Reef Sponge Research Articles

Deep genetic divergences among Indo-Pacific populations of the coral reef sponge Leucetta chagosensis (Leucettidae): Founder effects, vicariance, or both?

BackgroundAn increasing number of studies demonstrate that genetic differentiation and speciation in the sea occur over much smaller spatial scales than previously appreciated given the wide distribution range of many morphologically defined coral reef invertebrate species and the presumed dispersal-enhancing qualities of ocean currents. However, knowledge about the processes that lead to population divergence and speciation is often lacking despite being essential for the understanding, conservation, and management of marine biodiversity. Sponges, a highly diverse, ecologically and economically important reef-invertebrate taxon, exhibit spatial trends in the Indo-West Pacific that are not universally reflected in other marine phyla. So far, however, processes generating those unexpected patterns are not understood.ResultsWe unraveled the phylogeographic structure of the widespread Indo-Pacific coral reef sponge Leucetta chagosensis across its known geographic range using two nuclear markers: the rDNA internal transcribed spacers (ITS 1&2) and a fragment of the 28S gene, as well as the second intron of the ATP synthetase beta subunit-gene (ATPSb-iII). This enabled the detection of several deeply divergent clades congruent over both loci, one containing specimens from the Indian Ocean (Red Sea and Maldives), another one from the Philippines, and two other large and substructured NW Pacific and SW Pacific clades with an area of overlap in the Great Barrier Reef/Coral Sea. Reciprocally monophyletic populations were observed from the Philippines, Red Sea, Maldives, Japan, Samoa, and Polynesia, demonstrating long-standing isolation. Populations along the South Equatorial Current in the south-western Pacific showed isolation-by-distance effects. Overall, the results pointed towards stepping-stone dispersal with some putative long-distance exchange, consistent with expectations from low dispersal capabilities.ConclusionWe argue that both founder and vicariance events during the late Pliocene and Pleistocene were responsible to varying degrees for generating the deep phylogeographic structure. This structure was perpetuated largely as a result of the life history of L. chagosensis, resulting in high levels of regional isolation. Reciprocally monophyletic populations constitute putative sibling (cryptic) species, while population para- and polyphyly may indicate incipient speciation processes. The genetic diversity and biodiversity of tropical Indo-Pacific sponges appears to be substantially underestimated since the high level of genetic divergence is not necessarily manifested at the morphological level.

Deep genetic divergences among Indo-Pacific populations of the coral reef sponge Leucetta chagosensis (Leucettidae)

Background: An increasing number of studies demonstrate that genetic differentiation and speciation in the sea occur over much smaller spatial scales than previously appreciated given the wide distribution range of many morphologically defined coral reef invertebrate species and the presumed dispersalenhancing qualities of ocean currents. However, knowledge about the processes that lead to population divergence and speciation is often lacking despite being essential for the understanding, conservation, and management of marine biodiversity. Sponges, a highly diverse, ecologically and economically important reef-invertebrate taxon, exhibit spatial trends in the Indo-West Pacific that are not universally reflected in other marine phyla. So far, however, processes generating those unexpected patterns are not understood. Results: We unraveled the phylogeographic structure of the widespread Indo-Pacific coral reef sponge Leucetta chagosensis across its known geographic range using two nuclear markers: the rDNA internal transcribed spacers (ITS 1&2) and a fragment of the 28S gene, as well as the second intron of the ATP synthetase beta subunit-gene (ATPSb-iII). This enabled the detection of several deeply divergent clades congruent over both loci, one containing specimens from the Indian Ocean (Red Sea and Maldives), another one from the Philippines, and two other large and substructured NW Pacific and SW Pacific clades with an area of overlap in the Great Barrier Reef/Coral Sea. Reciprocally monophyletic populations were observed from the Philippines, Red Sea, Maldives, Japan, Samoa, and Polynesia, demonstrating longstanding isolation. Populations along the South Equatorial Current in the south-western Pacific showed isolation-by-distance effects. Overall, the results pointed towards stepping-stone dispersal with some putative long-distance exchange, consistent with expectations from low dispersal capabilities. Conclusion: We argue that both founder and vicariance events during the late Pliocene and Pleistocene were responsible to varying degrees for generating the deep phylogeographic structure. This structure was perpetuated largely as a result of the life history of L. chagosensis, resulting in high levels of regional isolation. Reciprocally monophyletic populations constitute putative sibling (cryptic) species, while population para- and polyphyly may indicate incipient speciation processes. The genetic diversity and biodiversity of tropical Indo-Pacific sponges appears to be substantially underestimated since the high level of genetic divergence is not necessarily manifested at the morphological level.

