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     

Endofauna differences between two temperate marine sponges (Demospongiae; Haplosclerida; Chalinidae) from southwest Australia

The endofaunal assemblages associated with two species of sponge from the family Chalinidae (Haliclona sp. 1 and Haliclona sp. 2) were studied at four locations along the south west coast of Australia. The species have distinct morphologies and inhabit similar microhabitats; there is also considerable scientific interest in Haliclona sp. 1 (green Haliclona) due to the unique bioactive compound it produces. A total of 948 and 287 endofaunal individuals were found associated with 16 specimens of both the green Haliclona and Haliclona sp. 2 (brown Haliclona), respectively. Twenty-four endofaunal taxa were found (from mysid shrimps to teleost fish), with the brown Haliclona having a greater density of endofaunal species and individuals than the green Haliclona. The endofaunal assemblages of both species of sponge were significantly different, but only the endofaunal assemblage within the green Haliclona differed significantly among locations. Differences in the abundance and biomass of associated endofauna of each species of sponge can be related to differences in their morphologies, size and internal structure. In the green Haliclona, differences in endofaunal assemblages among locations are unlikely to be due to environmental influences as taxa discriminating each locations assemblage were common to both species of sponge. Numerous endofaunal individuals were found to be reproductively active, and it is clear that the species of sponge provide important habitats for their associated endofauna. This provision of habitat needs to be taken into account when harvesting green Haliclona biomass for supply of its target bioactive compound for further pharmaceutical development.     

Sponge-feeding by the Caribbean starfish Oreaster reticulatus

The common Caribbean starfish Oreaster reticulatus (Linnaeus) feeds on sponges by everting its stomach onto a sponge and digesting the tissue, leaving behind the sponge skeleton. In the San Blas Islands, Republic of Panama, 54.2% of the 1549 starfish examined from February 1987 to June 1990 at eight sites were feeding, and 61.4% of these were feeding on sponges, representing 51 species. Sponges were fed on disproportionately heavily in comparison to their abundance, which was only 9.7% of available prey. In feeding choice experiments, 736 pieces of 34 species of common sponges from a variety of shallow-water habitats, and also 9 ind of a coral, were offered to starfish in individual underwater cages. Acceptance or rejection of sponge species was unambiguous for 31 of the 34 species, and there was a clear relationship between sponge acceptability and sponge habitat. Starfish ate 16 of 20 species that normally grow only on the reefs, but only 1 of 14 species that live in the seagrass meadows and rubble flats surrounding the reefs. The starfish live in the seagrass meadows and rubble flats, and avoid the reefs, and so the acceptable reef sponges are generally inaccessible until a storm fragments and transports them into starfish habitat. After Huricane Joan washed fragments of reef sponges into a seagrass meadow in October 1988, starfish consumed the edible species. When the seagrass meadow was experimentally seeded with tagged reef sponge fragments in June 1994, O. reticulatus consumed edible species and accumulated in the area seeded. Reef sponges that were living in a seagrass meadow, from which O. reticulatus had been absent for at least 4 yr (from 1978 to 1982), were eliminated when the starfish migrated into the area, and the sponges have been unable to recolonize up to June 1994. O. reticulatus feeding and habitat preferences appear to restrict distributions of many Caribbean reef sponge species to habitats without O. reticulatus and may have exerted significant selective pressure on defences of those sponges that live in O. reticulatus habitats.     

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.     

Symbiotic zooxanthellae enhance boring and growth rates of the tropical sponge Anthosigmella varians forma varians

Several species of boring sponges harbor symbiotic zooxanthellae, and it is believed that the symbiont enhances boring activity of host sponges. This hypothesis was tested using manipulative field experiments to assess the effect of intracellular zooxanthella populations on boring rates of the tropical sponge Anthosigmella varians forma varians. Portions of sponge were attached to 60 calcium carbonate blocks of known weight. Three sets of 10 blocks were grown at high light levels and three sets of 10 blocks were grown at low light levels for 105 d in the Florida Keys, Florida, USA. Boring rates, growth rates (lateral growth and within-substratum tissue penetration), and zooxanthella populations were measured at the end of the experiment. Absolute rates of boring and growth of A. varians forma varians were significantly greater when zooxanthella densities were higher. Boring rate and tissue penetration related to final surface area of sponge attachment was also enhanced when zooxanthella densities were higher, suggesting that the symbiont plays a physiological role in the decalcification process. This is in contrast to the role that zooxanthellae play in coral hosts. Based on the results of this study, it appears that the presence of zooxanthellar symbionts has important ecological and life-history consequences for host sponges. Ability to laterally overgrow competitors will be correlated with the size and activity of zooxanthella populations. In addition, the fitness of host sponges will be enhanced by algal symbionts, since greater penetration within substrata will result in an increase in production of tissue that can be converted into storage, feeding and reproductive functions.     

