Animal propulsors such as wings and fins bend during motion and these bending patterns are believed to contribute to the high efficiency of animal movements compared with those of man-made designs. However, efforts to implement flexible designs have been met with contradictory performance results. Consequently, there is no clear understanding of the role played by propulsor flexibility or, more fundamentally, how flexible propulsors should be designed for optimal performance. Here we demonstrate that during steady-state motion by a wide range of animals, from fruit flies to humpback whales, operating in either air or water, natural propulsors bend in similar ways within a highly predictable range of characteristic motions. By providing empirical design criteria derived from natural propulsors that have convergently arrived at a limited design space, these results provide a new framework from which to understand and design flexible propulsors.

Jellyfish have provided insight into important components of animal propulsion, such as suction thrust, passive energy recapture, vortex wall effects, and the rotational mechanics of turning. These traits are critically important to jellyfish because they must propel themselves despite severe limitations on force production imposed by rudimentary cnidarian muscular structures. Consequently, jellyfish swimming can occur only by careful orchestration of fluid interactions. Yet these mechanics may be more broadly instructive because they also characterize processes shared with other animal swimmers, whose structural and neurological complexity can obscure these interactions. In comparison with other animal models, the structural simplicity, comparative energetic efficiency, and ease of use in laboratory experimentation allow jellyfish to serve as favorable test subjects for exploration of the hydrodynamic bases of animal propulsion. These same attributes also make jellyfish valuable models for insight into biomimetic or bioinspired engineeringof swimming vehicles. Here, we review advances in understanding of propulsive mechanics derived from jellyfish models as a pathway toward the application of animal mechanics to vehicle designs.

The lobate ctenophore Mnemiopsis leidyi occurs throughout Narragansett Bay, Rhode Island, during warm summer months but is often undetectable in the central portion of the bay during winter months. During 2 yr of weekly sampling, we found that M. leidyi populations in a shallow embayment, Greenwich Cove, either overwintered or were only briefly absent during winter. The Greenwich Cove population reproduced weeks earlier and reached higher average and peak population concentrations than open‐bay populations. Shallow embayment populations such as that in Greenwich Cove probably serve as source populations that inoculate the main region of the bay by advective transport in the spring months. We propose that earlier occurrences of M. leidyi during recent years are due to amplification of pulsed spring warming events that permit early reproduction in the shallow embayments that serve as source regions for M. leidyi in Narragansett Bay. We further suggest that the source‐sink perspective we describe is relevant not only to Narragansett Bay but other temperate regions of the world persistently occupied by M. leidyi.

Species-specific differential responses to climate warming that alter phenologies can dramatically affect community function. Using time series data from a Northwest Atlantic estuary, we show that the phenology of a top zooplankton predator, the ctenophore Mnemiopsis leidyi, has shifted more in response to climate warming over the past ∼50 years than that of its major prey species, the copepod Acartia tonsa. Before climatic warming, A. tonsa was the dominant secondary producer in the estuary and its main period of production occurred before the seasonal appearance of M. leidyi. However, since 2000, the seasonal peak abundances of the two species have overlapped, intensifying the predator–prey relationship and resulting in the near extirpation of the once-abundant copepod from the estuary. We propose that the physical mechanism driving the different phenological responses of the two species is differential spring warming of the winter refugia of these two species. Substantial amplification of warming patterns in shallow embayments affects overwintering M. leidyi but has little influence over seasonal excystment of overwintering A. tonsa eggs located in the broader, deeper regions of the Bay. In this way, large-scale climatic changes are expressed as local-scale temperature variations that differentially affect alternate planktonic life histories to produce novel spring population growth dynamics of the two species and, ultimately, a new summer planktonic community dynamic in Narragansett Bay.