Date of Award


Document Type


Degree Name

Master of Science (MS)


College of Science and Mathematics



Thesis Sponsor/Dissertation Chair/Project Chair

Paul Bologna

Committee Member

John Gaynor

Committee Member

Lisa Hazard


Gonionemus vertens, often referred to as the clinging jellyfish, is an invasive hydrozoan first documented in 2016 in New Jersey. Populations of the adult medusa stage bloom in May and continue to persist through the middle of July, during which time it is of particular concern from a public health standpoint. G. vertens 'clings' to sea grasses and other submerged aquatic vegetation in shallow coastal waters, which are highly utilized for recreational activities, and its sting is highly toxic, which can hospitalize victims for days with both physical and psychiatric symptoms. Encounters with highly toxic G. vertens are, unfortunately, becoming more frequent in areas such as the estuaries of Barnegat Bay, New Jersey and Potter Pond, Rhode Island; which could be a deterrent to those visiting popular beaches and shoals for recreational purposes.

Laboratory experiments and field observations demonstrate that several factors seem to contribute to the cessation of bloom conditions such as top-down pressure by sea nettles, water temperatures exceeding 28° C, or a combination of both. Medusae were collected from various locations in Barnegat Bay and Potter Pond during several field surveys in the summers of 2018 and 2019, as well as from Cape May, NJ and Mumford Cove, CT in 2019. Medusae were maintained in holding tanks in the laboratory under stable temperature (~21-22°C) and salinity (20-25 ppt) before being allocated to experimental treatments. The majority ofmedusae were used in heat tolerance experiments, which ran for 96 hours at temperatures between 22°C-32°C. Significant mortality of G. vertens from all locations occurred when temperatures met or exceeded 28°C for 72h, suggesting that G. vertens 'thermal tolerance is 28°C and that populations in the field are at least partially controlled by water temperatures. Understanding the thermal decline in areas where predatory species are not present is critical for managing public awareness of this hazard. Monitoring of high human use areas for thermal minimums can reduce potential encounters with this highly venomous species. In Barnegat Bay, for instance, water temperatures may exceed 28°C by the end of June into the beginning of July, which was confirmed by deploying temperature recorders.

Predation experiments were also conducted to confirm that Chrysaora chesapeakei is a predator of G. vertens and to determine the bell diameter ratio at which they could be killed or consumed. C. chesapeakei is indeed capable of killing G. vertens, even at ratios of 1.19:1, and partially or completely consumed G. vertens when bell ratios approached 1.67:1. Therefore, it seems that C. chesapeakei likely also plays a role in the decline of G. vertens populations in Barnegat Bay, which decline throughout the month of July.

Lastly, G. vertens medusae were sent to the Cornell Isotope Laboratory along with samples of potential prey items and plants from the same areas in which the medusae were collected for Stable Isotope Analysis (SIA). The δ15N and δ13C data obtained from SIA were plotted to determine the trophic position of these organismal groups, which confirmed that amphipods and copepods are likely very important prey items for G. vertens.

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