Species density and associations in Caribbean reef corals

The density of scleractinian corals on portions of two reefs in the Grenadine Islands, W. I. has been investigated by direct observation by SCUBA divers. Grid, transect, and random quadrat methods were compared with total samples to determine the precision and accuracy of these techniques. Transect methods were generally satisfactory provided at least 15% of a 400 m² total grid area was included in the sample. The data strongly indicated clumped distributions of all species, although numerical analysis does not indicate the distinct zones reported by other workers. Species associations based on Jaccard's coefficient and cluster analysis showed possible similarities in physical requirements, although few strong associations were found. Data based on 4 m² quadrats generally provided a more reliable estimate of species associations than did data based on 1 m² quadrats. It is suggested that surveys of these reef types may be better based on a number of parallel transects rather than a single transect, and that well-defined zones are more likely to be the exception than the rule.     

Different algal symbionts explain the vertical distribution of dominant reef corals in the eastern Pacific

Symbiotic reef corals occupy the entire photic zone; however, most species have distinct zonation patterns within the light intensity gradient. It is hypothesized that the presence of specific symbionts adapted to different light regimes may determine the vertical distribution of particular hosts. We have tested this hypothesis by genetic and in situ physiological analyses of the algal populations occupying two dominant eastern Pacific corals, over their vertical distribution in the Gulf of California. Our findings indicate that each coral species hosts a distinct algal taxon adapted to a particular light regime. The differential use of light by specific symbiotic dinoflagellates constitutes an important axis for niche diversification and is sufficient to explain the vertical distribution patterns of these two coral species.     

Macroalgae reduces survival of nursery‐reared Acropora corals in the Florida reef tract

Recent declines in coral populations along the Florida reef tract have prompted the establishment of coral restoration programs which raise coral species, such as the threatened Acropora cervicornis, in nurseries ready for outplanting. Large numbers of nursery‐reared coral colonies have been outplanted along the Florida reef tract in recent years, yet few studies have characterized benthic habitats that are considered optimal for colony survival. In 2016, we surveyed 23 A. cervicornis restoration sites, located at six different reefs in the upper Florida Keys. We examined the condition of the outplanted corals and quantified the benthic assemblages adjacent to the outplanted coral colonies. We found that where A. cervicornis survived for more than 1 year, the substrate significantly supported less brown macroalgae of the genus Dictyota than at sites where A. cervicornis had died. Coral survival was highest at sites with less than 15% Dictyota cover. These results suggest that the habitat conditions that supported Dictyota spp. were not conducive to A. cervicornis growth and survival. Restoration practitioners should avoid attaching nursery‐raised corals to substrate with Dictyota spp. cover greater than 15%.     

Incongruence between life-history traits and conservation status in reef corals

Coral Reefs - Comparative lists of species’ extinction risk are increasingly being used to prioritise conservation resources. Extinction risk is most rigorously assessed using quantitative...     

Copepods associated with reef corals: a comparison between the Atlantic and the Pacific

Endoparasitic copepods are very numerous in Indo-West Pacific corals. In West Indian corals they were thought to be absent, but recent studies have shown that a varied endoparasitic copepod fauna exists as well. Striking is the taxonomic composition of the coral-inhabiting copepods:In the Indo-West Pacific Lichomolgidae and Xarifiidae are the dominant families, both are absent in the West Indies. On the other hand, Corallovexiidae and Asterocheridae dominate in the West Indies; the former family is absent and the latter is apparently rare and not very diversified in the Indo-West Pacific.     

Remote monitoring of chlorophyll fluorescence in two reef corals during the 2005 bleaching event at Lee Stocking Island, Bahamas

Zooxanthellae fluorescence was measured in situ, remotely, and in near real-time with a pulse amplitude modulated (PAM) fluorometer for a colony of Siderastrea siderea and Agaricia tenuifolia at Lee Stocking Island, Bahamas during the Caribbean-wide 2005 bleaching event. These colonies displayed evidence of photosystem II (PS II) inactivation coincident with thermal stress and seasonally high doses of solar radiation. Hurricane-associated declines in temperature and light appear to have facilitated the recovery of maximum quantum yield of PS II within these two colonies, although both corals responded differently to individual storms. PAM fluorometry, coupled with long-term measurement of in situ light and temperature, provides much more detail of coral photobiology on a seasonal time scale and during possible bleaching conditions than sporadic, subjective, and qualitative observations. S. siderea displayed evidence of PS II inactivation over a month prior to the issuing of a satellite-based, sea surface temperature (SST) bleaching alert by the National Oceanic and Atmospheric Administration (NOAA). In fact, recovery had already begun in S. siderea when the bleaching alert was issued. Fluorescence data for A. tenuifolia were difficult to interpret because the shaded parts of a colony were monitored and thus did not perfectly coincide with thermal stress and seasonally high doses of solar radiation as in S. siderea. These results further emphasize the limitations of solely monitoring SST (satellite or in situ) as a bleaching indicator without considering the physiological status of coral-zooxanthellae symbioses. Communicated by Environment Editor Prof. Rob van Woesik     

