Wednesday, 5 June 2013

DIFS/SAIAB Seminar Dr Jackie Hill Community dynamics of an invaded ecosystem

Dr Jackie Hill

Community dynamics of an invaded ecosystem: investigation of a Pterygoplichthys disjunctivus invasion in the Nseleni River system, KwaZulu-Natal, South Africa.

Venue: Lecture Room, SAIAB
Date:     Thursday, 6 June 201
Time:    3.30pm

Increases in urbanization and anthropogenic activity within watersheds is globally recognized as one of the main drivers of eutrophication to date, and excessive nitrogen loads in aquatic systems can result in widespread ecosystem degradation including: hypoxia, toxic algal blooms, increased turbidity, disruption of ecosystem functioning and the loss of biodiversity. Aquatic ecosystems compromised by increased N-loading have a lower capacity for system resilience and often face further threats to ecological integrity by the establishment of invasive species. Despite existing legislation regarding the import and sale of exotic species worldwide, the establishment of invasive species in many aquatic ecosystems has been the result of accidental or deliberate introduction via the aquarium trade.

The South American loricariid catfish Pterygoplichthys disjunctivus for example, is popular with home aquarists and has been an ornamental fish export worldwide since the mid-20th century. This highly fecund, fast growing fish is extremely invasive and to date congeners have been confirmed throughout central and southern Florida, Hawaii, Puerto Rico, Asia and South Africa. In some habitats they have become the dominant fish taxa, outcompeting their endemic counterparts. This study aimed to examine determine the dietary and niche width variation amongst the fish community in the highly invaded Nseleni River system, Kwazulu Natal, South Africa. Stable isotope analysis provided clearer insights into community dietary and niche width variation, confirming a trophic position for P. disjunctivus consistent with a detritivorous diet. Isotopic niche width comparisons using SIBER suggested slight overlaps in occupied niches between four fish species: P. disjunctivus, Barbus paludinosus, Marcusenius macrolepidotus and Oreochromis mossambicus, indicating a strong potential for the disturbance of native species, with important implications for ecosystem functioning