This study explores the achievement of gametes maturity and biometric analysis of Phragmatopoma caudata Krøyer in Mörch, 1863 to endorse a methodology and provide a proper technique for studies aiming to assess the population ecology. Analysis via Pearson's test confirmed a significant evidence of positive correlation (r = 0.90, P <0.0001) between body length and length of the opercular crown. Individuals with opercular crown < 0.9 mm can be regarded as juvenile due to the absence of gametes. Therefore, through the endorsed method to separate the size classes aimed to analyze the population density and seasonal pattern of the juvenile class. The reef population of P. caudata in the Xixová-Japuí State Park (PEJX) at the Santos Bay, state of São Paulo, was examined for two years. In the highest rate of juveniles, population density reached 128,115 ind./m², however, the average was 65,090 ind./m². Statistical analyzes (Kruskal-Wallis H = 1.475, p < 0.01) showed that significant temporal variation occurs in the juvenile composition between rainy and dry seasons. Despite the presence of representatives in the population during the dry months, rainy seasons encompassed 92.1% of juveniles sampled. The observed pattern of juveniles may be associated to biological factors (e.g. gametogenesis and life cycle) and abiotic (e.g. food supply and ocean currents). These results highlight the need for long-term monitoring programs that integrate ecological and abiotic elements to obtain a more complete understanding of the ecology of these worms and providing feedback for a better conservation of the marine biodiversity in the PEJX.
Morphometric analysis; population dynamics; rocky shore; benthic invertebrates
