Ocean currents and marine life Graeme C. Hays  Current Biology  Volume 27, Issue 11, Pages R470-R473 (June 2017) DOI: 10.1016/j.cub.2017.01.044 Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 1 Complexity and variability in ocean currents (A) Major ocean currents are well described, such as those associated with the North Atlantic gyre which flows clockwise around the North Atlantic basin. For example, the Gulf Stream and North Atlantic Current form the western and northern boundaries of this gyre. Textbook descriptions of these currents, such as the one illustrated, often fail to show the true complexity of the flow pattern. Adapted with permission from Carr, A. (1987) New perspectives on the pelagic stage of sea turtle development. Conserv. Biol. 1, 103−121. (B) Individually tracked Lagrangian drifters show that these currents have complex flow patterns. These patterns are often difficult to fully resolve. For example, an animal or plant drifting east off Florida might simply circulate within the Sargasso Sea (indicated in red) or alternatively might be carried across to northern Europe in the Gulf Stream and North Atlantic Current. Figure modified from Fossette, S., Putman, N.F., Lohmann, K.J., Marsh, R., and Hays, G.C. (2012). A biologist’s guide to assessing ocean currents: a review. Mar. Ecol. Prog. Ser. 457, 285–301, created by S. Fossette. Current Biology 2017 27, R470-R473DOI: (10.1016/j.cub.2017.01.044) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 2 Impact of ocean currents on swimming animals. Animals ranging from vertebrates, such as turtles, to invertebrates, such as jellyfish, can be equipped with satellite tags and tracked in relation to the local currents. However, some animals are too small to track. (A) A small loggerhead sea turtle equipped with a satellite tag (Photo: Jim Abernethy, NMFS permit #1551). These young turtles are pelagic, living in the open ocean where they show directional swimming to avoid being carried to unfavorable areas. Adults often migrate thousands of kilometers across the open ocean between coastal breeding and foraging sites. While they have the swimming ability to overcome currents, tracking data suggest they do not follow the optimum routes to make the best use of current flows. (B) A barrel jellyfish (Rhizostoma sp.) being equipped with a tracking tag (Photo: Gower Coast Adventures). These jellyfish are surprisingly powerful swimmers and can adjust their swimming direction in relation to tidal flows to help avoid being carried away from coastal zones. (C) A copepod, only a few mm long, that is too small to track directly so its drift patterns are estimated by ocean currents (Photo: Russ Hopcroft). (D) If an animal can be tracked, as well at its speed through the water and heading recorded, then the ocean current flow can be assessed by vector addition. Current Biology 2017 27, R470-R473DOI: (10.1016/j.cub.2017.01.044) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 3 Ocean heterogeneity and animal movement patterns. Assessing how ocean heterogeneity influences animal movements is a hot topic with work on many species of marine birds (e.g. penguins and albatrosses), marine mammals (e.g. seals and whales), fish (e.g. tuna and sharks) and turtles. (A) A leatherback turtle ashore nesting (Photo: Tom Doyle). (B) The track of a leatherback turtle travelling southwards from Ireland and targeting an ocean mesoscale eddy evident in satellite imagery of sea surface height. The turtle remained in the clockwise circulating eddy for many weeks, presumably feeding upon abundant prey. Direction of turtle travel indicated by the black arrows. Modified with permission from Doyle, T.K., Houghton, J.D.R., O’Súilleabháin, P.F., Hobson, V.J., Marnell, F., Davenport, J. and Hays, G.C. (2008). Leatherback turtles satellite tagged in European waters. Endangered Species Res. 4, 23–31. Current Biology 2017 27, R470-R473DOI: (10.1016/j.cub.2017.01.044) Copyright © 2017 Elsevier Ltd Terms and Conditions