5:15 PM - 6:30 PM
[MIS11-P04] Effects of migratory fish on particlate organic matter and filter-feeding insects in a river flowing into the Lake Biwa
Keywords:Migratory fish, particulate organic matter, Lake Biwa
Migratory fish can affect the structure and function of river ecosystems by transporting materials and nutrients from the oceans or lakes to rivers. Previous studies have shown that fish can increase the nutrient level in the stream water by their excretion, and often elevate the primary production by periphyton. Yet, little is known about the impact of fish on particulate organic matter (POM), which can be used as food resource, are thought to be important in the impact of the migratory fish on consumers. In this study, we investigated the effects of the migratory fish on POM and aquatic insects that forage on POM in the Lake Biwa watershed.
The survey was conducted in the South branch and North branch of Ado River, which flow into Lake Biwa. There were yana, traps to capture migratory fishes across both channels, and the density of migratory fish, Opsariichthys uncirostris were significantly higher downstream of the structure. We collected benthic algae, POM in the river water, and caddisflies that filter feed POM at three sites above and below the yana in both channels. We measured carbon and nitrogen isotope ratios (δ13C, δ15N) of these samples, chlorophyll-a concentration of the benthic algae, and particulate organic carbon (POC), organic nitrogen (PON), total phosphorus (TPP), and inorganic phosphorus (PIP) concentrations of the POM.
The results showed that the POC, PON, TPP, and PIP concentrations were approximately twice as high, and the δ13C and δ15N values were approximately 3‰ higher downstream of the yana than upstream. However, C/N, C/P, and N/P ratios of the POM were not significantly different between the up- and downstream of yana. These ratios were closer to the value of benthic algae. There was an increase in chlorophyll-a concentration and δ15N values of the benthic algae in the downstream of the yana compared to those in upstream. In addition, δ15N values of filter-feeders from downstream were higher than those from upstream. These results suggest that the benthic algae increased by nutrient supply from fish were lifted up into the water column by the spawning behavior of the fish. The lifted benthic algae became POM, feeding filter-feeders.
The survey was conducted in the South branch and North branch of Ado River, which flow into Lake Biwa. There were yana, traps to capture migratory fishes across both channels, and the density of migratory fish, Opsariichthys uncirostris were significantly higher downstream of the structure. We collected benthic algae, POM in the river water, and caddisflies that filter feed POM at three sites above and below the yana in both channels. We measured carbon and nitrogen isotope ratios (δ13C, δ15N) of these samples, chlorophyll-a concentration of the benthic algae, and particulate organic carbon (POC), organic nitrogen (PON), total phosphorus (TPP), and inorganic phosphorus (PIP) concentrations of the POM.
The results showed that the POC, PON, TPP, and PIP concentrations were approximately twice as high, and the δ13C and δ15N values were approximately 3‰ higher downstream of the yana than upstream. However, C/N, C/P, and N/P ratios of the POM were not significantly different between the up- and downstream of yana. These ratios were closer to the value of benthic algae. There was an increase in chlorophyll-a concentration and δ15N values of the benthic algae in the downstream of the yana compared to those in upstream. In addition, δ15N values of filter-feeders from downstream were higher than those from upstream. These results suggest that the benthic algae increased by nutrient supply from fish were lifted up into the water column by the spawning behavior of the fish. The lifted benthic algae became POM, feeding filter-feeders.