Sponge-feeding fishes of the West Indies

In an analysis of the stomach contents of 212 species of West Indian reef and inshore fishes, sponge remains were found in 21 species. In eleven of these, sponges comprised 6% or more of the stomach contents; it is assumed that these fishes feed intentionally on sponges. Sponges comprise over 95% of the food of angelfishes of the genus Holacanthus, over 70% of the food of species of the related genus Pomacanthus, and more than 85% of the food of the filefish, Cantherhines macrocerus. Lesser quantities of sponges are ingested by the remaining fish species. Fishes that feed on sponges belong to highly specialized teleost families, suggesting that this habit has evolved in geologically late time. The small number of fish species that concentrate on sponges as food suggests that the defensive characters of sponges—mineralized sclerites, noxious chemical substances, and tough fibrous components—are highly effective in discouraging predation. The two sponges most frequently eaten by fishes have a low percentage of siliceous spicules relative to organic matter, but among the 20 next most frequently consumed species no striking correlation occurs with respect to spicule content. Color and form of the sponge show no special correlation with frequency of occurrence in fish stomachs. Three species of fishes appear to concentrate on one species of sponge, but in these cases over 60% of the food taken consists of a variety of other organisms. Those fishes, more than half of whose diet consists of sponges, tend to sample a wide variety of species. No strong evidence is provided by our data that fish predation is a significant factor in limiting sponge distribution in the West Indian region.     

Evidence for morphology-induced sediment settlement prevention on the tubular sponge<Emphasis Type="Italic"> Haliclona urceolus</Emphasis>

Several mechanisms are known to assist the survival of sponges in highly sedimented environments. This study considers the potential of sponge morphology and the positioning of exhalant water jets (through the osculum) in the adaptation of Haliclona urceolus to highly sedimented habitats. This sponge is cylindrical with an apical osculum, which is common in sedimented subtidal habitats at Lough Hyne Marine Nature Reserve, Cork, Ireland. Fifteen sponges were collected, preserved (killed with the structure and morphology maintained) and then replaced in a high sediment environment next to a living specimen (at 24 m). After 5 days, the sediment settled on both living and preserved sponges was collected and dried. No sediment was collected from living sponges, while preserved specimens had considerable amounts of settled sediment on their surfaces. The amount of sediment collected on these preserved specimens was significantly linearly correlated with sponge dry weight, maximum diameter and oscula width (R²>0.70, P<0.001, df=14). Observations of flow direction (using coloured dye) through H. urceolus showed that water is drawn into the sponge on its underside and exits via a large vertically pointing osculum. Sponge morphologies (shape) have often been considered as a means of passive adaptation to a number of different environmental parameters with oscula position enabling entrained flow through the sponge in high flow conditions. However, this study shows how the combination of sponge morphology (tubular shape) and positioning of the osculum may enable H. urceolus to survive in highly sedimented environments. Similar mechanisms may also aid the survival of some deep-water sponge species with similar morphologies.Communicated by J.P. Thorpe, Port Erin     

Reproductive strategies of Mycalecontarenii (Porifera: Demospongiae)

The sexual and asexual phases of the reproductive cycle of the sponge Mycalecontarenii (Martens, 1824) were studied from samples collected over a period of 2 years (June 1994 to May 1996) in a Mediterranean coastal basin (Porto Cesareo, southwestern Apulia). The species is viviparous; year round it shows a discontinuous oocyte production. No males were found, possibly owing to the very short period of spermatogenesis. M.␣contarenii produces asexual buds during autumn and winter, and this process seems to be related to changes in water temperature. Even though, at present, we cannot evaluate the incidence of larval recruitment, we postulate that asexual reproduction in M.contarenii plays a crucial role in maintaining the sponge population. Received: 8 July 1997 / Accepted: 5 November 1997     

Photoadaptation of zooxanthellae in the sponge Cliona vastifica from the Red Sea, as measured in situ

