Preliminary Data on Euphausiid Distribution and Growth in the Northern Gulf of Alaska.
1
Preliminary Data on Euphausiid Distribution and Growth in the Northern Gulf of Alaska. A.I. Pinchuk, R.R. Hopcroft, K.O. Coyle Institute of Marine Science, University of Alaska Fairbanks, AK 99775-7220 Abstract Seasonal and interannual variability in distribution and population structure of two major euphausiids species Thysanoessa spinifera and Euphausia pacifica were studied in the northern Gulf of Alaska in 1998-2001. Other common euphausiid species were T. inermis, T. longipes, T raschii and T. inspinata. Euphausiid aggregations were related to water mass properties with E. pacifica frequently observed on outer shelf during years, when a strong shelf break front was developed. In contrast, T. spinifera was more abundant on the inner shelf in spring. Individual euphausiid growth rates were positive in first 4 days after capture, showing indications of body shrinkage under unfavorable food conditions later on. Intermoult periods averaged ~11-12 days at 5oC and ~7-8 at 8oC. Reproduction of T. spinifera seemed to coincide with the phytoplankton bloom in spring, while E. pacifica continued to spawn from May through October. Clutch size of E. pacifica tended to be higher in mid summer. - 128(n/a) n=2 - Thysanoessa spinifera 87.6(41.6) n=7 123.4(16.4 ) n=51 60.7(34.8) n=6 Euphausia pacifica October August July Species Table 4. Mean clutch size (95% confidence interval) of E. pacifica and T. spinifera. The gravid females of E. pacifica and T. spinifera first were observed in May, but actual spawning in captivity occurred from early July through October. The number of gravid females of E. pacifica and their clutch size appeared to be higher in August then in July. 6.87(0.66) n=15 6.59(0.34) n=39 8 - 10.1(1.46) n=7 5 Thysanoessa spinifera juveniles 7.5(n/a) n=2 7(1.09) n=8 8 13(n/a) n=2 9.75(1.24) n=8 5 Thysanoessa inermis juveniles 7.07(0.77) n=14 6.87(0.53) n=30 8 10.7(2.87) n=3 11.2(1.04) n=5 5 Thysanoessa inermis males 7.7(1.4) n=3 6.8(0.47) n=20 8 10.75(0.59) n=8 10.7(0.52) n=39 5 Euphauisa pacifica juveniles 8.6(0.89) n=8 6.6(0.38) n=37 8 14(n/a) n=1 11.2(0.92) n=19 5 Euphauisa pacifica , males Intermolt Period 2 (95% Confidence Interval), days Intermolt Period 1 (95% Confidence Interval), days Temperature, o C Species Table 2.Consecutive intermoult periods(IP) of euphausiids measured directly from laboratory experiments. IP did not differ between seasons, locations nor between species, but were significantly (P<0.05) different for selected temperatures. There was no significant difference between consecutive IPs. 11.6(1.22) 8.6(0.79) n=5 8 8.3(1.85) 12.6(2.81) n=5 5 Daily moulting Equivalent in % of population IP (95% confidence interval) Temperatur e ( o C) Table 3. Percentage of animals moulting and equivalent IP measured from shipboard experiments at 5 o C and 8 o C (n – number of experiments). Moulting rates derived from observed numbers of successfully moulted animals were significantly (P<0.05) different between selected temperatures. Figure 1.Relative size change of E. pacifica, T. inermis and T. spinifera shown as the percentage change in uropod length per day. Most of the euphausiids that moulted during the first 4 d following collection showed positive growth. Body shrinkage was observed for all species after day 5, reflecting unfavorable conditions in captivity, which could include limited food, low oxygen and high ammonia concentrations as well as restriction of animal movement. E uphausia pacifica males -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Euphausia pacifica juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Thysanoessa inermis juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange E uphausia pacifica males -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Euphausia pacifica juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Thysanoessa inermis juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange E uphausia pacifica males -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange E uphausia pacifica juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Thysanoessa inermis juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange E uphausia pacifica males -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange E uphausia pacifica juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange Thysanoessa spinifera juveniles -15 -10 -5 0 5 10 15 0 5 10 15 20 Days % Size C hange H X 2 4 1 H X 2 4 3 HX246 H X 2 4 8 Conclusions 1. The close agreement between consecutive intermoult periods at a given temperature as well as consistent percentage of daily moulting suggest that the experimental euphausiids moulted at the same rate. 2. The moulting rate appeared to be affected largely by temperature, rather then other environmental conditions such as food limitation. 