In This Issue

Upside-down jellyfish from the Florida Keys. ### How upside-down jellyfish engineer mangrove ecosystems Winds and tides roil the still waters of shallow coastal ecosystems, aiding nutrient transport, gas exchange, and predator–prey encounters. In contrast, sheltered habitats, such as mangroves, where such physical forces are rare, rely on biotic agents for water mixing. David Durieux et al. report that the upside-down jellyfish Cassiopea sp. plays a major role in water column mixing in mangrove ecosystems. With arms facing upward and bell resting on the benthic substrate, Cassiopea pulses continuously to create a vertical jet several meters tall that can propel hundreds of liters of seawater per hour. Using high-resolution velocimetry in the lab and at field sites on Long Key and Lido Key, Florida, the authors found that the jellyfish, which dwell beneath dense stands of red mangroves ( Rhizophora mangle ) at depths of up to 2 m, continuously pump water upward, each average-sized animal with an 8.6-cm-wide bell pumping at a rate of 212 liters per hour. With an observed median density of 29 jellyfish per square meter, this pumping action turns over the entire water column every 15 minutes—a rate higher than that of other water-pumping animals such as oysters and mussels. Further, each jellyfish speeds the release of nutrient-rich …