Hjalmar Thiel

Phytodetritus on the deep-sea floor in a central oceanic region of the Northeast Atlantic

In a midoceanic region of the northeast Atlantic, patches of freshly deposited phytodetritus were discovered on the sea floor at a 4500 m depth in July/August 1986. The color of phytodetritus was variable and was obviously related to the degree of degradation. Microscopic analyses showed the presence of planktonic organisms from the euphotic zone, e.g., cyanobacteria, small chlorophytes, diatoms, coccolithophorids, silicoflagellates, dinoflagellates, tintinnids, radiolarians, and foraminifers. Additionally, crustacean exuviae and a great number of small fecal pellets, “minipellets,” were found. Although bacteria were abundant in phytodetritus, their number was not as high as in the sediment. Phytodetrital aggregates also contained a considerable number of benthic organisms such as nematodes and special assemblages of benthic foraminifers. Pigment analyses and the high content of particulate organic carbon indicated that the phytodetritus was relatively undegraded. Concentrations of proteins, carbohydrates, chloroplastic pigments, total adenylates, and bacteria were found to be significantly higher in sediment surface samples when phytodetritus was present than in equivalent samples collected at the same stations in early spring prior to phytodetritus deposition. Only the electron transport system activity showed no significant difference between the two sets of samples, which may be caused by physiological stress during sampling (decompression, warming). The chemical data of phytodetritus samples displayed a great variability indicative of the heterogeneous nature of the detrital material. The gut contents of various megafauna (holothurians, asteroids, sipunculids, and actiniarians) included phytodetritus showing that the detrital material is utilized as a food source by a wide range of benthic organisms. Our data suggest that the detrital material is partly rapidly consumed and remineralized at the sediment surface and partly incorporated into the sediment. Incubations of phytodetritus under simulated in situ conditions and determination of the biological oxygen demand under surface water conditions showed that part of its organic matter can be biologically utilized. Based on the measured standing stock of phytodetritus, it is estimated that 0.3–3% of spring primary production sedimented to the deep-sea floor. Modes of aggregate formation in the surface waters, their sedimentation, and distribution on the seabed are discussed.

Meiobenthic stocks and benthic activity on the NE-Svalbard shelf and in the Nansen Basin

SummaryHigh Arctic meiofaunal distribution, standing stock, sediment chemistry and benthic respiratory activity (determined by sediment oxygen consumption using a shipboard technique) were studied in summer 1980 on the NE Svalbard shelf (northern Barents Sea) and along a transect into the Nansen Basin, over a depth range of 240–3920 m. Particulate sediment proteins, carbohydrates and adenylates were measured as additional measures of benthic biomass. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigments (chlorophylls, pheopigments) were assayed. Pigment concentrations were found comparable to values in sediments from the boreal and temperate N-Atlantic. Meiofauna, which was abundant on the shelf, decreased in numbers and biomasses with increasing depth, as did sediment proteins, carbohydrates, adenylates and sediment oxygen consumption. Meiofaunal abundances and biomasses within the Nansen Basin were comparable with those observed in abyssal sediments of the North Atlantic. Nematodes clearly dominated in metazoan meiofauna. Protozoans were abundant in shelf sediments. Probably in response to the sedimentation of the plankton bloom, meiofauna abundance and biomass as well as sediment proteins, carbohydrates and adenylates were significantly correlated to the amount of sediment bound chloroplastic pigments, stressing the importance of food quantity to determine benthic stocks. Ninety-four percent of the variance in sediment oxygen consumption were caused by chloroplastic pigments. Benthic respiration, calculated per unit biomass, was 3–10 times lower than in the East Atlantic, suggesting low turnover rates in combination with a high standing stocks for the high Arctic benthos.

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.

The Size Structure of Deep-Sea Meiobenthos in the North-Eastern Atlantic: Nematode Size Spectra in Relation to Environmental Variables

The size distribution of benthic nematodes was investigated along different gradients of food availability in various regions of the north-eastern Atlantic: I, across the continental margin and II, with increasing distance from the continental rise. An overall trend for miniaturization with increasing distance from the food source was found. Moreover, our results indicate that seasonally varying food supply or a periodically pulsed input of organic matter to the sea floor affects nematode size spectra. The hypothesis is proposed that the life cycle of deep-sea nematode species and hence the size structure of their populations are related to seasonal energy availability. This dependence might result in one year life spans of deep-sea nematodes and probably other meiofauna.

