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

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.

Introduction of the euryhaline epibenthic hydromedusa Vallentinia gabriellae Vannucci Mendes, 1948 (Hydrozoa: Limnomedusae) to Indian waters

“…An example of an enigmatic hydrozoan species with a complex invasion history is Gonionemus sp., which is native to the northwest Pacific, where it is notorious for causing painful stings to humans. Gonionemus s p. is introduced in other parts of the world (Rodriguez et al ., 2014; Gaynor et al ., 2016; Govindarajan and Carman, 2016; Govindarajan et al ., 2017, 2019), but identification is sometimes challenging due to its similarity to the less toxic, closely related Gonionemus vertens lineage (Govindarajan and Carman, 2016). Some other globally invasive hydrozoans are B. virginica (Thiel, 1935; Mills and Sommer, 1995; Wintzer et al ., 2013; Freire et al ., 2014), Maeotias marginata (Mills and Sommer, 1995; Mills and Rees, 2000), Turritopsis dohrnii (Miglietta and Lessios, 2009), and Craspedacusta sowerbii (Jankowski et al ., 2007).…”

Setting the baseline for the dynamics of siphonophores and hydromedusae in Oslofjorden

“…These organisms feed on other zooplankton, preying on and competing with a wide array of invertebrates and fish (Matsakis & Conover 1991, Purcell 1991, Nicholas & Frid 1999, Purcell & Arai 2001, Wintzer et al 2011. Some species are of medical and economic importance, as they negatively impact aquaculture and tourism through their detrimental effects on animal and human health (Båm stedt et al 1998, Baxter et al 2011, Govindarajan et al 2019. They have a highly seasonal presence in the ecosystem, sometimes forming massive, short-lived blooms and occasionally becoming the most abundant invertebrate predators (Purcell 1981, Lucas et al 1995, Robi son et al 1998, Gorsky et al 2000, Hosia & Båmstedt 2007, Boero et al 2008, Genzano et al 2008.…”