Abstract
Plankton are widely considered to be at the mercy of ocean currents, even after decades of research revealing that plankton regulate dispersal by positioning themselves in surface and bottom currents flowing in different directions. The degree of effectiveness of these behaviors remains controversial, because tiny plankters cannot be tracked at sea. Here, we experimentally tested the effectiveness of 3 vertical positioning behaviors in nature by developing a biomimetic robot that emulates them. We conducted a challenging test by deploying them in complex circulation during strong upwelling winds and wind relaxation and reversal events. Behavior alone dramatically affected transport. Transport trajectories of robots with 3 different behaviors diverged markedly while those sharing the same behavior were very similar. Moreover, all 3 behaviors produced trajectories that matched previously modeled projections during both upwelling and relaxation conditions at the study site: shallow plankton disperse far, deep plankton move little, and plankton migrating from depth during the day to the surface at night travel an intermediate distance. The ability of weakly swimming plankton to control their fate and replenish populations in a dynamic ocean is of central importance to the ecology and evolution of marine life and to the management of resources in a changing climate.
Highlights
Dispersal is fundamental to the ecology and evolution of marine life, with implications for spawning migrations, species range extensions due to climate change, the spread of invasive species, management of commercial species as one or more stocks, and the design, siting, and evaluation of networks of marine protected areas (Strathmann et al 2002, Morgan 2014, Burgess et al 2016)
We developed a novel instrumented robot, the Autonomous Behaving Lagrangian Explorer (ABLE; Fig. 1), that mimics verti
When flow reversed during wind relaxations and reversals, deep ABLEs moved little, while near-surface ABLEs moved quickly out of Bodega Bay and northward (Fig. 4D−F), like larvae displaying these behaviors did in a previous study (Morgan et al 2012)
Summary
Dispersal is fundamental to the ecology and evolution of marine life, with implications for spawning migrations, species range extensions due to climate change, the spread of invasive species, management of commercial species as one or more stocks, and the design, siting, and evaluation of networks of marine protected areas (Strathmann et al 2002, Morgan 2014, Burgess et al 2016). Dispersal is challenging to determine in the sea, where most marine animals produce vast numbers of microscopic larvae that develop for weeks in the plankton. DeWolf 1973, McCleave & Wippelhauser 1987) They argued that zooplankton drifting in open water do not have fixed visual or tactile references to judge speed and direction of water flow, and they remain in the same parcel of water over a tidal cycle, lacking changes in cues to stimulate TVMs. responses of zooplankton to isolated variables in static laboratory conditions and complexes of variables in the field do not always match (Cronin & Forward 1986, Young 1986, James et al 2019), and depth regulation may be more challenging for weakly swimming ciliated larvae, such as polychaetes and mollusks, than stronger swimming larvae, such as crabs and fishes (Young 1995)
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