Bythograea Thermydron Research Articles

The megalopal stage of the hydrothermal vent crab Austinograea rodriguezensis Tsuchida amp; Hashimoto, 2002 (Decapoda: Bythograeidae): a morphological description based on CLSM images.

The Bythograeidae is unique amongst brachyuran crab taxa as it is the only family where all 6 genera and 16 species are endemic to hydrothermal vents. During the research conducted by German Federal Institute for Geosciences and Natural Resources to identify inactive polymetallic sulphide deposits along Central and Southeast Indian Ridges, the INDEX project collected from hydrothermal vent fields 6 Bythograeidae megalopae. Entire specimens and dissected appendages were stained, mounted on slides and examined using Light Microscopy and Confocal Laser Scanning Microscopy. Additional molecular analysis using mtCOI confirmed the identification of the specimens as Austinograea rodriguezensis Tsuchida Hashimoto, 2002. The megalopal stage of A. rodriguezensis shows similarities and distinctions between the characters of two other bythograeid megalopae, Bythograea thermydron Williams, 1980, and B. microps Saint Laurent, 1984. Unlike other brachyuran megalopae, B. thermydron and A. rodriguezensis lack long serrate setae and stout serrate spines on the dactylus of the fifth pereiopod. In both species no coxal spines on the pereiopods were observed. The elliptical carapace of B. thermydron is broader than long vs longitudinally rectangular in A. rodriguezensis. This carapace shape resembles B. microps more than B. thermydron, however, the dorsal surface of B. microps carapace is densely covered in short setae vs only covered with short setae on the anterior 1/4 and the posterior 1/6 length of carapace in A. rodriguezensis. Furthermore, the amount of plumose natatory setae on the pleopods in B. microps is in total larger and more variable, than in A. rodriguezensis. Bythograeid megalopae seem quite generalized and miss specific features that reveal them distinctively as endemic vent crab. A distinction from other species is possible by observing the unique combinations of certain characters. This is the first megalopal stage description of Austinograea and the fourth within the Bythograeidae.

Ecology, adaptation and acclimatisation mechanisms of Bythograeidae Williams, 1980, a unique endemic hydrothermal vent crabs family: current state of knowledge

Diversified fauna have colonised the deep-sea hydrothermal vents, an environment characterised by high metallic concentrations and sulfide-rich waters. In 1977–79, brachyuran crabs were collected in hydrothermal vents around the Galapagos Rift, allowing description in 1980 of Bythograea thermydron and the new family Bythograeidae (and the superfamily Bythogreoidea). This family has a worldwide distribution and currently includes 13 species classified in 6 genera: Allograea (1 species), Austinograea (3 species), Bythograea (5 species), Cyanagraea (1 species), Gandalfus (2 species) and Segonzacia (1 species). These crabs have distinctive morphological and physiological characteristics, which reflect adaptations to particular deep-sea hydrothermal vent conditions. This review is the first on Bythograeidae, documenting the state of our knowledge regarding their taxonomy, evolution, ecology, morphology and physiology (i.e. osmoregulation, oxygen consumption, sulfide and metal detoxification, temperature tolerance). We also report on recent progress in maintaining bythograeids in an artificial ex situ environment.

Diversity and distribution of mobile genetic elements in marine invertebrates genomes

