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OXB2005 Zooplankton

Faraday
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OXB2005 Zooplankton

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    1. OXB2005 Zooplankton Indicator species

    3. Why are indicator species important? We can use some zoo-plankton species as INDICATORS of different water masses and environmental changes. Water quality indicators (pollution) Climate changes indicators (global warming) Predict changes in World fisheries (food of fish-larva)

    4. Zoo-geography of the Zooplankton How can we have indicator species? Oceans/water masses are very different in their chemical and physical properties. Temperature Salinity Chemical constituents and also Plankton communities

    5. Zoo-geography of the Zooplankton Characteristics of water masses can change between: Regions Ocean Basins Seasons Each water mass is associated with a different abundance and composition of plankton since: plankton species are very sensitive to environmental conditions their distribution is dictated by the species ability to survive and /or to reproduce in a given water mass.

    6. Zoo-geography of the Zooplankton Regional differences in Zoo-plankton distribution results in: Neritic species Oceanic species Intermediate species Cosmopolitan species

    7. Zoo-geography of the Zooplankton Neritic species are found in coastal waters where the conditions of temperature and salinity show large changes. Examples are: Sagitta setosa (Chaetognath) Temora longicornis (copepod) Centropages hamatus (copepod) Larvae of benthic species (e.g. Barnacles)

    8. Zoo-geography of the Zooplankton Oceanic species: live in more stable ecological conditions (temperature, salinity) and often in a greater range of water depths. Pleuromamma gracilis (copepod) Siphonophores (Cnidaria) Heteropods (mollusca)

    9. Zoo-geography of the Zooplankton Intermediate species are found between neritic and oceanic areas. Sagitta elegans (Chaetognaths) Euphasids (Crustacea)

    10. Zoo-geography of the Zooplankton Cosmopolitan species: few species have an ocean-wide distribution. Examples of such species are: Oithona similis (copepod) Beroe cucumis (ctenophore) Pleurobrachia pileus (ctenophore)

    11. Zoo-geography of the Zooplankton Expatriation areas (Ekman, 1953) Species distribution is controlled mainly by temperature. A large body of water can carry zoo-plankton to new areas hundreds of miles from where they reproduced. They may stay alive but cannot reproduce or may die due to slow temperature changes with time of original water mass. Lusitanian plankton carried by deep currents (600 m depth) from Mediterranean up to the Shetlands islands (Scotland). Species: Sagitta lyra and Pelagia noctiluca, salps.

    12. Zoo-geography of the Zooplankton Latitudinal differences in distribution Zooplankton can be divided into geographical areas based on temperature. Tropical Temperate Polar

    13. Zoo-geography of the Zooplankton Tropical seas: Lower water density Higher surface temperatures Great species diversity Salps Heteropods Majority of pteropods Several siphonophores (Velella and Physalia)

    14. Zoo-geography of the Zooplankton Temperate oceanic waters: Lower diversity (few species dominant) Calanus community Calanus finmarchicus (dominant) Metridia lucens Eucheta norvegica Pseudocalanus sp. Oithona similis Euphasids (Thysanoessa sp.) Intermediate waters Meganictiphanes norvegica (Euphasids), Sagitta elegans (Chaetognaths), Centropages typicus (copepod).

    15. Zoo-geography of the Zooplankton Polar Latitudes: High water density Large body sizes Low diversity Euphasia superba (Euphasid, Krill) Calanus glacialis (copepod) Calanus hyperboreus (copepod) Metridia longa (copepod) Limacina helicina (pteropod) Martensia ovum (ctenophore)

    16. Zoo-geography of the Zooplankton Seasonal differences in Zoo-plankton living in Temperate latitudes Seasonal changes in Zoo-plankton species are due to different life/reproductive cycle, resistance to environmental factors, competition/predation among species. Thus, the plankton composition can also be used to identify the season.

    17. Zoo-geography of the Zooplankton Seasonal changes in zoo-plankton of the Menai Strait, North Wales, UK Winter: Low diversity, mainly holoplankton species large adult copepods like Pseudocalanus elongatus (dominant, cold water species), Temora longicornis, Centropages hamatus, Sagitta sp., some flat-fish larva and egg. Sparse meroplankton mostly eggs of Littorina sp. (gastropod) and sparse crab zoea. No or limited larval stages.

