Effects of Anadromous Sea Lamprey As Vectors of Marine-Derived Nutrients in Freshwater Ecosystems

Historically, many freshwater systems in Maine were linked to the marine environment by spawning migrations of adult anadromous fishes and subsequent seaward migration of juveniles.  These fish served as vectors of marine-derived nutrients that were transported into oligotrophic freshwaters and incorporated into stream and lake food webs.  Many anadromous fish populations have declined due to migration barriers, habitat loss, and overfishing, reducing or eliminating nutrient subsidies.  We examined the nutrient dynamics of semelparous Sea Lamprey Petromyzon marinus carcasses.  In the laboratory, carcass decay liberated phosphorus and nitrogen (NH₄⁺, NO₃^-) for up to three weeks and was faster at warmer temperatures.  In the field, nutrients from carcasses placed in a small stream enriched the system over a three week period.  Nutrient diffusing substrates were used to demonstrate increased algal growth (chlorophyll a) by 57 - 71% and nitrogen limitation in the stream.  Results identifying nutrient assimilation in stream food webs using stable isotopes (δ¹⁵N and δ¹³C) are preliminary.  This research provides quantitative results as to the ecological role of anadromous Sea Lamprey and underscores the importance of freshwater-marine connectivity to coastal streams.