Effects of Landscape Disturbance on Animal Communities in Lake Tanganyika, East Africa

Abstract

Watershed deforestation, road building, and other anthropogenic activities result in sediment inundation of lacustrine habitats. In Lake Tanganyika, this threatens the survival of many rock‐dwelling species by altering the structure and quality of rocky habitats. We investigated the relationship between habitat quality, as related to watershed disturbance intensity, and the biodiversity of faunal communities at three rocky littoral sites of low, moderate, and high disturbance. Turbidity measurements and other environmental observations confirmed that our lake sites represented a gradient of disturbance conditions. We documented differences in species density (number of species per constant area or time), species richness, abundance, and trophic ecology for fishes, molluscs, and ostracods. Fish censuses were performed by scuba divers at 1–20 m and by remotely operated vehicle (ROV) at 40–80 m. In the fish surveys, abundance, species density and richness, and herbivory reached their maxima at intermediate water depths. The depth range of herbivores, however, was restricted at higher‐disturbance sites. The ROV fish surveys at the high‐disturbance site showed high species richness despite low species density and abundance, and piscivores were proportionally more prevalent than in all other surveys. Molluscs censused by diver quadrats and sieve samples showed decreasing species richness and species density (sieve samples only) with increasing disturbance and no significant abundance trend. Ostracod species richness was similar between low‐ and moderate‐disturbance sites but was markedly lower at the high‐disturbance site (species density and abundance data were not available). Our faunal analyses suggest that all three taxonomic groups are negatively affected by sediment inundation but may have varying response thresholds to disturbance. Further, this study emphasized the utility of using complementary survey techniques to monitor and ultimately manage biodiversity in complex freshwater ecosystems.

Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

“…Secondly, densities of crabs in rocky areas are highest at shallow depths (5-10 m), and typically decrease sharply by 20 m depth. Similar patterns have been observed in many trophic guilds of Wshes in Lake Tanganyika (Alin et al 1999). Higher densities of crabs in rocky habitats at shallow depths may be attributable to a higher abundance of food resources compared to greater depths.…”

“…Rocky sites without such a sediment layer were considered reference sites. Results of this qualitative evaluation agreed with quantitative analyses of sedimentation at many of the same 1 C sites (Alin et al 1999;McIntyre et al 2005). Five of the rocky sites (MWG, KLG, NDW, LUA, HTP) were categorised as sediment-impacted sites, and the other four rocky sites (MTB, EUP, JKB, KTW) categorised as reference sites.…”

“…One of the most pervasive environmental problems is sedimentation on Lake Tanganyika's littoral habitats caused by watershed deforestation, resulting in a decline in diversity of lacustrine species (Alin et al 1999;Cohen et al 2005). Accumulation of sediment on the substrate can adversely aVect benthic organisms by reducing habitat quality and heterogeneity, compromising foraging and respiration eYciency, decreasing reproductive success, and altering predator-prey and host-parasite interactions (McIntyre et al 2005, and references therein).…”

Microhabitat differences surrounding a pond affects the distribution of trematode parasites among a pulmonate snail community

“…Habitat disturbance (e.g., landscape changes, pollution, climate change) can have a major impact on the distribution of animals in both terrestrial and aquatic habitats (Khan, 1991;Lafferty, 1997;Alin et al, 1999;Rodríguez-Prieto & Fernández-Juricic, 2005;Marcogliese & Pietrock, 2011). Microhabitat changes caused by either natural or anthropogenic damage can alter the community composition and distribution of plants and animals within it.…”

“…This situation can be extremely important for host species with low vagility (e.g., molluscs) via enhancement of the efficiency of parasite transmission by increasing proximity and encounter rate of parasites with their hosts. Changes to the environmental landscape (Alin et al, 1999;Gill et al, 2001;Beale & Monaghan, 2004;Lafferty & Kuris, 2005;Rodriguez-Preito & Fernandez-Juricic, 2005), pollution (MacKenzie et al, 1995;Morley, 2006;Sures, 2008;Morley, 2010;Marcogliese & Pietrock, 2011), and other alterations to the aquatic environment (Lafferty, 1997;Gerard, 2001;Lafferty & Kuris, 2005;Koprivnikar et al, 2007;Gerard et al, 2008) can influence digenetic trematodes due to their complex life cycles. Multiple hosts involved in these life cycles result in a greater potential for at least one of them to be affected by changes in microhabitat.…”