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Hot Topics:  Sea nettles in Barnegat Bay

Sea nettle in the medusa stage of its life cycle_Photo source: http://express.howstuffwords.com

Sea nettles (Chrysaora quinquecirrha), a type of stinging jellyfish, are present in the waters of Barnegat Bay and other coastal waterways of New Jersey. For a quick overview of the jellyfish situation, watch the video below from July 2010.


 What do they look like?

The adult sea nettle is bell-shaped and pale white and often has reddish markings along the surface. It has long thin tentacles around the edge of the bell (see image above right).  Watch the animated video below to learn about the fascinating life cycle of the sea nettle!



Sea nettles have always been a part of the Barnegat Bay’s ecosystem; their apparent increase in abundance is a relatively recent phenomenon. A number of potential causes for this increase have been suggested by scientists.  Increased development around the bay, including bulkheads, pilings, and floating docks, may be providing more places for the scyphistoma to attach. A single floating dock can hold thousands of scyphistoma, which asexually produce millions of jellyfishes, such as sea nettles. Sea nettles, and some other jellyfish, have a relatively narrow salinity preference, so development of the waterfront within that salinity zone, especially pilings, floating docks, and bulkheads, may have inadvertently contributed to the spread of sea nettles and other jellyfish.

Changes in the bay’s salinity may also have an effect. Sea nettles prefer a lower salinity zone, so large-scale natural changes in salinity, such as dry years, may affect their abundance and distribution in the bay. Certain human activities affecting the water cycle (e.g., large offshore discharges of treated sewage effluent, dams, reservoirs, shallow wells) also cause large-scale changes in salinity and may also affect the distribution of jellies in the bay. Both the increasing water consumption throughout the watershed and sea level rise may further change salinities in the bay and affect the distribution and abundance of jellies.

The removal of predators and potential competitors for food through increased fishing pressure may also affect sea nettle abundance. However, we do not know which species of fish or other animal, if any, prey on sea nettles in Barnegat Bay. Lastly, the bay’s eutrophication may also be creating favorable conditions for sea nettles and other jellies (see diagram below). First, the nutrient inputs to the bay often lead to high production (i.e., growth) of certain flagellates and other small zooplankton, known as microplankton. Some jellies can feed efficiently on micoplankton in the bay’s turbid waters and may out-compete fishes and other visually-feeding predators. Lastly, some jellies are less sensitive to low dissolved oxygen, which occurs episodically during summer and early fall in certain parts of the bay.

Conceptual diagram depicting why sea nettles are present in the Barnegat Bay estuary


There are at least five potential factors contributing to the expansion of the sea nettle population in the Barnegat Bay estuary. 


1. The “hardening” of shorelines throughout the bay (e.g., bulkheads, pilings, docks) provides habitat for jellyfish “polyps.” Each jellyfish polyp buds off many baby jellyfish.

2. Changes in the salinity in the bay can shift the distribution of jellies in the bay, as some jellies, including sea nettles, have a “narrow” salinity tolerance. Examples of factors that can cause large-scale changes in salinity include weather conditions, increased potable water use, and large offshore discharges of sewage effluent.

3. Increasing water temperature accelerates growth rates and maturation of sea nettles.

4. Fishing  affects the abundance of jellies in the bay: different fish species may eat polyps, larvae, and adult jellies. Some fishes and other animals also compete with jellies for their microscopic food, such as copepods.

5. Eutrophication, an increase in the bay’s production due to nutrient loading (see a,b, and c, above), also may affect the abundance of jellies. Nutrients stimulate the production (growth) of phytoplankton, which leads to increases in small zooplankton (such as copepods) which are the favorite food of jellies. Phytoplankton production also makes the water more turbid, making it difficult for visually-feeding animals, such as fishes, to find food. Eutrophication may also reduce the oxygen in the water. Unlike fishes and most other invertebrates, most jellies are tolerant of low oxygen conditions.

Can we get rid of them?

Since jellyfish have always been a part of the bay’s ecosystem, the goal would be population control, not complete eradication. There have been a number of attempts to control jellyfish worldwide, but none have been particularly effective. Nets and bubble screens have been used to keep them away from swimming areas, but the jellyfish either clogged the mesh of the nets or the tentacles were broken into pieces that continued to sting. The bottom-living stage of their life was targeted with chemicals, but that also killed many other organisms. A combination of actions that target the potential reasons for their increase as outlined above may be the best long-term solution.


Prevention of stings through the use of lightweight protective clothing (lycra "rash guards” or panty hose), or petroleum jelly spread on unprotected skin, is recommended for areas with high concentrations of sea nettles. If you are stung, clean the affected area with salt water to remove any tentacles remaining on the skin (fresh water may cause more stings from any tentacles remaining on the skin).  Apply shaving cream, or a paste of baking soda and salt water, and scrape it off to help remove any remaining stingers.  Ice may help with pain and itching.  Seek medical attention for any serious reactions.

See BBP's Get informed about Stinging Jellyfishes in these waters for more information about sea nettles in Barnegat Bay.