Suchergebnisse

4 páginas, 3 figuras. ; Intraorganism genetic stability is assumed in most organisms. However, here we show for the first time intraorganism genetic heterogeneity in natural populations of marine sponges. A total of 36 different multilocus genotypes (MLGs) were detected in 13 individuals of Scopalina lophyropoda sampled at 4 distant points within each sponge. All genotypes (showing a mosaic distribution), were transmitted to the progeny, thus contributing to the high genetic diversity and low clonality reported for this species, although its populations are small and structured and show high fission rates. There did not seem to be intraindividual genotype conflicts; on the contrary, chimeric individuals are expected to show low mortality thanks to the differential mortality of their different MLGs. This novel mechanism may also counterbalance genetic constraints in other benthic invertebrate species. The presence of sponge chimerism also suggests that results from previous population genetics studies could have been misinterpreted. ; This work was supported by the Spanish Government (CICYT) (BENTHOMICS CTM2010-22218) to M.J.U. ; Peer reviewed

9 pages, 3 figures, 5 tables. ; [Background] Rare species have seldom been studied in marine habitats, mainly because it is difficult to formally assess the status of rare species, especially in patchy benthic organisms, for which samplings are often assumed to be incomplete and, thus, inappropriate for establishing the real abundance of the species. However, many marine benthic invertebrates can be considered rare, due to the fragmentation and rarity of suitable habitats. Consequently, studies on the genetic connectivity of rare species in fragmented habitats are basic for assessing their risk of extinction, especially in the context of increased habitat fragmentation by human activities. Sponges are suitable models for studying the intra- and inter-population genetic variation of rare invertebrates, as they produce lecitotrophic larvae and are often found in fragmented habitats. ; [Results] We investigated the genetic structure of a Mediterranean sponge, Scopalina lophyropoda (Schmidt), using the allelic size variation of seven specific microsatellite loci. The species can be classified as "rare" because of its strict habitat requirements, the low number of individuals per population, and the relatively small size of its distribution range. It also presents a strong patchy distribution, philopatric larval dispersal, and both sexual and asexual reproduction. Classical genetic-variance-based methods (AMOVA) and differentiation statistics revealed that the genetic diversity of S. lophyropoda was structured at the three spatial scales studied: within populations, between populations of a geographic region, and between isolated geographic regions, although some stochastic gene flow might occur among populations within a region. The genetic structure followed an isolation-by-distance pattern according to the Mantel test. However, despite philopatric larval dispersal and fission events in the species, no single population showed inbreeding, and the contribution of clonality to the population makeup was minor (only ca. 4%). ; [Conclusions] The structure of the S. lophyropoda populations at all spatial scales examined confirms the philopatric larval dispersal that has been reported. Asexual reproduction does not seem to play a relevant role in the populations. The heterozygote excess and the lack of inbreeding could be interpreted as a hitherto unknown outcrossing strategy of the species. The envisaged causes for this strategy are sperm dispersal, a strong selection against the mating of genetically related individuals to avoid inbreeding depression or high longevity of genets combined with stochastic recruitment events by larvae from other populations. It should be investigated whether this strategy could also explain the genetic diversity of many other patchy marine invertebrates whose populations remain healthy over time, despite their apparent rarity. ; This research was supported by an I3P predoctoral fellowship from CSIC to AB and funded by project CMT2007-66635-C02-01 of the Spanish Government (CICYT) to MJU. ; Peer reviewed

8 páginas, 3 figuras, 1 tabla. ; This study was financed by INTERGEN CTM-2004-05265-CO2/MAR (Spanish Government). A.B. was granted with an I3P fellowship from the CSIC. ; Peer reviewed

