Fig 1.
Sampling sites of Lady Elliot Island.
Map of Lady Elliot Island (24°07’S, 152°43’E) in the southern Great Barrier Reef, Australia. Plus signs indicate the three in-situ sampling sites of Lighthouse Bommie, Sunset Drift and Encounters. High-resolution image obtained from the Quickbird satellite (Geoimage Pty Ltd., www.geoimage.com.au) and processed using ArcGIS 10.
Fig 2.
ZooScan system analysis and output.
Using ZooScan to measure the size and composition of zooplankton at Lady Elliot Island: a) Scanned image of a zooplankton subsample, and b) examples of digitally-separated vignettes.
Fig 3.
Zooplankton biomass and manta ray foraging behaviour.
Zooplankton density in relation to reef manta ray behaviour at Lady Elliot Island: a) mean zooplankton biomass (mg m-3, ±standard error; feeding n = 17, non-feeding n = 12, absent n = 61); and b) mean zooplankton abundance (m-3 ±standard error; feeding n = 17, non-feeding n = 12, absent n = 21).
Fig 4.
Zooplankton composition and manta ray foraging behaviour.
Zooplankton composition at Lady Elliot Island in relation to reef manta ray behaviour showing little differences in composition: a) Feeding (n = 17), b) Non-feeding (n = 12), and c) Absent (n = 21). Nonmetric multidimensional scaling analysis of the community: d) with no transformation, and e) after a presence-absence transformation (n = 50).
Fig 5.
Zooplankton size spectra analysis.
Normalised Biovolume Size Spectra of the zooplankton community showing higher biovolume across all size classes (body volume intervals) when reef manta rays are feeding (n = 17) than when non-feeding (n = 12) or absent (n = 21). Dashed lines represent 95% confidence intervals.
Fig 6.
Critical prey density foraging threshold.
Logistic regression of reef manta ray behaviour (feeding n = 17, non-feeding n = 12) in relation to zooplankton biomass (mg m-3). The black dashed line represents the critical density threshold of zooplankton biomass required to trigger reef manta ray feeding from in-situ sampling (11.2 mg m-3) and the red dashed line represents the theoretical calculation of the density threshold (25.24 mg m-3).
Fig 7.
Oceanographic drivers of zooplankton biomass and manta ray feeding.
Final generalized additive models for: a) Zooplankton biomass as the response and Trip, Time to low tide and Temperature as predictors (r2 = 42.8%, n = 70), and b) Manta ray behaviour (0 = non-feeding; 1 = feeding) as the response and Month, Time to low tide and Temperature as predictors (r2 = 5.3%, n = 2973). For each plot, the y-axis is a relative scale, and its magnitude reflects the importance of each variable. Dashed lines and error bars represent 95% confidence intervals.