Biodiversity and rockfish recruitment in sponge gardens and bioherms of southern British Columbia,Canada

In the Strait of Georgia and Howe Sound, British Columbia, colonies of individual cloud sponges, growing on rock (known as sponge gardens) receive resource subsidies from the high biodiversity of epifauna on adjacent rock habitats. Bioherms are reefs of glass sponges living on layers of dead sponges. In the same area as the sponge gardens, newly discovered bioherms in Howe Sound, BC (49.34.67 N, 123.16.26 W) at depths of 28- to 35-m are constructed exclusively by Aphrocallistes vastus, the cloud sponge. The sponge gardens had much higher taxon richness than the bioherms. The sponge garden had 106 species from 10 phyla, whereas the bioherm had only 15 species from 5 phyla. For recruiting juvenile rockfish (quillback, Sebastes maliger), the food subsidy of sponge gardens appears to be missing on bioherms of cloud sponge, where biodiversity is relatively low. While adult and subadult rockfishes (S. maliger, S. ruberrimus, S. proriger, and S. elongatus) were present on bioherms, no evidence for nursery recruitment of inshore rockfishes to bioherms was observed, whereas the sponge gardens supported high densities of newly recruited S. maliger, perhaps owing to the combination of both refuge and feeding opportunities. These results indicate that sponge gardens form a habitat for early stages of inshore S. maliger, whereas A. vastus bioherms are associated only with older juvenile and adult rockfishes.     

Video-monitored predation by Caribbean reef fishes on an array of mangrove and reef sponges

Although predation by fishes is thought to structure benthic invertebrate communities on coral reefs, evidence to support this claim has been difficult to obtain. We deployed an array of eight sponge species on Conch Reef (16 m depth) off Key Largo, Florida, USA, and used a remote video-camera to record fish activity near the array continuously during five daylight periods (6 h for 1 d, at least 11.5 h for 4 d) and one night period (11 h). Of the eight sponge species, four were from adjacent reefs (Agelas wiedenmayeri, Geodia neptuni, Aplysina fistularis, and Pseudaxinella lunaecharta), and four were from a nearby mangrove habitat (Chondrosia collectrix, Geodia gibberosa, Halichondria sp., andTedania ignis). Each species of reef sponge was chosen to match the corresponding mangrove species in form and color (black, brown, yellow, and red, respectively). Predation events only occurred during daylight hours. Tallies of the number of times fishes bit sponges revealed intense feeding by the expected species of sponge-eating fishes, such as the angelfishHolacanthus bermudensis, H. tricolor, andPomacanthus arcuatus, the cowfishLactophrys quadricornis, and the filefishCantherhines pullus, but surprisingly also by the parrotfishSparisoma aurofrenatum andS. chrysopterum. Of 35 301 bites recorded, 50.8% were taken by angelfish, 34.8% by parrotfish, and 13.7% by trunkfish and filefish. Mangrove sponges were preferred by all reef fishes; 96% of bites were taken from mangrove species, with angelfish preferringChondrosia collectrix and parrotfish preferringGeodia gibberosa. Fishes often bit the same sponge repetitively, and frequently consumed entire samples within 30 min of their deployment. Sponge color did not influence fish feeding. Two of the four mangrove sponge-species deployed on the array were also found living in cryptic habitats on adjacent reefs and were rapidly consumed by fishes when exposed. Our results demonstrate the importance of fish predation in controlling the distribution of sponges on Caribbean reefs.     

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.     

Surface sequestration of chemical feeding deterrents in the Antarctic sponge<Emphasis Type="Italic"> Latrunculia apicalis</Emphasis> as an optimal defense against sea star spongivory

