The herbivorous, detrital and microbial pathways are major components of marine food webs. Although it is commonly recognized that these pathways can be linked in several ways, elucidating carbon transfers between or within these pathways remains a challenge. Intertidal flat communities are driven by a wide spectrum of organic matter sources that support these different pathways within the food web. Here we reconstruct carbon pathways using inverse analysis based on mass balancing, stable isotope signatures and tracer data. Data were available on biomass, total carbon production and processing, integrated diet information from stable isotope signatures and the transfer of recently produced carbon through the food web from an isotope tracer study. The integration of these data improved the quality of the inverse food web reconstruction considerably, as demonstrated explicitly by an uncertainty analysis. Deposition of detritus (detrital pathway) from the water column and subsequent assimilation and respiration by bacteria and to a lesser extent by microbenthos (microbial pathway) dominated the food web. Secondary production was dominated by bacteria (600 mg C m −2 d −1 ), but transfer to higher trophic levels was limited to 9% and most bacterial carbon was recycled back to dissolved organic carbon (DOC) and detritus. Microbenthos secondary production (77 mg C m −2 d −1 ) was supported by DOC (73%) and detritus (26%) and was entirely transferred up the food web. The higher trophic levels consisting of nematodes, meiobenthos (copepods, ostracods and foraminifera) and macrobenthos fed highly selectively and relied primarily on microphytobenthos and pelagic primary production (herbivorous pathway). Deposit feeding is a common feeding mode among these sediment dwelling fauna, but detritivory was negligible due to this selective feeding. This strong resource selectivity implies that the herbivorous and detrital-microbial pathways function more or less autonomously, with limited interaction.

The nematode community structure of several shelf break and deep-sea stations in the North Atlantic and the Mediterranean is compared using data from the literature. Samples from 2 Mediterranean deep-sea canyons have a unique fauna of predatory and scavenging nematodes (e.g. Synonchiella, Halichoanolairnus, Gammanerna) which comprise some 20 to 30% of the community, while some of the typical deep-sea genera (Therjstus, Acantholaimus) are only marginally present. The nematode generic composition of the other sites reveals a gentle transition from the shelf break (Bay of Biscay; Mediterranean) over the slope (Me&terranean) towards the continental rise, abyssal plain and hadal depths (Bay of Biscay, Puerto Rico Trench, HEBBLE site, Hatteras Abyssal Plain). At all these sites predators and omnivores are less abundant (

Total biomass and biomass of large taxonomic groups (polychaetes, molluscs, crustaceans, echinoderms) and species diversity of the macrofauna were determined for almost 200 North Sea stations sampled synoptically by seven vessels during Spring 1986 and for 120 additional stations sampled in earlier years by the Marine Laboratory in Aberdeen. There exists a clear and significant decreasing trend in biomass with latitude, both in total biomass and for the different taxonomic groups. Apart from latitude, sediment composition and chlorophyll a content of the sediment also infuence total biomass and biomass of most groups significantly. Biomass increases consistently in finer sediments and sediments with a higher chlorophyll a content. The same trends are found for the results within laboratories. Some interaction exists, indicating weak laboratory and zonal effects. Diversity, as measured by Hill's diversity index N, = (exp H') shows a clear and significant trend with latitude. Towards the north of the North Sea diversity increases considerably. The trend is also found for laboratories separately and is everywhere equally strong. Also longitude and depth show an effect on diversity. Sediment variables have no clear influence on diversity. Other diversity measures show the same trend but are more variable than N,. Total density tends to increase towards the north, but sediment related variables have a larger influence. Mean individual weight becomes considerably smaller towards the northern part of the North Sea.

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Meiobentho:, dcnsitics (excluding hard-shcllcd foraminifcrans) wcrc compared along a Mcditcrranean dcep-sca transect off Calvi (Corsica) and in an adjaccnt canyon. Chloroplastic Pigment Equivalent values (CPE) provided an cstimate of the amount of primary production reaching the bottom.The stations along the transect werc charactcrizcd by a low CPE contcnt of thc scdimcnt. decreasing with incrcasing station depth. CPE values in thc canyon wcrc much highcr, which probably resulted from import of material from the adjacent bay of Calvi. Similarly, mciobcnthos dcnsities along the transect were much lower than at comparable dcpths along the canyon.Meiobenthos density was significantly and positively correlated with CPE values.Nematodes were the most abundant taxon at all stations, followed by copepods + nauplii and thc soft-shelled foraminiferans. The rneiobenthos was most abundant in the upper half centimeter. Nematode and foraminiferan densities tended to decline less rapidly with increasing depth into the sediment. Specimens belonging to the recently described phylum Loricifera, larvae of the parasitic crustacean class Tanrulocurida, and fragments of an infaunal Xenophyophoria (large protozoans) are reported for the first time from the Mediterranean. ProblemSince the first quantitative investigation on deep-sea meiobenthos by WIG-LEY & MCINTYRE (1964), information on this subject has been gathered from all oceans and attempts have been made to relate these abundances with various environmental factors.In comparison with the vast oceanic deep-sea regions, the Mediterranean Sea exhibits some unique hydrographic features. There is no deep-water connection between this semi-enclosed sea and the adjacent Atlantic Ocean, and the deepwater formation for the entire Western Basin occurs in winter in an area south of Toulon (MEDOC group, 1970). The salinity, temperature, and oxygen conditions of these surface waters in winter therefore determine the hydro-U. S.