Showing papers by "Andrew J. Gooday published in 2009"

Effects of natural and human-induced hypoxia on coastal benthos

Abstract: . Coastal hypoxia (defined here as Hypoxia alters both the structure and function of benthic communities, but effects may differ with regional hypoxia history. Human-caused hypoxia is generally linked to eutrophication, and occurs adjacent to watersheds with large populations or agricultural activities. Many occurrences are seasonal, within estuaries, fjords or enclosed seas of the North Atlantic and the NW Pacific Oceans. Benthic faunal responses, elicited at oxygen levels below 2 ml L−1, typically involve avoidance or mortality of large species and elevated abundances of enrichment opportunists, sometimes prior to population crashes. Areas of low oxygen persist seasonally or continuously beneath upwelling regions, associated with the upper parts of oxygen minimum zones (SE Pacific, W Africa, N Indian Ocean). These have a distribution largely distinct from eutrophic areas and support a resident fauna that is adapted to survive and reproduce at oxygen concentrations

Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna

Abstract: The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150–1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140–1850 m water depth) across the OMZ during the 2003 intermonsoon (March–May) and late/post-monsoon (August–October) seasons. All groups exhibited some drop in abundance in the OMZ core (250–500 m water depth; O2: 0.10–0.13 mL L?1=4.46–5.80 ?M) but to differing degrees. Densities of foraminiferans >63 ?m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 ?m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O2 0.2 mL L?1=8.92 ?M). The progressively deeper abundance peaks for foraminiferans (>63 ?m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136–300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mL L?1(=5.80 ?M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side.

Historical records of coastal eutrophication-induced hypoxia

Abstract: . Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical indicators (proxies) derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Those based on (1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), (2) sedimentary features (e.g. laminations) and (3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on (4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), (5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and (6) organic C, N and their stable isotope ratios reflect conditions in the water column. However, the interpretation of these indicators is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment caused by eutrophication, making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific proxies, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, together with multi-proxy approaches, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.

Europe’s Grand Canyon: Nazaré submarine canyon

Abstract: The Nazare submarine canyon extends similar to 210 km westward from the coast of Portugal, down to a water depth of > 4300 m. The considerable habitat heterogeneity found throughout the canyon is affected by strong currents and high turbidity, especially in the upper parts of the canyon. The canyon morphology comprises steep slopes, scarps, terraces, and overhangs, and a deeply incised thalweg is found in the lower part of the canyon. The seabed within the canyon is composed of varying proportions of rock and sediments that range from sand to fine mud. This great variation in physical environment is reflected by the varied fauna inhabiting the canyon. Diversity tends to decrease with depth, but there is also continual replacement of species with increasing water depth. Certain groups, such as the gorgonians and sea lilies, tend to be found on rocky surfaces, while large protozoans dominate the sediments at 3400-m depth. In addition to describing the fauna of Nazare Canyon, we discuss experiments undertaken as part of the HERMES project to elucidate the ecosystem function processes operating in the deeper parts of the canyon.

Foraminiferal faunal responses to monsoon-driven changes in organic matter and oxygen availability at 140 and 300 m water depth in the NE Arabian Sea

Abstract: The faunal responses of benthic Foraminifera were investigated during 2003 at two contrasting sites in the Pakistan margin oxygen minimum zone (OMZ) Bottom-water-dissolved oxygen concentrations at the seasonally hypoxic 140 m site varied from 206 ml l−1 (92±4 μM) during the intermonsoon period (April) to 011 ml l−1 (50±04 μM) during the post-monsoon period (October); corresponding values at the 300 m site in the OMZ core, were 0053 and 0057 ml l−1 (236±009 and 256±029 μM) Live macrofaunal (>300 μm) Foraminifera (including soft-walled species) and Metazoa were examined in replicate multicore samples taken at each site during the 2003 intermonsoon and post-monsoon seasons A low-diversity foraminiferal assemblage was dominated (>60%) by calcareous species at both sites A total of 36 species was recognised and diversity was not greatly affected by water depth or season At both sites, >86% of Foraminifera were restricted to the 0–1 cm layer of sediment and the ALD5 decreased from the intermonsoon to the post-monsoon periods Densities increased from 124 (intermonsoon) to 153 (post-monsoon) indiv 10 cm–2 at 140 m and from 86 to 122 indiv 10 cm−2 at 300 m Much of this increase was accounted for by the dominant species, Uvigerina ex gr semiornata At 140 m, Foraminifera were 36 times more abundant than metazoans during the intermonsoon period, rising to 139 times during the post-monsoon period The corresponding proportions at 300 m, where metazoans were rare, were 124 and 145 We conclude that calcareous Foraminifera, in particular U ex gr semiornata, play a central role in OM cycling on the sea floor in the upper part of the Pakistan margin OMZ

