scholarly journals Accounting for biological and physical sources of acoustic backscatter improves estimates of zooplankton biomass

2008 ◽  
Vol 65 (7) ◽  
pp. 1321-1333 ◽  
Author(s):  
Joseph D. Warren ◽  
Peter H. Wiebe
Keyword(s):  
Water Column ◽  
Gulf Of Maine ◽  
Acoustic Scattering ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Acoustic Energy ◽  
Acoustic Backscatter ◽  
Data Sets ◽  
Measured Temperature ◽  
Acoustic Frequency

To convert measurements of backscattered acoustic energy to estimates of abundance and taxonomic information about the zooplankton community, all of the scattering processes in the water column need to be identified and their scattering contributions quantified. Zooplankton populations in the eastern edge of Wilkinson Basin in the Gulf of Maine in the Northwest Atlantic were surveyed in October 1997. Net tow samples at different depths, temperature and salinity profiles, and multiple frequency acoustic backscatter measurements from the upper 200 m of the water column were collected. Zooplankton samples were identified, enumerated, and measured. Temperature and salinity profiles were used to estimate the amount of turbulent microstructure in the water column. These data sets were used with theoretical acoustic scattering models to calculate the contributions of both biological and physical scatterers to the overall measured scattering level. The output of these predictions shows that the dominant source of acoustic backscatter varies with depth and acoustic frequency in this region. By quantifying the contributions from multiple scattering sources, acoustic backscatter becomes a better measure of net-collected zooplankton biomass.

scholarly journals Investigation of seabed fishing impacts on benthic structure using multi-beam sonar, sidescan sonar, and video

2007 ◽  
Vol 64 (5) ◽  
pp. 1053-1065 ◽  
Author(s):  
Mashkoor A. Malik ◽  
Larry A. Mayer
Keyword(s):  
Gulf Of Maine ◽  
Fishing Ground ◽  
Sidescan Sonar ◽  
Data Sets ◽  
Frequency Filtering ◽  
Data Set ◽  
Detection And Identification ◽  
Spatial Frequency Filtering ◽  
Disparate Data ◽  
Fishing Impacts

Abstract Malik, M. A., and Mayer, L. A. 2007. Investigation of seabed fishing impacts on benthic structure using multi-beam sonar, sidescan sonar, and video. – ICES Journal of Marine Science, 64: 1053–1065. Long, linear furrows of lengths up to several kilometres were observed during a recent high-resolution, multi-beam bathymetry survey of Jeffreys Ledge, a prominent fishing ground in the Gulf of Maine located about 50 km from Portsmouth, NH, USA. These features, which have a relief of only a few centimetres, are presumed to be caused either directly by dredging gear used in the area for scallop and clam fisheries, or indirectly through the dragging of boulders by bottom gear. Extraction of these features with very small vertical expression from a noisy data set, including several instrumental artefacts, presented a number of challenges. To enhance the detection and identification of the features, data artefacts were identified and removed selectively using spatial frequency filtering. Verification of the presence of the features was carried out with repeated multi-beam bathymetry surveys and sidescan sonar surveys. Seabed marks that were clearly detected on multi-beam and sidescan sonar records were not discernible on a subsequent video survey. The inability to see the seabed marks with video may be related to their age. The fact that with time, the textural contrasts discernible by video imagery are lost has important ramifications for the appropriateness of methodologies for quantifying gear impact. The results imply that detailed investigations of seabed impact are best done with a suite of survey tools (multi-beam bathymetry, sidescan sonar, and video) and software to integrate the disparate data sets geographically.

Implications of a regional-scale process (the Lakshadweep low) on the mesozooplankton community structure of the Arabian Sea

2019 ◽  
Vol 70 (3) ◽  
pp. 345 ◽  
Author(s):  
K. K. Karati ◽  
G. Vineetha ◽  
T. V. Raveendran ◽  
P. K. Dineshkumar ◽  
K. R. Muraleedharan ◽  
...  
Keyword(s):  
Physical Process ◽  
Arabian Sea ◽  
Mixed Layer Depth ◽  
Regional Scale ◽  
Zooplankton Community ◽  
Ocean Basin ◽  
Zooplankton Biomass ◽  
Global Ocean ◽  
Mesozooplankton Community ◽  
Tropical Ocean

The Arabian Sea, a major tropical ocean basin in the northern Indian Ocean, is one of the most productive regions in the global ocean. Although the classical Arabian Sea ‘paradox’ describes the geographical and seasonal invariability in zooplankton biomass in this region, the effect of the Lakshadweep low (LL), a regional-scale physical process, on the zooplankton community has not yet been evaluated. The LL, characterised by low sea surface height and originating around the vicinity of the Lakshadweep islands during the mid-summer monsoon, is unique to the Arabian Sea. The present study investigated the effect of the LL on the zooplankton community. The LL clearly had a positive effect, with enhanced biomass and abundance in the mixed-layer depth of the LL region. Copepods and chaetognaths formed the dominant taxa, exhibiting strong affinity towards the physical process. Of the 67 copepod species observed, small copepods belonging to the families Paracalanidae, Clausocalanidae, Calanidae, Oncaeidae and Corycaeidae dominated the LL region. Phytoplankton biomass (chlorophyll-a) was the primary determinant influencing the higher preponderance of the copepod community in this region.

