Trophic complexities in a diverse gelatinous community : An isotopic perspective

1. Trophic complexities in a diverse gelatinous community: An isotopic perspective Nicholas Fleming1, Jonathan Houghton1, Jason Newton2 & Chris Harrod1,3 1Queen’s University Belfast, 2NERC Life Science Mass Spectrometry Facility & 3University of Antofagasta, Chile

2. Until recently gelatinous zooplankton (GZ) were viewed as peripheral or transient components within marine ecosystems…this perception is rapidly changing Negative effects (coastal industries, fisheries recruitment, disease vectors) Positive effects (developmental habitat for commercial fish species)

3. Background to present study It has been suggested that gelatinous zooplankton (GZ) blooms might fill the niche left by declining fish populations Yet very few marine ecosystem models currently include GZ, & those that do rarely capture their complex life history & ecology as required to successfully simulate alternate fish–jellyfish stable states Here we investigated the trophodynamics of a multi-species gelatinous assemblage within a temperate coastal marine system

4. Study site: Strangford Lough, Northern Ireland Strangford Lough

5. Diverse assemblage of gelatinous zooplankton Ctenophores & scyphozoan jellyfish Pluerobrachiapileus Bolinopsis infundibulum Beroecucumis Cyanealamarckii Cyaneacapillata Aurelia aurita

6. Sample collection & processing • GZ collected with hand nets • Monthly sampling (May-August 2010) • Putative prey sampled with plankton nets • All samples dried @ 60oC to dry mass • Samples processed fresh to avoid preservation effects • (Fleming et al. 2010. Marine Biology. 158: 2141-2146) • Jellyfish bells provided integrative measure of prey assimilation over time • Isotope analysis: NERC Life Science Mass Spectrometry Facility

7. Stable isotopes in food webs: you are what you eat + x: Where x = Δ13C  1 ‰ and Δ15N  3.4 ‰. 1‰ ≈ 1 trophic level

8. Q1: Were there distinct inter-specific differences in trophic ecology? Fleminget al. (in prep.)

9. Q1: Were there distinct inter-specific differences in trophic ecology? PERMANOVA (δ13C & δ15N) Species: Pseudo F2,118 = 3.7, P = 0.01; Month: Pseudo F3,118 = 17.9, P = 0.001 Species x Month: F6,118 = 1.97, P = < 0.05 Fleminget al. (in prep.)

10. Q2: Did the trophic position of individual species scale allometrically? NB: Baseline δ15N (estimated via blue mussel) did not change temporally allowing direct comparison of δ15N values. No Yes – shift by 6.4 ‰ (ca. 3 TLs) Yes –shift by 8.4 ‰ (ca. 4 TLs) Fleminget al. (2010); Fleminget al. (in prep.)

11. Q3: How did the trophic position of gelatinous zooplankton (all species combined) change over the duration of the summer? Fleminget al. (in prep.)

12. Q4: Was there any evidence of trophic overlap with the fish community? Some overlap, e.g. with pelagic and commensal species but overall, GZ and fish inhabit distinct foodwebs PERMANOVA (δ13C & δ15N) Pseudo F1,405= 394.9 P = 0.0001 Fleminget al. (in prep.)

13. Summary • To better integrate GZ into food web models we asked 4 specific questions: • Inter-specific differences in trophic ecology? YES • Trophic position scales allometrically within species? YES (A.a & C.c) • Shifts in trophic position of GZ community throughout summer? YES • Trophic overlap with fish community? YES (but evidence of distinct food webs) • Salient point: GZ play a complex & ever changing role in marine food webs

14. Acknowledgements (funding): Acknowledgements (field and lab work): QUB: Natalie McCullagh, Phillip Johnston & Julia Sigwart

15. How did the trophic niche of gelatinous zooplankton (all species combined) change over the duration of the summer? INCREASE IN ISOTOPIC NICHE WIDTH Ellipses = Bayesian estimates of isotopic niche width occupied by GZ community in each month Using SIBER (Jackson et al. 2011 J Anim. Ecol. 80: 595–602)