A Visit from Velella Velella

Last spring persistent southwesterly winds pushed Velella velella onto Sanctuary beaches. photo Kelly Newton for NOAA/MBNMS

During April and May of 2002 sanctuary beaches were bombarded with millions of by-the-wind sailors (Velella velella). The sanctuary office as well as the California Department of Fish and Game received several calls reporting oil slicks off the coast of Big Sur. These reported slicks turned out to be thousands of these iridescent Velella floating at the surface.

Velella are bright blue pelagic colonial hydrozoans (a type of cnidarian) distributed worldwide in temperate and tropical seas. They float at the surface, mouth down due to their gas-filled bodies, and travel using a transparent sail that is formed by a chitinous exoskeleton. The sail is angled at 45 degrees to the right or left of the main body axis, allowing the animal to drift at a 45-degree angle to the wind direction, hence the name ‘by-the-wind sailor.’

Velella are normally found in the central water masses of the Pacific Ocean, where the prevailing northwesterly winds hold the population offshore of California. Last spring persistent southwesterly winds pushed the Velella onto sanctuary beaches from Cambria to north of San Francisco. All sizes of Velella, ranging from one to eight centimeters in length, were found. Several weeks after the initial strandings, all that remained of the Velella were clear chitinous exoskeletons.

While at sea, these animals feed upon fish eggs, crustacean larvae, and other zooplankton. Velella also contain single-celled symbiotic algae (zooxanthellae) in their tissues. It is thought that they may gain some nourishment from the photosynthetic activity of these algae. Pelagic gastropods, along with the ocean sunfish (Mola mola), feed on Velella.

The life cycle of Velella includes both asexual and sexual stages. This type of reproduction is known as alternation of generations. The asexual stage, or polyp, is the bright blue animal that washed ashore in 2002. The asexual polyp is made up of two different types of polyp: the central feeding polyp, or mouth, and smaller polyps surrounding the mouth that are both reproductive and used for feeding. From these smaller polyps small medusae bud off. Each medusa is either male or female, representing the sexual stage of Velella. These medusae sink to depths of 600 to 1,000 meters, where eggs and sperm are then released. A planula larva is formed that develops into the next larval stage, or conaria. This very small asexual polyp secretes an oil droplet, causing it to float back up to the surface where it will develop into the larger animal with sail.

In general, the Velella population spends three to four months on the surface in the spring, two to three months at depth, and then three to four months in the late summer on the surface before sinking to depth for two to three months in the fall. The Velella on the surface are larger in the spring than in the late summer. The late summer Velella rarely wash ashore, due to the prevailing northwesterly winds.

Velella wash ashore every few years. It has been several years since the last time they were cast upon sanctuary beaches, and it is likely that it will be several more before they return again.

Kelly Newton
Monterey Bay National Marine Sanctuary

Status of the Western Snowy Plover in the Monterey Bay Region

The next time you go for a walk on a sandy beach, keep your eyes open for what appears, at first glance, to be a drift of small snowballs. These diminutive fluffballs are actually roosting flocks of Western Snowy Plovers (Charadrius alexandrinus), small shorebirds that nest and winter on the sandy beaches of Monterey Bay.

Western Snowy Plover male and chick photo Greg Smith

In the Monterey Bay region during spring and summer, Western Snowy Plovers nest and raise their chicks along the shoreline from Sunset State Beach south to Marina, at saline flats within the Moss Landing Wildlife Area, and at several small pocket beaches in northern Santa Cruz County. In winter large roosting flocks congregate at these locations, often near river mouths.

In 2002 Western Snowy Plovers nesting locally fledged more than 210 chicks – the second greatest number ever documented in the Monterey Bay region. The number of chicks fledged per breeding male was 1.4, well over the estimated 1.0 chicks per male necessary to stabilize the population. In 1997 and 1998 La Niña conditions over winter resulted in high adult mortality, but the high level of fledging success of the past three years has nonetheless resulted in a measurable increase in the size of the local breeding population (see Figure 1, opposite).

Despite these increases, the range of the plover in Monterey Bay has contracted, and nesting success at historic sites on the fringes has declined. As recently as five years ago, Western Snowy Plovers occupied nesting sites as far south as Monterey State Beach in southern Monterey Bay.

In 2002, however, the southernmost nesting attempt documented was north of Reservation Road in Marina. Prospecting pairs were observed at Marina State Beach and at Sand City, but nesting was not confirmed at these locations. Similarly, although 2002 was a banner year for plovers nesting at Sunset State Beach, it was the first time this site had been occupied in three years.

The success of plovers attempting to nest at pocket beaches in northern Santa Cruz County gradually has decreased. (Pocket beaches are small and bound at each end by a physical barrier that chicks cannot cross, so adults are unable to move their chicks large distances away from disturbances such as humans or predators.) At these beaches only 60 percent of fifteen nests hatched successfully, and only two fledglings were produced, in 2002. In response to their lack of success at their traditional nesting beaches, some pocket beach nesters have defected to the beaches of central Monterey Bay for their second nesting attempt.

Figure 1. Number of Western Snowy Plovers nesting in Monterey Bay and northern Santa Cruz County

What are the factors that influence Western Snowy Plovers’ reproductive success? These shorebirds require relatively undisturbed areas to nest and rear chicks. They lay a clutch of three sand-colored eggs directly on the bare sand on the middle to upper beach area, above the wrack line but below the heavily vegetated dune. Because plovers must incubate the clutch around the clock for twenty-eight days, any disturbance that prevents the bird on duty from returning to the nest jeopardizes the survival of the eggs. Nests are also susceptible to trampling from humans, dogs, horses, and vehicles.

Plover chicks are precocial (active from birth), leaving the nest within hours of hatching, but they remain flightless for about one month. The male plover usually rears the brood alone. He protects them from danger, broods them until they can thermoregulate, and leads them to foraging areas. The birds feed primarily on small invertebrates associated with beach wrack, and chicks often make treacherous daily trips down to the wet wrack line, where they are susceptible to predators, trampling, and separation from the male parent. Because young chicks must be brooded regularly by the male to stay warm during the chilly Monterey Bay summers, prolonged separation can mean death for the chicks.

Urbanization, degradation and loss of coastal habitat, and the effects of introduced predators and invasive vegetation led to the listing of the Pacific Coast population of the Western Snowy Plover as threatened by the U.S. Fish and Wildlife Service in 1993. Currently, an estimated 1,200 to 1,500 Western Snowy Plovers compose the Pacific Coast population, which ranges from southern Washington south to Baja. Ten years after the plover’s listing, the same factors continue to affect the breeding success of these birds locally and throughout their range. Around Monterey Bay, recreational use of beaches continues to grow, causing an increase in human-related disturbance to nesting plovers. Habitat fragmentation and urbanization have enhanced the accessibility of beach habitat to non-native predators such as the red fox (Vulpes vulpes regalis) and invasive predators such as the Common Raven (Corvus corax) and American Crow (Corvus brachyrhynchos). Red foxes have been actively controlled since 1993 but are still present on beaches at the start of each nesting year. In 2002 ravens depredated twelve nests at the Pajaro River mouth – the first documented nest losses in the central Monterey Bay region attributed to this increasingly abundant predator.

The future of the Western Snowy Plover depends on several factors. As plovers are increasingly concentrated into smaller habitat areas, we have an obligation to protect them in their remaining habitat from the effects of our activities. This will mean active management of non-native and invasive predators, restoration of habitat, and a basic willingness on our part to share beaches and coastal areas with species that depend on these areas for basic life functions.

Kriss Neuman
Point Reyes Bird Observatory