Benthic macrophytes

The Norwegian coastline is more than 100,000 km long including skerries and islands. The most common coastal biotope is rocky shores, occurring at both exposed and protected stretches. Rocky shores from the intertidal zone and down to around 40 - 50 m depth are dominated by macroalgae. On sandy and muddy bottoms eelgrass, Zostera marina, can grow found from just below the intertidal zone and down to >10 m depth. Macroalgae and eelgrass are forming lush vegetation habitats along our coast and can by a common name be referred to as macrophytes. These macrophyte beds are considered as an important contributor to primary production in shallow areas and in addition to create habitats for other plants and animals.


Eelgrass is a higher plant, and is one of approx. 60 different species of seagrass worldwide. Seagrass species have an upright above ground biomass (above the sediment surface) consisting of stems and photosynthetic leafs, and a below ground biomass consisting of horizontal rhizomes and roots. Eelgrass reproduce sexually by having pollination under water, the pollen is tread-like and drifts in the water until it finds a female flower.  After fertilization a seed is formed. Fertile shoots are round in cross-section and branched and thereby easy to separate from the flat, unbranched vegetative blades. The above ground biomass is important as habitat for other organisms, as algal epiphytes, macrofauna and fish. The below ground biomass is important in order to transport oxygen down into the sediments and thereby preventing the sediment to go anoxic, which in turn is important for the sediment living fauna (infauna). During surveys of 4 eelgrass sites in Norway a total of 130 taxa of epiphytes, 127 taxa of macrofauna connected to the blades, and 113 species of infauna were recorded. Beach seine hauls in eelgrass beds catches astonishing amounts of small fish, dominated by gobies, but also sticklebacks and pipefish are common. Eelgrass meadows are also important as habitat for juvenile cod and other fish of commercial interest. 


The intertidal is mostly dominated by different fucoids. These brown algae form vertical belts, zonation patterns, caused by the ability to retain photosynthesis after desiccation when the tide is out, and their competitive ability with other species in the intertidal. The dominating genus is Fucus, with species like F. spiralis, F. vesiculosus and F. serratus. In addition a sheltered areas will have species such as Pelvetia canaliculata and Ascophyllum nodosum. More exposed areas are dominated by filtering organisms, such as blue mussels and barnacles, in addition to some small red algae.  The fucoids that dominated the sheltered shores are replaced by Fucus distichus and Himanthalia elongata, two species that better can tolerate the high-energy environment.


Below the littoral zone is the sublittoral. This zone goes down to the depth where there is to little light for algal growth, in Norway this may be around 40 – 50 m, depending on the  turbidity of the water. This sublittoral zone is dominated by kelp. In the shallow part Laminaria digitata dominate, and in sheltered sites this is followed by Saccharina latissima. In more exposed sites Laminaria hyperbora is the dominant species. Kelp forests are known as species rich habitats that house a variety of different species of crustaceans, gastropods, echinoderms and fish. At the most, 100 000 individuals of invertebrates has been recorded form one kelp plant.


Laminaria hyperborea is used as raw material for production of alginates. These are salts of two organic acids, guluronic acid and mannuronic acid. Depending on which positive ion that replaces the H+ in the acid group different properties of alginates can be made. Alginates are today used in many products such as bakery, colored clothes, pet food as well as medicine and pharmaceutical products.


Saccharina latissima are today cultivated to produce biofuel. The alga is grown in so-called multitrophic systems where the algae are using waste products from fish farms. The harvested biomass can then be fermented into methane or other biofuel products.


The green sea urchin Strongylocentrotus droebachiensis is able to graze down the kelp forests. This was discovered in the late 1960s early 1970s. Grazing has been observed from Trøndelag and north to the Russian border. After the kelp forests have disappeared a " stone desert under water " or a so-called “barren ground” with nothing left than denuded rock, except for the urchins. However, there are signs that the kelp is returning in the southernmost areas where grazing have been prominent. The reason for this regrowth may be a combination of elevated temperature and the increased abundance of predators, mainly crabs.



Selected papers:


Fredriksen S. & H. Christie 2003. Zostera marina (Angiospermae) and Fucus serratus (Phaeophyceae) as habitat for flora and fauna – seasonal and local variation. Proceedings 17th International Seaweed Symposium, Cape Town, South Africa. pp 357-364

Norderhaug K.M., S. Fredriksen & K. Nygaard 2003. The trophic importance of Laminaria hyperborea to kelp forest consumers and the importance of bacterial degradation on food value. Marine Ecology Progress Series 255:135-144

Fredriksen S. 2003 Food web studies in a Norwegian kelp forest based on stable isotope (13C and 15N) analysis. Marine Ecology Progress Series  260:71-81.

