Search

The spatial patterns of taxonomic diversity of annelid polychaete species from the continental shelf in the Southern Gulf of Mexico were examined in this study. We used taxonomic distinctness and its spatial variations to explore the diversity patterns and how they change between Southern Gulf of Mexico regions. In addition, using taxonomic distinctness as a dissimilarity measure and Ward's Clustering, we characterized three distinct faunal assemblages. We also investigated patterns of richness, taxonomic distinctness, and distance decay of similarity between sampling stations as a ß-diversity measure. Finally, we examined the spatial relationships between polychaete assemblages and environmental variables to test the relative importance of spatial and environmental components in annelid polychaete community structure from the Southern Gulf of Mexico. We used a combination of eigenvector-based multivariate analyses (dbMEMs) and distance-based redundancy analysis (dbRDA) to quantify the relative importance of these explanatory variables on the spatial variations of taxonomic distinctness. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of the variance than those parameters could alone. [ABSTRACT FROM AUTHOR]

The small Lumbrineridae Gallardoneris iberica Martins, Carrera-Parra, Quintino & Rodrigues, 2012 was first described as new to science based on specimens from Portuguese waters. Then, it was successively reported from several south European areas, including Spain, Italy, Greece, and Cyprus. Here evidence is presented that G. iberica should be placed in synonymy with Lumbrineris nonatoi Ramos, 1976, originally described from NW Mediterranean waters, a species that fits with the diagnosis of Gallardoneris. Based on specimens from the French coasts of the NW Mediterranean, this paper (1) redescribes the species using the new combination Gallardoneris nonatoi (Ramos, 1976) and (2) provides a morphometric analysis of its main morphological characters. The lack of recent reports of G. nonatoi comb. nov. in Mediterranean waters is presumably due to the recent redescription of the species as L. nonatoi based on specimens from the Gulf of Mexico. However, these specimens belong to Lumbrineris, as currently defined. By assessing their morphological differences, it is concluded that the specimens from the Gulf of Mexico represent a different and new species, namely Lumbrineris jan sp. nov. Also discussed is the possible assignation of Lumbrineris longipodiata Cantone, 1990, a poorly known species seldom recorded since its original description from the Gulf of Catania (Mediterranean Sea) to Gallardoneris, as well as on whether it is a valid species or may be an additional junior synonym of G. nonatoi comb. nov. [ABSTRACT FROM AUTHOR]

Sthenelais simplex Ehlers, 1887 was described from the Gulf of Mexico, but it is currently regarded as a junior synonym of Leanira incisa (Grube, 1877) described from the Congo. The latter is now included in Ehlersileanira Pettibone, 1970 as its type species. However, the redescription of L. incisa was based on specimens from several distant localities, including the type material of S. simplex. Through the revision of material from the University of Miami Deep-Sea Expeditions along the tropical Atlantic, including the Gulf of Guinea, specimens corresponding to S. simplex and E. incisa were found and carefully studied. The main results include the restriction of E. incisa and the reinstatement of S. simplex as a different species under the name E. simplex (Ehlers, 1887) comb. nov., reinst. Ehlersileanira simplex differs from E. incisa by having large auricles, as long as the median antennal ceratophore; median antenna with ceratophore and style of similar length; rectangular elytra in segment 4; branchiae beginning at segment 16; ctenidial pads beginning at segment 9; and tubular segmental papillae beginning at about segment 20. A key to all the species of Ehlersileanira is also included. [ABSTRACT FROM AUTHOR]

This study focused on spatial-temporal variations in the composition and structure of polychaete communities associated with two coexisting oyster species in a southern Gulf of Mexico coastal lagoon, showed that Crassostrea rhizophorae hosted 23 polychaete species and C. virginica only four. The observed variability was mainly explained by differences in salinity and sedimentation rate, two factors that also influenced the host species distribution. The highest values of richness and diversity occurred at C. rhizophorae sites during the rainy season, coinciding with increased salinity and a decrease in sedimentation rate. The shell-borer species Nereis garwoodi and Polydora websteri occurred in both oysters, but showing higher frequencies in C. virginica during the Nortes season (i.e., the cold fronts season). Our results underscore the contrasting diversity of associated polychaetes with two coexisting oyster species and emphasize the need for considering additional environmental parameters to allow better understanding of the factors that are driving the structure of these communities. • Polychaete assemblages varied between the congeneric and sympatric oyster species. • Salinity and sedimentation rate influenced the polychaete distribution. • Shell-boring polychaete species were more frequent in C. virginica [ABSTRACT FROM AUTHOR]

