María Jesús Uriz

Decline in Mesozoic reef-building sponges explained by silicon limitation

Several unrelated clades of siliceous sponges proliferated on the shelves of the Jurassic Tethys Sea, becoming prominent builders in reefs and near-shore mounds. Many of these builders are characterized by massive, rock-like skeletons made of spicules with a characteristic terminal hypersilicification. Such hypertrophied spicules are generically known as desmas, irrespective of their phylogenetic origin. Desma-bearing sponges virtually disappeared from reefs and other neritic environments during the Cretaceous and the Early Tertiary, but have subsisted in relict populations in deeper, bathyal waters. The causes of the decline and bathymetric shift of these sponges remain obscure. Here we show experimentally that the concentration of silicic acid in seawater modulates the phenotypic expression of the various spicule types genetically available in a sponge species. We also show that the concentration of this nutrient in Recent surface waters is insufficient for this species to secrete its desmas. These findings indicate that silicon limitation, probably aggravated in shallow waters by the diatom burst around the Cretaceous–Tertiary boundary, may have forced neritic sponges with desmas to either lighten their skeletons or move to deeper, silicon-rich environments.

Antimicrobial activity and surface bacterial film in marine sponges

The antimicrobial activity of three sponge species was tested against marine benthic bacteria and the presence of epibiotic bacteria on their surfaces was investigated. The aim of the present study was to determine whether there is a correlation between antimicrobial activities and the presence of a bacterial film. Seven benthic bacterial strains were isolated from the vicinity of the sponges and used as assay organisms. Gram-positive and Gram-negative bacteria were equally affected by all the sponge extracts. The encrusting sponge Crambe crambe featured the strongest antimicrobial activity in the assays and no bacteria were found on its surface. The other two sponges, Ircinia fasciculata and Spongia officinalis, featured lower antimicrobial activity than C. crambe and the number of bacteria found on their surfaces was of the same order of magnitude as that found on immersed glass slides used as controls. It was concluded that antimicrobial activities detected in laboratory assays were effective as mechanisms to combat microfouling in only some cases, and other possible interpretations are considered.

MULTIPLE FUNCTIONS FOR SECONDARY METABOLITES IN ENCRUSTING MARINE INVERTEBRATES

We used three chemical fractions (spanning a wide range of polarities) from the extracts of four marine invertebrates, the spongesCrambe crambe andHemimycale columella and the ascidiansCystodytes dellechiajei andPolysyncraton lacazei, to test inhibition of cell division, photosynthesis, and settlement. We used assay organisms from the same habitat, seeking to determine whether a species may display diverse, ecologically relevant bioac-tivities and, if so, whether the same types of compound may be responsible for such activities. Cell division was strongly inhibited by the spongeC. crambe. A dichloromethane fraction fromC. crambe prevented development of sea urchinParacentrotus lividus eggs at a concentration of 10 μg/ml, as did the butanolic fraction, but at higher concentrations (50 and 100 μg/ml). At 50 μg/ml, the aqueous fraction ofC. crambe allowed cell division but prevented eggs from developing beyond the gastrula stage. Similar results were recorded with the dichloromethane fraction ofP. lacazei and from the aqueous fraction ofH. columella. Photosynthesis was unaffected by any of the species at 50 μg/ml. Larval settlement was inhibited by one or another fraction from the four species surveyed at a concentration of 50 μg/ml, althoughC. crambe exhibited the greatest amount of activity. We therefore found that various fractions displayed the same type of bioactivity, while compounds from the same fraction were responsible for multiple activities, suggesting that secondary metabolites are multiple-purpose tools in nature, which is relevant to our understanding of species ecology and evolution. Moreover, results showed that the assessment of the role of chemical compounds is significantly influenced by the assay organism, fractionation procedure, concentration, and duration of experiments. All these factors should be carefully considered when testing ecological hypotheses of the roles of chemically-mediated bioactivities.

