Environmental and spatial drivers of beta diversity components of chironomid metacommunities in contrasting freshwater systems

Marine sponges are exposed to predation as well as to a wide array of potentially harmful microorganisms, and therefore they often possess chemical activity against putative predators and/or pathogens. Some crude extracts from sponges are effective in avoiding microbial colonization or potential infections, and in protecting them against predation. Here, the antibacterial activity of 18 sponge species of Antarctic shallow-waters was tested against four Antarctic and four human pathogenic bacteria. Moreover, all sponge extracts were tested for feeding repellence against the seastar Odontaster validus, one of the main predators living in those habitats. All the sponges showed antibacterial activity against at least one bacterial isolate, although not all of them were active against pathogenic bacteria. The antibacterial effect against sympatric bacteria was stronger than to pathogenic bacteria. In contrast, feeding deterrence was low, with similar activities in both hydrophilic and lipophilic extracts. Only four sponges (Myxilla lyssostyla, Phorbas areolatus, Polymastia invaginata and Iophon sp.), presented repellent chemical defenses. Therefore, we conclude that chemical defenses are widespread in Antarctic shallow-water sponges, and in fact, these sponges are better protected against bacteria than against the seastar predator. We conclude that Antarctic sponges represent a valuable source of biological active compounds with pharmacological and potential ecological relevance.     

Chemical defenses against diatom fouling in Antarctic marine sponges

Antarctic sponges are commonly fouled by diatoms, sometimes so heavily as to occlude pores employed in filter feeding and respiration. This fouling becomes heavier during the annual summer microalgal bloom. Polar and non‐polar extracts of eight species of marine sponges from McMurdo Sound, Antarctica were assayed for cytotoxicity against sympatric fouling diatoms. To identify compounds potentially released by sponges as defenses against diatom biofouling, only fractions of crude extracts that were soluble in seawater or 2% methanol in seawater were assayed. Significant bioactivity was present in seven of the eight species. Both Mycale acerata and Homaxinella balfourensis displayed moderate levels of defense against diatoms even though they are not or are only weakly chemically defended against bacteria and predators. Calyx acuarius extracts, which do have antipredator and antibacterial effects, had no effect on diatoms except at levels many fold higher than present in the intact animal. These results strongly suggest some level of specificity for chemical defenses against diatom fouling in antarctic sponges.     

Diverse microbial communities inhabit Antarctic sponges

Genetic techniques were employed to investigate the archaeal, bacterial and eukaryotic communities associated with the Antarctic sponges Kirkpatrickia varialosa, Latrunculia apicalis, Homaxinella balfourensis, Mycale acerata and Sphaerotylus antarcticus. The phylogenetic affiliation of sponge-derived bacteria was assessed by 16S rRNA sequencing of cloned DNA fragments. Denaturing gradient gel electrophoresis (DGGE) was used to determine the stability of bacterial associations within each sponge species and across spatial scales. Of the 150 archaeal clones from L. apicalis, K. varialosa and M. acerata screened by restriction fragment length polymorphism (RFLP) analysis, four unique operational taxonomic units (OTUs) were observed and all clustered closely together within the Crenarchaeota. Of the 250 sponge-derived bacterial clones screened by RFLP analysis, 61 were unique OTUs that were not detected during examination of 160 seawater-derived clones. Rarefaction analysis indicated that the clone libraries represented between 44 and 83% of the total estimated diversity. Phylogenetic analysis of sequence data revealed that the bacterial communities present in Antarctic sponges primarily clustered within the Gamma and Alpha proteobacteria and the Cytophaga/Flavobacterium of Bacteroidetes group. Bacterial DGGE analysis for replicate sponge and seawater samples at each Antarctic site revealed that bacterial communities were consistently detected within a particular species regardless of the collection site, with six bacterial bands exclusively associated with a single sponge species. Phylogenetic analysis of sequence data from eukaryotic DGGE analysis revealed that the communities present in Antarctic sponges fell into diatom and dinoflagellate clusters with many sequences having no known close relatives. In addition, seven eukaryotic sequences that were not detected in seawater samples or other sponge species were observed in K. varialosa.     