Introduction: The Río Lagartos lagoon, located in the Ría Lagartos Biosphere Reserve, Yucatán, Gulf of Mexico, is a coastal hypersaline system ca. 80 km long (east-west). It comprises three basins: western (close to Río Lagartos fishermen village), middle (Las Coloradas) and eastern (close to El Cuyo fishermen village), that communicate through very narrow natural channels. Despite several studies have been performed on the vertebrate fauna, the aquatic invertebrates, and especially polychaetes, remain largely unknown. Objective: The objective of this study is to describe the composition and distribution of the benthic polychaete community, and to analyse potential environmental drivers. Methods: The biological material was collected in 16 stations distributed along the lagoon during the rainy season (September 2017). Two replicates per station were obtained using a Ponar standard dredge or cores (6" diameter). Environmental variables such as grain size, organic carbon content in the sediments, and salinity, among others, were measured. Results: A total of 827 specimens belonging to 26 species and 16 families were identified. Of these, 23 species are new records for the Río Lagartos lagoon. Community composition changed between the different basins associated with strong gradients in salinity, subaquatic vegetation (algae and seagrasses) proportions in the samples and grain size. No polychaetes were recorded at the easternmost basin (El Cuyo basin), where salinity was between 67-80 psu. In the rest of the lagoon, the distribution of polychaetes was heterogeneous, especially near the mouth (western basin), where the highest and lowest density, species richness and diversity were recorded. The highest density was found at station 6, where dense algal mats of the genus Avrainvillea dominated. The families Syllidae and Nereididae were the most abundant and widely distributed families in the lagoon. The species Syllis lagunae and Nereis pelagica dominated the western basin and Prionospio heterobranchia and Sphaerosyllis taylori dominated the middle basin. Conclusions: The salinity records associated with some species were well above the top limits previously reported, establishing the euryhaline character of many species in the region. [ABSTRACT FROM AUTHOR]

The impacts of the 2010 Deepwater Horizon (DWH) disaster on deep-sea Gulf of Mexico benthic communities were analyzed one year after the blowout. Richness, diversity, and evenness were severely impaired within a radius of approximately 1 km around the DWH wellhead. However, lower diversity than background was observed in several stations up to 29 km to the southwest of the wellhead. Compared to samples from 2010, abundance near the DWH wellhead increased in 2011 with some of the highest values found at stations within the 1 km radius. The increase was mostly caused by the high abundance of opportunistic polychaetes of the family Dorvilleidae, genus Ophryotrocha . At contaminated stations near the DWH wellhead, diversity did not change with increased sampling area, whereas a steep increase of diversity with increasing sampling area was observed at stations farther from the wellhead. The spatial extent of DWH impacts appeared to decrease from 2010 to 2011. Impacts on diversity near the wellhead were still observed; however, the large increase in abundance may indicate the initial stages of recovery, year-to-year variability, or an early stage of succession following a disturbance; and this can be resolved only with additional temporal sampling. [ABSTRACT FROM AUTHOR]

Community structure and abundance of benthic polychaetes along a transect on the central northern Gulf of Mexico continental slope were examined. Spatial, seasonal, short- (~1 year), and long-term (~16-17 years) temporal comparisons of assemblages were conducted with samples collected in 1983-1984 and 2000-2001. Polychaete abundance did not consistently decrease between 325 and 1500 m, but sharply decreased between 1500 and 2100 m. On the upper slope (325-1500 m) polychaete abundance approximately doubled between fall 1983 and spring 1984, but had returned to initial levels by fall 1984. On the lower slope (2500 m) seasonal variations in abundance were less pronounced. The taxonomic composition of the polychaete assemblages changed continuously along a depth gradient; however, temporal variations of the assemblages at all water depths were generally minor. This study provides a baseline for naturally occurring spatial and temporal dynamics of benthic polychaete communities on the northern Gulf of Mexico continental slope. [ABSTRACT FROM AUTHOR]

