Blackfordia virginica

The medusae predation impact on the zooplankton community was estimated for copepods, the most abundant zooplankter and also the main metazooplanktonic prey for B. virginica medusae observed during a previous work in the same estuary (Marques et al., 2015). The copepod mortality rate due to medusae predation and the half-life of copepods are presented in Table 2. The analyses undertaken by estuarine site highlighted the patchiness of medusae and zooplankton distributions, therefore prey mortality estimations were higher in regions of higher medusae density and/or lower copepod abundances. Due to higher medusae density during the summer of 2013, the estimated copepod mortality by medusae predation was higher than in the autumn of 2012, with a median predation impact of 0.113 d−1 (excluding site 5, the zooplankton density estimation in this site was likely underestimated due to sampling constraints) and 0.059 d−1, respectively. In agreement with the mortality rates, the estimated median half-life of copepods would be lower in the summer of 2013 than in the autumn of 2012, thus the reduction of 50% of the copepod population caused by medusae predation would occur in 6.1 days, considering the values in the summer of 2013, and in 17.8 days in the autumn of 2012.

Medusae were pelagic feeders, consuming both invertebrates and fish larvae. Copepod nauplii were by far most numerous prey in the guts, followed by cyclopoid copepods and mysids. Further studies of B. virginica are needed to understand its potential impacts on estuarine ecosystems, which may be great where it is abundant.