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Annual, seasonal and spatial differences in the growth rate of Baltic cod larvae and early juveniles in relation to zooplankton biomass fluctuations in 2006-2014

Katarzyna Spich
Katarzyna Spich
 and 
Dariusz Piotr Fey
Dariusz Piotr Fey
   | Dec 31, 2023
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Article Category: Original Research Paper
Published Online: Dec 31, 2023
Page range: 399 - 419
Received: Jul 30, 2023
Accepted: Nov 15, 2023
DOI: https://doi.org/10.26881/oahs-2023.4.02
© 2023 Katarzyna Spich et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1

Location of ichthyoplankton and zooplankton sampling stations between 2006 and 2014. Black circles indicate WP-2 stations. Sub-areas of the study area are indicated: BB – Bornholm Basin, yellow points; GB – Gdańsk Basin, red points; and SF – Słupsk Furrow, blue points.
Location of ichthyoplankton and zooplankton sampling stations between 2006 and 2014. Black circles indicate WP-2 stations. Sub-areas of the study area are indicated: BB – Bornholm Basin, yellow points; GB – Gdańsk Basin, red points; and SF – Słupsk Furrow, blue points.

Figure 2

Dependence of SL on larval and juvenile cod age during the 2006-2014 period described by simple linear regression separately for specimens younger and older than 60 d (A); and the same data described by a best-fit 4th order polynomial function with the aim of determining residuals reflecting the growth rates of specific individuals in comparison to the mean for the entire population (B).
Dependence of SL on larval and juvenile cod age during the 2006-2014 period described by simple linear regression separately for specimens younger and older than 60 d (A); and the same data described by a best-fit 4th order polynomial function with the aim of determining residuals reflecting the growth rates of specific individuals in comparison to the mean for the entire population (B).

Figure 3

Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea in the 2006-2014 period: differences between seasons (spring and summer).
Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea in the 2006-2014 period: differences between seasons (spring and summer).

Figure 4

Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea in the 2006-2014 period: differences among geographical areas (Bornholm Basin, BB; Słupsk Furrow, SF; and Gdańsk Basin, GB).
Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea in the 2006-2014 period: differences among geographical areas (Bornholm Basin, BB; Słupsk Furrow, SF; and Gdańsk Basin, GB).

Figure 5

Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea by year: inter-annual differences (2006–2014). Dotted lines indicate the mean calculated separately for two periods: 2006–2011 and 2012–2014.
Median (square), 25 and 75 percentile (box), non-outlier range (whiskers), and mean (diamond) values of the GR index (%) of larval and juvenile cod in the southern Baltic Sea by year: inter-annual differences (2006–2014). Dotted lines indicate the mean calculated separately for two periods: 2006–2011 and 2012–2014.

Figure 6

Biomass of the dominant zooplankton taxonomic groups in the southern Baltic during the 2006 – 2014 period by size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD) and study season (spring and summer).
Biomass of the dominant zooplankton taxonomic groups in the southern Baltic during the 2006 – 2014 period by size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD) and study season (spring and summer).

Figure 7

Mean biomass of the four zooplankton taxonomic groups (Acartia spp., Pseudocalanus spp., T. longicornis, C. hamatus) in the southern Baltic in the 2006–2014 period by geographical region (Bornholm Basin, BB; Gdańsk Basin, GB; Słupsk Furrow, SF) and size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD).
Mean biomass of the four zooplankton taxonomic groups (Acartia spp., Pseudocalanus spp., T. longicornis, C. hamatus) in the southern Baltic in the 2006–2014 period by geographical region (Bornholm Basin, BB; Gdańsk Basin, GB; Słupsk Furrow, SF) and size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD).

Figure 8

Relative (deviation from the mean) biomass of the four zooplankton taxonomic groups (Acartia spp., Pseudocalanus spp., T. longicornis, C. hamatus) in the 2006-2014 period by geographical region (Bornholm Basin, BB; Gdańsk Basin, GB; Słupsk Furrow, SF), size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD), and season (spring and summer).
Relative (deviation from the mean) biomass of the four zooplankton taxonomic groups (Acartia spp., Pseudocalanus spp., T. longicornis, C. hamatus) in the 2006-2014 period by geographical region (Bornholm Basin, BB; Gdańsk Basin, GB; Słupsk Furrow, SF), size fraction (small zooplankton, NP+C3; large zooplankton, C4+AD), and season (spring and summer).

Figure 9

Long-term temperature variations (means for all stations in a given year) by two water layers (surface layer above the thermocline; deep water layer below the thermocline). (A) spring; (B) summer; T1 – average temperature from surface to thermocline, T2 – average temperature from thermocline to the bottom.
Long-term temperature variations (means for all stations in a given year) by two water layers (surface layer above the thermocline; deep water layer below the thermocline). (A) spring; (B) summer; T1 – average temperature from surface to thermocline, T2 – average temperature from thermocline to the bottom.

S2

Mean growth rates of larval and juvenile cod in the southern Baltic in the 2006-2014 period. Each point represents the values of an individual specimen.
Mean growth rates of larval and juvenile cod in the southern Baltic in the 2006-2014 period. Each point represents the values of an individual specimen.

S3

Residuals of the SL-at-age relationship described with 4th order polynomial function.
Residuals of the SL-at-age relationship described with 4th order polynomial function.

S4

Geographical differences in the GR index (%) along longitude and latitude in spring and summer.
Geographical differences in the GR index (%) along longitude and latitude in spring and summer.

