Among-individual diet variation within a lake trout ecotype: lack of stability of niche use

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes

The role of phosphatidylglycerol in phospholipid analysis of tracheal and gastric aspirate in premature infants

Peer Reviewe

Enrichment of silicate and CO2 and circulation of the bottom water in the Weddell Sea

Deep and bottom water from the Enderby basin, which is strongly enriched in silicate, enters the Weddell Sea off Kapp Norvegia parallel to the coast. However, the bottom water in this region originates from the northern Weddell Sea, indicating a southward return flow of bottom water west of the prime meridian. The eastern Weddell Sea margin was identified as the place where a significant silicate enrichment (at least 15 µmol kg-1) and a weak CO2 enrichment of the bottom water takes place, related to a regional recirculation cell. The deep and bottom water continue their course through the Weddell Sea along the base of the continental slope, where further in the west they are underridden by a thin layer of new, silicate-poor bottom water. A silicate maximum and weak TCO2 maximum are formed at the interface between deep and bottom water at approximately 4000 m. This silicate maximum occurs in the central Weddell Sea as well. This indicates an exchange of the deep water between the boundaries and the interior of the Weddell basin; as an important site for this the northwestern Weddell Sea was identified. Bottom layer enrichment by CO2 in the central Weddell Sea (3 µmol kg-1) is comparable to that in the eastern Weddell Sea, but silicate enrichment in the former is much less than in the latter. The extent of bottom layer enrichment suggests that about 2% of the primary produced material reaches the seafloor, supporting the view that the biological pump mechanism in this area is effectively transporting down a significant amount of CO2

Surface layer balance of the southern Antarctic Circumpolar Current (prime meridian) used to derive carbon and silicate consumptions and annual air-sea exchange for CO2 and oxygen

A simple model, using concentrations of nitrate and phosphate in austral winter 1992, reveals that the Antarctic Surface Water (AASW) of the southernmost Antarctic Circumpolar Current (ACC) between the Southern ACC Front and the Weddell Front is made up of about 90% Upper Circumpolar Deep Water (UCDW) and 10% northward-flowing AASW from the Weddell Gyre. With a typical time scale of about 1 year, the upwelling velocity was calculated to be as high as 60-100 m y-1. Knowing the composition of the surface water with respect to its sources, changes due to several processes in the surface layer were deduced for carbon dioxide, oxygen and silicate. As the time scale of changes in the surface layer of the southern ACC is about 1 year, this allows us to calculate changes on an annual basis without interference of short-term variations. Balancing the contributions by upwelling, biological activity and air-sea exchange to the concentrations in the surface layer, the area was found to be a large sink for atmospheric oxygen of 6.0 mol m-2 y-1 (53 µmol kg-1) and a small sink for atmospheric carbon dioxide of 1.0 mol m-2 y-1 (9 µmol kg-1). The most important cause for the oxygen sink is the upwelling of oxygen-poor UCDW, which surpasses the oxygen-elevating effect of primary productivity. This large oxygen sink, in between areas to the north and south which are only a small sink or even a source, conforms with the latitudinal distribution of atmospheric oxygen. The small CO2 sink is largely brought about by biological activity. The annual carbon utilization amounts to 76 ± 22 g C m-2 y-1, which is relatively high for an open ocean region in the Antarctic. However, it supports recent estimates of primary production of the Antarctic Ocean that are higher than early published values. The annual silicate consumption was calculated to be 126 ± 19 g Si m-2 y-1. This is considerably higher than the Southern Ocean mean in current estimates. Although the southernmost ACC may be atypical for the Southern Ocean, the current estimate for Southern Ocean silica production may well be an underestimation. The silicate to carbon utilization ratio derived here is 0.53 which aligns with investigations on Antarctic phytoplankton and thus underscores the consistency of our results