Growth of the Sea Urchin, Strongylocentrotus intermedius in the Eastern and Northern Coasts of Hokkaido

Abstract

The growth of the sea urchin, Strongylocentrotus intermedius, collected in the coasts of eastern (coast of the Pacific Ocean) and northern (coast of the Japan Sea) Hokkaido was examined based on growth formulae applying ages estimated by annual rings on the 5 th genital plate. Sea urchins in the coast of northern Hokkaido showed a rapid growth at their early ages, but a gradually reduced growth with ageing. On the other hand, sea urchins in the coast of eastern Hokkaido showed a linear growth curve.
Daily growth increments of the sea urchins indicated no significant difference between the two areas until the age of 3 years, but sea urchin groups over the age of 4 years in the northern coast of Hokkaido showed gradually decreased on growth rate with ageing compared with those in the eastern coast of Hokkaido.
No significant difference in the assimilation coefficient was found between the sea urchins in the eastern and northern coasts of Hokkaido, but their dissimilation coefficient showed a significant difference between sea urchins in two areas. The sea urchins in the northern coast of Hokkaido showed a lower growth efficency with ageing than those in the eastern coast of Hokkaido.
It was considered that higher water temperature have caused a higher metabolic activity in sea urchins in the northern coast than those in the eastern coast. The high metabolic activity resulted from increased assimilation and dissimilation of ingested food seemed to be reduce the growth efficiency of the northern coast sea urchins, particularly for aged individuals. Smaller size of sea urchins living in the northern coast of Hokkaido might be caused by the higher temperature waters.