Chemo–ecological interactions in Antarctic bryozoans

The role of bioactive metabolites in ecological interactions involving Antarctic bryozoans has been scarcely studied. Bryozoans are one of the most abundant and diverse members of the Antarctic benthos and are preyed upon by diverse kinds of predators. They seem to be casual food items of the common Antarctic sea urchin Sterechinus neumayeri and the ubiquitous omnivorous amphipod Cheirimedon femoratus. In this study, the cytotoxic activity against embryos and sperm of the sea urchin S. neumayeri and the substrate preferences of the amphipod C. femoratus were assessed using organic extracts from Antarctic bryozoans, in order to determine the presence of chemical defenses. New adapted protocols were designed using a solidifying gel for simulating bryozoans’ surface. We analyzed 32 organic extracts from 16 samples that belonged to 13 different bryozoan species. No cytotoxicity was detected against embryos of S. neumayeri, while 12 of the 13 bryozoan species were cytotoxic to sperm at natural concentrations. In the substrate preference assays, the amphipod C. femoratus was repelled by ten species. The variable bioactivities found in both types of organic partitions of extracts indicated the presence of both lipophilic and hydrophilic defenses. Inter- and intraspecific variability of chemical defenses was detected also, suggesting environmental-induced responses, symbiotic production, and/or genetic variability. Possible alternative defensive mechanisms are also discussed for species with low or no chemical defense. Our results clearly support the fact that chemically mediated bioactivity in Antarctic bryozoans is common, and there is a likely ecological role of cytotoxic and repellent compounds for their protection.     

Diversity in a Cold Hot-Spot: DNA-Barcoding Reveals Patterns of Evolution among Antarctic Demosponges (Class Demospongiae,Phylum Porifera)

Background

The approximately 350 demosponge species that have been described from Antarctica represent a faunistic component distinct from that of neighboring regions. Sponges provide structure to the Antarctic benthos and refuge to other invertebrates, and can be dominant in some communities. Despite the importance of sponges in the Antarctic subtidal environment, sponge DNA barcodes are scarce but can provide insight into the evolutionary relationships of this unique biogeographic province.

Methodology/Principal Findings

We sequenced the standard barcoding COI region for a comprehensive selection of sponges collected during expeditions to the Ross Sea region in 2004 and 2008, and produced DNA-barcodes for 53 demosponge species covering about 60% of the species collected. The Antarctic sponge communities are phylogenetically diverse, matching the diversity of well-sampled sponge communities in the Lusitanic and Mediterranean marine provinces in the Temperate Northern Atlantic for which molecular data are readily available. Additionally, DNA-barcoding revealed levels of in situ molecular evolution comparable to those present among Caribbean sponges. DNA-barcoding using the Segregating Sites Algorithm correctly assigned approximately 54% of the barcoded species to the morphologically determined species.

Conclusion/Significance

A barcode library for Antarctic sponges was assembled and used to advance the systematic and evolutionary research of Antarctic sponges. We provide insights on the evolutionary forces shaping Antarctica''s diverse sponge communities, and a barcode library against which future sequence data from other regions or depth strata of Antarctica can be compared. The opportunity for rapid taxonomic identification of sponge collections for ecological research is now at the horizon.     

Biogeography of sponge chemical ecology: comparisons of tropical and temperate defenses

Examples from both marine and terrestrial systems have supported the hypothesis that predation is higher in tropical than in temperate habitats and that, as a consequence, tropical species have evolved more effective defenses to deter predators. Although this hypothesis was first proposed for marine sponges over 25 years ago, our study provides the first experimental test of latitudinal differences in the effectiveness of sponge chemical defenses. We collected 20 common sponge species belonging to 14 genera from tropical Guam and temperate Northeast Spanish coasts (Indo-Pacific and Mediterranean biogeographic areas) and conducted field-based feeding experiments with large and small fish predators in both geographic areas. We use the term global deterrence to describe the deterrent activity of a sponge extract against all of the predators used in our experiments and to test the hypothesis that sponges from Guam are chemically better defended than their Mediterranean counterparts. Sympatric and allopatric deterrence refer to the average deterrent activity of a sponge against sympatric or allopatric predators. All of the sponges investigated in this study showed deterrent properties against some predators. However, 35% of the sponge species were deterrent in at least one but not in all the experiments, supporting the idea that predators can respond to chemical defenses in a species-specific manner. Tropical and temperate sponges have comparable global, sympatric, and allopatric deterrence, suggesting not only that chemical defenses from tropical and temperate sponges are equally strong but also that they are equally effective against sympatric and allopatric predators. Rather than supporting geographic trends in the production of chemical defenses, our data suggest a recurrent selection for chemical defenses in sponges as a general life-history strategy.     

