Distribution Of Zooplankton Biomass Research Articles

Cascading effect of three-spined stickleback Gasterosteus aculeatus on community composition, size, biomass and diversity of phytoplankton in shallow, eutrophic brackish lagoons

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 279:305-309 (2004) - doi:10.3354/meps279305 Cascading effect of three-spined stickleback Gasterosteus aculeatus on community composition, size, biomass and diversity of phytoplankton in shallow, eutrophic brackish lagoons Tue Stenholm Jakobsen1, Pia Borch Hansen1,2, Erik Jeppesen1,2,*, Martin Søndergaard1 1Department of Freshwater Ecology, National Environmental Research Institute, Vejlsøvej 25, PO Box 314, 8600 Silkeborg, Denmark 2Department of Plant Biology, Biological Institute, Aarhus University, Nordlandsvej 68, 8240 Risskov, Denmark *Corresponding author. Email: ej@dmu.dk ABSTRACT: We conducted a 4 mo mesocosm experiment to elucidate the cascading impact of the zooplanktivorous three-spined stickleback Gasterosteus aculeatus on phytoplankton in slightly brackish lakes. The mesocosms were nutrient-enriched with low salinity (2 psu) and contrasting densities of sticklebacks (0 to 10 fish m-2). Total phytoplankton biovolume increased by 2 orders of magnitude when stickleback density increased from 0 to 3 to 6 to 10 fish m-2, most likely reflecting a parallel change in zooplankton biomass and size distribution. Phytoplankton size distribution was affected in that large forms dominated at high fish density, which most likely reflects a parallel reduction in size of zooplankton. A few taxa (especially Cryptophyceae) dominated at fish densities above 3 to 6 fish m-2, whereas higher diversity (characterised by taxa of Bacillariophyceae and Chlorophyceae) was recorded at fish densities below 3 to 6 m-2. However, genera richness showed no significant relationship with fish density. The threshold fish density for a transition from low to high phytoplankton biovolume at these high nutrient levels was 3 to 6 fish m-2. This level lies well below stickleback densities found in many eutrophic, low-salinity lagoons, implying that the intensity of the cascading top-down effect exerted by planktivorous fish on the phytoplankton abundance and community structure is of importance. KEY WORDS: Sticklebacks · Phytoplankton diversity · Top-down control · Trophic cascade · Saline · Brackish lakes Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 279. Online publication date: September 28, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Biomass and taxonomic composition of micronekton in the western tropical–subtropical Pacific

AbstractThe biomass distribution, community structure and species composition of the dominant micronektonic animals were determined in the western tropical Pacific, using day/night sampling from upper 200 m depth with a commercial midwater otter trawl in fall‐winter of 1994, 1995 and 1997. Night‐time micronekton biomass was significantly higher than daytime biomass except for a few cases. All the night‐time catches had similar taxonomic composition, dominated by myctophid fishes, small squids, shrimps and euphausiids. Night‐time micronekton biomass in the upper 200 m was assumed to be higher in the North Equatorial Counter Current than in the North Equatorial Current, reflecting the zooplankton biomass distribution which micronektons feed on at night. A total of 42 species of myctophid fishes, 34 species of squids, 27 species of shrimps and six species of euphausiids were collected. Community types of each dominant taxonomic group were classified by cluster analysis based on the species composition. A station located north of the subtropical convergence zone was distinct from other tropical stations south of the convergence zone, having significantly different species composition in three of the four dominant taxonomic groups (myctophids, squids and shrimps). The interaction between the larvae of commercially important fishes and micronektonic animals is discussed.

