Physiological response of the stipitate understory kelp, Pterygophora californica Ruprecht, to shading by the giant kelp, Macrocystis pyrifera C. Agardh

107

122

Two catastrophic-scale storm disturbances of a giant kelp forest community were followed by very different oceanographic conditions, the warm. nutrient-stressed period of the 1982-1984 El Nino and the cold, nutrient-rich La Nina of 1988-1989. Here w e compare the fates of the 2 postdisturbance algal communities, or '2 cohorts', under condltions determined by large-scale, lowfrequency oceanographic events. Succession and population dynamics of the competitive d o m~n a n t kelp. Macrocystis pyrifera, and understory kelps, Pterygophora californlca and Laminaria farlowu, were followed a t 5 permanent sites in the Point Loma kelp forest near San Diego. California, USA. where kelps have been mapped quarterly since 1983. There was intense kelp recruitment after both disturbances. The different oceanographic cond~tions, however, strongly affected the population dynamlcs of M. pynfera and ~t s competitive interactions with the lower standing species. Poor M pyrifera growth, canopy formation, and survival during the El Nino apparently allowed the persistence of understory populations. Extraordinary conditions for M. pyrifera growth during the La Niria were associated with the near extinction of understory populations. The number of stipes per plant and stipe dens~ty are indices of IM, pyr~fera growth and carrying capacity, respect~vely, which appear to be very senslt~ve to environmental condltions. The 2 cohorts exh~blted very different stipe patterns. In both cases, the anomalous oceanographic conditions lasted for about 2 yr after the disturbances, but the effects on kelp community structure persisted for the lives of the M. pyrifera cohorts, despite average or relatively poor conditions later In summary, these data suggest that large-scale, low-frequency oceanographic phenomena are important to kelp forest successional processes, population dynamics, and competitive interactions among kelp guilds

Section: U)mentioning

confidence: 89%

Section: U)mentioning

confidence: 99%

Large-scale, low-frequency oceanographic effects on kelp forest succession:a tale of two cohorts

Tegner¹,

Pk²,

Pb³

et al. 1997

107

122

“…For example, Edwards (1998) observed that the increases in Desmarestia abundance following kelp-canopy removal was due to the enhanced recruitment of its sporophytes (by means of reproduction of its microscopic gametophytes; Edwards 2000), while Watanabe et al (1992) observed that Pterygophora exhibited a positive physiological response (increased growth, fecundity and photosynthesis) following removal of the Macrocystis canopy. Similarly, Roberts (1996) observed that at least some red algae (e.g.…”

Section: Discussionmentioning

confidence: 99%

Effects of shade from multiple kelp canopies on an understory algal assemblage

Clark¹,

Edwards²,

Foster³

2004

114

We examined the effects of shade from multiple kelp canopy layers (surface Macrocystis pyrifera canopy, understory Pterygophora californica canopy), both individually and in combination, on an understory algal assemblage in a central Californian kelp forest. The removal of both kelp canopies resulted in a dense recruitment of the understory brown alga Desmarestia ligulata that formed a third canopy layer, which significantly decreased bottom light and the abundance of understory red algae. We subsequently created an additional canopy treatment by removing this third canopy layer. In general, the understory red algae fluctuated seasonally with winter swell intensity, changes in kelp canopy cover, and grazing; and although species richness increased significantly with increased bottom light, red algal bottom cover did not respond significantly to the canopy clearings until 2 yr after the canopies were initially cleared. Red algal cover within the Pterygophora canopy treatment was similar to that in the control treatment. In the absence of Pterygophora, the Macrocystis canopy treatment and 'no canopy' treatment were found to have greater red algal cover and species richness. Individual understory species were rare, which resulted in small effects sizes and thus low statistical power. However, when grouped post hoc, according to how they responded to the canopy clearings (i.e. response groups), we were able to detect canopy treatment effects as much as 1 yr earlier. This method identified that some understory red algae adapted to areas of canopy removal (light-adapted), and others adapted to a variety of light regimes (shade-tolerant). We were able to classify the light-adapted algae into 2 subgroups: the high-light species and the intermediate-light species. Although this method of grouping was done post hoc, our results indicate that it may provide the clearest assessment of how understory algae respond to shading from kelp canopies.KEY WORDS: Canopy shading · Community structure · Kelp forest · Light-adapted · Macrocystis · Pterygophora · Red algae · Shade-tolerantResale or republication not permitted without written consent of the publisher

