Hartmut Bluhm

Re-establishment of an abyssal megabenthic community after experimental physical disturbance of the seafloor

The suitability of deep-sea megafauna as indicators of environmental change has been demonstrated by a large-scale and long-term disturbance and recolonisation experiment (DISCOL) established in the deep Peru Basin in 1989. The experiment was designed to show what effects physical disturbances, such as those caused by future commercial deep-sea mining, might have on the seafloor and its inhabitants. A plough-harrow was used to create a large-scale disturbance on the seafloor. It destroyed megafauna within the plough tracks to a large extent and buried the manganese nodules in the area. As a result fauna that lived attached to the nodules disappeared. The soft-bottom community, however, did show signs of recovery in the seven years of the study. The repopulation of the disturbed areas by highly motile and scavenging animals started shortly after the area was ploughed. Seven years later hemisessile animals had returned to the disturbed areas, but the total abundance of soft-bottom taxa was still low compared to the pre-impact study. Nearby reference areas not impacted by the experiment showed natural changes in animal densities during the study. The ploughing activities created a sediment plume that resettled in the surrounding areas. In these not directly impacted areas animal densities declined immediately after the ploughing event, but later appeared to be greater than in the reference areas of the pre-impact study. Possible reasons for this are discussed.

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.

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...

DESCRIPTION OF A NEW SPECIES OF PACHYCARA ZUGMAYER, 1911 FROM THE ABYSSAL SOUTH-EASTERN PACIFIC AND REDESCRIPTION OF P. THERMOPHILUM GEISTDOERFER, 1994, WITH A NEW KEY TO THE SPECIES

SUMMARY A new species of the eelpout genus Pachycara Zugmayer is described from the abyssal south-eastern Pacific Ocean on the basis of five males and eight females. It is distinguished mainly by its single mediolateral lateral line, furcate gill rakers, lack of pelvic fins and lack of scales on the anterior portion of the body. Pachycara thermophilum Geistdoerfer is redescribed from the two adult type specimens and two additional juveniles from the Mid-Atlantic Ridge. It is distinguished by its single mediolateral lateral line (said to be absent in the original description), furcate gill rakers, two pelvic fin rays, dorsal fin origin associated with vertebrae 7–8 and 31 precaudal vertebrae. A revised key to all 16 species of Puchycara is presented.

Reaktionen benthischer Tiefsee-Lebensgemeinschaften auf mechanische Störungen der Sedimente

Das Okosystem der Tiefsee wird zunehmend durch industrielle Eingriffe beeinflusst. Uber die Auswirkungen dieser Aktivitaten auf das Benthos wurden bisher nur Vermutungen angestellt. Innerhalb der vom BMBF geforderten Forschungsvorhaben DISCOL (1988–1993) und ATESEPP (1995–1998) wurden zum ersten Mal Forschungsergebnisse publiziert, die es moglich machen, den Einfluss von Sedimentumlagerungen wie sie durch den zukunftigen Bergbau erzeugt werden anhand konkreter Daten zu beurteilen.