Seasonal changes in taxon richness and abundance of mobile invertebrates inhabiting holdfast of annual kelp Ecklonia radicosa (Phaeophyceae, Lessoniaceae) at the central Pacific coast of Japan

摘要

To investigate seasonal changes in the taxon richness and abundance of mobile invertebrates inhabiting holdfasts of the warm temperate annual kelp Ecklonia radicosa, five holdfasts were collected monthly at the central Pacific coast of Japan from April to November 2014. During the study period, there was little variation in holdfast height and diameter, which ranged from 5.9 to 8.5 cm and from 7.1 to 10.8 cm, respectively. In total 7087 animals were collected from 40 holdfasts (177.2 individuals inds./holdfast, on average). The number of mobile invertebrates gradually increased from May (15 +/- 9.9 inds./holdfast) to August (346 +/- 152.5 inds./holdfast), with over 300 inds./holdfast until October before rapidly decreasing in November (110 +/- 85.6 inds./holdfast). Similarly, taxon richness increased gradually from April (4.3 +/- 1.0 taxa/holdfast) to August (11.0 +/- 3.7 taxa/holdfast), and decreased in November (8.6 +/- 2.3 taxa/holdfast). Interestingly, hundreds of mobile invertebrates inhabited holdfasts of kelp plants that had shed their blade in October and November. Taxon composition from August to October and the number of invertebrates from July to November were comparable to data previously reported for perennial kelps. In this study, the importance of annual Ecklonian species as biogenic habitats was demonstrated for the first time.