Three specimens of a keratose sponge not ascribable to any known Mediterranean genus were collected by trawling off the continental shelf of the Blanes littoral (NE Spain, western Mediterranean). The sponge is foliose, erect, attached to the substratum by one or several short stalks. The stalks skeleton is formed by ascendant fascicled fibres, which repeatedly divide, anastomose, and reticulate in the foliose part, to form a dendro-reticulate network. The surface is conulose with long conules, up to 5 mm apart. Fibres have distinct pith filled with noticeable amounts of foreign debris, and a multi-stratified bark. The skeleton features do not match those of any genus known from the Mediterranean Sea but are similar to a new genus recently described from the Indo-Pacific: Acanthodendrilla Bergquist, which was represented up to now by the species A. australis. The Mediterranean species, here described as Acanthodendrilla levii n. sp., differs from A. australis in its dendro-reticulate skeleton (instead of that totally reticulated in the Pacific species), the way the sponge attaches to the substratum by means of one or several short stalks (which are absent from A. australis), and its foliose thin growth habit (instead of that massive and thicker in A. australis). The finding of a second species confirms the validity of the genus Acanthodendrilla. This is the first record of the genus outside the type locality, and the first time that a representative of the family Dictyodendrillidae has been reported in the Mediterranean Sea. ; Le genre Acanthodendrilla en Méditerranée, avec la description d'une nouvelle espèce. Trois échantillons d'une éponge cornée qui n'appartient à aucun genre connu jusqu'à présent en Méditerranée ont été récoltés par chalutage au large de Blanes (NE de l'Espagne, Méditerranée occidentale). L'éponge est foliacée, dressée, fixée au substratum par un ou plusieurs pédoncules. Les pédoncules sont formés de fibres fasciculées qui suivent une direction ascendante en se divisant et s'anastomosant plusieurs fois pour former un réseau dendro-réticulé. La surface est conuleuse avec de longs conules distants de 5 mm. Les fibres possèdent une moelle claire contenant des corps étrangers et une écorce multistratifiée. Les caractéristiques du squelette ne correspondent à aucun genre déjà connu en Méditerranée. L'espèce appartient sûrement au genre Acanthodendrilla Bergquist, qui était représenté jusqu'à présent par une seule espèce, A. australis. L'espèce méditerranéenne, décrite ici comme Acanthodendrilla levii n. sp., diffère de A. australis par son squelette dendro-réticulé (au lieu de complètement réticulé dans l'espèce du Pacifique), la façon dont l'éponge est attachée au substratum au moyen d'un ou plusieurs pédoncule(s) (absents chez A. australis) et la forme de croissance, mince et foliacée (au lieu de massive et plus épaisse chez A. australis). La signalisation d'une seconde espèce confirme la validité du genre Acanthodendrilla. C'est la première signalisation du genre Acanthodendrilla hors de la localité-type et aussi la première signalisation en Méditerranée d'un représentant de la famille Dictyodendrillidae. ; This research has been partially funded by projects BIOMARK PL961088 from the European Union (MAST-III program), CICYT MAR98-1004-C02 of the Spanish Government, and 1997SGR 00084 of the "Generalitat de Catalunya" to M. J. U. ; Peer reviewed

Este artículo contiene 14 páginas, 6 figuras ; Sponges establish tight associations with both micro- and macroorganisms. However, while studies on sponge microbiomes are numerous, nothing is currently known about the microbiomes of sponge-associated polychaetes and their relationships with those of their host sponges. We analyzed the bacterial communities of symbiotic polychaetes (Haplosyllis spp.) and their host sponges (Clathria reinwardti, Amphimedon paraviridis, Neofibularia hartmani, and Aaptos suberitoides) to assess the influence of the sponges on the polychaete microbiomes. We identified both eukaryote partners by molecular (16S and COI genes) and morphological features, and we identified their microbial communities by high-throughput sequencing of the 16S rRNA gene (V4 region). We unravel the existence of six Haplosyllis species (five likely undescribed) associated at very high densities with the study sponge species in Nha Trang Bay (central Vietnam). A single polychaete species inhabited A. paraviridis and was different from the single species that inhabited A. suberitoides. Conversely, two different polychaete species were found in C. reinwardti and N. hartmani, depending on the two host locations. Regardless of the host sponge, polychaete microbiomes were species specific, which is a widespread feature in marine invertebrates. More than half of the polychaete bacteria were also found in the host sponge microbiome but at contrasting abundances. Thus, the associated polychaetes seemed to be able to select, incorporate, and enrich part of the sponge microbiome, a selection that appears to be polychaete species specific. Moreover, the bacterial diversity is similar in both eukaryotic partners, which additionally confirms the influence of food (host sponge) on the structure of the polychaete microbiome. IMPORTANCE The symbiotic lifestyle represents a fundamental cryptic contribution to the diversity of marine ecosystems. Sponges are ideal targets to improve understanding the symbiotic relationships from evolutionary and ecological points of view, because they are the most ancient metazoans on earth, are ubiquitous in the marine benthos, and establish complex symbiosis with both prokaryotes and animals, which in turn also harbor their own bacterial communities. Here, we study the microbiomes of sponge-polychaete associations and confirm that polychaetes feed on their host sponges. The study worms select and enrich part of the sponge microbiome to shape their own species-specific bacterial communities. Moreover, worm microbiome diversity runs parallel to that of its food host sponge. Considering our results on symbiotic polychaetes and previous studies on fishes and mammals, diet appears to be an important source of bacteria for animals to shape their speciesspecific microbiomes. ; This research was funded by the PopCOmics (CTM2017-88080, MCIU/AEI/FEDER/UE) project from the Spanish Government and the 2017SGR-378 group of Benthic Ecology from the Catalan Government ; Peer reviewed

