Spatial and temporal patterns of scyphozoan jellyfish abundance and growth in Icelandic coastal waters – a climate change perspective

ABSTRACT

Scyphozoan jellyfish in Icelandic waters have received limited attention, despite apparent recent increases in blooms and changes in the regional oceanographic setting. The objectives of this study were to describe the species composition, abundance, phenology, and growth of scyphomedusae around Iceland and explore changes by comparing our findings with reports from the 1930s. Specimens were collected with a Bongo net in five regions around Iceland in the spring, summer, and autumn of 2008. Three jellyfish species were collected in the study, Aurelia aurita, followed by Cyanea capillata, and C. lamarckii. In the western and northwestern parts of Iceland, A. aurita abundance was highest in spring and summer, whereas in the North and East, abundances were highest in autumn. Cyanea capillata was not encountered in the Southwest, but in the west, Northwest, and North. There, numbers were highest in spring, whereas in the East, abundance was highest in autumn. Clockwise coastal current dispersal and regional interconnectivity are indicated. Weight-specific growth rates varied between 7.0 and 8.5% d⁻¹ for A. aurita and 11.1 and 15.7% d⁻¹ for C. capillata and are comparable to rates from often food-limited ecosystems at temperate latitudes. Presented evidence suggests that ephyrae and small medusae appear earlier in the season and in previously (in the 1930s) not occupied regions, while some regions (Southwest for C. capillata) were not populated anymore.

KEYWORDS:

• Climate change
• Cnidaria
• gelatinous zooplankton
• seasonality
• subarctic
• warming

Acknowledgements

We wish to thank the captains Tryggvi Sveinsson (Einar í Nesi EA), Matthías Ágústsson (Jörundur BA), Jóhann Egilsson (Anný SU), and Friðrik Jóhannsson (Ramóna ÍS) for their skilful help and plenty of patience under challenging circumstances during the sampling. We further appreciate the help from Fannar Þeyr Guðmundsson, Halldór Pálmar Halldórsson, Sindri Gíslason, and Marinó Fannar Pálsson during the field sampling, comments provided by Hans Ulrik Riisgård on growth rates, and language editing by Marcus Runge. We also thank two anonymous reviewers for constructive comments made on an earlier version of the manuscript.

Data availability

Jellyfish abundance and size data have been deposited in PANGAEA (https://doi.pangaea.de/10.1594/PANGAEA.962521). Temperature data can be accessed from the Marine and Freshwater Research Institute, Iceland, at https://sjora.hafro.is/siritar/vefur/.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This project was funded by the AVS R&D Fund of the Icelandic Ministry of Fisheries and funds from the Icelandic Marine and Freshwater Research Institute. Florian Lüskow was supported by an International Doctoral Fellowship granted by the University of British Columbia.