Water Motion, Marine Macroalgal Physiology, and Production

Abstract

Water motion is a key determinant of marine macroalgal production, influencing directly or indirectly physiological rates and community structure. Our understanding of how marine macroalgae interact with their hydrodynamic environment has increased substantially over the past 20 years, due to the application of tools such as flow visualization to aquatic vegetation, and in situ measurements of seawater velocity and turbulence. This review considers how the hydrodynamic environment in which macroalgae grow influences their ability to acquire essential resources and how macroalgae might respond physiologically to fluctuations in their hydrodynamic regime with a focus on: (1) the biochemical processes occurring within the diffusion boundary layer (DBL) that might reduce rates of macroalgal production; (2) time scales over which measurements of velocity and DBL processes should be made, discussing the likelihood of in situ mass transfer limitation; (3) if and how macroalgal morphology influences resource acquisition in slow flows; and (4) ecobiomechanics and how hydrodynamic drag might influence resource acquisition and allocation. Finally, the concept that macroalgal production is enhanced in wave-exposed versus sheltered habitats is discussed.

Osmotrophy in modular Ediacara organisms

“…Osmotrophy is an effective means of gathering nutrients in microscopic organisms. Osmotrophy relies on a large SA/V ratio so as to ensure proper diffusion throughout the entire organism or cell (21). In microscopic organisms, ensuring a large SA/V ratio is achieved easily.…”

Interactive effects of grazing and environmental stress on macroalgal biomass in subtropical rocky shores: Modulation of bottom-up inputs by wave action

“…Ephemeral algae are characterized for their ability to rapidly capture nutrients (Steneck and Dethier, 1994) and, therefore, this algal group may be particularly favored by the pulsed nutrient inflows. This is achieved by creating turbulence and reducing the thickness of the boundary layer over the plant surface, thus increasing the flux of molecules from the external fluid to plant cells (Hurd, 2000;Wheeler, 1980). Lower on the shore, effective immersion time is increasingly dominated by tides and less by waves (Harley and Helmuth, 2003) and, therefore, nutrient fluxes among shores of different wave exposure should be more similar and more dependent on local currents and turbulence.…”

Partitioning of primary production among giant kelp (Macrocystis pyrifera), understory macroalgae, and phytoplankton on a temperate reef

“…Other factors besides light that may be affected by a dense kelp canopy include nutrients and water flow (Hurd 2000). Extensive prior work at Mohawk Reef has shown that the kelp forest does slow water flow going through it (Gaylord et al 2007;Stewart et al 2009) but that this dampening of flow does not limit nutrient uptake for kelp inside the forest (Fram et al 2008).…”

“…However, these perspectives ignore the potential for interactions between benthic and pelagic autotrophs on intermediate scales, from hundreds of meters to kilometers, such as among reefs with and without kelp canopies, and much of the variation in coastal production can occur at this scale (Broitman and Kinlan 2006). Giant kelp, Macrocystis spp., a foundation species and ecosystem engineer, creates dense forests that provide food and physical habitat to many animal species (Foster and Schiel 1985;Graham 2004), slow water flow (Jackson and Winant 1983;Gaylord et al 2007), absorb light (Stewart et al 2009), and take up nutrients (Hurd 2000), thus shaping the entire benthic community (Dayton 1985;Clark et al 2004;Arkema et al 2009). Controlled removal experiments have shown that giant kelp suppresses the biomass of understory macroalgae (Dayton et al 1984;Reed and Foster 1984;Clark et al 2004).…”