An intercomparison of the taxonomic and size composition of tropical macrozooplankton and micronekton collected using three sampling gears

Kwong, Lian E.; Pakhomov, Evgeny A.; Suntsov, A. V.; Seki, Michael P.; Brodeur, Richard D.; Pakhomova, Larisa G.; Domokos, Réka

doi:10.1016/j.dsr.2018.03.013

Cited by 16 publications

(21 citation statements)

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“…However, if our abundance estimates were to be converted to a more useful currency in food web models (e.g., biomass or carbon content per individual), then the shifts observed in 2015 and 2016 are likely to be even more dramatic. Many of the crustaceans normally caught in this survey (e.g., euphausiids, sergestid shrimp) are at the smaller (15-25 mm) end of the micronekton size spectrum (Kwong et al, 2018). For example, the average weight of an adult E. pacifica is 0.10 g and the average weight of an adult T. spinifera is 0.12 g (based on collections in both warm and cold years, Elizabeth Daly, Oregon State University, unpublished data).…”

Section: Discussionmentioning

confidence: 99%

Major Shifts in Pelagic Micronekton and Macrozooplankton Community Structure in an Upwelling Ecosystem Related to an Unprecedented Marine Heatwave

2019

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The community structure of pelagic zooplankton and micronekton may be a sensitive indicator of changes in environmental conditions within the California Current ecosystem. Substantial oceanographic changes in 2015 and 2016, due to the anomalously warm ocean conditions associated with a large-scale marine heatwave perturbation, resulted in onshore and northward advection of warmer and more stratified surface waters resulting in reduced upwelling. Here we quantify changes in the macrozooplankton and micronekton community composition and structure based on five highly contrasting ocean conditions. Data from fine-mesh pelagic trawl surveys conducted off Oregon and Washington during early summer of 2011 and 2013-2016 were examined for interannual changes in spatial distribution and abundance of fish and invertebrate taxa. Overall species diversity was highest in 2015 and lowest in 2011, but 2016 was similar to the other years, although the evenness was somewhat lower. The community of taxa in both 2015 and 2016 was significantly different from the previously sampled years. Crustacean plankton densities (especially Euphausiidae) were extremely low in both of these years, and the invertebrate composition became dominated mostly by gelatinous zooplankton. Fishes and cephalopods showed mixed trends overall, but some species such as age-0 Pacific hake were found in relatively high abundances mainly along the shelf break in 2015 and 2016. These results suggest dramatically different pelagic communities were present during the recent warm years with a greater contribution from offshore taxa, especially gelatinous taxa, during 2015 and 2016. The substantial reorganization of the pelagic community has the potential to lead to major alterations in trophic functioning in this normally productive ecosystem.

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Section: Discussionmentioning

confidence: 99%

Major Shifts in Pelagic Micronekton and Macrozooplankton Community Structure in an Upwelling Ecosystem Related to an Unprecedented Marine Heatwave

2019

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“…Echo-integrations of acoustic data were performed on 1-m layers at a threshold of -80 dB to exclude scatterers not representative of the micronekton community (Béhagle et al, 2017 expressed as abundance within the backscattering layer (ind. m -2 ) (as in Kwong et al, 2018).…”

Section: Acoustic Surveysmentioning

confidence: 99%

“…The reasons for the observed variability in mean backscatter at MAD-Ridge summit compared to the immediate vicinity and the reasons for the observed decrease in trawl abundance/biomass estimates at the summit are further discussed with respect to the sampling strategy and IYGPT net used. Although trawl surveys are necessary to determine the taxonomic composition of micronekton present in the water column in space and time, the composition and biomass obtained largely depend on the type of trawl used (Kwong et al, 2018), their catchability towards various taxonomic groups of nekton and the depth range sampled. Trawl sampling is difficult on shallow topographies because of the high risk of damaging the sampling gear…”