In the Red Sea, the zooxanthellate sponge Cliona vastifica (Hancock) is mainly present at >15 m depth or in shaded areas. To test whether its scarcity in unshaded areas of shallower waters is linked to the functional inefficiency of its photosymbionts at high irradiances, sponges were transferred from 30 m to a six times higher light regime at 12 m depth, and then returned to their original location. During this time, photosynthetic responses to irradiance were measured as rapid light curves (RLCs) in situ by pulse amplitude modulated (PAM) fluorometry using a portable underwater device, and samples were taken for microscopic determinations of zooxanthellar abundance. The zooxanthellae harboured by this sponge adapted to the higher irradiance at 12 m by increasing both their light saturation points and relative photosynthetic electron transport rates (ETRs). The ETRs at light saturation increased almost fourfold within 15–20 days of transfer to the shallower water, and decreased back to almost their original values after the sponges were returned to 30 m depth. This, as well as the fact that the photosynthetic light responses within an individual sponge were in accordance with the irradiance incident to specific surfaces, shows that these photosymbionts are highly adaptable to various irradiances. There was no significant change in the number of zooxanthellae per sponge area throughout these experiments, and the different photosynthetic responses were likely due to adaptations of the photosynthetic apparatus within each zooxanthella. In conclusion, it seems that parameters other than the hypothesised inability of the photosymbionts to adapt adequately to high light conditions are the cause of C. vastifica's rareness in unshaded shallow areas of the Red Sea. Received: 25 April 2000 / Accepted: 13 October 2000     

Cellular localisation of secondary metabolites isolated from the Caribbean sponge <Emphasis Type="Italic">Plakortis simplex</Emphasis>

The Caribbean sponge, Plakortis simplex, is known to contain a large array of secondary metabolites, including the antimalarial polyketide plakortin, several unusual glycolipids, and some hopanoids, which closely resemble typical bacterial metabolites. The hypothesis that they could be products of bacterial metabolism was tested by localizing specific metabolites in cells using physical separation of sponge cells, bacterial symbionts and supernatant by differential centrifugation. The obtained fractions were analysed separately for the typical P. simplex metabolites by NMR and mass spectrometry, and most of them were shown to be present in the bacterial cells but not in the sponge cells. In addition, PCR screening showed that the biosynthetic pathway for glycosphingolipids was present in the bacterial cells. Isolation of a Sphingomonas strain PS193 from P. simplex and subsequent glycosphingolipid analysis resulted in the detection of a known glycosphingolipid, GSL-1, that did, however, not match the glycosphingolipid profile of P. simplex. Therefore, it is unlikely that Sphingomonas strain PS193 is an abundant member of the microbial community associated with P. simplex. Other glycosphingolipid producing bacteria in P. simplex remain to be identified. In conclusion, this study provides experimental evidence that the glycolipids and hopanoids and possibly also the polyketide plakortin are produced by microbial symbionts rather than the sponge from which the metabolites were originally isolated.     

Sponge-specific bacterial symbionts in the Caribbean sponge, Chondrilla nucula (Demospongiae, Chondrosida)

Marine sponges harbor dense and highly diverse bacterial communities, and some percentage of the microflora appears to be specialized for the sponge habitat. Bacterial diversity was examined in Chondrilla nucula Schmidt to test the hypothesis that some subset of sponge symbiont communities is highly similar regardless of the species of host or habitat requirements of the host. C. nucula was collected from a mangrove channel on Lower Matcumbe Key in the Florida Keys (25°53′N; 80°42′W) in August 1999. Domain-specific universal bacterial primers were used to amplify the 16S rDNA gene from genomic DNA that had been extracted from sponges and the surrounding water. An RFLP technique was used to assess diversity of sponge-associated and environmental bacterial communities. The clone library from C. nucula contained 21 operational taxonomic units (OTUs). None of the 53 OTUs from adjacent water samples were found in the C. nucula library indicating that a distinct community was present in the sponge. Sequence analysis indicated that C. nucula harbors a microbial community as diverse as the microbes from other sponges in different habitats around the world. Phylogenetic analysis placed several C. nucula clones in clades dominated by bacteria that appear to be sponge specialists (e.g., Acidobacteria, Bacteroidetes, and Cyanobacteria). Proportional representation of major bacterial taxonomic groups represented in symbiont communities was compared as a function of geographic location of sponge hosts. This study supports the hypothesis that sponges from different oceans existing in dissimilar habitats harbor closely related bacteria that are distinct from other bacterial lineages and appear specialized for residing within sponges.     

