NORTH PACIFIC RESEARCH BOARD PROJECT FINAL REPORT
Gulf of Alaska Long-term Observations: the Seward Line
NPRB project 520 & 603
Russell R. Hopcroft, Kenneth O. Coyle,
Thomas J. Weingartner, Terry E. Whitledge
Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK
99775-7220. (907) 474-7842 hopcroft@ims.uaf.edu
December 2007
1
Abstract
Long times-series are required for scientists to tease out pattern and cause from simple year-to-year
variability. In 2005, 2006 and early 2007, we continued multi-disciplinary oceanographic observations
begun in 1998 in the northern Gulf of Alaska. Cruises occurred each year, in early May and early
September, to capture the typical spring bloom and summer conditions, respectively, along a 150 mile
transect across shelf to the south of Seward, Alaska. We determined the physical-chemical structure,
primary (algal) production and the distribution and abundance of zooplankton, along with their seasonal
and inter-annual variations, to understand how different climatic conditions influence the biological
condition in each year. To date, we have observed both extremely warm years where spring zooplankton
biomass was low, and extremely cold years where spring biomass was high. Spring 2007 appears to be
the coldest since the 1970s. We have also observed seasonal invasion of more southern species during
warm years such as 2005. Popular climatic indices do not fully predict these patterns. Our observations
continue to show that spring and summer zooplankton biomass, as well as community composition, are
correlated with hatchery-released Pink Salmon survival in this region.
Key Words
Gulf of Alaska, Alaska Coastal Current, physical oceanography, chemical oceanography, biological
oceanography, nutrients, primary production, phytoplankton, chlorophyll, zooplankton
Citation
Hopcroft, R.R., Coyle, K.O., Weingartner, T.J., and Whitledge, T.E. 2007. Gulf of Alaska Longterm Observations: the Seward Line, Anchorage. 38p.
2
Table of Contents
Abstract
…2
Study Chronology
…5
Objectives
…7
Methods
…8
Results
…11
Discussion
…31
…33
Projections for 2008
Conclusions
…34
Publications
…34
Outreach
…35
Acknowledgements
…35
References
…36
Table of Figures
Fig.1. Anomalies from the long-term mean for the (a) PDO, (b) the CalCOFI zooplankton
displacement, (c) Spring Chinook salmon survival for Oregon and Washington States
and (d) the contribution of sub-arctic copepods to the copepod community off Newport
Oregon (modified from Peterson and Schwing 2003)
…6
Fig. 2. Anomalies of winter sea-surface temperature (SST – top panels), atmospheric sea-level
pressure and wind velocities (lower panels) in the Pacific Ocean for (a) the new regime
in 1999-2001, (b) the pre 1976 regime shift and (c) post 1976 regime shift (from
Peterson and Schwing 2003)
.
Fig. 3. LTOP stations. In addition basic sampling, purple stations have primary production and
zooplankton growth or reproduction incubations. Grey stations occupied only if time
permits
…7
Fig.4. A) The El Niño Southern Oscillation (ENSO) and B) Pacific Decadal Oscillation (DFO)
indices. C) The average salinity and temperature of the upper 100m along the Seward
Line in May.
…12
Fig.5. Temperature and salinity profiles at Gak1 for May and September of sampling years
compared to the long-term means and their standard deviations.
…13
Fig.6. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the
Seward Line May 8-12, 2005
…14
3
…8
Fig.7. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the
Seward Line Sept 9-12, 2005
…14
Fig.8. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the
Seward Line May 8-12, 2006
…15
Fig.9. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the
Seward Line Sept 14-19, 2006
Fig.10. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the
Seward Line May 7-11, 2007
15
…16
Fig. 11. Intregated chlorophyll a concentration in the upper 50m of the Seward Line Duing A)
Mayand B) early September.
…16
Fig 12. Surface concentrations of nitrate along the Seward Line during A) 2005 B) 2006.
…17
Fig.13. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS
collections during May 2005
…18
Fig.14. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS
collections during May 2006
…19
Fig.15. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS
collections during September 2005
…20
Fig.16. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS
collections during September 2006
…21
Fig.17. Abundance and biomass of zooplankton along the Seward Line in the Quadnet
collections during May 2005.
…22
Fig.18. Abundance and biomass of zooplankton along the Seward Line in the Quadnet
collections during May 2006.
…23
Fig.19. Abundance and biomass of zooplankton along the Seward Line in the Quadnet
collections during September 2005.
Fig.20. Abundance and biomass of zooplankton along the Seward Line in the Quadnet
collections during September 2006.
…24
Fig.21. Abundance of the dominant copepod species along the Seward Line during May. Upper
5 panels from MOCNESS collections, lower 3 panels form 150µm quadnet 95%
confidence errors are indicated for the long term mean (red symbol, green bar) and
each year (black).
…26
Fig.22. Stage distribution of the Neocalanus copepods along the Seward Line during May.
…27
4
…25
Fig.23. Abundance of the pteropod Limacina helicina and the larvacean Oikopleura along the
Seward Line during May from Quadnet collections.
…27
Fig.24. Abundance of the two most dominant zooplankters in Quadnet collections along the
Seward Line during late summer.
…28
Fig.25. Abundance of southern affinity zooplankters in Quadnet collections along the Seward
Line during late summer.
…28
Fig 26. Clutch size, length and weight specific reproductive rate of Pseudocalanus females
along the Seward Line
…29
Fig 27. Clutch size, length and weight specific reproductive rate of Pseudocalanus mimus
females along the Seward Line
…30
Fig.27. Survival of Prince William Sound hatchery Pink Salmon referenced to year of release
(2006 data is preliminary). Data provided by Lew Halderson.
