between 1995 and 2012. Live (cytoplasm-bearing) specimens were counted for each depth interval and the vertical habitat at each station was expressed as average living depth (ALD). This allows us to differentiate species showing an ALD consistently in the upper 100 m (e.g., Globigerinoides ruber white and pink), indicating a shallow habitat; species occurring from the surface to the subsurface (e.g., Globigerina bulloides, Globorotalia inflata, Globorotalia truncatulinoides); and species inhabiting the subsurface (e.g., Globorotalia scitula and Globorotalia hirsuta). For 17 species with variable ALD, we assessed whether their depth habitat at a given station could be predicted by mixed layer (ML) depth, temperature in the ML and chlorophyll a concentration in the ML. The influence of seasonal and lunar cycle on the depth habitat was also tested using periodic regression. In 11 out of the 17 tested species, ALD variation appears to have a predictable component. All of the tested parameters were significant in at least one case, with both seasonal and lunar cyclicity as well as the environmental parameters explaining up to &gt; 50 % of the variance. Thus, G. truncatulinoides, G. hirsuta and G. scitula appear to descend in the water column towards the summer, whereas populations of Trilobatus sacculifer appear to descend in the water column towards the new moon. In all other species, properties of the mixed layer explained more of the observed variance than the periodic models. Chlorophyll a concentration seems least important for ALD, whilst shoaling of the habitat with deepening of the ML is observed most frequently. We observe both shoaling and deepening of species habitat with increasing temperature. Further, we observe that temperature and seawater density at the depth of the ALD were not equally variable among the studied species, and their variability showed no consistent relationship with depth habitat. According to our results, depth habitat of individual species changes in response to different environmental and ontogenetic factors and consequently planktonic foraminifera exhibit not only species-specific mean habitat depths but also species-specific changes in habitat depth.

Carbon, nitrogen and phosphorus content of seston and zooplankton in tropical Lake Malawi: Implications for zooplankton nutrient cycling

Differences in chemical composition among zooplankton and their food sources can have important consequences for nutrient cycling in lakes. To date, studies of the interaction between plankton stoichiometry and nutrient cycling have focused primarily on temperate lakes. Here we explore the implications of plankton stoichiometry for nutrient cycling in tropical Lake Malawi. Three seston size fractions (picoplankton, nanoplankton and net plankton) displayed seasonal variations in C:P, C:N and N:P ratios. On average, picoplankton displayed lower C:P, C:N, and N:P ratios than nanoplankton and net plankton. Average C:N and C:P ratios for all seston size classes were much higher than Redfield ratios (C:N:P = 106:16:1). The elemental composition of individual species of crustacean zooplankton showed little temporal variation. However, there were large inter-species differences in P and N content, which can be expected to result in differences in N:P recycling ratios. The zooplankton community of Lake Malawi is dominated by copepods (&amp;gt;80% of total zooplankton biomass), which have a relatively low P content and high N:P ratio, resulting in a relatively low N:P recycling ratio. This might be expected to promote N limitation of phytoplankton and dominance of N-fixing cyanobacteria, but in some seasons the effects of zooplankton nutrient cycling appears to be masked by nutrient inputs from rivers, the atmosphere and vertical mixing.

In situ filtering rate variability in egg and larval surveys off the Pacific coast of Japan: Do plankton nets clog or over-filter in the sea?

In situ filtering rate variability was examined for vertical tows of plankton nets in egg and larval surveys off the Pacific coast of Japan, based on a data set pooled over large spatial and temporal scales (76,444 sampling tows from 1978 to 2013). The filtering rate showed unimodal distributions and was highly variable for the four net types: Long NORPAC (LNP), NORPAC (NOR), Maru-toku B (MTB), and Maru-naka (MNK). Despite the high variability at the individual tow level, the median values of the filtering rate for the overall data approximated the theoretical value of 1.0, in particular, for LNP, although the median values differed among the net types. For LNP, the differences in the median values among the 26 years, the 12 months, and the 4 regions were small relative to the overall variability at the individual level. The present study quantified the extent of underestimation/overestimation when the theoretical value of 1.0 is used due to the lack of the actual filtering rate data. The filtering rate was almost on a balance of resistance effect of net and cod-end, clogging effect of collected organisms, and over-inflow effect of currents over large scales. The present analysis implies that the filtering rate is mainly influenced by small-scale transient variability of ocean conditions such as wind speed, current intensity, rolling, turbulence, and mixing rather than large-scale variability related to climate regime, seasonality, or water masses. The results will allow the utilization of historical data lacking flow-meter data for large-scale comparative analyses.