Screening of the Antarctic marine sponges (Porifera) as a source of bioactive compounds

Sponges (Porifera) currently represent one of the richest sources of natural products and account for almost half of the pharmacologically active compounds of marine origin. However, to date very little is known about the pharmacological potential of the sponges from polar regions. In this work we report on screening of ethanolic extracts from 24 Antarctic marine sponges for different biological activities. The extracts were tested for cytotoxic effects against normal and transformed cell lines, red blood cells, and algae, for modulation of the activities of selected physiologically important enzymes (acetylcholinesterase, butyrylcholinesterase, and α-amylase), and for inhibition of growth of pathogenic and ecologically relevant bacteria and fungi. An extract from Tedania (Tedaniopsis) oxeata was selectively cytotoxic against the cancer cell lines and showed growth inhibition of all of the tested ecologically relevant and potentially pathogenic fungal isolates. The sponge extracts from Isodictya erinacea and Kirkpatrickia variolosa inhibited the activities of the cholinesterase enzymes, while the sponge extracts from Isodictya lankesteri and Inflatella belli reduced the activity of α-amylase. Several sponge extracts inhibited the growth of multiresistant pathogenic bacterial isolates of different origins, including extended-spectrum beta-lactamase and carbapenem-resistant strains, while sponge extracts from K. variolosa and Myxilla (Myxilla) mollis were active against a human methicillin-resistant Staphylococcus aureus strain. We conclude that Antarctic marine sponges represent a valuable source of biologically active compounds with pharmacological potential.     

Mesofauna associated with the marine sponge Amphimedon viridis. Do its physical or chemical attributes provide a prospective refuge from fish predation?

Marine sponges often harbor an abundance of associated organisms. We characterized mesofauna associated with the common tropical sponge Amphimedon viridis, and then tested whether physical (spicules) or chemical (lipophilic or hydrophilic extracts) properties of this sponge provide a prospective refuge for mesofauna from fish predation. Sponge analyses revealed a moderately diverse and numerically rich community of sponge-associated mesofauna comprised primarily of mesocrustaceans (82% of total fauna). Eighty-nine percent of these were amphipods, but smaller numbers of tanaids, decapods, and isopods also occurred. Quantitative sampling of outer surfaces and interstices of fifteen A. viridis yielded a total mean ± 1 SD density of sponge–associated mesofauna of 53 ± 9.3 individuals per 100 cm³ wet sponge tissue. Among the numerically dominant amphipods, 65% occurred on outer sponge surfaces where they are most vulnerable to fish predators. We evaluated whether A. viridis provides a prospective refuge from predation by assessing the palatability of this sponge to the sympatric generalist pinfish Lagodon rhomboides. When presented small (2 mm) bite-size pieces of whole sponge tissue, similar in size to what fish might incidentally ingest should they attempt to consume sponge-mesofaunal associates, pinfish displayed strong feeding deterrence. Alginate food pellets containing tissue-level concentrations of sponge spicules caused a weak but significant deterrent response. In contrast, alginate pellets containing tissue-level concentrations of either lipophilic or hydrophilic extracts of A. viridis were highly deterrent to pinfish. Thus, chemical, and to a considerably lesser degree, physical defenses (spicules) may contribute to this sponge serving as a protective refuge for associated mesofauana.     

Latitudinal variation in spongivorous fishes and the effectiveness of sponge chemical defenses

It has been proposed that predation pressure declines with increasing latitude and a positive correlation exists between predation intensity and the investment into chemical defenses. However, little direct evidence supports the idea that tropical species are better defended chemically than their temperate counterparts. Temperate reefs of the South Atlantic Bight (SAB) off Georgia, USA, provide a unique opportunity to study tropical sponges in a temperate environment. We documented sponge species richness and abundance, sponge predator density, and examined the ability of eight sponge species to chemically deter predation by fishes on two reefs in the SAB. We used rarefaction analysis and ANOVA to compare our results for sponge species richness and density, respectively, with similar published studies conducted on reefs of the sub-tropical Atlantic (i.e., Florida Keys). These analyses were combined with similar statistical comparisons for spongivorous fish species richness and density. Results showed that sponge species richness was lower, but sponge density was higher, on the temperate SAB reefs than on the subtropical reefs. Both spongivorous fish diversity and density were lower on the SAB reefs. The greater abundance of sponges and lower density of predators on SAB reefs suggest a lower frequency of predation on sponges on SAB reefs. Of the eight sponge species assayed from the SAB reefs, five possessed chemical extracts that were significantly less deterrent to fish predators than their tropical/subtropical conspecifics. When the results were combined across all sponge species, the chemical deterrence of fish predators was significantly lower for extracts obtained from the temperate sponge community as compared to the tropical/subtropical assemblage. These results support the more general hypothesis that a lower density and diversity of sponge predators occurs at high as compared to low latitudes in the western Atlantic and may contribute to decreased investment in chemical defenses.     

