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Kelp Detritus as an Autochthonous Resource to Subtidal Invertebrates.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Kelp Detritus as an Autochthonous Resource to Subtidal Invertebrates./
Author:	Yorke, Christie Emily.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
Description:	118 p.
Notes:	Source: Dissertations Abstracts International, Volume: 80-11, Section: B.
Contained By:	Dissertations Abstracts International80-11B.
Subject:	Ecology. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13808777
ISBN:	9781392100400

Kelp Detritus as an Autochthonous Resource to Subtidal Invertebrates.
Yorke, Christie Emily.

Kelp Detritus as an Autochthonous Resource to Subtidal Invertebrates. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 118 p.

Source: Dissertations Abstracts International, Volume: 80-11, Section: B.

Thesis (Ph.D.)--University of California, Santa Barbara, 2019.

This item must not be added to any third party search indexes.

Primary productivity, as the base of all food webs, fundamentally structures ecosystem complexity and function. Understanding the trophic fates or pathways of primary productivity is necessary for understanding drivers of ecosystem change. Most macrophyte primary productivity is not grazed, but ends up in the detrital pool where it remineralizes, is sequestered, or enters detrital food webs. In subtidal marine ecosystems, detrital trophic exchanges can be larger than those associated with grazing; however, these exchanges are difficult to quantify because 1) complex flow regimes in near-shore systems can transport detritus in ways that are difficult to track, 2) small suspended detrital particles are difficult to separate from phytoplankton and other carbon sources, and 3) gut content analysis of the suspension feeding animals that seem well positioned to benefit from detrital inputs have been historically difficult. In temperate, rocky subtidal regions with low terrestrial inputs, kelp and phytoplankton are the two main sources of primary productivity. More than 20 scientific studies dating back to the late 1980s assert that small particles of kelp detritus shed from the eroding edges of live kelp lamina are a primary food source to benthic suspension feeders. These attempts to quantify kelp detrital pathways focus on either natural abundance stable isotope mixing models with phytoplankton and kelp as endmembers, or artificial feeding studies using ground kelp without consideration for ecological relevance. Both approaches rely on untested assumptions and mixing model studies are only an indirect inference of detrital pathways at best. In this dissertation, I directly quantify and characterize kelp detritus shed from live kelp, I assess the importance of live kelp versus phytoplankton on suspension feeder growth, and I examine a novel pathway in which sea urchins mediate detrital kelp availability to benthic consumers. To quantify and characterize kelp detritus shed from live kelp, I conducted experiments on two foundational kelp species, Macrocystis and Ecklonia radiata, in which kelp lamina were enclosed with seawater for 24 hour periods, the seawater was than sieved to fractionate shed particle sizes and analyzed for carbon and nitrogen content. These results were used alongside kelp biomass and suspended particulate organic matter (POM) data to assess the reef-scale abundance of small kelp particles relative to total POM. To assess suspension feeder reliance on phytoplankton versus live kelp erosion, I measured the growth of an array of suspension feeders in a 2x2 factorial experiment with mechanically agitated kelp (presence or absence) separated from the suspension feeders by a 1cm2 mesh and phytoplankton (presence or absence). To evaluate the role of sea urchins in mediating detrital kelp availability, I isotopically labelled kelp fronds with 13C and 15N and placed them in mesocosm experiments containing an array of invertebrate suspension feeders and other benthic consumers with purple sea urchins (presence or absence). I then conducted isotope analyses on the suspension feeders and benthic consumers and used MixSIAR Bayesian mixing models to assess the proportion of labeled kelp comprising each species by treatment. We used data on urchin abundance, apparent kelp litter availability, and published feeding rate data to assess the relevance of this pathway in Santa Barbara coastal kelp forests. In both kelp detritus shedding studies the majority of shed particles were in size fractions consumed by suspension feeders, but were dilute (<2%) when compared to total POM availability. In the suspension feeder growth studies, suspension feeders only grew in response to phytoplankton, but not kelp, availability. The combined results of these studies suggest that, contrary to conclusions drawn from decades of natural abundance stable isotope studies, small kelp detrital particles do not represent a significant food source to suspension feeders. In the sea urchin experiments, presence of sea urchins had a modest positive effect on increasing the proportion of kelp in the diet of a select group of species. These results suggest that sea urchins act to retain and shred kelp litter that might otherwise be swept out of the kelp forest, making it more available to some benthic consumers. Based on the ecosystem data, sea urchins are unlikely to be food limited most of the time and rely primarily on detrital kelp litter rather than active grazing.

