Overview of the chemical ecology of benthic marine invertebrates along the western Antarctic peninsula

Thirteen years ago in a review that appeared in the American Zoologist, we presented the first survey of the chemical and ecological bioactivity of Antarctic shallow-water marine invertebrates. In essence, we reported that despite theoretical predictions to the contrary the incidence of chemical defenses among sessile and sluggish Antarctic marine invertebrates was widespread. Since that time we and others have significantly expanded upon the base of knowledge of Antarctic marine invertebrates' chemical ecology, both from the perspective of examining marine invertebrates in new, distinct geographic provinces, as well as broadening the evaluation of the ecological significance of secondary metabolites. Importantly, many of these studies have been framed within established theoretical constructs, particularly the Optimal Defense Theory. In the present article, we review the current knowledge of chemical ecology of benthic marine invertebrates comprising communities along the Western Antarctic Peninsula (WAP), a region of Antarctica that is both physically and biologically distinct from the rest of the continent. Our overview indicates that, similar to other regions of Antarctica, anti-predator chemical defenses are widespread among species occurring along the WAP. In some groups, such as the sponges, the incidence of chemical defenses against predation is comparable to, or even slightly higher than, that found in tropical marine systems. While there is substantial knowledge of the chemical defenses of benthic marine invertebrates against predators, much less is known about chemical anti-foulants. The sole survey conducted to date suggests that secondary metabolites in benthic sponges are likely to be important in the prevention of fouling by benthic diatoms, yet generally lack activity against marine bacteria. Our understanding of the sensory ecology of Antarctic benthic marine invertebrates, despite its great potential, remains in its infancy. For example, along the WAP, community-level non-consumptive effects occur when amphipods chemically sense fish predators and respond by seeking refuge in chemically-defended macroalgae. Such interactions may be important in releasing amphipods from predation pressure and facilitating their unusually high abundances along the WAP. Moreover, recent studies on the sensory biology of the Antarctic keystone sea star Odontaster validus indicate that chemotactile-mediated interactions between conspecifics and other sympatric predatory sea stars may have significant ramifications in structuring community dynamics. Finally, from a global environmental perspective, understanding how chemical ecology structures marine benthic communities along the WAP must increasingly be viewed in the context of the dramatic impacts of rapid climatic change now occurring in this biogeographic region.     

The peril of the plankton

The pelagic environment is characterized by unevenly distributed resources and risks. Such unpredictability presents adaptive challenges to diverse planktonic organisms including the larvae of benthic marine invertebrates. Estimates of mortality during planktonic development are highly variable, ranging from 0% to 100% per day. Predation is considered a significant source of this mortality, but what explains the variability in estimates of the mortality of marine invertebrate larvae? While differential exposure of larval prey to predators may explain these widely variable estimates, adaptations that reduce vulnerability of marine larvae to predators may also be important. Although there are excellent reviews of predation upon larvae and of larval mortality and defenses, nearly 15 years have elapsed since these topics were formally reviewed. Here, we highlight recent advances in understanding the behavioral, chemical, and morphological defenses that larvae possess and assess their effectiveness in reducing the risk of predation. While recent work confirms that larval mortality is generally high, it also demonstrates that larvae can reduce their risk of predation in several ways, including: (1) temporarily escaping the benthos during vulnerable early stages, (2) producing chemical compounds that reduce palatability, (3) possessing morphological defenses such as spines and shells, and (4) exhibiting induced defensive responses whereby larvae can alter their behavior, morphology, and life histories in the presence of predators. Taken together, these studies indicate that marine invertebrate larvae possess a sophisticated suite of defensive phenotypes that have allowed them to persist in the life cycle of benthic invertebrates for eons.     

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.     