Mobile genetic elements (MGE) play an important role in genome structure and gene expression changes. All types of MGE are subdivided to two classes – retrotransposons and DNA-transposons. MGE were found in genomes of all main taxa of marine invertebrates and are represented by both classes. MGEs were found in genomes of Cnidaria species: Aurelia aurita, Acropora millepora, A. palmata, A. digitifera, Nematostella vectensis. MGE were studied in two flatworms (Platyhelminthes) species - Stylochus zebra and Bdelloura candida. In Annelida taxa, MGE were studied for Capitella capitata species. Echinodermata were represented in the review study by species Strongylocentrotus purpuratus, S. franciscanus, S. drobachiensis, Tripneustes gratilla, Lytechinus pictus, L. variegatus, Arbacia punctulata, and Eucidaris tribuloides. A quantity of MGE in Mollusca was studied for following species: Mytilus galloprovincialis, Chione cancellata, Crassostrea gigas, C. virginica, Anadara trapezia, Aplysia californica, Gibbula cineraria, Littorina littorea, and L. saxatilis. The type of Arthropoda is the most studied for MGE presence. MGE presence was studied for following Arthropoda species: Bythograea thermydron, Ventiella sulfuris, Maia brachydactila, Cancer pagurus, Pachygrapsus marmoratus, Penaeus monodon, P. vannamei, Litopenaeus stylirostris, Agononida laurentae, Galathea squamifera, Munida acantha, M. thoe, M. gregaria, M. zebra, Munidopsis recta, Eumunida annulosa, E. sternomaculata, and Rimicaris exoculata. A part of Chordata taxon, which is not included in Vertebrata subtupe, was studied too. This part was represented in the review by species Ciona intestinalis, Oikopleura dioica, and Branchiostoma floridae. A diversity of MGEs and their characters and its role in ontogenesis, in evolution and in changes of functions of genes and genomes were discussed.

Molecular cloning of manganese superoxide dismutase gene in the cladoceran Daphnia magna: Effects of microcystin, nitrite, and cadmium on gene expression profiles

Superoxide dismutases (SODs) are metalloenzymes that represent one important line of defense against oxidative stress produced by reactive oxygen species in aerobic organisms. Generally, waterborne pollutants caused by irregular anthropogenic activities often result in oxidative damage in aquatic organisms. The aim of this study was to molecularly characterize the manganese superoxide dismutase gene (Dm-MnSOD) in the waterflea, Daphnia magna, and evaluate the mRNA expression patterns quantified by real-time PCR after exposure to three common waterborne pollutants (microcystin-LR, nitrite, and cadmium). The results showed that the full-length Dm-MnSOD sequence consists of 954bp nucleotides, encoding 215 amino acids, showing well-conserved domains that are required for metal binding and several common characteristics, such as two MnSOD domains. The deduced amino acid sequence of Dm-MnSOD shared over 70% similarity with homologues from Bythograea thermydron, Dromia personata, Cancer pagurus, and Scylla paramamosain. Dm-MnSOD gene expression was up-regulated in response to exposure to the three chemicals tested. The overall results indicated that Dm-MnSOD gene is an inducible gene and potential biomarker indicating these pollutants in the environment.

Morphological adaptations to chronic hypoxia in deep-sea decapod crustaceans from hydrothermal vents and cold seeps

Animals inhabiting hydrothermal vents and cold seeps face conditions that are challenging for survival. In particular, these two habitats are characterized by chronic hypoxia, sometimes reaching complete anoxia. The characteristics of the scaphognathite and gills were studied in four species of shrimp and three species of crabs from hydrothermal vents and cold seeps, in order to highlight potential adaptations that could enhance oxygen acquisition in comparison with shallow-water relatives. All the vent and seep species studied here exhibit significantly larger scaphognathites, likely allowing more water to flow over their gills per stroke of this appendage. This is probably more energetically efficient that prolonged hyperventilation. In contrast to annelids, vent and seep decapods usually do not possess enlarged gills, a phenomenon likely due to the physical limitations imposed by the size of the gill chamber. In the vent shrimp Rimicaris exoculata and the vent crab Bythograea thermydron, however, there is a significantly higher specific gill surface area linked to a higher number of lamellae per gram of gill. Again in contrast to annelids, the diffusion distance through the gills is not strikingly different between the vent shrimp Alvinocaris komaii and the shallow-water species Palaemon spp. This may indicate that the epithelium and cuticle of the decapod gills are already optimized for oxygen uptake and that reducing the thickness of these compartments is not physically possible without affecting the physical integrity of the gills.