Aim To test the hypothesis that low productivity drives the nestedness component of β-diversity in polychaetes at the deep-sea floor. Location Western Gulf of Mexico. Methods We used A. Baselga's (2010, Global Ecology and Biogeography, 19, 134-143) metrics of species replacement and nestedness to assess their overall significance with differences in depth and particulate organic carbon ( POC) flux to the seafloor. We used M. A. Rodríguez-Gironés & L. Santamaría's (2006, Journal of Biogeography, 33, 924-935) BINMATNEST to calculate the significance and direction of nestedness with depth and POC flux. Results Nestedness was the most significant part of β-diversity with depth and POC flux. The rank order of nestedness increased significantly with increasing depth, and decreased significantly with increasing POC flux. There was little endemism below 2000 m. Main conclusion The polychaete fauna in the deepest western Gulf of Mexico is largely a nested subset of the shallower upper to mid-bathyal fauna. While the causes of β-diversity in the deep sea are undoubtedly multivariate, the relative importance of turnover and nestedness appears to be modulated by productivity in the form of POC flux to the seafloor. Under circumstances of extremely low POC flux and animal density in the deepest reaches of the Gulf, nestedness may be caused by some populations being maintained by immigration from larger populations upslope, or by biogeographic filtering for tolerance to abyssal conditions. Resources at great depths in regions of exceptionally low productivity may be too limited to permit adaptation resulting in endemism and continued downslope turnover. If productivity helps to explain the nestedness part of β-diversity, this may lead to a more unified theory of deep-sea biodiversity. [ABSTRACT FROM AUTHOR]

Polychaete worms (Annelida), the dominant macrofaunal taxon in most fine-grained marine sediments, were sampled in 1983–85 and then again in 2000–02 at nine locations at depths of 324–1454 m. on the upper continental slope of the northern Gulf of Mexico (GoM). The assemblages exhibited relative stability in abundance and diversity, but fell into six separate groups of species (>35% similarity) that were related to time-of-sampling, location, depth. This depth gradient experiences an increase in oxygen from 2.5 to 4.5 ml/L, a six degree decrease in temperature (10–12° down to 4 °C) and a decline of 30–37 mg C m −2 day −1 down to 7 mg C m −2 day −1 in estimates of the particulate organic carbon (POC) input to the sea floor, but these steep gradients had secondary effects on species turnover or depth-related zonation (Beta diversity). The species composition of four of the six groups was separated on the basis of sampling between 1983–85 and 2000–02 as opposed to depth or location. The species composition of the two groups on the eastern transect was different from the western sites and the two eastern groups differed in species composition from each other between 1983–85 and 2000–02. The two groups of species at the three deeper sites to the west (864–1410 m) were also separated on the basis of time-of-sampling but the group of species located at the three shallow locations (324–625 m) was not; it was a mixture of the two sampling periods. Significantly higher densities (p<0.05) in April 1984, on the eastern transect, suggest that seasonal recruitment may have occurred but the higher densities were attributed to only two species. [ABSTRACT FROM AUTHOR]

The genus Amphictene is reported for the first time from Mexico. Previous records for America are restricted to Brazil (A. catharinensis) (Grube, 1870), and Guatemala (A. guatemalensis) (Nilsson, 1928). In this paper we describe a new species, Amphictene helenae sp. n., characterized by the presence of three pairs of tentacular cirri, while other species have only two pairs. The new species is closely similar to Amphictene catharinensis, and can be distinguished by the presence of a circular group of glandular papillae inserted between the lines of glandular cirri present from the second segment. A. guatemalensis is redescribed based on type material; it differs from the new species in the presence of two pairs of tentacular cirri on segments 1 and 2, six pairs of glandular cirri on the third segment, and four glandular lobes fused in pairs on the fourth segment. [ABSTRACT FROM AUTHOR]