Latitudinal comparisons of equatorial Pacific zooplankton

Abstract Zooplankton biomass and rates of ingestion, egestion and production in the equatorial Pacific Ocean along 140°W and 180° exhibit maximum values in the High-Nutrient Low-Chlorophyll (HNLC) zone associated with equatorial upwelling (5°S–5°N) as compared to the more oligotrophic regions to the north and south. Zooplankton biomass and rates are not usually highest on the equator, but increase “downstream” of the upwelling center as the zooplankton populations exhibit a delayed response to enhanced phytoplankton production. The vertical distribution of zooplankton biomass in the equatorial HNLC area tends to be concentrated in surface waters and is more uniform with depth in oligotrophic regions to the north and south of the equatorial upwelling zone. In general, the amount of mesozooplankton (>200 μm) carbon biomass is approximately 25% of estimated phytoplankton biomass and 30% of bacterial biomass in the HNLC area of the equatorial Pacific Ocean. Zooplankton grazing on phytoplankton is low in the equatorial Pacific Ocean, generally −1 for 64–200 μm zooplankton to 0.08 d −1 for 1000–2000 μm zooplankton. Thus, the numerical and functional response of equatorial zooplankton to increases in phytoplankton production are more rapid than normally occurs in sub-tropical and temperate waters. Potential zooplankton fecal pellet production, estimated from metabolic demand, is approximately 1.6 times the estimated gravitational carbon flux at 150 m in the zone of equatorial upwelling (5°S–5°N) and 1.1 times the export flux in the more oligotrophic regions to the north and south. The active flux of carbon by diel migrant zooplankton in the HNLC zone is a minor fraction of the gravitational flux (2% at 140°W, 4% at 180°) but increases in the more oligotrophic regions to the north and south where there is a deeper mixed layer and a greater relative proportion of diel migrant zooplankton.

Zooplankton spatial distributions in coastal waters of the northern Arabian Sea, August, 1995

Abstract The spatial distribution of zooplankton biomass was surveyed in coastal waters of the northern Arabian Sea during the 1995 Southwest Monsoon (August) on cruise MB 95-06 of the NOAA Ship Malcolm Baldrige . Vertical patterns of displacement volumes from a limited set of paired day–night MOCNESS tows suggest there was little diel vertical migration in the coastal waters off the southern Arabian Peninsula. Zooplankton biomass varied from 5.2 to 15.1 g dw m −2 (178–517 mM C m −2 ) in the upper 200–300 m of Omani coastal waters. Distributions of acoustic backscatter were mapped in eight daytime acoustic Doppler current profiler transects in coastal waters off Oman and Somalia. Several transects contained maxima in acoustic backscatter that coincided with cool, fresh surface features that were several tens of kilometers wide. Although there was considerable scatter in the relationship between acoustically determined biomass (ADB) of zooplankton and surface temperature, there was a trend of increased biomass in the cool surface temperatures of the Omani upwelling zone. Acoustic transects crossed two filaments that extended seaward from upwelling centers off Oman and Somalia. Estimated zooplankton ADB exported from the upwelling zones in the surface features was on the order of 300 kg dw s −1 . The physical and biological characteristics of filaments maintain zooplankton associated with upwelling areas, such as Calanoides carinatus , as they are advected offshore from coastal upwelling zones.

Is Oithona the most important copepod in the world's oceans?

Oithona has been described as the most ubiquitous and abundant copepod in the world's oceans. Most of our knowledge of zooplankton abundance and distribution is derived from net samples whose mesh size is often 200 μm or greater, and researchers have commented on losses of smaller organisms such as Oithona and Oncaea, as well as juvenile forms of larger copepods, from these nets. We review the literature on this subject over the last 50 years, and note that such nets remain in common use for estimating the abundance, biomass and productivity of mesozooplankton. We show that an important fraction of mesozooplankton between 200 and 800 μm in length is significantly under-represented in many current and historical data sets. A 5 year study of the abundance and size distribution of zooplankton biomass on the Atlantic Meridional Transect has produced a very large data set covering a wide range of ecosystem types across the Atlantic Ocean, from subtropical oligotrophic to areas of upwelling and vernal blooming. We use these data to derive estimates of mesh selection effects for commonly used nets on measures of zooplankton abundance, biomass and secondary production, and compare these estimates to those derived from the literature. We estimate that the conventionalWP-2 net with a 200 μm mesh may capture <10% of conventional mesozooplankton numbers, whilst underestimating biomass by one-third and leading to an underestimate of secondary production by two-thirds. This has serious implications for estimates of zooplankton-mediated fluxes and for the modelling of ecosystem dynamics.

