Isotopic niche variability in macroconsumers of the East Scotia Ridge (Southern Ocean) hydrothermal vents: What more can we learn from an ellipse?

Aspects of between-individual trophic niche width can be explored through the isotopic niche concept. In many cases isotopic variability can be influenced by the scale of sampling and biological characteristics including body size or sex. Sample size-corrected (SEAc) and Bayesian (SEAb) standard ellipse areas and generalised least squares (GLS) models were used to explore the spatial variability of δ13C and δ15N in Kiwa tyleri (decapod), Gigantopelta chessoia (peltospirid gastropod) and Vulcanolepas scotiaensis (stalked barnacle) collected from 3 hydrothermal vent field sites (E2, E9N and E9S) on the East Scotia Ridge (ESR), Southern Ocean. SEAb only revealed spatial differences in isotopic niche area in male K. tyleri. However, the parameters used to draw the SEAc, eccentricity (E) and angle of the major SEAc axis to the x-axis (θ), indicated spatial differences in the relationships between δ13C and δ15N in all 3 species. The GLS models indicated that there were spatial differences in isotope-length trends, which were related to E and θ of the SEAc. This indicated that E and θ were potentially driven by underlying trophic and biological processes that varied with body size. Examination of the isotopic niches using standard ellipse areas and their parameters in conjunction with length-based analyses provided a means by which a proportion of the isotopic variability within each species could be described. We suggest that the parameters E and θ offer additional ecological insight that has so far been overlooked in isotopic niche studies

Mass deposition of jellyfish in the deep Arabian Sea

In December 2002 large numbers of dead jellyfish, Crambionella orsini (Vanhöffen 1888), were observed on the seabed over a wide area of the Arabian Sea off the coast of Oman, at depths between 350 and 3300 m. Moribund jellyfish were seen tumbling down the continental slope. Large aggregations of dead jellyfish were evident within canyons and on the continental rise. At the deepest stations, patches of rotting, coagulated jellyfish occurred. The patches were several metres in diameter, at least 7 cm thick and covered about 17% of the sediment surface. At other locations on the continental rise the seafloor was covered in a thin, almost continuous, layer of jelly “slime,” a few millimetres thick, or was littered with individual jellyfish corpses. Photographic transects were used to estimate the amount of carbon associated with the jelly detritus. The standing stock of carbon varied between 1.5 and 78 g C m-2, the higher figure exceeding the annual downward flux of organic carbon, as measured by sediment traps, by more than an order of magnitude. The episodic nature of jellyfish blooms, which may be modulated by global change phenomena, provides a hitherto unknown mechanism for large-scale spatial and temporal patchiness in deep-sea benthic ecosystems

Reproductive biology of the abyssal holothurian Amperima rosea: an opportunistic response to variable flux of surface derived organic matter?

A radical change in the abundance of invertebrate megafauna has occurred over a vast area of the Porcupine Abyssal Plain, north-east Atlantic, in recent years. In particular, the holothurian Amperima rosea has increased in abundance by three orders of magnitude. The sudden increase in abundance of A. rosea appears to be the result of environmental forcing rather than localized stochastic population variations. Amperima rosea produces small eggs ([less-than-or-eq, slant]200 [mu]m) indicating (1) planktotrophic larval development or (2) lecithotrophic larval development with an abbreviated larval stage. It also reaches maturity at a very small size. The reproductive biology of A. rosea indicates that it can increase rapidly in population size and can colonize large areas quickly. It has high fecundity, as predicted by gonad indices and observed in histological studies. Fecundity was greater in winter than in summer months, but there was no clear evidence of seasonal or episodic reproductive events. All males, irrespective of sample season or year, were mature with spermatozoa. Most oocytes were of an intermediate size (70 to 120 [mu]m), either at the late previtellogenic (70–90 [mu]m) or early vitellogenic (100–120 [mu]m) stage of development. It is postulated that development of full vitellogenesis, leading to episodic spawning, might be dependent on certain environmental stimuli. The most likely stimulus is food supply. Amperima rosea has been shown to feed preferentially on phytodetritus and to have a requirement for certain sterols in its diet. Qualitative changes in the flux of organic matter to the sea-floor may control vitellogenesis and fecundity, and hence have an effect on the population dynamics of the species

