One of the questions that I am asked most often is: “Are there more jellyfish (Mi’kmaq: sasap) in the Bras d’Or estuary now than there used to be?”
I have a lot of trouble answering that for two reasons. The first reason is that we don’t have very good records and the second is that there are now more people looking which means that sightings are expected to increase even if the jellyfish don’t.
Recently, a team of American researchers examined available data on jellyfish abundance around the world. The results, published in 2012 by Lucas Brotz and his colleagues in the journal Hydrobiologica, provided the first rigorous demonstration that jellyfish populations are increasing in coastal ecosystems worldwide. There are various proposed reasons for this but they all boil down to the peculiar life cycle of jellyfish which has helped them survive and thrive in the world’s changing oceans since before the time of the dinosaurs.
Most jellyfish (including the two species that call the Bras d’Or estuary home) have two very distinct phases in their life cycles. The first phase is called a polyp and it is attached to the bottom. Through a process called strobilation, these polyps are capable of producing large numbers of offspring without having to mate (clones).
Their offspring are not attached to the bottom, but join the plankton, floating freely in the water. They grow rapidly to form medusae, the common form of jellyfish that we are more familiar with. Medusae get together and sexually reproduce. Researchers from the Bras d’Or Institute have observed several of these jellyfish orgies in the Bras d’Or estuary over the years with the common moon jellyfish (scientific name: aurelia aurita). The eggs are fertilized internally and develop into free-swimming larvae which float about for a brief period and then settle to the sea floor and develop into polyps. The cycle begins again.
However, researchers have been finding that some species, including the moon jelly, can have many detours and work-arounds in their life cycles as a function of environmental conditions. The polyps of this jellyfish can clone more polyps or form dormant cysts capable of surviving harsh environmental conditions. When conditions become better, they can then rapidly reproduce. The moon jelly has a worldwide distribution in between 70◦ N and 40◦ S and is found in many coastal and estuarine environments.
The Bras d’Or estuary is a perfect environment for moon jellies, a shallow, semi-enclosed system with limited tidal exchange. Researchers from the Bras d’Or Institute have estimated swarm densities approaching 40 metric tons, a potential food source for many species including the sunfish and leatherback turtles that have been recently sighted in the estuary. We will, no doubt, be seeing more of these jellyfish swarms (technically called smacks) in the future as our climate warms.
The moon jellyfish in the medusa phase is a clear bell shape with visible horseshoe structures (gonads). This species does have stinging cells but they are well-buried in the bell of the medusa. The other common species in the Bras d’Or has the unfortunate local name of blood sucker. This name for the large, coloured Lion’s Mane jellyfish (scientific name: Cyanea capillata) is a little confusing as it does not suck blood. However, it may have been given this name because of its readily accessible stinging cells in the tentacles, catching many summer Bras d’Or swimmers off-guard.
This jellyfish is the world’s largest known species of jellyfish and is found only in the cold waters of the northern oceans as well as the Arctic. The adults are bell shaped and the bell is divided into eight lobes which give it the appearance of an eight-pointed star. It has trailing tentacles which it uses to catch food. The Lion’s Mane jellyfish remain near the surface at no more than 20 metres depth and their slow pulsations move them slowly forward. These adult jellyfish floating in the water are the male and female medusa stages of the life cycle.
Their life cycle is the typical textbook style as described above. The Lions Mane jellyfish eats small zooplankton and it also preys on the other common Bras d’Or Lake jellyfish, the moon jelly! It is best to give the Lions Mane Jellyfish a wide berth because it does have trailing, stinging tentacles. A sting is usually temporarily painful and may cause some redness. The stinging cells that may be embedded in your skin can be deactivated with a five per cent solution of white vinegar in water. In 2018 we did not see many of these jellyfish during Bras d’Or Watch field day. Join us on the shores of the Bras d’Or on July 13 and help us determine whether this year may be different! Let’s see.
Dr. Annamarie Hatcher is a consulting ecologist and a board member of the Bras d’Or Lake Biosphere Reserve Association. For more information about the Bras d’Or Lake Biosphere Reserve Association, please visit http://blbra.ca/ or our Facebook page (https://www.facebook.com/blbra/). To see a video of a Bras d’Or moon jelly smack, see the Bras d’Or Watch Facebook page (https://www.facebook.com/BrasdOrWatch/).