Chemical defence against predators in a sub-Arctic fjord

The development of chemical defences in marine organisms is supposed to be driven by intense pressure of predation and competition. While benthic communities in tropical and also Antarctic regions are thought to be mainly structured by intra- and interspecific interactions, these factors are proposed to be less important in northern high latitudes. Consequently, selective pressure for chemical defence should be low in these regions. To investigate the incidence of chemical defence against predation in northern high latitudes, crude extracts of 18 abundant sessile or slow-moving invertebrate species (4 sponges, 3 actinians, 1 soft coral, 4 bryozoans, 3 ascidians and the egg mass of a gastropod) from Kongsfjord (Spitsbergen) were tested for feeding deterrent activity. Laboratory assays were performed by offering artificial food with extracts to two different predators, the amphipod Anonyx nugax which is a common species in Kongsfjord, and the starfish Asterias rubens from the North Sea. Of the 18 extracts tested, 2 (Haliclona viscosa, Hormathia nodosa) exhibited significant feeding deterrent effects in the amphipod assay. Furthermore, 6 extracts had a significantly stimulating effect on the amphipod feeding, and 10 extracts did not affect consumption. In the starfish assay, only the crude extract of H. viscosa was significantly rejected. For H. viscosa, feeding deterrence could be established for two pure compounds, and for H. nodosa for one fraction. The present data show that feeding deterrent compounds are present in sub-Arctic marine invertebrates from Kongsfjord but are less abundant than in temperate, tropical and Antarctic species.     

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.     

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.     

Diversity and distribution patterns in high southern latitude sponges

Sponges play a key role in Antarctic marine benthic community structure and dynamics and are often a dominant component of many Southern Ocean benthic communities. Understanding the drivers of sponge distribution in Antarctica enables us to understand many of general benthic biodiversity patterns in the region. The sponges of the Antarctic and neighbouring oceanographic regions were assessed for species richness and biogeographic patterns using over 8,800 distribution records. Species-rich regions include the Antarctic Peninsula, South Shetland Islands, South Georgia, Eastern Weddell Sea, Kerguelen Plateau, Falkland Islands and north New Zealand. Sampling intensity varied greatly within the study area, with sampling hotspots found at the Antarctic Peninsula, South Georgia, north New Zealand and Tierra del Fuego, with limited sampling in the Bellingshausen and Amundsen seas in the Southern Ocean. In contrast to previous studies we found that eurybathy and circumpolar distributions are important but not dominant characteristics in Antarctic sponges. Overall Antarctic sponge species endemism is ～43%, with a higher level for the class Hexactinellida (68%). Endemism levels are lower than previous estimates, but still indicate the importance of the Polar Front in isolating the Southern Ocean fauna. Nineteen distinct sponge distribution patterns were found, ranging from regional endemics to cosmopolitan species. A single, distinct Antarctic demosponge fauna is found to encompass all areas within the Polar Front, and the sub-Antarctic regions of the Kerguelen Plateau and Macquarie Island. Biogeographical analyses indicate stronger faunal links between Antarctica and South America, with little evidence of links between Antarctica and South Africa, Southern Australia or New Zealand. We conclude that the biogeographic and species distribution patterns observed are largely driven by the Antarctic Circumpolar Current and the timing of past continent connectivity.     

Ecology of Caribbean Sponges: Are Top-Down or Bottom-Up Processes More Important?

Benthic-pelagic coupling and the role of bottom-up versus top-down processes are recognized as having a major impact on the structure of marine communities. While the roles of bottom-up processes are better appreciated they are still viewed as principally affecting the outcome of top-down processes. Sponges on coral reefs are important members of the benthic community and provide a critically important functional linkage between water-column productivity and the benthos. As active suspension feeders sponges utilize the abundant autotrophic and heterotrophic picoplankton in the water column. As a result sponges across the Caribbean basin exhibit a consistent and significant pattern of greater biomass, tube extension rate, and species numbers with increasing depth. Likewise, the abundance of their food supply also increases along a depth gradient. Using experimental manipulations it has recently been reported that predation is the primary determinant of sponge community structure. Here we provide data showing that the size and growth of the sponge Callyspongia vaginalis are significantly affected by food availability. Sponges increased in size and tube extension rate with increasing depth down to 46 m, while simultaneously exposed to the full range of potential spongivores at all depths. Additionally, we point out important flaws in the experimental design used to demonstrate the role of predation and suggest that a resolution of this important question will require well-controlled, multi-factorial experiments to examine the independent and interactive effects of predation and food abundance on the ecology of sponges.     