Biogeochemical cycling in the Strait of Georgia

The papers in this special issue present the results of a five-year project to study sedimentary biogeochemical processes in the Strait of Georgia, with special emphasis on the near-field of a large municipal outfall. Included in this special issue are overviews of the sedimentology, benthic biology, status of siliceous sponge reefs and distribution of organic carbon in the water column. Other papers address the cycling of contaminants (PCBs, PBDEs) and redox metals in the sediment, a method to map the extent of the influence of municipal effluent from staining on benthic bivalves, and the relationships among geochemical conditions and benthic abundance and diversity. The latter set of papers addresses the role of municipal effluent as a pathway of organic carbon and other contaminants into the Strait of Georgia and the effect of the effluent on benthic geochemistry and biology.

Incidence and identity of photosynthetic symbionts in Caribbean coral reef sponge assemblages

Marine sponges are abundant and diverse components of coral reefs and commonly harbour photosynthetic symbionts in these environments. The most prevalent symbiont is the cyanobacterium, Synechococcus spongiarum, isolated from taxonomically diverse hosts from geographically distant regions. We combined analyses of chlorophyll-a (chl-a) concentrations with line-intercept transect surveys to assess the abundance and diversity of reef sponges hosting photosymbionts on Caribbean coral reefs in the Bocas del Toro Archipelago, Panamá. To identify symbionts, we designed PCR primers that specifically amplify a fragment of the 16S ribosomal RNA gene from S. spongiarum and used these primers to screen potential host sponges for the presence of this symbiont. Chlorophyll-a data divided the sponge community into two disparate groups, species with high (>125 μg/g, N=20) and low (<50 μg/g, N=38) chl-a concentrations. Only two species exhibited intermediate (50–125 μg/g) chl-a concentrations; these species represented hosts with reduced symbiont populations, including bleached Xestospongia muta and the mangrove form of Chondrilla nucula (C. nucula f. hermatypica). Sponges with high and intermediate chl-a concentrations accounted for over one-third of the species diversity and abundance of sponges in these communities. Most (85%) of these sponges harboured S. spongiarum. Molecular phylogenies reveal that S. spongiarum represents a sponge-specific Synechococcus lineage, distinct from free-living cyanobacteria. The prevalence of sponge–photosymbiont associations and dominance of symbiont communities by S. spongiarum suggest a major role of this cyanobacterium in sponge ecology and primary productivity on coral reefs.

Disease prevalence and population density over time in three common Caribbean coral reef sponge species

Reports of disease in sponges are increasing, but the paucity of data on disease prevalence over time makes it uncertain how much this trend reflects increased attention to sponges rather than increased sponge disease. Population and community influences on disease dynamics, and the consequences of disease at these levels, are also little known. Five censuses, over 14 y, of a small plot on a shallow coral reef at San Blas, Panama, provide data for the three most abundant species on population dynamics (number of individuals and total volume) and disease prevalence (number of individuals with active lesions). Although data for the three species, combined in broad categories (i.e. high vs low), support a general conclusion that disease prevalence was greater from 1994–1998 than from 1984–1988, the data do not demonstrate a steady increase over time, and disease prevalence for two of the species decreased in each of the final two censuses from a high in 1994. Fluctuations in population density (total volume) and disease prevalence were nearly synchronous within individual species, but asynchronous among the three species, suggesting that population density, measured as total sponge volume per unit area, may influence disease dynamics in these sponges.