The feeding behaviour of a deep-sea holothurian, Stichopus tremulus (Gunnerus) based on in situ observations and experiments using a Remotely Operated Vehicle

Using a Remotely Operated Vehicle (ROV) to deploy an in situ cage experiment incorporating fluorescent Luminophore particle tracers, the gut throughput time of the deposit feeding holothurian, Stichopus tremulus (Gunnerus) was determined as 23.73 h (S.D.F2.3). For a range of individuals examined at different depths (350–500 m) and locations, throughput times varied between 19 and 26 h irrespective of animal size or gut tract length. In situ video observations of feeding behaviour showed that this species uses fine oral papillae in a ‘sweeping’ motion to target particles on the seafloor. Following detection of a food source fine-branched digitate tentacles collect a large range of sediment fragments from the seabed. The main types of particles ingested include silica fragments ( < 20 > 500 Am), pelagic foraminifera, benthic foraminifera, fine phytodetrital remains and occasional larger rock fragments (f1 cm). Ingested sediment consisted mainly of very fine silica fragments (f50 Am) accounting for over 50% of the total gut contents. Frame-by-frame video analysis revealed that the particle handling time (i.e. the time taken for a tentacle insertion and the subsequent collection of food) was found to be f54 s. Only 10 of the 20 feeding tentacles were simultaneously employed during feeding. Use of tentacles appeared to be in sequence, alternating between the reserve and active tentacles. Estimating the rate of movement over the seabed and the total effective capture area of each tentacle, the impact of this animal on the turnover and quality of surface sediment at this deepwater site is potentially substantial. The in situ experiments provided a significant improvement over previous methods used to investigate deep-sea deposit feeders and represent a useful concept for further in situ deep-sea research using an industrial ROV

A review of the uses of work-class ROVs for the benefits of science: lessons learned from the SERPENT project

This paper reviews the contributions of underwater science in continuing to develop new technology to explore the marine environment and how collaborations taking place between the oil and gas industry and science are facilitating this process. A case study focuses on some of the results and highlights from the SERPENT Project. SERPENT (Scientific and Environmental ROV Partnership using Existing Industrial Technology) is a collaboration programme that was designed to make better use of remotely operated vehicle (ROV) technology and data available through links with marine operations in the oil and gas industry. Oil and gas exploration and production activities in the marine environment are increasing. The amount of global hydrocarbon reserves removed from below the seafloor is set to increase over the next 5–10 years with exploration heading into deeper, more remote waters, many of which have yet to be fully explored. The only way that these remote areas may be documented is through a working relationship with industry, with mutual benefit for both sides, and learning from technology that is already in place for the benefit of science

Seasonality and selectivity in the feeding ecology and reproductive biology of deep-sea bathyal holothurians

Chlorophyll and carotenoid pigments were determined from the gut sediments of five species of bathyal holothurian in the NE Atlantic, sampled shortly after the spring/summer phytoplankton bloom in 2001 and prior to the spring bloom in 2002. Three species, Laetmogone violacea, Paroriza pallens and Bathyplotes natans, sampled within a similar depth range (900–1100 m) in the summer of 2001 showed significant differences in their chlorophyll and carotenoid pigment concentrations. This suggests they may select for slightly different components from the available food resource. Four species sampled in early spring 2002, Laetmogone violacea, Paroriza pallens, Benthogone rosea and Benthothuria funebris, also had significant differences in their pigment concentrations. These species were sampled over a wider depth range (1000–3100 m) showing a bathymetric trend in pigment concentrations. There was a distinct seasonal change in the composition and concentration of the pigments, linked to a reduction in the availability of fresh organic material during autumn and winter periods.Ovarian tissue was also examined. The carotenoid pigments found in the ovary also occurred in the OM ingested by the holothurians. The dominant gonadal carotenoid pigments were beta-carotene, echinenone and zeaxanthin. The potential for using these carotenoids to gain a competitive advantage through selectivity of chlorophyll and carotenoid pigment biomarkers are discussed in relation to competition for food resources by deposit-feeders. The results were also compared with selectivity in abyssal species

Temporal variability in phytodetritus and megabenthic activity at the seabed in the deep northeast Atlantic