Paleodictyon nodosum: a living fossil on the deep-sea floor

Abstract: We report new in situ observations and laboratory studies of specimens of a small (diameter 2.4–7.5 cm) strikingly hexagonal form originally described from sedimented steps in a wall of the axial valley of the Mid-Atlantic Ridge (water depth 3430–3575 m) near 26°N, 45°W that appears to be identical to the iconic form Paleodictyon nodosum described as a trace fossil from Eocene flysch deposits at sites in Europe and Wales. Our findings follow: • The form is apparently agglutinated in sea floor sediment (a veneer of calcareous lutite over red metalliferous sediment) and consists of three equidistant rows of tiny holes (diameter 1 mm) that intersect at an angle of 120° and continuously connect through vertical shafts (length 2–3 mm) with an underlying horizontal network of tubes or tunnels identical with the fossil form. • The number of rows of holes and spacing of rows increase with overall diameter of the form indicative of organic growth. • The form is shaped like a shield surrounded by a lip and moat with surface relief (0.5 cm) that is absent in the fossil form. The surface relief exposes the underlying red sediment and may have been produced either by excavation (constructional origin) or by infaunal growth (body form). • Protoplasm is absent in recovered specimens, as indicated by negative results of staining techniques, explained by either initial absence or loss. • Genetic sequencing of material from the form identified different foraminifera that had settled on the pattern of holes which acts as a baffle to trap organic matter. • Models in flume tanks show that the shield-like form deflects flow of ocean currents into a self-ventilating structure capable of aerating and of circulating organic particles through the tubes or tunnels. • Microbial counting techniques indicated background abundances within and outside the form. We come to two alternative interpretations of the findings resolvable with further studies: • The modern P. nodosum is a burrow consistent with interpretation of the ancient form as a trace fossil. • The modern P. nodosum is a compressed form of a hexactinellid sponge adapted to a sedimentary substrate, which means that the ancient form is a body fossil with possible affinity to the Ediacara fauna.

Global genetic homogeneity in the deep-sea foraminiferan Epistominella exigua (Rotaliida: Pseudoparrellidae)

Abstract: Epistominella exigua is one of the most common deep-sea foraminiferal morphospecies and has a world-wide distribution. A recent molecular study revealed high genetic similarity between Arctic, Atlantic and Antarctic populations of this species. Here, we show that the small-subunit (SSU) and internal transcribed spacer (ITS) rDNA sequences of an E. exigua population from Pacific are almost identical to those reported previously from the other three oceans. This result confirms the genetic homogeneity of E. exigua, which contrasts with the prevalence of highly differentiated populations in planktonic and shallow-water benthic foraminiferans. We discuss special features of diversifications mechanisms in the deep sea that may be responsible for the lack of genetic differentiation and global distribution of some meiofauna species.

Megafaunal responses to strong oxygen gradients on the Pakistan margin of the Arabian Sea

