Palolo swarming

Once or twice a year, palolo swarm to the surface of the sea in great numbers. Samoans eagerly await this night and scoop up large amounts of this delicacy along the shoreline with hand nets. This gift from the sea was traditionally greeted with necklaces made from the fragrant moso’oi flower and the night of the palolo was and still remains a happy time of celebration. The rich taste of palolo is enjoyed raw or fried with butter, onions or eggs, or spread on toast.

Palolo is the edible portion of a polychaete worm (Eunice viridis) that lives in shallow coral reefs throughout the south central Pacific, although they do not swarm at all of these locations. This phenomenon is well known in Samoa, Rarotonga, Tonga, Fiji, the Solomon Islands and Vanuatu.

Palolo are about 12 inches long and live in burrows dug into the coral pavement on the outer reef flat. The worm is composed of two distinct sections (see drawing). The front section is the basic segmented polychaete with eyes, mouth, etc., followed by a string of segments called the “epitoke” that contain reproductive gametes colored blue-green (females) or tan (males). Each epitoke segments bear a single, tiny eyespot that can sense light (that's why islanders are able to use a lantern to attract the palolo to their nets).

Palolo underwater

When it comes time to spawn, palolo will back out of their burrows and release the epitoke section from their body. The epitokes then twirl around in the water in vast numbers and look like dancing spaghetti. Around daybreak, the segments dissolve and release the eggs and sperm that they contain. The fertilized eggs hatch into small larvae that drift with the plankton until settling on a coral reef to begin life anew.

The swarming of palolo is a classic example of the coordinated mass spawning of a simple marine organism. The worms emerge from their burrows during a specific phase of the moon, but the actual date is a bit complicated. The swarms occur on the evenings of the last quarter moon of spring or early summer. In Samoa, this is seven days after the full moon in October or November. Swarming occurs for two or three consecutive nights with the second night usually having the strongest showing.

Palolo usually appear here in October, but sometimes in November or sometimes during both months. This difference is due to the fact that there are approximately thirteen lunar months in one calendar year and the palolo use primarily the moon to time their spawning activity. However, if they always spawned every twelve lunar months, their time of spawning would occur earlier every year. After a few years, they would be spawning in August or July (midwinter). In order to make up for this difference, the worms will delay spawning in some years to the thirteen lunar month.

The fact that palolo adjust their spawning time means that there are other factors beside the moon that determine the time of year they begin to mature and are ready to release their epitokes. Several studies on this matter have suggested that rising seawater temperatures, tides, weather, moonlight or other biological signals may play a role in starting the maturation and release of the epitokes. Once the swarming begins, the presence of the palolo spawn in the water probably stimulates other palolo to release their mature epitokes.

Rules For Predicting Emergence. Everyone seems to have their own methods for predicting when the best palolo rising will occur. Several natural clues that preceded the palolo rising enabled islanders to predict the correct timing for palolo swarming. These included the flowering of the moso’oi tree, the closing of the palulu flower (a morning glory), a strong smell from the reef, brown foamy scum (from coral spawn) on the ocean, toxins occurring in reef fish, and abrupt weather changes or bad weather such as thunderstorms or lightning.

A good catch of palolo

So, will palolo swam seven days after the full moon in October or November? One set of rules used to predict the main night of emergence depends on the calendar date of October's third quarter moon (seven days after October's full moon). If it occurs:

1. From October 1 to 8, palolo will not appear until November.
2. From October 8 to 18, palolo will not appear in October or the swarming will be weak followed by a stronger appearance in November.
3. From October 19 to November 7, there will be a single, strong swarming centered on this date.
4. From November 8 to 17, there will be a strong appearance on this date, possibly following a weaker swarming during the previous month (see number 2 above).

To further complicate matters, the actual time of emergence of palolo in Samoa differs between islands. They usually appear around 10 pm in the Manu’a Islands (however, it has occurred at 1 am there), 1 am on Tutuila and closer to 4 or 5 am in western Samoa. This difference is somewhat consistent from year to year and cannot be accounted for by difference in tides or moonrise. The difference in tides between islands is far less than one hour and the time of moonrise is only minutes apart.

David Itano, DMWR

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