The comparative ecology of two sympatric polychromatic populations of Xererpes fucorum Jordan & Gilbert (Pisces: Pholididae) from the rocky intertidal zone of Central California

Abstract

A total of 517 Xererpes fucorum Jordan & Gilbert (422 red and 95 green) were collected near Piedras Biancas, California during 13 consecutive monthly transects through the exposed intertidal zone at 3 sites. Xererpes was most abundant ( N = 274) and had its highest mean vertical distribution (+0.42 m) in the summer (June–August) and was least abundant ( N = 17) in the winter (December–February) and had its lowest mean vertical distribution ( +0.06 m) in the spring (March–May). The times of peak abundance, mean standard length frequencies, and intertidal vertical distributions of the red and green populations, however, differed over the year. The species occupied agal substrata (23 spp.), mainly Gigartina papillota, Pelvetia fastigiata and Rhodoglossum affine (73.4% incidence), which matched its body coloration in 95.6% of 580 field substrata recorded. A skin-diving operation conducted at high tide and the release and recapture of marked Xererpes at low tide indicated that the species does not occupy typical low tide habitats when immersed, but re-occupies its original habitat upon emersion in a high percentage (56.3%) of cases. Laboratory substratum preference experiments confirmed field observations in most cases, and laboratory color change experiments, in conjunction with field and published data, suggested that the polychromatism of Xererpes may result in intraspecific resource partitioning, thereby broadening the utilization of available resources within the intertidal zone.