J. Moll. Stud. (2002), 68, 79-86
© The Malacological Society of London
2002
SPATIAL AND TEMPORAL FLUCTUATION IN THE DENSITY OF THE INTERTIDAL LIMPET, PATELLOIDA STRIATA QUOY & GAIMARD, ON SUBTROPICAL COBBLED SHORES
Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Ishigaki Island, Okinawa 907-0451, Japan
On cobbled shores, limpets are exposed to various abiotic environmental factors whose harshness and patterns of seasonal fluctuation differ from shore to shore. As a result, the density of limpets in each season and the pattern of their seasonal fluctuation might also vary among shores. This idea was examined by investigating the relationship between coverage of cobbles, an important abiotic factor, and the density of Patelloida striata, an abundant species of limpet in subtropical Japan. These were estimated by seasonal quadrat samplings on three cobbled shores on Ishigaki Island, Okinawa, from June 1997 to September 1998. The above-mentioned idea was supported by the following two results: (1) The coverage of cobbles showed a sharp seasonal fluctuation on only one shore on which freshwater runoff sporadically transported sand onto cobbles; on this shore, the density of P. striata was significantly higher than on the other shores in most seasons; and (2) on this shore, which was severely disturbed, seasonal fluctuation in the density of P. striata correlated significantly with a sharp seasonal fluctuation in the coverage of cobbles; as a consequence, the seasonal fluctuation in density was greater on this shore than on the other shores. The first result is discussed in relation to the small body size (<24.3mm in shell length) and ephemerality (<2 years in life-span) of P. striata, both suggesting that this species adapts to abiotically harsh environments. The second result is discussed in relation to the functions of cobbles for P. striata such as the providing of feeding grounds and shelter.
(Received 28 December 2000; accepted 3 July 2001)