| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | January 8, 2015 |
| Latest Amendment Date: | January 8, 2015 |
| Award Number: | 1514893 |
| Award Instrument: | Standard Grant |
| Program Manager: |
David Garrison
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | December 15, 2014 |
| End Date: | November 30, 2016 (Estimated) |
| Total Intended Award Amount: | $199,187.00 |
| Total Awarded Amount to Date: | $199,187.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1850 RESEARCH PARK DR STE 300 DAVIS CA US 95618-6153 (530)754-7700 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
CA US 95618-6153 |
| 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: |
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| 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
The usual expectation is that when populations of plants and animals experience repeated losses to predators or human harvest, they would decline over time. If instead these populations rebound to numbers exceeding their initial levels, this would seem counter-intuitive or even paradoxical. However, for several decades mathematical models of population processes have shown that this unexpected response, formally known as overcompensation, is not only possible, but even expected under some circumstances. In what may be the first example of overcompensation in a marine system, a dramatic increase in a population of the non-native European green crab was recently observed following an intensive removal program. This RAPID project will use field surveys and laboratory experiments to verify that this population explosion results from overcompensation. Data will be fed into population models to understand to what degree populations processes such as cannibalism by adult crabs on juvenile crabs and changes in maturity rate of reproductive females are contributing to or modifying overcompensation. The work will provide important insights into the fundamental population dynamics that can produce overcompensation in both natural and managed populations. Broader Impacts include mentoring graduate trainees and undergraduate interns in the design and execution of field experiments as well as in laboratory culture and feeding experiments. The project will also involve a network of citizen scientists who are involved with restoration activities in this region and results will be posted on the European Green Crab Project website.
This project aims to establish the first example of overcompensation in marine systems. Overcompensation refers to the paradoxical process where reduction of a population due to natural or human causes results in a greater equilibrium population than before the reduction. A population explosion of green crabs has been recently documented in a coastal lagoon and there are strong indications that this may be the result of overcompensation. Accelerated maturation of females, which can accompany and modify the expression of overcompensation has been observed. This RAPID project will collect field data from this unusual recruitment class and conduct targeted mesocosm experiments. These will include population surveys and mark-recapture studies to measure demographic rates across study sites. Laboratory mesocosm studies using this recruitment class will determine size specific mortality. Outcomes will be used in population dynamics models to determine to what degree overcompensation has created this dramatic population increase. The project will seek answers to the following questions: 1) what are the rates of cannibalism by adult green crabs and large juveniles on different sizes of juvenile green crabs, 2) what are the consequences of smaller size at first reproduction for population dynamics and for overcompensation and 3) how quickly will the green crab population return to the levels observed prior to the eradication program five years earlier?
PROJECT OUTCOMES REPORT
Disclaimer
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.
Our results demonstrate that the invasive crab predator Carcinus maenas population in Seadrift Lagoon, Stinson Beach, CA underwent overcompensation in response to attempts to locally eradicate this population. After five years of active crab removal (2009-2013) resulting in >90% reduction of the adult population, the population underwent a 30 fold increase resulting in three times more crabs than the pre-removal level (2009). The 2014 population was heavily dominated (>97%) by small crabs. We found that following this population explosion the population in 2015 was substantially reduced with many fewer juvenile crabs. Other populations in the region that were similarly surveyed did not have any significant increase in population size in contrast to Seadrift. Mesocosm cannibalism experiments showed high levels of size-specific cannibalism by adult crabs on recruiting juveniles, which models indicate can easily explain the dynamics we witnessed. Additional molecular data not supported by this project strongly supports the idea that this population is almost entirely self-recruiting. We also found evidence, though limited, of early maturation with females reproducing at a smaller size consistent with overcompensation predictions. In summary, the results of this study provide convincing evidence of the first experimental demonstration of overcompensation following population reduction in a marine system. These conclusions have important implications for invasive species management as well as for fisheries management and other activities that involve harvest or other population reduction activities.
Last Modified: 04/23/2017
Modified by: Edwin D Grosholz
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