Food web structure and mercury transfer in two contrasting Ugandan highland crater lakes (East Africa)

Abstract

Volcanic crater lakes scattered throughout western Uganda are important local sources of water and fish. Two representative but contrasting crater lakes near the Kibale National Park were sampled in 2000; the hyper-eutrophic Lake Saka, which is highly affected by agricultural practices, and the mesotrophic Lake Nkuruba that is still surrounded by intact forest. The food web structures in these two lakes were assessed using stable nitrogen (d that food webs in both lakes are abbreviated, with only one to two trophic levels from primary consumers. The Lake Saka biota had distinctively enriched d 13 C values compared with those in Lake Nkuruba, which may be due to 12 C-limited phytoplankton blooms in this lake. In Lake Nkuruba, two introduced tilapiine species and the introduced guppy Poecilia reticulata fed predominantly upon invertebrates and decomposed terrestrial plant material. In Lake Saka, the introduced Nile perch Lates niloticus appeared to occupy the top trophic position, but stable isotope values of the endemic haplochromine cichlids exclude those as Nile perch prey items. THg was found to biomagnify through the food web, reaching highest concentrations in P. reticulata in Nkuruba, which tended to be higher than for L. niloticus in Saka, suggesting increased bioavailability of THg in Nkuruba. Maximum THg concentrations in fish never approached WHO recommended guidelines (200 ng g )1 ) designed to protect at-risk groups.

Bioaccumulation and biomagnification of mercury in African lakes: The importance of trophic status

“…The food webs observed for these Ugandan lakes (Figures S1, S2) had several general characteristics, many of which have been described in detail in other studies (Campbell et al, 2003b(Campbell et al, , 2005(Campbell et al, , 2006Mbabazi et al, 2004;Poste et al, 2012). With the exception of Lakes George, Edward and Albert, strongly piscivorous fish appeared to be rare, meanwhile omnivory was common, with few apparent obligate feeding relationships.…”

The importance of size and growth rate in determining mercury concentrations in European minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) in the subalpine lake, Øvre Heimdalsvatn

“…Stunting in growth of individuals with long lifespan may cause higher mercury levels than in individuals under good growth conditions because of an increasing proportion of mercury per unit body mass (Campbell et al, 2006;Desta et al, 2007a). Growth in length of European minnow and brown trout stagnates at ages of around 5 and 8 years, and at lengths around 8 and 30 cm, respectively, but no marked change in mercury contamination seems to occur in either of the species.…”

Molecular barcoding reveals mislabelling of commercial fish products in Italy

“…Major frauds concerned the Mediterranean grouper (no labelled scientific name) substituted by the Nile tilapia Oreochromis niloticus originating from Africa. One gurnard Trigla lucerna substituted by the Nile perch Lates niloticus often farmed in polluted waterbodies of African countries (Campbell, Hecky, Dixon, & Chapman, 2006;Campbell, Hecky, Nyaundi, Muggide, & Dixon, 2003;MacHiwa, 2005). One halibut Renharditus hippoglossus was identified as Pangasianodon hipophthalmus at molecular level, a common freshwater species having very low commercial value with respect to the halibut and farmed in highly polluted waters Fig.…”