Zooplankton Biomass Variability in the Mexican Eastern Tropical Pacific

The time and space distribution of zooplankton biomass recorded during a year cycle (December 1995-1996) off the Pacific coast of central Mexico is analyzed. Samples were obtained by surface (42-86 m) oblique hauls at 12 sampling sites using a Bongo net. The overall average displacement volume biomass of zooplankton during the surveyed period was 1138 cm3 / 1000 m3 . Principal component analysis indicated that highest biomass concentrations occurred at coastal stations. The months with highest biomass values were those in which the lowest sea surface temperature values occurred (January-May). This was the same period in which the California Current was strongest and clearly influenced the hydrological conditions of the surveyed area. In these months, advective processes are active along the outer shelf, favoring upwelling of colder, relatively nutrient-richer waters that promote an overall local increase of zooplankton activity and populations. The high variability of biomass values is indicative of episodic, localized processes that enhance productivity in the area.

Temporal and spatial patterns of zooplankton in the Chesapeake Bay turbidity maximum

We measured the distribution of hydrographic parameters, currents, phytoplankton flu- orescence, suspended sediments and zooplankton in axial transects through the Chesapeake Bay estuarine turbidity maximum (ETM) seasonally (May, July and October 1996) and over tidal cycles within seasons. Zooplankton abundance was estimated with a 6-frequency, Tracor Acoustical Profil- ing System (TAPS-6) at the same vertical (0.25 to 0.50 m) and horizontal (0.5 to 1.5 km) resolution as hydrographic parameters and suspended sediments. The general pattern exhibited in axial transects through the Chesapeake Bay ETM is that sediments, fluorescence and zooplankton are in higher concentrations up-Bay of the salt wedge (defined as the intersection of the 1 isohaline with the bot- tom). The salinity front appears to trap these particles in the upper portion of Chesapeake Bay. The highest acoustically determined zooplankton biomass generally occurred near the bottom, at the toe of the salt wedge. The convergence zone associated with this feature concentrates sediments and zooplankton (primarily the copepod Eurytemora affinis). Advection appeared to dominate changes in zooplankton abundance during time series studies at a fixed station in the ETM. Zooplankton bio- mass at the fixed ETM station increased/decreased with the tidal excursion of the salt wedge. Water column zooplankton concentrations and the vertical distribution of zooplankton biomass appeared to be influenced by currents. We often found that during maximum ebb and flood tidal currents, zoo- plankton biomass and sediments in the mid and upper water column increased. Thus the hydrody- namic processes that resuspend, advect and trap suspended sediments in the ETM likely have the same effects on zooplankton. The ETM of the Chesapeake Bay appears to act as an entrapment zone for zooplankton. The lack of diel vertical migration, carrying eggs until they are ready to hatch, pos- sible reduced predation by visual predators in the turbid waters, and the ability to consume phyto- plankton, protozoa and detritus all may allow Eurytemora to persist at high concentrations in the Chesapeake Bay ETM.

Climate change causes contrasting trends in reproductive performance of planktivorous and piscivorous alcids

