MEPS 265:57-76 (2003)  -  doi:10.3354/meps265057

ABSTRACT: Kelps (benthic algae in the order Laminariales) live in a highly dynamic fluid environment, and exhibit many adaptations to meet the challenges imposed by hydrodynamic forces. We examined flow effects (direct and indirect) on understory kelp population dynamics, morphology and biomechanics along gradients of current velocity and wave accelerations in the San Juan Archipelago, Washington. Costaria costata, Agarum fimbriatum, and Laminaria complanata all exhibited significantly higher mortalities at wave-impacted sites, but no gradient was detectable in the effects of tidal currents on survival, despite the strong tidal signal in waters of the archipelago. This pattern stands in contrast to that reported earlier for the surface-canopy bull kelp Nereocystis luetkeana in these waters; N. luetkeana mortality was strongly correlated with current, but not wave energy. The higher wave-driven mortalities of the understory species occur, even though a suite of morphological and biomechanical attributes (thallus size and thickness, holdfast area and biomass, stipe cross-sectional area, holdfast strength, blade toughness) indicate that kelps at sites characterized by high flow energy are better adapted to resist the forces imposed by waves and currents. While the forces imposed by strong currents have little effect on survival, they do have significant effects on morphology and biomechanical strength. We propose that morphological plasticity in A. fimbriatum and C. costata ameliorates the effects of both currents and waves on their survival.

KEY WORDS: Kelp · Hydrodynamics · Flow · Biomechanics · Costaria costata · Agarum fimbriatum · Laminaria complanata