Biological Activity of Extracts from Some Mediterranean Macrophytes

Seventy one species of marine macrophytes from the Central Mediterranean have been screened for the production of antibacterial, antifungal, antiviral, cytotoxic and antimitotic compounds. Sixty five of the species displayed some kind of activity and most of them were active on more than one organism or cell tested. Antifungal activity was the most widespread (70% of the plants), whilst the incidence of antibacterial activity was extraordinarily low (6% of the plants). Of the plants tested 21% showed antiviral activity, 35% were cytotoxic and nearly 50% had antimitotic properties. The maximum level of activity was found among the Chlorophyfa; some members of the Bryopsidales (Flabellia petiolata, Caulerpa prolifera, Halimeda tuna) were the most active species. Most of the dominant species in Mediterranean phytobenthic communities (Corallina elongata, Lithophyllurn lichenoides, Phyllophora crispa, Cystoseira spp., Halopteris spp., Codium spp., Halimeda tuna, Valonia utricularis, Posidonia oceanica, Zostera noltii and Cyrnodocea nodosa) exhibited strong antifungal properties.

Sponge Mass Mortalities in a Warming Mediterranean Sea: Are Cyanobacteria-Harboring Species Worse Off?

Mass mortality events are increasing dramatically in all coastal marine environments. Determining the underlying causes of mass mortality events has proven difficult in the past because of the lack of prior quantitative data on populations and environmental variables. Four-year surveys of two shallow-water sponge species, Ircinia fasciculata and Sarcotragus spinosulum, were carried out in the western Mediterranean Sea. These surveys provided evidence of two severe sponge die-offs (total mortality ranging from 80 to 95% of specimens) occurring in the summers of 2008 and 2009. These events primarily affected I. fasciculata, which hosts both phototrophic and heterotrophic microsymbionts, while they did not affect S. spinosulum, which harbors only heterotrophic bacteria. We observed a significant positive correlation between the percentage of injured I. fasciculata specimens and exposure time to elevated temperature conditions in all populations, suggesting a key role of temperature in triggering mortality events. A comparative ultrastructural study of injured and healthy I. fasciculata specimens showed that cyanobacteria disappeared from injured specimens, which suggests that cyanobacterial decay could be involved in I. fasciculata mortality. A laboratory experiment confirmed that the cyanobacteria harbored by I. fasciculata displayed a significant reduction in photosynthetic efficiency in the highest temperature treatment. The sponge disease reported here led to a severe decrease in the abundance of the surveyed populations. It represents one of the most dramatic mass mortality events to date in the Mediterranean Sea.

Sexual propagation by sponge fragments

Habitat fragmentation means that many species occur in discrete populations, so it is important for sessile species to colonize new areas. It has not been clear how sponges whose larvae disperse over short distances achieve this. Fragments may break off sponges as a result of physical and biological disturbance and are then dispersed by currents and recruited as independent individuals or colonies,. Local populations are expected to have high genetic relatedness as a result, but most sponge populations have high levels of genetic variability,. We suggest that this discrepancy results from an interaction between fragmentation and sexual reproduction.

Distribution of brominated compounds within the sponge Aplysina aerophoba: coupling of X-ray microanalysis with cryofixation techniques.

Abstract. The major secondary metabolites of the sponge Aplysina aerophoba are brominated compounds. X-ray energy dispersive microanalysis was therefore used to locate secondary metabolites via the Br signal in energy emission spectra from sponge sections. To test the reliability of this method in the face of the loss or redistribution of metabolites during processing, we compared the results obtained by conventional aldehyde fixation with those obtained by cryofixation and cryosubstitution with and without cryoembedding. Bromine appeared to be concentrated in two sponge structures, viz. fibres and spherulous cells, when cryofixed material was examined. However, X-ray microanalysis failed to demonstrate the presence of bromine in spherulous cells in chemically fixed samples, showing the need for cryotechniques to avoid the loss of compounds. Cryofixation plus cryosubstitution methods performed best regarding structural preservation and the immobilization of metabolites. The presence of bromine in the spherulous cells suggests that this cell type is the producer of the secondary metabolites, as described for other sponge species. Nevertheless, the presence of bromine in sponge fibres indicates that they can accumulate metabolic substances, although we have been unable to assess whether the chemicals are in their original form or in a modified state within the fibres. A. aerophoba has both bacterial and cyanobacterial symbionts in its mesohyl; the absence of brominated compounds in them contrasts with previous findings in other sponges with prokaryote symbionts.

