Wave-swept coralliths of Saba Bank, Dutch Caribbean

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 freeliving 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.

Unusual high coral cover in a Southwestern Atlantic subtropical reef

“…Both coral species are widely distributed along the Brazilian coast and its oceanic islands, with M. hispida occurring from northern from Parcel do Manuel Luiz (0º latitude; Cordeiro et al 2015) to São Paulo (24°S) and M. decactis from the Amazon Reefs (3ºN; Moura et al 2016) to Santa Catarina (27ºS; Castro and Pires 2001;Leão et al 2003) in Brazil but also occurring in the Caribbean and Florida in the USA (Jaap et al 1989;Vermeij and Bak 2003). The coral M. decactis is a nodular hermaphrodite and brooder species found in a variety of habitats, from shallow to more than 100 m deep areas (Moura et al 2016), and from shadowed vertical substrates to lightened zones (Neves and Johnsson 2009), either in attached or free-living forms (Capel et al 2012;Hoeksema et al 2018). By having the widest distribution in the Western Atlantic, M. decactis demonstrates its great plasticity, dispersal ability, and tolerance to variable abiotic factors.…”

“…The reason for such difference in coral dominance between the biogenic bank (dominated by M. decactis) and the adjacent rocky reefs (dominated by M. hispida) is unclear. However, while M. decactis is widely distributed in the Western Atlantic (Jaap et al 1989;Capel et al 2012) and presents high morphological plasticity, being able to encrust over several surfaces and to form coralliths (Hoeksema et al 2018), the coral M. hispida has a massive growth form and is not frequent a major component in the construction of biogenic reefs (Leão et al 2003), but is commonly abundant in subtropical rocky reefs (Banha et al 2019). Therefore, differences in coral dominance can be more linked to biological attributes of each species regarding growth form and habitat use than to differences in abiotic variables at such a small spatial scale.…”

The Role of Maximum Shelf Depth versus Distance from Shore in Explaining a Diversity Gradient of Mushroom Corals (Fungiidae) off Jakarta

“…Small, unattached mushroom corals can survive on sandy substrates because they are able to shed sediments [144,145] and they can move themselves away from direct threats [146][147][148]. Nevertheless, unattached fungiids are not unique as free-living and mobile corals on reefs worldwide and in the fossil record [78][79][80]149,150], which implies that the Fungiidae still constitute a suitable model taxon for Indo-Pacific coral diversity surveys.…”

A New Northernmost Distribution Record of the Reef Coral Duncanopsammia axifuga at Bird’s Head Peninsula, West Papua, Indonesia

“…The branching shape of D. axifuga appears to facilitate fragmentation, which explains its occurrence as free-living corals on soft substrates. This mechanism resembles asexual reproduction in various other branching coral species [25][26][27][28][29][30] and also in some free-living mushroom corals, which are well known for their capacity to form dense aggregations on sandy bottoms [30][31][32][33][34]. Owing to aquarium experiments it is also known that D. axifuga fragments can easily regenerate and grow into new colonies, making it suitable for aquaculture [35].…”