Having roamed the seas for 500 million years, jellies are one of the most remarkable animals found throughout the global ocean. These gelatinous umbrella-shaped creatures can be found from the coastal sea surface all the way to the deep-sea, thousands of metres beneath the waves. Jellies are from the phylum Cnidaria and are most closely related to sea anemones, corals and sea pens.
Jellies come in all shapes and sizes, ranging from just one millimetre to a metre in diameter, such as the Lion’s Mane Jelly that can be found off the coast of B.C. However, the largest jelly recorded to date is the Nemopilema nomurai, which was two metres in diameter and weighed close to 200 kg! Jellies also range in colour from completely translucent to bright yellows, oranges, reds, purples and blues.
Most jellies that are most commonly seen and thought of are free-swimming and are referred to as medusae, after Medusa in Greek Methology. Some jellies, however are stationary and are referred to as polyps, like a sea anemone. These stationary or stalked-jellies can be found attached to various substrates, such as algae or rocks. Stalked jellies can be found around Oak Bay, but one must look closely as they are often fairly small and tend to camouflage well with their chosen substrate.
Jellies are rather primitive creatures and do not have any specialized digestion, circulatory, nervous, or respiratory systems. However, for being considered one of the oldest multi-cellular organisms jellies still have some amazing body features, including a nerve net, ocelli and nematocysts. A nerve net is kind of like a primitive nervous system which helps jellies detect stimuli, such as the touch of another animal. Ocelli or light sensitive organs, help jellies respond to changes in light (i.e. sunlight), helping them determine up from down. Nematocysts or stinging cells are the jelly’s primary defence mechanism. Most animals in phylum Cnidaria have them. These stinging cells are like barbed harpoons that can be shot out of the jelly’s tentacles to catch, stun or even kill prey. This mechanism is one of the fastest movements in the entire animal kingdom. The stinging effect of the nematocysts can be extremely painful in some species, such as the Box Jelly, and can even be fatal to humans. But don’t worry you won’t find Box Jellies anywhere near Willows Beach.
Jellies have been around for millions of years – what is their secret?
Jellyfish do not have too many predators; I mean, who really wants to eat several pounds of tasteless jelly? Sharks, tuna, swordfish, sea turtles and other jellies are of their greatest concern. However, many of their predators are being over-fished, especially the tuna, sharks and swordfish; so with less predation, jelly numbers have increased. Plastic bags drifting in the ocean can resemble jellies gracefully pulsing away and turtles have been known to prey upon bags rather than jellies by mistake.
It is thought that jellies are taking advantage of human-induced changes. For example, as humans add nutrients to the ocean through agricultural runoff (i.e. fertilizers), a process called eutrophication, these extra nutrients can cause phytoplankton blooms. If the excess phytoplankton do not get eaten, decomposition occurs, which uses up oxygen. Low oxygen zones, or hypoxic zones, have also seen an increase in jellies as they are more tolerant to changing ocean chemistry. This tolerance in jellies has also been seen with lowering ocean pH (i.e. more acidic) levels throughout the global ocean in response to increased CO2 in the atmosphere.
These rather primitive and beautiful – but often deadly –creatures seem to have mastered being able to survive changing conditions. It is suggested that perhaps a global increase in jellies is something to pay attention to; a symptom that the ecosystem is being altered.