The REAL High Seas Drifter
By Mary Jane Schramm
The Ranger 85 chugged resolutely through the water, headed to the Farallon Islands and beyond. Suddenly, the engine slowed, shuddering to a stop. We watched as we drifted toward an estimated seven-foot long leatherback turtle munching meditatively on something reddish-gold and droopy - a huge jellyfish. The rarity of the leatherback sighting was enough to marvel at; but watching it chomp on the giant jelly was truly impressive. It methodically consumed its meal, a super-sized specimen of a Pacific sea nettle, Chrysaora fuscescens, one of many species found off our coast.
The term, “jellyfish” is a misnomer: they’re not fishes, but marine invertebrates of the phylum Cnidaria, so scientists use the term, “jelly.” These are ancient creatures, yet unevolved. Jellies are simple animals, comprised 95% of water. Like other cnidarians including sea anemones, sea whips, and hydrozoans, they are radially symmetrical The classic umbrella or bell shapes allow them to sense danger (and opportunity) from all sides. They lack hearts, circulatory systems, lungs, or brains. A rudimentary nerve network allows jellies to detect light, odors, and other stimuli. Their bell surrounds an internal cavity housing reproductive and digestion parts; and from its rim, oral arms and tentacles stretch. When touched, the tentacles’ stinging cells, nematocysts, are fired harpoon-like into prey, which compensates for their limited mobility. They move slowly, by pulsating their bell. Jellies are an important food source for seabirds and fish - and clearly, sea turtles.
These gelatinous creatures are passive predators that troll with long oral arms for anything edible that drifts by.They feed on various zooplankton such as salps, jellies, sea snails, fish eggs and larvae; even small fish and crustaceans. The digestive cavity has only one opening, efficiently serving as both mouth and anus.
Reproduction is both sexual and asexual. Adults - medusas - produce eggs or sperm, or both: some are hermaphroditic. Once fertilized, they drift in larval (planular) form, then as juvenile polyps attach to a hard surface and bud asexually. Once fully developed, they become free swimming medusas. Some local species include:
Brainless Wonders: Even without brains, some jellies evolved clever defenses. The bright red crown jelly, Atolla wyvillei, is known as the “alarm” jelly. When threatened, its tentacles flash bright bioluminescent blue signals. This “alarm” is believed to attract larger predators that might attack the jelly’s attacker instead; a literal bait-and-switch!
Moonstruck: Moon jellies, Aurelia aurita, have a shallow, translucent white bell, lending them a lunar aura. The disc reveals horseshoe-shaped gonads, pink or blue. The bell is just 16 inches across, and fringed with many short, neat, undulating tentacles that sweep food toward its gastric opening.
Nettlesome: The Pacific sea nettle (chrysaora fuscescens) sports a characteristic golden brown or reddish bell which can span over three feet in diameter. The ribbonlike spiraling oral arms and the 24 undulating tentacles may trail up to 15 feet. The oral arms begin digestion even as they transport the prey to its mouth. Its sting is rarely dangerous - to us.
Majestic: The giant lion’s mane (Cyanea capillata) is the most ancient, living in cold Northern Hemisphere seas for over 650 million years. It is also the largest. An East Coast specimen measured seven feet across. Its eponymous “mane” of tentacles, up to 120 feet long, administer a strong venom, very painful to humans, dangerously so to some. One even figured in a Sherlock Holmes mystery!
Bloomin’ Crazy: Recently, mega-blooms of jellies have increased globally. They have fouled ship and power plant intakes, and clogged fishing nets. Possible causes include plankton (algae) booms on which they feed. Overfishing has depleted their fish predators. The National Oceanic and Atmospheric Administration (NOAA) co-sponsored a study indicating that human-made structures may contribute to nearshore blooms. They found that jelly larvae settle more readily on artificial structures than on natural surfaces. With sea level rise and storms, coastal armoring (riprap) has increased. Underwater aquaculture pens, platforms and sunken ship hulls add to the problem. Scientists and ocean and coastal managers worldwide continue to follow this issue through monitoring, research, and regulations.
Photo credits From Top
atolla-Tentacles-750 NOAA-OE
Pacific_Sea_Nettles;
LionsManeJelly-MBNMS-NOAA.