…33
Study Chronology
Year
Date
Event
2005
April
Project funded
May 8-12
First cruise R/V Thompson
July 2005
First Progress Report
September 9-14
Second cruise M/V Tiglax
December
Project renewed
March
Second Progress Report
May 14-18
Third cruise R/V Thompson
July
Third Progress Report
September 13-18
Fourth cruise M/V Tiglax
March
Fourth Progress Report
May 6-11
Fifth cruise M/V Tiglax
July
Fifth Progress Report
December
Final Report
2006
2007
5
Introduction
We now recognize that we live in a constantly changing world, driven by a combination of stochastic
events, natural cycles, longer-term oscillations, and the accelerating impact of human activities. Where
we once thought the oceans housed relatively stable ecosystems, in the last decade we have come to
appreciate that they fluctuate between multiple states or “regimes” apparently coupled to major climatic
shifts such as the Pacific Decadal Oscillation (PDO). This appreciation has come initially from long-term
and more global views of the physical changes in the ocean and atmospheric, but most importantly from
long-term biological observations that have demonstrated the impact of “regime shifts” (Francis & Hare,
1994; Manuta et al., 1997). We are now beginning to recognize that such events may be common (Hare
& Mantua, 2000), and we are just beginning to appreciate the mechanisms by which these physical
changes impact ecosystems (McGowan et al., 1998; Beaugrand, 2004).
Our understanding of community level changes would not be possible without long-term observation
programs (LTOPs), whose value has not been fully appreciated until recently (Nisbet 2007, Editor, 2007).
Biological time-series such as CalCOFI (e.g. Roemmich & McGowan, 1995) and Station/Line P (Mackas
et al., 2004) in the North Pacific, and the CPR series in the North Atlantic (Richardson & Schoeman,
2004) are proving invaluable at documenting the shifts in species distributions (Beaugrand & Ibanez,
2002; Beaugrand & Reid, 2003) and timing of life histories (Mackas et al., 1998; Edwards & Richardson,
2004). Understanding how
complex pelagic ecosystems
work, and how they might be
affected by climate change
was the most fundamental
goal of the Global
Ecosystem Dynamics
(GLOBEC) that has now
ended its field sampling
phase. One of the core
hypotheses of that program
revolved around the
observed out-of-phase
covariance of the production
regimes by zooplankton
Fig.1. Anomalies from the long-term mean for the (a) PDO, (b) the CalCOFI
zooplankton displacement, (c) Spring Chinook salmon survival for Oregon and
(Brodeur et al., 1996), and
Washington States and (d) the contribution of sub-arctic copepods to the copepod
community off Newport Oregon (modified from Peterson and Schwing 2003)
the fish populations such as
6
salmon that feed on them (Hare et al., 1999).
The Gulf of Alaska GLOBEC program began its sampling activities in October 1997, coincident with
one of the larger El Niño events in recent decades. Observations from sampling programs around
Vancouver and to the south suggest this may also have represented the transition to a new regime in the
North Pacific (Fig. 1),
corresponding with a change
in the PDO (Fig. 1a), an
increase in zooplankton
volume (Fig. 1b) due to
greater contribution from
more northern species (Fig
1d), and an apparent
improvement in Chinook
survival in Oregon and
Washington states (Fig. 1c).
Fig. 2. Anomalies of winter sea-surface temperature (SST – top panels),
atmospheric sea-level pressure and wind velocities (lower panels) in the
Pacific Ocean for (a) the new regime in 1999-2001, (b) the pre 1976 regime
shift and (c) post 1976 regime shift (from Peterson and Schwing 2003).
Based on our understanding
of the 1976 regime shift
which resulted in a profound
shift in Alaska from a shrimp dominated fisheries to one dominated by pollock, salmon and halibut
(Francis & Hare, 1994), there was concern that Alaskan fisheries might return to such a pre-1976 state.
However, unlike the pre-1976 regime (Fig. 2b) the new regime is characterized by two nodes of
atmospheric pressure over the North Pacific Ocean (Bond, 2003; Fig. 2a) that appears to maintain warm
water anomalies in the coastal Gulf of Alaska and the Bering Sea (Peterson & Schwing, 2003). More
recent data suggests this “shift” may not be as definitive as initially believed. If this is true, then it is
difficult to predict what biological changes might occur in Alaskan waters, and how this might impact
fisheries. Continued observations are therefore necessary to observe the state of this ecosystem and
assess the impact the ongoing changes in the North Pacific.
Objectives
The scientific purpose of this project is to develop an understanding of the response of this marine
ecosystem to climate variability. Toward this end, the Seward Line cruises on the Gulf of Alaska shelf
determined the physical-chemical structure, primary production, the distribution and abundance of
zooplankton, and growth or reproduction of key zooplankton species, along with their seasonal and interannual variations in 2005 and 2006.
7
Specifically, we:
1. Determine thermohaline (temperature & salinity), and nutrient structure of the Gulf of Alaska shelf,
emphasizing Seward Line, and Prince William Sound stations.
2. Determine primary production and phytoplankton biomass distribution.
3. Determine the distribution and abundance of zooplankton.
4. Determine copepod rates of somatic growth and egg production for selected species
Methods
General Considerations
For a long-term observation series, one of the most critical requirements is consistency of sampling
locations, timing of observations and methodology. We employed the same set of 13 primary stations
(~18km spacing) and 9 intermediate stations along the Seward Line sampled by the GLOBEC program,
which extends from the coast, across the shelf break, to the inner portion of the Alaska Stream (Fig. 3).
