Turtle Beach

Setting

• Turtle Beach is a shallow snorkel transect on the fringing reef off Necker Island in the British Virgin Islands, covered here in 63 usable reef frames out of 70 total (seven early- and mid-transect frames are topside surface, sunset, or beach shots and are excluded from this description).
• The substrate throughout is a low-relief limestone hardground and coral-rubble pavement, alternating between patches of standing dead branching-coral skeleton, pink crustose-coralline rock, sand channels, and denser live patch-reef structure.
• Water clarity varies substantially along the route, from clear blue water in places (e.g., Image 47, Image 55, Image 56) to markedly turbid, greenish conditions through a mid-transect sand-and-rubble stretch (e.g., Image 35, Image 37, Image 38, Image 39, Image 40, Image 41, Image 42).
  47555635373839404142

Benthos

• Where live coral occurs, it is dominated by small mounding colonies of Porites astreoides-type coral and scattered brain-type heads (cf. Pseudodiploria/Diploria-complex) (e.g., Image 2, Image 9, Image 34, Image 44, Image 46), with occasional small finger or branching colonies (cf. Porites porites, or small-polyp branching recruits resembling juvenile Acropora cervicornis) clustered on dead rock (e.g., Image 3, Image 10, Image 49, Image 50, Image 51, Image 52).
  2934444631049505152
• Two substantial live elkhorn coral (Acropora palmata) colonies appear mid-transect, both showing extensive golden-tan branching tissue with white growing tips and no obvious partial mortality (e.g., Image 55, Image 56), in contrast to the standing-dead elkhorn skeletons that dominate elsewhere on the transect.
• A probable fire coral (cf. Millepora complanata) blade colony appears early in the transect (e.g., Image 8), and gorgonians -- sea rods and sea fans -- are consistently present and in several frames form the dominant living cover on otherwise bare hardground (e.g., Image 15, Image 25, Image 61, Image 62, Image 63).
  81525616263
• A larger mounding coral head, its bioeroded pink-white crust ringed by sea rods, rises off the bottom early in the transect (e.g., Image 17), and elsewhere a live plating or lobed colony (cf. Orbicella-complex) sits low on the reef rock with pale growing margins around otherwise even tan tissue -- a normal growth-edge appearance, with no sign of disease or recent mortality (e.g., Image 53).
  1753
• Sponges, including a red-orange encrusting form and a pink boring sponge riddling dead coral rock, are present but not counted as coral cover (e.g., Image 23, Image 24, Image 54).
  232454

Along the transect

• The transect opens on a shallow, heavily bioeroded standing-dead elkhorn (Acropora palmata) ridge with scattered small live encrusting corals and turf-filled crevices (e.g., Image 1, Image 2, Image 3), continuing through habitat frames of a spiny lobster (e.g., Image 4, Image 5) before reaching one of the better-condition patches of the whole transect: a large live elkhorn colony standing over a sea fan (e.g., Image 6, Image 7).
  14567
• Through the first third the reef alternates between dead-rubble ridges, sparse live patches, and gorgonian-dominated low-relief hardground, with a brief richer mixed patch of gorgonians, branching coral, and reef fish partway through this stretch (e.g., Image 11). A dead-elkhorn ridge partway through this stretch also hosts an orange cushion sea star (cf. Oreaster reticulatus) moving among small live elkhorn-type recruits on the rubble (e.g., Image 21), and a second spiny lobster shelters among sea rods and a purple sea fan a little further along (e.g., Image 26).
  112126
• The transect resumes over a turbid, low-relief sand-and-rubble zone where wildlife dominates the frames -- a nurse shark and a spotted eagle ray -- and coral cover is minimal (e.g., Image 35, Image 36, Image 37, Image 38, Image 39, Image 40, Image 41).
  36
• Visibility and structure improve through the middle of this second segment, with small mounding and finger-coral colonies becoming more frequent, including a cluster resembling coral recruits (e.g., Image 49, Image 50, Image 51, Image 52), before culminating in the transect's two healthiest live elkhorn colonies (e.g., Image 55, Image 56).
• The final third returns to eroded, pink-coralline-crusted dead coral boulders and gorgonian-dominated hardground with low hard coral cover, and the last frame is a close view of bare, turf-covered dead rock with no live coral visible (e.g., Image 63, Image 64, Image 65, Image 66, Image 67, Image 68, Image 69, Image 70).
  64656667686970

Condition

• Standing dead coral skeleton -- overwhelmingly elkhorn-form -- is a dominant feature of this transect, appearing repeatedly as heavily eroded, algae-covered framework with little to no living tissue (e.g., Image 1, Image 12, Image 13, Image 14, Image 18, Image 19, Image 20, Image 57, Image 65), and a wide view near the surface confirms the same dead-elkhorn field extends well into the shallows (e.g., Image 48).
  1213141819205748
• No active bleaching or disease signs were noted on any live colony; the two large elkhorn colonies mid-transect appeared fully pigmented with no visible tissue loss (e.g., Image 55, Image 56).
• A later stretch of dead-elkhorn rubble carries numerous small tan elkhorn-type recruits growing directly on the standing-dead framework, passed over by schools of grunts and sergeant majors (e.g., Image 58, Image 59, Image 60) -- the clearest recruitment signal on this transect.
  585960
• The overall pattern is a reef with substantial standing-dead structure and low background live cover, interrupted by isolated better-condition patches -- the large elkhorn colony near the start, the mid-transect finger-coral cluster, the two large live elkhorn colonies, and the late recruit patch -- rather than uniform decline or uniform recovery.

% cover

• Reference: Claude CV point count (this site's photos)
• A blind Claude computer-vision point count puts hard coral cover here at 3.1% ± 5.6 (mean ± standard deviation across 83 photos, 30 points per photo); other computer-vision methods are compared in the table below.