The executive summary from a report for the Crown Estate detailing the evidence for declines in large brown macroalgae.
A literature review was undertaken of the changes that have been reported in the distribution of fifteen large brown macroalgal species that characterise temperate rocky shores and the shallow subtidal in the marine environment in the UK and related areas in the North East Atlantic. The 15 species included eight kelps (Alaria esculenta, Chorda filum, Laminaria digitata, Laminaria hyperborea, Laminaria ochroleuca, Saccharina latissima, and Undaria pinnatifida [nonnative]), the kelp-like Saccorhiza polyschides and seven fucoids (Ascophyllum nodosum, Fucus serratus, Fucus spiralis, Fucus vesiculosus, Himanthalia elongata, Pelvetia canaliculata, and Sargassum muticum [non-native]). The northern and southern limits of these species occur outside the UK, with the exception of Laminaria ochroleuca, which is at its northern limit in the UK, and Alaria esculenta with its southern limit just into northern France. This makes the UK a stronghold for these large brown algae. Changes in the distribution of these species can be summarized as follows: i) decline in distribution: Alaria esculenta, Ascophyllum nodosum, Chorda filum, Himanthalia elongata, Laminaria digitata, Laminaria hyperborean, Pelvetia canaliculata, Saccharina latissima, and Saccorhiza polyschides, ii) depleted genetic diversity: Fucus serratus at southern end of its range, iii) range expansion: Fucus vesiculosus, Laminaria ochroleuca, Sargassum muticum and Undaria pinnatidfida and iv) no change: Fucus spiralis. Although explanations for the documented changes tend to be attributed to climate change, reasons are multiple and complex, including reproductive biology, impact of mild winters on the interaction between grazers and sporelings, increase in non-native species, change in current regimes and turbidity in the North East Atlantic and change in nutrients. Most of the decline that has been reported is not for the UK. It is therefore concluded that there is a need for an assessment of change in distribution of these species for this geographical region.
Bush L, Davies AJ, Maggs CA, Yesson C & Brodie J (2013) Review of evidence for the loss of large brown macroalgae. A report for the Crown Estate. (Full report as PDF).