The Davis Strait - DCE - Nationalt Center for Miljø og Energi

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Sea urchins (Strongylocentrotus droebachiensis) are the most forceful grazers
on kelp forests. A high density of sea urchins can result in grazing down
of kelp forests leaving ‘barren grounds’ of stones, boulders and rocks, which
may be covered by coralline red algae only. If barren grounds are due to
grazing by sea urchins and not by ice scouring, the barren grounds will be
found below the intertidal vegetation as the sea urchins do not tolerate desiccation
(Christensen 1981).
Isotope (δ 13 C) analyses used to trace kelp-derived carbon in Norway suggest
that kelp may serve as carbon source for marine animals at several trophic
levels (e.g., bivalves, gastropods, crab, fish), and mainly enters the food web
as particulate organic material (Fredriksen 2003). Especially during the dark
winter period when phytoplankton is absent, an increased dependence on
kelp carbon has been measured (Dunton & Schell 1987). A study on fishmacrofauna
interactions in a Norwegian kelp forest showed that kelpassociated
fauna was important prey for the 21 fish species caught in the
kelp forest (Norderhaug et al. 2005). A reduction in kelp forest cover due to
harvest thus affected the fish abundance and diminished coastal seabird foraging
efficiency (Lorentsen et al. 2010).
Climate change will probably affect the macroalgal vegetation, primarily
due to a longer season with less ice and thereby a longer season for growth.
A change in northward distribution of species is therefore an scenario expected
to be coupled to oceanic warming (Müller et al. 2009). Furthermore, a
study of climate forcing on benthic vegetation in Greenland (Krause-Jensen
et al. 2011) suggests that depth range, abundance and growth of subtidal
vegetation belts will expand in correlation to a warmer climate; but the
study also concluded that those species with the most northern distribution
responded negatively to warming. In addition, melting of inland ice caps
leads to an increase in freshwater runoff, which may result in lowered salinity
and increasing water turbidity (Borum et al. 2002, Rysgaard & Glud 2007),
having a negative impact on the local macroalgae vegetation.
There are different reports on the impact of oil contamination on macroalgal
vegetations and communities. The macroalgal cover lost in connection with
the Exxon Valdez oil spill in 1989, as observed for Fucus gardneri PC Silva in
Prince William Sound, has taken years to fully re-establish as a result of the
grazer-macroalgae dynamics as well as intrinsic changes in plant growth
and survival (Driskell et al. 2001), and is still considered to be recovering
(NOAA 2010). In contrast, no major effects on shallow sublittoral macroalgae
were observed in a study conducted by Cross et al. (1987). It was discussed
that this might be due to a similar lack of impact on the herbivores as
well as the vegetative mode of reproduction in the dominant macroalgal
species. Thus, it has been shown that petroleum hydrocarbons interfere with
the sex pheromone reaction in the life history of Fucus vesiculosus
(Derenbach & Gereck 1980).
4.3.2 The macroalgal vegetation in the assessment area
A checklist and distribution of the marine macroalgal species in the assessment
area are presented in Table 1 based on Pedersen (1976) and Andersen
et al. (2005). Caution should be taken in interpreting the species distribution
as the species list is a positive list, which means that the species was registered
if it was collected and identified.