Responses of deep-sea benthos to sedimentation patterns in the North-East Atlantic in 1992

In an extended deep-sea study the response of the benthic community to seasonally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L2 at 47°N–20°W, water depth >4500 m) on four legs of METEOR expedition 21 between March and August 1992. The vertical flux at 3500 m depth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phospholipids, measures of benthic biomass, and of activity of hydrolytic enzymes were observed. The flux patterns in moored sediment traps of total chlorophyll, POC and total flux showed an early sedimentation peak in March/April 1992, followed by low fluxes in May and intermediate ones from June to August. Thus 1992 differed from other years, in which one large flux peak after the spring phytoplankton bloom was observed. Unusually high concentrations of chloroplastic pigments were consistently observed in March 1992, reflecting the early sedimentation input. At the same time biomass of small benthic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following months in 1992. In May and August 1992 pigment concentrations and biomass and activity parameters in the sediment were lower than during previously observed depositions of phytodetrital matter in summer. The data imply that the deep ocean benthic community reacts to small sedimentation events with transient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannual variability in surface water production is “mirrored” by deep-sea benthic processes.     

A multiple-scale analysis of metazoan meiofaunal distribution in the deep Mediterranean Sea

In order to identify environmental factors driving the distribution and functioning of deep-sea fauna and the spatial scales of interactions, we carried out a multiple-scale investigation in the Mediterranean basin in which we compared two bathyal plains, located at the same depth (ca. 3000 m), but characterised by contrasting trophic conditions. We investigated meiofaunal abundance, biomass, community structure and biodiversity (expressed as richness of taxa) in relation to sediment characteristics, downward fluxes and food availability in the sediment. Samples were collected at all spatial scales (from small to macroscale) in two seasons. Our results indicated that deep-sea systems with different trophic conditions displayed different responses to the distribution of available energy and its spatio-temporal variability in the sediment. The analysis at a macroscale (>1000 km) indicated that meiofauna were controlled primarily by the trophic inputs to the deep-sea system. Spatial variability of meiofaunal parameters at a mesoscale (>50 km) was highest in the eastern Mediterranean and lowest in the western Mediterranean. Such differences are the consequence of the unpredictable inputs of organic matter in the oligotrophic eastern Mediterranean versus a more homogeneous distribution of food inputs in the mesotrophic western Mediterranean. At a smaller scale (local scale 7 km), in the western Mediterranean, the distribution of meiofaunal parameters was highly homogeneous, reflecting the homogeneous distribution of the food availability in the sediment. Our results indicated that the highly variable input and distribution of food sources in the deep eastern Mediterranean did not provide any “insurance” for the sustainability of the deep-sea faunal assemblages in the long term, thus leading to an uncoupling between resource availability and distribution of organisms. We conclude that the influence of energy availability on the deep-sea faunal distributions change at different spatial scales and that the analysis of spatial variability at mesoscales is crucial for understanding the relationships between deep-sea benthic fauna and environmental drivers.     

Nucleic acid concentrations (DNA,RNA) in the continental and deep-sea sediments of the eastern Mediterranean: relationships with seasonally varying organic inputs and bacterial dynamics

