Papers from the Echinoderm Conference. 11. A stable system of predation on a holothurian by four asteroids and their top predator

Abstract

Seven species of asteroids feed on Cucumaria lubrica, but together they harvest only 3% of the population or 10% of the standing crop biomass per year at the locality of the study. The rates of predation by the asteroid Solaster dawsoni on the predators of C. lubrica are high enough and the rates of growth and successful recruitment into the area by the predators of C. lubrica are low enough to indicate that [he predators of C. lubrica are possibly kept low in abundance by the higher predator Solaster dawsoni. Solaster stimpsoni, the most abundant predator of C. lubrica in the area, has a behavioural escape mechanism which becomes increasingly effective as S. stimpsoni grows large and when it is on vertical rock surfaces. While S. dawsoni removes about 24–32% of the S. stimpsoni population each year, probably preventing a buildup in numbers, the refuge in size of a reproductive stock allows the persistence of the long-lived, slow-growing, S. stimpsoni. Dermasterias, a predator of C. lubrica with a refuge in size but with no behavioural escape mechanism to S. dawsoni, is 0.07 times as common as S. stimpsoni with a size-frequency distribution represented predominantly by large adults. Solaster endeca and Leptasterias, predators of C. lubrica with no known refuge to S. dawsoni, are 0.004 and 0.008 times as common as S. stimpsoni and may be considered strays from other habitats. No significant changes in abundance were observed in the 3 trophic levels of the association from 1965 to 1976: C. iubrica, 4400 m-2; S. stimpsoni, 0.5 m-2; S. dawsoni, 0.007 m-2. The stability of the system results from different control mechanisms and refuges at each trophic level.