Impact of an experimental benthic disturbance event on high Antarctic meiobenthic assemblages: developments after 7

years

F. Hauquier (UGENT), A. Rose (FIS-DZMB) Objectives

Few papers deal with the influence of iceberg disturbance on meiobenthos. These demonstrated that catastrophic iceberg disturbances lead to impoverished meiofaunal assemblages in fresh scours. Meiofaunal abundance and taxonomic diversity were significantly reduced in those.

Older scours showed highest abundance and diversity values, even higher than those for an undisturbed area. The return of major meiofauna groups was accomplished 30 days after a disturbance event, compared to a control site. Since under normal circumstances it is difficult to assess the age of natural iceberg scours and the time scale of the ongoing succession, an experimental approach was chosen that was supposed to lead to a disturbed area with a defined starting point in time (December 2003, ANT-XXI/2). The BENDEX (benthos disturbance experiment) area was intended to be visited by later expeditions in order to assess the time scale of the ongoing succession of benthic organisms and the development of environmental parameters. This will be done during the actual cruise leg. BENDEX was mainly designed for the removal of macrofauna. It is suggested that a lot of meiofauna were whirled into the water column during bottom trawling and re-sedimentated afterwards. Hence, at least for meiofauna bottom trawling did not resemble a real iceberg disturbance event. Since it was not possible to remove all material from the area and some stripes had been left undisturbed, central stations of the area probably resembled marginal stations in so far that edge effects occurred.

Therefore, the process of trawling did not allow a clearly defined disturbed area. Finally and taking into account the mentioned literature, seven years is probably a too long interval to assess the process of meiobenthic succession after a disturbance of this scale.

work at sea

Near Austasen (Weddell Sea, Antarctica), a 1,000 m x 100 m area of approximately 300 m depth with an old sponge community was disturbed by 11 bottom trawls, removing much of the macrofauna (ANT-XXI/2, December 2003). Three benchmark sample series had been taken in order to assess the impact of the experimental disturbance on meiobenthic assemblages.

Since the preferred multicorer did not work properly due to thick sponge spicule mats, other gears were used. Within the experimental area stations were located both in central and marginal parts. Two of five pre-disturbance stations and three reference stations were sampled around the disturbed area in 50 m to 800 m distance. The pre-disturbance series consisted of three multiboxcorer (MG) hauls taken on 11 December, 2003 (PS65/116, 124, 125), of which 8 subcores á 10 cm² were taken out of two adjacent boxes, and two giant boxcorer (BC) hauls on 10 and 11 December, 2003 (PS65/107, 123), of which the same number of subcores was taken. Two stations (116, 124) were positioned outside and three stations (107,123,125) inside the subsequently disturbed area. The initial post-disturbance series one week later consisted of four MG hauls taken (PS65/183, 187, 199, 202), of which 8 subcores á 10 cm² were taken out of two adjacent boxes, and one BC haul (PS65/203) with the same number of subcores. In the surrounding of the experimental area three reference MGs were deployed after the disturbance. 8 resp. 7 subcores out of two adjacent boxes, and 4 cores out of one box were taken and processed on 17 to 18 December, 2003. Resampling of these initial BENDEX stations during the actual cruise leg is intended to be restricted to the 7 MG hauls of the post-disturbance and reference sampling series. Preferably 6 - 8 subcores will be taken out of 1 - 2 MG boxes at each station. These are to be processed as follows: Up to three cores will be prepared for quantitative morphological analysis of meiofaunal diversity and fixated with formaldehyde (4 %). One of these should be split into 5 layers (0 - 1, 1 - 3, 3 - 5, 5 - 10, 10 -

15 cm), the other ones taken as a bulk (0 - 5 cm). One core is reserved for molecular analysis of nematode diversity (conservation with ethanol 98 %) and taken as a bulk (0 - 5 cm). Above standing water will be sampled together with the uppermost layer for all of these 2-4 cores. The last three cores will be processed for analysis of chemical and physical parameters. The stable isotope core should be split into two layers (0 - 1, 1 - 2 cm; deep-frozen at –20° C, best at –80°

C). One core will be prepared for analysis of phytopigments (layers: 0 - 1, 1 - 2 cm, deepest possible cm), another one for organic matter and sediment structure (layers: 0 - 1, 1 - 2, 2 - 3, 3 - 4, 4 - 5 cm, deepest possible cm). These two cores will be kept deep-frozen (–20° C, best at –80° C).

3. BeTeIlIgTe INSTITuTe / PARTICIPATINg INSTITuTeS

Adresse / Address

AWI Alfred-Wegener-Institut für Polar- und

Meeresforschung

in der Helmholtz-Gemeinschaft Am Handelshafen 12

27570 Bremerhaven Germany

CADIC-Centro Austral de Investigaciones Científicas CONICETHoussay 200

V9410CAB Ushuaia - Tierra del Fuego Argentina

CEAB- Centre d’Estudis Avançats de Blanes-CSIC

CISICAccess a la Cala St. Fransesc 14 17300 Blanes

Spain

DWD Deutscher Wetterdienst

Geschäftsbereich Wettervorhersage Seeschifffahrtsberatung

Bernhard-Nocht-Str. 76 20359 Hamburg

Germany

ECM-UCV Escuela de Ciencias del Mar

Pontificia Universidad Católica de Valparaíso.

Av.Altamirano #1480 Valparaiso

Chile

FS Forschungsinstitut und Naturmuseum

Senckenberg

Sektion Marine Evertebraten I Senckenberganlage 25 61350 Frankfurt am Main Germany

FS-DZMB Forschungsinstitut Senckenberg

Abt. DZMB - Deutsches Zentrum für Marine Biodiversitätsforschung

Südstrand 44

26382 Wilhelmshaven Germany

Adresse / Address

GU-LOVEN Göteborgs Universitet

Sven Lovén centrum för marina vetenskaper 452 96 Strömstad

ICM-CISIC Institut de Ciencies del Mar-CSIC

Passeig Maritim de la Barceloneta 37-49 08003 Barcelona

Spain

ICTA-UAB Institut de Ciència I Tecnologia Ambientals ICTA Universitat Autònoma de Barcelona UAB UAB Campus Cn s/n Cerdanyola del Vallés 08193 Barcelona

Spain

IRSNB Institut royal des Sciences naturelles de

Belgique Aqua-tiques CP 26, 43, rue Cuvier

75005 Paris

Adresse / Address

Laboratoire de systématique et diversité ani-male- Chargée de recherches FNRS

UNIFI Università degli Studi di Firenze

Laboratori di Zoologia integrata ed applicata Via Romana, 17