Figure 1.
The Drifting In Situ Chamber (DISC).
A) schematic view of the Lagrangian observational system. The hardware includes a main underwater unit [red rectangle] composed of a cylindrical frame (H 1.2 m× ∅ 0.63 m) made of clear acrylic bars (a) holding a behavioral mesh chamber (∅ 0.38 m, mesh-size ∼1 mm) (b), a pressure enclosure (c) housing an electronic compass and the imaging system composed of a camera with high capacity memory card, a time lapse, and a large battery, allowing for up to 8 hours of continuous recording at 1 HD frame per second. Other instruments include an analog compass (d) and a mini-CTD (e) that senses the ambient conductivity, temperature, and depth. The underwater unit is locked into the current by a drogue (f) and connected to a surface float (g) and Global Positioning System (GPS) (h) by a 3 mm-diameter nylon line attached with three stainless steel bridles (i) to the top ring of the underwater unit; the length of the line is adjusted the target deployment depth. B) In situ view of the DISC deployed off One Tree Island (OTI), Great Barrier Reef. The immersed underwater unit is symmetrical and becomes transparent, minimizing visual disturbances to the tested larva. Graphic courtesy of Bellamare LCC [drogue and surface float not to scale]; photo credit M. Kingsford.
Figure 2.
Sampling Site and DISC deployments.
A) One Tree Island (24°30′ S, 152° E, teal square) belongs to the Capricorn Bunker Reef at the southern end of the Great Barrier Reef at the edge of the Coral Sea; B) double odor-plumes (gray shade) observed during Northwest-North winds and ebb flow; B) twenty-minute trajectories of the DISC deployed north and south of One Tree island (OTI) in ocean (dark blue) and plume water (green). The ebb flow (green trajectories) is mainly towards the north-northeast on the northern side of OTI and towards the east on the southern side. A total of 83 DISC trajectories are shown for February 8–22, 2009.
Table 1.
Summary of the data collection and analysis.
Figure 3.
Histograms of in situ swimming speed frequencies computed for individual larvae of the Apogonidae (left panel) and Pomacentridae (right panel) families are compared between ocean (blue) and plume (green) water masses. The data are normally distributed and the mean indicated by the vertical solid lines were significantly different for both families (t-test, Table 1); the distributions of speeds in ocean and plume water were significantly different (Kolmogorov-Smirnov, p<10-4) for the Pomacentridae.
Figure 4.
Orientation for Apogonidae (left panels) and Pomacentridae (right panels) larvae compared between ocean (blue) and plume (green). Larval mean individual bearings were computed relative to (A) a cardinal frame of reference (B) the reef crest coastline (C) the direction of the current and (D) the direction of the wind. Apogonid orientation was never significant when tested in a cardinal reference or relative to the reef crest. Pomacentrids were significantly oriented only in plume water, cardinally towards the West (p = 0.008) and alongshore when viewed relative to the reef crest (p<0.005). Each dot on the graphs represents an average individual bearing. Orientation at the population level is significant when all the larvae tested have statistically similar bearings; this is shown with an arrow pointed in the mean orientation direction of individual-level bearings, the length is proportional to the r-value.
Figure 5.
Relationship between temperature and larval swimming speed. Points are temperature averages per deployment. Solid lines are least square regression lines simple linear regression. Grey areas are 95% confidence intervals. The fact that the zero slope dashed lines stay within the confidence intervals shows visually that the regressions are not significant (p = 0.97 for Apogonidae, p = 0.22 for Pomacentridae).