Phenotypic plasticity in a mutualistic association between the sponge Haliclona caerulea and the calcareous macroalga Jania adherens induced by transplanting experiments. I: morphological responses of the sponge

The mutualistic association between the sponge Haliclona caerulea and the calcareous red macroalga Jania adherens is conspicuous on shallow rocky regions of Mazatlán Bay (eastern tropical Pacific, Mexico). Transplanting experiments were carried out to examine the morphological responses of the association to an environmental depth gradient. Simultaneously, we conducted caging experiments to examine the effects of predation (mainly by angelfishes) on association morphology. For this, we transplanted specimens of the association from a control area at 3 m depth to depths of 1 and 5 m, and measured the morphological responses in the association (macro- and microstructure) from the three sites before and after 103 days. The association had the capacity to adjust both macro and micromorphologically, and both external morphology and body structure changed significantly with depth. The specimens grown at 1 m developed a larger surface area of attachment, higher organic density and higher inorganic content than the control specimens at 3 m, and the organisms grown at 5 m depth. We also detected significant differences in the aquiferous system of the sponge, which developed smaller and more numerous oscula at 1 m than at 5 m depth. These differences seem to be consistent with the wave movement as one of the main regulatory factors of the morphology of the association. However, the spicules from H. caerulea were most slender in shallow water, which is not consistent with increasing robustness in the face of greater wave force. The algal skeleton supplied up to 27% of the total inorganic structure of the association; thus, algal contribution significantly reduces the energy costs of spicule production, specifically under high wave exposure, when H. caerulea requires structural reinforcement relative to organic content. The contribution of the sponge to the association (as ratio Si to CaCO₃) increased significantly from 3 to 5 m (12% in the uncaged specimens and 22% in the caged specimens), showing that the mutualistic relationship decreases with depth. The production of sponge branches in caged individuals was the most notable difference from uncaged morphs, which could suggest the effect of predators like angelfishes. However, branches could also be a response to the reduction in water movement and irradiance inside the cages. Sponges are known to show morphological acclimation in response to habitat variation, but this is the first study to show it in a sponge living in association with a macroalga.     

Microbial associations in sponges. II. Numerical analysis of sponge and water bacterial populations

Three taxonomically distant sponges Pericharax heteroraphis, Jaspis stellifera and Neofibularia irata contain phenotypically similar bacterial symbionts which differ from bacteria in the ambient water. These symbionts are predominant in the sponges and were detected after computer analysis of 526 heterotrophic bacterial strains tested for 76 characters. These facultative anaerobic symbionts metabolize a wide range of compounds and may be important in removing waste products while the sponges are not circulating water. The bacteria produce sticky-mucoid colonies and thus would contribute to sponge structural rigidity. The fourth sponge Ircinia wistarii contains a mixed aerobic population similar to that in the ambient water. The majority of the bacteria are located around the inhalant canals, facilitating the uptake of dissolved organic matter and oxygen from the incoming water.     

The culturable microbial community of the Great Barrier Reef sponge Rhopaloeides odorabile is dominated by an α-Proteobacterium

The microbial community cultured from the marine sponge Rhopaloeides odorabile Thompson et al. is dominated by a single bacterium, designated strain NW001. Sequence analysis of 1212 bp of the16S rRNA gene of strain NW001 indicates that it is a member of the α-subgroup of the class Proteobacteria. The association between this bacterium and its host sponge was observed in healthy R. odorabile collected from six different reefs in the Great Barrier Reef representing a geographic distance of 460 km, and in four collections in different seasons in 1997–1998 at Davies Reef (18°49.6′S; 147°34.49′E). The proportion of colonies of strain NW001 in samples from R. odorabile, expressed as a percentage of the total heterotrophic bacterial colony count, showed no significant spatial (range: 81–98%) or temporal differences (range: 81–99%), although colony counts of strain NW001 varied by up to two orders of magnitude between reef sites and sampling periods. The location of strain NW001 within the sponge mesohyl was visualized by in situ hybridization, using fluorescently labeled probes based on the 16S rRNA gene sequence of this strain. Cells of strain NW001 surround the choanocyte chambers, suggesting that these bacteria may play a role in nutrient uptake by the sponge. The absence of strain NW001 from corresponding seawater samples indicates that it has a specific, intimate relationship with R. odorabile and is not being utilized as a food source. A unique cyanobacterium related to the genera Leptolyngbya and Plectonema was also isolated from R. odorabile and characterized by 16S rRNA gene sequencing. Received: 19 May 2000 / Accepted: 18 November 2000     

A brominated secondary metabolite synthesized by the cyanobacterial symbiont of a marine sponge and accumulation of the crystalline metabolite in the sponge tissue