Fredriksen S., H. Christie & C. Boström. 2004. Deterioration of eelgrass (Zostera marina L.) by destructive grazing by the gastropod Rissoa membranacea (J. Adams) Sarsia 89:218-222.

Abdullah M.I. & S. Fredriksen. 2004. Production, Respiration and Exudation of Dissolve Organic Matter by the kelp Laminaria hyperborea (Gunnerus) Foslie along the west coast.of Norway. Journal of the Marine Biollogical Association of the  United Kingdom. 84:887-894

Fredriksen S., H. Christie & B.A. Sæthre 2005. Species richness in macroalgae and macrofauna assemblages on Fucus serratus L. (Phaeophyceae) and Zostera marina L. (Angiospermae) in Skagerrak, Norway. Marine Biology Research 1:2-19.

Norderhaug K.M., H. Christie, J.H. Fosså & S. Fredriksen. 2005. Fish-macrofauna interactions in a kelp (Laminaria hyperborea) forest. Journal of the Marine Biological Association of the United Kingdom. 85:1279-1286.

Norderhaug K.M., K. Nygaard & S. Fredriksen. 2006. Importance of phlorotannin content and C:N ratio of Laminaria hyperborea in determining its palatability as food for consumers. Marine Biology Research 2:367 – 371.

Norderhaug K.M., H. Christie & S. Fredriksen. 2007. Is habitat size an important factor for faunal abundance on kelp (Laminaria hyperborea)? Journal of Sea Research 58:120-124.

Christie H., K.M. Norderhaug & S. Fredriksen 2009. Macrophytes as habitat for fauna. Marine Ecology Progress Series. 396:221-233

Fredriksen S., A. de Backer, C. Boström & H. Christie 2010. Infauna from Zostera marina (L.) meadows in Norway. Differences in vegetated and unvegetated areas. Marine Biology Research 6:189-200.

Andersen G. S., H. Steen, H. Christie, S. Fredriksen & F. Moy 2011. Seasonal patterns of sporophyte growth, fertility, fouling and mortality of Saccharina latissima in Skagerrak, Norway. Implications for forest recovery. Journal of Marine Biology (Open access journal). Volume 2011. doi:10.1155/2011/690375

Pedersen MF, Nejrup LB, Fredriksen S, Christie H &  KM Norderhaug 2012. Effects of wave exposure on population structure, demography, biomass and productivity of the kelp Laminaria hyperborea. Marine Ecology Progress Series 451:45-60.

Boström C, Baden S, Bockelman AC, Dromph K, Fredriksen S, Gustavsson C, Krause Jensen D, Möller T, Nielsen SL, Olesen B, Olsen J, Pihl L & E Rinde 2014. Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: implications for coastal management and conservation. Aquatic conservation: Marine and freshwater ecosystems. DOI: 10.1002/aqc.2424

Abdullah MI & S Fredriksen 2014. The exudation of nitrate by the kelp Laminaria hyperborea, an observation during in situ incubation experimants. Marine Biology Research 10: 725-730

Fagerli CW, Norderhaug KM, Christie H, Pedersen MF & S Fredriksen 2014. Predators of the destructive sea urchin grazer Strongylocentrotus droebachiensis on the Norwegian coast. Marine Ecology Progress Series 502: 207-218

Fagerli CM, Stadnizenko SG, Pedersen MF, Christie H, Fredriksen S & KM Norderhaug 2015. Population dynamics of Strongylocentrotus droebachiensis in kelp forest and barren grounds in Norway. Marine Biology DOI 10.1007/s00227-015-2663-3

Duffy Emmett J., Pamela L. Reynolds, Christoffer Boström, James A. Coyer, Mathieu Cusson, Serena Donadi, James G. Douglass, Johan S. Eklöf, Aschwin H. Engelen, Britas Klemens Eriksson, Stein Fredriksen, Lars Gamfeldt, Camilla Gustafsson, Galice Hoarau, Masakazu Hori, Kevin Hovel, Katrin Iken, Jonathan S. Lefcheck, Per-Olav Moksnes, Masahiro Nakaoka, Mary I. O'Connor, Jeanine L. Olsen, J. Paul Richardson, Jennifer L. Ruesink, Erik E. Sotka, Jonas Thormar, Matthew A. Whalen & John J. Stachowicz 2015. Biodiversity mediates top–down control in eelgrass ecosystems: a global comparative-experimental approach. Ecology letters 18: 696-705. DOI: 10.1111/ele.12448


By Stein Fredriksen
Published Nov. 1, 2016 9:31 PM - Last modified Feb. 9, 2017 5:20 PM