Silica deposition in Demosponges: spiculogenesis in Crambe crambe.

Abstract. Transmission electron-microscopy images coupled with dispersive X-ray analysis of the species Crambe crambe have provided information on the process of silica deposition in Demosponges. Sclerocytes (megasclerocytes) lie close to spicules or surround them at different stages of growth by means of long thin enveloping pseudopodia. Axial filaments occur free in the mesohyl, in close contact with sclerocytes, and are triangular in cross section, with an internal silicified core. The unit-type membrane surrounding the growing spicule coalesces with the plasmalemma. The axial filament of a growing spicule and that of a mature spicule contain 50%–70% Si and 30%–40% Si relative to that contained in the spicule wall, respectively. The extracellular space between the sclerocyte and the growing spicule contains 50%–65%. Mitochondria, vesicles and dense inclusions of sclerocytes exhibit less than 10%. The cytoplasm close to the growing spicule and that far from the growing spicule contain up to 50% and less than 10%, respectively. No Si has been detected in other parts of the sponge. The megascleres are formed extracellularly. Once the axial filament is extruded to the mesohyl, silicification is accomplished in an extracellular space formed by the enveloping pseudopodia of the sclerocyte. Si deposition starts at regularly distributed sites along the axial filament; this may be related to the highly hydroxylated zones of the silicatein-α protein. Si is concentrated in the cytoplasm of the sclerocyte close to the plasmalemma that surrounds the growing spicules. Orthosilicic acid seems to be pumped, both from the mesohyl to the sclerocyte and from the sclerocyte to the extra-cellular pocket containing the growing spicule, via the plasmalemma.

Clearance rates and aquiferous systems in two sponges with contrasting life-history strategies

The clearance rates and microarchitecture of the aquiferous systems of two sympatric sponge species, Crambe crambe (Schmidt) and Dysidea avara (Schmidt), are compared. We performed a filtration experiment with fluorescent latex microspheres with diameters ranging from 0.2 to 4 μm. Microsphere concentration in the water was measured by flow cytometry, and the particles ingested were detected within the sponge cells through confocal microscopy. The two species studied showed contrasting life-history strategies, reflected by different structural organizations of the aquiferous system, which in turn correlate with clearance rates measured in the filtration experiment. The species with higher growth and regeneration rates also showed the highest clearance rates at all particle sizes assayed and displayed larger ostia, a thicker choanosome layer, and larger flagellate chambers and choanocytes. The particle size most efficiently retained by both species was 1 μm, and maximal clearance rates were obtained in all cases after 15 min of incubation. The sites of particle capture were the choanocytes, which retained small particles (0.2, 0.5, and 1 μm) and, in the case of D. avara, also 4 μm particles. The pinacocytes captured the largest particles assayed (6 μm) and, in the case of C. crambe, also retained particles of the smaller sizes. It is concluded that there is an adaptive interspecific variation in structure and efficiency of the filtering systems in sponges which correlates with diverse biological strategies. The clearance rates obtained, coupled with the abundance of sponge populations in the community studied, point to a significant grazing impact of sponges on the picoplankton of the area. J. Exp. Zool. 278:22–36, 1997.

Chemically-mediated interactions in benthic organisms: the chemical ecology of Crambe crambe (Porifera, Poecilosclerida)

We studied the chemically-mediated interactions of the encrusting sponge Crambe crambe, one of the most toxic and widespread species in rocky sublittoral habitats in the Northwestern Mediterranean. Guanidine alkaloids accounted for C. crambe’s toxicity, which seems to have multiple functions in nature, as evidence has been found for antifouling, antipredation, and space competition roles.