Season structures prokaryotic partners but not algal symbionts in subtropical hard corals

Applied Microbiology and Biotechnology - Coral reef ecosystems have great economic, social, and ecological value. The ecological success of coral reef ecosystems critically depends on coral-algal...     

Ubiquitous associations and a peak fall prevalence between apicomplexan symbionts and reef corals in Florida and the Bahamas

Although apicomplexans are a widely recognized and important parasitic group, little is known about those associated with invertebrates, such as reef-building scleractinian corals. To resolve the potential impact of apicomplexans on coral health, it is first necessary to further describe this group of putative parasites and determine their prevalence among host species. Here, it was hypothesized that apicomplexan prevalence would vary seasonally, similar to what occurs in other marine apicomplexans as well as some coral symbionts. To test this, Caribbean scleractinian species Porites astreoides, Montastraea (=Orbicella) annularis, M. (=O.) faveolata, and Siderastrea siderea were sampled seasonally from two reefs each in the Florida Keys and the Bahamas for 9- and 5.5-year periods, respectively. Utilizing a PCR-based screening assay, apicomplexan DNA was detected from most Floridian (80.1 %: n = 555/693) and Bahamian (90.7 %: n = 311/343) coral tissue samples collected over these multi-year periods. Furthermore, apicomplexan DNA was detected from nearly all (98.7 %: n = 78/79) single polyps sampled at multiple locations within six M. faveolata colonies, indicating little to no intracolonial variation in the screening assay. Mixed-model logistic regression was utilized to determine the effects of season, host species, and reef on apicomplexan prevalence. The model identified a significant seasonal effect, with the highest apicomplexan prevalence occurring during fall. There also was a large effect of host species, with apicomplexan prevalence significantly lower among S. siderea colonies relative to the other species. While reef did not have a significant effect in the full model, there was a significant difference in apicomplexan prevalence between Floridian and Bahamian reefs for S. siderea, implying regional differences in this host species. Despite seasonal and species-specific differences in prevalence, apicomplexans are ubiquitous constituents of these particular scleractinian coral species from Florida and the Bahamas.     

Environmental influences on skeletal banding in eastern Pacific (Panama) corals

The timing of skeletal band formation and concomitant changes in calcification rates and linear skeletal extension were investigated in Pavona corals growing under two distinct thermal regimes along the Pacific coast of Panama: fluctuating, marked by seasonal upwelling (Gulf of Panama) and stable, nonupwelling (Gulf of Chiriqui). The purpose of this study was to test the hypothesis that banding in corals is largely mediated by seasonal variations in temperature (Highsmith 1979). Our results indicate that the timing of band formation is synchronous at these two environmentally distinct locations. The low density (LD) portion of the annual band is accreted over a five month period (January–June) and represents an increase in linear skeletal extension (mm/mo.) as well as a marked increase in calcification rate (g CaCO₃ · cm^-2 · mo^-1) relative to the high density portion which forms over the remaining seven month period (July through December). In contrast to the predictions of the Highsmith model these findings indicate that variations in light levels rather than fluctuation in temperature is a better correlate to changes in skeletal density. Qualitatively, banding patterns were similar at the two sites; however, higher growth rates (particularly with respect to the LD band) for Pavona clavus in the Gulf of Panama indicate that lower water temperatures and higher productivity, or both, may be responsible for quantitative differences in banding between sites. We found that formation of the HD band corresponds to lower light levels and the production of gametes. We propose that banding in corals is a complex phenomenon governed by endogenous processes (e.g. reallocation of energy from growth to reproduction) which may be mediated by exogenous factors (e.g light and productivity).     