Section: Micronekton Scattering Layers and Assemblages At La Pérouse mentioning

confidence: 99%

Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data

Annasawmy

Ternon

Cotel

et al. 2019

Progress in Oceanography

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Micronekton distributions and assemblages were investigated at two shallow seamounts of the southwestern Indian Ocean using a combination of trawl data and multi-frequency acoustic visualisation techniques. La Pérouse (∼60 m) seamount is located on the outskirts of the oligotrophic Indian South Subtropical Gyre province with weak mesoscale activities and low primary productivity all year round. The "MAD-Ridge" seamount (thus termed in this study; ∼240 m) is located in the productive East African Coastal (EAFR) province with high mesoscale activities to the south of Madagascar. This resulted in higher micronekton species richness at MAD-Ridge compared to La Pérouse. Resulting productivity at MAD-Ridge seamount was likely due to the action of mesoscale eddies advecting larvae and productivity from the Madagascar shelf rather than local dynamic processes such as Taylor column formation. Mean micronekton abundance/biomass, as estimated from mesopelagic trawl catches, were lower over the summit compared to the vicinity of the seamounts, due to net selectivity and catchability and depth gradient on micronekton assemblages. Mean acoustic densities in the night shallow scattering layer (SSL: 10-200 m) over the summit were not significantly different compared to the vicinity (within 14 nautical miles) of MAD-Ridge. At La Pérouse and MAD-Ridge, the night and day SSL were dominated by common diel vertical migrant and non-migrant micronekton species respectively. While seamount-associated mesopelagic fishes such as Diaphus suborbitalis (La Pérouse and MAD-Ridge) and Benthosema fibulatum performed diel vertical migrations (DVM) along the seamounts' flanks, seamount-resident benthopelagic fishes, including Cookeolus japonicus (MAD-Ridge), were aggregated over MAD-Ridge summit both during the day and night. Before sunrise, mid-water migrants initiated the first vertical Highlights ► MAD-Ridge seamount is located in a productive region with significant mesoscale activities compared to La Pérouse seamount. ► Micronekton species richness were greater at MAD-Ridge compared to La Pérouse. ► The shallow scattering layer (10-200 m) during the night and day were dominated by common vertically migrating and non-migrating micronekton taxa ► Seamount-associated/resident species occurred in dense aggregations close to the summit and flanks of both La Pérouse and MAD-Ridge seamounts.

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“…This issue is accentuated when the sampling aims to collect biological information from one of the DSLs commonly observed in open ocean ecosystems, which are distributed vertically at different depth ranges. To overcome this limitation, we need to move away from traditional single cod end trawl nets to use trawls with opening-closing mouths or cod ends, or in-trawl stereo cameras, or combine different types or trawls, or use acoustic and optic sampling (AOS) devices mounted on trawls and combine their information (Pearcy, 1983;Rosen and Christian, 2013;Kwong et al, 2018). Sampling of micronekton is still a topic that requires further research and development, as all sampling methods have their particular biases (often referred to as catchability).…”

Section: Mark Classificationmentioning

confidence: 99%

Acoustic Assessment of the Micronekton Community on the Chatham Rise, New Zealand, Using a Semi-Automated Approach

2019

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Micronekton are a key component of the pelagic food web of the Chatham Rise east of New Zealand. The Chatham Rise is an important fishing area for hoki (Macruronus novaezelandiae), New Zealand's largest finfish fishery, and a predator on mesopelagic fish. Four fisheries oceanographic voyages provided multi-frequency acoustic data (18, 38, 70, 120, and 200 kHz) and midwater trawls, which were used to define a classification tree to separate micronektonic organisms. We carried out validation and sensitivity analyses that showed that we were able to classify pearlside (Maurolicus australis) and euphausiids. Other mesopelagic targets (mainly myctophids) were classified together based on their acoustic frequency response. Using scripting in the open-source software ESP3, we applied our classification tree to an independent time series of acoustic data from trawl surveys on the Chatham Rise between 2009 and 2018, that was not used for model development or validation. Our methodology allowed us to study temporal and spatial patterns of M. australis, euphausiids, and total backscatter in the water column. Total backscatter associated with micronekton has varied over the last 10 years, with no clear trend. The abundance of euphausiids showed a significant decreasing trend over the last 10 years. Abundance of M. australis also decreased since 2012, though this was not significant. This work contributes to ongoing efforts to monitor and detect changes in the pelagic ecosystems.

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An intercomparison of the taxonomic and size composition of tropical macrozooplankton and micronekton collected using three sampling gears

Cited by 16 publications

References 50 publications

Major Shifts in Pelagic Micronekton and Macrozooplankton Community Structure in an Upwelling Ecosystem Related to an Unprecedented Marine Heatwave

Major Shifts in Pelagic Micronekton and Macrozooplankton Community Structure in an Upwelling Ecosystem Related to an Unprecedented Marine Heatwave

Micronekton distributions and assemblages at two shallow seamounts of the south-western Indian Ocean: Insights from acoustics and mesopelagic trawl data

Acoustic Assessment of the Micronekton Community on the Chatham Rise, New Zealand, Using a Semi-Automated Approach

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