A new year means a new monthly series for our e-newsletter, the Heron Herald. This year, we’ve decided to focus on a different animal each month throughout the year. Our plan is to feature seasonally relevant animals that can be found right here in the Chesapeake Bay waters around Talbot County (and beyond).
For January, we are featuring the cold weather jellyfish that visits the Bay during winter months; the lion’s mane jellyfish. We haven’t yet started seeing them here locally but they should start showing up soon as they are typically around from November through March. Their actual presence varies from year to year though and we saw a huge number of them in the St. Michaels harbor in January 2024. Last year, they actually stuck around through April and even into the beginning of May.
All jellyfish are considered a type of plankton. While most plankton are tiny, what makes something plankton is that it drifts with the water current, so even the largest jellyfish is plankton because they are not strong enough to swim against water currents. Jellyfish are also invertebrates and have what is called a hydrostatic skeleton, which means the difference in water pressure between inside their bodies and outside is what gives them structure. This is why when you remove them from the water, they don’t look like much.
Jellyfish have tentacles that extend from the ‘bell’ or the main portion of their body. These tentacles have stinging cells called nematocysts, which are used to paralyze prey. For Lion’s Mane Jellyfish, this includes small fish and shrimp, along with another type of gelatinous organisms known as comb jellies. In some species, these stinging cells can cause reactions in humans, however, the stinging cells in bay nettles and lion’s mane jellyfish are small enough that they can’t sting you through the thicker skin on the palms of your hands and feet. However, they can sting you everywhere else.
For some people, a sting might cause some redness and unpleasant itching. For others, several reactions might occur which include welts and hives, even anaphylaxis. It is recommended that people seek medical attention when stung over large portions of their body due to the potential for systemic and more severe reactions.
Lion’s mane jellyfish are the largest known species of jellyfish in the world, with one recorded specimen having a bell that was almost 7 feet wide and tentacles stretching to 120 feet long.
However, in the Chesapeake Bay they tend to be about 5 inches or less in diameter across the bell. It’s believed that there may be different species or subspecies of lion’s mane jellyfish, which is why the ones in the Chesapeake Bay are smaller than those found elsewhere. It may also be that as a cold water jellyfish, the Chesapeake Bay is at the southern edge of their range and so they are unable to grow as large under these less optimal conditions [1]. It might also be that the lion’s mane jellyfish we see in the Chesapeake are relatively young and therefore not very big.
It turns out that lion’s mane jellyfish don’t just suddenly appear in the Bay as adults. Their juvenile form, known as ephyra, have been here for awhile, feeding and growing and eventually metamorphosing into their adult form, known as the medusa stage [2].
An important thing to realize about jellyfish is that they have a polyp stage that requires a hard surface for them to attach to. They look similar to anemones in this stage (which they are related to) and in the Chesapeake Bay one of the ideal surfaces for them to attach to are oysters. This is yet another reason why oyster reefs are such an important habitat in the Bay; they provide substrate (aka a surface) for many different animals to attach to.
There’s not much information about what eats lion’s mane jellyfish in the Chesapeake Bay specifically, but general predators include sea turtles, birds, predatory fish, and even other jellyfish. The smaller the jellyfish, the more likely it is to be eaten by other jellyfish, including by other lion’s mane jellyfish [3]. Since we shouldn’t be seeing sea turtles in the Chesapeake Bay during the time of year when we commonly have lion’s mane jellyfish (cold winter months), it seems unlikely for them to be a major predator in this region.
Many people in our area dislike jellyfish, largely because they can be a nuisance when trying to enjoy the water. However, most of us aren’t swimming in the Bay between November and March, so I think we can appreciate the lion’s mane jellyfish for using the water during off months. The bay nettles that are here in the summer months are a different story, which we’ll save for the July edition of the Heron Herald.
References:
[1] https://www.marylandbiodiversity.com/species/13651