Summary 1. Eight years of observations on seabird reproductive success and oceanographic change in Tauyskaya Bay (Okhotsk Sea, north‐western Pacific) were used to evaluate the hypothesis that interannual climate change causes opposite trends in reproductive performances of planktivorous auklets (Aethia cristatella and Cyclorhinchus psittacula) vs. piscivorous puffins (Lunda cirrhata and Fratercula corniculata). 2. The climate change was assessed by examining changes in sea‐surface temperature (SST), time of permanent ice disappearance (ID), wind (WV) and current vectors (CV). Changes in the distribution of zooplankton biomass in the study region were used to assess changes in prey communities. Bird reproductive success was determined as the number of chicks fledged per nest occupied. 3. There were two distinct sets of oceanographic conditions in the study region, as reflected in the SST, ID, WV and CV. Strong northerly winds in the spring produced a late ice disappearance in the study region, whereas easterly winds determined an early ice disappearance. The patterns in ice disappearance were significantly correlated with SST anomalies during the summer. A negative SST anomaly (– 1·2 °C) defined a ‘cold’ regime, whereas a positive SST anomaly ( + 1·2 °C) defined a ‘warm’ regime. 4. Reproductive success of planktivorous auklets was negatively correlated with the SST in the western part of Tauyskaya Bay, whereas reproductive success of piscivorous puffins was positively correlated with the SST. The ‘cold’ season in 1988 was characterized by a strong in‐flow of water masses into the bay area. The ‘warm’ season in 1989 was characterized by well‐mixed warm water inside the bay that were separated from colder water masses outside the bay. Macro‐zooplankton, which were the main prey of planktivorous auklets, were more abundant during the ‘cold’ regime of the ecosystem. Meso‐zooplankton, a potential prey of juvenile pelagic fish, were more abundant during the ‘warm’ regime of the ecosystem. 5. Interannual oceanographic change probably impacts alcid reproductive performances by affecting food accessibility to planktivorous auklets and piscivorous puffins in opposite ways.

Estimating the spatial distribution of zooplankton biomass by combining Video Plankton Recorder and single-frequency acoustic data

Estimation of zooplankton biological parameters such as biomass distributions from single-frequency acoustic surveys of zooplankton is generally not possible because of the diversity of taxa present in assemblages and resultant ambiguities in acoustic analysis. We present an approach that assumes that at a given, fixed depth, the relative proportions of sizes across species remains constant. Using this assumption, along with independently sampled Video Plankton Recorder (VPR) data on the species and size composition of the sound scattering assemblage, single-frequency acoustic data have been used to estimate the spatial distribution of zooplankton taxa and their biomass within a region of ocean without the use of acoustic scattering models. The data from a joint-ship study of the fine-scale physical and biological structure of a 3.5 km×4.5 km×75 m deep region of Georges Bank were used to demonstrate the utility of this approach. The spatial distributions of zooplankton biomass were estimated for pteropods, copepods, amphipods, euphausiids, chaetognaths and fish. Within each of the six parallel cruise legs that constituted the joint-ship survey, we estimated the relationship between mean zooplankton concentration from the VPR and mean acoustic volume backscatter within each 2 m depth bin. These relationships were used to scale the volume backscatter data throughout the transect into estimates of total zooplankton concentrations. The relative proportion of each taxon was estimated from the VPR for each 2 m depth bin within each leg and used to convert total zooplankton concentrations to taxon-specific concentrations. We then estimated biomass for each taxon using VPR estimates of mean sizes along the transect in conjunction with length-wet mass morphometric relationships. Several large acoustic patches were detected within the surveyed volume of water. Volume backscattering within the 10–20 m depth strata was largely associated with copepod biomass, while deeper scattering appeared to be a consequence of pteropod biomass. Amphipods contributed to scattering in the upper 10 m of the sixth leg of the grid. Euphausiids made minor contributions to the observed volume backscattering, while scattering due to chaetognaths and fish appeared to be negligible. Our results suggest that these patches were primarily due to the presence of copepods and pteropods. Our biomass estimates were highly correlated with data from a 1 m 2 MOCNESS tow in leg 6; however, they predicted only 19–29% of the measured silhouette biomass from the net tow. This discrepancy was explained by a systematic underestimation of zooplankton concentrations by the semi-automatic image analysis system used to process VPR data. The results described herein suggest that the combination of independent data from optical samplers, nets or pumps and single frequency acoustic surveys may provide a viable method for generating near real-time estimates of zooplankton biomass distributions.

