Rings & Branches

The reported deep cave of Ant Atoll is the final dive of this unforgettable trip. The continual mission to document and collect deep-reef fish and gorgonian corals is fueled by anticipation of what else may be encountered during these brief sojourns into the depths. Here, caves and caverns adorn the sheer, vertical wall on the western side of Ant Atoll and at 120 m (394 ft) I scour the reported cave to see, perhaps, what relictual delights may reside. These ancient structures are geological sinks through time harbouring a wealth of information of past climate events; melt water pulses and the like. They can provide essential habitat and relief from the competition that can be encountered on the open reef, with the potential to enable novel adaptations to life on a deep and secluded reef. I descend - with all this in mind - into the cave.

Coelocanth_site_W-Atoll_15_7_2014_BLOG.jpgFigure 1. Cave hunting >120 m (394 ft) at Ant Atoll. Images by SJ. Rowley.

As I slowly drift further into the cave the persistent squeaky helium voices attenuate, the rocks become increasingly barren, and I am at peace. Initially, colourful invertebrates pepper the walls: gorgonians, soft corals, zoanthids, small sponges, ascidians, bryozoans, and hydroids. The cave comes to an end. I wonder precisely how this formed... Nonetheless, there is no sign of the mysterious coelacanth that the boys had so eagerly anticipated!
Gorgs_N_Forams[PSs]_BLOG.jpgFigure 2. Gorgonian colonies Paracis sp. (95 m/312 ft) and Keroeides sp. (80 m/260 ft) with the discoid benthic foraminifera Cycloclypeus carpentari Brady, 1881 (blue arrows). Images by SJ. Rowley.

Out on the open walls the fish frenzy ensues, and I select colonies of sea fan corals specific to my research objectives. Time seems to stop somehow and I notice more of our little microfossils the forams, Cycloclypeus carpenteri Brady, 1881 at the base of the fans. These are fascinating. The concentric rings depict age, inform of temperature, carbon dioxide, and nutrient levels; environmental variables that appear to work in synergy, having a greater effect than if considered alone. Thus, these paper-thin discs are information-archives and little do I know how they would soon become an integral part of my research with experts on these fascinating organisms. 

DSC08691_BLOG-2.jpgFigure 3. Young scleractinian (hard) corals, typical of the shallow reefs of the region. Evidence of clear reef-building capacity. Image by SJ. Rowley.

Whilst the gorgonian corals on these isolated reefs dominate at depth the scleractinians prevail in the shallows. Oceanic islands and atolls are exposed to extreme natural disturbances - the weather and ocean can be harsh and destructive. The shallow reefs of Ant and Pohnpei show particular evidence of these harsh environmental conditions with dead stands of scleractinian corals also liberally populated with reef-building corals, crustose coralline algae, and numerous benthic invertebrates. At less than 3 m (10 ft) depth the transition from coral to coralline algae is clear, yet below this depth the reef seems to be in a constant state of repair, particularly on the atolls, which is very heartwarming to see sans human intervention, and also in the absence of coral disease.  

Atoll_Microatoll_Scaling[PSs]_BLOG.jpgFigure 4. The atoll paradigm: scaling atoll's and microatolls. Images by SJ. Rowley.

Venturing further into the shallows of the leeward and lagoonal reef flats, numerous microatolls populate the seabed. At first take, you can see an analogous 'micro-'process of Darwin's description of atoll formation (Darwin 1842) where in this instance the upward and lateral growth of the coral results in a circle of [coral] islands. With microatolls, the peripheral growth persists laterally whereas the centre and, formally the highest point of the coral head, has died due to aerial exposure. As with the foraminifera above, the rings of microatolls are also indicative - by proxy - of dynamic sea levels over time. Yet, what is also apparent is that the majority of nature consists of rings and branches - when you really think about it!Rings_&_Branches[PSs]_BLOG.jpgFigure 5. Rings and branches: Porites microatoll ~2 m (6.5 ft) and, right, Paracis sp. at 115 m (377 ft). Images by SJ. Rowley.

This area of Micronesia - the Caroline Island - was originally colonised by travellers from Papua New Guinea nearly three thousand years ago. Generations of sustainable living have persisted, yet only in recent decades has the alarming effects of sea-level rise begun to emerge. As Brian (Greene) and myself travel to arrange permits, he tells of his youth having been raised on the atoll of Kwajalein. We discuss the evolution of languages, with new ones created by settlers on high islands to mark a communities territory and, therefore, protect their high land. Atoll settlers, on the other hand, need to travel to other islands and atolls for trade and, therefore, speak numerous languages. But, the undisturbed tranquility of these low island dwellers is in peril, with sea level rising 2-3 ft (~1 m) in recent decades for the first time in history; their appeal for 'Some place with a Mountain' is essential to survive. Islanders and atoll-dwellers alike note the changes in the fruiting seasons, ocean temperatures, brackish waters leading to small crops, the loss of land, and the falling of entire coconut stands into the ocean. These climatic refugees’ are the recipients of the ever burgeoning 'civilized' world. 

The effects of sea level rise at Yap and Micronesia on homes and coconut groves[PSs]_BLOG.jpgFigure 6. The effects of sea-level rise at Yap, FSM showing flooding of the homes and coconut groves on the atoll. Images courtesy of Fletcher & Richmond (2010).

Our research extends the tropical Pacific, placing us in a highly unique position to document biodiversity over a wide geographic range. Mapping biodiversity and species distributions reveal the intricate branches of connectivity between islands in addition to the evolution of species differences over space and time (e.g., ring species). With this growing body of information we can assit with informed conservation management decisions, simply by sharing what we find, providing an invaluable resource available to researchers and lay-folk alike. When put in this context, the value of what we do becomes even more compelling and motivating. 

Invert_Biodiversity_Riot_BLOG.jpgFigure 7. A riot of invertebrate biodiversity at 75 m (246 ft), Ant Atoll. Image by SJ. Rowley.

However, the primary concern is anthropogenically accelerated sea-level rise with low-lying atolls being the most vulnerable. Nature will continuously persist irrespective of our presence, yet it is hoped that this work will contribute to the growing body of awareness that we do have a choice as to which aspects of nature will persist.

This research was generously supported by: 

The Seaver Foundation


Adapted from Rowley SJ. 2014. Rings and Branches. Bernice P. Bishop Museum. 17th July 2014.