Testing for defensive synergy in Caribbean sponges: Bad taste or glass spicules?

Chemical and physical defenses of sessile organisms against consumers are well described for both terrestrial and marine systems. However, previous studies have focused on chemical or physical defenses in isolation, and have not considered their interaction. Marine sponges provide a model system for testing this interaction. Some sponge species produce secondary metabolites that deter predation; they may also contain siliceous spicules, but previous studies have provided little evidence that spicules in isolation offer any defense against generalist fish predators. To determine whether the two components have an additive, antagonistic, or synergistic interaction, crude organic extracts and spicules from individuals of 8 Caribbean sponge species were isolated and tested in laboratory feeding assays. These included one chemically defended reef sponge (Agelas clathrodes) and seven known to be intermediately deterrent: six from reef habitats (Cinachyrella alloclada, Clathria virgultosa, Cribrochalina infundibulum, Niphates digitalis, Svenzea zeai, and Xestospongia muta) and one from mangrove habitats (Tedania ignis). Extracts and spicules were assayed at various concentrations, both individually and in combination, in laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum. A SAS based GENMOD procedure based on an isobolographic analysis model was used for statistical comparisons. Four sponges (A. clathrodes, C. alloclada, C. virgultosa, and one of three individuals of X. muta) showed evidence of synergisms. Of these, synergy in C. alloclada, C. virgultosa, and X. muta was caused by approximately natural concentrations of extracts and spicules. The extract of A. clathrodes was deterrent, but combination assays required nearly a 3-fold reduction in extract concentration and an 8-fold increase in spicule concentration to show the synergistic effect. Contrary to previous findings, spicules from C. infundibulum and two of three individuals of X. muta were deterrent at natural concentrations. Sponge spicules may be defensive in isolation, or may enhance chemical defenses against consumers, but the lack of synergisms for individuals in 4 of 7 species with intermediate levels of chemical defense suggests that defensive synergy is not the general rule and, when present, may be an example of an exaptation.     

Diversity of cultivable fungi associated with Antarctic marine sponges and screening for their antimicrobial, antitumoral and antioxidant potential

The diversity of sponge-associated fungi has been poorly investigated in remote geographical areas like Antarctica. In this study, 101 phenotypically different fungal isolates were obtained from 11 sponge samples collected in King George Island, Antarctica. The analysis of ITS sequences revealed that they belong to the phylum Ascomycota. Sixty-five isolates belong to the genera Geomyces, Penicillium, Epicoccum, Pseudeurotium, Thelebolus, Cladosporium, Aspergillus, Aureobasidium, Phoma, and Trichocladium but 36 isolates could not be identified at genus level. In order to estimate the potential of these isolates as producers of interesting bioactivities, antimicrobial, antitumoral and antioxidant activities of fungal culture extracts were assayed. Around 51 % of the extracts, mainly from the genus Geomyces and non identified relatives, showed antimicrobial activity against some of the bacteria tested. On the other hand, around 42 % of the extracts showed potent antitumoral activity, Geomyces sp. having the best performance. Finally, the potential of the isolated fungi as producers of antioxidant activity seems to be moderate. Our results suggest that fungi associated with Antarctic sponges, particularly Geomyces, would be valuable sources of antimicrobial and antitumoral compounds. To our knowledge, this is the first report describing the biodiversity and the metabolic potential of fungi associated with Antarctic marine sponges.     