Abstract: The Arabian Sea oxygen minimum zone (OMZ), which intersects the continental margin between approximately 100 and 1200 m, is one of the world's largest deep-water oxygen-deficient water masses. We analysed megafaunal organisms seen in images obtained using a wide-angle survey photographic (WASP) system at nine sites (140–1850 m water depth) across the OMZ on the Pakistan Margin during the late-monsoon period (August–September 2003). The visible megafauna comprised: (1) the megabenthos sensu strictu (s.s.), (2) large polychaetes and (3) the benthopelagic megafauna (fish, natant decapods and octopods). Large protozoans, mainly the foraminiferan Pelosina sp., were counted but not included in the megafauna. The megabenthos s.s. were rare at the seasonally hypoxic 140-m site (O2=0.11 ml l?1), entirely absent in the OMZ core and most of the lower transition zone (300–900 m; O2=0.12–0.15 ml l?1), but peaked in abundance (27.94 indiv. m?2) at 1000 m (O2=0.16 ml l?1). Densities were much lower at 1100 and 1200 m (0.52–0.69 indiv. m?2; O2=0.25–0.38 ml l?1), and declined to minimal values (0.01 indiv. m?2) at 1850 m (O2=1.68 ml l?1). There was no correlation with depth, dissolved-oxygen concentration or sediment organic chemistry variables (%Corg, %Total N, C:N, ?13C, ?15N). Pelosina sp. was the only strictly benthic organism visible at 400 and 700 m. Fish and natant decapods were fairly common at 300 m, and fish were the only metazoans seen in photographs from 700 m. Large polychaetes, almost certainly Linopherus sp., were very abundant in photographs from 900 m, where megabenthos s.s. were absent, and somewhat less abundant at 1000 m. Suspension-feeding cnidarians and tunicates were abundant at 1100 and 1200 m, respectively. The number of megabenthos s.s. species visible at each site ranged from six (1000 and 1850 m) to 11 (1100 and 1200 m). Diversity (H?(loge)) was the lowest at 1000 and 1850 m and the highest at 1100 m, with intermediate values at 140 and 1200 m. Dominance was the highest (>99%) at 1000 m, high (87%) at 1200 m and lower (32–50%) at 140, 1100 and 1850 m. Benthopelagic megafauna appeared more tolerant of dysoxia than the megabenthos s.s., although densities peaked at 1100 m, slightly deeper than for the megabenthos s.s.. The presence of uneaten carrion (dead fish and natant decapods) between 300 and 900 m suggests that scavengers were either not active or not present within the OMZ. The megabenthos s.s. appeared to respond to oxygen concentrations above a threshold value (0.15–0.16 ml l?1). The ophiuroid-dominated abundance peak at 1000 m, and the abrupt changes in megabenthic assemblage composition between 1000 and 1200 m, were probably expressions of an ‘edge effect’, known from other OMZs and believed to reflect a threshold release from physiological oxygen limitation accompanied by an abundant food supply.

Molecular analyses reveal high levels of eukaryotic richness associated with enigmatic deep-sea protists (Komokiacea)

Abstract: Komokiaceans are testate agglutinated protists, extremely diverse and abundant in the deep sea. About 40 species are described and share the same main morphological feature: a test consisting of narrow branching tubules forming a complex system. In some species, the interstices between the tubules are filled by sediment, creating a mudball structure. Because of their unusual and sometimes featureless appearance, komokiaceans were frequently ignored or overlooked until they formal description in 1977. The most recent taxonomy places the Komokiacea within the Foraminifera based on general morphological features. To examine their taxonomic position at the molecular level, we analysed the SSU rDNA sequences of two species, Normanina conferta and Septuma ocotillo, obtained either with specific foraminiferal or universal eukaryotic primers. Many different sequences resulted from this investigation but none of them could clearly be attributed to komokiaceans. Although our study failed to confirm univocally that Komokiacea are foraminiferans, it revealed a huge eukaryotic richness associated with these organisms, comparable with the richness in the overall surrounding sediment. These observations suggest strongly that komokiaceans, and probably many other large testate protists, provide a habitat structure for a large spectrum of eukaryotes, significantly contributing to maintaining the biodiversity of micro- and meiofaunal communities in the deep sea.

Large organic-walled Protista (Gromia) in the Arabian Sea: Density, diversity, distribution and ecology

Abstract: The genus Gromia includes large marine protists (‘gromiids’) with filose pseudopodia and sack-like organic tests. The first deep-water species were discovered in the 1990s on the Oman Margin of the Arabian Sea and subsequently found on the Pakistan Margin. We present a survey of gromiids in samples collected off Oman in 2002 and off Pakistan in 2003. In addition to the two species (Gromia sphaerica and Gromia pyriformis) already described from this area, at least eight undescribed gromiid species were present. Sausage shaped, grape shaped and spherical morphotypes were represented among this material. On the Oman Margin, gromiids occurred in densities up to several thousand individuals m−2 at 1400 and 1700 m but were much less common at 1100 and 2000 m. Apart from G. pyriformis, which was fairly common (several hundred individuals m−2) at 1000 m, gromiids were uncommon in core samples taken off Pakistan, with 11 indiv. m−2 at 1200 m and 19 indiv. m−2 at 1850 m. On both margins, these protists occurred at depths >1000 m where bottom-water oxygen concentrations exceeded ∼0.2 ml l−1 (=8.92 μM l−1) land sediments were fully bioturbated and oxidised. However, they were not observed at similar oxygen levels above the OMZ. Most gromiids lived on the sediment surface with their apertures facing down and their pseudopodia presumably deployed into the sediment to feed on surficial material and associated bacteria. We conclude that these large protists may play an important ecological role in the bathyal Arabian Sea, particularly in carbon cycling but also in structuring the surficial sediments. In addition, their tests, particularly those of G. sphaerica, provide substrates for attached Foraminifera.

