Storm-generated sediment deposition on rocky shores: Simulating burial effects on the physiology and morphology of Saccharina latissima sporophytes

Kelps inhabiting wave-exposed coasts are frequently exposed to disturbance such as storm-generated sediment deposition on blades which can be resuspended and removed by local hydrodynamic processes. However, in extreme cases, whole thalli can be buried under sediment for a period of time. The objectives of the present study are to determine the proximate effects of long-term sediment burial on kelp physiology and to confirm whether transient sediment load have functional significance in mitigating the negative effects of saturating light intensity normally encountered in the field. We simulated sediment burial to evaluate its impact on the vitality, in terms of photosystem II (PSII) function, pigments and morphology, of Saccharina latissima on different time scales. The effect was compared to the negative controls, kelps without sediment cover exposed to the whole radiation treatment. Results of our study showed that short-term burial under different sediment types (gravel, sand, and silt and clay) has no negative effect on the physiology and morphology of S. latissima, whereas sediment-free algal discs exposed to high PAR and UVR were bleached and photoinhibited. Conversely, long-term burial under silt and clay showed adverse smothering effect leading to bleaching, loss of PSII function and tissue decay. We observed that burial under gravel and sand (up to a period of 7 days), e. g. after storm slowdown and settlement of sediment particles, showed some protective function in mitigating the negative effect of photoinhibiting high light intensities naturally encountered by most intertidal and upper subtidal macroalgae.