Diversity and specificity of Caribbean sponge-zoanthid symbioses: a foundation for understanding the adaptive significance of symbioses and generating hypotheses about higher-order systematics

The diversity and specificity of symbiotic associations may be useful in revealing the underlying ecology of symbioses and evolutionary relationships of symbiotic species. Symbioses between coral reef sponges and zoanthids are widespread and common in the greater Caribbean region, although the diversity and specificity of the species involved have only been explored at a few sites and the adaptive significance has only been examined for three combinations. We identified extensive diversity among sponges that associate with zoanthids by compiling sponge–zoanthid species associations from field surveys, the literature, and museum collections, and examined the patterns of specificity at multiple levels of sponge and zoanthid taxonomy. The results obtained indicate that facultative sponges are highly specific to the species of their partners whereas obligate zoanthids are not. The patterns of specificity among sponges and zoanthids suggest that many of these associations are not likely to be parasitic. Sponges harbouring photosynthetic endosymbionts associate at a disproportionately high frequency with zoanthids that harbour photosynthetic endosymbionts. Zoanthids embed in the surfaces of sponges to various degrees, resulting in a range of intimacy that negatively correlates with the number of hosts and polyp volume of zoanthids. Dendrograms based on the similarity among associations are largely consistent with current hypotheses of sponge higher-order systematics, but inconsistent with the current hypotheses of zoanthid systematics, and they highlight the potential utility of ecological characters in systematic analyses.

Production of Manoalide and Its Analogues by the Sponge Luffariella variabilis Is Hardwired

The Great Barrier Reef sponge Luffariella variabilis (Poléjaeff 1884) produces a range of potent anti-inflammatory compounds as its major metabolites. These major metabolites-manoalide monoacetate, manoalide, luffariellin A and seco-manoalide-were monitored temporally and spatially to quantify the potential yield from wild harvest or aquaculture. Production of the major metabolites was hardwired at the population level with little variation in space and time over meters to tens of kilometers in the Palm Islands, Queensland, Australia. Manoalide monoacetate (35 to 70 mg g(-1) dry weight of sponge) was consistently the most abundant compound followed by manoalide (15 to 20 mg g(-1) dry weight). Luffariellin A and seco-manoalide were 10 to 70 times less abundant and varied between 0 and 3 mg g(-1) dry weight. On a larger spatial scale, L. variabilis from Davies Reef and Magnetic Island contained the same rank order and yields of compounds as the Palm Islands, indicating a generality of pattern over at least 100 km. The "hardwiring" of metabolite production at the population level by L. variabilis was also reflected in the lack of any inductive effect on metabolite production. In addition, individually monitored sponges produced fixed ratios of the major metabolites over time (years). However, these ratios varied between individuals, with some individuals consistently producing high levels of manoalide and manoalide monoacetate, providing the potential for selection of high-yielding stocks.

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm−2) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.