A new genus and two new species of saccamminid foraminiferans (Protista, Rhizaria) from the deep Southern Ocean*

Abstract: We describe two new species of spherical single-chambered ('saccamminid') foraminifera from the bathyal and abyssal Weddell Sea (Southern Ocean), collected in epibenthic sledge and Agassiz trawl samples obtained during the 2005 ANDEEP III campaign. Both are assigned to Leptammina gen. nov. The new genus is similar in overall test morphology to Saccammina Carpenter, 1869; it is distinguished mainly by its test wall, which is delicate, flexible and composed of fine mineral grains, rather than being rigid and coarsely agglutinated. In Leptammina grisea gen. et sp. nov., the test wall is relatively thick, grayish with a violet tinge and a dull surface; the cytoplasm is dark greenish. In Leptammina flavofusca gen. et sp. nov., the test is yellowish brown, with a very finely, almost transluscent agglutinated wall; the cytoplasm is pale yellowish. Both species have prominent circular apertures. Maximum likelihood phylogenetic analysis of SSU rRNA gene data showed that both species group together with an undescribed shallow-water Antarctic species (“silver saccamminid”) in a very strongly supported clade (100 %). Leptammina grisea gen. et sp. nov. is a relatively uncommon species (29 specimens from 3 stations), found at 1580–4822 m depth in the central and north–western Weddell Sea; Leptammina flavofusca gen. et sp. nov. is common (398 specimens from 4 stations) at depths of 3138–4795 m in the central Weddell Sea and off Kapp Norvegia. Both species are presently known only from ANDEEP III samples.

A minute new species of Saccammina (monothalamous Foraminifera; Protista) from the abyssal Pacific

Abstract: . Saccammina minimus sp. nov., a spherical agglutinated organism presumed to be a foraminiferan, is described from the Kaplan Central site in the abyssal eastern Equatorial Pacific (5042 m water depth). The new species is minute in size ( 32 μm of samples collected at the KC site. In six subcores (6.6 cm2 surface area, 0–1 cm layer) from two cores obtained during a single deployment of a multiple corer, it represented 59% of all stained foraminifera in the samples. However, it had an extremely patchy small-scale distribution on a scale of centimetres; for example, 3, 285 and 1090 specimens were extracted from three subcores. A separate study has reported similar patterns among other minute indeterminate monothalamous foraminifera at the Kaplan East site (4032–4089 m water depth) located to the east, c. 1200 km from our study site. The reason for these very patchy distributions is not clear.

New species of Leptohalysis (Rhizaria, Foraminifera) from an extreme hadal site in the western Pacific Ocean

Abstract: Leptohalysis kaikoi sp. nov., a new hormosinacean foraminiferan, is described from a core sample collected using the Japan Agency for Marine-Earth Science and Technology’s Remote Operated Vehicle, KAIKO, in the Challenger Deep (10,896 m water depth, Izu-Bonin-Mariana-Arc-trench system). The agglutinated test is <130 ?m long and approximately 20 ?m wide, and more or less confined to the 32-63 ?m sieve fraction. It consists of a linear series of chambers with a simple terminal aperture. The new species differs from typical members of the genus Leptohalysis in the following features: 1) the chambers are rounded and abut closely with a distinct suture between them, rather than being flask-shaped with more or less flat, truncated bases; 2) the wall structure is less regular and consists mainly of grains with flat exposed faces that abut to create an outer surface resembling an uneven pavement, the edges of the grains being obscured by copious amounts of organic cement; 3) the proloculus is sometimes followed by a single “adventitious”chamber, located to one side of the axis of growth. A second species with similar characteristics is represented by a single individual in our material. These two species may represent a new genus. However, we prefer to retain them within Leptohalysis pending a detailed comparison of their wall structure with that of typical members of this genus. We also briefly describe a single specimen of a typical Leptohalysis morphotype. Leptohalysis kaikoi sp. nov. was the most common multilocular agglutinated foraminiferan in the 32-63 ?m sieve fraction of the Challenger Deep sample. It has not been found in the same size fraction of samples from abyssal depths in the North and eastern equatorial Pacific Ocean.