    18. Zoo-geography of the Zooplankton Spring: Higher diversity, mainly meroplankton species including the larvae of many benthic species like barnacle nauplii, crab zoea, mollusc larvae, Terebellid larvae (tube worm). Holoplankton: Herrings, sprat (fish larvae), Temora and Centropages (dominant), many copepodite stages, increase in Pleurobrachia pileus, Beroe sp. (predators on copepods).

    19. Practical use of indicators An unknown zoo-plankton samples can be analysed and described to a seasonal and a geographical area based on the species of holoplankton and the meroplankton it contains. Thus, we can identify the origin of the plankton and of its water mass. Water masses can be followed not only by their temperature, salinity chemical composition but also by their planktonic organisms which TAG them and are called INDICATOR SPECIES.

    20. Zoo-geography of the Zooplankton Summer: high diversity, mainly copepod of small sizes. Holoplankton: Acartia clausii (dominant, from resting eggs hatching in summer), Pseudocalanus sp. (lowest). Meroplankton: polychates, mollusks and crab larvae (megalopa). Autumn: Lower diversity, small copepods. Holoplankton: majority Pseudocalanus sp. (dominant), numerous Sagitta setosa and Pleurobrachia pileus, numerous bivalve larvae.

    21. Practical use of indicators How do we use INDICATOR species ? A good indicator species should: Be common enough in all samples in a given area Be easy to pick out under low magnification Be linked with the original centre of abundance Be restricted in his reproductive ability

    22. Practical use of indicators Changes in the abundance of some marine zoo-plankton species are associated with long-term changes in the oceanic climates: Examples: Russell Cycle (British Isle) Calanus finmarchicus & NAO-index (North Atlantic Oscillation Index) Peruvian Anchovy & ENSO (El-Nino Southern Oscillation)

    23. Practical use of indicators Russell Cycle The development of the study of plankton indicators was greatly stimulated by the work of: Russell (1939) English Channel, Western Approaches Meek (1921-27) North Sea, Northumberland coast Documented a complex series of changes in the plankton community around the British Isle .

    24. Practical use of indicators Study of Chaeognaths species Saggita elegans and S. setosa and their associated plankton community as indicators of the water masses movements around British Isle. Chaetognaths are easy to identify, are big and are restricted to certain water masses.

    25. Practical use of indicators Sagitta elegans: Intermediate species (e.g. between oceanic and neritic waters). Max body length 30 mm Long ovary in adult Conical seminal vescicles, far from lateral fins Stiff body when preserved Distribution: Northern North Sea, Western English Channel, Western Irish Sea.

    26. Practical use of indicators Richer waters: high plankton diversity, high plankton concentration, high salinity & nutrients. S. elegans water : Calanus finmarchicus, Centropages typicus, Euphasids (meganictiphane), Aglantha digitale (trachimedusa), Cosmetira pilosella (hydroid), Candacia sp., Tomopteris (polychaete), Euthemisto (hyperid), sparse larvae, herring and/or mackerel.

    27. Practical use of indicators Sagitta setosa: Neritic species Max body length 14 mm; Short ovary in adult Wedge shaped seminal vescicles, near lateral fins Flexible body when preserved Poorer waters: Low plankton diversity, low plankton concentration, low salinity, low nutrients. S. setosa water: Temora longicornis, Centropages hamatus, Isias claviceps, Oithona nana, mysids, numerous larvae, pilchard. Distribution: Southern North Sea, Eastern English Channel, Eastern Irish Sea.

    28. Practical use of indicators The Russell Cycle Northumberland coast Meek observed that the relative abundance of the two Sagitta species fluctuates around the Northumberland coast He concluded that hydrographic conditions affected the extent of distribution: Strong flow of Atlantic water in North Sea ? S. elegans spreads South. Weak flow of Atlantic water in North Sea ? S. setosa spreads North

    29. Practical use of indicators The Russell Cycle -English Channel Russell investigated the long term distribution of S. elegans and S. setosa in the English channel between 1930-60. Observed fluctuation in Chaetognaths species abundance and water mass characteristics over time at Plymouth station.