Consumption of coral propagules represents a significant trophic link between corals and reef fish

Mass spawning of corals provides a large seasonal pulse of high-energy prey that potentially benefits reef fish that are capable of capturing and digesting coral propagules. This study examines the range of fish species that consume coral propagules and also tests whether reef fish experience a significant increase in physiological condition when feeding on coral propagules. Thirty-six species of diurnal reef fish were seen to consume coral propagules released during mass coral spawning. Stomach content analyses of three reef fish species (Pomacentrus moluccensis, Abudefduf whitleyi, and Caesio cunning) revealed that both P. moluccensis and A. whitleyi feed almost exclusively on coral propagules during mass coral spawning. Fish feeding extensively on coral propagules also amassed considerable lipid stores, which could greatly improve the quality and survivorship of their progeny. In contrast, C. cunning consumed only very small quantities of coral propagules, and showed no detectable change in lipid stores during the course of the study. This study provides the first direct evidence that reef fish benefit from mass coral spawning, and reveals a potentially significant trophic link between scleractinian corals and reef fish. Accepted: 9 June 2000     

Correction to: Incongruence between life-history traits and conservation status in reef corals

Coral Reefs - This erratum is published as vendor overlooked corrections with misspelt scientific wording of family Siderastreidae.     

Severe 2010 cold-water event caused unprecedented mortality to corals of the Florida reef tract and reversed previous survivorship patterns

Background

Coral reefs are facing increasing pressure from natural and anthropogenic stressors that have already caused significant worldwide declines. In January 2010, coral reefs of Florida, United States, were impacted by an extreme cold-water anomaly that exposed corals to temperatures well below their reported thresholds (16°C), causing rapid coral mortality unprecedented in spatial extent and severity.

Methodology/Principal Findings

Reef surveys were conducted from Martin County to the Lower Florida Keys within weeks of the anomaly. The impacts recorded were catastrophic and exceeded those of any previous disturbances in the region. Coral mortality patterns were directly correlated to in-situ and satellite-derived cold-temperature metrics. These impacts rival, in spatial extent and intensity, the impacts of the well-publicized warm-water bleaching events around the globe. The mean percent coral mortality recorded for all species and subregions was 11.5% in the 2010 winter, compared to 0.5% recorded in the previous five summers, including years like 2005 where warm-water bleaching was prevalent. Highest mean mortality (15%–39%) was documented for inshore habitats where temperatures were <11°C for prolonged periods. Increases in mortality from previous years were significant for 21 of 25 coral species, and were 1–2 orders of magnitude higher for most species.

Conclusions/Significance

The cold-water anomaly of January 2010 caused the worst coral mortality on record for the Florida Reef Tract, highlighting the potential catastrophic impacts that unusual but extreme climatic events can have on the persistence of coral reefs. Moreover, habitats and species most severely affected were those found in high-coral cover, inshore, shallow reef habitats previously considered the “oases” of the region, having escaped declining patterns observed for more offshore habitats. Thus, the 2010 cold-water anomaly not only caused widespread coral mortality but also reversed prior resistance and resilience patterns that will take decades to recover.     

Allorecognition and xenorecognition in reef corals: a decade of interactions

Xenorecognition phenomena in coral reefs are expressed by a striking array of morphological and cytological responses. Corals encountering conspecifics further elicit additional repertoires of effector mechanisms, specific to allogeneic challenges. Both inducible sets of antagonistic machineries of allo- and xenoresponses are highly specific. In many cases, they are predictable, reproducible, and reveal the hallmark of coral tissue capacity to distinguish between self and non-self. This essay summarizes a decade (1992 –2002) of published results on reef coral immune features. While studies on xenorecognition uncovered the existence of established, non-transitive hierarchies and the importance of antibacterial/cytotoxic compounds secreted by corals, allorecognition assays disclosed the presence of specific and complex non-transitive hierarchies dictated by the expression of a variety of effector mechanisms (‘tailored’ against different conspecifics), the existence of gradual maturation of alloresponses (important in the formation of natural chimeras), the debatable issue of allorecognition memory, and the appearance of delayed, second sets of alloresponses. A critical evaluation of historecognition reveals that expressed responses in different coral systems are phenotypically matched with counterpart outcomes recorded in the mammalian immune systems. Histocompatibility in corals, as in vertebrates, relies on recognition elements (not yet disclosed on the molecular level) as well as on effector mechanisms.     

