Life history characteristics of Alticus monochrus, a supratidal blenny of the southern Indian Ocean

Abstract

The blenny Alticus monochrus Bleeker inhabits exposed rocky shores of Mauritius and other islands of the southwestern Indian Ocean. A. monochrus is an amphibious species and remains almost exclusively above the water line, migrating vertically with the tide while feeding on a thin algal layer scraped from the moist substratum. Spawning activity peaks were observed at Pointe aux Caves, Mauritius, during the full moon periods of October and November and two corresponding oocyte size cohorts were identified in excised ovaries collected over the breeding season. Larvae hatched in approximately four days and otolith ring counts showed that settlement occurred 28 days later. Initial post-settlement growth was rapid but growth rate in length declined linearly beyond 50 mm. Length frequency time series showed that the 1991 cohort reproduced at age one, but that none of this cohort survived into the 1993 breeding season, consistent with annual semelparity. By contrast, other expected correlates of semelparity were not observed: fecundity in A. monochrus was lower than in some iteroparous blennies, and there was no obvious physical deterioration of adults following the breeding season, despite their high mortality rate.