Succession of sessile organisms on experimental plates immersed in Nabeta Bay, Izu Peninsula, Japan. II. Succession of invertebrates

Abstract

The succession of sessile invertebrates over ca 3 yr was studied by suspending concrete plates at depths of 1.0, 2.5, 4.0 and 5.5 m in Nabeta Bay, Shimoda, Pacific coast of Japan. A total of 28 species of sessile invertebrates appeared dunng colonization. Their succession was divided into 3 stages by dendrogram analysis: Stage 1 is characterized by the earliest colonizers of the barnacle Balanus trigonus and the spirorbid Dexlospira foraminosus; Stage 2 by the ascidian Diplosoma mitsukuni; and Stage 3 by the oyster Crassostrea nippona. The earliest colonizers were overgrown by colonial ascidians, bryozoans and sponges recrulhng a little later. The overgrowth of these colonists, especially D. mitsukurii, affected the subsequent community structure of sessile invertebrates. The pattern of transition of sessile invertebrates differed with depth. At depths of 1.0 and 2.5 m, C. nlppona finally dominated by overgrowing other sessile invertebrates. Communities at these 2 depths reached Stage 3 between 13 and 37 mo after immersion. At a depth of 4.0 m, C. nippona finally decreased in coverage, while B. trigonus, D. mitsukurii and the bryozoans Watersipora subovoidea and Amathja distans increased. The community at this depth reached Stage 3 after 13 to 37 mo from immersion. At a depth of 5.5 m, C. nlppona did not appear at all, but the barnacles Megabalanus volcano and M. rosa as well as B. tngonus, D. mitsukurii, W. subovoidea and A. distans increased in coverage 37 mo after immersion. At this depth, the community remained at Stage 2 dunng the period from 4 to 37 mo after immersion. In the penod from 13 to 37 mo the number of species remained almost unchanged at depths of 1.0 and 2.5 m, but tended to decrease at 4.0 and 5 5 m. The communities at the 2 upper depths dominated by C. nippona were regarded as a persistent climax community in the succession, because C. nippona can settle easily on the shells of barnacles having high recruitment capability, it can avoid the intensive overgrowth by later colonists, and it has a long life span. On the other hand, the communities at the 2 lower depths dominated by colonial animals seem to inhibit the invasion of other sessile invertebrates through competition for space.