3. In contrast, the size change expressed as % of uropod length change did not appeared to be affected by temperature, but controlled by other conditions, presumably food availability. 4. While the spawning season of E. pacifica in the Gulf of Alaska extended from early May to October, the maximum clutch size seemed to occur in August. This research is supported by the U.S. GLOBEC Northeast Pacific Program. Methods Euphausiids were collected at the 13 stations on the Seward Line using a 1-m MOCNESS with 0.5 mm mesh nets. The net were fished from 100 m to the surface in 20 m increments. Collected specimens were preserved in 10% formalin. To collect live animals for experiments, location and depth of euphausiid aggregations were identified with an HTI acoustic system operating at 42, 120, 240 and 420 kHz during night time acoustic survey along the Seward Line. The detected aggregations were fished using MOCNESS with 100 μm mesh nets. Euphausiids were gently removed from the catch and placed in individual 750 ml tissue flasks filled with seawater collected simultaneously at the site. The animals were maintained at the ambient mixed layer water temperature in the dark and were checked every 12-24 hours for moults and egg production. If an animal moulted the exuviae were removed and preserved in 5% formalin. If a female produced eggs, they were removed with a pipette and either preserved or incubated. At the end of each experiment all animals were preserved individually. The length of uropods were measured on all moults and preserved animals using a digitized measuring system (Roff & Hopcroft, 1986). 633 70 Total animals incubated 90 - 48 - 60 - 60 - 60 - 45 14 45 - 75 - 50 18 50 - 50 10 - 28 - 7 5 5 5 5 5 8 8 8 8 8 8 8 8 GAK13 CCSE GAK13 GAK9 CCSE GAK9 GAK7 CCSE GAK12 GAK9 GAK6 GAK1 GAK13 04.06.01 04.10.01 05.06.01 05.08.01 05.10.01 06.30.01 07.02.01 07.07.01 07.31.01 08.01.01 08.02.01 08.04.01 10.13.01 HX241 HX243 HX246 HX248 HX252 # of euphausiids in experiment moulting egg production Temperatu re ( o C) Stati on Date Cruise Meters Below Mean Sea Level Map showing the location of the study site, the Seward Line stations (labeled GAK), and the Prince William Sound stations. Table 1. Summary of moulting rates and egg production experiments 0 100 200 D ista n ce (k m) 0 0 .2 0 .4 0 .6 0 .8 A b u n d an ce (n o/m -3 ) A p ril 2 0 0 0 0 100 200 D ista n ce (k m) 0 0 .2 0 .4 0 .6 0 .8 A b u n d an ce (n o/m -3 ) A p ril 1 9 9 9 0 50 100 150 200 D ista n ce (k m) 0 0 .2 0 .4 0 .6 0 .8 A b u n d an ce (n o/m -3 ) T axa E U P H A U S IA P A C IF IC A JU V E N ILE S E U P H A U S IA P A C IF IC A AM E U P H A U S IA P A C IF IC A AF A p ril 1 9 9 8 0 50 100 150 200 D ista n ce (k m) 0 1 2 3 4 5 A b u n d an ce (n o/m -3 ) T axa T H Y S A N O E S S A S P IN IF E R A MALES T H Y S A N O E S S A S P IN IF E R A JU V E N ILE S T H Y S A N O E S S A S P IN IF E R A FEMALES A p ril 1 9 9 8 0 100 200 D ista n ce (k m) 0 0 .2 0 .4 0 .6 0 .8 A b u n d an ce (n o/m -3 ) A p ril 1 9 9 9 0 100 200 D ista n ce (k m) 0 0 .2 0 .4 0 .6 0 .8 A b u n d an ce (n o/m -3 ) A p ril 2 0 0 0 Figure 2. The cross- shelf distribution of E. pacifica and T. spinifera in April in 1998-2000. E. pacifica occurred on the outer shelf during years when a strong shelf break front was developed. T. spinifera was common on the inner shelf, but occasionally it formed large aggregations
description
Preliminary Data on Euphausiid Distribution and Growth in the Northern Gulf of Alaska. A.I. Pinchuk, R.R. Hopcroft, K.O. Coyle Institute of Marine Science, University of Alaska Fairbanks, AK 99775-7220. Species. Temperature, o C. Intermolt Period 1 (95% Confidence Interval), days. - PowerPoint PPT Presentation
Transcript of Preliminary Data on Euphausiid Distribution and Growth in the Northern Gulf of Alaska.