The dictyoceratid marine sponge Dysidea herbacea (Keller, 1889) is common in shallow waters of the tropical Pacific Ocean. Polybrominated biphenyl ethers such as 2-(2,4-dibromophenyl)-4,6-dibromophenol (1) are characteristic secondary metabolites of some specimens of this sponge and may represent as much as 12% of the dry weight. We have found 1 to be deposited as conspicuous crystals throughout the sponge tissue. The dominant prokaryotic endosymbiont in the mesohyl of the sponge is a filamentous cyanobacterium (Oscillatoria spongeliae), although a vacuole-containing, heterotrophic bacterium is also present. The cyanobacteria were separated from the sponge cells and heterotrophic bacteria by flow cytometry. Coupled gas chromatography—mass spectrometry and proton nuclear magnetic-resonance spectroscopy revealed that the major brominated Compound 1 isolated from the intact symbiotic association is found in the cyanobacteria and not in the sponge cells or heterotrophic bacteria. This suggests that the production of the compound is due to the cyanobacterium, and not to the sponge or symbiotic heterotrophic bacteria, as had been suggested earlier.     

Biochemical genetic divergence and systematics in sponges of the genera Corticium and Oscarella (Demospongiae: Homoscleromorpha) in the Mediterranean Sea

The sponge sub-class Homoscleromorpha is generally considered to include just two families, the Oscarellidae (without spicules) and the Plakinidae (with simple spicules). In May 1990, an unusual sponge was found deep inside a submarine cave in the western Mediterranean Sea. On the basis of externally visible characters this sponge appeared indistinguishable from the common plakinid species Corticium candelabrum Schmidt, 1862. However, on closer examination in the laboratory the new sponge proved to be devoid of spicules. Therefore, despite great morphological similarities to C. candelabrum, the new sponge should, by taxonomic convention, have been placed in the Oscarellidae. On the basis of other criteria, the similarities to C. candelabrum were great and the new sponge was at first considered to be conspecific. Thus, the taxonomic position of the new sponge and its relationship to C. candelabrum are highly confusing. It could be an aspiculate morph of C. candelabrum, or a new and undescribed related species or, lacking spicules, it could justifiably be placed in a different family (Oscarellidae). The relationship of the new sponge to C. candelabrum and also to two species of Oscarella (Oscarellidae) was assessed by the use of enzyme electrophoresis to estimate genetic divergence between species. It was found that the new sponge was reproductively isolated from sympatric C. candelabrum, with 6 of 16 loci proving diagnostic. Thus it is clear that the new sponge belongs to a different biological species. Surprisingly it was also found that, although this new species was fairly closely related to C. candelabrum (level of genetic identity, I0.47), the two Oscarella species were similarly closely related to C. candelabrum (I0.31 to 0.41) and rather less closely to the new species (I0.17 to 0.28). Indeed from genetic identity estimates, O. tuberculata is more closely related to C. candelabrum than it is to O. lobularis. It is concluded that all homoscleromorph sponges should be placed in the single family Plakinidae.     

The encrusting spongeHalisarca laxus: population genetics and association with the ascidianPyura spinifera

The encrusting spongeHalisarca laxus forms a seemingly obligate association with the stalked solitary ascidianPyura spinifera. In 1991 we examined spatial variation and short-term temporal variation in this association at three neighbouring sites in southeastern Australia. This sponge dominated the surface of almost all the 500 individual ascidians examined, with mean cover usually exceeding 90%. This pattern was consistent among sites and throughout the year of the study. The domination of a small isolated patch of habitable substratum by a sponge is most unusual, given that they are regarded as relatively poor recruiters. To understand how this association might be maintained, we determined the underlying genotypic diversity of the sponge population using starch-gel electrophoresis.P. spinifera is a clump-forming ascidian and usually occurs in clumps of up to 22 individuals. Electrophoretic surveys, based on six variable allozyme loci, revealed that at a total of five plots within three neighbouring New South Wales populations, single sponge genotypes may cover entire ascidian clumps; although a clump sometimes played host to more than one sponge clone. Allele frequencies (averaged across four loci that appear to conform to Mendelian inheritance) showed little variation among populations (standardised genetic variance,F _ST=0.013). Nevertheless, sponge populations were genotypically diverse, with samples from 63 of 172 individual clumps displaying unique clonal genotypes. Moreover, multi-locus genotypic diversity within all sites approached the level expected for sexual reproduction with random mating. Taken together, these data imply thatH. laxus produces sexually-derived larvae that are at least moderately widelly dispersed. Given the relatively small size of the patches that this sponge inhabits, we also conclude that these larvae are good colonists and good spatial competitors on their ascidian hosts.     

