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Changes in Intertidal Communities in Strangford Lough

Changes in Intertidal Communities in Strangford Lough. S. Vize, S.J. Preston & A. Portig. Introduction. Northern Ireland Littoral Survey (NILS) Strangford Lough Ecological Change Investigation (SLECI) Sites Methodology Summary of SLECI intertidal findings Conclusions.

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Changes in Intertidal Communities in Strangford Lough

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  1. Changes in Intertidal Communities in Strangford Lough S. Vize, S.J. Preston & A. Portig

  2. Introduction • Northern Ireland Littoral Survey (NILS) • Strangford Lough Ecological Change Investigation (SLECI) • Sites • Methodology • Summary of SLECI intertidal findings • Conclusions

  3. Northern Ireland Littoral Survey (NILS) completed in 1980’s (Wilkinson et al., 1988) • 200 sites around Northern Ireland • 59 sites in Strangford Lough • 29 sediment sites • 30 rocky shore sites • Strangford Lough Ecological Change Investigation (SLECI) 2003-’04 • 17 sites in Strangford Lough • 8 sediment sites • (4 firm, 4 soft) • 9 rocky shore sites

  4. Shores of Strangford Lough • Major rocky shore habitat – boulder in nature; ranging from cobbles to large boulders • Boulder shores may be steep & narrow or gently sloping & extensive • Areas of muddy sand & muddy gravel & pebbles – often associated with boulder shores • Rocky shores on eastern side of lough physically more diverse than western • Western shores are siltier than slightly more wave exposed eastern shores • North end – wide sedimentary flats, mainly muddy sand

  5. Soft-Sediment Sites Mahee Island North • Black Causeway, Mahee Island North, Quarterland Bay & Taggart Island • Sampling from boat at high water • 10 x Van Veen grabs (0.0625m2) • Sieved (1 mm), retained, preserved and identified • 2 grabs (abundance); 8 grabs (presence/absence)

  6. Firm-Sediment Sites Greyabbey Bay Mid Island Bay Reagh Bay NewtownardsA - E

  7. Firm-Sediment Sites • Location descriptions & sketch maps from NILS survey examined • Samples from upper, upper-mid, mid, mid-lower and lower shore • 5 cores at each shore height/location • NILS survey: 5 x box cores (0.01 m3) • SLECI survey: 5 x cylinder cores (0.025 m3) • Sieved (1 mm), retained, preserved and identified • 1 core (abundance); 4 cores(presence/absence)

  8. Rocky Shore Sites Green Island Mahee Island Marlfield Rocks Long Sheelah Kircubbin Point

  9. Rocky Shore Sites • Original NILS transect locations revisited and re-surveyed • All zones described and compared to NILS • NILS survey methodology repeated: 8-point abundance scale • Species composition within each zone: abundance of species identifiable in the field determined; unknown species collected for identification in the lab. • Voucher specimens collected and preserved

  10. Soft-Sediment Sites Total number of species during NILS and SLECI survey, along with mean ( se) number of species per site recorded by SLECI. Pooled data from 10 x 1 litre Van Veen grabs

  11. Firm-Sediment Sites Newtownards Sites A - E +16 +19 +13 +8 +10 +3 +4 +11 +3;; Total number of species at Newtownards sites A - E Strangford Lough. NILS survey: 5 x box cores (0.01 m3) pooled and SLECI survey: 5 x cylinder cores (0.025 m3) pooled.

  12. Firm-Sediment Sites Newtownards Sites A - E Two-dimensional MDS plot showing similarity relationships between the community composition at firm sediment sites (A-E) located at Newtownards, from NILS and SLECI surveys.

  13. Firm-Sediment Sites Greyabbey Bay +3;; Number of species recorded at different shore heights during the NILS survey and the SLECI survey at Greyabbey Bay. NILS survey: 5 x box cores (0.01 m3) pooled and SLECI survey: 5 x cylinder cores (0.025 m3) pooled

  14. Firm-Sediment Sites Mid Island Bay Number of species at different shore heights from NILS survey and SLECI survey, Mid Island Bay. NILS survey: 5 x box cores (0.01 m3) pooled and SLECI survey: 5 x cylinder cores (0.025 m3) pooled.

  15. Firm-Sediment Sites Reagh Bay Number of species at different shore heights from NILS survey and the SLECI survey at Reagh Bay. NILS survey: 5 x box cores (0.01 m3) pooled and SLECI survey: 5 x cylinder cores (0.025 m3) pooled.

  16. Rocky Shore Sites ANOSIM R = 0.176, p = 0.001 Two-dimensional MDS plot showing similarity relationships between the community composition at different zones on the shore at rocky shore sites. ANOSIM R = 0.122, p = 0.002 Two-dimensional MDS plot showing similarity relationships between the community composition at different zones on the shore at rocky shore sites. BEFORE AFTER

  17. Species Average Abundance Percent Contrib. NILS SLECI (average dissim.= 73.56) Verrucaria maura 1.86 2.19 1.87 Hildenbrandia rubra 1.64 3.31 1.61 Ascophyllum nodosum 2.00 2.24 1.58 Fucus spiralis 1.02 1.45 1.58 Littorina saxatilis 0.62 2.02 1.52 Semibalanus balanoides 2.36 2.50 1.48 Fucus serratus 2.12 2.00 1.46 Pelvetia canaliculata 0.86 1.14 1.41 Spirorbis spp. 1.95 2.17 1.40 Gibbula cineraria 1.45 2.50 1.40 Patella spp. 2.00 2.71 1.34 Polysiphonia spp. 1.45 2.33 1.31 Carcinus maenas 1.24 2.52 1.29 Littorina littorea 1.67 2.07 1.26 Rocky Shore Sites SIMPER analysis results: the average abundance and percentage contributions of the species that contributed most to the Bray-Curtis dissimilarity for each survey.

  18. Rocky Shore Sites South Island Photo from SLECI survey - 2003 Photo from NILS survey - 1986

  19. North end - 2001 North end - 2002

  20. Invasive Alga Sargassum muticum present: Chapel Island Causeway Kircubbin Point Marlfield Rocks Limestone Rock Long Sheelah South Island

  21. Summary • Soft-sediment sites: high spatial variability – not indicative of temporal change • Firm-sediment sites: expected increase in numbers of species due to doubling sampling effort • Rocky shore sites: significant difference between NILS & SLECI surveys – difference still apparent after species repertoires refined to reduce survey/species expertise • Loss of Ascophyllum nodosum at Marlfield Rocks, Mahee Island, Kircubbin Point, South Island. • Japanese alga Sargassum muticum now present in Strangford Lough.

  22. Acknowledgements • Investigation commissioned by the Environment and Heritage Service, Northern Ireland • Adam Mellor (DARD) for assisting with boat work • David Hall (Unicomarine) NMBAQCS quality control • Mark Johnson (QUB) and James Strong (DARD) for assisting with data analysis • Christine Maggs (QUB) for assisting with algal identification

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