Biomass of Scyphozoan Jellyfish, and Its Spatial Association with 0-Group Fish in the Barents Sea

Abstract

An 0-group fish survey is conducted annually in the Barents Sea in order to estimate fish population abundance. Data on jellyfish by-catch have been recorded since 1980, although this dataset has never been analysed. In recent years, however, the ecological importance of jellyfish medusae has become widely recognized. In this paper the biomass of jellyfish (medusae) in 0–60 m depths is calculated for the period 1980–2010. During this period the climate changed from cold to warm, and changes in zooplankton and fish distribution and abundance were observed. This paper discusses the less well known ecosystem component; jellyfish medusae within the Phylum Cnidaria, and their spatial and temporal variation. The long term average was ca. 9×108 kg, with some years showing biomasses in excess of 5×109 kg. The biomasses were low during 1980s, increased during 1990s, and were highest in early 2000s with a subsequent decline. The bulk of the jellyfish were observed in the central parts of the Barents Sea, which is a core area for most 0-group fishes. Jellyfish were associated with haddock in the western area, with haddock and herring in the central and coastal area, and with capelin in the northern area of the Barents Sea. The jellyfish were present in the temperature interval 1°C<T<10°C, with peak densities at ca. 5.5°C, and the greatest proportion of the jellyfish occurring between 4.0–7.0°C. It seems that the ongoing warming trend may be favourable for Barents Sea jellyfish medusae; however their biomass has showed a recent moderate decline during years with record high temperatures in the Barents Sea. Jellyfish are undoubtedly an important component of the Barents Sea ecosystem, and the data presented here represent the best summary of jellyfish biomass and distribution yet published for the region.

Ecosystem relevance of variable jellyfish biomass in the Irish Sea between years, regions and water types

“…varied between years and sub-regions (Table 2, Fig. 2 and Figure A-1), suggesting the existence of species-specific and regional-specific inter-annual dynamics, as documented elsewhere (Suchman and Brodeur, 2005;Lynam et al, 2005;Brodeur et al, 2008;Eriksen et al, 2012).…”

“…With values ranging 8.6e42.4 g m À2 (wet mass), the overall jellyfish biomass density in the Irish Sea seem to be greater than in several other regions where fisheries bycatch has been recorded e.g. the Sea of Okhotsk (0.166e1.27 g m À2 ), and the Barents Sea (0.78 g m À2 ) (Zavolokin, 2010;Eriksen et al, 2012); however, the relatively coarse fisheries nets used in the latter studies may underestimate the catch of smaller or more fragile gelatinous species compared to the MIK net used in the present study . In the South East Bering Sea where a MIK net was used an abundance of 114.9 g m À2 was reported in 1999 (Brodeur et al, 2002).…”

“…However, the synchronising of juvenile fish and jellyfish may not be detrimental, as some juvenile gadoid species are known to associate with scyphomedusae and with Cyanea capillata in particular (Nagabhushanam, 1959;Russell, 1970;Purcell and Arai, 2001). Therefore, exactly which species in the Irish Sea ultimately benefit or lose out as a result of the presence of scyphomedusae remains unknown for now, and the response will most likely depend on the life-stages (Purcell and Arai, 2001;Masuda, 2009) and regions (Eriksen et al, 2012) considered. Importantly, another exploited species that may be affected by high scyphomedusae abundance is the Norway lobster (Nephrops norvegicus).…”

Marine living resources of the Barents Sea – Ecosystem understanding and monitoring in a climate change perspective

“…Time series for krill, pelagic amphipods (hyperiids), jellyfish and non-commercial fishes (family level) have been developed based on the 0-group data Eriksen et al 2012b). The distribution and biomass data for these groups are used to monitor the food availability (krill, hyperiids) for higher trophic levels, species interactions and the effects of climate change.…”

Jellyfish summer distribution, diversity and impact on fish farms in a Nordic fjord

“…The debate over whether jellyfish blooms have actually increased in magnitude and frequency (Richardson et al 2009, Brotz et al 2012 or simply that reporting has improved (Condon et al 2013) is ongoing, but dramatic fluctuations in jellyfish biomass are known from high latitude systems (Eriksen et al 2012). Knowledge gaps in basic jellyfish ecology, diversity and bloom dynamics along the northern Norwegian coast and in the Barents Sea, however, prevent effective monitortowards the year 2050, particularly in northern regions (DKNVS/NTVA 2012).…”