The 3 Knight Island Passage stations within Prince William Sound represent key “upstream” sources to
also be sampled. Dependent on the sampling platform, sampling was conducted on 4-6-day cruises in
May and September of each year.
Timing of May cruise was consistent
with GLOBEC cruise timing, while
September sampling occurred 2-4 weeks
later than GLOBEC, a delay imposed
due to the timing of ship availability.
Oceanographic sampling methodology
was nearly identical to that employed by
the previous 7 years of the Gulf of
Alaska GLOBEC LTOP program (i.e.
U.S. GLOBEC, 1996; Weingartner et al.,
Fig. 3. LTOP stations. In addition basic sampling, purple stations
have primary production and zooplankton growth or reproduction
incubations. Grey stations occupied only if time permits.
2002), although reduced in breath of
some measurements.
Physical, Chemical, and Phytoplankton
A Seabird SBE 911 CTD with fluorometer and transmissivity, PAR, was logging real-time was
employed on May 2005 & 2006 cruises (R/V Thompson). A SBE 19 with fluorometer and PAR was
employed on Sept 2005 & 2006 cruises operating in logging mode due to lack of a conduction cable. The
availability of a conducting cable in May 2007 again allowed real-time data logging. Discrete bottle
samples for nutrients and chlorophyll where taken with either 5 or 10L Niskin Bottle Rosette, and
8
operated through a Seabird AFM during September 2005 & 2006. Surface measurements of temperature,
salinity, fluorescence and water column velocities were collected and logged automatically by the
Thompson’s underway sampling system, were not available on Tiglax cruises.
Nutrient measurements were made onboard during Thompson cruises using an Alpkem Rapid Flow
Analyzer (Whitledge et al., 1981) and conform to WOCE standards (Gordon et al., 1993). Nutrients were
frozen on other cruises and analyzed soon after each cruise. Chlorophyll a concentrations were measured
at all stations, typically at 0, 10, 20, 30, 40 and 50 m, collected from rosettes on upcasts. Additional
chlorophyll depths were sampled inconjunction with primary production (PP) stations, Gak 1, 4, 9, 13 and
KIP2. Size fraction was conducted at 10 m for primary stations, and PP stations. Extracted chlorophyll a
was determined fluorometrically post-cruise (Parsons et al., 1984).
Daily measurement of primary production rates was estimated for large (>20 µm) and small (< 20
µm) size classes by the modified 14C-uptake technique (Parsons et al., 1984). Primary production
estimates were made at the 4 stations along the Seward Line, plus one in the sound. Water samples
inoculated with 13C-labeled Na2CO3 were incubated in 1-liter polycarbonate bottles under natural light ondeck. Following the incubations, both light and dark bottles were filtered, purged of inorganic carbon, and
analyzed by mass spectrometry. Hourly and daily estimates of primary production rates were calculated
for each sampled site. Concurrent assessments of phytoplankton nutrient utilization were performed using
amendment bioassays (nitrogen, phosphorus and silicate) and trace metals. Emphasis was placed on iron
enrichments in order to assess potential effects on primary productivity rates. Particulate carbon and
nitrogen samples were obtained for each productivity sample.
The physical (including transmissivity and PAR) and chemical data was used to quantify the seasonal,
interannual, and along- and cross-shelf distributions of water masses, their variability, and to aid in
interpreting zooplankton distributions. The ADCP data was used to describe vertical and horizontal shears
and convergences, which are valuable in understanding the dynamical structure of the flow (Danielson et
al., 1999). These structures, in conjunction with surface measurements, are especially helpful in
interpreting biological features and patch sizes (Coyle et al., 1998). Data was used along with historical
data from this region (i.e. Seward Line data plus temperature and salinity record at GAK1 since 1970) to
examine spatial and temporal variations in both physical and chemical variables and processes.
Interdecadal time scales are addressed through the use of sea surface temperatures (available from Scripps
since 1947), Sitka air temperatures (since 1828), upwelling indices (from the Pacific Oceanographic
Group/NOAA since 1946), the Pacific Decadal Oscillation (since 1900), oceanographic buoy data (from
NOAA since ca. 1975) and the EVOSTC-supported continuous measurements at GAK 1.
9
Zooplankton
Plankton nets: Day time zooplankton samples were collected with a Quadnet consisting of 25 cm
diameter nets of 1.6 m length equipped with GO flowmeters. A pair of these nets were constructed of 0.15
mm mesh and sample small, primarily early copepodid stages of calanoids (e.g., Coyle et al., 1990; Coyle
& Pinchuk, 2003), while nauplii and the smallest copepodid stages of neritic species were sampled with
the pair constructed of 0.05 mm mesh. The tows were made from 100 m to the surface at the 13 stations
along the Seward Line, plus the 3 stations within Prince William Sound. At these same stations a 1-m2
MOCNESS system (on Thompson cruises) or 0.25 m2 Hydrobios Multinet system (Tiglax cruises), both
with 0.5 mm mesh nets, were fished at night to assess large zooplankton and micronekton, such as
euphausiids, that are important components in the diet of many fish, sea-birds and marine mammals. The
MOCNESS is equipped with nine nets that were opened and closed electronically from the deck, while
the 5 nets on the Multinet could also be programmed to fire automatically at specific depths. At each
station, 5 samples were collected at 20 m depth intervals from 100 m depth to the surface, with typically
~150 m3 of water filtered by each net. Additional collections were made to 600 m at Gak13 and PWS2 to
assess over-wintering populations of Neocalanus spp. The MOCNESS simultaneously records depth,
salinity, temperature, net angle, flow meter counts, volume filtered, latitude, longitude, and GMT time at
2 second intervals, while the Multinet only records depth and flow meters. All samples were preserved in
10% formalin for later analysis by LTOP methods to the lowest taxonomic category possible.
