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Authors: SØREN LAURENTIUS NIELSEN, KAJ SAND-JENSEN, JENS BORUM AND OLE GEERTZ-HANSEN

Depth Colonization of Eelgrass ( Zostera marina ) and Macroalgae as Determined by Water Transparency in Danish Coastal Waters (2002). Authors: SØREN LAURENTIUS NIELSEN, KAJ SAND-JENSEN, JENS BORUM AND OLE GEERTZ-HANSEN. The main Actors. Outline of the paper.

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Authors: SØREN LAURENTIUS NIELSEN, KAJ SAND-JENSEN, JENS BORUM AND OLE GEERTZ-HANSEN

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  1. Depth Colonization of Eelgrass (Zostera marina) and Macroalgaeas Determined by Water Transparency in Danish Coastal Waters (2002) Authors: SØREN LAURENTIUS NIELSEN, KAJ SAND-JENSEN, JENS BORUM AND OLE GEERTZ-HANSEN

  2. The mainActors

  3. Outline of the paper • A comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalga • 162 transects in 27 Danish fjords and coastal waters • Coupled to 1400 dataseries of water chemistry (nitrogen) and Secchi depth Why is it important to now how Secchi depth and nitrogen affect the lower limits of eelgrass and macroalgea?

  4. Introduction • Eelgrass is a rooted macrophyte • Eelgrass and macroalgea are important for the structure and function of coastal marine ecosystem • Both macroalgea and eelgrass increase sedimentation • Eelgrass stabilise the sediment • Refuge for fish and invertebrates

  5. Introduction • Depth distribution of eelgrass and macroalgae decrease with increasing eutrophication • The main parameter limiting macrophyte depth colonization is light • Macrolagea can grow deeper than seagrass • Probably due to less non photosynthetic tissue • Light penetration depth is meassured as Secchi depth

  6. The Secchi Disc

  7. Secchidepth • Correlates to 5-20% irradiance left • Easy meassuring protocol • Often used due to the convenience of the method • Secci depth is strongly dependent on nutrient concentration • Nitrogen is often the most important nutrient controlling net primary production and Secchi depth in coastal marine areas

  8. Hypothesis • “Under the assumption that light penetration limits macrophyte depth colonization there will be a linear relationship between Secchi depth and maximum depth of colonization of macrophytes” • ”Due to the higher proportion of non-photosynthetic tissue in eelgrass (e.g., roots and rhizomes), leading to relatively higher respiratory costs, we expect eelgrass to exhibit lower absolute depth limits”

  9. Results Median: 3,6m Median: 550ug N*l-1 Extremely high value for marine areas

  10. Results Brown algea is also dependent on appropriate substrate

  11. Results

  12. Results

  13. Conclusion • There is highly significant, simple linear relationships between Secchi depth and maximum depth of colonization for both eelgrass and macroalgae. • These relationships, although highly significant, show a relatively wide scatter and can only serve as models describing the overall trend and the relative change in depth limit of macrophytes occurring with a certain change in Secchi depth.

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