Rapid tissue reduction and recovery in the sponge <Emphasis Type="Italic">Aplysinella</Emphasis> sp.

We observed a pronounced, yet reversible tissue reduction in the tropical sponge Aplysinella sp. under non-experimental conditions in its natural habitat, after transfer into seawater tanks, as well as after transplantation from deep to shallow water in the field. Tissue reduction resulted in the formation of small “reduction bodies” tightly attached to the sponge skeleton. Although volume loss and gain were substantial, both tissue reduction and regeneration were often remarkably rapid, occurring within few hours. Microscopic analysis of the reduction bodies revealed morphological similarities to previously described sponge primmorphs, with densely packed archaeocytes and spherulous cells enclosed by a thin layer of epithelial-like cells. Denaturing gradient gel electrophoresis (DGGE) revealed pronounced changes in the sponge-associated microbial community upon tissue reduction during laboratory and field experiments and following changes in ambient conditions after transplantation in the field. Generally, the microbial community associated with this sponge proved less stable, less abundant, and less diverse than those of other, previously investigated Verongid sponges. However, one single phylotype was consistently present in DGGE profiles of Aplysinella sp. This phylotype clustered with γ-proteobacterial sequences found previously in other sponge species of different taxonomic affiliations and geographic provenances, as well as in sponge larvae. No apparent changes in the total secondary metabolite content (per dry weight) occurred in Aplysinella sp. upon tissue reduction; however, comparative analysis of intact and reduced tissue suggested changes in the concentrations of two minor compounds. Besides being ecologically interesting, the tissue reduction phenomenon in Aplysinella sp. provides an experimentally manipulable system for studies on sponge/microbe symbioses. Moreover, it may prove useful as a model system to investigate molecular mechanisms of basic Metazoan traits in vivo, complementing the in vitro sponge primmorph system currently used in this context.     

Rapid tissue reduction and recovery in the sponge Aplysinella sp.

We observed a pronounced, yet reversible tissue reduction in the tropical sponge Aplysinella sp. under non-experimental conditions in its natural habitat, after transfer into seawater tanks, as well as after transplantation from deep to shallow water in the field. Tissue reduction resulted in the formation of small “reduction bodies” tightly attached to the sponge skeleton. Although volume loss and gain were substantial, both tissue reduction and regeneration were often remarkably rapid, occurring within few hours. Microscopic analysis of the reduction bodies revealed morphological similarities to previously described sponge primmorphs, with densely packed archaeocytes and spherulous cells enclosed by a thin layer of epithelial-like cells. Denaturing gradient gel electrophoresis (DGGE) revealed pronounced changes in the sponge-associated microbial community upon tissue reduction during laboratory and field experiments and following changes in ambient conditions after transplantation in the field. Generally, the microbial community associated with this sponge proved less stable, less abundant, and less diverse than those of other, previously investigated Verongid sponges. However, one single phylotype was consistently present in DGGE profiles of Aplysinella sp. This phylotype clustered with γ-proteobacterial sequences found previously in other sponge species of different taxonomic affiliations and geographic provenances, as well as in sponge larvae. No apparent changes in the total secondary metabolite content (per dry weight) occurred in Aplysinella sp. upon tissue reduction; however, comparative analysis of intact and reduced tissue suggested changes in the concentrations of two minor compounds. Besides being ecologically interesting, the tissue reduction phenomenon in Aplysinella sp. provides an experimentally manipulable system for studies on sponge/microbe symbioses. Moreover, it may prove useful as a model system to investigate molecular mechanisms of basic Metazoan traits in vivo, complementing the in vitro sponge primmorph system currently used in this context.     