The distribution and composition at the genus level of polychaetes greater than 500 μm of 54 sites in the southwestern Gulf of Mexico in a depth range of 185–3762 m were analyzed. Samples were collected on board the R/V Justo Sierra (Universidad Nacional Autónoma de México) in two cruises carried out in June 2015 and September 2016. Sixty-nine genera belonging to 33 families were recorded. The families with the highest abundance were: Spionidae, Paraonidae, Pilargidae and Capitellidae. Spionidae, Capitellidae and Paraonidae families presented the highest genus richness. The highest abundance was observed in the southern region of the study area and in the upper bathyal zone while the highest taxonomic richness was registered in the Campeche Bay, in the northwestern region of the study area and in intermediate depths. Polychaeta community functional diversity (bioturbation traits and feeding guilds) was also analyzed. A general decrease in functional diversity was observed as depth increased, presenting a partial biodiffusors and deposit-feeders dominance in the deepest zones. Distribution was highly related with depth, sediment granulometry, temperature and dissolved oxygen concentration of the bottom water. • A Polychaeta abundance depth related pattern was found. • High Polychaeta diversity was related to hydrocarbons seep areas. • Polychaeta functional diversity decreased with increasing depth. • Temperature, O 2 and granulometry are the main drivers of Polychaeta community structure. [ABSTRACT FROM AUTHOR]

Abstract: Patterns of taxonomic and functional diversity in polychaete assemblages were examined in the deep northern Gulf of Mexico, including the first analysis of polychaete feeding guild distribution. An analysis of samples from a total of 51 stations located along 7 transects plus additional nearby sites, indicated that density decreased exponentially with depth, with the central locations having higher densities than the eastern and western regions. Alpha diversity was also highest at the central stations associated with the Mississippi trough. The samples can be grouped into three significant clusters based on thirty percent similarity of species composition. BIO-ENV indicated depth, sediment particle size, and export POC were most important variables explaining distributions. The diversity of polychaete feeding guilds was high in the Mississippi trough, upper and mid-slope regions but declined to a few guilds on the Sigsbee abyssal plain. Combining feeding guild analysis with traditional analysis of species diversity contributes to a clearer understanding of trophic diversity in deep-sea benthic assemblages. [Copyright &y& Elsevier]

Polychaetes belonging to the Capitella 'capitata' species complex thrive in polluted or disturbed marine sediments. Sibling species differ in their reproductive and developmental features. Here we examine the life cycle of Capitella sp. G from Galveston Bay, TX. This species was collected in Galveston Bay and cultured in the laboratory. Brooding tubes were isolated from the culture and observed every 24 h. In addition to documenting normal development, we manipulated three brooding tubes by cutting them in half transversely and freeing the larvae in one of the fragments. In the unmanipulated cultures, development was direct, with the offspring emerging from the tubes after an average of 8 days as juveniles, following a trochophore and metatrochophore stage inside the brood tube. Individuals that were freed from the brood tubes in an early trochophore stage went through the same developmental stages as their siblings from the same brood; however, they showed large variation within a single brood and remained in the larval stage up to 33% longer. [ABSTRACT FROM AUTHOR]

Abstract: At least six morphospecies of vestimentiferan tubeworms are associated with cold seeps in the Gulf of Mexico (GOM). The physiology and ecology of the two best-studied species from depths above 1000m in the upper Louisiana slope (Lamellibrachia luymesi and Seepiophila jonesi) are relatively well understood. The biology of one rare species from the upper slope (escarpiid sp. nov.) and three morphospecies found at greater depths in the GOM (Lamellibrachia sp. 1, L. sp. 2, and Escarpia laminata) are not as well understood. Here we address species distributions and boundaries of cold-seep tubeworms using phylogenetic hypotheses based on two mitochondrial genes. Fragments of the mitochondrial large ribosomal subunit rDNA (16S) and cytochrome oxidase subunit I (COI) genes were sequenced for 167 vestimentiferans collected from the GOM and analyzed in the context of other seep vestimentiferans for which sequence data were available. The analysis supported five monophyletic clades of vestimentiferans in the GOM. Intra-clade variation in both genes was very low, and there was no apparent correlation between the within-clade diversity and collection depth or location. Two of the morphospecies of Lamellibrachia from different depths in the GOM could not be distinguished by either mitochondrial gene. Similarly, E. laminata could not be distinguished from other described species of Escarpia from either the west coast of Africa or the eastern Pacific using COI. We suggest that the mitochondrial COI and 16S genes have little utility as barcoding markers for seep vestimentiferan tubeworms. [ABSTRACT FROM AUTHOR]

