Lamprey larvae as ecosystem engineers: physical and geochemical impact on the streambed by their burrowing behavior

Larval lampreys are thought to have a significant impact on freshwater ecosystems because of their high densities and broad distributions. However, the significance of their role in the stream ecosystem remains unclear. In general, it is reported that filter feeders alter their habitat conditions (oxygen, organic matter, and nutrients levels). We evaluated the impacts of two lamprey species larvae on the physical and geochemical factors in streambed by their burrowing and feeding behavior using in situ enclosures in a mountainous river located in northern Japan. During a 21-day field experiment, we found that the larvae treatments compared to the controls (no larvae) caused increased oxygen levels in the streambed, maintained the relative softness of the streambed and increased the FPOM abundance on the streambed surface. The substantial impact of the lamprey larvae on the physical and geochemical conditions in the streambed may be attributable to their burrowing and feeding behavior. Hence, our findings contribute to understanding the importance of the conservation and management of lamprey populations in order to maintain the freshwater ecosystem. Additional experiments using lamprey larvae are needed to reveal their impact on biotic factors (aquatic insects, algae, etc.) in and around the larval habitats.