S5

The relationships between the GR index and zooplankton biomass in spring and summer. Mean values for station are presented. Green squares indicate p < 0.05.
The relationships between the GR index and zooplankton biomass in spring and summer. Mean values for station are presented. Green squares indicate p < 0.05.

S6

The relationships between the zooplankton biomass and surface water temperature in spring and summer. Mean values for stations are presented. Green squares indicate p < 0.05.
The relationships between the zooplankton biomass and surface water temperature in spring and summer. Mean values for stations are presented. Green squares indicate p < 0.05.

S7

The relationships between the GR index and surface water temperature in spring and summer. Mean values for station are presented.
The relationships between the GR index and surface water temperature in spring and summer. Mean values for station are presented.

An overview of the most important parameters (SL in mm and age in d) of the larval and juvenile cod caught in the 2006-2014 period, the number of individuals caught in the spring (April-May-June) and summer (July-August), and in the other sub-areas of the Baltic Sea (BB – Bornholm Basin; GB – Gdańsk Basin; and SF – Słupsk Furrow).

Year Area Spring Summer
SL (mm) Age (days) n SL (mm) Age (days) n
2006 BB - - 0 9.9-39.2 14.5-105.5 95
GB - - 0 10.9-27.9 34.0-109.0 9
SF - - 0 8.5-25.2 26.0-76.0 21
2007 BB - - 0 6.3-18.9 4.0-70.5 22
GB - - 0 - - 0
SF - - 0 - - 0
2008 BB 4.9-9.3 2.0 - 15.0 8 4.5-28.1 2.0-100.5 51
GB - - 0 7.5-23.9 10.0-86.0 7
SF 4.1-4.5 2.0-3.0 2 6.8-31.7 10.0-136.0 12
2009 BB 10.5 25.5 1 - - 0
GB - - 0 11.1-26.1 26.5-74.5 7
SF - - 0 21.1-22.7 65.5-67.5 2
2010 BB - - 0 8.5-14.1 9.0-40.0 6
GB - - 0 12.7-15.9 47.5-68.0 6
SF - - 0 7.9-13.9 15.0-46.5 5
2011 BB 33.1 131.0 1 6.3-24.1 4.0-91.5 68
GB - - 0 - - 0
SF - - 0 8.9-16.9 5.0-62.0 11
2012 BB 5.3-14.5 4.0-56.0 32 6.7-18.9 8.0-80.5 42
GB 4.9-8.9 2.5-20.0 5 12.7 52.0 1
SF 5.5-5.9 7.0-10.0 2 7.5-9.3 15.0-45.0 8
2013 BB 4.9-9.9 4.0-24.0 26 7.1-14.1 5.0-39.0 8
GB 5.7-6.9 8.0-15.0 4 - - 0
SF 4.9-8.1 6.0-10.0 8 13.1 15.0 1
2014 BB 4.5-7.9 2.0-20.0 11 8.1-12.1 22.0-32.0 2
GB 5.9-10.1 15.0-33.0 4 8.7-10.1 24.0-40.0 3
SF - - 0 - - 0

The results of correlation analysis (r values) for the relationships between the GR index and environmental variables (zooplankton biomass and water temperature) and between zooplankton biomass and surface temperature. Mean annual values were used for each of the relationships. The analysis covers the period between 2006 and 2014 (spring n = 34; summer n = 60). Pseudocalanus spp. (P), Temora longicornis (T), Acartia spp. (A), Centropages hamatus (C) and temperature (T), and all four zooplankton groups together (All). Significance levels:

Season Parameter Zooplankton biomass T (oC)
All P T A C
Spring NP+C1
%GR_cod 0.42* 0.29 0.40* 0.24 0.44* 0.15
T (oC) 0.37* 0.46* 0.15 0.04 0.01
C4+AD
%GR_cod 0.06 0.39* 0.03 0.16 0.15 0.15
T (oC) 0.58* 0.15 0.62* 0.54* 0.59*
Summer NP+C1
%GR_cod 0.02 0.01 0.04 0.05 0.08 0.13
T (oC) 0.35* 0.27* 0.28* 0.09 0.38*
C4+AD
%GR_cod 0.22 0.17 0.14 0.17 0.13 0.13
T (oC) 0.29* 0.04 0.35* 0.00 0.38*

The list of all cruises conducted during research period 2006-2014 and an inventory of collected samples.

No Year Start Stop No of zooplankton samples No of ichthyoplankton samples
1. 2006 18.04.2006 28.04.2006 22 0
2. 26.06.2006 07.07.2006 22 25
3. 14.08.2006 25.08.2006 18 28
4. 2007 14.06.2007 25.06.2007 26 0
5. 16.08.2007 27.08.2007 20 15
6. 2008 17.04.2008 28.04.2008 22 7
7. 22.08.2008 31.08.2008 24 33
8. 2009 29.04.2009 09.05.2009 22 1
9. 14.08.2009 25.08.2009 16 4
10. 2010 04.05.2010 14.05.2010 18 0
11. 16.08.2010 31.08.2010 18 12
12. 2011 05.05.2011 13.05.2011 14 1
13. 18.08.2011 28.08.2011 20 27
14. 2012 12.05.2012 16.05.2012 20 19
15. 20.08.2012 27.08.2012 20 21
16. 2013 10.05.2013 20.05.2013 22 25
17. 14.08.2013 24.08.2013 20 10
18. 2014 16.06.2014 23.06.2014 18 10
19. 18.08.2014 23.08.2014 - 5
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