Emergent Aquatic Insects

115 Pages·2008·0.52 MB·English

Emergent Aquatic Insects: Assemblage Structure and Patterns of Availability in
Freshwater Wetlands of the Lower Columbia River Estuary

Mary Frances Ramirez

A thesis submitted in partial fulfillment
of the requirements for the degree of

Master of Science

University of Washington

2008

Program Authorized to Offer Degree:
School of Aquatic and Fishery Sciences
University of Washington
Graduate School

This is to certify that I have examined this copy of a master’s thesis by

Mary Frances Ramirez

and have found that it is complete and satisfactory in all respects,
and that any and all revisions required by the final
examining committee have been made.

Committee Members:

_____________________________________________
Charles Simenstad

_____________________________________________
Dan Bottom

_____________________________________________
Claire Horner-Devine
Date _____________________________________________

In presenting this thesis in partial fulfillment of the requirements for a master’s degree at
the University of Washington, I agree that the Library shall make its copies freely
available for inspection. I further agree that extensive copying of this thesis is allowable
only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright
Law. Any other reproduction for any purposes or by any means shall not be allowed
without my written permission.

Signature______________________

Date__________________________
TABLE OF CONTENTS

Page
List of Figures.....................................................................................................................ii
List of Tables.....................................................................................................................iii
Chapter 1. Introduction........................................................................................................1
Study Objectives..........................................................................................7
Chapter 2. Spatial and Temporal Patterns in Insect Emergence........................................10
Introduction................................................................................................10
Methods......................................................................................................13
Results........................................................................................................16
Discussion..................................................................................................20
Chapter 3. Insect Emergence and Export...........................................................................45
Introduction................................................................................................45
Methods......................................................................................................48
Results........................................................................................................52
Discussion..................................................................................................55
Chapter 4. Final Synthesis.................................................................................................81
References..........................................................................................................................85
Appendix A. 2006 Emergent insect densities....................................................................96
Appendix B. 2006 Proportional composition by trap type................................................98
Appendix C. 2006 SIMPER results of dissimilarity between microhabitats.....................99
Appendix D. 2006 SIMPER results of similarity within microhabitats..........................100
Appendix E. 2006 Chironomid genera densities.............................................................101
Appendix F. Sample site metrics.....................................................................................103
Appendix G. 2007 Emergent insect densities..................................................................104
Appendix H. 2007 Chironomid genera denisities............................................................106
Appendix I. 2007 Export quantities standardized by site metrics...................................108

i
LIST OF FIGURES

Figure Number Page
1.1. The four life stages of chironomids..............................................................................9
2.1. Map of 2006 sample locations at Russian Island, Columbia River estuary................28
2.2. Emergent insect composition and daily density, Russian Island 2006.......................29
2.3. NMDS plot of emergent insect abundance data coded by sample month, 2006........30
2.4. Monthly density of insects collected by emergent and fallout traps, 2006.................31
2.5. Daily density by microhabitat, 2006...........................................................................32
2.6. Proportional occurrence by microhabitat of common emergent insects, 2006...........33
2.7. NMDS plots of emergent insect abundance data coded by microhabitat, 2006.........34
2.8. Densities of the two dominant chironomid subfamilies, 2006...................................35
2.9. Temporal distribution of daily chironomid genera densities, 2006............................36
2.10. Proportional chironomid emergence by microhabitat, 2006.....................................37
2.11. NMDS plot with dominant chironomid densities, 2006...........................................38
2.12. Area curves for emergent insect and chironomid densities, 2006............................39
2.13. Shannon-Wiener diversity values, 2006...................................................................40
3.1. Map of 2007 sampling sites, Columbia River estuary................................................61
3.2. Emergent abundance trends, 2007 diel study.............................................................62
3.3. Daily emergent densities of select insects, 2007........................................................63
3.4. Daily emergent densities of major insect families, 2007............................................64
3.5. Shannon-Wiener diversity values for emergent insects, 2007....................................65
3.6. Daily emergent densities of major chironomid taxa, 2007.........................................66
3.7. Shannon-Wiener diversity values for chironomid genera, 2007................................67
3.8. Composition of export samples, 2007........................................................................68
3.9. Standardized counts of export samples, 2007.............................................................69
3.10. Correlation between total chironomid export and emergence, 2007........................70
3.11. Probability of export by sample month, 2007...........................................................71
3.12. Daily densities of major chironomid genera collected in 2006 and 2007.................72
3.13. Neuston sample composition and quantity from distributary sloughs, 2007............73
i i
LIST OF TABLES