During sample processing, all larger organisms (primarily shrimp and jelly fish) were removed and
enumerated, then the sample was Folsom split until the smallest subsample contained about 100
specimens of the most abundant taxa. The most abundant taxa were identified, copepodites staged,
enumerated and weighed. Each larger subsample was examined to identify, enumerate and weigh the
larger, less abundant taxa. Blotted wet weights of all specimens of each taxa and stage were taken on each
sample until the coefficient of variation for any given taxa and stage changed by less than 5%, after which
point the wet weight biomass was estimated by multiplying the specimen counts by the mean wet weight.
In practice, only calanoid copepods have consistent wet weights after weighing each taxa and stage in
about 10-15 samples; wet weights on euphausiids, shrimp and other larger taxa were always measured
and recorded individually for each sample. Wet weight measurements were generally taken to ±1 μg on a
Cahn Electrobalance. The data was uploaded to a Microsoft Access database for sorting and analysis. At
present, multidimensional scaling of percentage dissimilarities between samples has proven an effective
method of revealing cross-shelf patterns (Coyle & Pinchuk, 2005).
Growth/reproduction Studies of growth and reproduction targeted the large Neocalanus spp. the
dominate the spring, and smaller Pseudocalanus species that dominate late summer and fall (Coyle &
10
Pinchuk, 2003). Both were collected using fine mesh nets at the process stations spaced along the Seward
Line, plus one inside the sound, as was done in the GLOBEC program (e.g. Napp et al., 2005; Liu &
Hopcroft 2006a). For Pseudocalanus, we monitored egg production, because it appears to be reflective of
growth in most developmental stages in this system (Liu & Hopcroft, unpublished), and generally reflects
the current food climate (Runge & Roff, 2000). For these experiments, 100 females representing a
mixture of the 2 species were incubated individually in 70 ml flasks, and the number of eggs produced
over each of 2 days was determined (Napp et al., 2005). In contrast, Neocalanus only spawn at great
depth during the winter months, thus we must directly assess the growth rates. In their case, single stages
of Neocalanus flemingeri/plumchrus were selected and incubated at low densities in 20L carboys (with
natural food concentration) for 5 days, harvested, preserved, and the increase in stage and size later
determined from the samples (Liu & Hopcroft 2006a).
Results
Physics
The Seward Line observations are largely restricted to the periods where the both ENSO (Fig 4a) and
PDO (Fig 4b) have been undergoing changes. In terms of average May temperature and salinity averaged
over the upper 100m across the Seward Line, 2005 and 2006 appear roughly comparable to other years
while 2007 is anomalously cold (Fig. 4c). Looking specifically at Gak1, where data exist back to the
1970s, May 2005 had surface water that was warmer and more stratified than typical for May (Fig. 5b),
and these conditions persisted through September (Fig.5b), 2006 was relatively typical of the long-term
means (Fig. 5c,d), while Spring 2007 temperatures were anomalously cold (Fig. 5e), colder than any year
since the early 1970s. The early spring 2007 (March and April) water column was less stratified than
normal suggesting low winter runoff, strong winter mixing and anomalously high salinities at the surface
and low salinities at depth. [Anomalously low temperatures have persisted below 100 m through
September (Fig. 5f) and into December 2007 (at least) and these cold temperatures along with an evolving
La Niña in the Pacific and a negative Arctic Oscillation suggest that GOA shelf temperatures will remain
anomalously low through spring 2008.] Cross shelf profiles of temperature, salinity and density, support
these general patterns, and illustrate the relatively cool, and weakly stratified, conditions during spring
compared to the strongly stratified conditions during late summer (Fig. 6-10)
11
A
summer PDO
15
WARM
COOL
WARM
?
10
B
5
0
-5
a
-10
1940
1950
1960
1970
1980
1990
2000
C
Fig.4. A) The El Niño Southern Oscillation (ENSO) and B) Pacific Decadal Oscillation (DFO) indices.
C) The average salinity and temperature of the upper 100m along the Seward Line in May.
Chlorophyll and nutrients
Measurements of chlorophyll over the time-series reveal the brief and transitory form of the spring
bloom in the Gulf of Alaska (Fig. 11a), and the generally lower concentration of chlorophyll during late
summer (Fig. 11b). Few of the May cruises over the past decade have captured the spring bloom with the
exception of May 2002, and to a lesser extent May 1999 and May 2004, all of which were characterized
by cool surface waters with poor stratification that significantly delayed the spring bloom. The very low
concentration of nitrate in surface waters during May 2005 (Fig. 12a) confirms the bloom has already
occurred. In contrast, the high concentration of nitrate in May 2006, and low concentrations of
chlorophyll, indicate the bloom had yet to occur. Nutrient concentrations during May 2007 are not yet
available (part of project 708), but cold temperatures and intermediate chlorophyll suggest that we are
12
Fig.5. Temperature and salinity profiles
at Gak1 for May and September of
sampling years compared to the longterm means and their standard
deviations.
only observing the beginning of the spring bloom. This is supported by the higher “bloom”
concentrations of chlorophyll observed within Prince William Sound during May 2007 than observed
across the Seward Line: in all years the sound blooms prior to the Seward Line.
Nutrient concentrations during September 2005 are low (Fig. 12b), and consistent with expected
nutrient limitation during summer stratified conditions. In contrast, the higher nutrient concentrations
during September 2006, suggest storms have already begun the mixing normally characteristic of the fall
period.
