Differences in growth, morphology and tissue carbon and nitrogen of Macrocystis pyrifera within and at the outer edge of a giant kelp forest in California, USA

Abstract

To investigate the extent to which alteration of physical factors by giant kelp beds affects the growth of kelp within the bed, we conducted analyses of frond morphometrics at 2 mo intervals, elongation rates and tissue chemistry of individuals of Macrocystis pyrifera on the interior and edge of a kelp bed off the coast of Santa Barbara, California, USA. The density of the kelp canopy varied greatly during the 13 mo study, ranging from 0.03 to 8.03 m 2 blade tissue m -2 sea surface. Time series analysis of flow velocity, light, temperature and seawater nitrate concentrations inside and outside of the bed indicated that when canopy density was high (May to September) current speeds in the bed were 25% of incident flow, and light below the canopy (at 1 m depth) was reduced to 10% surface irradiance. Nitrate concentrations were highly variable and similar between inside and outside moorings. When the canopy was well developed, kelp fronds on the seaward edge of the bed had faster elongation rates and larger blades, resulting in higher overall growth rates (mass added per day) than interior fronds. Carbon and nitrogen accumulation by edge fronds was also higher during this period, which fueled growth rates of edge fronds that were nearly twice as high as interior fronds when the canopy was densest. Thus, the growth and tissue chemistry of M. pyrifera within the kelp bed depended on the extent to which the bed modified ambient physical conditions. KEY WORDS: Kelp bed · Macrocystis pyrifera · Ecosystem engineering · Growth · Morphology · Nitrogen · Carbon · Light · Water flow Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 375: [101][102][103][104][105][106][107][108][109][110][111][112] 2009 with flow can attenuate currents and internal waves (Jackson & Winant 1983, Jackson 1984, 1997, Gaylord et al. 2007, Fram et al. 2008). As such, giant kelp is a classic autogenic ecosystem engineer (sensu Jones et al. 1994), altering physical conditions by its presence and creating habitats very distinct from adjacent waters. However, giant kelp beds are dynamic systems, and the extent to which they modify their surrounding physical environment is a function of their areal extent and the density of individuals within them, which change with seasonal and inter-annual variability in nearshore physical conditions.Patterns of productivity and abundance of Macrocystis pyrifera off the coast of California are influenced by seasonal changes in light, water motion and nitrate availability (Dayton & Tegner 1984, Dayton et al. 1992, Edwards & Estes 2006. The abundance of kelp in turn influences these physical processes in and around a kelp bed. For example, giant kelp canopies, which in southern California tend to be densest in summer when ambient seawater nitrate concentrations are typically lowest, can retard currents and reduce the amount of nitrate delivered to the bed interior (Jackson 1997, Gaylord et al. 2007, Fram et al. 2008. Similarly, light availability within a kelp b...

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

“…The large influence of Macrocystis on light and flow in the Mohawk kelp forest (Gaylord et al 2007;Fram et al 2008;Stewart et al 2009) coupled with the close proximity and similar biological and physical features of the MR and MC sites (see Results) greatly reduced the chance that factors other than the presence of giant kelp would cause differences in NPP between the two sites. NPP and biomass of Macrocystis were measured monthly at a similar depth , 10 m west of the MC site as part of the Santa Barbara Coastal Long-Term Ecological Research Program's ongoing investigations.…”

“…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).…”

Photosynthetic oxygen flux by Macrocystis pyrifera: a mass transfer model with experimental validation

“…We chose data from November to match environmental conditions that affect C s , such as light availability and water temperature. The depth-averaged velocity measured in November 2006 within the Mohawk Reef kelp bed was 2.5 cm s -1 (Stewart et al 2009). Using .…”

“…To illustrate the simplicity and validity of the derived model, we determined the forest-averaged daily NPP for the Mohawk Reef forest off the coast of Santa Barbara, California, USA, using reported data from November 2006 , Stewart et al 2009). We chose data from November to match environmental conditions that affect C s , such as light availability and water temperature.…”

“…From the CO 2 flux we could determine the molar carbon flux and convert that to grams of carbon per blade surface area per time ). This was converted to forest-averaged daily NPP using the reported blade density for November 2006 of 2 m 2 blade area m -2 sea surface area (Stewart et al 2009 , the same value determined by Reed et al (2008).…”