Characterization and sequence analysis of manganese superoxide dismutases from Brachyura (Crustacea: Decapoda): Hydrothermal Bythograeidae versus littoral crabs

Hydrothermal vent conditions are particular and organisms living in these environments may have developed detoxification mechanisms and/or genetic adaptations. In particular, physico-chemical conditions are thought to generate reactive oxygen species, highly toxic for organisms. The enzyme superoxide dismutase constitutes the first line of defense against oxidative damage. To improve our understanding of the environmental impacts exerted on the vent organisms, we have characterized the two manganese superoxide dismutase cDNAs (mitochondrial: mMnSOD and cytoplasmic: cMnSOD) of three members of the Bythograeidae (Bythograea thermydron, Cyanagraea praedator and Segonzacia mesatlantica), the only endemic crab family living in hydrothermal vents. In comparison, the isolation of manganese superoxide dismutase cDNAs was also carried out in several littoral crab families. MnSOD signatures were found in both sequences from each species studied, as well as different residues involved in metal coordination and protein activity. The phylogenetic analysis performed confirms the probable ancient duplication that gave rise to the two MnSODs (cMnSOD and mMnSOD). This study describes two potential distinct mMnSOD isoforms presenting particular peptide signals. Nevertheless, no sequence particularity that could support the hypothesis of a genetic adaptation was found in Bythograeidae's MnSODs compared to the other sequences. The mRNA expression analysis performed by real-time PCR on B. thermydron and S. mesatlantica compared to Cancer pagurus and Necora puber revealed a higher cMnSOD and mMnSOD mRNA expression in hydrothermal crabs compared to littoral crabs.

Metallothionein genes from hydrothermal crabs (Bythograeidae, Decapoda): Characterization, sequence analysis, gene expression and comparison with coastal crabs

Hydrothermal vent conditions can alter DNA and hydrothermal organisms may develop detoxification mechanisms and/or genetic adaptations. Hydrothermal vent animals notably synthesize a high quantity of metallothioneins (MT). Recent studies have revealed that the levels of MT within hydrothermal crustacean tissues are higher than those found in other vent animals. To improve our understanding of the environmental impacts exerted on the vent organisms, we characterized the metallothioneins (cDNA and Mt genes) of several members of the Bythograeidae ( Bythograea thermydron, Cyanagraea praedator and Segonzacia mesatlantica) which is the only endemic hydrothermal crab family. In comparison, the isolation of metallothionein cDNA was also carried out in several coastal crab families. The results showed that the hydrothermal crabs possess Mt composed of three exons and two introns presenting conserved splicing signals. The cDNA sequences isolated from distinct crabs showed multiple substitutions. In spite of the unique environmental conditions, the protein sequence analysis revealed no specific amino acid residue for the MT of the three hydrothermal crabs. However, gene expression analysis performed by real-time PCR based on S. mesatlantica (hydrothermal crab) compared to Pachygrapsus marmoratus (coastal crab) confirmed the higher metallothionein induction in hydrothermal crabs suggested by others authors.

Biology of the Vent Crab Bythograea thermydron: A Brief Review

This paper provides a review of relevant literature concerning the vent crab Bythograea thermydron. This body of work describes a crab species that shares fundamental biological characteristics with typical shallow-water brachyuran crabs, yet possesses a suite of highly evolved traits specific for life at hydrothermal vents. Bythograea thermydron is one of only six known species of Bythograea and is very abundant at vent sites along the East Pacific Rise. Because of the large amount of scientific work at this location, almost everything known about bythograeid vent crabs is based on studies of this single species. This review specifically deals with biogeography, systematics, and evolution; morphology, physiology and special adaptations; ovarian development; mating, brooding, and hatching; and larval biology and dispersal. The various sections emphasize comparisons with shallow-water crabs and highlight characteristics such as: (1) the unique eye structure in the adult stage, which is adapted for sensing the exceptionally dim light that is generated by the vents themselves; (2) the extreme tolerance of adults and juveniles to conditions of low oxygen and high sulfides; (3) the exceptional eurythermal character of juvenile and adult physiology; and (4) the seasonality of ovarian development and subsequent reproductive activity. Discussion of larval biology presents various scenarios of larval dispersal and recruitment back to the vent sites.

