David S.M. Billett

Global Patterns and Predictions of Seafloor Biomass Using Random Forests

A comprehensive seafloor biomass and abundance database has been constructed from 24 oceanographic institutions worldwide within the Census of Marine Life (CoML) field projects. The machine-learning algorithm, Random Forests, was employed to model and predict seafloor standing stocks from surface primary production, water-column integrated and export particulate organic matter (POM), seafloor relief, and bottom water properties. The predictive models explain 63% to 88% of stock variance among the major size groups. Individual and composite maps of predicted global seafloor biomass and abundance are generated for bacteria, meiofauna, macrofauna, and megafauna (invertebrates and fishes). Patterns of benthic standing stocks were positive functions of surface primary production and delivery of the particulate organic carbon (POC) flux to the seafloor. At a regional scale, the census maps illustrate that integrated biomass is highest at the poles, on continental margins associated with coastal upwelling and with broad zones associated with equatorial divergence. Lowest values are consistently encountered on the central abyssal plains of major ocean basins The shift of biomass dominance groups with depth is shown to be affected by the decrease in average body size rather than abundance, presumably due to decrease in quantity and quality of food supply. This biomass census and associated maps are vital components of mechanistic deep-sea food web models and global carbon cycling, and as such provide fundamental information that can be incorporated into evidence-based management.

Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic)

A radical change in the abundance of invertebrate megafauna on the Porcupine Abyssal Plain is reported over a period of 10 years (1989–1999). Actiniarians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increased significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977–1999) show that prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a localised event. Several dominant holothurian species show a distinct trend in decreasing body size over the study period. The changes in megafauna abundance may be related to environmental forcing (food supply) rather than to localised stochastic population variations. Inter-annual variability and long-term trends in organic matter supply to the seabed may be responsible for the observed changes in abundance, species dominance and size distributions.

Does Presence of a Mid-Ocean Ridge Enhance Biomass and Biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Climate, carbon cycling, and deep-ocean ecosystems

Climate variation affects surface ocean processes and the production of organic carbon, which ultimately comprises the primary food supply to the deep-sea ecosystems that occupy ≈60% of the Earths surface. Warming trends in atmospheric and upper ocean temperatures, attributed to anthropogenic influence, have occurred over the past four decades. Changes in upper ocean temperature influence stratification and can affect the availability of nutrients for phytoplankton production. Global warming has been predicted to intensify stratification and reduce vertical mixing. Research also suggests that such reduced mixing will enhance variability in primary production and carbon export flux to the deep sea. The dependence of deep-sea communities on surface water production has raised important questions about how climate change will affect carbon cycling and deep-ocean ecosystem function. Recently, unprecedented time-series studies conducted over the past two decades in the North Pacific and the North Atlantic at >4,000-m depth have revealed unexpectedly large changes in deep-ocean ecosystems significantly correlated to climate-driven changes in the surface ocean that can impact the global carbon cycle. Climate-driven variation affects oceanic communities from surface waters to the much-overlooked deep sea and will have impacts on the global carbon cycle. Data from these two widely separated areas of the deep ocean provide compelling evidence that changes in climate can readily influence deep-sea processes. However, the limited geographic coverage of these existing time-series studies stresses the importance of developing a more global effort to monitor deep-sea ecosystems under modern conditions of rapidly changing climate.

The institute of oceanographic sciences biology programme in the porcupine seabight : background and general introduction

An intensive investigation of the benthic biology of the Porcupine Seabight, to the south-west of Ireland, was carried out by biologists from the Institute of Oceanographic Sciences Deacon Laboratory (IOSDL) between 1977 and 1986. More than 400 benthic samples were obtained during the study using towed gears and corersover the depth range 200 to 4500 m. Transect and time-lapse photography was used extensively. This paper summarises the techniques employed and provides an analysis of the depth and seasonal coverage. In addition a review is provided of available data on the physical, chemical and geological characteristics of the Porcupine Seabight area, including information collected during the IOSDL study. Finally, existing publications based on the study are listed.