    30. Practical use of indicators Prior 1930s S. elegans dominant West of Plymouth and S. setosa dominant to the East 1950s - 60s S. elegans retreat west of Plymouth Increase in Temperature (~ 0.5 ?C mean) Decrease in nutrients Phosphate Decrease in herring , increase in pilchard

    31. Practical use of indicators 1970s-90s Shift Reverse of trend prior to 1930s S. elegans advance East of Plymouth Decrease in Temperature Increase Phosphate Increase in Sardina pilchardus which replaced Clupea harengus

    32. Practical use of indicators These shifts in water masses caused the collapse of the herring fisheries and replacement with the pilchard in the 50-60s. Reverse of cycle in the 70s with the collapse of pilchard and the reappearance of the herrings with the mackerel. Duration of the Cycle from the 1930s to 70s was 40 years

    33. Russell Cycle

    34. Causes of plankton changes Why should one plankton community replace another with a 40 years cycle? Nutrient changes (phosphate) Over-fishing Natural cycles Direct Climate effect Indirect Climate effect

    35. Causes of plankton changes Nutrient changes Due to variation in the flow of water in the channel, from elegans (mixed water) to setosa waters (coastal). Lower levels of Phosphate in the 1950-60's, but increase of S. elegans preceded nutrients increase.

    36. Causes of plankton changes Over-fishing community controlled by the top predator. If herring was over-fished the Pilchard would replace it. However, all the species including herrings, mackerel and pilchard were heavily-fished. Natural fluctuations Assume a change in the food of the plankton. However, primary production in the English Channel hasn't changed much over last century. Thus, zoo-plankton and fish change no due to phytoplankton production. No change in community but a shift in communities.

    37. Causes of plankton changes Direct climate changes Sun spot activity poorly correlated with plankton Indirect climate changes Change of the rate of water mass flows into channel have pushed setosa/elegans boundary backwards and forwards

    38. Causes of plankton changes North Atlantic drift (NAD): Warm periods extension of NAD spreads north into Arctic, Gulf Stream wider spread, weak flow in English Channel and S. setosa goes West Cold periods NAD spread south Gulf Stream tighten, strong flow in English Channel and the S. setosa retreats East. But, no evidences of salinity changes with different water masses.

    39. Causes of plankton changes There is general, agreement that the Russell cycle is associated with Climate changes. Ref: Southward (1980), Nature, 285:361-470 Russell Cycle has been recently linked with the NAO-index (Mann & Lazier, 1991)

    40. Definition ENSO and NAO-Index There are other evidences of indirect climate changes on plankton are: NAO-Index- The North Atlantic oscillation index is the dominant mode of inter-annual climate variability over the North Atlantic ocean (Northern Emi-sphere). ENSO El-Nio is a warm nutrient poor surface current that replaces the cold coastal up-welling off coast of Peru (Southern Emi-sphere).

    41. NAO-index and C. finmarchicus Long term fluctuation in NAO-index strength +ve correlation in C. finmarchicus abundance (PCA-Plankton Continuous Recorder) C. finmarchicus is an important in the diets of the fish larvae of many commercial fish stocks. Changes in Atlantic Salmon population Ref: Fromentin & Planque (1996), Marine ecology Progress Series, 134:111-18.

    42. NAO-Index & C. finmarchicus

    43. El-Nino and the Peruvian Anchovy Peruvian Fishery Developed in the 1950s to be a model of fisheries management. Anchovies eating plankton. Anchovy harvest 9-10 million Tons. Collapsed from 1970 onwards and has not recovered since. During El-Nio warm oligotrophic water pushed anchovies to feed deeper and birds starved. Ref.: Mann, K.H. & Lazier, J.R.N. (1991), Dynamics of marine ecosystem

    44. Peruvian Anchovy & El-Nio

    45. Suggested references 1) The Open Ocean, vol. 1, by Alister Hardy, (Wolfson Library) 2) Biological Oceanography an Introduction (1997), C.M. Lalli & T.R. Parson (Wolfson Library, QH91.L35.1997) 3) Mann, K.H. & Lazier, J.R.N. (1991), Dynamics of marine ecosystem, (Wolfson Library) 4) Southward (1980), The western English Channel - an inconstant ecosystem? Nature, 285:361-470 (Science Library) 5) Plankton and productivity in the Ocean, Vol. 2, J.E., Raymont (1980), Pergamon Press, (Wolfson Library, QH91.8.P5R3)

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