Colony size as a species character in massive reef corals

In a study of seven massive, Caribbean corals, I have found major differences in reproductive behavior between species with large maximum colony sizes and species with smaller maximum colony sizes. Four species (Diploria clivosa, D. strigosa, Montastrea cavernosa, Siderastrea siderea) which are large (<1000 cm² in surface area) broadcast gametes during a short spawning season. Their puberty size is relatively large (>100 cm², except M. cavernosa). In contrast, two small massive species (<100 cm², Favia fragum and S. radians), and one medium-sized (100–1000 cm², Porites astreoides) massive species, brood larvae during an extended season (year-round in Panama). The puberty size of the small species is only 2–4 cm². Given these close associations between maximum colony sizes and a number of fundamental reproductive attributes, greater attention should be given to the colony size distributions of different species of reef corals in nature, since many important life history and population characters may be inferred.     

Snorkeler damage to reef corals in the Maldive Islands

Rapid and intensive survey methods were used to measure coral breakage by snorkelers on a Maldivian resort reef. On the most impacted section of reef, breakage over a one month period was estimated at 17% of susceptible coral cover and 7% of total coral cover.     

Histological data in a combined phylogenetic analysis of scleractinian reef corals

Scleractinian systematics have undergone rapid changes due to increased use of molecular phylogenetics and new perspectives on skeletal morphology from micromorphology and microstructure. Despite this increase in characters there are still unresolved clades in the phylogeny, indicating that more characters are needed. This study investigates a new source of morphological data within the soft tissue of Indo‐Pacific scleractinian corals. Features of tissue layers, especially cnidocytes, are described in hematoxylin and eosin stained thin sections. Based on this new histological data source, a combined analysis with mitochondrial DNA and skeletal data is performed using parsimony and Bayesian analysis. Parsimony analysis yields three most‐parsimonious trees similar to trees based on Bayesian analysis. Character maps are also produced that show origination of histomorphological traits at deep nodes within the phylogeny. In general, both analyses retain the previously designated families Lobophylliidae and Merulinidae, but some genera are found to be paraphyletic. Nonetheless, the combined analysis produces a highly resolved and well‐supported phylogeny, which could lead to more effective use of biological conservation metrics based on evolutionary distinctiveness. These results show for the first time that inclusion of histomorphological characters improves the resolution of phylogenetic analyses of reef corals. J. Morphol. 277:494–511, 2016. © 2016 Wiley Periodicals, Inc.     

Recruitment hotspots and bottlenecks mediate the distribution of corals on a Caribbean reef

Recruitment hotspots are locations where organisms are added to populations at high rates. On tropical reefs where coral abundance has declined, recruitment hotspots are important because they have the potential to promote population recovery. Around St. John, US Virgin Islands, coral recruitment at five sites revealed a hotspot that has persistent for 14 years. Recruitment created a hotspot in density of juvenile corals that was 600 m southeast of the recruitment hotspot. Neither hotspot led to increased coral cover, thus revealing the stringency of the demographic bottleneck impeding progression of recruits to adult sizes and preventing population growth. Recruitment hotspots in low-density coral populations are valuable targets for conservation and sources of corals for restoration.     

Syntrophic-methanogenic associations along a nutrient gradient in the Florida Everglades

Nutrient runoff from the Everglades Agricultural Area resulted in a well-documented gradient of phosphorus concentrations in soil and water, with concomitant ecosystem-level changes, in the northern Florida Everglades. It was recently reported that sulfate-reducing prokaryote assemblage composition, numbers, and activities are dependent on position along the gradient (H. Castro, K. R. Reddy, and A. Ogram, Appl. Environ. Microbiol. 68:6129-6137, 2002). The present study utilized a combination of culture- and non-culture-based approaches to study differences in composition of assemblages of syntrophic and methanogenic microbial communities in eutrophic, transition, and oligotrophic areas along the phosphorus gradient. Methanogenesis rates were much higher in eutrophic and transition regions, and sequence analysis of 16S rRNA gene clone libraries constructed from samples taken from these regions revealed differences in composition and activities of syntroph-methanogen consortia. Methanogens from eutrophic and transition regions were almost exclusively composed of hydrogenotrophic methanogens, with approximately 10,000-fold-greater most probable numbers of hydrogenotrophs than of acetotrophs. Most cultivable strains from eutrophic and transition regions clustered within novel lineages. In non-culture-based studies to enrich syntrophs, most bacterial and archaeal clones were either members of novel lineages or closely related to uncultivated environmental clones. Novel cultivable Methanosaeta sp. and fatty acid-oxidizing bacteria related to the genera Syntrophomonas and Syntrophobacter were observed in microcosms containing soil from eutrophic regions, and different lines of evidence indicated the existence of novel syntrophic association in eutrophic regions.     

