NOAA - Black Coral Rock, Dry Tortugas

Setting

Black Coral Rock is a NOAA Dry Tortugas monitoring station on what Anderson's log calls 'a beautiful pinnacle in the middle of the open ocean'; the dive here on 28 June 2021, a temperature-logger swap, reached 25.6 m.

General benthic features

Many of the photographs show rubble-and-turf hard-bottom rather than a coral-crowded reef (e.g., Image 4, Image 12, Image 15, Image 19): brain corals and mounding heads shelter small yellow fish (e.g., Image 16, Image 18), a purple gorgonian and pale barrel sponge add color (e.g., Image 10, Image 17, Image 20), and loose schools of silvery reef fish drift through frame after frame (e.g., Image 3, Image 5, Image 6, Image 7, Image 21).

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A red tag is visible on one colony (e.g., Image 11), and divers can be seen at work in three frames (e.g., Image 8, Image 9, Image 13); the dive was a temperature-logger swap (Anderson's log).

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Coral cover

• Coral cover: 12% in 2021, from the FWC-FWRI Dry Tortugas CREMP point-count survey of the site's 4 permanent stations (831-834), the year Anderson dived here; the same 4 stations read 4.8% in 2024.
• The figure comes from the station values of the DTCREMP 2024 data release (9.5, 17, 12, and 11%).
• The four stations span 9.5% to 17%, so the site mean hides real patchiness.
• In August 2024 the same 4 stations read 3.7, 4.5, 5.9, and 4.9% (FWC-FWRI DTCREMP 2024 data release).
• For comparison only, computer vision on Anderson's own June 2021 photographs reads higher than the agency survey (method table below) because the photographs concentrate on coral heads rather than a systematic transect view; the agency survey is the site's cover.
• That figure does not agree with the transect data even after allowing for CoralSCOP's known over-read; the CREMP/NCRMP transect data remain the more defensible cover figures for this station.

Stressors

One massive colony shows a tissue-loss front: gray-purple live tissue, then a broad cream-white band of recently bare skeleton, then turf-covered skeleton, consistent with stony coral tissue loss disease (SCTLD) (e.g., Image 14).

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No corallivores were evident.

Comparisons with other data

FWC CREMP (Dry Tortugas, DTCREMP) surveyed this site (Black Coral Rock #831) in 2024, 0.00 km from the pin. Within 5 km, 88 independent stations recorded station-year means of 0.0–36% hard coral cover between 1999 and 2024; the nearest, FWC CREMP (Dry Tortugas, DTCREMP) at Black Coral Rock #831, 0.00 km away, read 2.0–25% between 1999 and 2024.