Advancing an Ecosystem Approach in the Gulf of Maine

2012 ◽  
Keyword(s):  
Gulf Of Maine ◽  
Historical Context ◽  
Zooplankton Community ◽  
Ecosystem Approach ◽  
Environmental Indicators ◽  
Zooplankton Abundance ◽  
The North ◽  
Oscillation Result ◽  
The North Atlantic Oscillation ◽  
Ecosystem Changes

<i>Abstract</i>.—Numerous studies have examined the dynamics of zooplankton in the Gulf of Maine. Here the authors reanalyze relationships found in these prior studies, using updated data, with the goal of evaluating previously identified zooplankton– environment linkages. These reanalyses support the finding that major changes occurred in the zooplankton community during the late 1980s and again in the late 1990s. Evidence for a broader change in the ecosystem during these periods and mechanisms responsible for changes in the zooplankton are discussed. In general, the results of previous studies are upheld, but it is shown that the relationship between the environmental indicators and zooplankton change through time. This result implies that all data collected in the Gulf of Maine must be considered within a historical context and that the observed environmental–zooplankton linkages are still not well understood. It is possible that changes in the seasonal cycle or shifts in the pressures systems responsible for the North Atlantic oscillation result in nonstationary environmental–zooplankton relations. These results indicate that a mechanistic understanding is required to explain the documented environment–zooplankton linkages rather than correlative explanations. Since the causes of the late-1980s and late-1990s regime shifts are still unclear, future ecosystem-based management in the Gulf of Maine must be supported by continued observation and analysis to identify ecosystem changes soon after they occur. Scenario-driven modeling also is needed to provide guidance as to how the ecosystem will respond to future changes in zooplankton abundance and community structure.

scholarly journals Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

2016 ◽  
Vol 13 (10) ◽  
pp. 3131-3145 ◽  
Author(s):  
Brian P. V. Hunt ◽  
Sophie Bonnet ◽  
Hugo Berthelot ◽  
Brandon J. Conroy ◽  
Rachel A. Foster ◽  
...  
Keyword(s):  
N2 Fixation ◽  
New Caledonia ◽  
Austral Summer ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Diazotrophic Cyanobacteria ◽  
Subtropical Oceans ◽  
Isotope Mixing Models

Abstract. In oligotrophic tropical and subtropical oceans, where strong stratification can limit the replenishment of surface nitrate, dinitrogen (N2) fixation by diazotrophs can represent a significant source of nitrogen (N) for primary production. The VAHINE (VAriability of vertical and tropHIc transfer of fixed N2 in the south-wEst Pacific) experiment was designed to examine the fate of diazotroph-derived nitrogen (DDN) in such ecosystems. In austral summer 2013, three large ( ∼  50 m3) in situ mesocosms were deployed for 23 days in the New Caledonia lagoon, an ecosystem that typifies the low-nutrient, low-chlorophyll environment, to stimulate diazotroph production. The zooplankton component of the study aimed to measure the incorporation of DDN into zooplankton biomass, and assess the role of direct diazotroph grazing by zooplankton as a DDN uptake pathway. Inside the mesocosms, the diatom–diazotroph association (DDA) het-1 predominated during days 5–15 while the unicellular diazotrophic cyanobacteria UCYN-C predominated during days 15–23. A Trichodesmium bloom was observed in the lagoon (outside the mesocosms) towards the end of the experiment. The zooplankton community was dominated by copepods (63 % of total abundance) for the duration of the experiment. Using two-source N isotope mixing models we estimated a mean  ∼  28 % contribution of DDN to zooplankton nitrogen biomass at the start of the experiment, indicating that the natural summer peak of N2 fixation in the lagoon was already contributing significantly to the zooplankton. Stimulation of N2 fixation in the mesocosms corresponded with a generally low-level enhancement of DDN contribution to zooplankton nitrogen biomass, but with a peak of  ∼  73 % in mesocosm 1 following the UCYN-C bloom. qPCR analysis targeting four of the common diazotroph groups present in the mesocosms (Trichodesmium, het-1, het-2, UCYN-C) demonstrated that all four were ingested by copepod grazers, and that their abundance in copepod stomachs generally corresponded with their in situ abundance. 15N2 labelled grazing experiments therefore provided evidence for direct ingestion and assimilation of UCYN-C-derived N by the zooplankton, but not for het-1 and Trichodesmium, supporting an important role of secondary pathways of DDN to the zooplankton for the latter groups, i.e. DDN contributions to the dissolved N pool and uptake by nondiazotrophs. This study appears to provide the first evidence of direct UCYN-C grazing by zooplankton, and indicates that UCYN-C-derived N contributes significantly to the zooplankton food web in the New Caledonia lagoon through a combination of direct grazing and secondary pathways.