Este artículo contiene 9 páginas, 2 tablas, 1 figura ; Antarctic bottoms harbor stable, benthic communities, subjected to low temperatures. Environmental stability may promote the asexual (clonal) reproduction of sponges to maintain adapted genotypes to those particular conditions. Stylocordyla chupachups forms patchy populations across the Antarctic continental shelf. Individuals are mostly similar in size without distinct cohorts, which indicates fast growth of the new recruits. Settlement of incubated (clonal?) functional sponges may accelerate sponge growth and success at early colonization phases. To analyze the weight of clonal reproduction in the species, a genetic study was performed on three close populations using eight polymorphic microsatellite loci that were designed from massive sequencing. The three study populations showed a relatively low genetic diversity and low loci polymorphism (from 2 to 6 alleles). The estimators of genetic structure, the Analysis of the Molecular Variance (AMOVA), and the presence of private alleles indicated low but significant structure between the populations. A relatively high rate of asexual reproduction (ca. 25% of the individuals) was detected. The program MLGsim found five identical multilocus genotypes (MLGs) with an asexual origin. An excess of heterozygotes (in five out of the eight loci genotyped) was found, which suggests a positive selection mechanism for heterozygotes. The relatively high rates of asexual reproduction may be the result of adaptation to the environmental stability, while heterozygote selection would help maintain some genetic diversity in the populations. S. chupachups has been reported to be one of the first sponge species recolonizing bare areas resulting from iceberg scouring, which indicates a high species fitness and adaptation to Antarctic bottoms. Two out of the three study populations showed bottleneck, which may indicate a recent founder effect and supports the pioneer nature of this species. ; The study has been partially funded by MarSymBiomics project (Spanish FECYT agency grant ref. CTM2013-43286-P), Benthic Ecology Consolidate Award (Generalitat of Catalonian ref. 2017SGR-378), PopComics (CTM88080AEI/FEDER/VE) from the Spanish Government, and BluePharmTrain FP7 People-INT no: 607786 to MJU. ; Peer reviewed

Este artículo contiene 18 páginas, 8 figuras. ; Sponges are key organisms in the marine benthos where they play essential roles in ecological processes such as creating new niches, competition for resources, and organic matter recycling. Despite the increasing number of taxonomical studies, many sponge species remain hidden, whether unnoticed or cryptic. The occurrence of cryptic species may confound ecological studies by underestimating biodiversity. In this study, we monitored photographically growth, fusions, fissions, and survival of two morpho- logically cryptic species Hemimycale mediterranea Uriz, Garate & Agell, 2017 and H. columella (Bowerbank, 1874). Additionally, we characterized the main environmental factors of the corresponding species habitats, trying to ascertain whether some abiotic factors were correlated with the distribution of these species. Sponge monitoring was performed monthly. Seawater samples were collected the same monitoring days in the vicinity of the target sponges. Results showed contrasting growth and survival patterns for each species: H. mediterranea totally disappeared after larval release while 64% of individuals of H. columella survived the entire two years we monitored. The species also differed in the number of fissions and fusions. These events were evenly distributed throughout the year in the H. mediterranea population but concentrated in cold months in H. columella. No measured environmental factor correlated with H. mediterranea growth rates, while temperature and dissolved organic nitrogen were negatively correlated with H. columella growth rates. The strong differences in depth distribution, survival, growth, fusions, and fissions found between these two cryptic species, highlights the importance of untangling cryptic species before ecological studies are performed in particular when these species share geographical distribution. ; MJU has received research grants from MarSymbiOmics from the Ministry of Economy and Competitivity (MINECO, I+D+I of Excellence, CTM2013-43287-P), the Benthic Ecology Consolidate Team (2014-SGR-120) from the Generalitat of Catalonian, and the BluePharm Train (FP7 People-INT) from the European Union. LG benefited from a fellowship (FPI BES-2011-049132) associated to the Benthomics' Project (ref. CTM2010-22218-C02-01) from the Ministry of Science and Innovation to MJU. ; Peer reviewed

