The Role of Fauna in Seagrass Habitats

Abstract

Though there is mounting evidence that climate warming is altering trophic interactions between organisms, its effects on non-trophic interactions remain relatively undocumented.In seagrass systems, the bioturbating activity of infauna influences annual seagrass growth by influencing seed burial depth and germination success as well as sediment properties. If bioturbation is altered by warming, consequences on seagrass may result. Here, we assessed how heatwaves alter seagrass seed burial depth and germination rates when no bioturbators (control), single bioturbators and mixtures of bioturbators of contrasting feeding activities are present. The three bioturbators manipulated were surface (top 1-2cm of sediment) biodiffusor, the brown shrimp (Crangon crangon), the shallow (top 3-8 cm) diffusor, the common cockle, (Cerastoderma edule) and the upward (5-15 cm) conveyor, the polychaete, Cappitellidae spp. We applied two temperature treatments: (1) a present-day scenario set at the average summer temperature of seagrass habitat (17ºC); and (2) a heat-wave scenario modeled on the maximum recorded temperature (26.6ºC). Under present-day conditions, seed burial was greater in the presence of bioturbators than the control where no infauna was added. Cockles had the greatest impact on seed burial among all the bioturbators. Under the heat-wave scenario, seed burial in the mixed bioturbator treatment increased to match that of the cockle treatment. Cockles and polychaetes elevated the germination rates of buried seeds under present-day temperature, but not under the heat-wave scenario. Overall, these results indicate that heatwaves have the potential both to amplify and disrupt nontrophic interactions, with implications for seagrass seed germination.