Spermatozoan ultrastructure of scleractinian corals from the eastern Pacific: Pocilloporidae and Agariciidae

Spermatozoa ofPocillopora damicornis, Pocillopora elegans (Astrocoeniina, Pocilloporidae) andPavona gigantea (Fungiina, Agariciidae) from the eastern Pacific (Isla del Caño, Costa Rica) were examined using transmission electron microscopy. The hermaphroditic pocilloporidsP. damicornis andP. elegans are spermiomorphologically very similar to hermaphroditic acroporids, being characterized by bullet-shaped nuclei and elongated mitochondria. Such traits have not been found in other families. Thus, the suborder Astrocoeniina, including pocilloporids and acroporids, can clearly be distinguished from other scleractinian suborders. This separation underlines the isolated position of the Astrocoeniina within the order Scleractinia following the evolutionary scheme of Wells. A conical sperm type, known from gonochoric species (sexes separate) from all families except Acroporidae and Pocilloporidae, was found in the gonochoric agariciidPavona gigantea. This supports previous findings that gonochoric corals share a unique and common sperm structure regardless of which family they belong to. However, no gonochoric Astrocoeniina have ever been examined. Hence, the question whether the sperm type common to gonochorists is also represented in Astrocoeniina, which would undermine the ultrastructural distinction of Astrocoeniina and other suborders seen among hermaphrodites, as well as the systematic value of sperm structure within scleractinian corals, remains open.     

Reversal of digestive interactions between Pacific reef corals: Mediation by sweeper tentacles

Summary Aggressive interactions among reef corals involving direct interference through extracoelenteric digestion has previously been considered as a potential mechanism for the maintenance of high species diversity. In this report I show that induced development of sweeper tentacles can reverse initial digestive interactions. In the eastern Pacific these reversals contribute to resource monopolization by fast growing pocilloporid corals. This suggests that other mechanisms must account for the maintenance of local species diversity.     

Threatened reef corals of the world

A substantial proportion of the world's living species, including one-third of the reef-building corals, are threatened with extinction and in pressing need of conservation action. In order to reduce biodiversity loss, it is important to consider species' contribution to evolutionary diversity along with their risk of extinction for the purpose of setting conservation priorities. Here I reconstruct the most comprehensive tree of life for the order Scleractinia (1,293 species) that includes all 837 living reef species, and employ a composite measure of phylogenetic distinctiveness and extinction risk to identify the most endangered lineages that would not be given top priority on the basis of risk alone. The preservation of these lineages, not just the threatened species, is vital for safeguarding evolutionary diversity. Tests for phylogeny-associated patterns show that corals facing elevated extinction risk are not clustered on the tree, but species that are susceptible, resistant or resilient to impacts such as bleaching and disease tend to be close relatives. Intensification of these threats or extirpation of the endangered lineages could therefore result in disproportionate pruning of the coral tree of life.     

A biogeographic analysis and review of the far eastern Pacific coral reef region

New information on the presence and relative abundances of 41 reef-building (zooxanthellate) coral species at 11 eastern Pacific and 3 central Pacific localities is examined in a biogeographic analysis and review of the eastern Pacific coral reef region. The composition and origin of the coral fauna and other reef-associated taxa are assessed in the context of dispersal and vicariance hypotheses. A minimum variance cluster analysis using coral species presence–absence classification data at the 14 localities revealed three eastern Pacific reef-coral provinces: (1) equatorial– mainland Ecuador to Costa Rica, including the Galápagos and Cocos Islands; (2) northern– mainland México and the Revillagigedo Islands; (3) island group– eastern Pacific Malpelo Island and Clipperton Atoll, and central Pacific Hawaiian, Johnston and Fanning Islands. Coral species richness is relatively high in the equatorial (17–26 species per locality) and northern (18–24 species) provinces, and low at two small offshore island localities (7–10 species). A high proportion (36.6%, 15 species) of eastern Pacific coral species occurs at only one or two localities; of these, three disappeared following the 1982–83 ENSO event, three occur as death assemblages at several localities, and five are endangered with known populations of ten or fewer colonies. Principal component analysis using ordinal relative density data for the 41 species at the 14 localities indicated three main species groupings, i.e., those with high, mid, and narrow spatial distributions. These groupings correlated with species population-dynamic characteristics. These results were compared with data for riverine discharges, ocean circulation patterns, shoreline habitat characteristics, and regional sea surface temperature data to help clarify the analyses as these measures of environmental variability affect coral community composition. Local richness was highest at localities with the highest environmental variability. Recent information regarding the strong affinity between eastern and central Pacific coral faunas, abundance of teleplanic larvae in oceanic currents, high genetic similarity of numerous reef-associated species, and appearances of numerous Indo-west Pacific species in the east Pacific following ENSO activity, suggest the bridging of the east Pacific filter bridge (formerly east Pacific barrier). Accepted: 20 September 1999     

