Insects and crustaceans flourish on lands and in oceans. In streams, between the lands and the oceans, insects and crustaceans co-occur. Many crustaceans in streams have planktonic larval stages and their larvae grow in the oceans like many marine crustaceans. In contrast, many aquatic insects have winged adult stages and their adults mate on lands like many terrestrial insects. Therefore, connectivity of the streams to the lands are important for aquatic insects, while connectivity of the streams to the oceans are important for stream crustaceans. Furthermore, movements of insects and crustaceans in the landscape link streams to land and marine ecosystems respectively by transporting resources. Therefore, I hypothesized that the dominance of insects or crustaceans in streams determine whether the stream habitat is more strongly linked to the land or marine ecosystems. In this presentation, I will present distributions and interactions of aquatic insects and amphidromous crustaceans in streams, and their ecological consequences.
In many mountainous streams in Japan, both aquatic insects and shrimps dominated stream biota. Amphidromous shrimps tended to dominate downstream habitats, and their distribution was constrained to downstream of dams. Aquatic insects dominated forested streams disconnected from the ocean. Both aquatic insects and shrimps played important roles as primary consumers in streams. Results of the preliminary experiments on interactions of aquatic insects and crustaceans will be also presented.