Changes in morphology and physiology of an East Mediterranean sponge in different habitats

The sponge Tetilla sp. (Tetractinomorpha: Tetillidae) is a common species in the eastern Mediterranean. This sponge inhabits four different habitat types differing in wave impact and irradiance levels. Two of these habitats (a shallow cave and deep water) are characterized by relatively calm water, whereas the other two (shallow exposed site and tide pools) are in turbulent water with high energy flow. The present study examined the influence of physical (depth, illumination and water motion) and biotic factors on morphology, skeletal plasticity and reproductive traits among the four spatially separated populations. Sponges from tidal pools had significantly larger body volume than sponges from deep water and from shallow caves (ANOVA: tidal-deep P<0.0001; tidal-shallow caves P<0.05). Sponges from exposed habitats were significantly larger than deep-water sponges (ANOVA: P=0.01). In addition, individuals from tide pools and from the exposed habitat had a significantly higher proportion of structural silica than sponges from the calmer deep water and from the cave sites. Oxea spicules in sponges from the calm habitats were significantly shorter than in those from the tidal pools and the exposed habitats. The percentage of spicules out of a sponges dry weight in individuals transplanted from deep (calm) to shallow (turbulent) water significantly increased by 21.9±12.9%. The new spicule percentage did not differ significantly from that of sponges originally from shallow water. Oocyte diameter differed significantly between habitats. The maximal size of mature eggs was found in deep-water sponges in June (97±5 m). In the shallow habitats, a smaller maximal oocyte diameter was found in the cave, in May (56.5±3 m). Furthermore, oocyte density in shallow-water sponges was highest in May and decreased in June (with 88.2±9 and 19.3±9 oocytes mm^–2, respectively). At the same time (June), oocyte density of deep-water sponges had just reached its maximum (155±33.7 oocytes mm^–2). The difference in oocyte size and density between deep- and shallow-water individuals indicates an earlier gamete release in the shallow sponge population. The results suggest that plasticity in skeletal design of this sponge indicates a trade off between spicule production and investment in reproduction.Communicated by O. Kinne, Oldendorf/Luhe     

Morphological analysis of growth forms of branching marine sessile organisms along environmental gradients

In this paper a series of growth forms of the sponge Haliclona oculata, the hydrozoan Millepora alcicornis and the scleractinian coral Pocillopora damicornis are morphologically analysed. The growth forms of these species were collected along a gradient of the amount of water movement. In this analysis it is demonstrated that, although these species are from very different taxonomical groups, the degree of compactness of the growth forms shows a similar trend as a response to the exposure to water movement. In all three species the growth forms gradually change from thin-branching to more compact shapes, as evaluated by measurements of various morphological characteristics. Other morphological measurements, in particular the average distance between branch tips and neighbouring branches (“branch spacing”) show a more species-specific pattern. Species in which fusion of branches is almost never observed, as for example P. damicornis, are characterized by a relatively low standard deviation of branch spacing. Species in which anastomosis frequently occurs (H. oculata and M. alcicornis) are characterized by a relatively high standard deviation in branch spacing. The final aim of this research approach is to use the morphological data acquired here in combination with morphological simulation models to gain a better understanding of the growth and form of these organisms and the impact of the physical environment (hydrodynamics and availability of light required for photosynthesis). Received: 8 July 1998 / Accepted: 9 February 1999     

Distribution of secondary metabolites in the sponge Oceanapia sp. and its ecological implications

The Micronesian sponge Oceanapia sp. has an unusual growth form that consists of an irregular turnip-shaped base, which is buried in the substrate. One to several fistules, which protrude through the sand, are attached to the base of the sponge. On top of each fistule is a small fragile capitum. We examined whether this conspicuous red-colored sponge was chemically defended and if intraspecimen variation existed in the distribution of secondary metabolites between different parts of the sponge. Furthermore we assessed the deterrent properties of the secondary metabolites to generalist and more specialized fish predators. We also wanted to see if the optimal defense theory holds in the case of a marine invertebrate. According to the theory, organisms evolve and allocate defenses in a way that maximizes individual fitness, assuming that defenses are costly to the fitness of the organisms. We were able to evaluate this hypothesis, since the different sponge parts in Oceanapia sp. were at different risk to damage by predators and had a different value in terms of fitness loss to the sponge (the capitum probably plays a role in asexual propagation). Concentrations of crude organic extract increased from the base to the capitum of the sponge. The major secondary metabolites kuanoniamine C and D also showed a sharp increase from the basal root to the capitum. There was no difference in structural material or ash content between the base and the fistule of the sponge, but fiber and protein content were significantly higher in the fistule. The methanol fraction was highly deterrent in field feeding assays towards generalist reef fish at base concentration. It also deterred feeding by the spongivorous angelfish Pomacanthus imperator in laboratory feeding experiments at the same concentration. The field feeding assays with pure compounds showed that kuanoniamine C and D deterred feeding by natural assemblages of reef fishes at fistule concentrations, confirming their role as defensive agents. The intraspecimen variation of secondary metabolites in Oceanapia sp. supports the optimal defense theory by showing the highest concentrations in those parts of the sponge that are most visible to predators and are likely to be most important for inclusive fitness. Received: 5 May 1999 / Accepted: 16 September 1999     