Temperature cues gametogenesis and larval release in a tropical sponge

Determining the reproductive processes of benthic invertebrates is central to our understanding of their recruitment and population dynamics. Sexual reproduction of the gonochoric and viviparous Great Barrier Reef sponge, Luffariella variabilis (Polejaeff 1884) was quantified from histological samples collected over two reproductive seasons (2004 and 2005). Gametogenesis commenced for females at a water temperature of 21°C, the lowest water temperature of the year. Spermatogenesis occurred above 22.5°C with sperm asynchronously developed and released from August or September to October. Oocytes developed asynchronously from July to September, embryos from September to December, and larvae from November to December. Female reproduction terminated in December (after larval release) prior to the highest mean annual water temperature of 30°C in January. There was a significant (35%) decrease in female reproductive output in 2005 compared to 2004, as measured by the reproductive index (0.68 ± 0.12 female reproductive propagules mm−2 of mesohyl in 2005 compared with 1.05 ± 0.10 mm−2 in 2004). This corresponded with delayed oogenesis and spermatogenesis, and a shortened larval development cycle corresponding with a delayed minimum temperature (21°C) in August of 2005 compared with July 2004. Accordingly, the maximum percentage of the mesohyl occupied by female reproductive propagules (eggs, embryos and larvae) was also reduced by 60% in 2005 (overall mean of 13.04% in October 2004 compared with 5.35% in October 2005). However, the mean sizes of individual female propagules remained the same from year to year. Males in contrast, showed no overall difference in either reproductive index or percentage occupation of the mesohyl between 2004 and 2005. The lowered reproductive output (∼35%) of females of L. variabilis associated with delayed minimum water temperatures may have important implications for population reproductive success where oogenesis and spermatogenesis and larval release are cued by minimum and maximum water temperatures, respectively.

Low genetic structuring among Pericharax heteroraphis (Porifera: Calcarea) populations from the Great Barrier Reef (Australia), revealed by analysis of nrDNA and nuclear intron sequences

A new nuclear marker system for sponges, the second intron of the nuclear ATP synthetase beta subunit gene (ATPSbeta-iII), was analysed together with nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences aiming to uncover phylogeographic patterns of the coral reef sponge Pericharax heteroraphis in the south-west Pacific, focussing on the Great Barrier Reef (GBR). Variation among ITS sequences was low (<1.1% p-distance), in contrast to ATPSbeta-iII (<8.3% p-distance). Single-Stranded Conformation Polymorphism (SSCP) analysis proved to be an effective tool for phasing ATPSbeta-iII alleles of 292 bp length. Although sample sizes were limited for most populations and these results await corroboration by an extended sampling regime, a past population subdivision with subsequent range expansion was indicated by a ‘dumb-bell’ shaped statistical parsimony network of GBR ATPSbeta-iII alleles. Although no clear phylogeographic break was discovered on the GBR, the northern GBR was genetically differentiated from the central/southern GBR and Queensland Plateau, based on significant pairwise F st values (0.137–0.275 and p ≤ 0.05) of pooled regional populations. The ATPSbeta-iII used in this study outperformed the frequently employed nrDNA ITS and might also turn out to be useful for phylogeographic studies of other coral reef taxa.

A NEW, LARGE, LATE PLEISTOCENE DEMOSPONGE FROM SOUTHEASTERN FLORIDA

Spectacular exposures of large, upright, vase- to barrel-shaped, late Pleistocene sponges are dramatically exposed as part of the Miami Limestone along margins of the C-100C Canal in east-central Miami-Dade County, southeastern Florida. The discovery of this sponge reef by K. J. Cunningham was made in 2004, during a routine drive across the bridge above the C-100C Canal on S.W. 97th Avenue in Miami-Dade County, southeastern Florida. A second location, where comparable sponges are exposed in walls of a burrow lake, was also discovered by K. J. Cunningham in 2004 upon visiting the site after personal communication with L. Noblick, Montgomery Botanical Center, and S. Zona, Fairchild Tropical Botanic Garden, about similarly shaped geologic structures. Subsequently, the C-100C Canal location was documented and some of the sponges were collected and thin sections and samples were sent to J. K. Rigby for examination and evaluation. This paper, on the description and possible taxonomy of the sponges, is a result of that joint effort. Sponges reported here were collected from banks of Canal C-100C, of the Cutler Drain System, near the bridge of S.W. 97th Avenue, which crosses over the canal. That site is at 25°38′58.9″ North Latitude, and 80°21′02.3″ West Longitude, referenced to the North American Datum of 1983. At this location the sponge reef is exposed on the north bank of the canal. Completion of construction of the bridge on S.W. 97th Avenue over the canal was in 1966 so, presumably, the sponge reef has been exposed there for almost 40 years, at least. Unfortunately, detailed coordinate positions of all the sponge samples were not taken as they were collected. However, they would have come from only a few meters east of the SW 97th Avenue bridge, on either the northern or southern bank of the canal, or up to 250 …

