Food of the sea urchins Strongylocentrotus nudus and Hemicentrotus pulcherrimus associated with vertical distributions in fucoid beds and crustose coralline flats in northern Honshu, Japan

The vertical distribution and food of Strongylocentrotus nudus and Hemicentrotus pulcherrimus in fucoid beds at depths of 0.3 to 2.4 m and coralline flats at depths of 2.4 to 4.7 m were studied monthly from May 2001 to May 2002 off the Oga Peninsula, Akita prefecture, northern Japan. No seasonal migration of S. nudus from coralline flats to the fucoid beds occurred, as sufficient food was available in the form of sessile animals. Crustose corallines were generally predominant in the gut contents of sea urchins in fucoid beds, where their density was extremely low. Hemicentrotus pulcherrimus inhabit both fucoid beds and coralline flats. The main foods reguired for this sea urchin's gonad production are the dominant algae and sessile animals found in each algal community. The low amounts of fucoids in the gut contents of each species suggest low consumption, possibly because of difficulty in grazing fully grown and erect thalli and feeding deterrents.