Dinâmica populacional da ostra nativa Crassostrea rhizophorae (Guilding 1828), e da ostra invasora Saccostrea cuccullata (Born 1778), em costões rochosos da Baía de Guanabara

Abstract

Marine ecosystems, such as rocky shores, are subject to several impacts caused by human activity, such as the introduction of species. Oysters are bivalve molluscs with wide geographic distribution, of great economic value and that play important roles in the ecosystem, being able to change the habitat in a positive or negative way. Thus, changes in population parameters such as growth, mortality and recruitment require long-term studies to be understood. This work is part of the Long-Term Ecological Project, carried out in Guanabara Bay, and its main objective was to compare the population dynamics of the native oyster Crassostrea rhizophorae with that of the invasive oyster Saccostrea cucullata on rocky shores of Boa Viagem Beach, Niterói, Rio de Janeiro. To assess the density of the two species, the percentage of mortality and recruitment, seasonal photographic samplings were carried out from July 2011 to March 2020 over the middle range of the intertidal zone, where five random squares were selected. These photos were analyzed in the laboratory, where individuals were identified and counted. The growth of species was assessed through biweekly photographic sampling carried out between August 2015 and June 2017 in random squares where all individuals were identified and measured and in July 2016 where 3 permanent squares were scraped and 30 random individuals were followed for one year. The measures taken were height and length. Growth curves were estimated for both species based on the von Bertalanffy model and longevity using its inverse formula. A model selection analysis was performed in order to verify the relationship between abundances and mortality and recruitment percentages with environmental factors. The abundance of the invasive oyster increased in relation to the abundance of the native oyster, mainly in the last two years of the sampling period. Through hierarchical analysis of variance, significant inter-annual differences were observed for all parameters and intra-annual differences for C. rhizophorae density and percentage of recruitment. The percentage of mortality showed an alternation in relation to the amount of Ostreidae alive and the percentage of recruitment exceeded 50% during the last two years of sampling. The main abiotic variables that influenced the population parameters were water and air temperature. The observed niche overlap occurred by chance and without competition, resulting from the influence of environmental variables on the species. The final growth curves and longevity (years) for height and length in the C. rhizophorae and S. cucullata modal progression method were respectively: L = 65.91 (1-e-0.003t) and 4.57; L = 61.17 (1-e-0.002t) and 6.83; L = 71.25 (1-e-0.002t) and 5.68; L = 63.30 (1-e-0.003t) and 4.99. And for the individual growth method they were respectively: L = 65.91 (1-e-0.003t) and 4.51; L = 61.17 (1-e-0.003t) and 3.71; L = 66.25 (1-e-0.002t) and 5.49; L = 63.30 (1-e-0.002t) and 6.31. The growth parameters (k, t0 and longevity) were compared between measurements, between methodologies and between species and showed significant differences in some cases. Therefore, the information generated by the present study is important to better understand the population dynamics and the interaction of these species. Only with continuous and long-term monitoring can changes in the interactions of these species be understood, which are extremely important for the management of bioinvasion.