Age distribution of the sea urchin Strongylocentrotus nudus (A. Agassiz) in relation to algal zonation in a rocky coastal area on Oshika Peninsula, northern Japan

Abstract

The age distribution of the sea urchin Strongylocentrotus nudus in relation to algal zonation was studied in a sublittoral rocky area on Oshika Peninsula, northern Japan, from June 1995 through to August 1996. The algal zonation observed there extends from a shallow area of cobbles to deeper areas dominated successively by Sargassum yezoense, Eisenia bicyclis and, finally, crustose coralline red algae. One‐year‐old sea urchins occurred only on the cobbles and crustose corallines in contrast to the presence of 2‐year‐old individuals from all areas and the restricted distribution of individuals aged 3 years and over to Eisenia and crustose corallines. Calculated mean body sizes in the Eisenia area became larger after the age of 2 years compared with those in the area of crustose corallines. Spawning was ascertained histologically in both the Eisenia and crustose coralline areas, although gonad indices were higher in the former area than in the latter throughout the year. Gut contents were dominated by E. bicyclis in the Eisenia area, and by crustose coralline red algae and small algae in the crustose coralline area. Thus, the sea urchin may settle most abundantly on crustose corallines and lives there for 1–2 years. Thereafter, they expand their habitat toward the Eisenia area, where there is richer sources of food for attaining a higher growth rate and to generate heavier gonads.

Population Dynamics of Edible Sea Urchins Associated with Variability of Seaweed Beds in Northern Japan

“…The seasonally maximum gonad indices of M. nudus were more than 30 in E. bicyclis kelp beds (Sano et al 2001;Agatsuma et al 2005b), 15-17 in fucoid beds (Nakabayashi et al 2006;Endo et al 2007) and less than 10 in barrens (Agatsuma 1997;Agatsuma et al 2005b). The gonad index in E. bicyclis bed was higher than that in Sargassum yezoense bed .…”

“…In relation to seaweed beds, gonads of Strongylocentrotid sea urchins in kelp beds commonly increase more in size than those in barrens (Gonor 1972;Lang and Mann 1976;Pearse 1980;Wharton 1980;Johnson and Mann 1982;Keats et al 1984;Scheibling and Stephenson 1984;Sivertsen and Hopkins 1995;Agatsuma 1997;Meidel and Scheibling 1998b;Sano et al 2001). As characteristic of the phenotypic plasticity in sea urchins, Centrostephanus rodgersii adjust its body growth with food availability (Ling and Johnson 2009).…”

“…The ages, which reached a legal size of 5 cm diameter are shown in Table 1. The growth rate was high in the beds of the perennial kelps E. bicyclis, S. japonica, S. angustata, Saccharina sculpera, and Alaria crassifolia, where M. nudus reached a test diameter of 5 cm at ages of 2-4 years (Agatsuma 1997;Sano et al 2001;Agatsuma et al 2005b). The growth rate was very low in barrens in the Sea of Japan off southwestern Hokkaido, where M. nudus reached the same size at ages of 7-8 years (Agatsuma 1997).…”

“…The growth rate was very low in barrens in the Sea of Japan off southwestern Hokkaido, where M. nudus reached the same size at ages of 7-8 years (Agatsuma 1997). While, the sea urchins on the barrens below E. bicyclis beds grow to 5 cm diameter at ages of 3-6 years (Sano et al 2001;Agatsuma et al 2005b). Mesocentrotus nudus reached 5 cm diameter after 3-4 years in the beds dominated by the large fucoids Coccophora langsdorfii, S. piluliferum and S. patens, 5-6 years in a red alga Chondrus ocellatus-dominated bed and 7-8 years in a red alga Laurencia spp.-dominated bed and barrens (Nakabayashi et al 2006).…”

“…The gonad size is determined by the algal standing crop and the kind of species that grows in the field, this size being largest in kelp beds and smaller in crustose coralline habitats (Agatsuma 1997;Sano et al 2001).…”