Herbivorous fish can increase coral growth and survival by grazing down algal competitors. With coral reefs in global decline, maintaining adequate herbivory has become a primary goal for many managers. However, herbivore biomass targets assume grazing behavior is consistent across different reef systems, even though relatively few have been studied. We document grazing behavior of two scarid species in Antigua, Barbuda, and Bonaire. Our analyses show significant differences in intraspecific feeding rates, time spent grazing, and intensity of grazing across sites, which may alter the ecological impact of a given scarid population. We suggest several hypothesized mechanisms for these behavioral variations that would benefit from explicit testing in future research. As managers set targets to enhance herbivory on reefs, it is critical that we understand potential differences in scarid grazing impact. Our findings demonstrate the variability of grazing behavior across different reef sites and call for further investigation of the drivers and ecological implications of these inconsistencies.
Sponges are major components of benthic ecosystems, particularly on Caribbean reefs, where their importance in carbon cycling and ecosystem function is only beginning to be understood. There is a recurring statement in the literature, herein called the “sponge increase hypothesis,” asserting that the biomass and diversity of sponges increase with depth on Caribbean reefs through the mesophotic zone (to 150 m). We reviewed evidence for the sponge increase hypothesis, beginning with electronically searchable contributions to the literature, then working backward in time through the bibliographies of more recent citations. We found 17 studies that report one or more metrics associated with sponge abundance or diversity as a function of depth through all or part of the mesophotic zone. None of these studies reported data on either overall sponge biomass or diversity as a function of reef surface area. Among abundance metrics, including cover and density, patterns as a function of depth were disparate across sites and locations. We conclude that there is no evidence to support the sponge increase hypothesis for Caribbean mesophotic reefs and suggest that patterns of sponge abundance as a function of depth are likely to vary for a number of reasons, including substratum type, slope, and orientation. General theories of sponge abundance and diversity as a function of depth await more sophisticated survey studies that employ standardized methods for relating sponge biomass and diversity to reef surface area.
Snails of the genus Coralliophila (Muricidae: Coralliophilinae) are common in the Caribbean as corallivores that feed on a large range of host species. The present study concerns the distribution of two Coralliophila snails, C. caribaeaand C. galea, at 5-m and 10-m depths at Curaçao (southern Caribbean), as associates of the common scleractinians Orbicella annularis and Pseudodiploria strigosa. Coralliophila galea was abundant on both host species, while C. caribaea was represented only by a single individual on a colony of P. strigosa. No significant differences in shell length were found between snails associated with O. annularis and P. strigosa. The distribution of C. galea on both host species deviated significantly from a random distribution. The snails were most abundant at 5-m depth, particularly on larger colonies of O. annularis, with > 60 % of large colonies colonized by snails, while snails were absent on small colonies. This distinction was not significant in P. strigosa at the same depth or in O. annularis at a depth of 10 m. The results suggest that host preference should be considered in assessments of reef health in connection to damage caused by Coralliophila spp.
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.
This study provides a baseline of the marine algal flora composition around St. Eustatius, Dutch Caribbean, by describing algal community structure in terms of species richness and beta diversity, and by providing a taxonomically reliable DNA barcode collection. A total of 156 species was found, including 91 that represent new records for St. Eustatius. Subtidal assemblages (126 species) and intertidal assemblages (48 species) showed little overlap. Algae assemblages in seagrass beds differed from those on hard substrates in species composition. In addition, seagrass communities contained a relatively high number of associated green algae species. Artificial substrates (such as shipwrecks) mimicked natural hard substrates in terms of species richness and composition, but missed some key species that characterize natural reef floras. Species accumulation curves and asymptotic species richness estimators show that the expected species richness is higher than the observed number of species, indicating that additional sampling is needed to record rare species. The phylogenetic trees provided in this study identified the presence of cryptic species and fills knowledge gaps in our understanding of Caribbean macroalgae.
In order to demonstrate how scleractinian corals contribute to marine biodiversity by their host function, information on associated fauna was gathered during a biological survey at St. Eustatius, eastern Caribbean. This knowledge is especially urgent for a host coral such as Helioseris cucullata (Agariciidae), which has undergone strong declines in abundance at various Caribbean localities and has a poor record of associated fauna. New records of H. cucullata as host are presented for the coral gall crab Opecarcinus hypostegus (Cryptochiridae), the Christmas tree worm Spirobranchus giganteus (Serpulidae) and an unidentified serpulid tube worm of the genus Vermiliopsis. A second association record is reported for the coral barnacle Megatrema madreporarum (Pyrgomatidae). Coral-associated copepods were not found on H. cucullata despite a search for these animals. The new records were compared with previous records of other host coral species that showed elements of the same associated fauna. The present findings indicate that new discoveries concerning Caribbean coral reef biodiversity can still be made during field expeditions by targeting the assemblages of associated fauna of specific benthic host species.
The genus Microcharon is known in the Caribbean from the widely separated islands of Bonaire and Cuba, occurring in brackish and freshwater subterranean environments. Here we describe a new species from reef sands off St. Eustatius, eastern Caribbean. Morphological differences are small between the eleven other marine or coastal groundwater Microcharon species that are known worldwide, and comparisons do not show a biogeographic pattern of sequential dispersion.
Interspecific relationships of invasive species hosting a native associated species are noteworthy, particularly if the invasive does not have a similar relationship in its native range. The azooxanthellate Indo-Pacific coral Tubastraea coccinea (Dendrophylliidae) has become a widespread invasive in the tropical western Atlantic, where it was probably introduced as a fouling organism in the 1930s. During recent coral reef surveys this invader has been observed as host for a native tube worm, Spirobranchus giganteus (Serpulidae), at Curaçao, where this association was most commonly found on a shipwreck. Although Spirobranchus species are known to live in association with various shallow-water corals in the Atlantic and the Indo-Pacific, none of them has been recorded as an associate of a dendrophylliid or of an azooxanthellate coral before. This new association may be possible because of the generalist host selection of S. giganteus, which could have been facilitated by the availability of shipwrecks and other man-made substrates.
The Polyphysaceae is a well-studied family of green algae occurring in tropical and warm-temperate regions around the world. One of its species, Parvocaulis exiguus (Solms-Laubach) S. Berger et al. (Phycologia 42:506–561, 2003), has previously been reported from both the Indian and the Pacific Oceans. This report presents the first record of Parvocaulis exiguus from the Atlantic Ocean. It was collected at 18 m depth from rocky substrata surrounded by seagrass off the Dutch Windward Caribbean island St. Eustatius. Owing to its small size and close resemblance to co-occurring species, it is possible that this species has been previously overlooked in the Atlantic. Although Polyphysaceae have been intensively studied in the Caribbean and other Atlantic regions, this is not the case for subtidal algal vegetation on St. Eustatius. Parvocaulis exiguus could have been present for a longer time around St. Eustatius or it could have been introduced with shipping. Future investigations may show if Parvocaulis exiguus will be observed in additional locations in the Caribbean.
Scleractinian reef corals have been acknowledged as the most numerous host group for associated hydroids belonging to the genus Zanclea. To date, their geographical distribution is known to include several Indo-Pacific regions. During the Statia Marine Biodiversity Expedition to St. Eustatius (Lesser Antilles, Dutch Caribbean), the Zanclea-coral association was observed for the first time for the Caribbean Sea as well as for the Atlantic Ocean. Our findings confirm that the biodiversity associated with coral reefs remains insufficiently explored worldwide.