Biologic and Ecologic Aspects of Sinelobus stanfordi (Richardson, 1901) (Crustacea, Tanaidacea) in the Martín García Island Natural Reserve, Río de la Plata, Argentina

We investigated the biology and ecology of the tanaidacean Sinelobus stanfordi from the littoral water of Martín García Island at five sites along the coast chosen for their substrate characteristics, and classified the individuals according to size (mm) and ectosomatic characterinalysisstics as: manca III (0.60-1.19), juvenile male and female I (0.90-1.49), juvenile female II and copulatory male I (1.2-1.79), preparatory female I (1.8-2.39), preparatory female II (2.40-2.99), copulatory female I (2.40-2.69), copulatory female II (2.99-4.19), ovigerous female (1.80-3.59), copulatory male II (1.5-1.79), copulatory male III (2.10-2.69) and copulatory male IV (2.40-3.89). The smallest female with rudimentary ovisacs measured 1.84 mm. The tanaid density ranged from 0 to 10,548 ind.m-2. The average female-to-male sex ratio was 3.04:1. An abundance analysis indicated no significant differences among the sampling sites (X2 =4.037, p>0.001), while the fecundity (number of eggs) did not vary significantly with female size (r2 =0.2164, n = 19). The almost permanent presence of all developmental stages during every season of the year suggested a likely continuous year-long reproduction of S. stanfordi. Relationship between the water variables and S. stanfordi populations: The lower than optimal average electrical conductivity (160.24 μS.cm-1) for the species did not seem to limit the population-growth kinetics. The postmarsupial development throughout almost all the stages evidenced a significant positive correlation with pH. The soluble-reactive-phosphorus levels were within the low tolerance values as well as the NO-3 and the NH4 + and both close to optimal along with the near-optimal percent saturation of oxygen.