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Alex Portig Quercus – The Queens University of Belfast.

Historical changes in Zostera spp. on Strangford Lough. Alex Portig Quercus – The Queens University of Belfast. Zostera marina (Kircubbin Bay). Zostera marina (subtidal) perennial. Zostera marina (intertidal) perennial. Zostera marina var. angustifolia (intertidal) annual .

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Alex Portig Quercus – The Queens University of Belfast.

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  1. Historical changes in Zostera spp. on Strangford Lough Alex Portig Quercus – The Queens University of Belfast.

  2. Zostera marina (Kircubbin Bay) Zostera marina (subtidal) perennial

  3. Zostera marina (intertidal) perennial

  4. Zostera marina var. angustifolia (intertidal) annual

  5. Zostera noltii (intertidal) perennial

  6. Importance of Seagrasses Primary production - Highly productive ecosystem Production = 2.7 g DW m-2 per day (Tropical forest 5.2 / Macroalgae 1.0) (Duarte, C.M. & Chiscano C.L. 1999 Aquatic Botany 65: 159-174) Other roles: • Provision of food for coastal food webs • Carbon sequestration from the atmosphere • Sediment stabilisation • Prevention of sediment re-suspension • Improvement of water transparency • Wave attenuation • Shoreline protection • Increased Biodiversity • Trapping and cycling of nutrients (Duarte, C.M. 2002 Environmental Conservation 29 (2): 192 – 206)

  7. Records of Zostera distribution - Strangford Lough • First detailed records Lynn 1936 • Bleakley 1971 • Corbett 1980 • Portig 1994 • No detailed records in between these times. • Late 1990s to present – research by QUB/Quercus funded by DARD (Rivers Agency) and EHS.

  8. 1930’s Based on Lynn’s descriptions and maps • Zostera marina (perennial) was widespread in the sub and intertidal and had declined dramatically in recent years. • Reasons for decline – has since been established as a wasting disease caused by a marine slime mould (Labyrinthula) • This occurred across the Atlantic seaboard and wide scale loss of Zostera marina on Strangford resulting in the break down of mud banks and sediment shift. • Zostera noltii considered rare. • Zostera marina var. angustifolia present.

  9. Records of Zostera marina on Strangford Lough – based on Lynn 1937

  10. Whiterock Bay 1936 (Degenerating Zosterentum)

  11. Relative Area 1970 - 100% 1980 - 49% 1990 - 30% 1970 – From Bleakley 1980 – From Corbett

  12. 1970 Based on Bleakley’s descriptions and maps • Zostera noltii dominant. • Zostera marina var. angustifolia present. • Widespread in the intertidal. • Patchy distribution in bays of Ardmillan and Whiterock. • No mention of Zosteramarina in intertidal.

  13. 1980 Based on Corbett’s descriptions and maps • Zostera noltii still dominant. • Zostera marina var. angustifolia present. • More restricted in distribution. • Loss chiefly from lower intertidal and from bays around Ardmillan and Whiterock. • No mention of Zosteramarina in intertidal.

  14. Early 1990’s • Zostera noltii still dominant. • Zostera marina var. angustifolia present. • Further restriction in its distribution. • Density considered low. • No Zostera marina in the intertidal found.

  15. Amount of Zostera calculated from counts of wildfowl (underlying trend). Using WEBS Data Blue line = raw data: Red line = underlying trend

  16. Early 2000’s • Zostera noltii still dominant. • Zostera marina var. angustifolia more widespread. • Limited expansion in distribution. • Density improved. • Zostera marina found in the intertidal !. • This was most apparent in the north end of the Lough.

  17. North end (1962)

  18. North end (1994)

  19. North end (2001)

  20. North end (1994) North end (1994)

  21. North end (2001)

  22. Brent Geese Total Birdmonths – North End Data WWT/NT - WEBS

  23. Causes of change? • Decline in 1930’s • Caused by wasting disease • Widescale loss of Z. marina from the intertidal • Likely to be also the case from the subtidal. • Not known if recovery occurred but by 1970 was absent from the intertidal. • Changed environmental conditions?

  24. Possible causes 1970 to present • Sediment stability ? • Competition with other species ? • Climate ? • Water clarity ? • Long term cycles ?

  25. Redrawn from Hemminga & Duarte 2000 Sediment Stability

  26. Damage caused by bait digging to Zostera noltii

  27. Browned Zostera noltii and Zostera marina var. angustifoliaStrangford Lough 2002

  28. North End Strangford Lough 2001

  29. North End Strangford Lough 2001

  30. North End Strangford Lough 2002

  31. Redrawn from: Kemp et al 2000

  32. Redrawn from: Kemp et al 2000

  33. The likely scenario ? • The restriction in distribution seen from 1970 to early 1990s most likely caused by reduced water clarity. • This is not to say that other factors do not play a role but are more likely to be localised. • Improvement over recent years is consistent with improved water clarity.

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