Table Number Page
2.1. ANOSIM results for assemblage differences by microhabitat, 2006.........................41
2.2. SIMPER results for chironomid taxa by microhabitat, 2006......................................42
2.3. Seasonal counts of emergence integrated over sample period, 2006..........................43
2.4. Examples of annual insect emergence from wetland systems....................................44
3.1. Sum of emergent insect densities over seasonal sample events, 2007.......................74
3.2. ANOSIM results for assemblage differences by site, 2007........................................75
3.3. Sum of emergent chironomid densities over seasonal sample events, 2007..............76
3.4. SIMPER results for chironomid taxa by site, 2007....................................................77
3.5. Counts of taxa collected in export samples by site, 2007...........................................78

ii i
ACKNOWLEDGEMENTS

I offer my sincere thanks to all those who supported me throughout this process. I am
very grateful for the guidance and advice from my thesis committee, Charles ‘Si’
Simenstad, Dan Bottom, and Claire Horner-Devine.

I could not have completed this work without the invaluable help from the entire Wetland
Ecosystem Team, especially Sarah Spilseth, Jeff Cordell, Jason Toft, Jennifer Burke,
Beth Armbrust, and Claire Levy. Additionally, I offer many thanks to Lia Stamatiou for
all her assistance in the field and lab. From how to pull start a dead boat to the local lore
of Astoria, I have truly learned a lot working with Lia. I am also very appreciative to
Susan Hinton, George McCabe, and Regan McNatt from NOAA Fisheries, for teaching
me about the estuary and working in the mud. Leonard Ferrington, with the University of
Minnesota Chironomid Research Group, graciously offered to verify some of my
chironomid identifications and advise me in the learning stages of this difficult task.

Financial support for my research and education came from the U.S. Army Corps of
Engineers, Bonneville Power Administration, and the School of Aquatic and Fishery
Sciences.

Finally, I am incredibly grateful for all the support and encouragement over the past few
years from my family and friends.