Latrunculia apicalis is a spherically shaped demosponge that previous investigations have shown is rarely preyed upon by sea stars which are the dominant spongivores in antarctic benthic communities. Prior studies have also demonstrated that L. apicalis produces organic compounds that elicit a tube foot retraction response in the keystone spongivorous sea star Perknaster fuscus that can be used as a reliable assay for feeding deterrence. L. apicalis is known to contain discorhabdin alkaloids which serve, among other roles, as the source of its green coloration. To assess the defensive nature of the discorhabdin alkaloids toward P. fuscus, we have determined discorhabdin G concentrations in discrete sponge layers and evaluated those concentrations in the P. fuscus bioassay. In discorhabdin G-bearing sponges, we found a gradient of discorhabdin G that falls off rapidly toward the center of the sponge. On average, 52% of total discorhabdin G in a given sponge was found within 2 mm of the sponge surface. Tube foot retraction responses to extracts from the surface tissues (0–2 mm depth) of L. apicalis were compared to those of an inner layer (8–10 mm depth) and to a sample comprised of the same inner layer spiked with discorhabdin G at a concentration equivalent to that of the surface tissues. Tube foot retraction response times to extracts of the surface layers and the spiked inner layers were not statistically different, but were significantly greater than responses to the unaltered inner layer and controls. These results support the predictions of the optimal defense theory as L. apicalis sequesters its defensive chemistry (discorhabdin G) in its most vulnerable surface tissues, where the likelihood of predation from sea stars is highest. As antarctic sponges are generally preyed upon by extraoral feeding sea stars rather than deeper biting predators such as fish, surface sequestration may be uniquely adaptive in sessile macroinvertebrates occurring in antarctic marine benthic environments.Communicated by P.W. Sammarco, Chauvin     

Habitat use by sponge-dwelling brittlestars

Cryptic organisms often associate with sessile invertebrates for refuge in space-limited environments. To examine interspecific habitat associations on coral reefs, tube- and vase-shaped sponges were surveyed for associated brittlestars at six sites on the coral reefs off Key Largo, Florida. Of 179 sponges encountered, Callyspongia vaginalis was the most abundant (43.0%), followed by Niphates digitalis (39.7%), and Callyspongia plicifera (4.5%). Three of eight sponge species surveyed did not differ from C. vaginalis in two physical refuge characteristics: oscular diameter and inner tube surface area. Brittlestars (416 total), all of the genus Ophiothrix, were only found in C. vaginalis, N. digitalis, and C. plicifera. The most abundant brittlestar, O. lineata (326), occurred on C. vaginalis (99.0%) and N. digitalis (1.0%), while O. suensonii (67) occurred on C. vaginalis (79.1%), N. digitalis (19.4%), and C. plicifera (1.5%). There was no pattern of co-occurrence of O. lineata and O. suensonii on C. vaginalis. The abundance of O. lineata increased with surface area of C. vaginalis. Differential habitat use was observed in O. lineata, with small individuals (<5 mm disk diameter) located inside and on the surface of sponge tubes and large individuals (5 mm) solely inside tubes. The number of large O. lineata in C. vaginalis never exceeded the number of tubes per sponge, and tagged O. lineata remained in the same sponge for at least 3 weeks. In density manipulations, no pattern of intraspecific competition among large O. lineata was observed; however, there was evidence for interaction between size-classes. Brittlestars selected live sponge habitat over a non-living refuge, suggesting a mechanism for sponge habitat recognition. Sponge-dwelling brittle stars prefer some tube- and vase-shaped sponge species despite similar oscular diameters and surface areas. Surprisingly, these preferred sponge species are known from previous studies to be chemically undefended against generalist fish predators; therefore, brittlestars that inhabit these sponges do not gain an associational chemical defense. Sponge habitat use by O. lineata may be governed by intraspecific interactions to maintain habitat and access to food. While past studies have suggested that O. lineata is an obligate sponge commensal, the present study suggests that O. lineata has a species-specific association with the tube-sponge C. vaginalis.Communicated by O. Kinne, Oldendorf/Luhe     

Management of nematocysts in the alimentary tract and in cnidosacs of the aeolid nudibranch gastropod<Emphasis Type="Italic"> Cratena peregrina</Emphasis>