Abstract: Vestimentiferan tubeworms are a group of large sessile marine polychaete annelids (family Siboglinidae) found in the regions of hydrothermal venting or seepage of the reduced chemical hydrogen sulfide. Hydrocarbon seeps on the Louisiana Slope of the Gulf of Mexico support large communities of the co-occurring vestimentiferan species Lamellibrachia luymesi and Seepiophila jonesi. These sessile species have the opportunity to disperse between the patchy sites of active seepage on the seafloor during a planktonic larval stage. However, it is unclear whether dispersal occurs at a local or global scale. Four (L. luymesi) and seven (S. jonesi) microsatellite loci were used to test for population substructure among ten hydrocarbon seep sites on the Louisiana Slope. Both species showed high levels of allelic diversity, averaging 18.5 (L. luymesi) and 22 (S. jonesi) alleles/locus, respectively, and high observed heterozygosity at all microsatellite loci (0.71–0.9 in L. luymesi, 0.27–0.84 in S. jonesi). The two species showed a significant deficiency in heterozygotes compared to that predicted under the Hardy–Weinberg equilibrium. L. luymesi showed a small but significant amount of population structure, with a positive correlation between genetic and geographic distance among the sample sites spanning 540km. S. jonesi, in contrast, showed no evidence for isolation by distance, but did show a significant genetic difference between aggregations of different ages. These results suggest that these two species differ in how larvae are able to colonize new seep sites through space (L. luymesi) and though time (S. jonesi). [ABSTRACT FROM AUTHOR]

We tested the mid-domain effect to evaluate the bathymetric patterns of annelid polychaete species richness from the Southern Gulf of Mexico as a possible hypothesis to explain the species richness gradient, exploring the overlapping of species depth ranges towards the middle continental shelf. The bathymetric gradient of the number of species was estimated using the depth ranges of 259 polychaete species and the mid-domain effect was tested using a Monte Carlo simulation program at bands of 10 m depth. The carbonate (234 species) and the terrigenous (121 species) Gulf shelves showed clear differences in species richness which was characterized by a highly significant presence of polychaetes with short depth ranges (<10 m). The distribution of richness could be described as a cubic polynomial curve but the maximum values for all case studied (200, 181 and 84 species, for the whole study area, and the carbonate and terrigenous shelves, respectively) are strongly skewed to shallow waters (40 m). This is not consistent with the peak of diversity at 60–70 m predicted by the model. Therefore, the observed patterns cannot be reproduced by the mid-domain effect, suggesting the existence of non-random factors affecting the species richness gradients in the Gulf. We also found a gradient from west to east in species richness with increasing species richness in the carbonate shelf. • Bathymetric gradients in species richness were estimated using 259 polychaete species. • The mid-domain effect was tested using Monte Carlo simulations. • The carbonated (238 species) and the terrigenous (122 species) Gulf shelves species richness was strongly skewed to shallow waters. • This pattern is not consistent with the peak of diversity predicted by the model. • The observed patterns cannot be reproduced by the mid-domain effect. • Suggesting the existence of non-random factors affecting the species richness gradients in the Gulf. • Species richness was higher in the carbonate shelf than in the terrigenous shelf. [ABSTRACT FROM AUTHOR]