Spatial distribution of zooplankton biomass size fractions in a bog lake: abiotic and (or) biotic regulation?

Although spatial heterogeneity of zooplankton has been explained by variations in abiotic and biotic factors as well as their cascading interactions, few studies have paid attention to the relative importance of these processes in structuring the vertical and horizontal distribution of zooplankton within a lake. The main objective of this study was to determine the relative importance of abiotic and biotic processes in the regulation of the vertical and horizontal distribution of four size fractions (53-100, 100-202, 202-500, and &gt;500 µm) of the zooplankton biomass in a bog lake (Lake Geai, Quebec). Spatial heterogeneity of zooplankton biomass was found in both the horizontal and the vertical dimensions of the lake, and spatial patterns were quite similar for all size fractions. On the horizontal axis, spatial heterogeneity was stronger in the epilimnetic stratum. Zooplankton biomass was mainly aggregated in the east side of the lake in an area of higher conductivity and greater density of small chaoborid larvae. On the vertical axis, zooplankton biomass was concentrated in the epilimnetic waters and decreased with depth. This vertical pattern of distribution might be due to the avoidance of cold and anoxic waters and a high density of large chaoborid larvae in the hypolimnion. In general, invertebrate predation has been identified as the primary factor regulating zooplankton biomass distribution in Lake Geai. However, the size structure of chaoborid predators was more important than their density in the control of the spatial distribution of zooplankton.

Biomass of zooplankton and micronekton in the southern bluefin tuna fishing grounds off eastern Tasmania, Australia

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 138:1-14 (1996) - doi:10.3354/meps138001 Biomass of zooplankton and micronekton in the southern bluefin tuna fishing grounds off eastern Tasmania, Australia Young JW, Bradford RW, Lamb TD, Lyne VD The southern bluefin tuna (SBT) supports a seasonal fishery off the east coast of Tasmania, Australia. The distribution of zooplankton biomass in this region was examined as a means of finding out why the SBT are attracted to this area. We examined whether there was a particular area or depth stratum that supported significantly greater amounts of potential feed, directly or indirectly, for SBT. Samples of zooplankton and micronekton were collected during the winter SBT fishery seasons in 1992-94. Five net types (mouth opening 0.25 to ~80 m2) with codend mesh sizes ranging from 100 to 1000 um were used. Samples were collected from 4 main hydrographic areas: warm East Australian Current water, cool subantarctic water, the front separating them (the subtropical convergence), and the adjacent shelf. Four depth strata (50, 150, 250 and 350 m) were also sampled. In contrast to our expectations, the biomass in the subtropical convergence was no greater than that in the 3 other areas. Rather, it was the shelf, albeit with some inconsistencies, that generally had the greatest biomass of both zooplankton and micronekton. Offshore, there was no significant difference in the biomass of the depth strata sampled, although the biomass of gelatinous zooplankton in the surface waters increased during the study period. We suggest that the higher biomass on the shelf is the result of increased nutrients derived from a mixture of subantarctic water and upwelling along the shelf break. This biomass is converted via krill and gelatinous zooplankton to small pelagics such as jack mackerel, and finally to top predators, amongst which is SBT. The SBT, particularly sub-adults, may time their migration eastward to take advantage of the concentrations of prey present at this time of year. Zooplankton . Micronekton . Biomass . Southern bluefin tuna Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 138. Publication date: July 25, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Multiscale variability of tropical ocean zooplankton biomass