The origin of deep-water, coral-topped mounds in the northern Rockall Trough, northeast Atlantic

Mounds associated with the cold water coral Lophelia pertusa are widespread in the North Atlantic, although the factors controlling their distribution are not well understood. Here we examine a group of small, coral-topped mounds (the Darwin mounds) which occur at 1000 m water depth in the northern Rockall Trough, northwest of the UK. Individual mounds are up to 75 m in diameter and 5 m high, although some ‘mound-like’ targets seen on sidescan sonar have little or even negative relief. Some mounds are associated with ‘tail-like’ features, imaged as elongate patches of moderate backscatter up to 500 m long, elongated parallel to prevailing bottom currents. High-resolution sidescan images and seabed photographs show hundreds of coral colonies, each a metre or so across, on each individual mound. Many other organisms, mainly suspension feeders, occur in association with the coral. Piston cores from the mounds contain predominantly quartz sand with only scattered coral fragments, showing that bioclastic material is not a major contributor to mound building. A field of seabed pockmarks occurs immediately south of the Darwin mounds. On sidescan sonar data, pockmarks are low relief, circular depressions, typically around 50 m in diameter. The seafloor around the pockmarks consists of uniform, heavily-burrowed, muddy sediments and no specific biological communities, nor any sedimentological or photographic evidence for active seepage, were observed. The distribution of mounds and pockmarks suggests a gradual transition from mounds in the north to pockmarks in the south. This, combined with the lack of bioclastic material in the mound sediments, suggests that both mounds and pockmarks are created by fluid escape from below the seafloor. Mounds occur where fluids carry subsurface sand to the surface, where it forms mounds because bottom currents are not strong enough to disperse it. Pockmarks form where muddy material is eroded by fluid escape but dispersed by bottom currents. Despite the origin of mounds through fluid escape, we suggest that it is the elevated mound topography, rather than any fluid escape, that is advantageous to the corals. This is supported: (1) by the wide variety of suspension-feeding organisms that occur on the mounds, since all of these are unlikely to have a specialised seepage-related lifestyle, and (2) because corals and their associated community do not occur around pockmarks, where seepage has also occurred but elevated topography is absent.

Temporal change in deep-sea benthic ecosystems: a review of the evidence from recent time-series studies

Societal concerns over the potential impacts of recent global change have prompted renewed interest in the long-term ecological monitoring of large ecosystems. The deep sea is the largest ecosystem on the planet, the least accessible, and perhaps the least understood. Nevertheless, deep-sea data collected over the last few decades are now being synthesised with a view to both measuring global change and predicting the future impacts of further rises in atmospheric carbon dioxide concentrations. For many years, it was assumed by many that the deep sea is a stable habitat, buffered from short-term changes in the atmosphere or upper ocean. However, recent studies suggest that deep-seafloor ecosystems may respond relatively quickly to seasonal, inter-annual and decadal-scale shifts in upper-ocean variables. In this review, we assess the evidence for these long-term (i.e. inter-annual to decadal-scale) changes both in biologically driven, sedimented, deep-sea ecosystems (e.g. abyssal plains) and in chemosynthetic ecosystems that are partially geologically driven, such as hydrothermal vents and cold seeps. We have identified 11 deep-sea sedimented ecosystems for which published analyses of long-term biological data exist. At three of these, we have found evidence for a progressive trend that could be potentially linked to recent climate change, although the evidence is not conclusive. At the other sites, we have concluded that the changes were either not significant, or were stochastically variable without being clearly linked to climate change or climate variability indices. For chemosynthetic ecosystems, we have identified 14 sites for which there are some published long-term data. Data for temporal changes at chemosynthetic ecosystems are scarce, with few sites being subjected to repeated visits. However, the limited evidence from hydrothermal vents suggests that at fast-spreading centres such as the East Pacific Rise, vent communities are impacted on decadal scales by stochastic events such as volcanic eruptions, with associated fauna showing complex patterns of community succession. For the slow-spreading centres such as the Mid-Atlantic Ridge, vent sites appear to be stable over the time periods measured, with no discernable long-term trend. At cold seeps, inferences based on spatial studies in the Gulf of Mexico, and data on organism longevity, suggest that these sites are stable over many hundreds of years. However, at the Haakon Mosby mud volcano, a large, well-studied seep in the Barents Sea, periodic mud slides associated with gas and fluid venting may disrupt benthic communities, leading to successional sequences over time. For chemosynthetic ecosystems of biogenic origin (e.g. whale-falls), it is likely that the longevity of the habitat depends mainly on the size of the carcass and the ecological setting, with large remains persisting as a distinct seafloor habitat for up to 100 years. Studies of shallow-water analogs of deep-sea ecosystems such as marine caves may also yield insights into temporal processes. Although it is obvious from the geological record that past climate change has impacted deep-sea faunas, the evidence that recent climate change or climate variability has altered deep-sea benthic communities is extremely limited. This mainly reflects the lack of remote sensing of this vast seafloor habitat. Current and future advances in deep-ocean benthic science involve new remote observing technologies that combine a high temporal resolution (e.g. cabled observatories) with spatial capabilities (e.g. autonomous vehicles undertaking image surveys of the seabed).