Seepiophila jonesi is a vestimentiferan tubeworm (Siboglinidae: Polychaeta) inhabiting the cold seeps of the upper slope of the Gulf of Mexico. It commonly co-occurs with Lamellibrachia luymesi, which is among the most long-lived non-clonal animals known. The growth pattern of S. jonesi is best described by a model including a size-specific probability of growth and an average growth rate that does not vary with individual size. This model, based on growth data from in situ staining and collection approximately 1 year later, predicts that S. jonesi is very slow growing and may attain ages comparable with L. luymesi. The efficacy of this model in describing L. luymesi growth rate was assessed, but the previously employed model of declining growth rate with individual size provided the better fit to the empirical data. Comparisons of both S. jonesi and L. luymesi growth rates among sites and among aggregations within a site indicate that there is some degree of habitat variability contributing to differences in growth rates. However, position of the anterior end of the worm within an aggregation did not have a significant effect on growth rate in comparisons among groups of L. luymesi from different distances from the center of an aggregation. The evolution of longevity in these species of vestimentiferans was favored by the relative stability of the seep habitat and sulfide sources, in contrast to the hydrothermal vent environment inhabited by relatively short-lived and fast-growing vestimentiferan species. [ABSTRACT FROM AUTHOR]

Bathynerita naticoidea (Gastropoda: Neritidae) and Methanoaricia dendrobranchiata (Polychaeta: Orbiniidae) are two of the most abundant invertebrates associated with cold-seep mussel beds in the Gulf of Mexico. At the methane seep known as Brine Pool NR-1 (27 °43.415 N, 91 °16.756 W; 650 m depth), which is surrounded by a broad band of mussels ( Bathymodiolus childressi), these species have distinctly different patterns of abundance, with the gastropod being found mostly at the outer edge of the mussel bed (average density in November 2003: 817 individuals·m−2 in outer zone, 20·m−2 in inner zone) and the polychaete being found almost exclusively near the inner edge (average density in November 2003: 3155 individuals·m−2 in inner zone, 0·m−2 in outer zone), adjacent to the brine pool itself. The salinity of the brine pool exceeds 120, so we hypothesized that M. dendrobranchiata should be more tolerant of high salinities than B. naticoidea. The opposite proved to be true. The gastropods were capable of withstanding salinities at least as high as 85, whereas the polychaetes died at salinities higher than 75. Both species were osmoconformers over the range of salinities (35–75) tested. Behavioral responses of B. naticoidea to salinities of 50, 60, and 70 were investigated in inverted vertical haloclines. Gastropods generally did not enter water of salinity greater than 60, but tolerated short periods at 60. Behavioral avoidance of brine should limit the vertical distribution of B. naticoidea in the inner zone to the top 2.5–5 cm of the mussel bed. Behavior is also a likely (though unproven) mechanism for controlling horizontal distribution of this species across the mussel bed. Methanoaricia dendrobranchiata can tolerate short excursions into the brine, but probably avoids hypersaline conditions by aggregating on the tops of the mussels. [ABSTRACT FROM AUTHOR]

Lamellibrachia luymesi (Polychaeta, Siboglinidae) is a deep-sea vestimentiferan tubeworm that forms large bush-like aggregations at hydrocarbon seeps in the Gulf of Mexico. Like all vestimentiferans, L. luymesi obtains its nutrition from sulfide-oxidizing endosymbiotic bacteria, which it houses in an internal organ called the trophosome. This tubeworm has a lifespan of over 170 years and its survival is contingent upon the availability of sulfide during this long period. In sediments underlying L. luymesi aggregations, microbes produce sulfide by coupling sulfate reduction with hydrocarbon oxidation. L. luymesi acquires sulfide from the sediment using a root-like posterior extension of its body that is buried in the sediment. Its symbionts then oxidize the sulfide to produce energy for carbon fixation, and release sulfate and hydrogen ions as byproducts. It is critical for the tubeworm to eliminate these waste ions, and it could do so either across its vascular plume or across its root. In this study, we measured sulfate and proton elimination rates from live L. luymesi and found that they eliminated approximately 85% of the sulfate produced by sulfide oxidation, and approximately 67% of the protons produced by various metabolic processes, across their roots. On the basis of experiments using membrane transport inhibitors, we suggest that L. luymesi has anion exchangers that mediate sulfate elimination coupled with bicarbonate uptake. Roots could be the ideal exchange surface for eliminating sulfate and hydrogen ions for two reasons. First, these ions might be eliminated across the root epithelium using facilitated diffusion, which is energetically economical. Second, sulfate and hydrogen ions are substrates for bacterial sulfate reduction, and supplying these ions into the sediment might help ensure a sustained sulfide supply for L. luymesi over its entire lifespan. [ABSTRACT FROM AUTHOR]

