Blog on ocean conditions along the Newport Line and the northern CA Current.
It would be remiss of us to not take note of the blue-hued visitors that have been washing ashore the past few months. I’m talking about the aptly named hydrozoan, By-the-wind sailor, or Velella velella. Velella are cosmopolitan hydroid colonies that use a gas-filled float and chitinous sail to float at the ocean’s surface. It feeds on zooplankton by extending short tentacles below the elliptical float.
For the past few years, people beachcombing along the Oregon coast have been encountering lines of these animals washing up along the shore. The densities vary, with stormy days bringing mass strandings where it can be hard to estimate abundances. If you’ve been observant the past few months, you’ve probably also noticed the Velella are getting larger. These observations are consistent with work in the Eastern Pacific commenting on the seasonal appearance of Velella. According to Bieri (1977), observations show small individuals, less than 10 mm, are seen December and January (Newportal Post) with the maximum size, about 80 mm, reached in late April with another peak in September. Interestingly, along Agate Beach this past week there was a large stranding that included size ranges from 2 mm to 65 mm!
As I continued my beachcombing, I noticed a dominant ‘handedness’ to the colonies. Velella sails are characterized as either left-handed or right-handed. In order to check for handedness, orient the colony vertically and examine the angle of the sail. If left-handed, the sail will start in the upper left and end in the lower right. Most individuals in the Eastern Pacific, whether washed ashore or at sea, are left-handed (Bieri, 1959 ; personal observations). The significance of this dimorphism is still debated and is often discussed in terms of zonal differences or prevailing winds. Can you find any right-handed Velella?
Thinking about size ranges and dimorphism calls into question what we know about Velella natural history. For such a charismatic species, their opportunistic nature makes them difficult to study. We still have much to learn about distribution, feeding, and reproductive strategies. Stay tuned as we continue to explore these mysterious sailors.
Bieri, R. (1959). Dimorphism and size distribution in Velella and Physalia. Nature, 184, 1333–1334
Bieri, R. (1977). The ecological significance of seasonal occurrence and growth rate of Velella (Hydrozoa). Publ.Seto Mar. Biol. Lab., 24, 63-67