Ecology of antarctic marine sponges: an overview

Sponges are important components of marine benthic communitiesof Antarctica. Numbers of species are high, within the lowerrange for tropical latitudes, similar to those in the Arctic,and comparable or higher than those of temperate marine environments.Many have circumpolar distributions and in some habitats hexactinellidsdominate benthic biomass. Antarctic sponge assemblages contributeconsiderable structural heterogeneity for colonizing epibionts.They also represent a significant source of nutrients to prospectivepredators, including a suite of spongivorous sea stars whoseselective foraging behaviors have important ramifications uponcommunity structure. The highly seasonal plankton blooms thattypify the Antarctic continental shelf are paradoxical whenconsidering the planktivorous diets of sponges. Throughout muchof the year Antarctic sponges must either exploit alternatesources of nutrition such as dissolved organic carbon or bephysiologically adapted to withstand resource constraints. Incontrast to predictions that global patterns of predation shouldselect for an inverse correlation between latitude and chemicaldefenses in marine sponges, such defenses are not uncommon inAntarctic sponges. Some species sequester their defensive metabolitesin the outermost layers where they are optimally effective againstsea star predation. Secondary metabolites have also been shownto short-circuit molting in sponge-feeding amphipods and preventfouling by diatoms. Coloration in Antarctic sponges may be theresult of relict pigments originally selected for aposematismor UV screens yet conserved because of their defensive properties.This hypothesis is supported by the bioactive properties ofpigments examined to date in a suite of common Antarctic sponges.     

Allelochemicals produced by Caribbean macroalgae and cyanobacteria have species-specific effects on reef coral microorganisms

Coral populations have precipitously declined on Caribbean reefs while algal abundance has increased, leading to enhanced competitive damage to corals, which likely is mediated by the potent allelochemicals produced by both macroalgae and benthic cyanobacteria. Allelochemicals may affect the composition and abundance of coral-associated microorganisms that control host responses and adaptations to environmental change, including susceptibility to bacterial diseases. Here, we demonstrate that extracts of six Caribbean macroalgae and two benthic cyanobacteria have both inhibitory and stimulatory effects on bacterial taxa cultured from the surfaces of Caribbean corals, macroalgae, and corals exposed to macroalgal extracts. The growth of 54 bacterial isolates was monitored in the presence of lipophilic and hydrophilic crude extracts derived from Caribbean macroalgae and cyanobacteria using 96-well plate bioassays. All 54 bacterial cultures were identified by ribotyping. Lipophilic extracts from two species of Dictyota brown algae inhibited >50% of the reef coral bacteria assayed, and hydrophilic compounds from Dictyota menstrualis particularly inhibited Vibrio bacteria, a genus associated with several coral diseases. In contrast, both lipo- and hydrophilic extracts from 2 species of Lyngbya cyanobacteria strongly stimulated bacterial growth. The brown alga Lobophora variegata produced hydrophilic compounds with broad-spectrum antibacterial effects, which inhibited 93% of the bacterial cultures. Furthermore, bacteria cultured from different locations (corals vs. macroalgae vs. coral surfaces exposed to macroalgal extracts) responded differently to algal extracts. These results reveal that extracts from macroalgae and cyanobacteria have species-specific effects on the composition of coral-microbial assemblages, which in turn may increase coral host susceptibility to disease and result in coral mortality.     

Sponge community structure and anti-predator defenses on temperate reefs of the South Atlantic Bight

Predator–prey interactions can play a significant role in shaping the structure of both terrestrial and marine communities. Sponges are major contributors to benthic community structure on temperate reefs and although several studies have investigated how abiotic processes control sponge distributions on these reefs, the role of predation is less clear. We investigated the relationship between sponge predators and the distribution of sponges on temperate reefs in the South Atlantic Bight (SAB), off Georgia, USA. We documented sponge species richness and abundance, spongivorous fish density, and examined the ability of 19 sponge species to chemically and structurally deter predation by fishes. We also conducted reciprocal transplant experiments to determine if predation by fishes contributes to the observed zonation of sponge species on these reefs. Our surveys revealed two distinct sponge assemblages: one characterized by amorphous and encrusting sponge morphotypes colonizing the vertical, rocky outcroppings (scarp sponge community), while the other consisted of pedunculate, digitate, and arborescent growth forms occurring on the sediment-laden reef top (plateau sponge community). Spongivorous fishes were more abundant on the scarp than the plateau and scarp sponges were found to be more effective than plateau sponges at chemically deterring generalist fishes. In contrast, plateau sponges were more reliant on structural defenses: a result consistent with the higher spicule content of their skeletons. Transplant experiments confirmed that predators prevent some plateau sponges from colonizing the scarp even though they possess structural defenses. Thus, predation appears to play a role in shaping sponge community structure on SAB reefs by restricting those species lacking adequate chemical defenses to habitats where there is a paucity of spongivores.     

