|Verticale distributie van benthische Foraminiferen in sediment van contrastrerende milieus en de relevantie van zeefgrootte|
Breur, E. [s.d.]. Verticale distributie van benthische Foraminiferen in sediment van contrastrerende milieus en de relevantie van zeefgrootte. [S.n.]: [s.l.].
In this study, a comparison is made between the vertical distribution (upper 10 cm) of living (stained) foraminifera in sediments from the shallow (19 & 20 m) eutrophic northwestern Adriatic Sea and the deep (1288 & 1300 m) oligotrophic Aegean Sea. Vertical distribution was examined in relationship to oxygen and food gradients in the sediment.Sediments in the Adriatic Sea supported a significantly large standing stock both in surface an subsurface layers. Although the oxygen penetration depth in the Adriatic does not exceed 2 mm, the habitat depth (defined as the depth above which 95 % of the total assemblage or population is found) range from 6 to 7 cm. Maximum oxygen penetration depth was found at the station in the southern Aegean Sea (E1, 10 cm) but the habitat depth was the shallowest (2 cm). The habitat depth was the deepest at the second Aegean Sea station (E2, 9 cm) in spite of a shallow oxic zone (27 mm). No relation between vertical distribution of total numbers and food (measured either as Chl a or nitogen content in the sediment or CO2 production rates in the different layers) was found.Dominant genera in the Adriatic Sea (Reophax, Nonionella, Stainforthia, Bolivina & Hopkinsina) had significantly higher densities in the upper 2-4 centimeters of the sediment but foraminifera are were found down to 10 cm. Although both Adriatic stations (A1 & A2) have comparable sediment characteristics and oxygen penetration depth, a relatively larger proportion of the assembages was found in deeper layers of the sediment at A2. On average, 70 % of the foraminifera were found below the main oxic zone at A2 and aproximately 34 % at at station A1. Vertical distribution patterns did not correlate with oxygen, grain size or food content. Epistominella was the most dominant genus at E1 in the Aegean and was found only in the upper 2 cm although the oxygen penetration depth was much deeper (10 cm). At the other Aegean station (E2) where oxygen penetrated to 27 mm, Epistominella was encountered down to 10 cm with no clear peak densities. The other dominant genus was Melonis that was irregularly distributed throughout the sediment. Brizalina was not dominant but exhibited a total different pattern; this genus was encountered only below the 0-1 cm layer. On average, 42 % of the foraminifera were found below the main oxic zone at E2.Most genera exhibited peak densities in the surface layers but were also present in deeper layers. Melonis (encountered only in the northern Aegean, 1300 m water depth) was the only genus that was irregularly distributed in the sediment (i.e. no significant diffference between depth layers). Brizalina (in very low numbers) was absent in the surface layer but occurred deeper. These trends show no direct relationship with oxygen availability or subsurface food concentrations. This suggests that site-specific factors (e.g. bioturbation, competition , species interactions) may be involved. This is supported by the fact that, in spite of similar abiotic conditions, different vertical distribution patterns are seen for common genera at different stations.On average, the > 63 µm fraction represented 40 - 60 % of the total assemblage in the Adriatic Sea and 55-74 % of the total assemblage in the Aegean Sea. Although the major trends remain evident in the 63 µm fraction, finer details are obscured; this was more so the case in the shallow Adriatic Sea sediments.
- Vertical distribution of benthic foraminifers in sediments of contrasting environments and the relevance of sieve size, more