11 pages, 6 figures, 3 tables. ; [EN] The bioactivity of the most abundant sponges from three communities in a Mediterranean cave was assessed by Microtox® assay in two seasons, spring (June) and autumn (November). We quantified bioactivity as a proxy for the investment in production of biologically active substances, and we related sponge bioactivity to growth form, growth rates, and physical contacts of each species with other species. We established a threshold for classifying a species as bioactive based on a comparison between the results of the Microtox® and the sea urchin embryo toxicity bioassay. A total of 30 species were included in the study, of which 50% were bioactive in some community or season. Significant ecological (between communities) and seasonal variation in mean bioactivity was found. When sponge bioactivity was related to sponge growth shape, it was found that the encrusting species tended to be more toxic than the non-encrusting ones. There was a negative relationship between bioactivity and sponge growth, suggesting a trade-off in energy allocation to defence and to other biological functions. Furthermore, a negative correlation was found between bioactivity and positive associations with other species. These results highlight the important role of chemically-mediated interactions in cave communities. ; [ES] La bioactividad de las esponjas más abundantes en tres comunidades a lo largo de una cueva mediterránea fue cuantificada por medio del bioensayo Microtox® en dos estaciones, primavera (junio) y otoño (noviembre). La bioactividad medida se usó como una aproximación a la inversión en producción de sustancias bioactivas, y se relacionó la bioactividad de las esponjas con su morfología, tasas de crecimiento, y contactos de cada especie con otras. Se estableció un umbral para determinar si una especie es bioactiva mediante una comparación entre el test Microtox® y el test de biotoxicidad en embriones de erizo. En total se estudiaron 30 especies, de las que un 50% fue bioactivo en alguna comunidad o estación del año. Se encontraron importantes diferencias ecológicas (entre comunidades) y estacionales en la bioactividad media. Cuando se relacionó la bioactividad con la morfología de las esponjas se encontró que las esponjas incrustantes tendían a ser más tóxicas que las de otras morfologías. Se detectó una correlación negativa entre bioactividad y crecimiento, lo que sugiere un balance entre inversión de energía en defensa y en otras funciones. Por otro lado, se encontró una correlación negativa entre bioactividad y las asociaciones positivas con otras especies. Estos resultados ponen de manifiesto el importante papel de las interacciones mediadas por sustancias químicas en comunidades de cuevas. ; This research was funded by the project CTM2007-66635 of the Spanish Government, and the ECIMAR project of the Agence Nationale de la Recherche (France). ; Peer reviewed

7 páginas, 9 figuras. ; Marine biodiversity is difficult to assess accurately in part because of the existence of sibling species, which are difficult to discern. This is particularly tricky when sibling species live in sympatry. We investigated biological and ecological traits in 2 sympatric sibling sponge species inhabiting the shallow north-western Mediterranean: Scopalina lophyropoda Schmidt, 1862 and S. blanensis Blanquer & Uriz, 2008. Growth, fissions, fusions, and survival were monitored twice monthly for 2 yr. S. lophyropoda slightly increased in area over the 2 yr period, whereas S. blanensis did not show effective growth, since gains in autumn to winter were offset by losses in spring to summer. Survival was significantly different in both species. By the end of the study (24 mo), 74% of the individuals of S. lophyropoda and 34% of S. blanensis survived. All individuals of S. lophyropoda and all but 5 of S. blanensis underwent fissions or fusions at least once during the study. The frequencies of multiple fissions and fusions were higher in S. blanensis than in S. lophyropoda. These 2 sympatric sibling species share common traits such as a high dynamism (higher than any other previously studied encrusting sponge species) and intra-species variability in growth. However, they showed contrasting ecological strategies (conservative in S. lophyropoda vs. opportunistic in S. blanensis), which favours species coexistence. This example shows for the first time how seasonality promotes the co-existence of sibling sponge species in the Mediterranean, and may represent an important step towards understanding species coexistence mechanisms. ; This study was funded by grants INTERGEN CTM2004- 05265-C02-02/MAR and MARMOL CMT2007-66635-C02 from the Spanish Government (CICYT) to M.J.U. and an I3P fellowship to A.B. ; Peer reviewed