13
Fig.6. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the Seward
Line May 8-12, 2005
Fig.7. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the Seward
Line Sept 9-12, 2005
14
Fig.8. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the Seward
Line May 8-12, 2006
Fig.9. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the Seward
Line Sept 14-19, 2006
15
Fig.10. Cross-shelf sections of temperature, salinity and inferred geostrophic velocity across the Seward
Line May 7-11, 2007
13
B
A
Chloro
-2
(mg m )
12
0
50
100
150
200
250
300
11
Seward Line Station
10
9
8
7
6
5
4
3
2
1
1998
1999
2000
2001
2002
2003
2004
2005
1998
2006
1999
2000
2001
2002
2003
2004
2005
2006
Fig.11. Intregated chlorophyll a concentration in the upper 50m of the Seward Line Duing A) May and B)
early September.
16
16
16
Nitrate (µM)
14
A
May 2005
Sept 2005
14
12
12
10
10
8
8
6
6
4
4
2
2
B
May 2006
Sept 2006
0
0
1
2
3
4
5
6
7
8
9
10
11
12
1
13
2
3
4
5
6
7
8
9
10
11
12
13
GAK Station
GAK Station
Fig.12. Surface concentrations of nitrate along the Seward Line during A) 2005 B) 2006.
Zooplankton
Larger zooplankton collected with the MOCNESS, show the night-time communities characteristic of
the Gulf of Alaska, with May samples dominated numerically and in biomass by Neocalanus species,
Metridia pacifica, and Calanus marshallae (Fig. 13, 14), and September samples dominated by Metridia
pacifica, Calanus sp., Eucalanus bungii, and euphausiids (Fig. 15, 16). It is notable that in both
Septembers, the more southern Calanus pacificus were obvious in most offshore samples, while in
September 2005 warmer-water salps were also obvious in most offshore samples.
Collections from the finer- meshed Quadnets made during daytime give a slightly different
impression of community composition, with May samples dominated numerically by Oithona similis,
Pseudocalanus spp. and calanoid nauplii, while biomass continues to show a dominance of Neocalanus
species, and Calanus marshallae, but with significant contribution by Pseudocalanus spp. (Fig. 17, 18). It
is notable, but expected, that the strong diel migratory Metridia pacifica was not dominant in daytime
collections. In September, samples remained numerically dominated by Oithona similis, Pseudocalanus
spp., but biomass then showed a dominance of Pseudocalanus spp., with notable contribution by Oithona
similis, as well as Calanus sp. (Fig. 19, 20). Calanus pacificus’s occurrence offshore was consistent
MOCNESS observations.
17
Fig.13. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS collections
during May 2005
18
Fig.14. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS collections
during May 2006
19
Fig.15. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS collections
during September 2005
20
Fig.16. Abundance and biomass of zooplankton along the Seward Line in the MOCNESS collections
during September 2006
21
Fig.17. Abundance and biomass of zooplankton along the Seward Line in the Quadnet collections during
May 2005.
22
Fig.18. Abundance and biomass of zooplankton along the Seward Line in the Quadnet collections during
May 2006.
23
Fig.19. Abundance and biomass of zooplankton along the Seward Line in the Quadnet collections during
September 2005.
24
Fig.20. Abundance and biomass of zooplankton along the Seward Line in the Quadnet collections during
September 2006.
25
Like all biological communities, we observed changes in abundances of species between years.
Viewed over the entire GLOBEC-NPRB period, several species-specific patterns are notable. From May
observations, of the large copepods that dominate the spring, the largest, Neocalanus cristatus, shows no
significant pattern across years, while the slightly smaller N. plumchrus/flemingeri show significantly
higher abundances in 3 years and lower abundances in 3 years, with 2006 along with 1998 and 2002
representing a “good” year (Fig. 21). Similarly, Eucalanus bungii, and Metridia pacifica, show significant
variation between years, while Calanus marshallae shows large increases in abundance during 2005&
2006. Smaller species (i.e. Oithona, Pseudocalanus, Acartia) are also variable, but there appears to be
little consistency in pattern between species. Although warm years may not always affect abundance, they
do affect growth rates & passage of stages through the ecosystem (Fig. 22), with both good years for N.
plumchrus/flemingeri since the change in sign of the PDO (i.e. 2002 & 2006) having delayed
180
18
140
120
100
80
60
40
20
0
14
12
10
8
6
4
2
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
140
25
20
15
10
5
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
2004
2005
2006
1998
1999
2000
2001
2002
2003
2004
2005
2006
Calanus marshallae (May MOC)
120
Mean Abundance (No m-3)
100
80
60
40
20
80
60
40
20
0
0
1998
1999
2000
2001
2002
2003
2004
2005
1998
2006
3000
1999
2000
2001
2002
2003
5000
Pseudocalanus spp. (May vert)
Mean Abundance (No m-3)
2500
2000
1500
1000
500
0
400
Oithona similis (May vert)
300
Mean Abundance (No m -3)
Mean Abundance (No m -3)
Eucalanus bungii (May MOC)
30
100
Metridia spp. (May MOC)
Mean Abundance (No m-3)
35
16
Mean Abundance (No m -3)
Mean Abundance (No m-3)
Mean Abundance (No m -3)
Neocalanus cristatus (May MOC)
N. plumchrus & N. flemingeri (May MOC)
160
4000
3000
2000
1000
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
Acartia spp. (May vert)
200
100
75
50
25
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
1998
1999
2000
2001
2002
2003
2004
2005
2006
Fig.21. Abundance of the dominant copepod species along the Seward Line during May. Upper 5 panels
from MOCNESS collections, lower 3 panels form 150µm quadnet 95% confidence errors are indicated
for the long term mean (red symbol, green bar) and each year (black).