In order to study temporal variations of the genetic material in the continental shelf and deep-sea sediments of the extremely oligotrophic Cretan Sea, samples were collected on seasonal basis from August 1994 to September 1995, with a multiple corer, at seven stations (from 40 to 1540 m depth). Surface sediments (0–1 cm) were sub-sampled and analyzed for nucleic acid content (DNA, RNA) and bacterial density. DNA concentrations in the sediments were high (on annual average, 25.0 μg g^-1) and declined with increasing water depth, ranging from 3.5 to 55.2 μg g^-1. DNA concentrations displayed wide temporal changes also at bathyal depths confirming the recent view of the large variability of the deep-sea environments. Also RNA concentrations decreased with increasing water depth (range: 0.4–29.9 μg g^-1). The ratio of RNA to DNA did not show a clear spatial pattern but was characterized by significant changes between sampling periods. DNA concentrations were significantly correlated with protein and phytopigment concentrations in the sediment, indicating a possible relationship with the inputs of primary organic matter from the photic layer. Bacterial densities were generally high (range: 0.9–4.6×10⁸ cells g^-1) compared to other deep-sea environments and decreased with increasing water depth. Estimates of the bacterial contribution to the sedimentary genetic material indicated that bacterial-DNA accounted, on annual average, for a small fraction of the total DNA pool (4.3%) but that bacterial-RNA represented a significant fraction of the total sedimentary RNA (26%). Bacterial contribution to nucleic acids increased, even though irregularly, with increasing depth. In deep-sea sediments, changes in RNA concentrations appear to be largely dependent upon bacterial dynamics. Estimates of the overall living contribution to the DNA pools (i.e. microbial plus meiofaunal DNA) indicated that the large majority (about 90%) of the DNA in continental and deep-sea sediments of the eastern Mediterranean was detrital. The non-living DNA pools reach extremely high concentrations up to 0.41 g DNA m^-2 cm^-1. Thus, especially in deep benthic habitats, characterized by low inputs of labile organic compounds, detrital DNA could represent a suitable and high quality food source or a significant reservoir of nucleic acid precursors for benthic metabolism.     

Deep-sea macrourid fishes scavenge on plant material: Evidence from in situ observations

Deep-sea benthic communities primarily rely on an allochthonous food source. This may be in the form of phytodetritus or as food falls e.g. sinking carcasses of nekton or debris of marine macrophyte algae. Deep-sea macrourids are the most abundant demersal fish in the deep ocean. Macrourids are generally considered to be the apex predators/scavengers in deep-sea communities. Baited camera experiments and stable isotope analyses have demonstrated that animal carrion derived from the surface waters is an important component in the diets of macrourids; some macrourid stomachs also contained vegetable/plant material e.g. onion peels, oranges, algae. The latter observations led us to the question: is plant material an attractive food source for deep-sea scavenging fish? We simulated a plant food fall using in situ benthic lander systems equipped with a baited time-lapse camera. Abyssal macrourids and cusk-eels were attracted to the bait, both feeding vigorously on the bait, and the majority of the bait was consumed in <30 h. These observations indicate (1) plant material can produce an odour plume similar to that of animal carrion and attracts deep-sea fish, and (2) deep-sea fish readily eat plant material. This represents to our knowledge the first in situ documentation of deep-sea fish ingesting plant material and highlights the variability in the scavenging nature of deep-sea fishes. This may have implications for food webs in areas where macrophyte/seagrass detritus is abundant at the seafloor e.g. canyon systems and continental shelves close to seagrass meadows (Bahamas and Mediterranean).     

Macrofaunal succession in sediments around kelp and wood falls in the deep NE Pacific and community overlap with other reducing habitats

Sunken parcels of macroalgae and wood provide important oases of organic enrichment at the deep-sea floor, yet sediment community structure and succession around these habitat islands are poorly evaluated. We experimentally implanted 100-kg kelp falls and 200 kg wood falls at 1670 m depth in the Santa Cruz Basin to investigate (1) macrofaunal succession and (2) species overlap with nearby whale-fall and cold-seep communities over time scales of 0.25–5.5 yr. The abundance of infaunal macrobenthos was highly elevated after 0.25 and 0.5 yr near kelp parcels with decreased macrofaunal diversity and evenness within 0.5 m of the falls. Apparently opportunistic species (e.g., two new species of cumaceans) and sulfide tolerant microbial grazers (dorvilleid polychaetes) abounded after 0.25–0.5 yr. At wood falls, opportunistic cumaceans become abundant after 0.5 yr, but sulfide tolerant species only became abundant after 1.8–5.5 yr, in accordance with the much slower buildup of porewater sulfides at wood parcels compared with kelp falls. Species diversity decreased significantly over time in sediments adjacent to the wood parcels, most likely due to stress resulting from intense organic loading of nearby sediments (up to 20–30% organic carbon). Dorvilleid and ampharetid polychaetes were among the top-ranked fauna at wood parcels after 3.0–5.5 yr. Sediments around kelp and wood parcels provided low-intensity reducing conditions that sustain a limited chemoautrotrophically-based fauna. As a result, macrobenthic species overlap among kelp, wood, and other chemosynthetic habitats in the deep NE Pacific are primarily restricted to apparently sulfide tolerant species such as dorvilleid polychaetes, opportunistic cumaceans, and juvenile stages of chemosymbiont containing vesicomyid bivalves. We conclude that organically enriched sediments around wood falls may provide important habitat islands for the persistence and evolution of species dependent on organic- and sulfide-rich conditions at the deep-sea floor and contribute to β and γ diversity in deep-sea ecosystems.     

