ABSTRACT The gonadal cycle of Tegula eiseni (Jordan, 1936) was determined on monthly samples (25-30 organistas) collected from a population in Bahia Asuncion, B.C.S., from January 2006 to December 2006. The results of the histological study indicate that both males and females show stages of gametogenesis and gonad maturation throughout the year and only two major spawning events: one in spring and another in fall. The species behaved as a partial spawner, and only at certain times was total spawning observed in females. Maturation and release or spawning times seem to be closely related to seasonal temperature rises and abrupt changes in surface sea water temperature, which occur at brief intervals for several days at certain times of year.

KEY WORDS: gonadal cycle, gametogenesis, gastropoda, Trochidae, Tegula eiseni

INTRODUCTION

The gastropod mollusc Tegula eiseni (Jordan, 1936) inhabits the rocky subtidal floor from the low tide line to a depth of 18m, obtaining its food from among pebbles and small cavities (Paine 1969, Wilson et al. 1999, Veliz & Vasquez 2000). In the rocky shelves of Baja California, this species stands out within the benthic invertebrate community because it is a major herbivore and carries a high importance value index (Guzman del Proo et al. 1991, Guzman del Proo 1994). It occurs in one of the major fishing areas of the Pacific coast of Baja California, coexisting with species of high economic importance such as abalone (Haliotis fulgens), snail (Megastrea undosa), and spiny lobster (Panulirus interruptus) (Guzman del Proo et al. 1991).

Studies on the biology of T. eiseni ate scarce. Padilla (2004 described the histology of the testicle and ovary of this species. Other studies conducted on other members of the genus describe larval development in T. funebralis (Hewatt 1934, Moran 1997, Guzman del Proo et al. 2006), and Paine (1969 examined changes in the energy content of females of the T. funebralis at different stages of sexual maturation, suggesting that a single annual spawning takes place in Mukkaw and Neah bays in Washington state. In the case of T. rustica, from Vostok Bay, Japan, its reproductive cycle and larval and juvenile development have been described by Kulikova and Omel'yanenko (2000).

Given its high abundance in shoals where abalone, lobster, and other economically important invertebrates are caught in Baja California, T. eiseni has been a part of recent ecological studies focusing on the rocky facies community, research that has sought to identify the animal's role in resource distribution within the benthic community. In the context of these studies, this paper examines gonad development of this species, as part of a wider project on the reproductive biology and ecology of major gastropods in the central Pacific region of Baja California.

MATERIALS AND METHODS

Bahia Asuncion, in Baja California Sur, was selected as the study area (Fig. 1). Samples were obtained monthly over the course of one year (2006) by skin diving in the rocky subtidal zone of Asuncion Island (27°06'00"N latitude. 114°18'00"W longitude) at a depth of 6-12 m. Samples ranged...