[PDF] Physical And Biological Consequences Of Giant Kelp Macrocystis Pyrifera Removals Within A Central California Kelp Forest By Steven Ryan Cunningham eBook

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Page : 34 pages
File Size : 47,66 MB
Release : 2017
Category : Electronic books
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Adult giant kelp, Macrocystis pyrifera, release billions of zoospores into the surrounding kelp forest community during each reproductive season. The young sporophytes that ultimately develop from these zoospores undergo a process of self-thinning until their densities are reduced to levels that can be sustained by environmental conditions at that time. We examined the effects of recruitment density on the survival of juvenile M. pyrifera within naturally occurring patches in the Point Loma kelp forest, San Diego, CA and found that the total density of all macroalgae within the patch had no effect on M. pyrifera survival. Instead, we found that density-dependent mortality within each patch was driven almost entirely by the density of conspecifics. This pattern, and the direct effects of recruitment density on juvenile M. pyrifera survival was further tested experimentally by oputplanting two size classes of juvenile M. pyrifera (medium size class, 5-25cm in height; large size class, ~1m in height) at three densities (20, 60 and 120 individuals m-2, and 2, 4 and 8 individuals m-2 for medium and large size classes, respectively). While the large size class exhibited the overall greatest survival, declines in survival were consistent through time for all density treatments and for each size class, with the surviving sporophytes converging on similar densities (8 m- 2 ±4 for the medium size class, and 1 m-2 ±1 for the large size class). Together, our observational and our experimental studies demonstrate that, regardless of the initial density at which M. pyrifera recruits, the resulting patches of juvenile sporophytes will thin to similar densities that are presumably appropriate for their survival under the existing environmental conditions. This self-thinning process is an example of density-dependent mortality that operates in addition to other stressors such as grazing, sand scour, entanglement and dislodgement due to wave energy, each of which effectively reduces the population size of new M. pyrifera recruits to a level that is sustainable by the kelp forest community.

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Page : 33 pages
File Size : 14,7 MB
Release : 2020
Category : Electronic books
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The forest-forming giant kelp, Macrocystis pyrifera, and the communities it supports have been decreasing across their native ranges in many parts of the world. The sudden removal of giant kelp canopies by storms enhances space and light for the colonization ofopportunistic understory macroalgae, such as Desmarestia herbacea, which can inhibit M. pyrifera recovery and alter local community composition. Understanding the mechanisms by which D. herbacea interacts with M. pyrifera can therefore provide insight into patterns of kelp forest recovery following these disturbances, and can aid in predicting future community structure. This study experimentally tested the independent and combined effects of two likely competitive mechanisms, namely shade and scour, by which D. herbacea might inhibit recovery of M. pyrifera in the Point Loma kelp forest in San Diego, CA. We conducted field experiments on SCUBA to study the individual and combined effects of shade and scour by D. herbacea on the survival of M. pyrifera microscopic life stages, and the recruitment, survival and growth of its young sporophytes. Our results show that scour (i.e. physical abrasion by D. herbacea thalli) had the strongest effect on the survival of M. pyrifera microscopic life stages and recruitment of its young sporophytes, but shade and scour were both important for survival and growth of these sporophytes as they grew larger. Canopy-removing storms are increasing in frequency and intensity, and this change could facilitate the rise of opportunistic species, like D. herbacea, which might alter community succession and recovery of kelp forests. Understanding the mechanisms by which these opportunistic species suppress kelp recovery can therefore enhance conservation efforts.

Author : Katherine Kimberlin Arkema
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Page : 294 pages
File Size : 12,24 MB
Release : 2008
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ISBN : 9780549841852

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I investigated the relationship between giant kelp, Macrocystis pyrifera, a large and dynamic structure-forming organism on temperate reefs, and the species that live beneath its canopy and on its surfaces. In particular, my research focused on how the attenuating effect of kelp on light influences the structure and dynamics of the understory community, and how the dampening effect of kelp on currents influences spatial variation in the abundance and demography of a suspension-feeding epiphyte, the colonial and encrusting bryozoan, Membranipora serrilamella.