Effects of Food Deprivation on Enzymatic Activities of the Mediterranean Deep-sea Crab, Geryon Longipes A. Milne-Edwards, 1882 and the Pacific Hydrothermal Vent Crab, Bythograea Thermydron Williams, 1980 (Decapoda, Brachyura)

Effects of Food Deprivation on Enzymatic Activities of the Mediterranean Deep-sea Crab, Geryon Longipes A. Milne-Edwards, 1882 and the Pacific Hydrothermal Vent Crab, Bythograea Thermydron Williams, 1980 (Decapoda, Brachyura)

Identification of new subgroup of HSP70 in Bythograeidae (hydrothermal crabs) and Xanthidae

Crabs of the Bythograeidae family (Crustacea: Brachyura: Bythogreoidea) are the only endemic crab family living in hydrothermal fields. The hydrothermal environment is characterized by unique ecological parameters, such as the high temperature gradient around the hydrothermal chimney (2–350 °C), a fluid environment containing high levels of metals and numerous gases. The 70-kDa Heat Shock Protein (HSP70) group is the most-studied HSP, because it is ubiquitous, and a strong positive correlation has been found between the amounts of HSP70 produced in response to stress, and the ability of the organism to withstand stressful conditions. The 70-kDa heat shock protein genes from Bythograeids (species analyzed: Bythograea thermydron, Cyanagraea praedator and Segonzacia mesatlantica) were characterized. Our results revealed that Bythograeidae possess genes which are similar with those present in Xanthids (coastal crabs). The deduced protein sequences displayed motifs distinct from those in the other crustacean HSC70/HSP70s available in the databases. Phylogenetic analysis showed that these members of HSP70 family identified in Bythograeidae and Xanthidae constitute a new subgroup within this family.

Species sympatry and horizontal transfers of Mariner transposons in marine crustacean genomes

Mariner-like elements ( MLEs) have been widely detected in terrestrial species. The first complete MLE isolated from a marine invertebrate was detected in the genome of the hydrothermal crab Bythograea thermydron by Halaimia-Toumi et al. [Halaimia-Toumi, N., Casse, N., Demattei, M.V., Renault, S., Pradier, E., Bigot, Y., Laulier, M., 2004. The GC-rich transposon Bytmar1 from the deep-sea hydrothermal crab, Bythograea thermydron, may encode three transposase isoforms from a single ORF. J. Mol. Evol. 59, 747–760] and called Bytmar1. Here, we report the isolation of three new Bytmar1 relatives from the genomes of one hydrothermal amphipod Ventiella sulfuris ( Vensmar1) and two coastal crustacea, Maia brachydactila ( Maibmar1) and Cancer pagurus ( Canpmar1). Like Bytmar1, these MLEs have an unusually high GC content, a high CpG ratio, and a low TpA ratio. Their consensus sequence encodes a transposase that is preceded by an N-flag, as in Bytmar1, which could be a marine feature. Only one of the 19 clones obtained, Vensmar1.3, encoded for a full-length transposase. The phylogenetic analyses revealed that all these Bytmar1-related elements can be differentiated into two clusters, corresponding to the coastal or hydrothermal origin of their hosts. They also confirmed that the irritans sub-family comprises at least four lineages that seem to depend on the taxonomical position and habitat of their hosts. Finally, we observed that elements coding for two potentially complete transposases exhibiting 99.5% similarity, Bytmar1.11 and Vensmar1.3, were present in the genome of two distantly related hydrothermal crustacea, one Amphipod and one Decapod. The hypothesis of horizontal transfers is discussed in the light of the sequence similarities observed.

