GET TO KNOW YOUR CARIBBEAN MARINE LIFE
by Darelle Snyman
These fascinating, gelatinous sea creatures have roamed the seas for at least 500 million years. At first glance jellyfish and comb jellies might appear similar, but they are actually not close relations. Jellyfish, like corals and anemones, belong to the phylum Cnidaria, a group of animals known for bearing nematocysts or stinging cells. Comb jellies, in contrast, belong to the phylum Ctenophora, which lack stinging cells and are noted for their use of cilia, which are commonly referred to as combs, to swim through the water column.
Of the two groups, the alien-looking jellyfishes are probably the most familiar to us, especially if you had your share of painful encounters with them. I love watching these fascinating creatures pulse elegantly through the water. They are, however, less attractive when you encounter them washed up on the beach as a jiggling mass of jelly. This appearance is because these brainless and bloodless creatures are actually about 95 percent water
The Moon Jellyfish
The Caribbean jellyfish resident I have encountered the most is the saucershaped Moon Jellyfish (Aurelia aurita). Moon Jellies are one of the most widespread jellyfish species in the world. This translucent critter lacks the distinctive, long tentacles we have come to associate with jellyfish. Their short tentacles form a fringe along the edge of their bell or medusa, as we refer to the adult form of a jellyfish. The distinctive horseshoe-shaped structures you can see in the bell are in fact its gonads.
Moon Jellies had the honor of traveling into outer space. In 1991 they were guests on the space shuttle Columbia where scientists studied the effect of microgravity on them. During their stint in space they continued with their life’s work, reproduction, and once back on earth it was discovered that the spaceborn jellies could not figure out how to deal with gravity, poor things. Sadly, Moon Jellies rarely live longer than six months and even though they are mostly water, they are preyed upon by a variety of predators, including leatherback sea turtles (Dermochelys coriacea) and the ocean sunfish (Mola mola).
The Sea Thimble Jellyfish
The most adorable Caribbean jellyfish resident you are likely to encounter is the tiny Sea Thimble Jellyfish (Linuche unguiculata). The bell or medusa of this small critter is straight-sided with a flat top, hence its common name, Thimble Jellyfish. The presence of symbiotic zooxanthellae (single-celled organisms that live in jellyfish, coral and other invertebrates) gives the bell an orangebrownish coloration.
Sea Thimble Jellyfish feed by pulsating their bells, rotating as they move, creating a flow that draws prey in. They breed seasonally and are known to form large swarms close to the water surface from March through April. These aggregations, also known as blooms or smacks, can cover a vast area and aggregations covering a million square metres have been recorded. People who have fallen victim to the larvae, commonly known as sea lice, of Thimble Jellyfish might disagree greatly with the adorable description. These minuscule irritants are the most common cause of sea-bather’s eruption, a nasty, itchy rash that can turn into blisters. In Spanish it is aptly named pica-pica, which means itchyitchy. It happens when the larvae that became entrapped in the swimmers clothing die, causing them to discharge their under-developed stinging cells in the process, with maddening results.
The Cannonball Jellyfish
Another jellyfish that lacks long, trailing tentacles is the spherical-shaped Cannonball Jellyfish (Stomolophus meleagris), also known as the CabbageHead Jellyfish. These ball-shaped critters have short, stubby tentacles and secondary mouth folds that peek out from underneath the brown-rimmed bells. It is these short oral arms with the secondary mouth folds that gave rise to their scientific name, which means “many mouthed hunter.” When disturbed, they secrete a very unpleasant, toxic mucus that drives away predators in the immediate area. This defense mechanism, however, does not deter their main predator, the endangered leatherback sea turtle. The fact
that they are such an important part of the turtle’s diet makes them ecologically important.
These cute little carnivores in turn feed on a variety of planktonic larvae and fish eggs that are sucked into their mouth folds when the bells contract. They can swim with their short oral arms, unlike most jellyfish that rely on the wind
and waves for movement.
The Sea Wasp
A jellyfish whose sting packs more of a punch is the sea wasp (Alatina alata), a box jellyfish notorious for inflicting pain. This Caribbean resident should not, however, be confused with the lethal box jellyfish, Chironex fleckeri, found only in the Pacific. These cube-shaped creatures bear four long tentacles and are not easy to spot, thanks to being mostly transparent and their tendency to hang around just below the water’s surface. Stings of these floating wasps can cause nausea, pain and a rash. Although not fun, symptoms tend to disappear without
treatment from 20 minutes to one day.
The Mangrove Upside-Down Jellyfish
A jellyfish that you are very likely to encounter in the shallows in lagoons and mangrove areas, resting casually on its bell with its frond-like tentacles facing upwards, is the Mangrove Upside-Down Jellyfish (Cassiopea xamachana). I have discussed this aptly named jellyfish in the April 2020 issue, highlighting one of its most unattractive features, its ability to sting you without you even touching them. My first encounter with its stinging arsenal of mucus bombs was in the shallows in Isla Mujeres, Mexico, where I was innocently and ignorantly trying to
photograph them. When the water around them is disturbed they release globules of mucus into the water that move around by means of cilia. These globules, termed cassiosomes, contain the stinging cells that can make life quite uncomfortable for you.
The Comb Jellies
Just as unique as the jellyfishes are the unusual, diaphanous-looking Comb Jellies, often referred to as the ctenophores. On a few occasions I have mistaken these transparent creatures for small pieces of floating plastic. This is actually a sad reflection on the state of our oceans if my first thought goes to “plastic” and not “animal” when I spot a transparent object floating in the sea.
Their transparency makes them masters of camouflage, difficult to identify, and annoyingly difficult to photograph. The common name of Comb Jellies relates to the eight rows of tiny, comblike plates they use for locomotion. As they swim, the beating cilia often scatter light in different directions to produce a shimmering, rainbow effect. If you have not been able to witness the coordinated movement of these cilia, do yourself a favor and watch a video taken of these amazing critters swimming.
Hard to believe that these transparent creatures are voracious predators that will even eat their own kind in the absence of other suitable prey. During times of food scarcity they will shrink in size and stop reproducing until they find enough food again.
The Spot-Wing Comb Jelly
The common Spot-Wing Comb Jelly (Ocyropsis maculata) is definitely the easiest to identify by the four brown to black spots on its rounded oral lobes.
The Sea Walnut
The colorless Sea Walnut (Mnemiopsis leidyi) is another story. It is not easy to make out the fine detail needed to identify it as it casually drifts past you. It can, in general, be identified by its oval-shape, four rows of ciliated combs and two body lobes that are longer than the rest.
The Venus Girdle
A Comb Jelly that deviates greatly from the typical Comb Jelly body plan is the Venus Girdle (Cestum veneris). These ribbon-shaped organisms have iridescent edges, without which they would be virtually invisible. They can grow up to a metre long — quite a length to reach for such a fragilelooking creature.
I hope you enjoyed learning more about the jellies and that your next foray into the underwater world includes encounters (from a safe distance) with some of these remarkable creatures.