NSF Org: |
OCE Division Of Ocean Sciences |
Recipient: |
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Initial Amendment Date: | April 6, 2010 |
Latest Amendment Date: | December 8, 2015 |
Award Number: | 0962306 |
Award Instrument: | Continuing Grant |
Program Manager: |
Michael Sieracki
OCE Division Of Ocean Sciences GEO Directorate For Geosciences |
Start Date: | April 1, 2010 |
End Date: | March 31, 2017 (Estimated) |
Total Intended Award Amount: | $869,438.00 |
Total Awarded Amount to Date: | $899,463.00 |
Funds Obligated to Date: |
FY 2011 = $275,064.00 FY 2012 = $263,014.00 FY 2013 = $84,934.00 FY 2014 = $9,025.00 |
History of Investigator: |
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Recipient Sponsored Research Office: |
3227 CHEADLE HALL SANTA BARBARA CA US 93106-0001 (805)893-4188 |
Sponsor Congressional District: |
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Primary Place of Performance: |
3227 CHEADLE HALL SANTA BARBARA CA US 93106-0001 |
Primary Place of Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | BIOLOGICAL OCEANOGRAPHY |
Primary Program Source: |
01001112DB NSF RESEARCH & RELATED ACTIVIT 01001213DB NSF RESEARCH & RELATED ACTIVIT 01001314DB NSF RESEARCH & RELATED ACTIVIT 01001415DB NSF RESEARCH & RELATED ACTIVIT |
Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
Intellectual Merit: Understanding trophic connections and how resource variability affects consumers is necessary if we are to predict how food webs may shift in the face of environmental change. Macroalgae and phytoplankton support highly productive marine ecosystems. Research based on stable isotope analyses has supported the idea that macroalgal detritus, especially the giant kelp Macrocystis, is a major source of dietary carbon to benthic suspension-feeders. However, recent findings by the investigator's four-year stable isotope study suggest that phytoplankton, not kelp, are the main food resource for benthic suspension-feeders on reefs in the Santa Barbara Channel, and that variation in phytoplankton abundance, combined with feeding selectivity and the scale of consumer tissue turnover times, may drive variability in consumer isotope values. The results suggest that a key assumption made in 'snapshot' isotope studies of coastal ecosystems over the past 20 years, which the isotope signature of coastal phytoplankton can be represented by that of offshore phytoplankton, could be incorrect. This assumption has been made because of the difficulty in separating phytoplankton from detritus to obtain an uncontaminated isotope signature, also a problem in freshwater systems.
The investigator will address two main objectives in this research project: 1) determining the contribution of phytoplankton and giant kelp detritus to the pool of suspended reef POM and whether POM composition varies with distance from kelp forests, and 2) evaluating how different components of the POM are used as food by reef suspension feeders. Two complementary approaches are designed to explore the contribution of phytoplankton and kelp detritus to POM in coastal waters: an advanced flow cytometry and cell-sorting system to separate phytoplankton from bulk POM, and analysis of essential polyunsaturated fatty acids (PUFA) in POM and consumers. The investigators have obtained preliminary data that demonstrate the feasibility of both of these methods. Isotope values of isolated inshore phytoplankton and kelp, and compound-specific PUFA, will be used in mixing models to estimate relative contributions of these two major primary producers to suspension feeder diets. Two hypothesized mechanisms that may influence isotopic composition of consumers will also be tested: selective feeding on particular fractions of the POM, and tissue turnover times.
This project will provide new insights into the trophic support of benthic suspension feeders, an ecologically and economically important guild in coastal ecosystems. The results will test the general hypothesis that giant kelp detritus is an important source of dietary carbon to suspension feeders, a commonly accepted idea that needs re-evaluation in light of key assumptions that have been made in its support. Stable isotope analyses are an ideal tool for testing this hypothesis given the spatial and temporal scales of variability that exist in the abundance of phytoplankton and giant kelp at our study sites. The sampling scheme combined with longer-term data on producer biomass provided by the Santa Barbara Coastal LTER will enable the investigators to capture this variability, which is generally missed by studies based on 'snapshot' stable isotope analyses.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
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This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Suspension feeders, sometimes called filter feeders, sustain themselves by filtering particles of food from the water around them. Susupension feeding is a widespread strategy in the oceans, especially in shallow water where single-celled plants or phytoplankton are an abundant food source. Suspension feeders include mussels, oysters, and other bivalves as well as a multitude of other species from sea anemones to tunicates or sea squirts. Suspension feeders often dominate shallow marine communities in their biomass, and are economically important to many fisheries as well as ecologically important as links between plankton and larger predators that eat them such as marine mammals, fish and crustaceans. Since the 1980's, researchers have speculated that forests of kelp, in particular giant kelp, that are found in temperate waters may serve as an important food source for suspension feeders, and may in many cases supercede phytoplankton and other particles in their role sustaining suspension feeders. The evidence for this idea has been based almost entirely on carbon stable isotope data. Carbon stable isotopes can be used to trace sources of food through food webs, particularly if the sources are known and have significant differences in their stable isotope composition. Many studies have used the perceived isotope differences between kelp and phytoplankton to estimate the contribution of these sources to coastal marine food webs, particularly kelp forests. We found, however, that phytoplankton carbon isotope values vary substantially and often approach or overlap those of kelp. We tested the hypothesis that kelp is an important food source for suspension feeders in kelp forests off Santa Barbara, California, in several ways, and we also conducted some work with collaborators on kelp forests in new Zealand. We compared isotope values of suspension feeders on reefs that varied widely in kelp abundance, including areas where kelp was experimentally removed. We did experiments where we supplemented the diet of suspension feeders in the lab with naturally sloughing kelp detritus. We used essential fatty acids as an alternative tracer of kelp-derived food. In all this work, we found no support for the idea that kelp detritus is an important source of food for suspension feeders. Instead we found that phytoplankton is their main food source. However, we also found support for the hypothesis that through shading the bottom, kelp does increase the abundance of suspension feeders by inhibiting other macroalgae that compete with them for space. We also found that small kelp grazers in the canopy are an important source of food to canopy fish like kelp bass and kelp rockfish, which are important in recreational and commercial fisheries. Our results provide better information on the role of giant kelp in the kelp forest ecosystem, and can be used to inform managers who with to restore fish populations and kelp forests along the California coast.
Last Modified: 07/17/2017
Modified by: Robert J Miller
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