S. Vanhove

Meiofauna response to iceberg disturbance on the Antarctic continental shelf at Kapp Norvegia (Weddell Sea)

The impact of iceberg scouring on meiofauna communities, especially nematodes, was studied on the Kapp Norvegia shelf in the Weddell Sea, Antarctica. Three stations with different stages of recolonisation following scour were selected on the basis of seafloor video images, sediment characteristics and faunal occurrences. These stations comprised a fresh scour, an older scour, and an undisturbed control site where a sponge spicule mat covered the sediment with dense epifauna. Meiofaunal abundance and taxonomic diversity of meiofauna groups were significantly reduced in the fresh scour. The highest abundance and diversity were found in the older scour as compared with the undisturbed site. The abundance and diversity of nematodes also decreased due to scouring. The abundance in the older scour recovered to the level of the undisturbed site whereas the diversity remained low. Scouring also changed the nematode community structure, with the suborders Desmoscolecina and Leptolaimina as the most sensitive groups. In addition, scouring resulted in the decrease of selective deposit feeders and the Maturity Index. The low diversity and the change in nematode generic composition in the older scour compared with the undisturbed site, despite the complete recovery in terms of abundance, suggest that the deep continental shelf nematode community in this area is sensitive to iceberg disturbance.

The metazoan meiofauna in its biogeochemical environment : The case of an Antarctic coastal sediment

The metazoan meiobenthos was investigated in an Antarctic coastal sediment (Factory Cove, Signy Island, Antarctica). The fine sands contained much higher abundances compared to major sublittoral sediments worldwide. Classified second after Narrangansett Bay (North Atlantic) they reached numbers of 13 × 106 ind m-2. The meiofauna was highly abundant in the surface layers, but densities decreased sharply below 2 cm. Vertical profiles mirrored steep gradients of microbiota, chloropigments and organic matter and were coincident with chemical stratification. Spatial patchiness manifested especially in the surface layer. Nematodes dominated (up to 90%), and Aponema, Chromctdorita, Diplolaimella, Daptonema, Microlaimus and Neochromadora constituted almost the entire community. Overall, the nematode fauna showed a strong similarity with fine sand communities elsewhere. The dominant trophic strategies were epistrarum and non-selective deposit feeding, but the applied classification for feeding guild structure of the nematodes of Factory Cove is discussed. High standing stock, low diversity and shallow depth distribution may have occurred because of the high nutritive (chlorophyll exceeded lOOOmgm-2 and constituted almost 50% of the organic pool) and reductive character of the benthic environment. These observations must have originated from the substantial input of fresh organic matter from phytoplankton and microphytobenthic production, typical for an Antarctic coastal ecosystem during the austral summer.

The meiobenthos of five mangrove vegetation types in Gazi Bay, Kenya

The vertical distribution of meiofauna in the sediments of Avicennia marina, Bruguiera gymnorrhiza, Ceriops tagal, Rhizophora mucronata and Sonneratia alba at Gazi Bay (Kenya), is described. Seventeen taxa were observed, with highest densities in the sediments of Bruguiera (6707 ind. 10 cm−2), followed by Rhizophora (3998 ind. 10 cm −2), Avicennia (3442 ind. 10 cm −2), Sonneratia (2889 ind. 10 cm−2) and Ceriops (1976 ind. 10 cm−2). Nematodes accounted for up to 95%, of total densities; other common taxa were copepods, turbellarians, oligochaetes, polychaetes, ostracods and rotifers. High densities occurred to about 20 cm depth in the sediment. Especially Ceriops sediments show still high densities of nematodes (342 ind. 10 cm−2) and copepods (11 ind. 10 cm−2) in the deepest layer (15–22 cm). Particle size and oxygen conditions were major factors influencing meiobenthic distribution; Uca burrows had a major impact on distribution and abundance of meiofauna.

A handy method for measuring meiobenthic respiration

Abstract Our current understanding of meiofaunal respiration rates, and especially of the way they are influenced by changing abiotic factors, is still far from complete. Meiofaunal respiration is traditionally measured using Cartesian divers or related manometric techniques, but these are extremely time-consuming and labour-consuming. We have evaluated the use of the Strathkelvin polarographic electrode model 1302 and the O 2 monitor model 781 in determining the O 2 consumption of meiofaunal animals. Respiration rates obtained in this way of the terrestrial nematode Caenorhabditis elegans compared well with results obtained from Cartesian diver respirometry. Experiments with 3 estuarine nematode species show that 5% accuracy levels are obtained with respiration rates down to 200 nl O 2 h −1 . This involves the use of a few tens to a few hundred individuals, depending on the size and the respiratory activity of the animals. Several practical problems that relate to accurate determinations of O 2 consumption are discussed. It is concluded that short-term measurements and fairly easy procedures make polarographic O 2 electrodes an interesting and reliable tool for routine measurements of meiofaunal community respiration and of the influence of abiotic factors on meiofaunal aerobic metabolism.