Nutritional importance of benthic bacteria for deep-sea nematodes from the Arctic ice margin: Results of an isotope tracer experiment

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Lanice conchilega structures carbon flows in soft-bottom intertidal areas

Biogenic reefs constructed by the tube-building ecosystem engineer Lanice conchilega (Terrebilidae, Polychaeta) have profound structuring impacts on the benthic environment by altering the biogeochemical and physical properties of the sediment. This study provides new insights in the functioning of L. conchilega reefs in intertidal sediments by quantifying the carbon flows in the food webs in the presence and absence of the tubeworm using linear inverse models (LIMs); yielding insights in the effects of L. conchilega reefs on food webs. The inverse food web models were based on an empirical dataset from two study sites, consisting of biomass and stable isotope data, and general physiological constraints from the literature. The carbon input into reef food webs (191 ± 50 mmol C m-2 d-1) is about 40 times higher compared to bare sand areas (5 ± 2 mmol C m-2 d-1) and is mainly derived from organic matter (OM) in the water column. Most of the OM input towards these reefs is consumed by suspension feeding macrofauna, particularly L. conchilega, however the worm is not an important source of carbon for other macrofaunal organisms. The ratio of OM input to primary production indicates that the OM needs to be produced in an area at least 15 times larger than the reef area, demonstrating significant OM ‘focussing’ within the reef food web. The reef structures created by L. conchilega act as a trap of OM, resulting in overall high macrofaunal biomass in the presence of the tubeworm, and much more diverse food webs

Has phytodetritus processing by an abyssal soft-sediment community recovered 26 years after an experimental disturbance?

The potential harvest of polymetallic nodules will heavily impact the abyssal, soft sediment ecosystem by removing sediment, hard substrate, and associated fauna inside mined areas. It is therefore important to know whether the ecosystem can recover from this disturbance and if so at which rate. The first objective of this study was to measure recovery of phytodetritus processing by the benthic food web from a sediment disturbance experiment in 1989. The second objective was to determine the role of holothurians in the uptake of fresh phytodetritus by the benthic food web. To meet both objectives, large benthic incubation chambers (CUBEs; 50 × 50 × 50 cm) were deployed inside plow tracks (with and without holothurian presence) and at a reference site (holothurian presence, only) at 4100 m water depth. Shortly after deployment, ¹³C- and ¹⁵N-labeled phytodetritus was injected in the incubation chambers and during the subsequent 3-day incubation period, water samples were taken five times to measure the production of ¹³C-dissolved inorganic carbon over time. At the end of the incubation, holothurians and sediment samples were taken to determine biomass, densities and incorporation of ¹³C and ¹⁵N into bacteria, nematodes, macrofauna, and holothurians. For the first objective, the results showed that biomass of bacteria, nematodes and macrofauna did not differ between reference sites and plow track sites when holothurians were present. Additionally, meiofauna and macrofauna taxonomic composition was not significantly different between the sites. In contrast, total ¹³C uptake by bacteria, nematodes and holothurians was significantly lower at plow track sites compared to reference sites, though the number of replicates was low. This result suggests that important ecosystem functions such as organic matter processing have not fully recovered from the disturbance that occurred 26 years prior to our study. For the second objective, the analysis indicated that holothurians incorporated 2.16 × 10⁻³ mmol labile phytodetritus C m⁻² d⁻¹ into their biomass, which is one order of magnitude less as compared to bacteria, but 1.3 times higher than macrofauna and one order of magnitude higher than nematodes. Additionally, holothurians incorporated more phytodetritus carbon per unit biomass than macrofauna and meiofauna, suggesting a size-dependence in phytodetritus carbon uptake

Spatial self-organization as a new perspective on cold-water coral mound development

Cold-water corals build extensive reefs on the seafloor that are oases of biodiversity, biomass, and organic matter processing rates. The reefs baffle sediments, and when coral growth and sedimentation outweigh ambient sedimentation, carbonate mounds of tens to hundreds of meters high and several kilometers wide can form. Because coral mounds form over ten-thousands of years, their development process remains elusive. While several environmental factors influence mound development, the mounds also have a major impact on their environment. This feedback between environment and mounds, and how this drives mound development is the focus of this paper. Based on the similarity of spatial coral mound patterns and patterns in self-organized ecosystems, we provide a new perspective on coral mound development. In accordance with the theory of self-organization through scale-dependent feedbacks, we first elicit the processes that are known to affect mound development, and might cause scale-dependent feedbacks. Then we demonstrate this concept with model output from a study on the Logachev area, SW Rockall Trough margin. Spatial patterns in mound provinces are the result of a complex set of interacting processes. Spatial self-organization provides a framework in which to place and compare these processes, so as to assess if and how they contribute to pattern formation in coral mounds