“…These stored carbohydrates are used to fuel 90% of annual plant growth during the winter period of darkness when nutrients are abundant. Laminariales can accumulate up to 15 to 20% DW in carbohydrates (German 1986, Watanabe et al 1992). The deep-water population of Pleurophycus gardneri examined here, however, only accumulated 5 to 9% DW as carbohydrates, with the stipe the main reservoir and the blade the main source.…”

Section: Discussionmentioning

confidence: 99%

“…Although light is also a common limiting factor for many marine ecosystems, including those dominated by the temperate to high latitude kelps (Dean 1985, Schiel & Foster 1986), very few algae exhibit a deciduous life history. Canopy cover of Macrocystis pyrifera can limit light availability to understory algae in temperate latitudes (Reed & Foster 1984, Watanabe et al 1992, and episodic disturbance by large storms can influence the growth and persistence of algae that would otherwise be excluded by light limitation (Edwards 1998). However, there is no clear evidence that the newly settled algae undergo a seasonally adjusted metabolic response to light availability.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of carbon allocation in a deep-water population of the deciduous kelp Pleurophycus gardneri (Laminariales)

Dominik¹,

Zimmerman²

2006

Pleurophycus gardneri (Laminariales) is common in the low intertidal of the Northeast Pacific, but dominates many deep (30 to 40 m) rocky reefs in central California. Seasonal dynamics of productivity and resource allocation of a deep-water population of this deciduous, stipitate kelp were studied to understand how blade abscission affects the annual carbon budget. Patterns of growth, metabolism, and carbon storage and mobilization were measured monthly for 1 yr relative to in situ light and temperature, and used to model the annual carbon budget. The resulting carbon budget was used to determine if blade abscission effectively reduced respiratory demand during the winter period of low light availability. Metabolic properties (photosynthesis, photoacclimation, and respiration) were seasonally constant and showed evidence of photoacclimation to this deep, low-light environment. Blades grew between February and July, followed by senescence and sloughing from August to December. Concentrations of laminaran and mannitol increased in the blades from the onset of sloughing in August until just prior to blade abscission in mid-December, suggesting translocation of these carbohydrates may have occurred from the blade to the stipe and holdfast. Carbon budget estimates revealed that scalar irradiance measures overestimated the light available for photosynthesis of these paddle-shaped kelp blades by 50 to 75%. The calculations also revealed that blade retention allowed for the maintenance of positive carbon balance throughout the year. Thus, conservation of the internal carbon reserve for metabolic survival during the low-light period does not appear to be a viable explanation for the deciduous life history of P. gardneri. Abscission may reduce hydrodynamic drag, thus minimizing the probability of dislodgment of entire plants during winter storm events, or promote spore dispersal as abscised blades and sori drift away from the parent holdfast. KEY WORDS: Carbon budget · Photosynthesis · Abscission · Light acclimation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 309: [143][144][145][146][147][148][149][150][151][152][153][154][155][156][157] 2006 excluded by light limitation (Edwards 1998). However, there is no clear evidence that the newly settled algae undergo a seasonally adjusted metabolic response to light availability. In northern latitudes where light limitation is seasonally predictable, perennial kelps have evolved a variety of physiological mechanisms that allow them to survive through summer periods of nutrient limitation and winter periods of light limitation (Gagne et al. 1982). Laminaria solidungula, for example, uses stored carbohydrates accumulated during summer to complete 90% of its annual linear blade growth during the virtual darkness of the Arctic winter (Mann 1973, Chapman & Craigie 1977, 1978, Dunton & Schell 1986. Another mechanism may involve cellular photoacclimation to increased photosynthetic efficiency in low-light environments, thr...