Laboratory observations on spawning and embryonic development of a blue-ringed octopus

The infratidal zonation of animals in a 35 m deep fjord-like South African estuary is described. The barnacle Balanus amphitrite Darwin and the bivalve Musculus virgiliae Barnard form the uppermost zone and extend to a depth of 9 m. The oyster Crassostrea margaritacea (Lam.) forms a zone between 1 and 3 m depth while the sponge Grantessa ramosa (Haeckel) occurs between 3 and 7 m. The tubiculous polychaete Mercierella enigmatica Fauvel is the only species found below 10 m, and attains a depth of 33 m. In the wet season (summer) the surface salinity dropped to 2 and temperatures rose to 24°C. In the dry season (winter) surface salinity rose to 24 and temperatures dropped to 16°C. Salinity and temperature of deep water (6 to 33 m) were more stable and varied only between 32.5 and 35 and between 19.6° and 20.5°C, respectively. In June, water below 12 m was 50 to 60% saturated with oxygen but this declined to less than 5% saturation in January.     

Cytotoxic haplosclerid sponges preferred: a field study on the diet of the dotted sea slug<Emphasis Type="Italic"> Peltodoris atromaculata</Emphasis> (Doridoidea: Nudibranchia)

Trophic specializations are widespread among opisthobranch molluscs. One purported example from the Mediterranean Sea is the dotted sea slug Peltodoris atromaculata. It has been hypothesized that this species is strongly monophagous on the sponge Petrosia ficiformis. However, the small amount of evidence that has been found for this hypothesis is based just on laboratory tests. Here we study the feeding habits and the diet of Peltodoris atromaculata in its natural habitat. We observed and videotaped 161 individuals together with the organisms on which they were found (their living substrata). Feeding scars were identified and videotaped as well. Individuals and their living substrata were sampled for further analysis in the laboratory. The composition of faeces of Peltodoris, especially undigested sponge spicules, was analyzed by light and scanning electron microscopy and compared to the composition of the living substrata. Most of the faecal samples consisted of undigested sponge spicules. Although Peltodoris was found on 11 species of sponges, only 2 of them, Petrosia spp. and Haliclona fulva, form its diet (76% out of n=121 samples). In accordance with this, feeding scars in the habitats were exclusively observed on these two sponges. Estimation of electivity indices suggests that Haliclona is preferred over Petrosia. One remarkable feature of the exclusive feeding of Peltodoris on Petrosia and Haliclona is that both sponges share specific fulvinol-like polyacetylenes that show cytotoxic activity in bioassays. Potential benefits and evolutionary aspects of this trophic specialization are discussed. Besides sponge-containing faeces, we found spicule-free faeces (24%, n= 29). These were very small in volume compared to sponge-containing faeces, and only few distinct structures were present. However, the use of food other than sponges is not necessarily indicated by this, because the spicule-free faeces might also represent left-overs from the stomach and digestive gland after sponge spicules have been released.Communicated by O. Kinne, Oldendorf/Luhe     

Transmission,plasticity and the molecular identification of cyanobacterial symbionts in the Red Sea sponge <Emphasis Type="Italic">Diacarnus erythraenus</Emphasis>

Cyanobacterial symbionts in the sponge Diacarnus erythraenus from the Red Sea were identified in both adult sponges and their larvae by 16S rDNA sequencing. A single cyanobacterial type was found in all samples. This cyanobacterial type is closely related to other sponge cyanobacterial symbionts. The cyanobacterial rDNA, together with the morphological analysis by electron and fluorescence microscopy, provided evidence for vertical transmission of the symbionts in this sponge. In addition, we show phenotypic plasticity of the symbionts inside the sponge, probably as a result of variability in light availability inside the sponge tissue. Finally, the reproduction of Diacarnus erythraenus is also described.Matan Oren, Laura Steindler have contributed equally to the work.