SE7ENth Heaven at Ant Atoll

We wait patiently as the boys get their nutriment for the day ahead. Ant Atoll is our destination and the suspense is rising. The ocean is mirror calm, the weather benign — perfect for our 1.5 hour journey across the water. Our initial sojourn to the south side two days ago equated such conditions and the reef did not disappoint: pure joy! Therefore, we anticipate more of the same. 

DJI_0037 (2) 2_ANT_ATOLL_AERIAL_2016.jpgFigure 1. Ant Atoll, 9 miles southwest from Pohnpei and now Micronesia's second official UNESCO Biosphere Reserve due to the efforts of the Conservation Society of Pohnpei (CSP). Image by R. Langston.

Ant Atoll is, in fact, a considerable size, being half the size of Pohnpei (129 square miles/334.1 square km), yet with a human population of 10 — how peaceful! Today we target the west side, with a supermoon rendering the corals of the reef flat exposed. From the reef crest a shear wall descends to more than 300 m (1000 ft) in depth, a small ledge is located and we anchor in. I drop in first and whilst awaiting the chaps I am met by a curious and somewhat territorial White-tip reef shark (Triaenodon obesus (Rüppell, 1837)).

Triaenodon obesus_Ant_Atoll[PSs]_BLOG.jpgFigure 2. Greeted by a curious White-tip reef shark Triaenodon obesus (Rüppell, 1837) before we descend the sheer wall into the mesophotic depths on the western side of Ant Atoll. Image by SJ. Rowley.

On descent the thermocline is unusually mild as we hit ~122 m (400 ft); now it’s time to get busy. Brian is to the right capturing an old friend: Chromis circumaurea Pyle et al. 2008, described previously by himself, Richard Pyle and John Earle.

Brian_Chromis_circumaurea[PSs]_BLOG.jpgFigure 3. Brian D. Greene having captured Chromis circumaurea (Pyle et al. 2008) from 122 m (400 ft) on the western side of Ant Atoll. Image by SJ. Rowley.

I’m surrounded by gorgonians sufficiently so that it’s overwhelming, perched on an overhang I collect in earnest, there’s not a moment to waste. Acanthogorgia, Paracis, Keroeides, Heliania, Annella, Astrogorgia…. hmmm finding those a little deep, interesting, yes Parisis – now I know we’re past the temperature gradient, this one’s fantastic and most definitely new. Brian glides past now to my left; “how’s it going Sonia?” “Awesome!” I reply in the typical ‘Smurf’ through-Trimix dialect; you can’t help but giggle when you sound like an animation – it never gets old.

Gorgonian_Chaos_120m[PSs]_BLOG.jpgFigure 4. A riot of azooxanthellate benthic cnidarians from gorgonians, soft corals, and zoanthids at 135 m (443 ft) depth, Ant Atoll. When faced with this biodiversity, where does one begin in such a brief window of time? Image by SJ. Rowley.

BOOM! This one is a new genus…. more comparative investigation awaits! At both the University of Hawai'i at Mānoa and the Bishop Museum there are excellent libraries of taxonomic literature. It is a peaceable past time to dissolve into this literature with numerous different languages and subjective taxonomic opinions that render an interesting experience and crowns the delight of collecting the colonies in the first place.

Blog_Gorgs_Se7enth_Heaven-2.jpgFigure 5. New gorgonian species (left) Acanthogorgia n.sp.,135 m (443 ft) depth, and (right)​ Paracis n.sp., 120 m (394 ft) at Ant Atoll. Image by SJ. Rowley.

The rush of being at depth and doing the work masks any awareness of the cold, which is typically less than 17°C/62 F. On ascent passing into warmer clines is always a welcome surprise, but not, however, for my catch! Gorgonians are particularly sensitive to temperature even more so than pressure — numerous species oxidise (begin to turn black) at elevated temperatures when bought up from the deep ocean (e.g., > 500 m) and this is also true for colonies at mesophotic depths.

Water_Clarity_W-Ant[PSs]_BLOG.jpgFigure 6. The water clarity on the western side of Ant Atoll from ~50 m (164 ft). The ocean is a majestic sapphire blue that captures the soul and stills the mind. Image by SJ. Rowley.​​​​​​​

Here, on the western side of the atoll, there appears two distinct differences to that of the southern side; firstly, there seems to be only a mild temperature gradient, whereas two thermoclines exist towards mesophotic depths on the southern side. Secondly, the topography involves a shear wall with enticing caves on the western side compared to a gradual incline on the south side. Both yield different results in terms of the biodiversity present, confirming the influence of the environment on the reef ,and thus, inherently intriguing to us all. The water clarity however, is astounding at both sites > 50 m (164 ft) for sure. The ocean is a majestic sapphire blue that captures the soul and stills the mind. 

S_&_W_Side_Ant_Atoll[PSs]_BLOG.jpgFigure 7. The mesophotic reefs of Ant Atoll. The south side (right) has a sloping sandy-rocky substratum, and the west side (right) has a sheer wall with wave-cut ledges with increasing distinction from 80 m (262 ft) depth. Images by SJ. Rowley.​​​​​​​

To me diving takes me to a place that is without definition. Using closed circuit rebreather (CCR) technology is very liberating, and so to feel so free and nimble under the water is ideal for what we do. Everything runs like clockwork, yet to understand the true algorithms behind this technology is no easy feat. 

Shark_4_Josh[PSs]_BLOG.jpgFigure 8. Greeted by our friend from the beginning of the dive Triaenodon obesus (Rüppell, 1837), whilst I investigate an abundance of Subergorgia rubra (Thomson, 1905) gorgonian colonies in a shallow cave during decompression, Ant Atoll. Image by SJ. Rowley.​​​​​​​

Greeted by my friend, the Whitetip reef shark Triaenodon obesus (Rüppell, 1837),  from the beginning of the dive, will he be here tomorrow?

This research was generously supported by: 

The Seaver Foundation


Adapted from Rowley SJ. 2014. SE7ENth Heaven at Ant Atoll. Bernice P. Bishop Museum. 14th July 2014.