Growth characteristics and population dynamics of Macrophthalmus japonicus with decreasing microphytobenthos biomass in muddy estuarine tidal flat

Abstract

The present study evaluated the population dynamics, growth, and biomass production of the ocypodid crab Macrophthalmus japonicus in muddy estuarine tidal flat through monthly surveys over a 10-year period. The mean annual biomass was 4.71–11.51 (7.9±2.5) g dry·m−2, and secondary production was 2.1–19.3 g dry·m−2·year−1 (11.3±5.3 g dry·m−2·year−1) and 1.59–6.16 (3.71±1.55) g C·m−2·year−1. Two to three cohorts of M. japonicus were observed in each year, with the population density of 10–61 individuals·m−2. New recruitment was noted around August in the summer of each year, with an estimated lifespan of 2–3 years. The production/biomass ratio was 0.46–2.02 (1.38±0.44). The population density of M. japonicus showed stable seasonal variations, while annual growth, production, and biomass decreased over the years. M. japonicus growth was associated with microphytobenthos biomass. In particular, long-term field investigations revealed the association between M. japonicus and microphytobenthos, suggesting that the feeding pressure of M. japonicus affected microphytobenthos biomass. Our findings will contribute to the better understanding of the growth characteristics and population dynamics of M. japonicus as well as the interactions between prey and predators in benthic tidal flat ecosystems, providing fundamental information for estimating material cycles.