Distributions of Zosteraceae species along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan

Abstract

Distribution and standing crops of Zosteraceae species were surveyed along the coasts of Aomori Prefecture, locating at the northernmost of Honshu, Japan, from 1999 to 2002. Sampling were made at depths of 2.5 m (1,079 points), 5 m (1,181 points) and 10 m (1,183 points) on transects set at about 500 m intervals along the whole coasts divided in four areas according to oceanographic and topographic characteristics: the Japan Sea coastal area affected by Tsushima (warm) Current, the Pacific coastal area affected by Oyashio (cold) Current, coastal areas facing to the Tsugaru Strait connecting the two seas, and coastal areas of Mutsu Bay embayed by Tsugaru and Shimokita Peninsula. Distribution patterns of Zosteraceae species can be summarized as below. Phyllospadix iwatensis Makino: common on bedrocks along the Tsugaru Straight and Pacific coast but absent in Mutsu Bay; Zostera marina Linnaeus: common on soft bottoms of Mutsu Bay and Tsugaru Straight areas but absent in the Pacific coast; Z. caespitosa Miki: common on soft bottoms of Tsugaru Strait and Mutsu Bay; Z. caulescens Miki: restricted to a depth of 10 m in Tsugaru Strait coast. In Mutsu Bay, distributions of Z. marina and Z. caespitosa rarely overlapped and the latter species showed a tendency to grow in deeper depths. Sediment analyses of their habitats revealed that Z. caespitosa were likely to grow in the habitat with thinner sediment layer and coarser particle than Z. marina.