Some aspects of the ecology of strongylocentrotus droebachiensis in eastern Newfoundland

Strongylocentrotus droebachiensis is the dominant macroscopic benthic animal along the exposed coasts of Newfoundland. The gonads ripen during the fall, reach a peak in size and maturity in February or March, and spawnout occurs by April. In exposed areas the density is very high (up to 350 urchins/m²) and small urchins are abundant. In sheltered areas the density is much lower but most of the individuals are large. The urchin populations are concentrated in shallow water where macrophytes, their main food, grow abundantly. Urchins have variable preferences for and abilities to consume different algae. Feeding is least in the winter, when the gonads are near their peak, and greatest following spawnout. The potential grasing rate is sufficient to restrict noncalcareous macrophytes to the sublittoral fringe where the abrasion of the gonads, as they are washed back and forth by waves, keeps the urchins from advancing and devouring them. Only Agarum cribrosum and Ptilota serrata, which are undesirable urchin foods, grow at greater depths in urchin dominated areas. Sea stars, other urchins, lobsters, crabs, a number of fishes, and birds are common predators of S. droebachiensis but are not very effective in limiting their numbers