Structural and functional shifts in zoobenthos induced by organic enrichment — Implications for community recovery potential

Habitat change induced by organic enrichment is a growing concern for the sustainability of benthic communities in coastal aquatic environments. This case study describes the spatial and temporal response patterns and the recovery potential of low-diversity benthic communities to organic enrichment at two fish farm locations, during the rearing periods (15 and 20 years, respectively) and the following recovery periods (2 years). The spatial extent of disturbance differed depending on the hydromorphological characteristics of the rearing sites, but degraded macrobenthic communities close to both fish farms were recorded soon after the activity started. Continued organic enrichment resulted in high species turnover-rates and in an altered benthic community composition at both locations. After fish farm abatement, a partial recovery was detected in species richness, but abundance and biomass values were reduced and changes in structural composition remained. Alterations in benthic biological traits were observed at both fish farm locations, implying that organic enrichment might cause changes in benthic community function within low-diversity benthic communities.     

Biological characterization of a whale-fall near Vancouver Island,British Columbia,Canada

Video analysis of a whale-fall discovered in the northeast Pacific Ocean, off Vancouver Island at a depth of 1288 m during ROV diving operations has identified 26 taxa of deep-sea benthic organisms inhabiting the seafloor immediately surrounding remnants of the whale skeleton. A photo-mosaic derived from high-definition video provides a quantitative visual record of the present condition of the site, the species richness, and substrate preference. Only the skull and caudal vertebrae remains of this large whale skeleton are estimated to have been approximately 16.5 m in length. Most organisms identified near the whale-fall are common benthic deep-sea fauna, typical of this water depth and seafloor composition. Much of this species richness comes from sessile suspension feeding cnidarians attached to the numerous glacial dropstones found throughout the area rather than the presence of the whale skeleton. Seep and bone specialists are rare (4 taxa) and may be, in part, a remnant population from a sulphophilic stage of whale-fall decomposition. Evidence of past colonization by Osedax sp. is visible on the remaining bones and we conclude that rapid degradation of the missing bones has occurred at this site as has been observed at whale-falls off central California in Monterey Canyon.     

Field and laboratory studies on the effect of particle size and composition on optical backscattering measurements in hydrothermal plumes

We describe the performance of an inexpensive but highly sensitive light backscattering sensor (LBSS) suitable for use in deep-sea waters, where particle concentrations are typically <∼0.1 mg/l. Laboratory calibrations using aluminosilicate particles and latex spheres show that the concentration-normalized backscattering of the LBSS, K_bs, is greatest for particles with a diameter close to the wavelength of light emitted by the LBSS (0.88 μm), declining by more than a factor of five for particles <0.1 μm or >10 μm. Field studies indicate that in hydrothermal plumes dominated by fine-grained metal precipitates the 95% confidence interval for predicting mass concentration with an LBSS ranges from ±0.004 mg/l for 0.03 mg/l suspensions to ±0.008 mg/l at 0.12 mg/l. Comparisons among a group of 19 LBSSs found between-instrument variability to reach 70%, but normalizing the raw data using a laboratory calibration procedure reduced the maximum variability to ∼8%.     