Food sources for the early life history stages of the hydrothermal vent crab Bythograea thermydron: a stable isotope approach

We used stable isotope analysis to examine food sources for early life-history stages of the vent crab Bythograea thermydron. During two cruises to a hydrothermal vent site along the East Pacific Rise, we collected a variety of endemic organisms, including approximately 300 specimens of B. thermydron. The crab collection consisted mainly of megalopae and early juveniles, but also included adults and a single zoea. As expected, the carbon-isotope composition of newly released zoeae (−12.2%) was similar to the female (−11.1%) and clearly different from megalopae (21.7%). Because we were unsuccessful in culturing the zoea larvae, we were not able to conduct experiments to determine the effect of diet on isotopic composition. The tissue of megalopae was depleted in 13C (−21.7%) when compared to indigenous prey species, but was similar to that expected for carnivorous zooplankton dependent on surface primary production. The nitrogen-isotope composition of megalopae was enriched in 15N (10%) relative to potential prey species, again suggesting a photosynthetic source of primary production. The mean carbon-isotope composition of newly metamorphosed juvenile crabs (−19.9%) resembled megalopae, while tissue from subsequent juvenile stages was enriched in 13C (−10.9%) with values similar to those measured in co-occurring prey species. These results imply that megalopae are dependent on a source of primary production exogenous to the vents, but switch to a vent-based food web soon after metamorphosis to the juvenile stage.

Lipid composition of deep-sea hydrothermal vent tubeworm Riftia pachyptila, crabs Munidopsis subsquamosa and Bythograea thermydron, mussels Bathymodiolus sp. and limpets Lepetodrilus spp.

Lipid composition was determined for hydrothermal vent species collected by the Deep Submergence Vehicle ALVIN from chimneys at 2,500 m depth on the East Pacific Rise. These are the first lipid biomarker studies for most of these species. Lipid content was low and dominated by polar lipid in the vestimentiferan tubeworm Riftia pachyptila, mussels Bathymodiolus sp. and limpets Lepetodrilus spp. The galatheid ( Munidopsis subsquamosa) and most brachyuran adult ( Bythograea thermydron) crabs were characterized by higher storage lipid (triacylglycerol). Total polyunsaturated fatty acids were similar in R. pachyptila plume and body, but higher in the posterior part of the soft body, which had more docosahexaenoic acid (2–5% of total FA) compared to the anterior and plume (≤ 0.3%). Two sulphur-oxidizing bacterial markers, 16 : 1( n − 7) c and 18 : 1( n − 7) c, were high in R. pachyptila and mussel (up to 23%), but lower in both crab species (4–17%). R. pachyptila had greater nonmethylene interrupted diunsaturated fatty acids (8–13%) than all other species (2–8%). R. pachyptila may desaturate and elongate 18 : 1( n − 7) c to obtain essential polyunsaturated fatty acids 20 : 5( n − 3) and 20 : 4( n − 6). The sterol composition of R. pachyptila included similar amounts of cholesterol and desmosterol, whereas the other species had a more diverse sterol composition. These differences in lipids, fatty acids and sterols reflect diverse nutritional strategies and possibly temperature regimes in these species.

The GC-Rich Transposon Bytmar1 from the Deep-Sea Hydrothermal Crab, Bythograea thermydron, May Encode Three Transposase Isoforms from a Single ORF

Mariner-like elements (MLEs) are classII transposons with highly conserved sequence properties and are widespread in the genome of animal species living in continental environments. We describe here the first full-length MLE found in the genome of a marine crustacean species, the deep-sea hydrothermal crab Bythograea thermydron (Crustacea), named Bytmar1. A comparison of its sequence features with those of the MLEs contained in the genomes of continental species reveals several distinctive characteristics. First, Bytmar1 elements contains an ORF that may encode three transposase isoforms 349, 379, and 398 amino acids (aa) in long. The two biggest proteins are due to the presence of a 30- and 49-aa flag, respectively, at the N-terminal end of the 349-aa cardinal MLE transposase. Their GC contents are also significantly higher than those found in continental MLEs. This feature is mainly due to codon usage in the transposase ORF and directly interferes with the curvature propensities of the Bytmar1 nucleic acid sequence. Such an elevated GC content may interfere with the ability of Bytmar 1 to form an excision complex and, in consequence, with its efficiency to transpose. Finally, the origin of these characteristics and their possible consequences on transposition efficiency are discussed.