The SCOC database, a large, open, and global database with sediment community oxygen consumption rates

Sediment community oxygen consumption (SCOC) rates provide important information about biogeochemical processes in marine sediments and the activity of benthic microorganisms and fauna. Therefore, several databases of SCOC data have been compiled since the mid-1990s. However, these earlier databases contained much less data records and were not freely available. Additionally, the databases were not transparent in their selection procedure, so that other researchers could not assess the quality of the data. Here, we present the largest, best documented, and freely available database of SCOC data compiled to date. The database is comprised of 3,540 georeferenced SCOC records from 230 studies that were selected following the procedure for systematic reviews and meta-analyses. Each data record states whether the oxygen consumption was measured ex situ or in situ, as total oxygen uptake, diffusive or advective oxygen uptake, and which measurement device was used. The database will be curated and updated annually to secure and maintain an up-to-date global database of SCOC data

Survival under conditions of variable food availability: Resource utilization and storage in the cold-water coral Lophelia pertusa

Cold‐water coral (CWC) reefs are hotspots of biodiversity and productivity in the deep sea, but their distribution is limited by the availability of food, which undergoes complex local and temporal variability. We studied the resource utilization, metabolism, and tissue storage of CWC Lophelia pertusa during an experimentally simulated 3‐day food pulse, of 13C15N‐enriched phytodetritus, followed by a 4‐week food deprivation. Oxygen consumption (0.145 μmol O2 [mmol organic carbon {OC}]−1 h−1), release of particulate organic matter (0.029 μmol particulate organic carbon [POC] [mmol OC]−1 h−1 and 0.005 μmol particulate organic nitrogen [mmol OC]−1 h−1), ammonium excretion (0.004 μmol NH4+ [mmol OC]−1 h−1), tissue C and N content, and fatty acid (FA) and amino acid composition did not change significantly during the experiment. Metabolization of the labeled phytodetritus, however, underwent distinct temporal dynamics. Initially, L. pertusa preferentially used phytodetritus‐derived C for respiration (2.2 ± 0.36 nmol C [mmol OC]−1 h−1) and mucus production (0.94 ± 0.52 nmol C [mmol OC]−1 h−1), but those tracer fluxes declined exponentially to <20% within 2 weeks after feeding and then remained stable, indicating that the remainder of the incorporated phytodetritus had entered a tissue pool with lower turnover. Analysis of 13C in individual FAs revealed a mismatch between the FAs incorporated from phytodetritus and the FA requirements of the coral. We suggest that feeding on other resources, such as lipid‐rich zooplankton, could fill this deficiency. A release of 10% of their total OC as respired C and POC during the 4‐week food deprivation underlines the importance of regular food pulses for CWC reefs.publishedVersio

Metabolic rates are significantly lower in abyssal Holothuroidea than in shallow-water Holothuroidea

Recent analyses of metabolic rates in fishes, echinoderms, crustaceans and cephalopods have concluded that bathymetric declines in temperature- and mass-normalized metabolic rate do not result from resource-limitation (e.g. oxygen or food/chemical energy), decreasing temperature or increasing hydrostatic pressure. Instead, based on contrasting bathymetric patterns reported in the metabolic rates of visual and non-visual taxa, declining metabolic rate with depth is proposed to result from relaxation of selection for high locomotory capacity in visual predators as light diminishes. Here, we present metabolic rates of Holothuroidea, a non-visual benthic and benthopelagic echinoderm class, determined in situ at abyssal depths (greater than 4000 m depth). Mean temperature- and mass-normalized metabolic rate did not differ significantly between shallow-water (less than 200 m depth) and bathyal (200–4000 m depth) holothurians, but was significantly lower in abyssal (greater than 4000 m depth) holothurians than in shallow-water holothurians. These results support the dominance of the visual interactions hypothesis at bathyal depths, but indicate that ecological or evolutionary pressures other than biotic visual interactions contribute to bathymetric variation in holothurian metabolic rates. Multiple nonlinear regression assuming power or exponential models indicates that in situ hydrostatic pressure and/or food/chemical energy availability are responsible for variation in holothurian metabolic rates. Consequently, these results have implications for modelling deep-sea energetics and processes