The distribution of dimethylsulfoniopropionate in tropical Pacific coral reef invertebrates

Dimethylsulfoniopropionate (DMSP) is an important component of the global sulfur cycle and may be involved, via its cleavage product dimethylsulfide, in climate regulation. Although it is common in many algae, reports of DMSP in animals, particularly tropical invertebrates, are limited. This study examined the distribution of DMSP in a diverse group of coral reef invertebrates. DMSP was present in all 22 species of cnidarians and ranged from 9 to 723 μmol g⁻¹ of dry mass (DM) with a mean (± 1SD) of 110 ± 180 μmol g⁻¹ DM. It was not detected in a flatworm and an ascidian or in two of five sponges. Concentrations in sponges ranged from undetectable to 16 μmol g⁻¹ DM with a mean of 4 ± 7 μmol g⁻¹ DM. Within the cnidarians, DMSP concentrations did not differ among orders. Among cnidarian species, DMSP concentrations were correlated with symbiotic zooxanthellae densities. Within cnidarian species, DMSP concentrations of individuals were positively correlated with zooxanthellae densities in three of the four species examined. We speculate that DMSP is dietarily derived in sponges and derived from zooxanthellae in the cnidarians. The functions of DMSP in coral reef invertebrates are not known.     

Effects of water movement on prey capture and distribution of reef corals

Coral reefs comprise a variety of microhabitats, each with a characteristic pattern of water movement. Variation in flow microhabitat is likely to influence the distribution and abundance of suspension feeders, including the corals. Water flow was measured concurrently with wave heights at 8 depths along the forereef slope in Salt River Canyon, St Croix, U.S.V.I. The greatest flow speeds occurred on the shallow forereef at 7 m depth, where oscillatory wave-induced flow reached speeds over 50 cm s^–1. From 7 m to at least 15 m depth, flow decreased and was primarily bidirectional. Below 15 m depth, flow decreased even further, to less than one fifth of that experienced by shallow corals, and was unidirectional. The relationship between particle capture by the corals Meandrina meandrites and Madracis decactis and water flow was studied in the field. Colony morphology and the resulting modification of flow influenced the relationship of flow to feeding success; prey capture by the branching Madracis colonies increased with flow, while that of the flat Meandrina colonies did not. Such relationships may contribute to differences in distribution of corals of divergent morphologies. In transect surveys from 7 to 45 m depth,; branching and mounding corals with tentacular feeding modes were most common in the shallow forereef habitats, and plating corals with small polyps (ciliary mucus feeders) were ubiquitous in the deeper zones.This paper was presented at the Fifth International Conference on Coelenterate Biology at Southampton, UK in July 1989. A synopsis appears in the Proceedings (Hydrobiologia 216/217: 247–248, 1991).This paper was presented at the Fifth International Conference on Coelenterate Biology at Southampton, UK in July 1989. A synopsis appears in the Proceedings (Hydrobiologia 216/217: 247–248, 1991).     

