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Edited by Mary E. Power, University of California, Berkeley, CA, and approved April 28, 2015 (received for review March 25, 2015)
Significance
Human populations are rapidly expanding along Earth's coastlines, increasing stress to coastal ecosystems and the services they provide. One of these stressors comes from an increase in nutrient inputs from coastal land development that can enter estuaries and coastal seas leading to algal blooms that deplete oxygen from the water, a condition known as hypoxia. In this study, we investigated how coastal hypoxia influences fish diversity, the nursery habitat for juvenile fish, and fisheries production in adjacent offshore waters. We found that severity in hypoxia corresponded with declines to fish diversity, nursery quality, and offshore fisheries. Furthermore, intensification of El Niño mediated hypoxia by improving dissolved oxygen conditions, demonstrating that climate can influence anthropogenic stressors affecting coastal ecosystem services.
Abstract
Coastal ecosystems provide numerous important ecological services, including maintenance of biodiversity and nursery grounds for many fish species of ecological and economic importance. However, human population growth has led to increased pollution, ocean warming, hypoxia, and habitat alteration that threaten ecosystem services. In this study, we used long-term datasets of fish abundance, water quality, and climatic factors to assess the threat of hypoxia and the regulating effects of climate on fish diversity and nursery conditions in Elkhorn Slough, a highly eutrophic estuary in central California (United States), which also serves as a biodiversity hot spot and critical nursery grounds for offshore fisheries in a broader region. We found that hypoxic conditions had strong negative effects on extent of suitable fish habitat, fish species richness, and abundance of the two most common flatfish species, English sole (Parophrys vetulus) and speckled sanddab (Citharichthys stigmaeus). The estuary serves as an important nursery ground for English sole, making this species vulnerable to anthropogenic threats. We determined that estuarine hypoxia was associated with significant declines in English sole nursery habitat, with cascading effects on recruitment to the offshore adult population and fishery, indicating that human land use activities can indirectly affect offshore fisheries. Estuarine hypoxic conditions varied spatially and temporally and were alleviated by strengthening of El Niño conditions through indirect pathways, a consistent result in most estuaries across the northeast Pacific. These results demonstrate that changes to coastal land use and climate can fundamentally alter the diversity and functioning of coastal nurseries and their adjacent ocean ecosystems.
Footnotes
- ↵1To whom correspondence should be addressed. Email: bbhughes{at}ucsc.edu.
Author contributions: B.B.H., M.D.L., M.C.F., A.B.C., and M.G.G. designed research; B.B.H., M.D.L., M.C.F., A.B.C., and F.P.C. performed research; B.B.H., M.D.L., A.B.C., F.P.C., and M.G.G. contributed new reagents/analytic tools; B.B.H., M.D.L., and A.B.C. analyzed data; and B.B.H., M.D.L., M.C.F., A.B.C., F.P.C., and M.G.G. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1505815112/-/DCSupplemental.
- Brent B. Hughesa,1,
- Matthew D. Leveyb,
- Monique C. Fountainc,
- Aaron B. Carlisled,
- Francisco P. Chaveze, and
- Mary G. Gleasonf
- aDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060;
- bSeaSpatial Consulting, Santa Cruz, CA 95060;
- cElkhorn Slough National Estuarine Research Reserve, Watsonville, CA 95076;
- dHopkins Marine Station, Stanford University, Pacific Grove, CA 93950;
- eMonterey Bay Aquarium Research Institute, Moss Landing, CA 95039;
- fThe Nature Conservancy, Monterey, CA 93940
Edited by Mary E. Power, University of California, Berkeley, CA, and approved April 28, 2015 (received for review March 25, 2015)
Significance
Human populations are rapidly expanding along Earth's coastlines, increasing stress to coastal ecosystems and the services they provide. One of these stressors comes from an increase in nutrient inputs from coastal land development that can enter estuaries and coastal seas leading to algal blooms that deplete oxygen from the water, a condition known as hypoxia. In this study, we investigated how coastal hypoxia influences fish diversity, the nursery habitat for juvenile fish, and fisheries production in adjacent offshore waters. We found that severity in hypoxia corresponded with declines to fish diversity, nursery quality, and offshore fisheries. Furthermore, intensification of El Niño mediated hypoxia by improving dissolved oxygen conditions, demonstrating that climate can influence anthropogenic stressors affecting coastal ecosystem services.
Abstract
Coastal ecosystems provide numerous important ecological services, including maintenance of biodiversity and nursery grounds for many fish species of ecological and economic importance. However, human population growth has led to increased pollution, ocean warming, hypoxia, and habitat alteration that threaten ecosystem services. In this study, we used long-term datasets of fish abundance, water quality, and climatic factors to assess the threat of hypoxia and the regulating effects of climate on fish diversity and nursery conditions in Elkhorn Slough, a highly eutrophic estuary in central California (United States), which also serves as a biodiversity hot spot and critical nursery grounds for offshore fisheries in a broader region. We found that hypoxic conditions had strong negative effects on extent of suitable fish habitat, fish species richness, and abundance of the two most common flatfish species, English sole (Parophrys vetulus) and speckled sanddab (Citharichthys stigmaeus). The estuary serves as an important nursery ground for English sole, making this species vulnerable to anthropogenic threats. We determined that estuarine hypoxia was associated with significant declines in English sole nursery habitat, with cascading effects on recruitment to the offshore adult population and fishery, indicating that human land use activities can indirectly affect offshore fisheries. Estuarine hypoxic conditions varied spatially and temporally and were alleviated by strengthening of El Niño conditions through indirect pathways, a consistent result in most estuaries across the northeast Pacific. These results demonstrate that changes to coastal land use and climate can fundamentally alter the diversity and functioning of coastal nurseries and their adjacent ocean ecosystems.
- ecosystem services
- El Niño
- fisheries
- hypoxia
- resilience
Footnotes
- ↵1To whom correspondence should be addressed. Email: bbhughes{at}ucsc.edu.
Author contributions: B.B.H., M.D.L., M.C.F., A.B.C., and M.G.G. designed research; B.B.H., M.D.L., M.C.F., A.B.C., and F.P.C. performed research; B.B.H., M.D.L., A.B.C., F.P.C., and M.G.G. contributed new reagents/analytic tools; B.B.H., M.D.L., and A.B.C. analyzed data; and B.B.H., M.D.L., M.C.F., A.B.C., F.P.C., and M.G.G. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1505815112/-/DCSupplemental.
Threats to fish at the land–sea interface
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