26
60
20
0
Stg3
40
Stg4
20
80
Stg3
Stage4
40
Stage5
60
Neocalanus cristatus
100
Percentage Stage
80
Neocalanus plumchrus/flemingeri
Stage5
Percentage Stage
100
0
1998 1999 2000 2001 2002 2003 2004 2005 2006
1998 1999 2000 2001 2002 2003 2004 2005 2006
Fig.22. Stage distribution of the Neocalanus copepods along the Seward Line during May.
1400
800
700
1200
1000
Mean Abundance (No m-3)
Mean Abundance (No m-3)
Limacina helicina
Inner
Trans
Outer
PWS
800
600
400
200
Oikopleura spp.
600
Inner
Trans
Outer
PWS
500
400
300
200
100
0
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
1998
1999
2000
2001
2002
2003
2004
2005
2006
Fig.23. Abundance of the pteropod Limacina helicina and the larvacean Oikopleura along the Seward
Line during May from Quadnet collections.
development, while two of the three years in between had accelerated development. When development is
delayed, Neocalanus remain in the surface waters longer before completing the growth phase of their life
cycle and descending to depth, making them available longer to their potential predators. In contrast, there
appears to be no relationship between population abundance and developmental stage in N. critatus.
Of the mucus-net feeders recently implicated as important items in the diets of juvenile Pink Salmon,
it is notable that in May, Limacina helicina abundance has been increasing significantly since 2003 in all
domains along the Seward Line, while Oikopleura spp. has shown no systematic pattern (Fig 23).
Similar to observations from May, during September zooplankton communities show notable year-toyear variation, as seen for example in the numerically dominant Oithona similis and Pseudocalanus spp.
27
(Fig 24). In cases such as these, there are no clear relationships to environmental parameters. The more
interesting patterns during late summer appear primarily in less common, and in particular species with
warmer water and more “southern” affinities. During the warm summer of 2005, the small southern
species Paracalanus parvus, became unusually common along the Seward Line, while the southern
Calanus pacificus has been increasingly common during the warm summers of 1998, 2003, 2005 & 2006
(Fig 25). Similarly, the copepods Mesocalanus tenucornis, and Clausocalanus spp, as well as salps are
3500
3500
3000
3000
Pseudocalanus spp.
Mean Abundance (No m-3)
Mean Abundance (No m-3)
more likely to be encountered during warmer summers (not shown).
2500
2000
1500
1000
500
2500
2000
1500
1000
500
Oithona similis
0
0
1998
1999
2000
2001
2002
2003
2004
2005
1998
2006
1999
2000
2001
2002
2003
2004
2005
2006
Fig.24. Abundance of the two most dominant zooplankters in Quadnet collections along the Seward Line
during late summer.
500
40
Mean Abundance (No m -3)
Mean Abundance (No m-3)
Paracalanus parva (Summer vert)
400
300
200
100
Calanus pacificus (Summer vert)
30
20
16
12
8
4
0
0
1998
1999
2000
2001
2002
2003
2004
2005
2006
1998
1999
2000
2001
2002
2003
2004
2005
2006
Year
Fig.25. Abundance of southern affinity zooplankters in Quadnet collections along the Seward Line during
late summer.
28
60
Pseudocalanus newmanii
PWS
Gak1
Gak4
Gak9
Gak13
Clutch size
50
40
30
20
10
Prosome Length (mm)
0
1.2
1.0
0.8
-1
Population SEP (% d )
0.0
36
32
28
24
20
16
12
8
4
0
May
Aug
2001
May
Aug
2002
May
Aug
2003
May
Jul
2004
May Sept May Sept
2005
2006
Fig 26. Clutch size, length and weight specific reproductive rate of Pseudocalanus newmanii females
along the Seward Line
29
50
Pseudocalanus mimus
PWS
Gak1
Gak4
Gak9
Gak13
Clutch size
40
30
20
10
Prosome Length (mm)
0
1.2
1.0
0.8
-1
Population SEP (% d )
0.0
36
32
28
24
20
16
12
8
4
0
May
Aug
2001
May
Aug
2002
May
Aug
2003
May
Jul
2004
May Sept May Sept
2005
2006
Fig 27. Clutch size, length and weight specific reproductive rate of Pseudocalanus mimus females along
the Seward Line
30
In terms of growth rates, Neocalanus plumchrus/flemingeri Stage 4 copepodites had an average
growth rate of 10% per day (SE of 1%), and stage duration averaged 8.5 days (SE of 1.3 days) in 2005,
with growth notably slower and development time longer than the rest of the Seward Line. Both these
rates suggest slightly faster growth and development than other years, consistent with the warmer surface
water temperatures of May 2005. In contrast, N. plumchrus/flemingeri C3 and C4 had an average growth
rate of only 4% per day (SE of 1%), and stage duration averaged 34.6 days (SE of 10.7 days) in 2005.
Although these rates are generally consistent with growth patterns established for this species along the
Seward Line once corrected for incubation temperature (Liu & Hopcroft, 2006), 2006 appears
comparatively low for reasons that are still unclear. The reproductive patterns of both Pseudocalanus
species were generally consistent with other years (Fig 26, 27), with clutch size and prosome length of
females greater in May than summer/fall, but weight-specific egg production showing far less seasonal
modulation. May 2005 had higher rates of reproduction than May 2006 for both Pseudocalanus species,
likely due to the warmer temperatures in May 2005.