ISBN: 9781392100400Subjects--Topical Terms:

516476
Ecology.

Kelp Detritus as an Autochthonous Resource to Subtidal Invertebrates.
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300 $a 118 p.
500 $a Source: Dissertations Abstracts International, Volume: 80-11, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Brzezinksi, Mark;Miller, Robert J.
502 $a Thesis (Ph.D.)--University of California, Santa Barbara, 2019.
506 $a This item must not be added to any third party search indexes.
506 $a This item must not be sold to any third party vendors.
520 $a Primary productivity, as the base of all food webs, fundamentally structures ecosystem complexity and function. Understanding the trophic fates or pathways of primary productivity is necessary for understanding drivers of ecosystem change. Most macrophyte primary productivity is not grazed, but ends up in the detrital pool where it remineralizes, is sequestered, or enters detrital food webs. In subtidal marine ecosystems, detrital trophic exchanges can be larger than those associated with grazing; however, these exchanges are difficult to quantify because 1) complex flow regimes in near-shore systems can transport detritus in ways that are difficult to track, 2) small suspended detrital particles are difficult to separate from phytoplankton and other carbon sources, and 3) gut content analysis of the suspension feeding animals that seem well positioned to benefit from detrital inputs have been historically difficult. In temperate, rocky subtidal regions with low terrestrial inputs, kelp and phytoplankton are the two main sources of primary productivity. More than 20 scientific studies dating back to the late 1980s assert that small particles of kelp detritus shed from the eroding edges of live kelp lamina are a primary food source to benthic suspension feeders. These attempts to quantify kelp detrital pathways focus on either natural abundance stable isotope mixing models with phytoplankton and kelp as endmembers, or artificial feeding studies using ground kelp without consideration for ecological relevance. Both approaches rely on untested assumptions and mixing model studies are only an indirect inference of detrital pathways at best. In this dissertation, I directly quantify and characterize kelp detritus shed from live kelp, I assess the importance of live kelp versus phytoplankton on suspension feeder growth, and I examine a novel pathway in which sea urchins mediate detrital kelp availability to benthic consumers. To quantify and characterize kelp detritus shed from live kelp, I conducted experiments on two foundational kelp species, Macrocystis and Ecklonia radiata, in which kelp lamina were enclosed with seawater for 24 hour periods, the seawater was than sieved to fractionate shed particle sizes and analyzed for carbon and nitrogen content. These results were used alongside kelp biomass and suspended particulate organic matter (POM) data to assess the reef-scale abundance of small kelp particles relative to total POM. To assess suspension feeder reliance on phytoplankton versus live kelp erosion, I measured the growth of an array of suspension feeders in a 2x2 factorial experiment with mechanically agitated kelp (presence or absence) separated from the suspension feeders by a 1cm2 mesh and phytoplankton (presence or absence). To evaluate the role of sea urchins in mediating detrital kelp availability, I isotopically labelled kelp fronds with 13C and 15N and placed them in mesocosm experiments containing an array of invertebrate suspension feeders and other benthic consumers with purple sea urchins (presence or absence). I then conducted isotope analyses on the suspension feeders and benthic consumers and used MixSIAR Bayesian mixing models to assess the proportion of labeled kelp comprising each species by treatment. We used data on urchin abundance, apparent kelp litter availability, and published feeding rate data to assess the relevance of this pathway in Santa Barbara coastal kelp forests. In both kelp detritus shedding studies the majority of shed particles were in size fractions consumed by suspension feeders, but were dilute (<2%) when compared to total POM availability. In the suspension feeder growth studies, suspension feeders only grew in response to phytoplankton, but not kelp, availability. The combined results of these studies suggest that, contrary to conclusions drawn from decades of natural abundance stable isotope studies, small kelp detrital particles do not represent a significant food source to suspension feeders. In the sea urchin experiments, presence of sea urchins had a modest positive effect on increasing the proportion of kelp in the diet of a select group of species. These results suggest that sea urchins act to retain and shred kelp litter that might otherwise be swept out of the kelp forest, making it more available to some benthic consumers. Based on the ecosystem data, sea urchins are unlikely to be food limited most of the time and rely primarily on detrital kelp litter rather than active grazing.
590 $a School code: 0035.
650 4 $a Ecology. $3 516476
650 4 $a Biological oceanography. $3 2122748
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710 2 $a University of California, Santa Barbara. $b Marine Science. $3 1924535
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