When asked to contribute something about marine life for the “In the Air” issue of the Salish Magazine, it seemed unlikely that I would find a topic matching my supposed expertise. For example, an indirect effect, like that of air on water currents, is not a good fit. Setting aside air breathing birds and mammals, nothing appeared obvious. Many fish will briefly leap clear of the water, but again, this is hardly an interaction worth embellishing. Flying fish of the tropics would qualify but geographically, not for the Pacific Northwest. Eventually one species did emerge as a possibility — the by-the-wind sailor Velella velella.

A recently stranded individual with its colour still intact. photo by Bernie Hanby

And as a result of its pedigree, it features alternation of generations, which results in the production of tiny jellies via reproductive polyps. These jellies enable the by-the-wind sailor to complete its “hydroid” lifecycle. But exactly how/where this happens has been subject to debate.

It has long been theorized that these jellies sink to the bottom (up to 3,300 ft or 1000 m), where the sexual portion of the alternation culminates. Then, the juvenile forms aggregate into surface-dwelling rafts, which then grow to adults. However, recent collections of the distinctive — two-tentacled, zooxanthellae-bearing — jellies at the surface suggest the entire life cycle of the by-the-wind sailor occurs near the ocean’s surface.

The by-the-wind sailor floats upon tropical and temperate seas world wide. Utilizing its above-the-water structure, it drifts about in any direction the winds blow. Large rafts of by-the-wind sailors are subject to the vagaries of changing winds.

Regular winds, common for much of the year, tend to keep this drifter on the high seas. However, the first south or westerly breezes can bring large rafts of by-the-wind sailors ashore. For the first few days, dying individuals retain their beautiful blue colour (although undersides are yellow due to presence of zooxanthellae). Eventually, their remaining hard-carcass portions become almost clear. At this point, these resemble plastic and incorrectly imply a pollution event.

It is usually the beaches of the outer coast from California to Alaska where beachcombers most often spot stranded by-the-wind sailors en masse. However, where the Pacific meets the entrance of the Salish Sea, sightings of this incredible wind-blown ocean dweller can occur. So, while strolling sandy beaches along the exposed Pacific Northwest shoreline, keep your face to the wind, and luck may grant you such a magnificent vision.

Let’s start at the beginning. Hydroids are members of the large, diverse group of animals in the phylum Cnidaria. Cnidarians are defined by having a single opening to their digestive system — yuk! This structure is surrounded by a ring of tentacles. Another definitive feature of Cnidarians are “stinging” single cells that cover these tentacles. Called cnidocytes, these cells have both feeding and defensive functions. Sea anemones and jellies (not jellyfish as they are not fish) are Cnidarian creatures almost certainly familiar to readers.

Almost all hydroids are colonial animals that feature a huge number of miniature feeding polyps with barely visible tentacles. These are festooned with cnidocytes.

A defining hydroid characteristic is alternation of generations. During spawning season, a hydroid colony will produce a second form of polyp that is strictly designed to produce many tiny jellies (medusae) that are either male of female. Eggs and sperm are shed into the water and tiny larvae called planulae result. A surviving planula settles upon a solid substrate, metamorphoses and grows into the recognizable “hydroid” colony. Thus the alternation of generations between polypoid and medusoid stages. The fine beard-like structures that hang from floats during the spring/summer period are a hydroid species easily observed by readers.

Finally, the above overview represents a general example, and the diversity of hydroids provides an amazing array of variation of the theme.

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