Spatial organization of the pelagic community Implications for community resilience

1. Spatial organizationofthepelagiccommunityImplications for communityresilience Mette Skern-Mauritzen BarEcore Spatial SynthesisWorkshop, Tromsø May 2012

2. Pelagiccommunity and resilience • Stability: highly dynamic, fluctuating species abundances; shifts in species distributions • Robustness: Strong responses to perturbations, such climate variation and fisheries • Functional redundancy: Low diversity at crucial intermediate trophic level; 3-4 species of pelagic fish – in separate habitats • Strong trophic interactions: Few main players with significant impact. Spatial distribution / species overlap determines interaction strength (e.g. Capelin and herring) • Hysteresis and regime shifts: Following perturbations, arrested in alternative states; • Top-down trophic regulation and trophic cascades; regime shifts following removal of top predators • Positive feedback mechanisms – predator-prey role reversal • High latitude pelagic systems; among the least resilient marine systems?

3. Resilience and spatial patterns Top predators Using a subsetofspecies from thepelagiccommunity; - 4 / all marine mammalspecies - 8 dominant seabirdspecies (4 alcids, fulmar, 4 gulls) - Cod • Pelagicfish, averageacousticdensities • Bluewhiting, herring, capelin, polar cod • 0- groupfish, pelagictrawl • 27 species • Macrozooplankton • 2 groups; krill and amhipods

4. Resilience and spatial patterns • Spatial organization of pelagic community (Species distributions, scales of distributions, species associations) • Species diversity within Atlantis polygons, within and across trophic levels • Primary production within Atlantis polygons My aims: - discuss general distributions vs compartmentalisation, cross scale redundancy and suitability of Atlantis polygons - species diversity patterns using Atlantis polygons - primary productivity vs species diversity

5. Spatial organisation of the pelagic community Blue whiting Herring Capelin Polar cod Mid and lower trophic levels 0 – 509 sA n mile-1 0 – 61 sA n mile-1 0 – 137 sA n mile-1 0 – 177 sA n mile-1 • Diverse spatial niches; • diffferent species use • different habitats • The pelagic fish species, • in non-overlapping • habitats O - Haddock O - Cod O - Capelin O – Polar cod 0 – 286 x 103 N n mile-1 0 – 623 x 103 N n mile-1 0 – 8363 x 103 N n mile-1 0 – 2004 x 103 N n mile-1 Krill Amphipods O - Herring 0 – 1769 tons n mile-1 0 – 3128 tons n mile-1 0 – 15161 x 103 N n mile-1

6. Cod < 20 cm Cod 20 - 50 cm Cod 50 - 70 cm Cod > 70 cm Top trophic levels 0 – 51.6 N n mile-1 0 – 99.0 N n mile-1 0 – 68.14 N n mile-1 0 – 3.26 N n mile-1 White-beaked d. Minke whale Fin whale Humpb. whale • Generally omnivorous; • Feeds on pelagic fish • and macrozoopl. • Diverse spatial niches; • diffferent species use • different habitats • closely related species • overlap – baleen whales • segregate - alcids 0 – 9.24 ind km-1 0 – 2.12 ind km-1 0 – 1.33 ind km-1 0 – 1.33 ind km-1 Puffin C. guillemot Br. guillemot Little auk 0 – 93.25 N km-1 0 – 6.09 N km-1 0 – 337.37 N km-1 0 – 336.19 N km-1 Fulmar Kittiwake 0 – 43.71 N km-1 0 – 63.81 N km-1

7. Spatial organisation of the pelagic community Predator niche diversity PCA on average distributions

8. Scalesofdistributions Correlograms Top predators narrower nichesthantheirprey Distance, km Distance, km

9. Spatial organisation of the pelagic community • Pelagic community; a niche based community in summer • relatively persistent niches, at least among top predators • weak spatial responses to changes in prey distributions / abundances • organization likely related to • migratory abilities • foraging habitat and thermal niches

10. Spatial organisation of the pelagic community • Implications for resilience: • Limited spatial match between specific predators and prey • Weak responses to prey - indicates omnivory • Reduced strength of trophic interactions? At least pairwise… • Summer diversity of prey species increases the buffering capacity • Cross scale functional redundancy • – within trophic levels: less importance in the pelagic • community compared to e.g. terrestrial systems (mice and elefant) • – but ’replaced’ by ’cross habitat functional redundancy’? • => both may reduce interspecific competition and increase response • diversities to changes in resources • Compartmentalization – high or low? • - high – relative to winter distributions • - ??

11. Spatial organisation of the pelagic community • SPATIAL PATTERNS IN PRIMARY PRODUCTION AND DIVERSITY

12. Average PP 03-07 Average PP 03-07 Aug - Sept CV PP 03-07 CV PP 03-07 Aug - Sept

13. Krill and amphipods Numberofgroups 03-07 (0-2)

14. 0-group fish Numberofspecies 03-07 (0-12) Average CV 03-07

15. Pelagicfish Numberofspecies 03-07 (0-4) Average CV 03-07

16. Marine mammals Effort 03-07 N arter 03-07, 0 – 17 arter Effort 03-07, 0 – 17 arter

17. Seabirds N arter 03-07, 0 – 9 arter

18. N top predator species, withwhaleeffort Marine mammals + seabirds + cod

19. N species, withwhaleeffort

20. Summary • (Very) preliminaryresultsindicate • Weak spatial gradients in speciesrichness • Highestspeciesdiversity in frontal areas – (and shallower areas?) and not in Arctic or Atlantic waters • No associationwithproductivity gradients Finally: • Suggest to focusonthreecommunities; • Benthic • Demersal • Pelagic; including zooplankton and top predators; - iffeasible; limited spatial coverage by top predator data

21. Seabirds, 4 alcid, fulmar, 4 gull species, 2003 - 2007 N seabirdindividuals Density, alcidindividuals Density, gull + fulmarindividuals

22. 2003 - 2007 Numberofwhalespeciesobserved Numberofwhaleindividualsobserved Numberofwhalespecies observed, effortcorrected Numberofwhaleindividuals observed, effortcorrected Effort