Fungi in deep-sea sediments of the Central Indian Basin

Although a great amount of information is available on bacteria inhabiting deep-sea sediments, the occurrence of fungi in this environment has been poorly studied and documented. We report here the occurrence of fungi in deep-sea sediments from ∼5000 m depth in the Central Indian Basin (9–16°S and 73–76°E). A total of 181 cultures of fungi, most of which belong to terrestrial sporulating species, were isolated by a variety of isolation techniques. Species of Aspergillus and non-sporulating fungi were the most common. Several yeasts were also isolated. Maximum species diversity was observed in 0–2 cm sections of the sediment cores. Direct staining of the sediments with Calcofluor, a fluorescent optical brightener, revealed the presence of fungal hyphae in the sediments. Immunofluorescence using polyclonal antibodies raised against a deep-sea isolate of Aspergillus terreus (# A 4634) confirmed its presence in the form of hyphae in the sub-section from which it was isolated. A total of 25 representative species of fungi produced substantial biomass at 200 bar pressure at 30° as well as at 5 °C. Many fungi showed abnormal morphology at 200 bar/5 °C. A comparison of terrestrial isolates with several deep-sea isolates indicated that the former could grow at 200 bar pressure when growth was initiated with mycelial inocula. However, spores of a deep-sea isolate A. terreus (# A 4634), but not the terrestrial ones, showed germination at 200 bar pressure and 30 °C. Our results suggest that terrestrial species of fungi transported to the deep sea are initially stressed but may gradually adapt themselves for growth under these conditions.     

Does Encope emarginata (Echinodermata: Echinoidea) affect spatial variation patterns of estuarine subtidal meiofauna and microphytobenthos?

Foraging macrofauna, such as the sand dollar Encope emarginata, can modify sediment properties and affect spatial distribution patterns of microphytobenthos and meiobenthos at different spatial scales. We adopted a spatial hierarchical approach composed of five spatial levels (km, 100 s m, 10 s m, 1 s m and cm) to describe variation patterns of microphytobenthos, meiobenthos and sediment variables in shallow subtidal regions in the subtropical Paranaguá Bay (Southern Brazil) with live E. emarginata (LE), dead E. emarginata (only skeletons — (DE), and no E. emarginata (WE). The overall structure of microphytobenthos and meiofauna was always less variable at WE and much of variation at the scale of 100 s m was related to variability within LE and DE, due to foraging activities or to the presence of shell hashes. Likewise, increased variability in chlorophyll-a and phaeopigment contents was observed among locations within LE, although textural parameters of sediment varied mainly at smaller scales. Variations within LE were related to changes on the amount and quality of food as a function of sediment heterogeneity induced by the foraging behavior of sand dollars. We provide strong evidence that top-down effects related to the occurrence of E. emarginata act in synergy with bottom-up structuring related to hydrodynamic processes in determining overall benthic spatial variability. Conversely, species richness is mainly influenced by environmental heterogeneity at small spatial scales (centimeters to meters), which creates a mosaic of microhabitats.     

On the spatial scale needed for benthos community monitoring in the coastal North Sea

In community monitoring an attempt is made to identify long-term trends by regular sampling of selected sites. Since the benthos is reputed to be fairly sedentary, the spatial resolution is often reduced to single sites. However, members of many benthic invertebrate species have been found drifting across sedimentary seabeds in shallow waters. Transportation by currents may result in changes of their spatial pattern in the sediment, thereby changing local community composition. The quantitative importance of drifting was tested by repeated sampling of a 2-km² shallow (10 m) offshore area west of the island of Sylt (North Sea). Within the fortnight period between two samplings the benthic community composition had changed dramatically. Despite fairly calm weather, translocation of organisms by currents exceeded 1 km. In about half of the species, the spatial changes in abundance within these two weeks roughly equalled the average variation between consecutive years. This example suggests that community monitoring needs a wide spatial scale to discriminate long-term temporal changes from short-term variability. Extending the sampling area from 2 to 180 km² strongly reduced the variability of abundance estimates. However, only in a few species was the spatial distribution over the sampling sites found on one sampling date a suitable estimator for the spatial pattern found one or two months later, at the same sites. Instead the spatial patterns of the fauna changed strongly during a single month with a spatial scale of re-distribution exceeding several km in some species. At the same time the granulometric sediment composition changed, indicating changes of habitat quality. Hence, sampling of a large area, with random selection of the sampling sites on each sampling date, is suggested to yield the most reliable estimates of population development in the coastal North Sea. However, in view of the expected spatial scale of re-distribution during storm tides and the spatial variability of recruitment, even a 180-km² sampling area may be too small.     