scholarly journals Contribution of Calanus species to the mesozooplankton biomass in the Barents Sea

2017 ◽  
Vol 75 (7) ◽  
pp. 2342-2354 ◽  
Author(s):  
Johanna Myrseth Aarflot ◽  
Hein Rune Skjoldal ◽  
Padmini Dalpadado ◽  
Mette Skern-Mauritzen
Keyword(s):  
Barents Sea ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Calanus Finmarchicus ◽  
The Arctic ◽  
Arctic Water ◽  
Mesozooplankton Biomass ◽  
The Barents Sea ◽  
Main Driver ◽  
Calanus Species

Abstract Copepods from the genus Calanus are crucial prey for fish, seabirds and mammals in the Nordic and Barents Sea ecosystems. The objective of this study is to determine the contribution of Calanus species to the mesozooplankton biomass in the Barents Sea. We analyse an extensive dataset of Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus, collected at various research surveys over a 30-year period. Our results show that the Calanus species are a main driver of variation in the mesozooplankton biomass in the Barents Sea, and constitutes around 80% of the total. The proportion of Calanus decreases at low zooplankton biomass, possibly due to a combination of advective processes (low C. finmarchicus in winter) and size selective foraging. Though the Calanus species co-occur in most regions, C. glacialis dominates in the Arctic water masses, while C. finmarchicus dominates in Atlantic waters. The larger C. hyperboreus has considerably lower biomass in the Barents Sea than the other Calanus species. Stages CIV and CV have the largest contribution to Calanus species biomass, whereas stages CI-CIII have an overall low impact on the biomass. In the western area of the Barents Sea, we observe indications of an ongoing borealization of the zooplankton community, with a decreasing proportion of the Arctic C. glacialis over the past 20 years. Atlantic C. finmarchicus have increased during the same period.

Westermann Morphospace displays ammonoid shell shape and hypothetical paleoecology

Paleobiology ◽  
2012 ◽  
Vol 38 (3) ◽  
pp. 424-446 ◽  
Author(s):  
Kathleen A. Ritterbush ◽  
David J. Bottjer
Keyword(s):  
Temporal Variation ◽  
Water Column ◽  
Ternary Diagram ◽  
New Method ◽  
Shell Shape ◽  
Ontogenetic Variation ◽  
Data Sets ◽  
Intraspecies Variation ◽  
Ideal Tool

The Westermann Morphospace method displays fundamental morphotypes and hypothesized life modes of measured ammonoid fossils in a ternary diagram. It quantitatively describes shell shape, without assumption of theoretical coiling laws, in a single, easy-to-read diagram. This allows direct comparison between data sets presented in Westermann Morphospace, making it an ideal tool to communicate morphology. By linking measured shells to hypothesized life modes, the diagram estimates ecospace occupation of the water column. Application of this new method is demonstrated with Mesozoic data sets from monographs. Temporal variation, intraspecies variation, and ontogenetic variation are considered. This method can address hypothetical ecospace occupation in collections with tight stratigraphic, lithologic, and abundance control, even when taxonomy is in dispute.

scholarly journals Effects of Consecutive Extreme Weather Events on a Temperate Dystrophic Lake: A Detailed Insight into Physical, Chemical and Biological Responses

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1411 ◽  
Author(s):  
Maria Calderó-Pascual ◽  
Elvira de Eyto ◽  
Eleanor Jennings ◽  
Mary Dillane ◽  
Mikkel René Andersen ◽  
...  
Keyword(s):  
Global Climate ◽  
Zooplankton Community ◽  
Fold Increase ◽  
Extreme Weather ◽  
Zooplankton Biomass ◽  
Trophic Levels ◽  
Extreme Weather Events ◽  
Weather Events ◽  
Fold Reduction ◽  
Stable Conditions