Depth-related distribution and abundance of seastars (Echinodermata: Asteroidea) in the Porcupine Seabight and Porcupine Abyssal Plain, N.E. Atlantic

The depth-related distribution of seastar (Echinodermata: Asteroidea) species between 150 and 4950 m in the Porcupine Seabight and Porcupine Abyssal Plain is described. 47 species of asteroid were identified from ~14,000 individuals collected. The bathymetric range of each species is recorded. What are considered quantitative data, from an acoustically monitored epibenthic sledge and supplementary data from otter trawls, are used to display the relative abundance of individuals within their bathymetric range. Asteroid species are found to have very narrow centres of distribution in which they are abundant, despite much wider total adult depth ranges. Centres of distribution may be skewed. This might result from competition for resources or be related to the occurrence of favourable habitats at particular depths. The bathymetric distributions of the juveniles of some species extend outside the adult depth ranges. There is a distinct pattern of zonation with two major regions of faunal change and six distinct zones. An upper slope zone ranges from 150 to ~700 m depth, an upper bathyal zone between 700 and 1100 m, a mid-bathyal zone from 1100 to1700 m and a lower bathyal zone between 1700 and 2500 m. Below 2500 m the lower continental slope and continental rise have a characteristic asteroid fauna. The abyssal zone starts at about 2800 m. Regions of major faunal change are identified at the boundaries of both upper and mid-bathyal zones and at the transition of bathyal to abyssal fauna. Diversity is greatest at ~1800 m, decreasing with depth to ~2600 m before increasing again to high levels at ~4700 m.

Biotic and Human Vulnerability to Projected Changes in Ocean Biogeochemistry over the 21st Century

Mora and colleagues show that ongoing greenhouse gas emissions are likely to have a considerable effect on several biogeochemical properties of the worlds oceans, with potentially serious consequences for biodiversity and human welfare.

Organic matter in deep-sea sediments from the Porcupine Abyssal Plain in the north-east Atlantic Ocean. I—Lipids

Abstract The extractable lipids of four undisturbed sediment cores from the Porcupine Abyssal Plain, in the north-eastern Atlantic Ocean, have been analysed. Several compound classes including n-alkanes, n-alcohols, alkanoic and alkenoic acids, sterols, triterpenoids and alkenones were present in most of the samples. Surficial sediments showed evidence of mixed marine and terrigenous organic matter, the latter presumably being higher plant-derived. There was, however, considerable variability in the distributions of lipids in the surficial sediments; this is consistent with photographic evidence of the patchiness of the Porcupine Abyssal Plain sediments, which are strongly influenced by the benthic faunal community. In general, the concentrations of most compounds (with respect to total organic carbon) are attenuated with depth in the sediments, although the “higher plant” signal is apparently more recalcitrant thanthe “marine” signal. There is also evidence of significant down-core variability in some of the cores.