The highly toxic and cryptogenic clinging jellyfish Gonionemus sp. (Hydrozoa, Limnomedusae) on the Swedish west coast

Annette F Govindarajan; Björn Källström; Erik Selander; Carina Östman; Thomas G Dahlgren

doi:10.7717/peerj.6883

The highly toxic and cryptogenic clinging jellyfish Gonionemus sp. (Hydrozoa, Limnomedusae) on the Swedish west coast

PeerJ. 2019 May 13:7:e6883. doi: 10.7717/peerj.6883. eCollection 2019.

Authors

Annette F Govindarajan^#¹, Björn Källström^#^{2

3

4}, Erik Selander², Carina Östman⁵, Thomas G Dahlgren^{2

3

6}

Affiliations

¹ Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA, USA.
² Department of Marine Sciences, University of Gothenburg, Göteborg, Sweden.
³ GGBC Gothenburg Global Biodiversity Centre, Göteborg, Sweden.
⁴ Gothenburg Marine Biological Laboratory, Göteborg, Sweden.
⁵ Evolutionary Biology Centre, EBC, Department of Organismal Biology, University of Uppsala, Uppsala, Sweden.
⁶ NORCE Norwegian Research Centre, Bergen, Norway.

^# Contributed equally.

Abstract

The clinging jellyfish Gonionemus sp. is a small hydromedusa species known historically from the Swedish west coast but not reported in recent times. This species is thought to be native to the northwest Pacific where it is notorious for causing severe stings in humans and is considered invasive or cryptogenic elsewhere. This year, unlike in the past, severe stings in swimmers making contact with Gonionemus sp. medusae occurred in Swedish waters from a sheltered eelgrass bed in the inner Skagerrak archipelago. To the best of our knowledge, this is only the second sting record of Gonionemus sp. from the Northeast Atlantic-with the first record occurring off the Belgian coast in the 1970s. Stinging Gonionemus sp. medusae have also been recently reported from the northwestern Atlantic coast, where, like on the Swedish coast, stings were not reported in the past. We analyzed sea surface temperature data from the past 30 years and show that 2018 had an exceptionally cold spring followed by an exceptionally hot summer. It is suggested that the 2018 temperature anomalies contributed to the Swedish outbreak. An analysis of mitochondrial COI sequences showed that Swedish medusae belong to the same clade as those from toxic populations in the Sea of Japan and northwest Atlantic. Gonionemus sp. is particularly prone to human-mediated dispersal and we suggest that it is possible that this year's outbreak is the result of anthropogenic factors either through a climate-driven northward range shift or an introduction via shipping activity. We examined medusa growth rates and details of medusa morphology including nematocysts. Two types of penetrating nematocysts: euryteles and b-mastigophores were observed, suggesting that Gonionemus sp. medusae are able to feed on hard-bodied organisms like copepods and cladocerans. Given the now-regular occurrence and regional spread of Gonionemus sp. in the northwest Atlantic, it seems likely that outbreaks in Sweden will continue. More information on its life cycle, dispersal mechanisms, and ecology are thus desirable.

Keywords: Biogeography; Burn; Climate change; Microscope; Nematocyst; Sea grass; Taxonomy; Tentacle; Ultrastructure; Zostera.

Grants and funding

Funding was provided by the Swedish Research Council (VR) to Erik Selander “Signals in the Sea” and from the Faculty of Science of Uppsala University to Carina Östman. Funding for the DNA sequencing analysis was provided by the Kathleen M. and Peter E. Naktenis Family Foundation and the Borrego Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.