Evaluation of the environmental consequences of polymetallic nodule mining based on the results of the TUSCH Research Association

Abstract Realising a need for increased general knowledge of the deep sea for environmental impact assessments related to the permanent storage of waste products and mining of metal resources, the German Bundesministerium fur Bildung und Forschung has funded targeted research in the deep sea for more than 10 years. The research was carried out in an area in the Southeast Pacific Ocean close to and within a German mining claim, to match the interests of German deep-sea polymetallic nodule mining enterprises and the developing mining code of the Preparatory Commission for the International Seabed Authority and the International Tribunal for the Law of the Sea. The “TUSCH (abbreviation for ‘Tiefsee-Umweltschutz’—deep-sea environmental protection) Research Association”, with members from various university and governmental institutions, was part of the ATESEPP (Effects of Technical Interventions into the Ecosystem of the Deep Sea in the Southeast Pacific Ocean) Project between 1996 and 1998. Geotechnical, sedimentological, geochemical, hydrographic, numerical modelling and ecological studies relevant to environmental impact assessment studies of polymetallic nodule mining were undertaken. Since general oceanographic knowledge of the deep sea is rather limited, these various projects also have increased our general understanding of this region. This paper describes the potential impacts of mining processes on the seafloor and the near-bottom water layer as well as on bathyal and abyssal pelagic zones that will receive processed water, sediment and abraded nodule fines (tailings) discharged after nodule transport to the mining vessel at the ocean surface. The TUSCH Research Association defined various recommendations to keep the unavoidable impacts to a minimum, such as • limited penetration of the mining system into the sediment, • confining intensive resedimentation to the area behind the miner, • minimising transport of sediment to the ocean surface, and • discharging all tailings at great depths, ideally close to the seafloor. The recommendations are not new, but the present studies have improved them from precautionary to scientifically based statements.

Abyssal nematode assemblages in physically disturbed and adjacent sites of the eastern equatorial Pacific

The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of the eastern equatorial Pacific were investigated 7 years after a physical disturbance. A total of 3048 nematodes belonging to 68 genera and 26 families were identified. The nematode fauna at both disturbed and control sites was dominated by specimens belonging to the genera Acantholaimus, Chromadorita, Thalassomonhystera, Desmoscolex, Halalaimus and Diplopeltula. These genera contribute to about 55% and 50% of total nematode fauna in the disturbed and control sites, respectively. The mean relative abundance of the dominant genus Acantholaimus amounted to about 20%. Generic diversity, evenness and richness at the undisturbed sites do not significantly differ from the corresponding median values at the disturbed sites. Mean k-dominance curves show differences in community structure between treatments. Ordination of square- and fourth-root-transformed family abundances revealed groupings of the disturbed and undisturbed samples (significant at the 5% level), whereas ordination of genus abundances did not. Sample variability was investigated by inspection of the relationship between variance and mean abundance of genera and families in each sample group and by calculating the comparative index of multivariate dispersion (IMD). There is a clear increase in the standard deviation for a given mean of genus or family abundances at the disturbed sites. A higher variability among the disturbed samples, however, does not appear to be true in the multivariate sense.

Manganese nodule crevice fauna

Abstract The surfaces of manganese nodules are inhabited by a diverse epigrowth composed of bacteria, protozoa and metazoa, typically hard bottom thriving taxa. While searching for epifauna on nodules, we also noted life in a new habitat, the crevices or interstitial space between subnodules. The faunal composition in the crevices differs from that in the sediment surrounding the nodules.

The large-scale environmental impact experiment DISCOL—reflection and foresight

It is now accepted that environmental impact studies should accompany societys growing interest in exploiting deep-sea resources. A large-scale experiment, DISCOL (Disturbance and recolonisation experiment in a manganese nodule area of the deep South Pacific) was conducted to evaluate potential impacts from mining on the deep-sea bed. DISCOL was the first of a series of projects aimed at better understanding impacts of industrial-scale mining of polymetallic nodules upon the seafloor and its biological community. A schedule of biological work, including a disturbance scheme and sampling patterns, for another 12-year period is described that builds on the DISCOL results, but is strictly valid only for this area. However, future experiments may use estimates from the DISCOL data as a first approximation in their planning phase, but will need to conduct site-specific sampling to establish a baseline.

Assessment of pollution-induced changes in benthic community structure

This article presents a brief summary of three ways in which the structure of marine benthic communities have been examined in the past. These approaches are considered in terms of their usefulness in assessing or forecasting changes in marine ecosystems through physical disturbance or chemical pollutants. No attempt has been made to review all pertinent literature. Rather, an overview of approaches is presented with comments on limitations and possibilities of these types of study for assessment of long and short-term changes in marine benthic environments.

Megabenthic recolonization in an experimentally disturbed abyssal manganese nodule area

The near total removal of manganese nodules during commercial deep‐sea mining will destroy the habitat of the benthic hard‐bottom fauna within the mined areas and result in the formation of a soft‐bottom community of lower diversity. In 1989 the first large‐scale and long‐term experiment, DISCOL, was initiated in the abyssal tropical southeastern Pacific Ocean to study the impact of disturbances similar to ocean mining on the deep‐sea fauna. The megabenthic assemblage and the recolonization of the disturbed area were monitored during three cruises of the German research vessel SONNE by use of an Ocean Floor Observation System with real‐time TV and “photo‐on‐command” capabilities. The results of the image analyses of the baseline and three postimpact studies demonstrate not only a direct impact within the disturber tracks, but also an apparent impact on areas that were not primarily disturbed. Commercial mining will create a sediment plume, which will drift away with near‐bottom currents and also affect an...