Farmers of the Underwater World: Lamprey Larvae as Ecosystem Engineers in Streams

Organism-driven environmental alteration can instigate drastic changes in ecosystem nutrient cycling and the development of biotic communities. The role of the ecosystem engineers that drive these changes have recently received more spotlight. Lampreys, which are found extensively across the northern hemisphere, spend its long larval stage within streambeds that often result in high density. Our recent study on the larval substratum movement of two Lethenteron species revealed their functional role in physical modification through the disturbance of the streambeds. Besides many evidences indicate that, lamprey numbers have declined sharply in recent years s have been showing tendency to decrease worldwide, and as a result their ecological functions are also moribund. In this presentation, we will discuss two subjects: 1) the larval lampreys role as ecosystem engineers, and 2) An estimation of spatial-temporal dynamics of lamprey larvae based on the ecological niche modeling (ENM). 1) Both lab and field experiments were conducted with the objectives to quantify larval substratum movement and to assess the level of abiotic and biotic modification of lamprey larvae based on presence/absence and various density levels (5,30,80/m²). Field and lab experiment confirmed that the substrate with larva became significantly more aerobic, increased the amount of FPOM and total phosphorus, and effectively maintained the soil hardness at a low value. Larvae also decreased the number of aquatic worms, and increased the amount of algae on streambed. These modifications were thought to occur as a result of the streambed disturbance induced by larval substratum movement and their pseudofeces. These results demonstrated that larval lampreys are ecosystem engineers that may play a major role in the biotic community and nutrient cycling through environmental modification. 2) ENM was conducted using MaXent and ArcGIS 9.3 with the objective to quantify both the present and future potential niche habitat for the L. camtschaticum larva. Using the dataset of 2080 obtained from WorldClim global climate layers, I showcase that the southern limit of larval distribution region in Japan could move about 200 km northward and the majority of current suitable habitats for L. camtschaticum were predicted to transfer into unsuitable conditions in the 2080. In conclusion, this will have enormous implications not only for the larvae but also for the benthic community biota that depend on their ecological functions, and it is reasonable to argue that biodiversity as well as a wide array of ecosystem functions depend on the existence of these larval lampreys.