Mr Hartvig Christie1, Dr Camilla Fagerli1
1Norwegian Institute For Water Research, NIVA, Oslo, Norway
An outbreak of the green sea urchin (Strongylocentrotus droebachiensis) along the Norwegian coast in the 1970-ies lead to extensive loss of Laminaria hyperborea and Saccharina latissima kelp forests between 63 and 71oN. More recent, kelp recovery has been observed. Introduction of the red king crab to some high latitude fjords and effects of increasing sea temperature on sea urchin and crab populations at lower latitudes, has caused the disappearance of sea urchins and rapid kelp ecosystem recoveries. Dynamics of the key species have been further documented along this large scale latitudinal gradient by quantitative recordings of 1) distribution of kelps and sea urchins over time, 2) distribution of sea urchin recruits, 3) distribution of crab species from fishery statistics and standardized fishing by baited traps, and 4) predation experiments with different size groups of crab species and sea urchins. Between 63 and 66oN sea urchin recruitment is affected by increasing temperature. Kelp recovery has lately increased north to 69oN in spite of high sea urchin recruitment, correlated with increasing crab populations north to this latitude. Further north, the sea urchins still dominate with exception of a few fjords with high densities of red king crabs. Experiments have shown predation efficiency particularly by the crab species Cancer pagurus and Paralithodes camtschaticus. This study underlines the importance of sea urchin predators for persistence of recovered and restored kelp forests.
Biography:
Camilla Fagerli and Hartvig Christie are marine biologist working with kelp forest ecosystems at Norwegian Institute for Water Research. They have many years of close cooperation in field as well as supporting experimental studies. A hot topic is sea urchin grazing of kelp forests.