Antarctic Porifera database from the Spanish benthic expeditions

The information about the sponges in this dataset is derived from the samples collected during five Spanish Antarctic expeditions: Bentart 94, Bentart 95, Gebrap 96, Ciemar 99/00 and Bentart 2003. Samples were collected in the Antarctic Peninsula and Bellingshausen Sea at depths ranging from 4 to 2044 m using various sampling gears.The Antarctic Porifera database from the Spanish benthic expeditions is unique as it provides information for an under-explored region of the Southern Ocean (Bellingshausen Sea). It fills an information gap on Antarctic deep-sea sponges, for which there were previously very few data.This phylum is an important part of the Antarctic biota and plays a key role in the structure of the Antarctic marine benthic community due to its considerable diversity and predominance in different areas. It is often a dominant component of Southern Ocean benthic communities.The quality of the data was controlled very thoroughly with GPS systems onboard the R/V Hesperides and by checking the data against the World Porifera Database (which is part of the World Register of Marine Species, WoRMS). The data are therefore fit for completing checklists, inclusion in biodiversity pattern analysis and niche modelling. The authors can be contacted if any additional information is needed before carrying out detailed biodiversity or biogeographic studies.The dataset currently contains 767 occurrence data items that have been checked for systematic reliability. This database is not yet complete and the collection is growing. Specimens are stored in the author’s collection at the Spanish Institute of Oceanography (IEO) in the city of Gijón (Spain). The data are available in GBIF.     

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 of tunicates of the genus Aplidium from the Weddell Sea (Antarctica)

Predation and competition are important factors structuring Antarctic benthic communities and are expected to promote the production of chemical defenses. Tunicates are subject to little predation, and this is often attributed to chemical compounds, although their defensive activity has been poorly demonstrated against sympatric predators. In fact, these animals, particularly the genus Aplidium, are rich sources of bioactive metabolites. In this study, we report the natural products, distribution and ecological activity of two Aplidium ascidian species from the Weddell Sea (Antarctica). In our investigation, organic extracts obtained from external and internal tissues of specimens of A. falklandicum demonstrated to contain deterrent agents that caused repellency against the Antarctic omnivorous predator, the sea star Odontaster validus. Chemical analysis performed with Antarctic colonial ascidians Aplidium meridianum and Aplidium falklandicum allowed the purification of a group of known bioactive indole alkaloids, meridianins A-G. These isolated compounds proved to be responsible for the deterrent activity.     

Secondary Metabolites as Mediators of Trophic Interactions Among Antarctic Marine Organisms

Secondary metabolites are widespread among lower phyla and understandingtheir functional role(s) in the producing organism has beenunder study in recent decades. Considerable progress has beenmade in understanding chemical ecological interactions amongterrestrial organisms, and similar research in the marine realmhas been initiated in recent years. Polar regions are more difficultto access and thus progress has been slower. Nevertheless, theextreme and often unique marine environments surrounding Antarcticaas well as the many unusual trophic interactions in antarcticmarine communities might well be expected to select for novelsecondary metabolites and/or novel functional roles for secondarymetabolites. Indeed, recent studies have documented novel, chemically-mediatedinteractions between molluscs and amphipods, between algae,urchins and anemones, and between sponges and their predators.The Porifera are the dominant phylum on the McMurdo Sound benthos,and representatives of this phylum have been shown to elaboratesea star feeding deterrents, inhibitors of fouling or infectiousorganisms, and metabolites which mediate predation via moltinhibition. As a result of studies on Antarctic sponges, newinsights into functional roles of pigments and the ability ofsponges to sequester metabolites have been gained, and a newmechanism of chemical defense has been described. Herein wedescribe recent results of our studies of trophic interactionsbetween sponges and their predators that are mediated by specificsponge secondary metabolites. Moreover, we highlight unusualchemically-mediated interactions in antarctic marine invertebratesother than sponges.     

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.     

On the origin of Antarctic marine benthic community structure

Environmental conditions fostering marine communities around Antarctica differ fundamentally from those in the rest of the world's oceans, particularly in terms of pronounced climatic fluctuations and extreme cold. Here, we argue that the rarity of pelagic larval stages in Antarctic marine benthic invertebrate species is a consequence of evolutionary temperature adaptation and that this has greatly contributed to the current structure of the Antarctic benthic community. In arguing this position, we challenge the likelihood of previously suggested survival strategies of benthic communities on the Antarctic continental shelf and slope during Cenozoic glacial periods. By integrating evidence from marine geology and geophysics, we suggest that the Antarctic continental shelf and slope were both unfavourable environments for benthic communities during glacial periods and that community survival was only possible in the deep sea or in shelters on the continental shelf as a result of the diachronism in maximum ice extent.     