Preliminary Data on Euphausiid Distribution and Growth in the Northern Gulf of Alaska.A.I. Pinchuk, R.R. Hopcroft, K.O. CoyleInstitute of Marine Science, University of Alaska Fairbanks, AK 99775-7220
AbstractSeasonal and interannual variability in distribution and population structure of two major euphausiids species Thysanoessa spinifera and Euphausia pacifica were studied in the northern Gulf of Alaska in 1998-2001. Other common euphausiid species were T. inermis, T. longipes, T raschii and T. inspinata. Euphausiid aggregations were related to water mass properties with E. pacifica frequently observed on outer shelf during years, when a strong shelf break front was developed. In contrast, T. spinifera was more abundant on the inner shelf in spring. Individual euphausiid growth rates were positive in first 4 days after capture, showing indications of body shrinkage under unfavorable food conditions later on. Intermoult periods averaged ~11-12 days at 5oC and ~7-8 at 8oC. Reproduction of T. spinifera seemed to coincide with the phytoplankton bloom in spring, while E. pacifica continued to spawn from May through October. Clutch size of E. pacifica tended to be higher in mid summer.
-128(n/a)
n=2
-Thysanoessa spinifera
87.6(41.6)
n=7
123.4(16.4)
n=51
60.7(34.8)
n=6
Euphausia pacifica
OctoberAugustJulySpecies Table 4. Mean clutch size (95% confidence interval) of E. pacifica and T. spinifera. The gravid females of E. pacifica and T. spinifera first were observed in May, but actual spawning in captivity occurred from early July through October. The number of gravid females of E. pacifica and their clutch size appeared to be higher in August then in July.
6.87(0.66)
n=15
6.59(0.34)
n=39
8
-10.1(1.46)
n=7
5Thysanoessa spinifera juveniles
7.5(n/a)
n=2
7(1.09)
n=8
8
13(n/a)
n=2
9.75(1.24)
n=8
5Thysanoessa inermis juveniles
7.07(0.77)
n=14
6.87(0.53)
n=30
8
10.7(2.87)
n=3
11.2(1.04)
n=5
5Thysanoessa inermis males
7.7(1.4)
n=3
6.8(0.47)
n=20
8
10.75(0.59)
n=8
10.7(0.52)
n=39
5Euphauisa pacifica juveniles
8.6(0.89)
n=8
6.6(0.38)
n=37
8
14(n/a)
n=1
11.2(0.92)
n=19
5Euphauisa pacifica , males
Intermolt Period 2 (95% Confidence Interval), days
Intermolt Period 1
(95% Confidence Interval), days
Temperature,
oC
Species
Table 2.Consecutive intermoult periods(IP) of euphausiids measured directly from laboratory experiments. IP did not differ between seasons, locations nor between species, but were significantly (P<0.05) different for selected temperatures. There was no significant difference between consecutive IPs.
11.6(1.22) 8.6(0.79)
n=5 8
8.3(1.85) 12.6(2.81)
n=5
5
Daily moulting Equivalent
in % of population IP
(95% confidence interval)
Temperature
(oC)
Table 3. Percentage of animals moulting and equivalent IP measured from shipboard experiments at 5oC and 8 oC(n – number of experiments). Moulting rates derived from observed numbers of successfully moulted animals were significantly (P<0.05) different between selected temperatures.
Figure 1.Relative size change of E. pacifica, T. inermis and T. spinifera shown as the percentage change in uropod length per day. Most of the euphausiids that moulted during the first 4 d following collection showed positive growth. Body shrinkage was observed for all species after day 5, reflecting unfavorable conditions in captivity, which could include limited food, low oxygen and high ammonia concentrations as well as restriction of animal movement.
Euphausia pacifica males
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
an
ge
Euphausia pacifica juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
an
ge
Thysanoessa inermis juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
an
ge
Euphausia pacifica males
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
an
ge
Euphausia pacifica juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Thysanoessa inermis juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Euphausia pacifica males
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Euphausia pacifica juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Thysanoessa inermis juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Euphausia pacifica males
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Euphausia pacifica juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
Thysanoessa spinifera juveniles
-15
-10
-5
0
5
10
15
0 5 10 15 20
Days
% S
ize
Ch
ang
e
HX
241
HX
243
HX
246
HX
248
Conclusions1. The close agreement between consecutive intermoult periods at a given temperature as well as
consistent percentage of daily moulting suggest that the experimental euphausiids moulted at the same rate.
