Angels and Aliens: Encounters with Zooplankton
I was bending down to pick up what I thought was a scrap of clear plastic, the kind that cigarette boxes are wrapped in, when I realized that what I had taken for a bit of litter was looking back at me out of a complex compound eye.
It’s humbling to encounter a species that one has never seen before, can’t identify even with an educated guess, and is so strange that one is uncertain where to start looking.
The creature was a couple of inches long, armed with claws like a miniature lobster, equipped with a segmented tail for swimming, and it was almost entirely transparent, except for that eye that seemed to be staring right at me.
My first thought was that this was some kind of ghost shrimp, but it wasn’t. Instead, it turned out to be a species of Phronima, a kind of free-floating deep-sea hyperiid amphipod. Phronima makes its home in deep water, living its entire life as much as 1,200 feet below the surface. It’s not uncommon off the coast of California, but it doesn’t show up on the beach very often. In fact, it doesn’t show up anywhere often—one of the advantages of being almost invisible is being hard to find. There are just nine other Phronima sightings for the entire West Coast of North America on the citizen science site iNaturalist.
Phronima is part of the strange and wonderful world of pelagic zooplankton—zoo, meaning animals; plankton, the Greek work for “drifting”; pelagic, the Greek word for the open ocean. Zooplankton is a huge category and includes everything from the microscopic larvae of fish and crustaceans that spend only part of their lives as plankton, to vast jellyfish, with tentacles that can be as much as 200 feet long. They live throughout the ocean’s column of water, the largest and deepest environment on Earth.
There are strange things in the perpetual twilight of the deep sea, including bioluminescent jellies, and sea slugs that have traded their single foot for translucent, winglike lobes that give them the semblance of butterflies or angels, but even in this bizarre Alice-in-Wonderland ecosystem, Phronima is weird.
Phronima is parasitic. It uses those wicked claws to carve out a home for itself from jellies and salps—a kind of jelly-like, barrel-shaped tunicate. Phronima devours the insides of its host and then uses the hollowed-out organism as a kind of diving bell.
Phronima lives its entire life cycle in the water column—hence the free-floating descriptor. It’s a tough environment, with no shelter or protection. Becoming a sort of ghost in the machine of a larger organism gives Phronima extra protection and it is theorized that it may help reduce the amount of energy this small amphipod expends on swimming and hunting. Females lay their eggs and hatch their young in the host, giving this species the common name “pram bug,” or the more sinister “monster in a barrel.” However, if the zombified host ends up in a current or a swell, it can carry its parasitic passenger with it, sometimes on a one-way trip to the shore.
Many types of zooplankton rise nearer the surface during the night, and sink back into deeper water during the day. There is more food closer to the surface where photosynthesis takes place, but it’s also dangerous near the surface. Predators are always a risk, but for animals that are weak swimmers, currents, waves, and wind are also a serious hazard.
The Phonima I encountered on the beach was alive and kicking, but most deep sea animals are not. Zooplankton that get caught in the wrong current or swept away by a strong wind eventually end up as flotsam on a beach.
Beachcombers often find strange fragments washed up on the tide: just this month there has been an abundance of crystal clear globs that were once jellies and salps; the rubbery, transparent shells of pteropods—sea butterflies; and the strange plastic-like sails of velella velella—the by-the-wind-sailor. The remains left by the retreating tide to dry out on the beach may bear little resemblance to the living creatures.
Jellies are especially hard to identify. One common species that has been turning up in abundance this spring is Aequorea victoria, the crystal jelly. Endemic to the California coast from Baja to Bodega Bay, this bioluminescent species is ethereally beautiful in the water, but resembles a puddle of melting ice on the beach.
The shells of sea butterflies can be mistaken for jellies or for shards of glass. There are several species of these free-swimming sea slugs in this part of the Pacific, but the slipper-like shell or pseudo-conch of Corolla spectabilis is the most common on local beaches this Spring. Sea butterflies are as fragile as they look and usually only their shells survive the journey through the surf to the beach.
Currently, there is another small, glass-like species washing up on the beach: Velella velella. Unlike Phronima and the jellies and sea butterflies, these raft-like colonies of hydrozoans live on the surface of the ocean. Velella has generated dramatic headlines in the past that proclaim that the jellies are “invading” local beaches, but these marine organisms aren’t invaders, since they have no means of self-propulsion and can only go where the currents and winds drive them. This explains their common name: by-the-wind sailor, and their Latin name, which is derived from the word vela, a ship’s sail.
Velella is a long-distance traveler, propelled across vast areas of the open ocean by a transparent, chitinous “sail.” Just like man-made sailing vessels, the by-the-wind sailor tacks with the wind. When the onshore wind is too strong, the Velella are blown off course and can end up stranded, sometimes in huge numbers. For Velella, and the jellies and sea butterflies, and Phronima, this is a one-way trip: the beach is as alien and deadly to them as their world would be to us.
Los Angeles Times staff writer John Balzar wrote “the beach remains our most vibrant connection to nature. Where the sand turns wet, the greatest wilderness on the planet begins.” Crystal jellies, sea butterflies, by-the-wind sailors. and the weird and rarely seen Phronima offer a tantalizing glimpse of that vast unseen world, one that is almost entirely unfamiliar to earthbound humans.
Full moon low tides during the week of the April full supermoon on April 27 offer an ideal opportunity for beachcombers to explore the edge of that wilderness.
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