Characterization of Bacterial,Archaeal and Eukaryote Symbionts from Antarctic Sponges Reveals a High Diversity at a Three-Domain Level and a Particular Signature for This Ecosystem

Sponge-associated microbial communities include members from the three domains of life. In the case of bacteria, they are diverse, host specific and different from the surrounding seawater. However, little is known about the diversity and specificity of Eukarya and Archaea living in association with marine sponges. This knowledge gap is even greater regarding sponges from regions other than temperate and tropical environments. In Antarctica, marine sponges are abundant and important members of the benthos, structuring the Antarctic marine ecosystem. In this study, we used high throughput ribosomal gene sequencing to investigate the three-domain diversity and community composition from eight different Antarctic sponges. Taxonomic identification reveals that they belong to families Acarnidae, Chalinidae, Hymedesmiidae, Hymeniacidonidae, Leucettidae, Microcionidae, and Myxillidae. Our study indicates that there are different diversity and similarity patterns between bacterial/archaeal and eukaryote microbial symbionts from these Antarctic marine sponges, indicating inherent differences in how organisms from different domains establish symbiotic relationships. In general, when considering diversity indices and number of phyla detected, sponge-associated communities are more diverse than the planktonic communities. We conclude that three-domain microbial communities from Antarctic sponges are different from surrounding planktonic communities, expanding previous observations for Bacteria and including the Antarctic environment. Furthermore, we reveal differences in the composition of the sponge associated bacterial assemblages between Antarctic and tropical-temperate environments and the presence of a highly complex microbial eukaryote community, suggesting a particular signature for Antarctic sponges, different to that reported from other ecosystems.     

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.     

Propagule pressure determines recruitment from a commercial shipping pier

Artificial structures associated with shipping and boating activities provide habitats for a diverse suite of non-indigenous marine species. Little is known about the proportion of invader success in nearby waters that is attributable to these structures. Areas close to piles, wharves and piers are likely to be exposed to increasing levels of propagule pressure, enhancing the recruitment of non-indigenous species. Recruitment of non-indigenous and native marine biofouling taxa were evaluated at different distances from a large commercial shipping pier. Since artificial structures also represent a desirable habitat for fish, how predation on marine invertebrates influences the establishment of non-indigenous and native species was also evaluated. The colonisation of several non-indigenous marine species declined rapidly with distance from the structure. Little evidence was found to suggest that predators have much influence on the colonisation success of marine sessile invertebrate species, non-indigenous or otherwise. It is suggested that propagule pressure, not predation, more strongly predicts establishment success in these biofouling assemblages.     

Benthic-pelagic coupling on coral reefs: Feeding and growth of Caribbean sponges

Benthic-pelagic coupling and the role of bottom-up versus top-down processes are recognized as having a major impact on the community structure of intertidal and shallow subtidal marine communities. Bottom-up processes, however, are still viewed as principally affecting the outcome of top-down processes. Sponges on coral reefs are important members of the benthic community and provide a crucial coupling between water-column productivity and the benthos. Other than scleractinian corals, sponges dominate many of these habitats where water column productivity is composed of mostly autotrophic and heterotrophic picoplankton that sponges actively filter. While predation upon sponges by invertebrates, fish, and turtles occurs, the sponges Callyspongia vaginalis, Agelas conifera, and Aplysina fistularis from Florida, Belize, and the Bahamas, respectively, exhibit a consistent and significant pattern of greater biomass, rates of growth, and feeding, as does their food supply, with increasing depth. Sponges consume 65-93% of the available particulate food supply and, at all sites, sponges increase in size and growth rate as depth increases, suggesting that food supply and, therefore, bottom-up processes significantly influence the distribution and abundance of sponges in these habitats.     

Antarctic marine biodiversity and deep-sea hydrothermal vents

The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60°S benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining.