SVG - Mayreau Gardens (CO2 vent site)

Setting

F1, the frame Anderson labels 'CO2 seep', shows the seep itself: two distinct strings of gas bubbles rising off a dark, undercut rocky outcrop, one from the shaded left flank and one from the middle of the mound, with small fish holding station in the plume. Visibility is poor and the water is green.

General benthic features

The pavement around it is a striking mosaic of magenta and rose coralline-crusted rubble and plates with yellow-brown turf between - crustose coralline algae and turf, not stony coral, hold this ground. The remaining frames (F3-F10) are the working plot. Low, silt-dusted carbonate pavement and cobble runs out flat, carpeted in dark brown and olive algal turf with clean white sand pockets in the hollows, and it is studded with survey markers: numerous magenta and red flagging tags, blue and yellow tags and white pins staked across the bottom, so densely in F4, F6, F7 and F8 that the plot layout itself is the subject. Small brown mounding and encrusting coral heads sit among the markers - discrete domes 10-30 cm across in F3, F6, F7 and F8, some crusted and partly overgrown - along with small sponges and encrusting growth on the harder blocks. This is a sparse, low-relief, turf-, and rubble-dominated bottom, not a coral framework. F5 shows a diver working head-down over the tagged plot, which gives the scale: the markers cover a patch of a few meters across. F2 is the equipment frame - a coiled yellow hose or line and dark gear resting on a heavily turf-covered pavement in very murky water. F9, his 'pseudo-mosaic', is the same plot shot near-vertically for photomosaic purposes, and F10 is a general 'vent site' overview of tagged pavement and rubble.

Coral cover

• Reference: Claude CV point count (this site's photos)
• Coral cover: 23% — a blind Claude computer-vision point count of 66 of Anderson's edited photographs (20 points per photo; water, fish, and obstructions excluded). The photos come from seven dives, including the old vent; the median is 18%. The mean is above the median because portraits of the sampled colonies sit beside wide reef and gear shots. Enochs et al. (2020, Coral Reefs 39:523-528; https://doi.org/10.1007/s00338-020-01927-5) report high hard and soft coral cover around the vents despite localized CO2 enrichment, but give no cover figure.

Stressors

No corallivores evident.

Comparisons with other data

No other surveys have been conducted at this site to date. Within 5 km, twenty independent stations recorded 1.2–44% hard coral cover between 1999 and 2019; the nearest, XL Catlin Seaview Survey at transect 22017, 0.16 km away, read 8.5% in 2013.

Other notes

Frame-level account of 10 frames documenting the seep and the marked study plot rather than the wider reef. Colonies here are tagged and the plot is marked out with numbered flagging, as expected for a vent-to-control gradient study; no tag or sample codes are reported, as they are not meaningful.