Mesophotic ecosystems of the unique South Atlantic atoll are composed by rhodolith beds and scattered consolidated reefs
- 290 Downloads
Rocas Atoll is the only atoll in the South Atlantic and one of the smallest atolls in the world, and is mainly built by coralline algae. Even being unique in the world, reefs from its mesophotic zone (i.e., >30 m depth) have never been described. For the first time, we surveyed the bottom features of Rocas Atoll mesophotic zone by using side scan sonar, a remotely operated vehicle and TRIMIX diving. Rhodolith beds were the main habitat observed, composed mainly by crustose coralline algae, and presenting different patterns of bed structure. In deeper areas (60–80 m), most rhodoliths were coalesced in patches of ∼1 m2, while in the shallow areas (20–50 m), the more typical pattern of free-living rhodoliths predominated. Depths between 50 and 65 m were marked as transitional zones in which a step-shaped carbonate reefs were discovered. In addition to describing the rhodolith beds and the formation of carbonate reefs by the coalescence of rhodoliths, we highlight the importance of oceanic areas such as the one investigated here. They are excellent models for testing and understanding the influence of rhodolith beds in supporting the marine biodiversity and in promoting demographic connectivity between shallow and mesophotic reefs.
KeywordsRocas Atoll Crustose coralline algae Step-shaped reefs Connectivity
We thank to the ICMBIO Atol das Rocas Marine Biological Reserve team and the “Borandá” crew for supporting the 2011 expedition. This work was financially supported by grants of the Brazilian Science Agencies CNPq, CAPES, FAPERJ and FAPES.
(MP4 30606 kb)
- Foster M, Amado-Filho GM, Steller D, Riosmena-Rodriguez R and Kamenos N (2013) Rhodoliths and rhodoliths beds. In: Lang MA, Martinelli RL, Roberts SJ, Taylor PR (eds) Research and discoveries: the revolution of science through scuba. Smithsonian Contribution to the marine sciences, Smithsonian Institution 39, pp 143-156Google Scholar
- Gherardi DFM (1996) Recent carbonate sedimentation on the coralline-algal Atol das Rocas, equatorial South Atlantic, Brazil. PhD thesis, Royal Holloway University of LondonGoogle Scholar
- Kikuchi RKP and Leão ZMAN (1997) Rocas (southwestern equatorial Atlantic, Brazil): an atoll built primarily by coralline algae. Proc 8th Int Coral Reef Symp 1:731-736Google Scholar