Thermal stress responses in the bacterial biosphere of the Great Barrier Reef sponge,Rhopaloeides odorabile

Marine sponges are diverse, abundant and provide a crucial coupling point between benthic and pelagic habitats due to their high filtration rates. They also harbour extensive microbial communities, with many microbial phylotypes found exclusively in sponge hosts and not in the seawater or surrounding environment, i.e. so‐called sponge‐specific clusters (SCs) or sponge‐ and coral‐specific clusters (SCCs). We employed DNA (16S rRNA gene) and RNA (16S rRNA)‐based amplicon pyrosequencing to investigate the effects of sublethal thermal stress on the bacterial biosphere of the Great Barrier Reef sponge Rhopaloeides odorabile. A total of 8381 operational taxonomic units (OTUs) (97% sequence similarity) were identified, affiliated with 32 bacterial phyla from seawater samples, 23 bacterial phyla from sponge DNA extracts and 18 bacterial phyla from sponge RNA extracts. Sublethal thermal stress (31°C) had no effect on the present and/or active portions of the R. odorabile bacterial community but a shift in the bacterial assemblage was observed in necrotic sponges. Over two‐thirds of DNA and RNA sequences could be assigned to previously defined SCs/SCCs in healthy sponges whereas only 12% of reads from necrotic sponges could be assigned to SCs/SCCs. A rapid decline in host health over a 1°C temperature increment suggests that sponges such as R. odorabile may be highly vulnerable to the effects of global climate change.     

The inhibitory properties of various sponges on Listeria spp.

Various retail and environmental sponges were tested for inhibitory properties against Listeria species and several other bacterial genera. Sterile sponges, unrinsed and rinsed in sterile distilled water or sterile neutralizing buffer, were placed on seeded plates of tryptic soy agar with 0.6% yeast extract. Plates were incubated at 30°C for 24 h and zones of inhibition measured.
The Systems Plus environmental sponge and the Technical Service Consultants Ltd sponge (sTc)© proved to be the only sponges which consistently demonstrated no inhibitory properties. Results using scanning electron microscopy showed considerable bacterial attachment to the Systems Plus sponge, further corroborating these findings.     

Feeding repellence of Antarctic and sub-Antarctic benthic invertebrates against the omnivorous sea star Odontaster validus

Antarctic and sub-Antarctic benthic invertebrates are subjected to intense predation by mobile macroinvertebrates. Accordingly, chemical protection as well as other defensive mechanisms are expected to be common in organisms inhabiting these ecosystems. In order to evaluate anti-predation activities and allocation of chemical defenses within the anatomy of marine benthic Antarctic and sub-Antarctic invertebrates, 55 species were tested for feeding repellence against the sea star Odontaster validus, a common eurybathic sympatric predator. The invertebrates tested were collected from the deep waters of two poorly surveyed areas in terms of chemical ecology studies: the eastern Weddell Sea (Antarctica) and the vicinities of Bouvet Island (sub-Antarctica). Experiments were conducted at the Spanish Antarctic Base in Deception Island. In the feeding deterrence experiments, shrimp pieces were treated with crude lipophilic fractions obtained from each species, and were offered to the sea stars. A total of 29 species (53 %) from 7 different phyla (Porifera, Cnidaria, Chordata, Bryozoa, Echinodermata, Mollusca, and Annelida) showed feeding repellence against O. validus, and are therefore chemically protected against this keystone predator. Furthermore, 25 species were dissected into parts to investigate the possible allocation of defensive compounds. Some of the results obtained from these analyses support the prediction that the most exposed/vulnerable tissues concentrate chemical defenses to avoid predation against the sea stars. In summary, the results obtained in our survey support the hypothesis that deep-water Antarctic and sub-Antarctic benthic invertebrates are well protected chemically against sympatric predators, similarly to what has been reported in previous studies investigating shallow-water Antarctic species.     

Does concentrating chemical defenses within specific regions of marine sponges result in enhanced protection from predators?