The nudibranch gastropod Cratena peregrina (Opisthobranchia: Aeolidaceae), when feeding on polyps of the hydrozoan Eudendrium racemosum (Cnidaria: Anthoathecata), devours masses of small microbasic eurytele and holotrichous isorhiza nematocysts. Large proportions of these nematocysts were found undischarged in the alimentary tracts of the snails. Feeding experiments in this study tracked the fate of nematocysts as they passed through the alimentary canal to the digestive gland in the dorsal appendages, the cerata, to the cnidosacs, and finally in the faeces. In digestive cells, many structurally intact nematocysts were present in large phagosomes that remained unaffected even after 2 days fasting, and phagosomes containing nematocysts were found in the faeces. Thus, it is inferred that fusion of nematocyst-containing phagosomes with lysosomes and subsequent digestion of nematocysts is blocked. Masses of exposed, undigested and structurally intact nematocysts were discarded in the faeces. In the tips of the cerata, other nematocysts were phagocytosed by cnidophages and stored in the cnidosacs. After release, in contact with seawater, cnidosac nematocysts were able to discharge. When cnidophore tentacles of E. racemosum with only holotrichous isorhizas were fed to the snails, the isorhizas arrived in the cnidosacs about 2 h after feeding and mixed with existing small euryteles. Some cnidosacs also contained very large microbasic eurytele or large macrobasic eurytele nematocysts, possibly from Eudendrium ramosum and Eudendrium glomeratum, respectively. This indicates that the various types of nematocysts from food were all incorporated into the cnidosacs. Evidence for a selection process or digestion of a certain nematocyst type in the cnidophages was not obtained. It is concluded that a large proportion of the nematocysts ingested with the food are not digested, but are eliminated, structurally and functionally intact, via the alimentary canal and the tips of the cerata.     

Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba

The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18–30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6–12 μmol cm⁻³ sponge day⁻¹. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm⁻³ sponge day⁻¹, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.     

Penetration and storage of sponge spicules in tissues and coelom of spongivorous echinoids

When echinoids feed on sponges, silicate spicules of the sponge were found to enter their body either by penetration through the wall of the food canal into coelomic cavities or by penetration into skeletal plates and spines. The spicules, which have penetrated into the coelom, obviously evoke a kind of protective answer. They were found to be entangled by clusters of cell remnants, the so-called brown bodies. The brown bodies contain melanin and gather at special sites of the echinoid body; these are the Stewart Organs, the gills and the inner side of the ambulacral plates. Sometimes the silicate spicule becomes surrounded by a calcareous sheath. The length of the sponge spicules makes their removal impossible, so that they are stored. The spicules penetrating into the plates are partly incorporated into the stereom. The four species examined in this study were Asthenosoma ijimai, Araeosoma owstoni, Diadema setosum (collected in Sagami Bay, Japan in 1991) and Hapalosoma gemmiferum (collected in Suruga Bay, Japan in 1991).     

Consistent association of crenarchaeal Archaea with sponges of the genus Axinella

The association of sponges with microorganisms has been accepted to be a common feature of the phylum Porifera. Herein we describe the association between filamentous Archaea and three Mediterranean species of sponges from the family Axinellidae (Porifera: Demospongiae). Axinella damicornis, A. verrucosa and Axinella sp. harbor a high concentration of filamentous Archaea in the collagen that surrounds the siliceous spicules that form their skeleton. These Archaea have been found in every axinellid specimen studied, regardless of their environment and collection time. The morphology of the filaments has been studied using transmission electron microscopy, and they all show similar characteristics. Their nature has been determined by in situ hybridization experiments and by PCR amplification and sequencing of their 16S DNA. Each sponge species contains a single filamentous archaeal phylotype. The Archaea of the three sponges are closely related to each other and to the marine "group 1" crenarchaeotes. Our findings suggest that this newly described association could be defined as a symbiosis, where biochemical and/or metabolic relationships between the sponge hosts and their symbionts remain to be determined.     

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     

Investigation of the relationship between invertebrate predation and biochemical composition,energy content,spicule armament and toxicity of benthic sponges at McMurdo Sound,Antarctica

The biochemical and energetic composition, spicule content, and toxicity of benthic sponges was investigated in McMurdo Sound, Antarctica from October through December 1984. The predominant organic constituent of sponges was soluble and insoluble protein. Levels of total protein ranged from 17.0 to 55.9% dr. wt. Levels of lipid and carbohydrate were low, ranging from 2.1 to 9.6 and 0.6 to 3.5% dr. wt, respectively. Levels of ash were high and variable (32 t0 79% dr. wt), reflecting species-specific differences in spicule contents. Calculated energy contents of sponges were low, with a mean of 9.8±3.5 kJ g^-1 dr. wt; ranging from 5.1 kJ g^-1 dr. wt in Sphaerotylus antarcticus to 17.4 kJ g^-1 dr. wt in Dendrilla membranosa. Insoluble protein accounted for the greatest contribution to the energetic composition of the sponges, while lipid and carbohydrate combined contributed to less than 25% of the overall energy. Normalized spicule volumes of sponges ranged from 0.15 to 0.38 cm³ g^-1 dr. wt. Ichthyotoxicity assays indicated that 9 (56%) of 16 antarctic sponge species were toxic. The most highly toxic species were Mycale acerata and Leucetta leptorhapsis. The high incidence of toxicity in antarctic sponges indicates that the current hypothesis suggesting a simple inverse relationship between toxicity and latitude in marine sponges is invalid. There was little correspondence between the energetic composition or spicule contents of the sponges and feeding patterns (electivity indices) of sponge-eating predators. Although the asteroid Perknaster fuscus antarcticus specializes on the highly toxic, fast-growing M. acerata, most antarctic sponge-eating predators appear to be generalists which feed on the more abundant, non- to mildly-toxic, sponge species. This feeding strategy is based on exploitation of low energy, sedentary prey, which require a minimal energy output to harvest.     