2. The moulting rate appeared to be affected largely by temperature, rather then other environmental conditions such as food limitation.
3. In contrast, the size change expressed as % of uropod length change did not appeared to be affected by temperature, but controlled by other conditions, presumably food availability.
4. While the spawning season of E. pacifica in the Gulf of Alaska extended from early May to October, the maximum clutch size seemed to occur in August.
This research is supported by the U.S. GLOBEC Northeast Pacific Program.
MethodsEuphausiids were collected at the 13 stations on the Seward Line using a 1-m MOCNESS with 0.5 mm mesh nets. The net were fished from 100 m to the surface in 20 m increments. Collected specimens were preserved in 10% formalin. To collect live animals for experiments, location and depth of euphausiid aggregations were identified with an HTI acoustic system operating at 42, 120, 240 and 420 kHz during night time acoustic survey along the Seward Line. The detected aggregations were fished using MOCNESS with 100 μm mesh nets. Euphausiids were gently removed from the catch and placed in individual 750 ml tissue flasks filled with seawater collected simultaneously at the site. The animals were maintained at the ambient mixed layer water temperature in the dark and were checked every 12-24 hours for moults and egg production. If an animal moulted the exuviae were removed and preserved in 5% formalin. If a female produced eggs, they were removed with a pipette and either preserved or incubated. At the end of each experiment all animals were preserved individually. The length of uropods were measured on all moults and preserved animals using a digitized measuring system (Roff & Hopcroft, 1986).
633 70Total animals incubated
90 -
48 -
60 -
60 -
60 -
45 14
45 -
75 -
50 18
50 -
50 10
- 28
- 7
5
5
5
5
5
8
8
8
8
8
8
8
8
GAK13
CCSE
GAK13
GAK9
CCSE
GAK9
GAK7
CCSE
GAK12
GAK9
GAK6
GAK1
GAK13
04.06.01
04.10.01
05.06.01
05.08.01
05.10.01
06.30.01
07.02.01
07.07.01
07.31.01
08.01.01
08.02.01
08.04.01
10.13.01
HX241
HX243
HX246
HX248
HX252
# of euphausiids in experiment
moulting egg production
Temperature
(oC)
StationDateCruise
Meters Below Mean Sea Level
Map showing the location of the study site, the Seward Line stations (labeled GAK), and the Prince William Sound stations.
Table 1. Summary of moulting rates and egg production experiments
0 1 0 0 2 0 0D ista n ce (k m )
0
0 .2
0 .4
0 .6
0 .8
Abun
dance
(no
/m -3
)
A p r il 2 0 0 0
0 1 0 0 2 0 0D ista n ce (k m )
0
0 .2
0 .4
0 .6
0 .8
Abundan
ce (no
/m -3
)
A p r il 1 9 9 9
0 5 0 1 0 0 1 5 0 2 0 0D ista n ce (k m )
0
0 .2
0 .4
0 .6
0 .8
Abu
nda
nce
(no
/m -3
) T a x aEU PH AU SIA PAC IF IC A JU VEN ILES EU PH AU SIA PAC IF IC A AM EU PH AU SIA PAC IF IC A AF
A p ril 1 9 9 8
0 5 0 1 0 0 1 5 0 2 0 0D ista n ce (k m )
0
1
2
3
4
5
Abundan
ce (no/m
-3 )
T a x aTH YS AN O ESSA SP IN IFER A M ALES TH YS AN O ESSA SP IN IFER A JU VEN ILES TH YS AN O ESSA SP IN IFER A FEM ALES
A p ril 1 9 9 8
0 1 0 0 2 0 0D ista n ce (k m )
0
0 .2
0 .4
0 .6
0 .8
Abunda
nce
(no
/m -3
)
A p r il 1 9 9 9
0 1 0 0 2 0 0D ista n ce (k m )
0
0 .2
0 .4
0 .6
0 .8
Abundan
ce (no/m
-3 )
A p r il 2 0 0 0
Figure 2. The cross-shelf distribution of E. pacifica and T. spinifera in April in 1998-2000. E. pacifica occurred on the outer shelf during years when a strong shelf break front was developed. T. spinifera was common on the inner shelf, but occasionally it formed large aggregations offshore.