Comparative degradation rates of chitinous exoskeletons from deep-sea environments

Hydrothermal vent environments, particularly those associated with the vestimentiferan Riftia pachyptila, are believed to be among the highest chitin-producing systems. In order to elucidate the chitin cycle in these environments, we estimate the in situ chitin degradation rates of tube-worm exoskeletons. Our in situ experiments show that the tubes of Riftia are highly stable structures. Comparative measurements of the degradation rates of Riftia tubes and crab shells immersed at deep-sea vents show that the tubes would be degraded within 2.5 years, whereas the time for the total degradation of the vent crab (Bythograea thermydron) carapaces would not exceed 36 days. The importance of the microbial participation in this degradation was estimated for Riftia tubes. Based on previous work, we calculated chitin production by a population of Riftia tubes of about 750 g m-2 year-1 (763). From our in situ experiments, we estimated a microbial chitinolysis rate of about 500 g m-2 year-1 (496) (65% of the chitin produced).Exoskeletons containing β-chitin appear more stable in natural environments than those containing α-chitin and would thus be less available as carbon and nitrogen sources. In contrast, isolated β-chitin was hydrolysed faster than α-chitin during in vitro degradation experiments; for instance, Riftia β-chitin was degraded about 3- to 4-fold faster than Bythograea α-chitin. A stabilization process by disulfide bonds of the proteins-chitin link, rather than the crystalline form of the chitin (α/β), accounts for the resistance of Riftia tubes to enzymatic attacks.

Comparative ESI-MS study of ∼2.2 MDa native hemocyanins from deep-sea and shore crabs: from protein oligomeric state to biotope

In the past years, the potential of electrospray ionization mass spectrometry (ESI-MS) for the observation of intact weak interactions, such as non-covalent protein-ligand, protein-protein, protein-DNA complexes, has spread out. The coupling of ESI with time-of-flight (TOF) and quadrupole-time-of-flight (Q-TOF) analyzers has even enabled the detection of larger complexes with molecular weights greatly higher than 200 kDa. In this paper, we report a comparative ESI-MS study on the protein quaternary structure of native hemocyanins (Hc) from crabs living in different biotopes: a shore crab ( Carcinus maenas) and two deep-sea crabs ( Segonzacia mesatlantica and Bythograea thermydron). Hc is an extracellular blood protein, composed of several protein chains which can associate in large multimers. The goal of this study is to point out that the oligomerization state of native Hcs is biotope-dependent. Depending on the crab, ESI-MS analyses under non-denaturing conditions reveal different oligomeric forms present in equilibrium in solution. Molecular weights up to 2,235 kDa were measured for the associations of 30 subunits of the Bythograea thermydron Hc. Thanks to ESI-MS analyses, it could be concluded for the first time that the oligomerization state of native Hcs is dependent on the crab environment. The investigation of these different non-covalent self-assemblies is very important for the life history of crabs, since they are directly related with different oxygen binding abilities and thus, with their ability to colonize habitats with different oxygen contents.

Spatial and temporal patterns in development of eggs in the vent crab Bythograea thermydron

In this paper we describe results of a study on the reproductive biology of the hydrother- mal vent crab Bythograea thermydron. At vent sites along the East Pacific Rise, histological analyses of gonads from adult female crabs collected in November 1997, May 1999 and May 2000 provide strong evidence that B. thermydron undergoes a seasonal cycle of reproductive activity, with egg hatching peaking in April-May. Females undergo a synchronous pattern of oocyte development, whereby one cohort of oocytes undergoes vitellogenesis, while a second cohort is present and remains immature until the initial cohort reaches full maturity and is extruded onto the pleopods. When mean oocyte-size-frequency distributions were compared across months, the 2 May samples were similar to each other, with a dominance of previtellogenic oocytes and a second, smaller group of vitellogenic oocytes also present. In contrast, the November sample exhibited a wide variety of oocyte sizes, with no one size class predominating. In addition, May samples from the vent periphery contained a high proportion of females that showed evidence of recent egg hatching, while females collected from the region near the vent orifice exhibited a wide range of the intermediate stages of gonadal development. This set of data suggests an annual cycle whereby a given cohort of oocytes is in a previtellogenic state in early spring (April-May), but has begun vitellogenesis by late autumn (November) and has developed to maximum maturity by the time the eggs are extruded the follow- ing spring. While the current clutch of eggs is being brooded, a second cohort of previtellogenic oocytes begins to develop in the ovary and the cycle is repeated. Superimposed on this annual cycle is a pattern of behavior whereby females with mature gonads migrate to the vent periphery where fertilized eggs are extruded, brooded, and hatched.