variability on the scale of tens of kilometres, and high-resolution sampling was used to investigate variability of kilometre scale. In the multiscale variability of zooplankton biomass, the maximum variability was observed on the thousands of kilometres scale, with the quantitative values of biomass represented in a form of normalized variance. The local peak of variability of zooplankton biomass in the range of hundreds of kilometres, in the tropical ocean, was probably due to the enhanced water dynamics with the same scale range. This activity is linked with open-ocean mesoscale eddy fields in the tropical zones of both oceans. The other typical feature of the structure of the zooplanktonic fields is its spatial anisotropy, which indicates different properties of spatial variation of parameters along directions through space. The anisotropy was evaluated by means of two-dimensional spatial autocorrelation functions. Two-dimensional correlation ellipses of the zooplankton biomass fields were orientated by their main axes in accordance with the direction of transport of the main water mass, the direction of motion of the eddies, and the orientation of divergence or convergence zones. The spatial heterogeneity of zooplankton biomass distribution in the horizontal plane can be characterized by the frequency of occurrence-of patches. On a log scale the frequency of occurrence of different size patches diminishes proportionally with their linear size. Zooplankton biomass is distributed more heterogeneously than that of phytoplankton (chlorophyll a). Synchronous measurements of the three-level system phytoplankton-mesozooplankton-flying fish (where each component acts as a prey item for the next one) exhibit the same trend of spatial autocorrelation functions, diminishing over the trophic levels on a scale from hundreds to tens of kilometres. This means that relatively heterogeneous fields of predators exist on more uniformly distributed fields of their prey. © 1995 International Council for the Exploration of the Sea

The relationship between suspended particulate material, phytoplankton and zooplankton during the retreat of the marginal ice zone in the Bellingshausen Sea

The distribution, abundance and composition of suspended particulates, phytoplankton and zooplankton biomass were investigated for the marginal ice zone in the Bellingshausen Sea during the Austral spring of 1992. Marked changes were observed between the amount and composition of particulates under the sea-ice and those in open waters. Measures of phytoplankton abundance (chlorophyll) ranged from ∼0.05 μg l −1 under the ice to 3 μg l −1 in the open waters to the north. The high nutrient concentrations and low level of phytoplankton under the ice suggest that this region is typical of over-wintering conditions and provides a suitable background comparison to the development of more productive, recently ice-free waters, further north. Nearly all basic measurements of particulate material showed a gradient from south to north. However, the biochemistry of particulates (lipid in particular), a more sensitive measure of environmental growth conditions, showed the area as a whole to be broadly split into two; under ice (light limited) and open water (no light limitation). Total particulate carbon was almost entirely composed of inorganic carbon under the ice; waters away from the ice edge also contained significant levels of inorganic carbon. Hence, C:chlorophyll was estimated from POC or phytoplankton carbon. There was no evidence of nutrient limitation at any of the stations investigated. Integrated phytoplankton carbon for the upper 100 m ranged from 0.1 gC m −2 under the ice to 11.5 gC m 2 in the diatom dominated bloom in open waters. The mesozooplankton biomass in the same depth interval increased from 0.02 gC m −2 under the ice to 0.21 gC m −2 in open waters. However, zooplankton biomass in the upper 600 m changed little from under the ice out to open waters north of the ice edge; although the northernmost station, in the region of highest chlorophyll, had approximately three times more zooplankton carbon (0.67 gC m −2 than the other stations. There is some evidence, however, that the northern station may be associated with a frontal feature, and that conditions observed may not be solely related to previous ice edge processes.

Zooplankton variability on the equator at 140°W during the JGOFS EqPac study

The vertical distributions of zooplankton biomass and community composition were measured on the equator at 140°W during March/April (19 days) and October 1992 (21 days). El Niño conditions prevailed during the March/April time series. The average integrated (200 m) zooplankton (>64 μm) biomass was 32 mM C m −2 in March/April and 41 mM C m −2 in October. The overall cruise means were not significantly different; however during October zooplankton were more aggregated in the upper euphotic zone, there were more copepods >200 μm, and there were more day/night differences in the vertical distribution of zooplankton biomass as a result of vertical migration behavior. Cyclopoid copepods were more abundant during the El Niño conditions of March compared to October. There were no apparent trends in integrated zooplankton biomass during the March/April time series. However, the species composition of the zooplankton community changed towards the end of the time series when meridional currents flowed to the south. Zooplankton biomass during the October cruise increased nearly five-fold with the passage of a tropical instability wave. A lag in the increase of zooplankton compared to nitrate and chlorophyll as well as changes in the zooplankton community composition over the time series reflect the response times of zooplankton to upwelling events.

The influence of a Gulf Stream meander on the distribution of zooplankton biomass in the Slope Water, the Gulf Stream, and the Sargasso Sea, described using a shipboard acoustic Doppler current profiler

Patterns in zooplankton biomass distribution in a Gulf Stream meander were documented using a ship-mounted acoustic Doppler current profiler (ADCP) in fall 1988 as part of the BIOSYNOP program. The dominant signal in biomass was the regional variation between water masses, with greatest biomass recorded in the Slope Water, intermediate biomass at the Slope Water-Gulf Stream front, and lowest biomass in the Gulf Stream/Sargasso Sea. Biomass was more variable in the Slope Water than in the Sargasso Sea. Diel variation, a consequence of diel vertical migration, was also observed. Comprehensive maps of the surveyed region documented meander associated enhancement of zooplantkton biomass. Elevated biomasswas documented in the region downstream of the meander crest, where determined of Slope Water and convergence of flow are hypothezised to occur. The ADCP was demonstrated to be an effective means of documenting patterns in zooplankton biomass, including estimates of the variabiity (patchiness).

Zooplankton dynamics in the northern Benguela ecosystem, with special reference to the copepod Calanoides carinatus

Main features of the zooplankton distribution and the ecological characteristics of the dominant species in the northern Benguela during different phases of upwelling are discussed. The composition of the zooplankton between 17 and 27°S was similar each year. Among the 20°30 most abundant species, 3°4 copepods dominated, influencing the distribution of total zooplankton biomass. During quiescent upwelling, zooplankton abundance was low and there were no significant differences in the inshore-offshore distribution of zooplankton biomass, the maximum occurring over the slope. During active upwelling, zooplankton biomass increased significantly, the maximum over the shelf being constituted almost entirely of developmental stages of herbivorous copepods. Over the inner shelf, all stages of the copepod Calanoides carinatus were feeding actively, removing up to 5 per cent per day of the standing stock of phytoplankton. Comparison of daily ration, respiration rate and biochemical composition of C. carinatus revealed active storage of energy inshore. Offshore populations of C. carinatus, found deeper than 200 m, comprised mainly copepodite stage V, which were not feeding and were characterized by decreased mobility and respiration and a high lipid content. It is estimated that the energy stored during active upwelling enables copepods to survive up to six months without any additional source of energy.

Vertical Size–Depth Distribution Properties of Midwater Fish off Bermuda, with Comparative Reviews for Other Open Ocean Areas

The nighttime (N) and daytime (D) size–depth distributions of mesopelagic fish at Ocean Acre, a typical deepwater site in the North Sargasso Sea, are described using archival discrete-depth data from the surface to about 1500 m. The N/D abundance distributions n(z) for a representative group of 18 swtmbladdered species indicate that fish are concentrated in the 0–150 m euphotic zone at night and in the 400–1000 m zone during the day in spring, summer, and winter. Seasonal succession in the average life stage size classes of the bladdered group occurs, but all classes are present year-round due to the variety of specific spawning patterns. The noncoincident N/D depth niches of individual bladdered species apparently are organized to reduce competition. Normalized N/D depth distributions [Formula: see text] for the bladdered group are similar throughout the year, and appear to be determined, respectively, by the N distribution of zooplankton biomass and the D underwater light field, other hydrographic variables having little direct influence. Also, it seems likely that the form of [Formula: see text] is relatively insensitive to species composition for such groups. These hypotheses are verified qualitatively by comparing specific and group distribution properties at other ocean sites with those at Ocean Acre.

