Eglė Jakubavičiūtė. Supervisor: dr. L. Ložys Co-supervisor: dr. J. Olsson

Transcription

1 Eglė Jakubavičiūtė Supervisor: dr. L. Ložys Co-supervisor: dr. J. Olsson

2 Background Objectives Results Diet composition Seasonality Diet overlap Selectivity 2

3 Mesopredators: Herring Sprat Three-spined stickleback 3

4 Can alter and lock food webs in a mesopredatordominated regime (Sieben et al., 2011; Eriksson et al., 2011, Bystrom et al., 2015) Eutrophication trigger Prey-to-predator loop Impact on piscivores populations at the coast 4

5 Abundance of sticklebacks has increased COAST OFFSHORE Feeding Spawning Feeding Competition? (Bergstrom et al., 2015) 5

6 What is the feeding niche and competitive interaction of three-spined stickleback with other major planktivorous fish species in the Baltic Sea, herring and sprat? 1. What are seasonal patterns of herring, sprat and stickleback diet in the Baltic (offshore)? 2. Does feeding niche of herring, sprat and stickleback overlap? 3. Is there a preference for certain prey species? 6

7 Kalmar Sound (western Baltic Sea) Fish sampling Zooplankton sampling

8 Visual inspection of stomach content (morphology based keys); % N i average proportion of i-th prey type with respect to the total number of prey consumed; % W i - average proportion of i-th prey mass with respect to the total weight of all prey consumed; Morisita similarity index for diet overlap; 8

9 Year Spring Summer Fall TOTAL x (September, October) N= x (April) N=52 2x (July, August) N=155 1x (October) N= x (April) N=79-1x (September) N=18 TOTAL

10 100 Copepoda Cladocera Malacostraca Other 80 % N Herring Sprat Stickleback Herring Sprat Stickleback Herring Sprat Stickleback Spring Summer Fall 10

11 Herring Sprat Stickleback % N Herring Sprat Stickleback Herring Sprat Stickleback Other Keratella Cercopagis Centropages Mysidae Podon Bosmina Temora Eurytemora Acartia Spring Summer Fall 11

12 % N Acartia Bosmina Stickleback, spring Temora Eurytemora % N % W Temora Herring, fall Acartia Mysidae Eurytemora Bosmina % W 12

13 1 Morisita diet overlap index Spring Fall Summer 0 St-Her St-Sprat Her-Sprat 13

14 Two-way ANOSIM Similarity Permutation N: St_Summer Her_Summer Sp_Summer St_Spring Sp_Spring Her_Spring Factor: Season R: p 1.00E-04 Factor: Species R: p 1.00E-04 Sp_Fall St_Fall Her_Fall 14

15 Fish size (not equally covered) 160 Her_TL>10 cm Fall Spring Summer Sprat_TL>10 cm Number of fish Her_TL<10 cm Sprat_TL<10 cm

16 Explanatory variable Variance explained, % Season 13 Species 2.5 Fish size 2.5 Residual 82 Total

17 Fish size vs diet Stickleback in the summer-time p< Acartia Fish length, cm 17

18 Fish size vs diet Herring in the fall Mysidae Fish length, cm 18

19 Herring in the fall p<0.01 Acartia Fish length, cm 19

20 The most important factor for the variation in herring, sprat and three-spined sticklebacks diet (among season, species and fish size) is season. 20

21 Is diet selectivity typical for the fish? Is it season-dependent? 21

22 22

23 Year Spring Summer Fall x (September, October) N= x (April) N=52 Selectivity index 1x (August) N=127 1x (October) N=27 V index (Pearre, 1982) [-1;1] 23

24 1 Herring Sprat Stickleback Selectivity V-index Acartia Eurytemora Temora Bosmina -1 24

25 1 Herring Sprat Stickleback Selectivity V index Acartia Eurytemora Temora Bosmina Podon -1 25

26 1 Herring Sprat Stickleback Selectivity V index Acartia Eurytemora Temora Bosmina Podon

27 Herring Fall Sept 2009 Oct 2010 Oct Selectivity V-index Acartia Eurytemora Temora Bosmina Podon Mysidae -1 27

28 Sprat Fall Sept 2009 Oct 2010 Oct Selectivity V-index Acartia Eurytemora Temora Bosmina Podon -1 28

29 Stickleback Fall Sept 2009 Oct 2010 Oct Selectivity V-index Acartia Eurytemora Temora Bosmina Podon -1 29

30 Selectivity V-index Acartia Herring Sprat Stickleback Spring Summer Fall2010 Fall2009Sept Fall2009Oct -1 30

31 1 0.5 Eurytemora Spring Summer Fall2010 Fall2009Sept Fall2009Oct Selectivity V-index Herring Sprat Stickleback -1 31

32 1 Temora Spring Summer Fall2010 Selectivity V-index Herring Sprat Stickleback Fall2009Sept Fall2009Oct

33 Selectivity V-index Bosmina Herring Sprat Stickleback Spring Summer Fall2010 Fall2009Sept Fall2009Oct -1 33

34 1 Mysidae Selectivity V-index Herring Sprat Stickleback 2009 Sept 2009 Oct -1 34

35 Selectivity seems to remain the same over the years, i.e. certain zooplankton species as diet items are more preferable than others. 35

36 Selectivity depends on the season Acartia is always deselected except for the spring-time Eurytemora is positively selected, especially in the summer-time Bosmina is positively selected, especially in the fall, and especially by stickleback Mysidae is selected by large herring in the fall; 36

37 Main prey items are calanoids Eurytemora, Temora, Acartia and cladoceran Bosmina; Diet overlaps significantly, mostly in summer-time and fall; Selectivity is typical for the species and depends on the season; 37

38 Sticklebacks - potentially very important competitors : Prefer the same species and preference for certain prey species seems to be stable over the years; High diet overlap even with bigger sprat and herring. 38

39 DNA barcoding other method for fish diet elucidation; Stomach content analysis Baltic-wide scale (samples already collected) 39

40 For all who collected the samples, who shared their ideas, who criticized and who encouraged... and for you who listened! Egle Jakubaviciute PhD student Laboratory of Marine Ecology Nature Research Centre, Akademijos str. 2, LT-08412, Lithuania 40