87.5 Sunday, Jan. 6 Plasticity in Hatching in Response to Predators and Individual Variation in Duration, Frequency, and Seasons of Brooding in the Barnacle Balanus glandula STRATHMANN, R.R.*; BRANSCOMB, E.S.; VEDDER, K.; Univ. of Washington, Friday Harbor email@example.com
Hatching in response to predation reduces a potential cost of holding larvae until conditions in the plankton are favorable. Broods of barnacles hatch when the clumps of embryos (lamellae) are dissected into smaller groups. Predation on brooding barnacles can have a similar effect. Escape or death of brooded offspring depends on the predator. In the laboratory, when crabs (Cancer oregonensis) ate adult barnacles (Balanus glandula), the barnacles’ tests were broken, and nauplii hatched from broods; in contrast, when the whelk Nucella ostrina ate barnacles, the barnacles’ wall plates and opercula remained in place, and fewer or no nauplii were released. In some cases numerous nauplii were trapped within the test of the killed mother. At a field site with abundant whelks, many dead barnacles had opercular plates in place. Hatching of some barnacles is also known to occur when phytoplankton induces the parent to stimulate hatching of its brooded larvae. To examine synchrony and variation in brooding among individuals of B. glandula, we non-destructively observed late-stage (dark-colored) broods in individuals that had settled on glass plates. For the first brood of the year, first appearances and disappearances of late-stage broods were consistent with a synchronizing environmental stimulus for hatching. The dates that broods reached advanced stages varied more than the dates that they were released. An exception to synchronization among individuals was that a few of the broods that reached advanced stages early also hatched early. In subsequent broods (later spring and summer), advanced stages were held more briefly. Either an environmental stimulus for hatching was not needed later in the season or it was more frequently present. Individuals appeared to vary greatly in number of broods per year.