Distribution patterns of mesozooplankton biomass in the North Sea

During spring 1986 and winter 1987, zooplankton samples were collected over the entire North Sea by means of a multi-closing net-system. Before taxonomic treatment, wet weight estimates and carbon content conversions were carried out. From this data set, 4 962 522 tons zooplankton biomass (dry weight) were estimated for the whole North Sea during the spring survey. High biomasses (more than 100 mg C/m3) were located in areas between the Orkneys and the Shetlands, off the mouth of the Firth of Forth, the Channel and the river Rhine. Considerable zooplankton biomass was also found parallel to the Danish west coast. Furthermore, a narrow tongue of high biomass (partly greater than 200 mg C/m3) intruded from the north, between 1 °E and 4 °E, into the northern North Sea, turning to the east at 56°N, and continuing into deeper water layers to form a left turning “helix” of high biomass in the central part of the North Sea. During the winter survey the carbon content of the zooplankton stock was a factor 10 lower than in summer. Altogether, 519340 tons of zooplankton biomass (dry weight) were estimated in winter. Centres of relatively high biomass were located off the mouth of the rivers Rhine, Weser and Elbe and off the British east coast moving in a cyclic way across the Dogger Bank into the central North Sea. A further maximum of zooplankton abundance was found in the Skagerrak region. However, an intrusion of zooplankton from the shelf edge into the North Sea was not observed in winter. A qualitative analysis of species composition showed that small copepods dominated the zooplankton in the southern and eastern North Sea. The “eddy” of high biomass in the northern North Sea observed in spring, however, was mostly shaped by the large copepodCalanus finmarchicus (70–90%). The distribution of zooplankton biomass in the North Sea is discussed in relation to the hydrographic conditions and to the biology of the dominant species.

Zooplankton-phytoplankton interactions in a eutrophic lake

Enclosure experiments were made in a cyanobacteria dominated lake (Lake Rotongaio) to assess the impact of zooplankton (>150 μm) grazing on algal growth rates and determine the effect of diel and vertical changes in zooplankton grazing intensity and nutrient (NH 4 -N) regeneration upon abundance of phytoplankton. The filamentous cyanobacterium Anabaena minutissima var. attenuata and diatom Cyclotella meneghiniana showed a negative linear change in abundance with a gradient in zooplankton grazing intensity. Phytoflagellates were not grazed and showed a positive linear change in abundance with increasing zooplankton biomass. These effects, as well as shortening of filament length of Anabaena , were caused by raptorial feeding by the alanoid copepod Boeckella propinqua which dominated the zooplankton. Phytoplankton growth was not stimulated by addition of nutrients, suggesting nutrient regeneration was not important. Diel and vertical changes in feeding and NH 4 -N regeneration rates were measured in March and June 1988. Diel differences were more pronounced in March when the water column was stratified. Specific feeding rates were more important than vertical changes in zooplankton biomass in determining community grazing rates in March, but in June when the water column was mixed, vertical distribution of zooplankton biomass was important. Zooplankton grazing was an important loss process for phytoplankton in the lower part of the epilimnion in Lake Rotongaio.

Vertical distribution of size-fractions in the zooplankton community in Lindåspollene, Western Norway. l. Seasonal variations

Abstract Zooplankton were collected in depth strata separated by 2 to 5 m. The samples were divided into five size-classes: > 1000 μm. 500–1000 μm, 250–500 μm. 125–250 μm, 60-125 μm, During spring and autumn there were maxima in the total biomass. about four times higher than during summer. At the time of biomass maxima, the total biomass showed a bimodal vertical distribution, with maxima in the upper and the lower part of the water column. The upper maximum was located between the surface and the base of the thermocline, the lower in the oxycline. During summer, when the total biomass was low. the vertical pattern diminished. The same trends were observed in 1983 in all size-classes, except for the > 1000-μm size-class. This size-class had a single biomass maximum during summer, located in the upper part of the water column. Seasonal variation in vertical distribution and in depth-integrated biomass increased from the smaller towards the larger size-classes. Relations between the vertical distribution of zooplankton biomass and other biotic and abiotic factors are discussed.