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Our current understanding of the silicon (Si) cycle in the ocean assumes that diatoms dominate not only the uptake of silicic acid, but also the production and recycling of biogenic silica (BSi), and that other organisms with siliceous skeletons, including sponges, radiolarians, and silicoflagellates, play a negligible role. In this study, we reexamine some aspects of the potential contribution by sponges and present in vitro evidence that BSi in the form of sponge spicules redissolves into silicic acid at far slower rates than those known for diatom frustules. We also show that the retention of Si by siliceous sponges in some sublittoral and bathyal environments is substantial and that sponge populations function as Si sinks. Additionally, by reanalyzing published information on sponge growth and BSi content, we estimate that BSi production rates by sublittoral sponges in Si-poor and Si-rich marine areas fall quite close to values known for diatom assemblages. Therefore, sponges may affect Si cycling dynamics and Si availability for diatoms, particularly in Si-depleted environments. Altogether, our data strongly suggest that the role of sponges in the benthopelagic coupling of the Si cycle is significant.

During spring and summer 2003, we measured a variety of chemical and biological parameters in five medium-sized, Mediterranean cage farms that exploit semi-offshore conditions, and controlled the supply of fodder. The objective was to assess whether modern cage farms proliferating at semi-offshore sites exert environmental impact levels equivalent to the levels described from more traditional cage farms located in shallow, sheltered sites. In the water column, we examined the concentration of dissolved inorganic nutrients and heterotrophic bacteria in both surface and near-bottom water. At the bottom, we examined the concentrations of benthic chlorophyll a, phaeophytin and organic matter in sediments, the granulometric structure of the sediment, and the taxonomic (at the family level) abundance of benthic macroinvertebrates. For most parameters, we found no substantial differences between farm and control sites. Rather, most variation was explained as a function of depth (surface versus bottom water) or season (spring versus summer conditions). Deviations of farm values from control values, when they occurred, were small and did not indicate any significant impact on either bacterioplankton or benthic chlorophyll. Only one of the five farms studied exerted a detectable impact on the benthic macroinvertebrate community immediately under the cages. These results suggest that medium-sized fish farms located on semiexposed western Mediterranean coasts have fewer environmental impacts than traditional fish farms located in shallow, sheltered sites. Impact characterization in these new farms may require refinement of the standard approach to deal with rapid dispersal of effluents and sub-lethal levels of environmental disturbance.

Three new sponge species are described from the Paci® c coast of Panama, namely Crambe panamensis n. sp., Discorhabdella urizae n. sp. and Discorhabdella littoralis n. sp. This is the ® rst record of the genera Crambe and Discorhabdella for the eastern Paci® c, which represents not only a considerable expansion in their known biogeographical distribution, but also empirical support for their Tethyan origin. The new species provide a better understanding of the skeletal evolution in these peculiar genera, representing a lineage in which aster-derived spicules occur within a typical poecilosclerid skeleton. The skeleton of C. panamensis consists of ectosomal subtylostyles, choanosomal tylostyles with smooth tyle, basal desmas of astroclone type only, and anchorate isochelae. The skeleton of D. urizae consists of ectosomal subtylostyles, choanosomal tylostyles with tuberose tyle, basal acanthostyles with aster-like tyle, anchorate isochelae, sigmas, and distinctive twisted microxeas. The skeleton of D. littoralis consists of ectosomal tylostyles, choanosomal tylostyles that occasionally show remains of tubercles in the tyle, basal acanthostyles with a tyle intermediate between aster-like and regular morphology, and sigmas. The skeletal a nities of Crambe and Discorhabdella with the genera Lithochela and Monanchora are discussed, and a new family concept based on all four genera is proposed. The name Crambeidae is proposed for such a family, to replace the pre-occupied name Crambidae.

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