Effect of a fluctuating thermal regime on adult and larval reef corals

Abstract. We compared responses of adults and larvae of the brooding corals Pocillopora damicornis and Seriatopora hystrix to 12-h exposures to constant temperature treatments (21°C, 28°C, or 30°C) and a treatment in which temperature fluctuated from 28° to 21°C, simulating daily temperature variation generated by tidally driven upwelling in their natural habitat (Nanwan Bay, southern Taiwan). In all treatments, the maximum dark-adapted quantum yield of photosystem II (F_V/F_M) of the larvae was ∼49% lower than that of adult corals; F_V/F_M in the larvae also differed among temperature treatments, with the highest values in the fluctuating treatment. These results show that the larvae of at least P. damicornis are more sensitive to temperature than adults, and suggest that larvae are physiologically well suited to fluctuating temperature regimes. To assess whether the timing of larval release affected their performance, larvae of P. damicornis were compared among release days within a single reproductive event. Groups of larvae released on nine consecutive days differed significantly in size, Symbiodinium content, and F_V/F_M. This demonstration of functional differences among coral larvae that are released on different dates within a single reproductive event creates the potential for advantages to accrue from the coincidence of larval phenotypes with temporally varying conditions. Adult colonies may experience selective advantages by producing broods of functionally variable larvae, in order to match extreme phenotypes to unusual environmental conditions.     

Post-settlement mortality and growth of newly settled reef corals in a subtropical environment

There are few studies of post-settlement mortality of newly settled corals, particularly on subtropical reefs. This study examined the mortality and growth of spat of three broadcast spawning coral species at the Solitary Islands, eastern Australia (30°S). Mortality of spat was high, with only 0.2–2.8% surviving their first year of life. Growth was slow, with coral spat achieving a maximum diameter of 2 mm after 8 months. High post-settlement mortality and slow growth rates are likely to contribute to low rates of recruitment of broadcast spawning species at the Solitary Islands.     

Evolutionary diversification of reef corals: a comparison of the molecular and fossil records

Understanding historical patterns of diversity dynamics is of paramount importance for many evolutionary questions. The fossil record has long been the only source of information on patterns of diversification, but the molecular record, derived from time-calibrated phylogenies, is becoming an important additional resource. Both fossil and molecular approaches have shortcomings and biases. These have been well studied for fossil data but much less so for molecular data and empirical comparisons between approaches are lacking. Here, we compare the patterns of diversification derived from fossil and molecular data in scleractinian reef coral species. We also assess the robustness of molecular diversification rates to poor taxon sampling. We find that the temporal pattern of molecular diversification rates is robust to incomplete sampling when rates are calculated per interval. The major obstacle of molecular methods is that rate estimates are distorted because diversification rates can never be negative, whereas the fossil record suffers from incomplete preservation and inconsistent taxonomy. Nevertheless, the molecular pattern of diversification is comparable to the pattern we observe in the fossil record, with the timing of major diversification pulses coinciding in each dataset. For example, both agree that the end-Triassic coral extinction was a catastrophic bottleneck in scleractinian evolution.     

Restoration and monitoring of a vessel grounding on a shallow reef in the Florida Keys

This paper summarizes the results of a monitoring event designed to track the recovery of a repaired coral reef injured by the M/V Alec Owen Maitland vessel grounding incident of October 25, 1989. This grounding occurred within the Florida Keys National Marine Sanctuary. Pursuant to the National Marine Sanctuaries Act, NOAA recovers money for injury to Sanctuary resources, and uses it to restore those resources. A monitoring program tracks patterns of recovery, in order to determine the success of restoration measures. To evaluate success, reference habitats adjacent to the restoration site are concurrently monitored to compare the condition of restored areas with natural areas. Restoration of this site was completed in September 1995 by means of cement and limestone rock, and the monitoring results from summer 2007 are presented. Monitoring consisted of comparison of the biological conditions in the restored area with the reference area. Monitored corals are divided into the Orders: Gorgonians, Milleporans, and Scleractinians. Densities at the restored and reference areas are compared, and are shown to be greater in the restored. Size-class frequency distributions for the most abundant Scleractinians are examined, and reveal that the restoration is converging on the reference area. Also, for the Scleractinians, number and percentage of colonies by species, as well as several common biodiversity indices are provided; measures for the restored area approximate the reference area. A quantitative comparison of colony substrate settlement preference in the restored area is provided for all Orders, and for Scleractinians is further broken down for the two most frequent Genera.