iv
1
Chapter 1. Introduction

Estuarine ecosystems often are characterized by high primary and secondary
productivity, allowing them to support a great diversity of fish and invertebrate species
(Teal 1962, Odum 1980, Kneib 1997, Simenstad and Cordell. 2000, Beck et al. 2001).
Tidal marshes in particular, produce large amounts of new plant tissue annually, which is
then converted by bacterial decomposition and physical breakdown into organic detritus.
In some estuarine systems marsh-derived detritus is a major food source for the majority
of consumers (Teal 1962), including abundant epibenthic crustaceans and diverse insect
assemblages. Wetland insects play a prominent role in the consumption and processing
of primary production and associated detritus and serve as an important food source for
higher trophic levels, including a large number of fish, invertebrate, and avian species
(Davies 1984, Stagliano et al. 1998). Here I investigate the composition of emergent
insects and their availability to juvenile salmon (Oncorhynchus spp.) in tidal wetlands of
the Columbia River estuary.
Recently, there has been an emerging recognition in the uniformity of wetland
insects in the diets of juvenile Chinook salmon (O. tshawytscha) rearing in estuaries of
the Pacific Northwest. There is, however, a lack of knowledge in the assemblage
structure, particularly within the Chironomidae (Diptera) family, and fine-scale
distribution of these emergent aquatic insects. Studying the patterns and processes of
their spatial and temporal distribution within tidal channel environments provides
important information on the availability of this essential prey resource to juvenile
Chinook salmon. Additionally, changes in the composition of an insect community occur
relatively quickly in time and space, making the group useful in monitoring the
ecological condition of an area simply by examining the insects that live there.
In this study, I focus on identifying patterns of insect emergence from tidal
wetlands of the Columbia River estuary. I was interested in how assemblages were
structured, with a particular emphasis on the chironomid family, and how the taxonomic
composition changed over both spatial and temporal scales. Further, I address questions
on the availability of these insects to juvenile Chinook salmon rearing in the estuary.
2
Availability may be enhanced in areas through the movement of wetland insects across
aquatic boundaries, potentially serving as a subsidized resource in open water habitats
away from where the insect was produced. Alternatively, their availability to juvenile
Chinook may be limited through such factors as synchronized daily patterns in
emergence or associations with inaccessible microhabitats.
The work presented here on aquatic insect emergence and availability is nested
within the larger research led by the National Oceanic and Atmospheric Administration
(NOAA) and University of Washington on population dynamics and habitat use of
juvenile Chinook salmon in the freshwater tidal marshes of the Columbia River. The
importance of Northwest estuaries as nursery habitat for juvenile salmon and other
nekton is well established in the literature (Healey 1982, Levy and Northcote 1982,
Simenstad et al. 1982, Kneib 1997, Beck et al. 2001). In addition to providing a
connection in the landscape between freshwater spawning and rearing grounds and the
nutrient rich marine waters of the Pacific Ocean, estuaries reportedly offer abundant
feeding opportunities, refuge from marine predators, and a physiological transition zone
where juvenile fish may acclimate to saline waters (Simenstad et al. 1982, Thorpe 1994,
Bottom et al. 2005). This study developed in response to questions related to this specific
aspect of abundant foraging opportunities, with numerous previous reports highlighting
the importance of wetland insects in the diets of juvenile Chinook salmon during their
migration through and residency in many coastal estuaries (Simenstad et al. 1982)
including those of the Fraser River (Levy et al. 1979, Levy and Northcote 1982),
Puyallup River (Shreffler et al. 1992), Salmon River (Gray et al. 2002), and Columbia
River (Lott 2004).
Among wetland insects consumed by juvenile Chinook, the Chironomidae, a
family of small aquatic flies, compose a large proportion, both numerically and
gravimetrically, of the diets of fish caught within a variety of wetland ecosystem types
(Simenstad and Cordell 2000, Lott 2004, Gray 2005). Indices of Relative Importance
(IRI) were shown to reach as high as 90% in an emergent marsh of the Columbia River
estuary for the chironomid family (Lott 2004). The IRI is a compound index that
describes the relative contribution of stomach contents to the diet (Pinkas et al. 1971).
3
This index is often used in many diet studies and facilitates comparisons among food
types (Cortes 1997). Additionally, Lott (2004) noted the significant observation of the
apparent targeting by juvenile Chinook salmon of the specific ‘emergent’ life stage in
chironomids from tidal marsh channels (Lott 2004). As opposed to feeding on adults
floating on the water’s surface, this behavior directly links the predator to the prey’s
habitat of origin.
Recent studies, however, have expanded our understanding of the importance of
wetland insects by demonstrating their contribution to consumers beyond their site of
origin. These insects, again particularly chironomids and other dipteran flies, constitute
at times the majority of prey in the diets of juvenile Chinook caught in open water
habitats, for example along mainstem beaches and in large distributary sloughs of the
Columbia River estuary (Bottom et al. 2008). Furthermore, an earlier study from the
Fraser River estuary, found chironomids in 31% of juvenile Chinook stomachs caught up
to 300 m offshore (Whitehouse et al. 1993). Such findings demonstrate the widespread
significance of wetland insects throughout the broader range of these estuarine systems.

Chironomidae
Chironomids, commonly known as midges, contribute to the food of an extensive
range of both small and large predators throughout all stages of their life cycle (Armitage
1995), and are especially important to waterfowl and waders (King and Wrubleski 1998,
Einarsson and Gardarsson 2004, Smith et al. 2007) and a vast number of fish species
(Mundie 1971, Jackson and Fisher 1986, Merz 2002, Lott 2004). The family is regularly
reported as the dominant insect group from wetland (Wrubleski 1987, Leeper and Taylor
1998, Stagliano et al. 1998, Whiles and Goldowitz 2001, MacKenzie and Kaster 2004)
and estuarine (Williams and Williams 1998a, Strayer and Smith 2000, MacKenzie 2005)
systems. They are the most widespread of all aquatic insect families, occurring on all
continents (Ferrington 2008). Chironomids are also exceptionally diverse, with estimates
as high as 15,000 species, and select taxa within the family are identified as able to
tolerate most climates and conditions, including a wide array of water quality (Cranston