Zooplankton community and copepod carcasses and non-predatory mortality in six tropical estuarine systems (Northeast of Brazil)

Copepod carcasses and non-predatory mortality can occur due to natural senescence, disease, pollution, and physicochemical stress. Our objective is to evaluate and characterize the rates of non-predatory mortality and the contribution of zooplankton community carcasses, represented by the copepods, in tropical estuarine ecosystems with different degrees of urbanization. During the study, there was a significant difference between environments and copepod carcasses, with Suape Bay (moderately urbanized) being the environment with the highest abundance of adult copepod carcasses (93.3%). The average non-predatory mortality rate of adult copepods was 0.15 day-1: Santa Cruz Channel (sparsely urbanized) contributed the lowest values, with a mortality rate of 0.01 day-1, and Suape (moderately urbanized) had the highest rate (2.80 day-1). The families Paracalanidae (0.554 day-1) and Oithonidae (0.122 day-1) had the highest values, with an average carcass decomposition of 4.7 days. Among the environments studied, there was little differentiation between carcass percentages and mortality rate, not supporting the hypothesis that the higher rates of mortality among non-predatory copepods were related to large urban centers. However, there was an almost proportional contribution of carcasses and non-predatory mortality in all but a few areas, agreeing with the hypothesis that there is spatial variation with respect to carcasses in tropical estuaries. With our work, we show that estuaries can provide the estuarine food web with a significant portion of copepod carcasses, which may vary by family, and that it is not necessarily environments with a higher degree of urbanization that will have higher mortality rates.