13 páginas, 7 figuras, 4 tablas. ; The toxicity of crude extracts of 32 seaweed species from the western Mediterranean was analysed by Microtox® assay in spring and autumn of 1996 and 1997. The species analysed represented more than 76% of seaweed coverage in the 3 algal communities studied: photophilic and sciaphilic communities from the Cabrera Archipelago (Balearic Islands), and a hemisciaphilic community from the Medes Archipelago (northeastern Iberian Peninsula). Most species showed seasonal variation of toxicity, which was greater in species from Cabrera than in those from Medes. Both, intra and interspecies variation of toxicity were found. Moreover, comparison of mean toxicity of these communities showed that toxicity was higher in November than in June in all cases, and that the photophilic community had both the highest number and the most toxic species. To make an ecologically relevant interpretation of the toxicity detected by Microtox®, we compared the toxicity of extracts analysed by the Microtox® test and those analysed by the commonly used sea urchin embryo assay. In addition to seaweeds, some species of invertebrates (sponges and ascidians) were compared to ascertain whether the relationship between the 2 tests was applicable to species belonging to different phyla. These comparisons allowed us to establish that 0.5 gamma units in Microtox® assay is the threshold value between toxic and non-toxic species. Following a light gradient from the photophilic to the sciaphilic communities, the seaweed species that were occasionally toxic increased while the always-toxic seaweeds decreased. Rhodophyta and Phaeophyta had a higher percentage of toxic species than Chlorophyta. Non-encrusting seaweed forms were more toxic than the encrusting ones, and in contrast to most other seaweeds, the non-encrusting calcareous species that increased coverage from June to November simultaneously displayed a marked decrease in toxicity. We conclude that the temporal variation of toxicity observed in the seaweeds studied may be partially explained by intrinsic factors of the species (growth rates and growth shapes). ; This research was funded by projects Mar95-1764 and REN2001-2312 of the Spanish Government and by the Interreg IIIA-1-72-E project of the European Union. ; Peer reviewed

5 páginas, 3 figuras, 1 tabla. ; In order to estimate the degree of implantation of excavating sponges in the oyster populations from the littoral zone at Blanes (north-western Mediterranean Sea), a representative sample of oysters (Ostrea edulis) was collected from depths between 0.5 and 4m in 1986. All oysters were infested by the excavating sponges Cliona viridis and Cliona celata. Infestation a¡ected always and exclusively the lower valve always reaching the inner side. The degree of infestation proved to be independent of oyster size and weight. Colonization by contact was considered the main means of dispersion of these sponges within the oyster population. Cliona viridis and C. celata emerged as the single excavating species able to e¡ectively compete with other non-excavating or excavating organisms when trying to colonize the particular calcareous substrate provided by oyster shells in the north-western Mediterranean Sea. ; Subsequent funds were provided by the projects DGCICYT PB94-0015, CICYT MAR95-1764 and the government of Catalonia (1995 SGR-00443 and 1997 SRG- 00084). ; Peer reviewed

14 pages, 4 figures, 1 table. ; [EN] This paper reports on the design and development of SPONGIA, an expert system to help in the identification of marine sponges. In this field, taxonomic difficulty is noticeable and systematists are scarce. SPONGIA is directed towards identification at any single taxonomic level starting from the class level. With this feature, the system is not restricted to identify only the species rank and the identification stops at a given taxonomic rank (order, family.) depending on the available data about the sample. The design of SPONGIA takes advantage of an architecture for the construction of expert systems in taxonomic domains. This architecture is based on the MILORD II language for expert systems construction. In this paper, we mainly focus on the conceptualisation and implementation of the sponges domain model which constitutes the main effort in the expert system development. We also refer to the particular classification task and problem-solving method for identification that we have adopted from those provided by the architecture to implement SPONGIA. ; [ES] En este artículo se describe el diseño y desarrollo de SPONGIA, un sistema experto para la ayuda a la identificación de esponjas marinas. En este campo, la dificultad taxonómica es notable y los especialistas son escasos. SPONGIA se dirige a la identificación de cualquier nivel taxonómico empezando por el nivel clase. Con esta característica, el sistema experto no se restringe únicamente a la identificación del nivel taxonómico de especie. ; This research has been funded by the projects CICYT TESEU-TIC91-0430 and MARS95-1764, and the Government of Catalonia: Fellowship (FI/91-193) to M. Domingo and grant 1995SGR00443. ; Peer reviewed

