As a follow-up to my recent post about "Jellies Invasion: Oceans Out of Balance," I caught up with general curator of the National Aquarium, Jack Cover. I asked him about local jelly populations and what, if anything, they can tell us about local waters. Apparently, an increase in jelly activity is typically attributed to increased human activity, as well as to warmer waters. In general, global warming has contributed to a longer jelly season and larger populations. Read more below.

What kinds of jellies people can expect to see in local waters?

Jellies are nearly invisible, but they are everywhere including the Atlantic Ocean, the Chesapeake Bay, and even in Baltimore’s Inner Harbor. Many of our local jellies are seasonal and a greater variety of jellies are found in the lower bay, in the coastal bays and offshore in the Atlantic Ocean were salinities are higher. Some of the more common species include:

Moon Jellies: Lower Bay and Atlantic Ocean. Summer the remains of moon jellies can often be found washed up on the beach at Ocean City
Atlantic Sea Nettles: Very common in the middle and lower bay- late spring, summer and early fall
Comb Jellies: Found throughout the bay and ocean, year-round, most common in the warmer months
Lion’s Mane Jellies: in the bay from late November through May, also known as the winter jelly

Are there certain local beaches where jellies are more abundant?

The abundance of jellies varies throughout the year and changes with the tides (incoming tides often bring them close to shore). Water temperatures, salinity and abundance of food greatly influences their population densities. Forecasts of Atlantic sea nettle populations in the Chesapeake Bay are regularly posted by scientists at the National Oceanic and Atmospheric Administration.

Which ones sting and which ones do not and how can you tell the difference?

Many jellies are harmless, but others can deliver a powerful sting. Locally, the Atlantic sea nettle and lion’s mane jelly can deliver an annoying, but not life-threatening sting. Atlantic sea nettles account for thousands of tourists seeking help each summer. Atlantic sea nettles can be recognized by their milky white color and three- to five-foot long tentacles. They are very abundant in the middle bay region at mid-summer.

Walnut-shaped comb jellies do not sting at all and can be distinguish from other local jellies by not having any stinging tentacles. Moon jellies have very short stinging tentacles that are mostly unable to penetrate the skin and are harmless to swimmers. The thick calloused skin of your hands are less vulnerable to a penetrating sting of our local jellies than the skin on other parts of your body. Many curious beachgoers pick up jellies and are not stung because of the thickened skin of the hands and by picking the jelly up by its non-stinging bell.

Are they around more during a particular time of the day?

They are active both night and day moving up and down the water column searching for food. Movements and abundance of jellies are affected by tides, winds and rainfall. Their abundance can be somewhat unpredictable as multiple factors affect their movements. They typically avoid coming to the surface of the water on windy days with lots of wave action.

Also, has there been an increase/decrease in the local jellyfish population and what does that tell us (if anything) about our local waters?

Local jelly populations fluctuate greatly from year to year. Species like the Atlantic sea nettle are naturally very abundant by mid-summer in the Chesapeake Bay. Long-term increases in local jelly populations or a lengthening of the jelly season could be the result of environmental degradation caused by human activities.

Cover offers basic facts on jellies survival:

As our exhibit points out, jellies are survivors. Jellies have survived for over 500 million years. They have survived environmental changes that have negatively affected other forms of sea life. The key to this survival is their ability to adapt and thrive to changes in the environment.

Jellies appear to be better able to survive in polluted water than other forms of aquatic life. Polluted runoff may be a cause for increases in jellies populations.

Polluted runoff from the land makes life impossible for many aquatic species, except for jellies. Fertilizer, manure, and sewage runoff into streams and the ocean decreases oxygen levels, leaving water hypoxic and unable to support many forms of aquatic life. When water conditions are poor, fish find it hard to breathe so they go elsewhere or die in large fish kills. But jellies have very low oxygen requirements and are able to survive, and even thrive, in these human created conditions.

Many seasonal jellies appear and reproduce when the ocean warms up. Global warming is making the ocean temperature warmer thus extending the growing, feeding, and breeding season of several jelly species. Some jellies also appear to be adapting and expanding their ranges due to this warming climate. Warmer water also speeds up the jellies' metabolism, causing them to consume more food, grow, and reproduce faster.

Image of moon jellies courtesy of lyng883.