César A. Cárdenas

Influence of environmental variation on symbiotic bacterial communities of two temperate sponges

Sponges are an important component of temperate subtidal marine ecosystems, with a range of important functional roles and extensive symbiotic relationships with microorganisms. However, much remains unknown about their relationships with these symbiotic microorganisms, and specifically, the role that these symbionts play in sponge physiology, feeding and adaptation to local environmental conditions. Changes in environmental factors may alter relationships between sponges and their symbionts, which could conceivably influence the abundance and distribution patterns of some temperate sponge species. Here, we analyzed the effect of transplantation of sponges between different habitats to test the effect of changes in environmental conditions on the stability of the bacterial communities in specimens of Tethya bergquistae and Ecionemia alata, based on pyrosequencing of amplified 16S rRNA genes. Bacterial communities differed markedly between the two host species. While some morphological changes were observed in transplanted sponges, transplantation had little overall effect on sponge-associated bacterial communities at either phylum or 97%-OTU level. Our results show the importance of host species and also the stability of sponge-associated bacterial communities under environmental variation.

Global conservation status of sponges

Sponges are important for maintaining ecosystem function and integrity of marine and freshwater benthic communities worldwide. Despite this, there has been no assessment of their current global conservation status. We assessed their status, accounting for the distribution of research effort; patterns of temporal variation in sponge populations and assemblages; the number of sponges on threatened species lists; and the impact of environmental pressures. Sponge research effort has been variable; marine sponges in the northeastern Atlantic and Mediterranean and freshwater sponges in Europe and North America have received the most attention. Although sponge abundance has increased in some locations since 1990, these were typically on coral reefs, in response to declines in other benthic organisms, and restricted to a few species. Few data were available on temporal trends in freshwater sponge abundance. Despite over 8500 described sponge species, only 20 are on threatened species lists, and all are marine species from the northeastern Atlantic and Mediterranean. Of the 202 studies identified, the effects of temperature, suspended sediment, substratum loss, and microbial pathogens have been studied the most intensively for marine sponges, although responses appear to be variable. There were 20 studies examining environmental impacts on freshwater sponges, and most of these were on temperature and heavy metal contamination. We found that most sponges do not appear to be threatened globally. However, little information is available for most species and more data are needed on the impacts of anthropogenic-related pressures. This is a critical information gap in understanding sponge conservation status.

Influence of canopy-forming algae on temperate sponge assemblages

Experimental removals of the dominant canopy-forming kelp Ecklonia radiata were conducted at two sites on rocky walls in New Zealand and monitored for approximately 1.5 years. We hypothesized that the removal of the E. radiata canopy would affect the structure of subcanopy assemblages, such that there would be a reduction in sponge species richness and abundance. Furthermore, we investigated the biological and physical (predictor) variables that best explained variability in sponge assemblages after canopy removal. Canopy removal led to a community dominated by turf algae, which corresponded with a decrease in sponge abundance and richness. Our results suggest that the Ecklonia canopy may positively influence the presence of sponge species such as Crella incrustans ; we propose that the canopy may allow its coexistence with turf algae underneath the canopy by altering the light regime and other environmental factors, which may be detrimental for some species. Our results highlight how any loss of canopy-forming species might have negative effects on sponge assemblages, which could affect the energy flow and the overall biodiversity found in these habitats.

Rocky reef benthic assemblages in the Magellan Strait and the South Shetland Islands (Antarctica)

Las comunidades submareales de arrecifes de gran parte de las costas del mundo han sido descritas en detalle, sin embargo, escasa informacion existe para los extensos arrecifes subantarticos. El objetivo fue describir estos sistemas costeros del sur y medir el grado en que varian en funcion de las medidas fundamentales de la estructura de la comunidad. La Region Magallanica constituye un sitio intermedio entre sitios relativamente bien estudiados en regiones temperadas y Antartica. Estudios previos sugieren que la especie de alga dominante (dosel) puede reflejar diferentes historias de perturbacion asi como diferencias en sus comunidades asociadas. Hipotetisamos que la variacion en los ensambles submareales sesiles en Magallanes, donde Macrocystis pyrifera domina ampliamente, sera menor a la que ocurre en sitios en Antartica, donde Desmarestia spp. o Himantothallus grandifolius dominan dependiendo de los regimenes de disturbios. Los resultados de este estudio muestran que los ensambles bentonicos en el Estrecho de Magallanes fueron similares en aquellos lugares donde la estructura fisica del arrecife fue similar, pero variaron fuertemente donde la forma del arrecife fue distinta. En los sitios de las Islas Shetland del Sur, los ensambles bentonicos fueron diferentes en terminos del alga dominante y la estructura comunitaria. No obstante, la evidencia previa acerca de que sitios dominados por Desmarestia presentan mayor evidencia de disturbios fue incorrecta. Probablemente el efecto de sombra producido por Macrocystis en Magallanes y el efecto del hielo en Antartica son fuertes factores estructuradores en sus respectivas comunidades, situacion que debe ser considerada al comparar las caracteristicas comunitarias.

First characterization of gastrointestinal culturable bacteria of Patagonian toothfish Dissostichus eleginoides (Nototheniidae)

The Patagonian toothfish Dissostichus eleginoides is one of the most important fisheries from the Southern Ocean. The biology of this species is relatively well studied and some nutritionals issues have also been reported; however there is no information about the composition of the bacterial community of the gastrointestinal tract, which is essential to characterize the microbiota of this fish. The bacterial flora of D. eleginoides is here described for the first time using culturable methods. By applying traditional culture-based techniques and 16S rDNA sequencing methods it was possible to characterize the families Vibronaceae and Moraxellaceae, which were mainly represented by Vibrio and Psychrobacter, respectively. This Patagonian fish shows a microbiota very similar to other cold waters fishes.

Presencia de Cistenides Elhersi Hessle, 1917 (Polychaeta Perctinariidae) en aguas someras magallánicas habitadas por praderas de Ruppia Filifolia: Evidencia de Euribatia, Eurihalididad y Euritermia?

A objeto de analizar los impactos potenciales que podrian tener los gradientes de salinidad, asi como los distintos regimenes termicos sobre la distribucion batimetrica de la fauna bentonica estuarina en la zona austral de Chile, se desarrollo una revision bibliografica sobre los hallazgos del poliqueto Cistenides elhersi recolectados en diferentes cruceros Cimar Fiordo. Se consideraron las caracteristicas oceanograficas de las estaciones con profundidades mayores a 50 m, y se adicionaron datos nuevos obtenidos en un sector de baja salinidad (25 psu) y somero del Seno Skyring (52°33’16” S, 71°51’34” W; 0,3 a 2 m profundidad), Region de Magallanes, donde predomina una pradera del pasto acuatico Ruppia filifolia. Los datos analizados en forma conjunta permiten proponer que C. elhersi muestra eurihalinidad, euritermia y euribatia. Se proporcionan antecedentes complementarios sobre la abundancia del poliqueto, tamano y ubicacion dentro de la matriz del pasto. Se destaca la necesidad de desarrollar nuevos estudios para identificar otro tipo servicios ecologicos prestados por esta pradera de R. filifolia.