8 páginas, 2 figuras, 2 tablas. ; Insight from the spatial genetic structure (SGS) of a species is fundamental to understanding the patterns of effective dispersal and gene flow among its populations. Despite the ecological importance of sponges and the variety of reproduction and dispersal strategies they present, which can strongly influence SGS, there is only 1 study assessing small-scale SGS in sponges. That species had a continuous distribution and relatively wide-scale larval dispersal. Here we study the contribution of sexual and asexual reproduction, and the breeding and mating system to the SGS of a sponge species, Scopalina lophyropoda, with a patchy distribution and more limited larval dispersal. All individuals from 3 populations were mapped and genetically characterised for 7 microsatellite loci. The extent of clonality was minor (ca. 7%), possibly caused by a balance between fissions and fusions. The scarce clonality did not contribute to the SGS, which was analysed by autocorrelation statistics at both the ramet (including clones) and the genet (excluding clones) levels. The spatial autocorrelation analyses elicited a pattern of strong SGS at the small scale, confirming the predictions of philopatric larval dispersal, which fosters isolation by distance. All these patterns, however, contrast with the conspicuous lack of inbreeding detected in the populations, which is in agreement with recent data on other marine modular invertebrates and confirms that strong SGS does not necessarily imply inbreeding. ; This study was funded by grant CTM2007-66635-CO2 from the Spanish Government to M.J.U. and an I3P fellowship to A.B ; Peer reviewed

7 páginas, 5 figuras, 1 tabla. ; Heavy metals are among the main pollutants of the Mediterranean coastal waters where they can harm sublittoral biota. Filter-feeder, long-living invertebrates that remain fixed to the rocky bottom, such as sponges, are good targets tometal contamination studies since theymay be exposed to potential lowlevels of contamination for years. Several molecular and biochemical mechanisms are developed by sponges to counteract the effects of noxious metals. As a result, some of the normal cell functions can be altered. Herewe showthat the main heavy metals that can be found in marine sublittoralwaters (i.e. copper, iron, zinc and manganese) may alter the immune system of sponges by inhibiting the activity of the sponge 2 ,5 -oligoadenylate synthetase (2-5A synthetase), which is an enzyme involved in the immune system of vertebrates. We selected the widespread Mediterranean sponges Geodia cydonium, Crella elegans and Chondrosia reniformis for the study. They exerted a high 2-5A synthetase activity and gave a unique profile of 2 ,5 -oligoadenylate product production. Several metals alter the 2-5A synthetase activity differently, in a species-specific manner. 2-5A synthetases from G. cydonium and C. elegans were inhibited by all the metal ions assayed. However, in C. reniformis, 2-5A synthetase was either activated or inhibited by the same ions depending on their final concentrations. Like in humans, metal contamination may have an effect on the OAS activity and thus it might alter the sponge immune system. However, since the effects are species-specific, 2-5A synthetase cannot be used as general biomarker of metal pollutions. ; This work was supported by the European Union with the Marie Curie Research Training Network, BIOCAPITAL FP6 and by the Spanish Government with the projects INTERGEN, CICYT: CTM2004-05265-C02/MAR and MARMOL, CICYT: CTM2007-66635-CO2. ; Peer reviewed

16 páginas, 5 figuras, 4 tablas ; Benthic assemblages of two Mediterranean submarine caves were compared. Species coverage and number of species were lower in internal (dark) communities than external. This feature was specially marked in the less illuminated cave. Ordination analyses performed on species coverage per community for each cave separately, distinguished several benthic communities from the outermost to the innermost zone of each cave. Cluster analyses on species coverage, taking into account all communities in both the caves, established similarities among communities: algal-dominated communities clustered according to the level of light received independently of the cave they inhabited, while animal-dominated communities were more similar within each cave than between the caves. Moreover, among the abiotic parameters measured irradiance was the only factor that clearly diminished from the entrance to the innermost zone in both the caves. In contrast, water movement and particulate organic matter varied di¡erently in each cave. Results indicate that the di¡erent topography, depth and geographic location of the two caves determine water movement, light penetration and nutrient availability along the caves. These factors are responsible for determining species abundance and diversity, as well as species growth habit in each community. ; This research was partially supported by INTERREG-IIIA K115C n 0123 (EU) and CICYT (Comision Interdepartmental de Ciencia yTechnología) REN2001-2312-CO3/MAR grants. It also benefited from Governments of Catalonia and Spain fellowships to R. Martí ; Peer reviewed