What is a naked retina good for?

The crab Bythograea thermydron has eyes that consist of large naked retinas. Studies of the crab's larval forms suggest that these eyes are a specific adaptation to the dim environment of oceanic volcanic vents.

Adaptive visual metamorphosis in a deep-sea hydrothermal vent crab.

Hydrothermal vents along the mid-ocean ridges host ephemeral ecosystems of diverse endemic fauna including several crustacean species, some of which undergo planktonic development as larvae up to 1,000 m above and 100 km away from the vents. Little is known about the role of vision in the life history of vent fauna. Here we report that planktonic zoea larvae of the vent crab Bythograea thermydron possess image-forming compound eyes with a visual pigment sensitive to the blue light of mesopelagic waters. As they metamorphose and begin to descend to and settle at the vents, they lose their image-forming optics and develop high-sensitivity naked-retina eyes. The spectral absorbance of the visual pigment in these eyes shifts towards longer wavelengths from larva to postlarva to adult. This progressive visual metamorphosis trades imaging for increased sensitivity, and changes spectral sensitivity from the blue wavelengths of the larval environment towards the dim, longer wavelengths produced in the deeper bathypelagic vent environment of the adults. As hydrothermal vents produce light, vision may supplement thermal and chemical senses to orient postlarval settlement at vent sites.

PREDATION STRUCTURES COMMUNITIES AT DEEP-SEA HYDROTHERMAL VENTS

The structure and dynamics of natural communities result from the interplay of abiotic and biotic factors. We used manipulative field experiments to determine the relative roles of abiotic conditions and biotic interactions in structuring deep-sea (2500 m depth) communities along environmental gradients around hydrothermal vents of the eastern tropical Pacific Ocean (East Pacific Rise, at 9°50′ N). We tested (1) whether predation by crabs and fishes affects the recruitment of benthic species and subsequent community structure and (2) whether the effects of predation vary along the steep gradients of temperature, oxygen, sulfide, and metal concentrations near vents. Recruitment substrates (basalt cubic blocks, roughly 10 cm on a side), both uncaged and caged to exclude predators (crabs, fishes, whelks, and octopi), were deployed along a decreasing vent fluid-flux gradient. The exclusion of predators for 8 mo increased the abundance of small mobile gastropods and amphipod crustaceans but decreased the abundance of sessile invertebrates, including juvenile vestimentiferan worms, tubiculous polychaetes, and mussels. Effects of predation were strongest nearest to hydrothermal vents, where abiotic environmental conditions were most extreme but productivity and the overall abundances of benthic invertebrates and mobile predators were the greatest. Additional 5-mo experiments conducted at three different locations showed similar trends at all sites, indicating that these effects of predation on benthic community structure are repeatable. Stomach-content analyses of the most abundant predators found at vents indicated that the zoarcid fish (Thermarces cerberus) primarily feeds on the vent snail Cyathermia naticoides, the limpet Lepetodrilus elevatus, and the amphipod crustacean Ventiella sulfuris, the very species that showed the greatest increase following predator exclusion. In contrast, brachyuran (Bythograea thermydron) and galatheid (Munidopsis subsquamosa) crab stomachs did not contain small mobile grazers, and crabs presented with arrays of the most common vent invertebrate species preferred mussels and vestimentiferans over limpets. Our results indicate that predation by large mobile predators influences the structure of hydrothermal vent communities, directly by reducing the abundance of gastropod prey species, and indirectly by reducing gastropod grazing and by bulldozing of recruits of sessile invertebrates.