Abiotic factors control sponge ecology in Florida mangroves

It is well documented that biotic effects play an important role in determining the distri- bution and abundance of sponges on Caribbean coral reefs: predation by fishes restricts some species to refugia, and allelopathic interactions result in a competitive hierarchy for space. Recently, it has been proposed that biotic effects are similarly important in mangrove habitats; specifically, that sponges common to mangrove habitats grow fast and rapidly out-compete species otherwise found in reef habitats for prop-root space. To begin to test this hypothesis, 9 species of common reef sponges were transplanted to prop roots at 3 mangrove sponge sites with different flow regimes (as measured with plaster clods) near Key Largo, Florida. Reef sponges transplanted to all 3 mangrove sites declined in health and died, most within 60 d, while those back-transplanted to a reef site survived and grew. Reef sponge decline was most rapid at sites with the lowest flow during periods of the month with the least tidal flux, when a combination of freshwater input, high temperature and turbid- ity were likely responsible for their demise. We conclude that some mangrove sites that support sponge growth do so because the species found there can endure the abiotic conditions of mangrove habitats, and not because of competitive dominance over species otherwise found on the reef.

Contrasting patterns of species and functional composition of coral reef sponge assemblages

There is mounting interest in studying the relationship between functional (FD) and species diversity (SD) in order to understand ecosystem functioning and develop effective measures to protect communities. Several studies have found strong positive correlations between SD and FD and in this study I used sponges to investigate this relationship and compare it with that of functional and species composition (FC and SC respectively). This study was conducted at 2 coral reef eco- systems in SE Sulawesi, Indonesia, which experience different sedimentation levels. Sponges fulfil a number of key functional roles on coral reefs, and, as many can be associated with specific morpho- logies, the measurement of morphological diversity (MD) should provide an approximation of FD. Previous sponge research has shown a strong correlation between MD and SD, and I hypothesise that spatial variation in MD, FD, SD and assemblage composition (FC and SC) will be determined by the same environmental gradients. Univariate measures of SD, MD and FD showed strong correlations, but not for multivariate data. Although different morphological assemblages (MC) were found at the 2 sites and between depth intervals, which correlated with SC data, no significant correlation was reported with FC data. FC was strongly influenced by depth, but not site, demonstrating that factors attributable to depth (e.g. light and wave action reduction) were more important in controlling FC, which contrasts with SC and MC patterns that were determined by sedimentation levels (i.e. be- tween site differences). Although sponges fulfilled several functional roles, most were performed by a large number of morphologies/species, indicating a high level of intra-phyletic functional redun- dancy. The data from this study asserts that the factors responsible for spatial variation in SC may not always reflect those responsible for FC patterns, which has widespread implications for marine con- servation, environmental management and Marine Protected Area (MPA) ecology. Environmental managers need to be aware of the factors controlling both SC and FC to ensure the protection of both biodiversity and ecosystem functioning.

Sexual reproduction of the brooding sponge Rhopaloeides odorabile

Sexual reproduction of Rhopaloeides odorabile, a common Great Barrier Reef sponge, was quantified using histological sections from samples collected over two reproductive seasons. Rhopaloeides odorabile is viviparous and gonochoristic with a male biased sex ratio (2.5:1). Commencement and cessation of gametogenesis coincides with rising and falling sea surface temperatures (≈24–29°C). Spermatogenesis occurs from October until January. Females initiate oogenesis in September with the asynchronous development of oocytes, embryos and larvae occurring within the brood chambers. A larval release period of 5–6 weeks occurs during January and February. The minimum size of reproductive individuals was 176 cm3 for females and 192 cm3 for males. The total reproductive output for both sexes shows a positive correlation with size. A relative reproductive output index quantified the maximum reproductive investment at approximately 1 and 3% of the total choanoderm for females and males, respectively, which represents a lower range of reproduction in comparison to other viviparous sponges. Low reproductive output in R. odorabile may be offset by an extended spawning period, alleviating the risk of releasing larvae in potentially adverse conditions via one synchronised spawning event and increasing overall larval survival.

Reef-Bank Features and Their Constraint to Reservoirs of Natural Gas, from Permian Changxing Formation to Triassic Feixianguan Formation in Daxian-Xuanhan Area of Sichuan Province, South China

Detail studies of the seismic section and certain wells, such as the Puguang-2, the Puguang-6, and the Maoba Wells, demonstrate that the reef facies from the Permian Changxing Formation to the Triassic Feixianguan Formation are expressed as the lens with medium-strong changing swings and chaotic images in the seismic section. The reef facies is made up of gray limestones and dolomites of both baffling sponge reef and the frame sponge reef. Moreover, the bank facies from the Permian Changxing Formation to the Triassic Feixianguan Formation is represented as the lens with medium-strong changing swings and discontinuity images in the seismic section, which is made up of several petrologic types, that is, the French gray thick-bedded to massive sparitic oolitic dolomite, the sparitic gravel-oolitic dolomite, the sparitic pisolitic-oolitic dolomite, the sparitic bioclastic dolomite, and the sparitic dolarenite. Both the reef facies and the bank facies concomitant are developed and distributed in space along the platform margin, which form a special reef-bank facies zone. This facies zone controls the petrological features, the reservoir qualities, and the spatial distribution of the reservoirs of natural gas in the Daxian-Xuanhan area.

First documentation of tidal-channel sponge biostromes (upper Pleistocene, southeastern Florida)

Sponges are not a common principal component of Cenozoic reefs and are more typically dominant in deep-water and/or cold-water localities. Here we report the discovery of extensive upper Pleistocene shallow-marine, tropical sponge biostromes from the Miami Limestone of southeastern Florida built by a new ceractinomorph demosponge. These upright, barrel- to vase-shaped sponges occur in monospecific aggregations constructed within the tidal channels of an oolitic tidal-bar belt similar to modern examples on the Great Bahama Bank. The biostromes appear to have a ribbon-like geometry, with densely spaced sponges populating a paleochannel along a 3.5 km extent in the most lengthy biostrome. These are very large (as high as 2 m and 1.8 m in diameter), particularly well-preserved calcified sponges with walls as hard as concrete. Quartz grains are the most common particles agglutinated in the structure of the sponge walls. Where exposed, sediment fill between the sponges is commonly a highly burrowed or cross-bedded ooid-bearing grainstone and, locally, quartz sand. It is postulated that the dense, localized distribution of these particular sponges was due to a slight edge over competitors for food or energy supply and space in a stressed environment of tidal-influenced salinity and nutrient changes, strong currents, and frequently shifting submarine sand dunes. To our knowledge, this represents the first documentation of sponge biostromes composed of very large upright sponges within high-energy tidal channels between ooid shoals. The remarkably well-preserved accumulations provide an alternative example of sponge reefs for comparative paleoenvironmental studies.

Cryptofaunal Associates of Spirastrella inconstans (Dendy) and S. inconstans var. digitata (Dendy), the Coral Reef Sponges of Palk Bay

Cryptofaunal Associates of Spirastrella inconstans (Dendy) and S. inconstans var. digitata (Dendy), the Coral Reef Sponges of Palk Bay

High-frequency palaeoenvironmental fluctuations recorded in Jurassic coral- and sponge-microbialite bioconstructions

During the Jurassic, coral and sponge reefs were particularly widespread along the northwestern Tethys. These bioconstructions occurred from shallow- to deep-shelf settings, in pure carbonate, carbonate-dominated or clay-rich mixed carbonate-siliciclastic sedimentary contexts. According to the depositional environment, the amount of microbialites strongly fluctuates, to form up to 70% of the reef volume. This study focuses on bioconstructions where microbialites constitute at least 15% of the reef volume. Analysis of the close relationships between the reef structures and the stacking pattern of laterally-deposited sediments reveals analogous architectures and growth modes between coral- and sponge-microbialite bioconstructions. Firstly, corals or sponges erected a primary framework more or less projected above the sea floor (constratal or superstratal growth fabrics). Contemporaneously, a thin microbialite layer encrusted the local dead parts of corals or sponges. In a second stage, microbialites largely developed and entirely covered the reef surface, becoming the main reef builders. The whole development of coral- and sponge-microbialite reefs corresponds to a ‘low-frequency reef-growth phase’. These bioconstructions also display surfaces of reef growth interruption delimiting ‘medium-frequency reef-growth phases’. They include several ‘high-frequency reef-growth phases’ (or elementary units) corresponding to coral or sponge frameworks plus microbialite crusts. At the scale of the elementary unit, microbialites are interpreted to reflect nutrient-richer conditions and developed to the detriment of phototrophic-, mixed- or heterotrophic-dominated assemblages of corals or sponges. The development of Jurassic coral and sponge bioconstructions was punctuated by high-frequency (millennial time-scale) ecological crises during which microbialites occurred at the reef surface. Such ecological shifts from skeletal reef metazoans (i.e. corals or sponges) to microbialite crusts were recorded whatever the palaeogeographical position (shallow-proximal platform or deep-distal shelf) along the northwestern Tethys margin. Three main orders of climatic oscillations, correlated to the ‘high-, medium- and low-frequency reef-growth phases’, could have directly regulated the amount of terrigenous materials and nutrients delivered to the ocean, which in turn controlled platform carbonate production and accumulation, as well as reef development.

Depth-specific differences in growth of the reef sponge Callyspongia vaginalis: role of bottom-up effects

Callyspongia vaginalis, a common reef sponge in the Florida Keys, USA, exhibits depth- specific differences in bioenergetics and growth that are a function of food availability. We measured several physiological parameters in situ to construct the bioenergetic budgets of sponges living in deep and shallow waters. Respiration rates were measured in a recirculating flow respirometer and pumping rates were measured by filming dye ejected from sponge oscula. In addition, inhalent and exhalent water sampled from around sponge colonies at both depths was analyzed using flow cyto- metry to quantify the concentration and clearance rates of picoplankton. These parameters were used to construct an energetic budget for sponges from each depth and revealed that the scope for growth was substantially greater for deep sponges compared to shallow sponges. The greater scope for growth of deep sponges is likely due to the greater abundance of picoplankton in the deep versus shallow habitat. Both naturally occurring sponges and those used in a reciprocal transplant experiment between 12 and 25 m exhibited significantly greater growth in the deep than the shallow habitat. Hence, bottom-up forcing in the form of increased food availability may be of principal importance to the growth and physiological ecology of suspension-feeding sponges.

Retention efficiencies of the coral reef sponges Aplysina lacunosa, Callyspongia vaginalis and Niphates digitalis determined by Coulter counter and plate culture analysis

Sponges are the dominant organisms on many coral reefs and through feeding they may greatly reduce the concentration of suspended food particles. Retention efficiencies of the tubular sponges Aplysina lacunosa, Callyspongia vaginalis and Niphates digitalis were examined on a coral reef located in the Florida Keys. Replicate ambient and exhalant water samples were collected in situ from individuals of each species and analysed using two methods. Retention efficiencies of suspended particles (0.75–18 µm) examined using Coulter counter analysis were similar among the three sponge species, averaging 86%. For all sponges, particle retention decreased as particle size increased from 0.7 to 18 µm. Water samples plated on to Marine Agar produced 54 microbial types. Retention efficiencies of culturable microbes were similar among the three species, averaging 82%. This study suggests that the coral reef sponges Aplysina lacunosa, Callyspongia vaginalis and Niphates digitalis play an important role in the transfer of energy between the pelagic and benthic environments.