Infauna, including foraminifera and metazoans, were enumerated and identified from five types of seep habitats and two adjacent non-seep habitats. Collections were made with the deep submergence research vessel‘Alvin’ from three areas of active seepage in the Gulf of Mexico (Alaminos Canyon [2220 m], Atwater Canyon [1930 m], and Green Canyon lease block 272 [700 m]) and on the Blake Ridge Diapir [2250 m], which is located off the southeastern coast of the United States. The seep habitats sampled included four types of microbial mats (Beggiatoa,Thioploca, thin and thickArcobacter) and the periphery of a large mussel bed. Sediments under large rhizopod protists, xenophyophores, were sampled adjacent to the mussel bed periphery. A non-seep site, which was>1 km away from active seeps, was also sampled for comparison. Densities of most taxa were higher in the Gulf of Mexico seeps than in Blake Ridge samples, largely because densities in the thick microbial mats of Blake Ridge were significantly lower. Diversity was higher in theThioplocamats compared to other microbial-mat types. Within an ocean basin (i.e., Atlantic, Gulf of Mexico) we did not observe significant differences in meiofaunal or macrofaunal composition inBeggiatoaversusThioplocamats or thin versus thickArcobactermats. Foraminifera represented up to 16% of the seep community, a proportion that is comparable to their contribution at adjacent non-seep communities. In general, the observed densities and taxonomic composition of seep sites at the genus level was consistent with previous observations from seeps (e.g., the foraminifersBolivinaandFursenkoina, the dorvilleid polychaeteOphryotrocha). [ABSTRACT FROM AUTHOR]

Material earlier recorded from the Grand Caribbean region as Paraprionospio pinnata (Ehlers, 1901) was reexamined and referred to two new species: Paraprionospio tamaii sp. nov. and P. yokoyamai sp. nov. Paraprionospio tamaii sp. nov. has dorsal crests on segments 20–29, notopodial lamellae oval on chaetigers 1–2, reniform on chaetiger four, neuropodial lamellae abovate on chaetiger three, and branchiae with two kinds of lamellae: (1) bifoliate, rounded lamellae positioned basally, and (2) flabellate lamellae positioned from the middle to distal region of branchiae. Paraprionospio yokoyamai sp. nov. has no dorsal crests, notopodial lamellae triangular and elongate on chaetiger 1–2, subtriangular on chaetiger four, neuropodial lamellae cordate on chaetiger three, and branchiae with three kinds of lamellae: (1) small subtriangular (unipinnate) in the basal region, (2) bifoliate in the middle region and (3) flabellate from the middle to distal region. None specimen revised from the Grand Caribbean region was identified as Paraprionospio pinnata. The geographic distribution of this `cosmopolitan' species should be carefully verified. An identification key to currently recognized species of Paraprionospio is provided. [ABSTRACT FROM AUTHOR]

The objective of this study was to contribute to the knowledge of the syllids distributed in the eastern coasts of Mexico (Gulf of Mexico and Caribbean) taking into consideration their composition, distribution and diversity. Sampling was done at 77 stations including 49 in soft bottoms (terrigenous and carbonate sediments), and 28 in hard bottoms (coralline substrates) sampled in nine reef zones included in three reef systems (Veracruz, Campeche and Cozumel). In all 2084 individuals were collected (13.5% in soft sediments and 86.4% in coralline areas). Forty-five species were identified: 31 in soft bottoms and 38 in corals, with 21 species common to both types of environments. In soft bottoms, the highest species richness and diversity were found in the Carbonate Zone, while syllids were uncommon in the Terrigenous Zone. In hard bottoms, the highest density, species richness and diversity values were found in the Veracruz Reef System, followed by the Campeche Bank and Cozumel Island Reef Systems. The dominant species in soft bottoms were Haplosyllis spongicola, Exogone lourei, Typosyllis cornuta and T. papillosus, whereas T. alosae, T. corallicola, T. cornuta and H. spongicola dominated in hard bottoms. The importance and success of the syllids in both soft bottoms and reef environments, particularly in those of the Gulf of Mexico is emphasized. [ABSTRACT FROM AUTHOR]