Biological sample processing for the May 2007 cruise is occurring under project 708, and is currently
in progress. Semi-quantitative impressions from live collections indicate that the zooplankton
communities were substantially retarded in their development in comparison to previous years. For
example, the mean developmental stage of Neocalanus species were at least one, if not 2 stages, behind
their normal status for May, with C5s being very uncommon over the shelf, but more abundant off the
shelf. Females of Pseudocalanus spp. were also extremely rare compared to earlier stages. This delayed
development is consistent with the lower than normal temperatures, and more similar to what was
observed for the April period during the GLOBEC sampling years. It is unclear what consequences this
will have for higher trophic levels, but we speculate that the peak of zooplankton biovolume (as measured
by the Prince William Sound hatcheries) has occurred much later than normal in 2007.
Discussion
The first extensive overview of the Gulf of Alaska (Hood & Zimmerman, 1986) now seems dated.
Observations over the past decade, many arising from the GLOBEC program (Weingartner et al., 2002)
have fundamentally revised our understanding of the coastal Gulf of Alaska ecosystem and allow us an
appreciation of not only its major properties, but also their inter-annual variability (Spies 2007). The
general behaviors of this ecosystem in terms of physics (Weingartner 2007), chemistry (Childers et al.
2005), and zooplankton communities (Coyle & Pinchuk, 2003, 2005) have been described from the first
phase of the GLOBEC program, and there is no need to repeat such information here. The goal of this
report is to highlights some of the newer observations and insights collected over the past few years, and
31
in particular place 2005 & 2006 in the context of the past decade of observations. It is also important to
state that observations along the Seward Line, remain very much an ongoing effort as this report is being
prepared.
When this project began in 2005, both atmospheric indices and observations from other West Coast
LTOP programs were suggesting the 1997 El Niño represented the transition to a new regime in the North
Pacific (Peterson & Schwing, 2003; Batten & Welch, 2004). More recent data from 2003-2007 suggest
this “shift” may not be as definitive as was initially believed, complicated by anomalously warm
conditions during 2005 and 2006 (Mackas et al., 2006, Hooff & Peterson, 2006). In contrast, spring
conditions in 2007 were anomalously cold, and seemly at odds with the existence of a moderate El Niño
occurring early in 2007 which was similar in magnitude to the El Niño in the winter of 2002/2003 that
resulted in the high temperatures during 2003. Nonetheless, this cool spring gave way to warm surface
waters by summer, even though deeper waters remained anomalously cool, with 2007 thus being in sharp
contrast to previous years where a clear long-term warming trend was apparent at depth for Gak1.
Clearly, the relationship between climate indices and conditions in the Gulf of Alaska are much more
complicated than we had begun to believe.
Of the more obvious biological patterns observed, our observations of the “invasion” of more
southern species during warmer years is consistent with observations of other sampling programs to the
south, and particularly observations in the transitions zone near Vancouver Island (Mackas et al., 2004,
2006). Such shifts appear to occur over the entire Gulf of Alaska domain for more oceanic species
(Batten & Freeland, 2007), such as we observed strongly with Calanus pacificus, but such shifts can be
restricted to neritic species (e.g. Paracalanus parvus, Clausocalanus spp.) transported within the rapidflowing Alaska Coastal Current (ACC) that are then sometimes subsequently distributed across the shelf.
The distribution and composition of zooplankton communities is further influenced by the degree to
which the ACC mixes with the “transitional” shelf waters (Coyle and Pinchuk 2005), as well as eddies
that propagate along the shelf break that enhance cross-shelf and oceanic-shelf exchange (Mackas &
Coyle 2005). Warming also has the potential to change important timing aspects of species season cycles
(such as we observe in Neocalanus stages), resulting in increased or decreased population success
(Mackas et al., 1998 & in press), and the degree of match or mismatch between predators and prey
(Edwards & Richardson, 2004). All of these factors have the potential to result in profound change of
ecosystem structure, with consequences to upper trophic levels of commercial and managerial interest.
Thus far, there appears to be no systematic trend in PWS Pink Salmon survival over the past decades
subsequent to the 1976 North pacific regime shift (Fig. 28). Recently, it has been suggested the
availability of preferential prey types for juvenile pinks during August and September (i.e. pteropods and
larvaceans - Armstrong et al., 2005) may be important determinants of juvenile pink survival (Cross et al.
32
2005; Halderson et al., unpublished). While this may prove to be true, our data remains consistent with
the more traditional belief that years of high spring-time Neocalanus abundance often result in higher
pink salmon survival at the critical periods of ocean entry (e.g. Cooney, 1993; Willette et al. 2001).
Therefore, continued monitoring of both physical and biological oceanographic state of the ecosystem
still holds the potential to help predict the success of higher trophic levels thereby aiding in management
decisions.
4
Pink Salmon
Survival
Anomoly (%)
2
0
-2
e
-4
1980
1990
2000
Fig.28. Survival of Prince William Sound hatchery Pink Salmon referenced to year of release (2006
data is preliminary). Data provided by Lew Halderson.
Projections for 2008
As indicated previously, conditions on the Gulf of Alaska shelf in spring 2007 were unusually cold
and salty. Monthly temperatures anomalies at GAK 1 were more than 1oC below normal throughout the
water column. The temperature anomalies were greatest (~1.3oC) at depths deeper than 100 m, with these
represneting the coldest temperatures observed since the mid-1970s. Data from the May 2007 cruise
showed that temperatures were colder inshore than offshore, in sharp contrast to previous years where a
clear long-term warming trend was apparent at depth for Gak1. The vertical salinity distribution in 2007
was also anomalous; salinities were fresher (saltier) below (above) about 150 m depth. The salinity
anomalies imply that stratification of the winter and early spring water column was unusually weak and
favorable to deep mixing. Deep mixing would have increased the supply of nutrients to the euphotic zone
in time for the onset of the spring bloom and would thus have enhanced primary production. On the other
hand the weak vertical stratification would have suppressed primary production because algal cells would
have been mixed below the euphotic zone. Ongoing chemical and biological analysis of samples will soon
allow us to know where these observations occurred relative to the spring bloom.