Chemical defenses are an effective mode of predator deterrence across benthic marine organisms, but their production may come with associated costs to the organism as limited resources are diverted away from primary processes like growth and reproduction. Organisms concentrating ecologically relevant levels of these defenses in tissues most at risk to predator attack may alleviate this cost while deterring predators. We addressed this hypothesis by investigating the deterrence of chemical extracts from the inner and outer regions of the sponges Aplysina fulva, Ircinia felix, and I. campana from a temperate hard-bottom reef in the South Atlantic Bight. Assays were conducted using natural fish assemblages and sea urchins. Although, A. fulva and I. felix have higher concentrations of defensive metabolites in the outer and inner regions, respectively, extracts from these regions did not display enhanced deterrency against fish or mobile invertebrate predators. Likewise, extracts from both regions of the sponge Ircinia campana, which has a uniform distribution of defensive chemicals throughout, did not differ in their ability to deter either group of predators. Since chemical defenses were effective deterrents at lower concentrations, secondary metabolite allocation patterns observed among these sponges are likely not driven by predation pressure from generalist fish and mobile invertebrate predators on these reefs. Alternatively, these patterns may be driven by other ecological stressors, another suite of predators, or may be more effective at deterring predators when combined with structural defenses.     

Sponge communities of the Antarctic Peninsula: influence of environmental variables on species composition and richness

Sponge communities on the Antarctic continental shelf currently represent one of the most extensive sponge grounds in the world, and all sponge classes are known to occur in the Southern Ocean. Main objectives of this study conducted at the tip of the Antarctic Peninsula were (1) to identify all sampled sponges and (2) to investigate whether the species composition and species richness of Southern Ocean sponge communities in the area of the Antarctic Peninsula are significantly influenced by environmental variables. The studied material originated from 25 AGT catches and was sampled during the expedition ANT-XXIX/3 of RV Polarstern. Samples were collected in three large-scale areas in the vicinity of the Antarctic Peninsula: Bransfield Strait, Drake Passage and Weddell Sea. The following six environmental variables were measured from bottom water samples (except for sea-ice cover): depth (m), light transmission (%), oxygen (µmol/kg), salinity, sea-ice cover (%) and temperature (°C). Two hundred and sixty-three sponge samples were analyzed, and 81 species of 33 genera from all Porifera classes (Calcarea, Demospongiae, Hexactinellida and Homoscleromorpha) were identified. Total numbers of sponge species per sample station ranged from 1 to 29. A detrended correspondence analysis and a backward-stepwise model selection were performed to check whether species composition and richness were significantly influenced by environmental variables. The analyses revealed that none of the measured environmental variables significantly influenced species composition but that species richness was significantly influenced by (1) temperature and (2) the combination of temperature and depth. Results of this study are of crucial importance for development, performance and assessment of future protection strategies in case of ongoing climatic changes at the Antarctic Peninsula.     

Fatty acid composition and antioxidant activity of Antarctic marine sponges of the genus <Emphasis Type="Italic">Latrunculia</Emphasis>

The fatty acid composition of marine cold-water sponges of genus Latrunculia, namely Latrunculia bocagei Ridley and Dendy, 1886, and Latrunculia biformis Kirkpatrick, 1907, for which no fatty acid data had been previously reported, has been examined. High levels of long-chain fatty acids (C_24–30) with high unsaturation levels (mainly polyunsaturation), and high incidence of branched- and odd-chain fatty acids in sponges are suggested to be partially connected with their specific cell membrane requirements to surmount the negative effects of low temperatures and to enable growth in extreme environments. Furthermore, variations in the fatty acid profile at the species level may reflect variations in compositions or quantities of symbiotic microorganisms that commonly represent up to 60 % of the sponge wet weight. The fatty acid compositions of lipid-rich sponge extracts from five Latrunculia specimens dredged from the Bransfield Strait near the Antarctic Peninsula, were obtained using supercritical carbon dioxide and analyzed using gas chromatography–mass spectrometry–flame ionization detection. Furthermore, the antioxidant activities of these extracts were determined using the photochemiluminescent method. Along with common fatty acids, the chemical analyses revealed very long-chain fatty acids (C22, C24). Differences were seen for the fatty acid levels between both species and different specimens of the same species. The observed differences do not seem connected to the habitat depth of the specimen, but rather indicate the variations within the associated microbiome. Furthermore, these sponge extracts showed antioxidant activities, confirming that they contain lipidic compounds that strongly scavenge free radicals.