Community composition of epipelagic zooplankton in the Eurasian Basin 2017 determined by ZooScan image analysis

Hauke.Flores [ at ]


The Arctic Ocean is especially vulnerable to the impacts of climate change. Warmer ocean temperatures and reduced sea ice coverage lead to a poleward shift of communities in the Arctic Ocean. This process, termed borealization, is considerably changing Arctic marine food web structure with implications for ecosystems dynamics and functioning. Zooplankton is a good indicator of climate change in the marine environment and helps understand what role aberrations in the water mass circulations could play for ecosystem functioning. To better understand how the communities adapt to the changing environment and what the potential impacts, such as borealization, could mean for the arctic habitats, monitoring the community composition on a regular basis is crucial. Traditional taxonomical analyses are time consuming while the semi-automatic image analysis using ZooScan was developed to reduce time. This study aims to provide further information on the composition of epipelagic zooplankton communities in the Arctic Ocean determined by ZooScan image analysis and to verify whether there is a biogeographical and hydrographical pattern on the shelf and slope of the Barents Sea and in the Nansen Basin. Additionally, this study tried to confirm whether the taxonomy-based optical method ZooScan leads to similar results as dry-weight measured biomass data in term of size distribution and total biomass in different size fractions. The expedition PS 106.2 with the research vessel Polarstern provided an opportunity to sample the epipelagic zooplankton community from the shelf of the Barents Sea into the Nansen Basin proper, crossing a gradient of decreasing influence of Atlantic Water (AW). This study confirmed the hypothesis that there was a biogeographical and more importantly hydrographical pattern of mesozooplankton community structure in the study area of PS106. The basin domain is characterized by two basic water masses. The Atlantic regime (AR) with near-surface Atlantic Water (AW) and the polar regime (PR) with AW at a greater depth, overlain with polar surface water and intermediate water. Biomass and abundance were highest along stations in the AR and lowest at stations in the PR. Smaller fractions with high abundances dominated the AR and bigger fractions the PR respectively. In warming Arctic Ocean, growing AW influences can therefore have consequences for the ecosystem structure and the sustainability for marine resources, such as commercially used fish and the characteristic megafauna. Calanus glacialis and the boreal species Calanus finmarchicus were found dominant in the AR. In contrast Calanus hyperboreus and Metridia longa dominated the PR. This study showed that a more traditional method for calculating biomass such as a dry weight measurement leads to similar relative proportions as ZooScan-based biomass. This would allow for a more rapid taxonomic analysis and biomass calculation of the vast number of samples. However, a correct parametrization of the conversion from 2-dimensional objects on ZooScan pictures to dry mass is critical for an accurate determination of dry weight. Finally, there was a link between high biomasses and high abundances, which could enable faster predictions based on biomass alone in well-studied ecosystems.

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Koplin, J. (2020): Community composition of epipelagic zooplankton in the Eurasian Basin 2017 determined by ZooScan image analysis , Bachelor thesis, University of Hamburg.

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