Exposure to solar radiation increases damage to both host tissues and algal symbionts of corals during thermal stress

Elevated seawater temperatures have long been accepted as the principal stressor causing the loss of symbiotic algae in corals and other invertebrates with algal symbionts (i.e., bleaching). A secondary factor associated with coral bleaching is solar irradiance, both its visible (PAR: 400–700 nm) and ultraviolet (UVR: 290–400 nm) portions of the spectrum. Here we examined the synergistic role of solar radiation on thermally induced stress and subsequent bleaching in a common Caribbean coral, Montastraea faveolata. Active fluorescent measurements show that steady-state quantum yields of photosystem II (PSII) fluorescence in the zooxanthellae are markedly depressed when exposed to high solar radiation and elevated temperatures, and the concentration of D1 protein is significantly lower in high light when compared to low light treatments under the same thermal stress. Both photosynthetic pigments and mycosporine-like amino acids (MAAs) are also depressed after experimental exposure to high solar radiation and thermal stress. Host DNA damage is exacerbated under high light conditions and is correlated with the expression of the cell cycle gene p 53, a cellular gatekeeper that modulates the fate of damaged cells between DNA repair processes and apoptotic pathways. These markers of cellular stress in the host and zooxanthellae have in common their response to the enhanced production of reactive oxygen species during exposure to high irradiances of solar radiation and elevated temperatures. Taking these results and previously published data into consideration, we conclude that thermal stress during exposure to high irradiances of solar radiation, or irradiances higher than the current photoacclimatization state, causes damage to both photochemistry and carbon fixation at the same time in zooxanthellae, while DNA damage, apoptosis, or necrosis are occurring in the host tissues of symbiotic cnidarians.Abbreviations _PSII Functional absorption cross-section for PSII - F_o, F_m Minimum and maximum yields of chlorophyll a fluorescence measured after dark acclimation (relative units) - F_v Variable fluorescence after dark acclimation (=F_m–F_o), dimensionless - F_v/F_m Maximum quantum yield of photochemistry in PSII measured after dark acclimation, dimensionless - F, F_m Steady-state and maximum yields of chlorophyll a fluorescence measured under ambient light (relative units) - F/F_m Quantum yield of photochemistry in PSII measured at steady state under ambient light Communicated by R.C. Carpenter     

Crossing the impassable: genetic connections in 20 reef fishes across the eastern Pacific barrier

The 'impassable' Eastern Pacific Barrier (EPB), ca 5000 km of deep water separating the eastern from the central Pacific, is the World's widest marine biogeographic barrier. Sequencing of mitochondrial DNA in 20 reef fish morphospecies encountered on both sides of the barrier revealed cryptic speciation in two. Among the other 18 species only two showed significant differentiation (as revealed by haplotype networks and FST statistics) between the eastern and the central Pacific. Coalescence analyses indicated that genetic similarity in the 18 truly transpacific species resulted from different combinations of ages of most recent invasion and of levels of recurrent gene flow, with estimated times of initial separation ranging from approximately 30000 to 1 Myr (ago). There is no suggestion of simultaneous interruptions of gene flow among the species. Migration across the EPB was previously thought to be exclusively eastward, but our evidence showed two invasions from east to west and eight cases in which subsequent gene flow possibly proceeded in the same direction. Thus, the EPB is sporadically permeable to propagules originating on either side.     

Analysis of the self-shading effect on algal vertical distribution in natural waters

Self-shading of light by algae growing in a column of water plays an important role in the dynamics of algal blooms. Thus without self-shading the algal concentration would increase more rapidly, making the nutrient limitation too strong. Apart from the practical importance of self-shading, its inherent nonlinearity in the growth dynamics leads to an interesting mathematical problem, which warrants detailed analytical investigation. Our mathematical model for the self-shading effect includes vertical diffusion, algal settling, gross production, and collective losses of algae. Steady-state solutions of the model equation are investigated in detail by the phase plane method, and their stability examined. Finally we discuss the vertical profile of algal concentration.Contribution No. 291 of the Marine Sciences Research Center     

Summer vertical distribution of paralarval gonatid squids in the northeast Pacific

