Molting behavior and growth in the giant barnacle austromegabalanus psittacus (molina, 1782)

Abstract

The effect of temperature and photoperiod on molt production in juvenile specimens of the acorn barnacle Austromegabalanus psittacus (Molina, 1782) was evaluated under controlled conditions. Growth was determined both under controlled and natural conditions. The molt frequency, intermolt period and instantaneous growth rates of the carino rostral lengths were measured in specimens subject to two temperature conditions (10 degrees C and 16 degrees C) and photoperiods (8 hours light: 16 hours darkness and 16 hours light: 8 hours darkness). Growth of specimens in natural conditions was evaluated in substrates suspended from floating rafts in Metri Bay (41 degrees 36'S; 72 degrees 43'W) at two depths: between 1 and 2 m and between 4 and 6 m, during the autumn-winter and spring-summer seasons. Molt frequency was greater at 16 degrees C than at 10 degrees C, with no evidence of variations due to photoperiod. The intermolt periods were greater at 10 degrees C than at 16 degrees C and during the photoperiods 8:16 than at 16:8. Instantaneous growth rates, on the other hand, were greater at 10 degrees C than at 16 degrees C and under photoperiod conditions of 8:16 than at 16:8. No relation was observed between instantaneous growth rate and molt frequency. Under natural conditions, a larger increase in length was observed in individuals growing at greater depths. The results obtained in a controlled environment and in the natural environment were consistent, given that the higher growth reported in suspended systems at greater depths, was associated with lower luminosity conditions and lower temperatures; a similar situation was observed under controlled conditions.