Wave-swept coralliths of Saba Bank, Dutch Caribbean

Bert W Hoeksema,Dahlia Hassell,Fleur C Van Duyl,Erik H W G Meesters

doi:10.1007/s12526-017-0712-5

Abstract

During a recent reef coral survey at the submarine Saba Bank (Eastern Caribbean), an uncommon and diverse assemblage of unattached scleractinian corals (coralliths) was encountered, which has not been reported from the Atlantic before. Four different types of these free-living (unattached) corals were distinguished. They were observed on a relatively flat seafloor (15–20 m deep) with poor coral cover and full exposure to oceanic swell. Much of the substratum was not consolidated and consisted mainly of sand and fragments of branching coralline algae. One of the four types is the (1) anthocyathus stage in the life history of the free-living species Manicina areolata and Meandrina danae. The other three are coralliths formed as ecophenotypic varieties: (2) spheroidal–amoeboidal (= globular and (sub)massive) in Porites astreoides, Siderastrea radians, S. siderea, and Stephanocoenia intersepta; (3) tumbleweed-like (= globular and ramose) in Porites divaricata and P. furcata; and (4) discoidal (flat and circular with short branches) in Madracis decactis and possibly in M. cf. auretenra. This assemblage of free-living corals is likely related to a combination of abiotic factors consisting of wave exposure (swell), depths that waves can reach, a horizontal sea floor with little relief, an unconsolidated substratum, and low coral cover.

Highlights

Saba Bank is a large submarine carbonate platform located to the west of the volcanic islands Saba and St
During a recent reef coral survey (November 2015) on Saba Bank, some scleractinian corals were found on unconsolidated substratum and appeared to be free-living instead of attached
The free-living coral fauna observed on Saba Bank appeared to consist of corals that were detached either by life history strategy as anthocyathus stage, which is free living as opposed to the attached anthocaulus stage (Wells 1966; Hoeksema 1989: Fig. 42), or by corallith forming after detachment from the substrate

Summary

Introduction

The stony coral fauna (Scleractinia, Milleporidae, Stylasteridae) of Saba Bank was studied during two exploratory expeditions by use of SCUBA, in 1972 (Van der Land 1977) and in 2006 (McKenna and Etnoyer 2010). The stony corals of Saba Bank were subject of more extensive surveys in 1996, 2011, and 2013, which eventually resulted in a total record of 39 species (Meesters et al 1996; Van Beek and Meesters 2013, 2014).

Results

Conclusion