|Vol. 7 (No. 2), pp. 47-78, 2014||doi:10.5047/absm.2014.00702.0047|
Laboratory of Marine Plant Ecology, Graduate School of Agricultural Science, Tohoku University, Tsutsumidori-Amamiya 1-1, Aoba, Sendai, Miyagi 981-8555, Japan
(Received on October 1, 2013; Accepted on December 24, 2013; Online published on June 30, 2014)
Abstract: Effects of variability of seaweed beds on population dynamics of sea urchins have not been studied in detail. The present study documents that population dynamics of edible sea urchins is closely associated with variability of seaweed beds in subtidal rocky regions in northern Japan, from larval settlement, gonad production, somatic growth, recruitment and seasonal migration of the sea urchins Mesocentrotus nudus, Strongylocentrotus intermedius and Hemicentrotus pulcherrimus. Dibromomethane (DBM), which is produced abundantly by crustose coralline algae, induced larval metamorphosis of more than 80% of individuals of M. nudus and S. intermedius in the presence of 34-61 ppm within 24 h, indicating its instantaneous effect on a high success of metamorphosis. Conversely, 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP), which are released from kelps Eisenia bicyclis and Ecklonia kurome, killed all eight-armed larvae of M. nudus and S. intermedius in the presence of 20-50 ppm. The larval metamorphosis were significantly reduced in the presence of 1-10 ppm. These suggest that the population size of these sea urchins is enhanced on coralline barrens and reduced in kelp forests. Population size of M. nudus was enhanced by episodic recruitment of juveniles on crustose coralline barrens affected by large-scale oceanographic processes. Growth and gonad production of M. nudus and H. pulcherrimus is greatly affected by the amount and the kind of seaweed beds, which alter the states of crustose coralline flats and large perennial kelp or fucoid forests in the course of algal succession through oceanographic condition. The sea urchins migrate to seaweed beds to increase in gonad size toward maturation and spawning in the species-specific reproductive cycles to succeed in reproduction. Release of hatchery-raised seeds of S. intermedius into the wild and aquaculture of wild or hatchery-raised sea urchins fed on surplus or low-priced sea foods for humans enabled the sea urchins to increase the population size and improve the gonad production and somatic growth.
Keywords: barren, fucoid, kelp, settlement, gonad production, somatic growth, recruitment, range extension, seasonal migration, reseeding, sea urchin, seaweed bed
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