Silica content and spicule size variations in Pellina semitubulosa (Porifera: Demospongiae)

 The variations in both silica content and spicular size were studied in two populations of the demosponge Pellina semitubulosa (Lieberkühn). Samples were collected over a period of 1 year (June 1994 to May 1995) in two Mediterranean coastal basins: Porto Cesareo (southwestern Apulia) and Marsala (northwestern Sicily). The values of spicule size (length and width) and sponge silica content were significantly higher in the population of Porto Cesareo, where the highest water silica concentration was recorded. In both Porto Cesareo and Marsala the sponge silica content showed a seasonal trend, positively correlated with water temperature values. In both populations, the smallest spicules were found in specimens collected from summer to late autumn, after sexual reproduction. Secretion of new spicules may be connected with the process of remodelling occurring in sponges after gamete and larval release. Received: 10 October 1999 / Accepted: 13 April 2000     

Parrotfish predation on cryptic sponges of Caribbean coral reefs

Some sponge species that live in crevices in the reef frame appear to be restricted to their cryptic habitat by predation. When cryptic sponges were excavated, on Guigalotupo reef, San Blas, Panama, exposing them to potential predators, they were eaten by fishes that are generally considered to be herbivores, primarily parrotfishes of the genus Sparisoma: S.aurofrenatum (Cuvier & Valenciennes), S.viride (Bonnaterre), and S.chrysopterum (Bloch & Schneider). Of the 9150 bites observed to be taken by these species during paired (i.e., with sponges versus without sponges) trials conducted in defined feeding areas during 1986, 1987, and 1988, 72% (i.e. 6581 bites) were on cryptic sponges, even though these were only offered during half of the total observation time and never constituted more than 7% of the cover of the feeding observation areas. Individual parrotfish returned over and over to take bites of the exposed cryptic sponges until they were entirely consumed. They vigorously chased each other away from the sponges, but exhibited no such defense of their usual algal foods. A total of 18 sponge species were tested. Of the cryptic and semi-cryptic sponge species tested, only one of six was rejected by the parrotfish. Two of these six sponge species were consistently consumed entirely, and two were consumed entirely whenever their surfaces were sliced off with a razor blade, demonstrating that these sponges concentrate defenses against predators in their surfaces. One semi-cryptic species and one semi-exposed species were fed upon, but not entirely consumed. By contrast, 11 of 12 of the exposed and semi-exposed species were rejected. Cryptic sponges grew out of their cavities in the reef only when protected by seasonally thick mats of macroalgae or by cages that excluded fish. Received: 10 January 1997 / Accepted: 4 February 1997     

Morphological evidence for vertical transmission of symbiotic bacteria in the viviparous sponge<Emphasis Type="Italic"> Halisarca dujardini</Emphasis> Johnston (Porifera,Demospongiae, Halisarcida)

All stages of vertical transmission of symbiotic bacteria, from the penetration into oocytes to the formation of rhagon, were investigated in the White Sea (Arctic) representatives of Halisarca dujardini Johnston (Demospongiae). Small populations of free-living specific symbiotic bacteria inhabit the mesohyl of H. dujardini. They are represented by a single morphotype of small spiral gram-positive bacteria. Vertical transmission of symbiotic bacteria between generations in sponges may occur in different ways. In the case of H. dujardini the bacteria penetrate into growing oocytes by endocytosis. A part of the bacteria plays a trophic role for oocytes and the other part remains undigested in membrane-bound vacuoles within the cytoplasm. In cleaving embryos bacteria are situated between the blastomeres or in the vacuoles. In the blastula all bacteria are disposed in the blastocoel. The symbionts are situated in intercellular spaces in free-swimming larvae and during metamorphosis. Symbiotic bacteria do not play any trophic role in the period of embryonic and postembryonic development of H. dujardini. No signs of destruction and digestion of bacteria were revealed at any stage of development.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.