Life history of the bathyal octopus Pteroctopus tetracirrhus (Mollusca,Cephalopoda) in the Mediterranean Sea

The life cycle of the deep-sea octopus Pteroctopus tetracirrhus was studied from monthly samples obtained throughout the year in different areas of the western Mediterranean (mainly around the Balearic Islands and along the coast of the Iberian Peninsula). A total of 373 individuals (205 females, 168 males) were analyzed; females ranged from 4.5 to 14.0 cm mantle length (ML) and males from 4.5 to 11.5 cm ML. There were few small-sized octopuses (<7 cm ML) in the samples, which might indicate that these individuals inhabit rocky grounds that are not accessible to trawlers or waters deeper than the maximum depth sampled (800 m). The species occurred more frequently around the Balearic Islands than along the Iberian Peninsula as they appeared in 20% and 7%, respectively, of the hauls in these areas. The octopus inhabits the lower continental shelf and upper slope in both areas, primarily between 200 and 500 m depth. Modal lengths were followed from autumn, when recruits were caught by trawlers, to summer, when reproduction took place. Females grew from 8 to 10 cm ML from winter to spring, but this modal size did not increase further in summer; males grew from 7 to 9 cm ML from winter to spring. The total disappearance of large individuals after summer suggests a life cycle lasting a single year. The evolution of the monthly mean sizes showed that the growth was best described by log-linear functions in both sexes. The length at first maturity was clearly higher in females (12 cm ML) than in males (8 cm ML). A total of 30 different prey items, belonging to four major taxonomic groups (crustaceans, osteichthyes, cephalopods and gastropods), were identified in the stomach contents. The diet of the octopus was based on crustaceans and teleosts, which accounted for 75% and 23% of the prey items, respectively. Cephalopods and gastropods were accessory prey as they only represented 1.6% and 0.7%, respectively, of the total. The octopus showed a marked preference for the benthic fish Symphurus nigrescens and the endobenthic crustacean Alpheus glaber. The bathymetric distribution of P. tetracirrhus coincides with those of these two main prey, which suggests that the distribution of the octopus might be strongly linked to its trophic resources.     

The response of abyssal organisms to low pH conditions during a series of CO2-release experiments simulating deep-sea carbon sequestration

The effects of low-pH, high-pCO₂ conditions on deep-sea organisms were examined during four deep-sea CO₂ release experiments simulating deep-ocean C sequestration by the direct injection of CO₂ into the deep sea. We examined the survival of common deep-sea, benthic organisms (microbes; macrofauna, dominated by Polychaeta, Nematoda, Crustacea, Mollusca; megafauna, Echinodermata, Mollusca, Pisces) exposed to low-pH waters emanating as a dissolution plume from pools of liquid carbon dioxide released on the seabed during four abyssal CO₂-release experiments. Microbial abundance in deep-sea sediments was unchanged in one experiment, but increased under environmental hypercapnia during another, where the microbial assemblage may have benefited indirectly from the negative impact of low-pH conditions on other taxa. Lower abyssal metazoans exhibited low survival rates near CO₂ pools. No urchins or holothurians survived during 30–42 days of exposure to episodic, but severe environmental hypercapnia during one experiment (E1; pH reduced by as much as ca. 1.4 units). These large pH reductions also caused 75% mortality for the deep-sea amphipod, Haploops lodo, near CO₂ pools. Survival under smaller pH reductions (ΔpH<0.4 units) in other experiments (E2, E3, E5) was higher for all taxa, including echinoderms. Gastropods, cephalopods, and fish were more tolerant than most other taxa. The gastropod Retimohnia sp. and octopus Benthoctopus sp. survived exposure to pH reductions that episodically reached −0.3 pH units. Ninety percent of abyssal zoarcids (Pachycara bulbiceps) survived exposure to pH changes reaching ca. −0.3 pH units during 30–42 day-long experiments.     

Spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the Gulf of Guinea

Density, taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics (pore water, nitrogen, organic carbon, sulfur, C/N ratio, n-alcohol biomarkers) were examined at three deep sites on the Congo–Gabon continental margin. This study was part of the multidisciplinary BIOZAIRE project that aimed at studying the deep benthic ecosystems in the Gulf of Guinea. Sampling of macrofaunal communities and of sediment was conducted during three cruises (January 2001, December 2001 and December 2003) at two downslope sites (4000 m depth), one located near the Congo submarine channel (15 km in the south) and the other one far from the channel (150 km in the South). The third area located 8 km north of the Congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in December 2003.At these three locations the macrofaunal communities presented relatively high densities (327–987 ind. 0.25 m⁻²) compared with macrofaunal communities at similar depths; that is due to high levels of food input related to the Congo river and submarine system activities that affect the whole study area. The communities were different from each other in terms of taxonomic composition at higher taxon level (phylum, class, order for all the groups except for the polychaetes classified into families). The polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites (4000 m) between January 2001 and December 2003 whereas the tanaidaceans, the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites. The community at 3150 m differed from the two deep communities by higher abundances in bivalves, nemerteans and holothuroids. The composition of the polychaete community also differed among sites.In the vicinity of the Congo channel, the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed, as the increase in densities during the study period was higher at the site located away from the Congo channel than near the channel (80% vs 30%). That may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites, and/or to the disturbance caused by these turbidites. Conversely, far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources, but also from continental sources, carried by the Congo plume or by near-bed currents across or along the continental slope. Spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities.The activities of the very active Congo system structure the deep macrofaunal communities on a large area in terms of densities, composition and vertical distribution. The food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics, mainly in terms of organic matter quality (marine vs terrigenous). In turn, the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution.     

Analysis of a PAH-degrading bacterial population in subsurface sediments on the Mid-Atlantic Ridge

Little is known about the types and concentrations of polycyclic aromatic hydrocarbons (PAHs) existing in the deep-sea subsurface environment, which is believed to be cold, oligothrophic and of high static pressure. PAHs in the upper layers of the water column are unavoidably subjected to degradation while they are deposited to the sea floor and become embedded in the deep-sea sediment. In this report, a high concentration of PAHs was discovered in the sediment 2.7 m beneath the bottom surface at a water depth of 3962 m on the Mid-Atlantic Ridge (MAR). The total concentration of PAHs was 445 ng (g dry wt sediment)^-1. Among the seven detected PAHs, the concentrations of phenanthrene (222 ng g^-1) and fluorene (79 ng g^-1) were relatively high. In addition, PAH-degrading bacteria were found within the sediments. As in a previously detected site on the MAR, in the PAH-enriched region of this site, a bacterium of the genus Cycloclasticus was found to be the predominant isolate detected by PCR-DGGE analysis. In addition, bacteria of the Halomonas, Marinobacter, Alcanivorax, Thalassospira and Maricaulis genera, were also included in the PAH-degrading community. In summary, a high concentration of PAHs was detected in the subsurface of the deep-sea sediment, and once again, the Cycloclasticus bacterium was confirmed to be a ubiquitous marine PAH degrader even in the subsurface marine environment. Considering the abundance of PAHs therein, biodegradation is thus thought to be inactive, probably because of the low temperature, limited oxygen and/or limited nutrients.     

Temporal variations in the deep-water colonization rates of small benthic foraminifera: the results of an experiment on Cross Seamount

Modern benthic foraminifera are important remineralizers of organic matter and a link between surface-ocean production and life in the deep sea. Assemblages of benthic foraminifera are preserved in the fossil record, providing clues to paleoceanographic conditions. These clues can be fully interpreted only when our knowledge of the biology and ecology of modern species is more complete. To study factors influencing foraminiferal colonization rates, artificial substrates were placed on Cross Seamount (18°40′N, 158°17′W) for 1 to 42 months between 1989 and 1994. The colonization rates of benthic foraminifera onto different substrates (five mineral types were used) at four water depths (800, 975, 1285 and 2000 m) were determined. Both calcareous and agglutinated foraminifera inhabited these artificial substrates at different rates. Many of the agglutinated forms colonized at a uniform rate through time. The colonization rates of other foraminifera, primarily calcareous forms, were not constant through time, nor could the variability be attributed to the controlled variables (water depth and substrate composition). Instead, these temporal variations in colonization rate corresponded with shifts in surface ocean conditions and export fluxes in the central Pacific. Other ecological observations are also presented, including size- and spatial-distributions.     