Between May and July 2018, Ireland experienced an exceptional heat wave, which broke long-term temperature and drought records. These calm, stable conditions were abruptly interrupted by a second extreme weather event, Atlantic Storm Hector, in late June. Using high-frequency monitoring data, coupled with fortnightly biological sampling, we show that the storm directly affected the stratification pattern of Lough Feeagh, resulting in an intense mixing event. The lake restabilised quickly after the storm as the heatwave continued. During the storm there was a three-fold reduction in Schmidt stability, with a mixed layer deepening of 9.5 m coinciding with a two-fold reduction in chlorophyll a but a three-fold increase in total zooplankton biomass. Epilimnetic respiration increased and net ecosystem productivity decreased. The ratio of total nitrogen:total phosphorus from in-lake versus inflow rivers was decoupled, leading to a cascade effect on higher trophic levels. A step change in nitrogen:phosphorus imbalances suggested that the zooplankton community shifted from phosphorus to nitrogen nutrient constraints. Such characterisations of both lake thermal and ecological responses to extreme weather events are relatively rare but are crucial to our understanding of how lakes are changing as the impacts of global climate change accelerate.

scholarly journals Spatial distribution and secondary production of Copepoda in a tropical reservoir: Barra Bonita, SP, Brazil

2007 ◽  
Vol 67 (2) ◽  
pp. 223-233 ◽  
Author(s):  
MJ. Santos-Wisniewski ◽  
O. Rocha
Keyword(s):  
Spatial Distribution ◽  
Secondary Production ◽  
General Pattern ◽  
Winter Season ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Tropical Lakes ◽  
Numerical Density ◽  
Dominant Group ◽  
Tropical Reservoir

The present paper aims to describe the spatial distribution of zooplankton copepods, their biomass and instantaneous secondary production, in Barra Bonita, a large eutrophic, polymitic reservoir (22° 29' S and 48° 34' W) on the Tietê River, of the Paraná basin. Sampling was carried out during two seasons: dry winter and rainy summer. Species composition, age structure and numerical density of each copepod species population were analyzed at 25 sampling stations. Secondary production was calculated for Copepoda, the dominant group in zooplankton communities, taking Calanoida and Cyclopoida separately. Copepoda represented the largest portion of the total zooplankton biomass, the dominant species being Notodiaptomus iheringi among the Calanoida and Mesocyclops ogunnus and Thermocyclops decipiens among the Cyclopoida. The production of Copepoda was higher during the rainy summer (23.61 mgDW.m-3.d-1 in January 1995) than during the dry winter season (14 mgDW.m-3.d-1 in August 1995), following the general pattern of abundance for the whole zooplankton community. Among the copepods, Cyclopoida production was higher than that of Calanoida, a pattern commonly observed for tropical lakes and reservoirs. Barra Bonita copepods are very productive, but there was a great degree of spatial heterogeneity, related to the physical and chemical conditions, particularly the level of nutrients and also to phytoplankton biomass.

Zooplankton and Trophic State Relationships in Florida Lakes

1983 ◽  
Vol 40 (10) ◽  
pp. 1813-1819 ◽  
Author(s):  
J. S. Bays ◽  
T. L. Crisman
Keyword(s):  
Trophic State ◽  
Size Structure ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Crustacean Zooplankton ◽  
Trophic State Index ◽  
Total Zooplankton ◽  
Eutrophic Lakes ◽  
Florida Lakes ◽  
Total Zooplankton Biomass

Zooplankton, including ciliated protozoans, were collected from 39 Florida lakes of widely ranging trophic state. Annual mean biomass values for different zooplankton groups were regressed against Carlson's Trophic State Index based on annual mean chlorophyll a concentration. Whereas total zooplankton biomass yielded a significant regression with increasing trophic state, microzooplankton (ciliates, rotifers, and nauplii) accounted for more of the relationship than macrozooplankton (cladocera, calanoids, and cyclopoids). Within the microzooplankton, the regression improved with decreasing body size. Macrozooplankton biomass exhibited a weak statistical relationship with lake trophic state, but the different component groups were variable in their response. The dominance within the zooplankton community shifts from macrozooplankton to microzooplankton with increasing trophic state, and the microzooplankton can constitute between 50 and 90% of the total zooplankton biomass in eutrophic lakes. Changes in zooplanktivore community structure with increasing trophic state show that whereas total fish biomass increases, dominance shifts from visually oriented predators, such as bass and bluegill, to pump filter-feeding planktivores, such as gizzard shad (Dorosoma cepedianum). While Florida zooplankton communities are similar in size structure to tropical communities, no statistically significant differences were found between empirical equations of crustacean zooplankton biomass and trophic state determined from temperate and Florida data bases.

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