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Grazing effects of an obligate herbivore fish species on periphyton biomass in a stream mesocosm study
Citation:
McKernan, C., E. Bryan, D. Speth, D. Sullivan, M. Booth, R. Martin, P. Weaver, AND C. Nietch. Grazing effects of an obligate herbivore fish species on periphyton biomass in a stream mesocosm study. SETAC North America 44th Annual Meeting, Louisville, KY, November 12 - 16, 2023.
Impact/Purpose:
In this study, we evaluated the effect of a native, free-roaming, herbivorous fish (Central Stoneroller, Campostoma anomalum, an obligate herbivore) on periphyton in a stream mesocosm set-up. The benefit of including free-roaming fish in mesocosm tests is to add realism to the experimental conditions.
Description:
In this study, we evaluated the effect of a native, free-roaming, herbivorous fish (Central Stoneroller, Campostoma anomalum, an obligate herbivore) on periphyton in a stream mesocosm set-up. The benefit of including free-roaming fish in mesocosm tests is to add realism to the experimental conditions. We tested the hypothesis that the presence of fish would affect periphyton dry weight (BP), ash free dry mass (AFDM), % organic matter (%OM, i.e., AFDM as a percentage of BP) and the inorganic sediment fraction (BP-AFDM). Six indoor stream mesocosms were prepared with and without grazing fish (three replicates each). The fish were approximately 85 mm long, had a mean weight of 6.24 g, and were obtained from a local small stream. After a 24 hr acclimation period inside the facility, the replicates with fish each received 6 non-sexed individuals. Survival over the experiment averaged 83%. Periphyton in the six mesocosms, were sampled weekly over a 46 day test. Irradiance, water quality, and water sources were identical among streams and sampling events. The periphyton responses were analyzed conditional on an interaction between time and fish treatment. There was no significant difference in periphyton dry weight, AFDM, or in its inorganic content. However, periphyton in streams with fish had a significantly higher fraction of organic matter (%OM). This resulted from relatively lower inorganic sediment and higher AFDM in the streams with fish. Periphytic BP, AFDM, and inorganic fraction all increased with time in both treatments, but in streams with fish, the accrual lagged until an observed increase occurred between the sampling events on days 32 and 39 of the experiment. The time by treatment interaction was not significant. Although, the presence of grazing fish did not affect periphyton biomass, they did affect its structure by increasing its organic fraction. We suspect this could be due to fish swimming or grazing behavior, which may act to prevent settling or retention of inorganic sediment in the periphytic matrix.
URLs/Downloads:
https://www.setac.org/discover-events/global-meetings/setac-north-america-44th-annual-meeting.html