We report a ten-year study of the abundance and activity of megabenthos on the Porcupine Abyssal Plain, northeast Atlantic, together with observations on the occurrence of phytodetritus at the deep-sea floor (4850 m). Using the Southampton Oceanography Centre time-lapse camera system, ‘Bathysnap’, we have recorded a radical change in the abundance and activity of megabenthos between the two periods of study (1991–1994 and 1997–2000). In 1991–1994, the larger megabenthos occurred at an abundance of c. 71.6/ha and were dominated by large holothurians. In addition, there were very substantial populations of smaller megabenthic ophiuroids (c. 4979/ha). Together, the total megabenthos are estimated to track over some 17 cm2/m2/d (exploiting 100% of the surface of the seabed in c. 2.5 years). In 1997–2000, the larger megabenthos increased to an abundance of c. 204/ha and were joined by exceptional numbers of a small holothurian species (Amperima rosea, 6457/ha) and ophiuroids (principally Ophiocten hastatum, 53,539/ha). The total megabenthos population was tracking at an estimnated rate of c. 247 cm2/m2/d (exploiting 100% of seabed in just 6 weeks). Coincident with these increases in the abundance and activity of the megabenthos, there were apparently no mass depositions of aggregated phytodetritus to the seabed in the summers of 1997–1999. Mass occurrences of phytodetritus had been noted during the summer months of the three years previously studied (1991, 1993 and 1994), with covering between 50 and 96% of the sediment surface. There is a statistically significant (p<0.02) negative correlation between maximum extent of this seabed cover of phytodetritus and seabed tracking by megabenthos. Additional studies [Lampitt et al., Progr. Ocean. 50 (2001)], indicate that there were no substantial changes in surface ocean primary productivity, in export flux, or in the composition of the flux that might otherwise account for the apparent absence of observable concentrations of phytodetritus during the summers of 1997–1999. We postulate that the marked increase in megabenthic tracking activity resulted in the removal (via consumption, disaggregation, burial etc.) of the bulk of the incoming phytodetrital flux during these years. A simple conceptual model, based on the apparent phytodetrital fluxes observed in 1991 and 1993, suggests that the megabenthos tracking rates estimated for 1997–1999 are sufficient to account for near-total removal of this flux. However, we are not able to estimate other processes removing phytodetritus (i.e. other elements of the benthos) that may also have increased between 1991–1994 and 1997–1999. Other independent studies [e.g. Ginger et al., Progr. Ocean. 50 (2001)] of flux constituents support the possibility that just a few species of megabenthos (e.g. A. rosea, and O. hastatum) could well have consumed a major proportion of the incoming flux and so substantially modified the composition of the organic matter available to other components of the benthos

Elucidating trophic pathways in benthic deep-sea assemblages of the mid-atlantic ridge north and south of the Charlie-Gibbs fracture zone

The Mid-Atlantic Ridge (MAR) is a topographically complex feature in the North Atlantic Ocean with little exploration of benthic fauna except in association with hydrothermal venting, resulting in the biodiversity and ecosystem functioning of the MAR benthos away from these sites remaining largely unknown. Stable isotope analysis of carbon, nitrogen and sulphur were undertaken on fauna collected north and south of the Charlie-Gibbs Fracture Zone, in areas believed to be devoid of hydrothermal venting, to investigate the trophodynamics of the benthic assemblage. δ13C and δ34S values of the benthic and bentho-pelagic fauna indicated a dependence on photosynthetic primary production, with no influence from an unknown chemosynthetic source. A large trophic discrimination in δ13C between consumers and potential food sources (particulate organic matter and surficial sediments) suggested reworking of organic carbon before assimilation by benthic fauna. Interpretation of sediment δ15N values was difficult as these ranged between −0.74 and 23.14‰, suggesting further work is required to understand nitrogen utilisation by benthic deposit feeders. Differences in trophic guilds (predators, predator–scavenger, surface deposit feeders, subsurface deposit feeders and suspension feeders) were evident for δ13C and δ15N, with the main difference between the mobile predators–scavengers and the benthic deposit feeders. Dividing the assemblage based on trophic guilds into food chains dependent on phytodetritus (deposit and suspension feeders) and predation–scavenging (fishes and crustaceans) resulted in strong positive correlations between δ15N and δ13C at both stations. These reflected the 2 dominant trophic pathways organic matter passed through deposit feeders and predatory and scavenging deep-sea fishes and crustaceans