Distribuição espaço-temporal e estresse termo-salino na anêmona-do-mar Anthopleura krebsi (Cnidaria: Actiniidae)

Abstract

Anemones are one of the least addressed biological groups in the intertidal zone. They have physiological and behavioral characteristics that allow them to survive under the varied pressures that exist in these ecosystems. My objective, therefore, was to characterize the population variation and the micro-habitat of occurrence of Anthopleura krebsi describing the distribution and population density of the species within two tropical environments in this zone. In one of these environments (artificial habitat), I evaluated the temporal space variation of population density by correlating the data obtained and the environmental variables measured for the same period. Monthly samplings were carried out between April 2018 and March 2019, being performed at 15 points, divided into five gabions, comprising three strata in the mesolitoral. The second area is a sandstone reef, where sampling followed the same period as the first in order to assess the species' occurrence points. Experiments were also carried out, 1) thermo tolerant limit with gradual increase in water temperature simulating tidal cycles; 2) preference of substrate in two different conditions of covering the bottom of the aquariums and 3) salt stress for two different values of salinity (30 and 40), in order to verify survival after ten days of exposure to treatment. In the artificial system, the spatial variation was well marked. The lower stratum presented the highest densities, with a monthly average ranging between 260 and 720 ind / m². In the upper two strata, the averages decreased. ANOVA indicated a difference (p <0.05) between the strata. The TUKEY post-test indicated similarity between densities in the shallower strata; both significantly smaller than the deepest strata. The population varied over time with a marked increase between October 2018 and February 2019. It was observed through a multiple regression that rainfall and air temperature, at first, did not exert temporal influence on the population in gabions. On sandstone reefs the species was found in a single location, rocks present in the mesolittoral, in groups never larger than 15 individuals, having been completely absent in a few months. The experiments demonstrated that there is a decrease in the survival of the species after 31ºC, with lethality for all individuals at 41ºC. The species did not show preference for substrate, and 100% of the individuals survived the exposure for 10 days to the tested salt concentrations. These results at first indicate that the environmental conditions are not the most determinant for the variation, however, there is a thermal limit that appears to be more important for the population than the type of substrate. The low amplitude of climatic variation in the tropical zone probably does not cause temporal changes in the population, leaving the causes of this variation open.