Pacific Coast Gelatinous Zooplankton


Monterey Bay in central California, and other Pacific Coast locations, are home to an astounding diversity of gelatinous zooplankton. The main feature uniting this disparate assemblage of marine organisms is the tendency to collapse into helpless, quivering blobs when held out of the supportive aqueous environment. With bodies composed of at least 95% water, there would appear to be little hope for such seemingly flimsy, frail creatures. Unlike a fish or a crab, jellies are not capable of holding their shape when taken out of the water.  Yet the gelatinous lifestyle does quite well, having been adopted by representatives from numerous phyla. We tend to be biased toward a life with strong bones, muscles and teeth (hopefully!). The JelliesZone will show that the quivering blobs may be on to something.

The true jellies (referred to here as “jellies” rather than “jellyfish” as most people know them) are cnidarians, relatives of corals and anemones. The central area of the cnidarian body consists of digestive cavity, which connects to the outside by a mouth. Many cnidarians have an alternation of generations, with an attached polyp stage and a free-swimming medusa stage. Both polyps and medusae have a body plan with a basic radial symmetry. Thus unlike a bilateral organism like a fish or person, similar repeated components of the body are arranged around the central body axis. At one end of the axis lies the mouth (the oral end); the opposite side is designated the aboral end. All cnidarians are endowed with nematocysts, microscopic stinging and sticky structures used primarily for prey capture. This characteristic is a uniquely defining trait of the phylum. Cnidarians are at the tissue level of organization – they lack any structures that can truly be called organs, like a heart or brain. 

True jellies are only part of the gelatinous zooplankton menagerie, however. An incredible array of comb jellies, gelatinous molluscs (primarily heteropods and pteropods) and pelagic tunicates (salps, doliolids and pyrosomes) have also adopted the gelatinous lifestyle, although without the aid of nematocysts. All make ends meet without the benefits of a hard skeleton or tough tissue. Lacking dense bodies and hard body parts does have its advantages. With a drifting lifestyle aided by the relatively buoyant tissue, little energy need be spent on resource-draining activities like swimming (although most can swim to some extent).

Some gelatinous animals, like the sea nettle, Chrysaora fuscescens and the purple-striped jelly, Pelagia colorata, make conspicuous sojourns into nearshore waters on a sporadic basis. Most types lead far less splashy lifestyles, however, and are overlooked by most people. Among their more attractive qualities, many of these produce light through bioluminescence (link from UC Santa Barbara), certainly among the most beautiful of all biological processes.

Don’t count on seeing any of these delicate creatures on your next ocean excursion however. You can go many weeks without seeing a hint of a gelatinous animal. When conditions are appropriate though, nearshore surface waters may be inundated with scores of gelatinous creatures. And then, as quickly as they appeared, the jellies may vanish again into a world of mystery, their whereabouts unknown to those of us confined to breathing air and living on land. Yet even when swarming by the thousands or millions, most folks are totally oblivious to the wonders that may lie just beyond the kelp bed.

Click on the links at the top of all pages to view some of the more common gelatinous zooplankton that venture into the waters of Monterey Bay and other West Coast locations and learn a bit about their mysterious lives. Many can be seen at the surface while boating in the bay. The best way to observe them, however, is to be immersed in their boundless environment while snorkeling or scuba diving. Only then can you see the stunning beauty of their delicate gelatinous tissue. Don’t worry too much about the nasty reputation of jellies. The vast majority of gelatinous animals are harmless to people. A few, such as sea nettles or the Portuguese man-of-war, do pack a respectable sting, but fortunately most jellies entering California waters lack the ability to cause serious harm. You should, of course, treat any unknown gelatinous animal with respect – even a dead sea nettle on the beach can make you regret touching it. For those that can’t venture out to sea, the next best thing is to view captive jellies at a public aquarium.

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