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. © 1997 Wiley‐Liss, Inc.

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The pattern of resource allocation in the sponge Crambe crambe (Schmidt) (Demospongiae, Poecilosclerida) in 2 contrasting habitats and in specimens of 3 size classes was studied. The sponge biomass per unit area increased with sponge size in both illuminated and dark environments. An increase with size was also found in the illuminated habitat for the investment in organic matter per unit area This parameter was almost constant among the 3 size classes from the shaded habitat, with values similar to those of the medium-slzed specimens from the lllum~nated environment The amount of sihca per mm2 was higher in the dark site where it proved size-dependent, whereas ~t dld not vary with size in the illuminated habitat Investment in reproduction per unit area was higher in the illuminated wall and was positively correlated with size in both habitats. The amount of calcareous debris included by the sponge during its growth did not vary across size classes in either habitat. All variables related to sponge thickness showed significant differences between the 2 sites studied, while neither the size nor the interaction of habitat and size significantly influenced their values. The specimens were thicker in the illuminated habitat, both in their choanosome and ectosome layers. No variations with size or site were found for the canal system. There was a significant habitat effect on the amount of matrix, which was higher in the illuminated environment. Sponges produced more collagen in the shaded environment than in the illuminated site. This was particularly true for specimens larger than 1000 mm2 (medium and large size classes). As for the number of fibres, there was also significantly more fibre material in the sciaphilous sponges. A significant Interaction was found between habitat and size effects on the number of cells per sponge section. The pattern of resource allocation to the different functions considered was similar in medium-sized specimens from the 2 contrasting habitats except for the number of cells and amount of collagen per sponge section. Small and large sponges, on the other hand, featured the highest between-habitat differences in resource allocation. Large sponges from the illuminated habitat invested relatively more energy in organic matter and less in mineral and collagen structures than their sciaphilous counterparts. Small photophilic sponges invested more in silica than small sciaphilous specimens. Investment in reproduction was notably hlgher In the whole size range of photophilic sponges than in the corresponding size classes from the dark site. Consequently, thls species seems able to shift its resource allocation as a function of size and environmental conditions. We propose an interpretation in terms of a higher competitive pressure in the shaded environment that results in increased investment in defensive/supportive (mineral and organic) structures and a lower investment in somatic growth (organic matter) and reproductive output (larvae).

Many sponges produce and store secondary metabolites with interesting pharmacological bioactivities. Identification of the cell type(s) responsible for the production and/or storage of these compounds may be a crucial step for the future culture and production of these substances if the biosynthesis is not envisageable and the producer organism is rare or too slow-growing for feasible exploitation. Localisation of these cells within the sponge may also contribute to ascertaining the ecological role of these compounds. The cell type containing the main bioactive metabolite (avarol) and its derivative avarone in the sponge Dysidea avara has been identified by cell isolation in a density gradient and by chromatographic techniques. Preliminary cytological characterisation of the cell types in each particular sponge species under study is required, otherwise the identification of the cells in suspensions is inaccurate. In contrast with the findings reported for other sponge species, the active metabolites of D. avara are not contained within spherulous cells but within choanocytes that line the chambers of the aquiferous system. The possible ecological role of avarol is discussed in the light of its internal position and the biological functions of the cells storing the bioactive compounds.& k w d :

 Abstract Galera, J., Turon, X., Uriz, M. J. and Becerro, M. A. 2000. Microstructure variation in sponges sharing growth form: the encrusting demosponges Dysidea avara and Crambe crambe. -Acta Zoologica (Stockholm) 81 : 93-107The goals of this study are to assess variability of microarchitecture in sponges with a similar growth form and to look for correlates between microstructural organization, biological functions and ecological strategies. A comparison of the microstructure of the encrusting sponges Dysidea avara (Dendroceratida) and Crambe crambe (Poecilosclerida) is performed. The species co-occur in sublittoral habitats of the western Mediterranean. Histological techniques, image analysis and corrosion castings are used in order to quantify thickness, degree of development of the aquiferous system, relative amount of structural and cellular materials, and size of the choanocyte chambers in both species. The fine structure and cellular types are described and analysed through SEM/ TEM. These sponges are known to feature contrasting ecological strategies: D. avara has higher growth and clearance rates than C. crambe , it is more susceptible to predation and uses a more opportunistic strategy of space acquisition and maintenance. C. crambe grows slowly, it is chemically protected from predation and it competes successfully for space with other invertebrates. These differences in biological strategies are here shown to have clear structural correlates: D. avara is structurally simpler, with fewer cell types and very scarce matrix material. Most of its section is occupied by the highly developed aquiferous system. Its construction is much looser than in C. crambe . In the latter species, structural complexity is higher, it produces long-lasting structures such as the spicules, and it is more compact and thinner. It is concluded that there is wide scope for microarchitectural patterns, even in species with similar growth form, and that structural and cytological characters may prove to be useful descriptors of biological strategies in sponges.