Emerging from the 12th International Seagrass Biology Workshop, held in October 2016, has been the view that grazing marine megafauna may play a useful role in helping to identify previously unknown seagrass habitats.¬†Just follow green turtles & dugongs to map global seagrass meadows…

Today our new paper came out in Frontiers of Marine Science. Here we describe this concept, showing how detailed information on the distribution of both dugongs (Dugong dugon) and green sea turtles (Chelonia mydas) obtained, for example, by aerial surveys and satellite tracking, can reveal new information on the location of seagrass meadows. Seagrasses are hugely valuable to human life, but the global extent of seagrass meadows remains unclear. As evidence of their value, a United Nations program exists (http://data.unep-wcmc.org/datasets/7) to try and assess their distribution and there has been a call from 122 scientists across 28 countries for more work to manage, protect and monitor seagrass meadows (http://www.bbc.com/news/science-environment-37606827). We show examples of how marine megaherbivores have been effective habitat indicators, revealing major, new, deep-water seagrass meadows and offering the potential for more informed estimates of seagrass extent in tropical and sub-tropical regions where current information is often lacking.

Figure 1. The use of green turtles and dugongs as habitat indicators. (A) A green turtle (Chelonia mydas) (B) A dugong (Dugong dugon). Both species feed on seagrasses and so the location of their foraging sites may indicate seagrass habitat. (C) Green turtles can be satellite tracked from their nesting beaches to their, sometimes, very discrete foraging grounds. Here the tracks of 8 green turtles that had nested on Diego Garcia, in the Chagos Archipelago, are shown. Red stars show the end point of each track, i.e., the location of each turtle’s foraging grounds. (D) Modern satellite tracking can provide very high accuracy locations (e.g., Fastloc-GPS) (black dots) allowing space use on foraging grounds to be accurately assessed. In this case the foraging home-range is shown for one of the turtles tracked in (C). Red, orange, blue colors show the 50, 90, and 95% kernel home-range estimates. On-site validation of the foraging habitats used by (E) dugongs and (F) green turtles in the Indo-Pacific has confirmed the hitherto unknown location of extensive seagrass beds. (E) An aerial photo of 50+ foraging dugongs. Black arrows indicate three of the dugongs. (F) An aerial photo (from a drone survey) of 20+ foraging green turtles. Black arrows indicate three of the green turtles. Note the grazed area (white) around each green turtle. Photo in (A) courtesy of RD and BS Kirkby in (B) courtesy of EH Meesters, (C,D) from Hays et al. (2014), (E) courtesy of Susan Sobtzick and (F) courtesy of MC.

Hays GC, Christianen MJA, Alcoverro T, Duarte CM, Hamann M, Macreadie PI, Marsh HD, Rasheed MA, Thums M, Unsworth RKF, York PH, Esteban N (2018) New tools to identify the location of seagrass meadows: marine grazers as habitat indicators. Frontiers in Marine Science. doi: 10.3389/fmars.2018.00009

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