The deep water polychaete fauna is analyzed in this study particularly regarding its composition and variations with depth in the Sigsbee Basin, northwestern region of the Gulf of Mexico. Samples were taken at 10 stations along a bathymetric gradient with depth ranges from 200 to 3760 m with a USNEL (0.25 m2) corer. A total of 287 individuals were identified, from 21 families and 65 species. The most important families, both in terms of abundance and species richness, were: Paraonidae (65.4 ind./0.25 m2, 9 spp.), Cirratulidae (28.93 ind./0.25 m2, 7 spp.) and Spionidae (18.07 ind./0.25 m2, 7 spp.). In general, density tended to decrease with depth with minima at around 2000 m, although two abundance peaks were detected at 3700 and 3760 m, making the pattern seem an inverted parabolic curve. The Shannon-Wiener diversity values varied from 0.54–0.92 at around 2000 m to 3.39 at 3620 m and 3.34 at 3760 m. These results contrast with what is already reported from the North Atlantic and the Tropical Pacific deep benthic communities, where highest diversities are found at 2000 m. Faunal changes evaluated through Beta Diversity (0.08–0.1) and the low similarity found between the stations, emphasized the high variability in the composition of the fauna in the Sigsee Basin, meaning that the faunal composition is practically different at all the sampling stations. Ten species are newly recorded for the Mexican fauna. [ABSTRACT FROM AUTHOR]

A comprehensive database was built to examine the spatial diversity patterns of polychaete species from the continental shelf in Southern Gulf of Mexico. Using Cluster and nMDS analysis we found the composition of polychaete species to be different between the terrigenous and carbonate regions of the Gulf. To test the relative importance of spatial and environmental components in the polychaetae community structure in the Southern Gulf of Mexico, we examined the spatial relationships between polychaetae assemblages and environmental variables over broad geographical scales. A distance-based redundancy analysis (dbRDA) and variation partitioning was used to quantify the relative importance of these explanatory variables on the spatial variations of species richness and composition. Variation partitioning is an important tool to investigate the importance of spatial structure to species distribution in communities, but it has not yet been used in marine ecosystems. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of variance than those parameters could alone. [ABSTRACT FROM AUTHOR]

Severe and persistent bottom-water hypoxia (≤2 mg O2 L−1) occurs on the Louisiana/Texas continental shelf from mid-May through mid-September over a large area (up to 23,000 km2 in mid-summer). Benthic infauna are less mobile than demersal organisms and become stressed by the low dissolved oxygen; benthic community composition, abundance, diversity, and biomass become altered. From the 1950s to the early 1970s, when sediment core indicators identified the initiation and subsequent worsening of dissolved oxygen conditions, there were no hydrographic data or benthic infaunal studies within the current area of frequent bottom-water hypoxia. This study highlights the impacts of severe hypoxia on benthic macroinfaunal communities and how they may have changed from less-hypoxic periods. Polychaetes were and are the dominant taxa in the available studies, but polychaete species richness in summer is now curtailed severely beginning with our 1985–1986 data. Species richness of polychaetes in summer hypoxia (1985–1986 and 1990–1991) was about 60% less than comparable taxa in 1972–1973. Abundance of polychaetes was much less in summer than spring, and recent infaunal biomass in summer was only 15% of what was found in spring. The result is less prey for demersal penaeid shrimp and fishes. Over the period of our comparison, infaunal feeding modes shifted from subsurface deposit feeders and surface deposit feeders to primarily surface deposit feeders (i.e., 95.5% of all polychaetes). Most were opportunistic, hypoxia tolerant, and recruited in high numbers following hypoxia abatement, some in fall and winter but most in spring. As benthic communities succumb to the stress of severe and continued seasonal low oxygen, they occupy the few upper centimeters of the sediment profile above the redox discontinuity layer with negative feedbacks to the water column by way of altered biogeochemical processes. [ABSTRACT FROM AUTHOR]