Trophic interactions and food web structure of aquatic macroinvertebrate communities in afromontane wetlands: the influence of hydroperiod

Hydroperiod is considered an important aspect in shaping community structure and ecosystem patterns in temporary wetlands. However, most studies have focused on the community structure, demonstrating that biotic diversity increases with hydroperiod. Theory suggests that ecosystem patterns like trophic interactions and food web structure will also respond to hydroperiod in the same way. However, there are limited studies exploring ecosystem structure and patterns to changing hydroperiod in temporary wetlands. Maloti-Drakensberg Mountain region of southern Africa has a series of rock pools (shorter hydroperiod) and tarns (longer hydroperiod) that allowed us to explore the effect of hydroperiod on aquatic biodiversity and trophic interactions using stable isotope techniques. We hypothesised that tarns will have higher biotic diversity and complex food web structure as compared to rock pools, which we expected to exhibit low biotic diversity and simple food web structure. Our results were in agreement with our hypothesis, where tarns were characterised by longer food chain length, higher trophic level diversity, greater trophic divergence and even species distribution in the isotopic space. Thus, demonstrating a well-developed and complex food web structure. In contrary, rock pools were characterised by shorter food chain length, small trophic diversity with trophic redundancies and species clustering. Thus, representing a simple and a poorly developed food web structure. Further, macroinvertebrate biotic diversity was significantly higher in longer hydroperiods, also longer hydroperiod exhibited less dramatic changes in the physicochemistry characteristics, representing a more stable environment than shorter hydroperiods. This study demonstrates that hydroperiod not only affects aquatic biological diversity but ecosystem structure, as well.