Department of Oceanography, National University of Ireland, Galway, Ireland

1. Copepods and other netplankton of the Shannon estuary, Ireland,and two tributary estuaries: Composition and grazing pressure Ian R. Jenkinson* and Tom Ryan† Department of Oceanography, National University of Ireland, Galway, Ireland *Present address:Agence de Conseil et de Recherche Océanographiques,19320 La Roche Canillac, France.ian.jenkinson@wanadoo.fr †Deceased

2. Co-author Tom Ryan was killed in a car accident, and this presentation is dedicatedto his memory.

3. Co-author Tom Ryan was killed in a car accident, and this presentation is dedicatedto his memory. Financed as a baseline study by Aughinish Alumina (Ireland) Ltd (Alcan Group) Thanks to John Bracken and Geoffrey O’Sullivan (National University of Ireland Dublin and Department of the Marine, Ireland) Thanks to Brian McK. Bary, Mary Hensey and colleagues at this conference for discussions Work done at National University of Ireland Galway. Thanks to John Coyne and Tom Furey for technical help.

4. Ireland

5. Ireland Shannon Estuary

7. Flowmeter not shown

8. Calibration • 37 m3 for adult copepods and larger copepodids, including Oikopleura (as their houses are destroyed) • 210 m3 for larger plankton

9. Temperature (°C)

10. Salinity (ppt)

11. 1) 3) Secchi depth (m) 4)

12. Copepods

13. 1) 3) 4) 37 m3.haul-1 Eurytemora affinis   Thanks to http://www.cnas.smsu.edu/zooplankton/eurytemora_affinis.htm 1000.m-3

14. Eurytemora affinis   • Salinity of abundancedistribution over year and over all stations • 5 to 26 psu • Maximum at 16 psu Thanks to http://www.cnas.smsu.edu/zooplankton/eurytemora_affinis.htm

15. 1) 37 m3.haul-1 Acartia bifilosa   3) Yoon et al. (1998)J. Plankt. Res. 2000 m-3 4)

16. 37 m3.haul-1 1) Acartia clausi 3) 35 m-3 4)

17. Acartia discaudata Only on cruises in July,August and October (least in August) and at Stations 3 and 4.

18. 1) 37 m3.haul-1 Centropages hamatus 3) 4) 20 m-3

19. 1) 37 m3.haul-1 Freshwater cyclopoids 3) 4)

20. Other zooplankton

21. Mesopodopsisslabberi 1) 3) 4) 210 m3.haul-1 Supposed to feed mostly on phytoplankton. Good food for fishes. ~50.m-3

22. 1) 3) 4) Neomysis integer 210 m3.haul-1 Photo: Marco Faasehttp://www.marlin.ac.uk/species/Neomysisinteger.htmSupposed to feed mostly on phytoplankton. Good food for fishes.

23. Oikopleura dioica 1) ~100 m3.haul-1 ? Length up to ~2 mm. From Hardy, A. (1962),The Open Sea. After Lohmann(1899). 3) ~100.m-3 4)

24. Pleurobrachia pileus 1) 1) 210 m3.haul-1 Length up to 1-2 cmFrom Hardy, A. (1962),The Open Sea. After Marie Lebour and Mrs M.A. Connell 3) 4) 0.5.m-3

25. Copepod abundance(nos/haul, corrected for flowmeter reading) Copepod diversity(Shannon-Wiener index, H’) Filled triangles: H’Open triangles: abundance 37 m3.haul-1

26. Copepod abundance(nos/haul, corrected for flowmeter reading) Copepod diversity(Shannon-Wiener index, H’) Filled triangles: H’Open triangles: abundance 37 m3.haul-1

27. Copepod abundance(nos/haul, corrected for flowmeter reading) Copepod diversity(Shannon-Wiener index, H’) Filled triangles: H’Open triangles: abundance 37 m3.haul-1 Open triangles: H’Filled triangles: abundance

28. Clearance rate by Eurytemora affinis, Poulet (1978) found that ingestion rate [µg . copepod-1.h-1] (wet wt.) y = 0.218 + 0.135.x where x is the concentration of particulate matter (g.m-3 wet wt.). [POC] in the Shannon estuary averages around 600 mg.m-3 (say, 800 mg.m-3 near the bottom, where E. affinis is most abundant). In the Shannon estuary, microplankton (20-200 µm) contributes about 100 mg C.m-3. Using a factor of 20 to convert to wet weight this gives xaround 16 g.m-3, and y of 2.4 µg wet wt. copepod-1.h-1 ~2.9 µg C.copepod-1.d-1. So, clearance rate by Eurytemora Ge = (y/x) = (0.218/x) + 0.135

30. Carbon demand by Eurytemora affinis, D = [(A.a) + (C.c) . P . (1/E)] where A and C are the concentrations of adults and copepodids, and a and c are there respective masses. P is the dailyproductivity (a function of temperature) taken from Heinle & Flemer (1975) and E is conversion efficiency, taken to be 50%.

31. 5

32. Clearance rate by Acartia spp, (Ga) Poulet (1978) found that ingestion rate [µg . copepod-1.h-1] (wet wt.) y = 1.43 + 1.09.x where x is the concentration of particulate matter (g.m-3 wet wt.). The Acartia spp adults in the Shannon are about the same size. As Acartia need more a higher proportion of phytoplankton than Eurytemora, it has been assumed that only half the POC is available to them, 460 mg.m-3, ~8.8 g.m-3 (wet weight). This gives Ga for adult Acartia of 3.0 cm3.copepod-1.d-1. By comparison experimentally determined Ga by Acartia tonsa of 1.5 to 3.7 cm3.copepod-1.d-1 were shown by Roman (1977). Assuming Ga = (Aa . 3) + (Ca . 1.5) where Aa and Ca are the respective concentrations of adults and copepodids.

35. Clearance rate by Oikopleura dioica (Go) King (1982) found that a concentration of 1,000 m-3 of Oikopleura dioica gave a clearance rate of 0.2 d-1 at 14°C. This gives Go of 200 cm3.larvacean.d-1. O. dioica feeds on bacterioplankton from less than 1 µm to phytoplankton of 30 µm, and it needs a minimum concentration of 40 to 60 mg C.m-3 of such plankton as POC. Without this concentration it dies in a few days, but with it, it doubles, on average every day (King, 1982).

36. Go 76

38. M. slabberi E. affinis 1) 1) 3) 3) 4) 4) 37 m3.haul-1 210 m3.haul-1