Population Dynamics, Life History, and Production of Cyathura Carinata (Krøyer) (Isopoda: Anthuridae) in the Mondego Estuary, Portugal

Abstract

Previous studies of the benthic community in the Mondego estuary revealed that Cyathura carinata has spatially and temporally stable populations, has significant biomass throughout the year, and is one of the most abundant species in the estuary. The present work was carried out to study its population dynamics and life cycle in relation to physicochemical factors, and to estimate its productivity within intertidal mud flats. Cyathura carinata was sampled every two weeks from November 1990 to December 1991. It exhibited a contagious spatial distribution within the eulittoral zone, and its abundance changed seasonally, decreasing gradually from midfall to late spring, and increasing again from early summer to the following fall. Abundance appeared to be inversely related to emersion periods, and positively correlated with salinity and nitrate concentrations, while higher temperature and sediment organic enrichment appeared to have a negative effect on the abundance of organisms. Nevertheless, the correlations between abundance and environmental factors could not be considered as defining cause-andeffect, since environmental factors were also intercorrelated. Protogynous hermaphroditism was hypothesized, with males being present from March to September. Sexual activity began in early spring and recruitment took place through the summer. Two cohorts were produced, one in June and a second in August. Fecundity was significantly correlated with female size. In addition, higher salinities and pH favored higher fecundity. Although seasonal variations in growth rates were observed, growth was continuous through the life of the animal. Growth rates practically ceased during the winter, increased gradually from late winter to a maximum between early summer and midfall, and decreased again until the following winter. Life span was roughly estimated at 18-22 months. Sexual differentiation was estimated to occur within a period of 49-54 days from birth, for females, and 146-208 days for males. Sexual maturation in females was estimated to occur in 240-357 days (8-12 months). Cyathura carinata is a semiannual species in the Mondego estuary, with iteroparous females and an univoltine life cycle. Growth production (P) and elimination production (E) were estimated as, respectively, 5.6-9.9 and 11.8-22.3 g·m^―2· year^―1 ash-free dry weight. P/B and E/B ratios were estimated, respectively, as 1.65-2.03 and 3.74-4.37. Despite several differences with regard to the reproductive period, all populations of C. carinata studied along the European coasts show univoltine life cycles. Due to stable populations and life cycle characteristics, this species appears ideal for comparative ecophysiological and ecotoxicological studies in European estuaries.