Biology, population dynamics and secondary production of Tylos europaeus (Isopoda, Tylidae) on the western coast of Portugal

Abstract

The biology, population dynamics, and pro- duction of Tylos europaeus were studied in two sandy beaches of the western coast of Portugal. At both sites, reproduction occurred seasonally, from April to July, with only one new cohort produced per year. Regarding population dynamics, cohort-splitting events were de- tected in males at the beginning of the reproduction period (April/May), resulting in two groups with distinct growth rates (fast-growing vs slow-growing males). Different biological characteristics were consequently detected in these two groups, namely regarding body size, lifespan, and contribution to the reproductive ef- fort. Lifespan was estimated as approximately 3 years, for females and fast-growing males, and 4 years for slow-growing males. Cohort-splitting among males ap- peared as a possible strategy to cope with the highly male-biased sex ratios observed, which could lead to a strong male-male competition for mating. T. europaeus appeared as an annual species, with a univoltine life- cycle (one generation per year), and iteroparous females reproducing twice during their lifespan. Average growth production (P) was estimated at 0.082 g.m � 2 .yr � 1 AFDW (ash-free dry weight) and the average annual biomass (�) (standing stock) at 0.052 g.m � 2 , resulting in a P/� B ratio of 1.58. These results produced baseline information for the construction of a population- dynamics model and highlighted the potential of this species as an environmental quality-assessment bioindi- cator on sandy shores.