Yvonne Vadeboncoeur (Biological Sciences) and Pete McIntyre (University of Michigan) have received news that their proposal entitled “Consumer control of high-productivity low-nutrient ecosystems: Enhancement of primary productivity by grazing fish in Lake Tanganyika” will be funded by NSF for $850,000. Lake Tanganyika is the second largest lake in the world, and its nearshore, or littoral, waters are home to hundreds of fish and invertebrate species found nowhere else in the world. Fish densities and diversity in the littoral zones of African rift valley lakes are unparalleled in freshwater ecosystems, and the productivity of fishes in littoral Lake Tanganyika is similar to marine coral reefs. This high animal productivity is energetically dependent on photosynthesizing algae that grow in the rocky littoral zone of the lake. The algae maintain astonishingly high productivity rates in the face of both intense grazing and an extreme scarcity of the inorganic nutrients necessary for plant growth. Vadeboncoeur and McIntyre will explore whether grazing fish actually have a net positive effect on their algal food resource by recycling nutrients necessary for algal growth. Furthermore, they will test whether grazing fish increase total ecosystem productivity by increasing the amount of nitrogen fixation while simultaneously increasing the efficiency of phosphorus retention.
This project will help to guide efforts to protect the hundreds of unique species and the globally-important fishery of Lake Tanganyika by clarifying two critical issues. First, fishermen are catching too many fish in many lakes worldwide, including Lake Tanganyika. This overharvest may remove too many nutrients from the lake, or reduce the rate of nutrient recycling so that algae grow more slowly. By that mechanism, fishing could actually undercut the future productivity of the lake. Second, climate change is warming the surface waters of the lake and reducing the seasonal winds that cause cold, nutrient rich waters to periodically well up from the depths of the lake. Reduction in the frequency of influx of these deep-water nutrients is cutting off the algal growth that sustains the fish. This research will offer the first thorough evaluation of how these human-imposed factors will affect the productivity of Lake Tanganyika, which supports a regional human economy. This project will support both African and American Ph.D. students and partnerships with African and global non-profit organizations will broaden the impact of the research.