Florida Current transport variability: An analysis of annual and longer-period signals

More than forty years of Florida Current transport estimates are combined to study annual and longer-term variability in this important component of the MOC and subtropical gyre. A detailed analysis with error estimates illustrates the difficulties in extracting annual and longer time scale variability given the strong higher frequency energy present. The annual cycle represents less than 10% of the total Florida Current transport variance in a 16 yr segment of the record, while interannual (13–42 month) variability represents only 13% of the total and periods longer than 42 months represents less than 10% of the total. Given the observed high frequency variability of the Florida Current, in order to get a monthly mean that is accurate to within 0.5 Sv (one standard error level) more than 20 daily observations are needed. To obtain an estimate of the annual climatology that is “accurate” to within 20% of its own standard deviation, at least 24 yr of data is needed. More than 40 observations spread throughout a year are required to obtain an annual mean that is accurate to within 0.5 Sv. Despite these daunting data requirements, there is sufficient data now to evaluate both the annual cycle of the Florida Current transport with a high degree of accuracy and to begin to determine the longer period transport variability. Comparison of the Florida Current, NAO and wind stress curl records shows that a recently described Sverdrup-based mechanism explains a significant fraction of the long-period variability primarily during the 1986–1998 time window, with other mechanisms clearly dominating before and after.     

The natural diet of a hexactinellid sponge: Benthic–pelagic coupling in a deep-sea microbial food web

Dense communities of shallow-water suspension feeders are known to sidestep the microbial loop by grazing on ultraplankton at its base. We quantified the diet, rates of water processing, and abundance of the deep-sea hexactinellid sponge Sericolophus hawaiicus, and found that, like their demosponge relatives in shallow water, hexactinellids are a significant sink for ultraplankton. S. hawaiicus forms a dense bed of sponges on the Big Island of Hawaii between 360 and 460 m depth, with a mean density of 4.7 sponges m⁻². Grazing of S. hawaiicus on ultraplankton was quantified from in situ samples using flow cytometry, and was found to be unselective. Rates of water processing were determined with dye visualization and ranged from 1.62 to 3.57 cm s⁻¹, resulting in a processing rate of 7.9±2.4 ml sponge⁻¹ s⁻¹. The large amount of water processed by these benthic suspension feeders results in the transfer of approximately 55 mg carbon and 7.3 mg N d⁻¹ m⁻² from the water column to the benthos. The magnitude of this flux places S. hawaiicus squarely within the functional group of organisms that link the pelagic microbial food web to the benthos.     

Depth zonation and bathymetric trends of deep-sea megafaunal scavengers of the Hawaiian Islands

The deep sea has been shown to exhibit strong depth zonation in species composition and abundance. Examination of these patterns can offer ecological insight into how organisms adapt and respond to changing environmental parameters that co-occur with depth. Here we provide the first tropical study on bathymetric zonation and other depth-related trends (size, abundance, and species richness) spanning shelf to abyssal depths of scavenging megafauna. Baited time-lapse free-vehicle cameras were used to examine the deep-sea benthic and demersal scavenging communities of the Hawaiian Islands, an area for which the biology and ecology have remained poorly studied below 2000 m. Twenty-two deployments ranging in depth from 250 to 4783 m yielded 37 taxa attracted to bait, including the first known occurrence of the family Zoarcidae in the Hawaiian Islands. Cluster analysis of Bray–Curtis similarity of species peak abundance (n_max) revealed four main faunal zones (250–500, 1000, 1500–3000, and ?4000 m) with significant separation (ANOSIM, global R=0.907, p=0.001) between designated depth groups. A major faunal break was identified at the 500–1000 m transition where species turnover was greatest, coinciding with the location of the local oxygen minimum zone. Dominance in species assemblage shifted from decapod crustaceans to teleosts moving from shallow to deeper faunal zones. Significant size differences in total length with depth were found for two of the four fish species examined. A logarithmic decline was observed in scavenger relative abundance with depth. Evidence of interaction between scavenging species was also noted between Synaphobranchus affinis and Neolithodes sp. (competition) and Histiobranchus sp. and aristeid shrimp (predation), suggesting that interactions between scavengers could influence indices of abundance generated from baited camera data.