The vertical distribution patterns of paralarvae from severalabundant cephalopod taxa were examined from depth-stratifiedtows in the northeast Pacific (44–56°N, 145–165°W)during three summer surveys in 1999–2001. A total of 309cephalopods representing 10 taxa in three families were collected.Gonatid squids composed 97% of the total catch, and the mostnumerous taxa were Berryteuthis anonychus (59% of the totalcatch), Gonatus spp. (21%) and Gonatopsis borealis (17%). B.anonychus and Gonatus spp. were both most abundant in the upper20 m; catches of both taxa varied significantly with depth andwere significantly higher above the thermocline than in andbelow the thermocline. Gonatopsis borealis was collected mostlybetween 20 and 50 m, and catches were significantly higher inthe thermocline than above and below the thermocline. Paralarvaeof the three major taxa showed no evidence of diel verticalmigration. Mantle lengths of Gonatus spp. and G. borealis eachvaried significantly with depth, and Gonatus spp. showed a strongpositive correlation between mantle length and depth.     

Oriented translocation of energy in grafted reef corals

Colonies of the Red Sea reef coral Stylophora pistillata were grafted with alien branches (alografts), which had been labelled by NaH¹⁴CO₃ in the light. The “cold” host-colonies translocated the ¹⁴C-containing photosynthetic metabolites in an oriented pathway from the grafted branches into their own tissues. The highest accumulations of ¹⁴C products were detected in specific branch-tips of the host, away from the contact zones. The “recipient” colonies utilize these energy-rich materials for their metabolic requirements. The ¹⁴CO₂ produced through respiration is consequently detected in the skeletal-carbonate of the tips as Ca¹⁴CO₃. The purple morph of S. pistillata is found to be superior to the yellow morph.     

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.     

The future of evolutionary diversity in reef corals

One-third of the world''s reef-building corals are facing heightened extinction risk from climate change and other anthropogenic impacts. Previous studies have shown that such threats are not distributed randomly across the coral tree of life, and future extinctions have the potential to disproportionately reduce the phylogenetic diversity of this group on a global scale. However, the impact of such losses on a regional scale remains poorly known. In this study, we use phylogenetic metrics in conjunction with geographical distributions of living reef coral species to model how extinctions are likely to affect evolutionary diversity across different ecoregions. Based on two measures—phylogenetic diversity and phylogenetic species variability—we highlight regions with the largest losses of evolutionary diversity and hence of potential conservation interest. Notably, the projected loss of evolutionary diversity is relatively low in the most species-rich areas such as the Coral Triangle, while many regions with fewer species stand to lose much larger shares of their diversity. We also suggest that for complex ecosystems like coral reefs it is important to consider changes in phylogenetic species variability; areas with disproportionate declines in this measure should be of concern even if phylogenetic diversity is not as impacted. These findings underscore the importance of integrating evolutionary history into conservation planning for safeguarding the future diversity of coral reefs.     

Abundance,population structure and vertical distribution of dominant calanoid copepods on the eastern Weddell Sea shelf during a spring phytoplankton bloom

The main emphasis of this study was to analyse the short-term development of abundance, population structure and vertical distribution of the dominant calanoid copepods during a phytoplankton bloom in the coastal area of the eastern Weddell Sea in December 2003. Microcalanus pygmaeus was by far the most abundant calanoid species. Metridia gerlachei, Ctenocalanus citer, Calanoides acutus, Calanus propinquus and the ice-associated Stephos longipes were also present in considerable proportions. The observed changes in the population characteristics and parameters of these species are described in detail and discussed in the context of the spring phytoplankton bloom. A conspicuous event occurring during the final stage of the study was the development of a strong storm. While the results suggest that this storm did not have any considerable influence on the populations of all other investigated copepod species, it very likely caused pronounced changes in the S. longipes population present in the water column. Before the storm, S. longipes was found primarily in the upper 100 m of the water column, and its population was dominated by adults (mean proportion = 41%) and the copepodite stage I (mean proportion = 30%). After the storm, the abundance increased considerably, and the copepodite stage I contributed by far the largest proportion (53%) of the total population indicating that the early copepodite stages probably had been released from the sea ice into the under ice water layer due to ice break-up and ice melt processes caused by the storm.