Observations at GAK 1 through summer and over the shelf during the NPRB September 2007 cruise
indicate that shelf waters below 75 m have remained cooler (by ~1oC) than normal, and that summer
heating and/or ocean advection did not ameliorated the cold anomaly initiated last winter. This suggests
33
that shelf water temperatures will be even colder in spring 2008 than in 2007 since fall temperatures at the
onset of the cooling season are lower than they were in 2006. Moreover, a La Nina is currently
developing in the equatorial Pacific, and the Arctic Oscillation Index is trending to negative values: both
of these broad-scale atmospheric indices tend to be associated with enhanced air-sea cooling and lower
than normal water temperatures in the Gulf of Alaska.
In general, cool springs are correlated with better than average years for Neocalanus
plumchrus/flemingeri. Analysis of 2007 zooplankton samples currently underway may help further
confirm such patterns. Strong years for Neocalanus plumchrus/flemingeri are in turn generally correlated
with above average survival years for juvenile pink salmon. Provided the expected cool conditions in
Spring 2008 do not result in a timing mismatch between the spring bloom and the critical Neocalanus
first-feeding stages, we can expect the pink salmon released in Spring 2008 to have a year of strong
survival.
Conclusions
Long-term observations along the Seward Line continue to advance our understanding of this large
marine ecosystem. A decade of observation not only allows us to recognize the degree to which
observations are typical, or atypical, of the average state of this ecosystem, but to relate such variations
the success of higher trophic levels. We have now reached a level of understanding of this ecosystem
where we can make some educated predictions on its performance several months in advance. Continued
long-term monitoring will be required to confirm, refine, and generate such predictions.
Publications
(most with shared credit: GLOBEC & NPRB)
Liu, H., and Hopcroft, R.R. 2006. Growth and development of Neocalanus flemingeri/plumchrus in the
northern Gulf of Alaska: validation of the artificial cohort method in cold waters. J. Plankton Res.
28: 87-101.
Hopcroft, R.R., Liu, H., and Clarke, C. Growth and development of Neocalanus flemingeri/plumchrus in
the northern Gulf of Alaska: II. lip accumulation in copepodite CV. Planned for second half of
2008
Hopcroft, R.R., Liu, H., Coyle, K.O., Pinchuk, A.I., and Clarke, C. planned. Secondary production of
zooplankton in the northern Gulf of Alaska, 2001-2007. Planned for second half of 2008
Hopcroft, R.R., Napp, J.M., Baier, C.T., and Clarke, C. in prep. Egg production rates of Pseudocalanus
mimus, Pseudocalanus minutus and Pseudocalanus newmani in the Gulf of Alaska. Planned for
first half of 2008. Mar. Ecol Prog. Ser.
Coyle, K.O., Hinkley, S., and Herman, A. planned. Validation of a coupled biophysical model using
GLOBEC - NPRB long-term observations on the northern Gulf of Alaska shelf.
Coyle, K.O., Hopcroft, R.R., and Pinchuk, A.I. planned. Long-term zooplankton abundance, biomass and
species composition on the northern Gulf of Alaska shelf.
34
Coyle, K.O., Hopcroft, R.R., Weingartner, T.J., Whitledge, T.E., Lessard, E.D., Strom, S.L., Dagg, M.J.,
and Napp, J.M. planned. Mechanistic links between climate forcing and the ecosystem response
on the northern Gulf of Alaska shelf: results from a biophysical lower trophic level model and
GLOBEC - NPRB field observations.
Stockwell, D.A. in prep. Primary productivity patterns in North East Pacific coast waters.
Stockwell, D.A., and Whitledge, T.E. in prep. Size-fractionated chlorophyll distributions in Alaskan
coastal waters.
Outreach
Web pages developed:
All data plots and posters presented from the combined GLOBEC & NPRB periods are posted at
http://www.ims.uaf.edu/GLOBEC/ as soon as they become available.
Conference presentations:
Inter-annual variations of zooplankton in the northern coastal Gulf of Alaska. Poster 4th International
Zooplankton Production Symposium, Hiroshima, Japan (May 2007)
The Gulf of Alaska Seward Line - 2005 & 2006. Poster Alaska Marine Science Symposium,
Anchorage (January 2007)
The consequences of climate change on Alaskan marine life. Presention Alaska Forum, Anchorage
(Feb 2006)
Climate change research in the Gulf of Alaska: the Seward Line. Presentation. Alaska Marine
Science Symposium, Anchorage (January 2006)
Workshop Participations:
GLOBEC Synthesis meeting/workshop. Anacortes, WA (May 2007)
GLOBEC Synthesis meeting/workshop. Anacortes, WA (Dec 2006)
GLOBEC PI meeting. Seattle (Jan 2006)
Images:
Some images taken during the NPRB funded period appeared on the cover of the 4th International
Zooplankton Production Symposium program book, others appeared in presentations by various
authors at that meeting.
Acknowledgments
We thank the captain and crew of the R/V Alpha Helix, R/V Thompson & M/V Tiglax for various forms of
assistance in execution of this work. This work would not have been possible without the students and
volunteers that provided much of the manpower during 2005-2007 cruises. This time-series has been
funded both by the North Pacific Research Board under grants 520 & 603, and by the US GLOBEC
35
program, jointly funded by the National Science Foundation and the National Oceanic and Atmospheric
Administration under NSF Grants OCE-0105236, OCE-9711482, and OCE 0109078.
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