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

Abstract

Keyword Clements Tsukidate 1992). Sargassum beds trap nutrients and contribute to high rates of primary production (e.g. Wanders 1976). The highest annual production of 8.25 kg dry/m 2 was recorded in Sargassum macrocarpum in Iida Bay, Ishikawa in the Sea of Japan (Taniguchi and Yamada 1978).Edible sea urchins are primary consumers in coastal rocky-bottom ecosystems and their main diet is marine algae (De Ridder and Lawrence 1982). About 20 species of sea urchins are consumed in the world. Most sea urchins belong to the order Echinoida. All the species inhabit shallow waters (Lawrence 2001). Since 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 eightarmed 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.

Estimation of the feeding pressure of a sea urchin (<i>Diadema setosum</i>) population on a barren ground in a temperate region of Japan

“…However, in this study, the population density was investigated only once, i.e., in May 2015. Agatsuma (2014) reported seasonal changes in the densities of M. nudus and Hemicentrotus pulcherrimus in northern Japan. We targeted a stable population with small changes in its average TD composition throughout the study period.…”

Influence of the 2011 Tohoku tsunami on the genetic structure of wild sea urchin (Mesocentrotus nudus) populations in Sanriku, Japan

“…The long planktonic stage of M. nudus (Agatsuma, 2014) could explain their high dispersal ability. In addition, we suggest that the high gene flow among the studied M. nudus populations may have provided new larval recruitment across differently sized and shaped bays in Sanriku.…”

“…An analysis of molecular variance (AMOVA) was used to compare genetic differentiation between pre-and post-earthquake populations (~2010 Touni and Okirai Bays versus 2011, 2012, 2013, 20142011, 2012, 2013, 2014 and between two bays (~2010, 2011, 2012, 2013, 2014Touni versus ~2010, 2011, 2012, 2013, 2014. Pairwise F ST was then estimated, and statistical significance was assumed at p < .05 with Bonferroni correction.…”

“…Gonads mature between April and August, while spawning occurs between September and October (Agatsuma, 1999). Like other edible sea urchins, M. nudus has a planktonic stage of 14–40 days (Agatsuma, 2014) and a lifespan of 14–15 years (Agatsuma, 2001).…”

Fabulous but Forgotten Fucoid Forests

“…Finally, better knowledge and valuation would perhaps also arise if fucoids are unified under a non-taxonomic common name, just like corals, kelps, seagrasses, salt marshes, and mangroves. Some marine scientists have previously used 'rockweed' to describe all fucoids (Estes et al 1989, Steinberg et al 1995, Van Alstyne et al 1999a, Van Alstyne et al 1999b, Tegner and Dayton 2000, Liu et al 2012, Agatsuma 2014, Duffy 2021, Elsberry and Bracken 2021, and fucoids and rockweeds are listed as synonyms in Webster's and The Free Dictionaries ("rockweeds are any of various coarse brown algae in the order Fucales") (Anon. 2021b, a).…”