Dynamics of a natural population of a hyallelid amphipod from Brazil

Abstract

Hyalella longistila is a freshwater amphipod found in streams in southeastern Brazil. We examined temporal variations in the population dynamics of this species by analyzing its abundance, size frequency distribution, proportion of mating pairs and brooding females, sex ratio and recruitment, as well as the possible influence of environmental variables on such parameters. Samples were made in a stream in the state of Minas Gerais from March 2012 to February 2013. The size frequency distribution was polymodal for most of the months, with more than one maximum for both juveniles and adults. The maximum size attained by females (brooding and non-brooding) was higher than in males and the mean size of males (paired and unpaired) was higher when comparing with paired and unpaired females, respectively. Hyalella longistila seems to reproduce continuously but more intensively twice a year, in the middle of winter and end of spring. Recruitment occurred during several months (April, May, October, November, and December 2012), which could have affected the observed polymodal distribution. It is likely that this continuous breeding activity was possible due to the abundant macrophyte stand where the population inhabits, which could have provided constant shelter and feeding for individuals, but this aspect still needs to be investigated further. Moreover, a positive effect of dissolved oxygen on the frequency of brooding females, as well as of temperature on the abundance were recorded. Our results can help future researches in the conservation of aquatic ecosystems as a whole, more specifically for the preservation of Hyalella longistila and its use as a test organism.