The Mad River watershed provides drinking water and recreational opportunities for over 100,000 Humboldt County residents and critical habitat for 5 listed fish species. In 2018, two potential threats were documented in the Mad River ecosystem for the first time: toxic blue green algae (BGA) and non-native New Zealand mud snails (NZMS).
Although there is no formal monitoring for BGA or NZMS in the Mad River, observations indicate that both were more abundant in 2020 than 2018. Increased populations of these species are problematic. The toxic BGA observed in the Mad River include taxa that produce both hepatotoxic microcystin and neurotoxic anatoxin. NZMS are a concern because they can reach enormously high abundance, co-opting most of the algae produced at a site and reducing the abundance of prey for endangered fish. Both BGA and NZMS thrive in areas in the lower watershed with slow flow, warm temperature, and elevated nutrient concentrations.
Beyond co-occurrence in the same habitats, we hypothesize that NZMS affect the growth of BGA. NZMS consume a wide variety of food, including BGA. In other rivers in CA, dense NZMS aggregations alter the species composition of algal primary producers. Because of their similar habitat requirements and potential interaction, a data collection effort that targets both BGA and NZMS can provide useful information on the distribution and spread of both organisms and their potential effects on each other.
We propose a study with two objectives: 1) Design a survey to evaluate the distribution and abundance of toxic BGA and NZMS, using low-cost visual methods for identifying potential hotspots. We will implement this protocol for two summers and document the methods for ongoing use. 2) Implement experiments to evaluate the interaction between NZMS and toxic BGA species, to determine if NZMS might increase or decrease toxic BGA production.