There is no doubt that seaweed and seagrass communities on shores and in shallow seas of the north-east Atlantic are changing, and that the pace of change is increasing at an alarming rate. If you take a look at the seashore along the south-west coast of England, for example, you will see rock pools stuffed full of seaweeds that, on closer inspection, are often dominated by non-native species such as the large brown seaweeds Sargassum muticum (wireweed) and Undaria pinnatifida (wakame). We know of 44 non-native seaweed species in the north-east Atlantic; whilst not all of these are invasive, species continue to arrive at an increasing rate. The region is undergoing such a rapid rate of acidification and warming that we expect this to combine with the spread of invasive species to drive radical changes in coastal ecosystems.

In June 2013, we brought together a group of phycologists to brainstorm these problems and deliberate on what will happen to marine plants and algae in the southern, mid and northern parts of the north-east Atlantic by 2100 if CO2 emissions are not reduced. The outcome is that predicted changes in ecosystem structure are expected to have serious implications for ecosystem functioning and services, and for the fortunes of fisheries that are supported by these communities. The workshop considered the fate of fleshy and calcified seaweeds, seagrasses and the microphytobenthos (MPB). The fleshy algae will be familiar to anyone who visits the shore, as these include the habitat-forming kelp (Laminariales) and the fucoids (Fucales) that cover many sea shores. Kelp forests are some of the most productive ecosystems on Earth and along with the fucoids cover approximately three times the area of woodland in the UK. The calcified seaweeds include crustose, free-living (maerl) and branched species. Maerl beds provide habitat for a rich flora and fauna forming ‘hotels’ for invertebrates and juvenile fish. Seagrass beds are extensive in the north-east Atlantic and play a vital role in storing carbon. Their leaves provide a habitat for a range of epiphytes, notably crustose calcified seaweeds. MPB include cyanobacteria, diatoms, dinoflagellates and life history stages of the seaweeds. They provide a food source for thousands of species of grazing and deposit-feeding organisms and stabilize coastal mud flats. Some of these algae are symbionts with other organisms and others live in shellfish and can be severely toxic to humans.

 Our predictions indicate that there will be some losers and some winners over the rest of this century. Warming will likely kill off kelp forests in southern parts of the northeast Atlantic; cool water adapted kelps and fucoids have already undergone significant changes in their distribution with losses reported from several regions of the north-east Atlantic. Maerl beds are predicted to disappear from the northern parts due to falling levels of carbonate (from which their calcified skeletons are made). We know from CO2 seeps around the world that calcified seaweeds are corroded and outcompeted in acidified seawater. Not only will fish that depend upon kelp be lost but so will shellfish from coral. The calcified algae may look like inert pink paint on the rocks but they emit chemicals that trigger shellfish settlement when they metamorphose from freeswimming larval forms to adulthood.

 Our predictions indicate that there will be some losersand some winners over the rest of this century. Warming will likely kill off kelp forests in southern parts of the northeast Atlantic; cool water adapted kelps and fucoids have already undergone significant changes in their distribution with losses reported from several regions of the north-east Atlantic. Maerl beds are predicted to disappear from the northern parts due to falling levels of carbonate (from which their calcified skeletons are made). We know from CO2 seeps around the world that calcified seaweeds are corroded and outcompeted in acidified seawater. Not only will fish that depend upon kelp be lost but so will shellfish from coral. The calcified algae may look like inert pink paint on the rocks but they emit chemicals that trigger shellfish settlement when they metamorphose from freeswimming larval forms to adulthood.

In contrast, we predict that invasive species will thrive, exploiting both niches left vacant by the loss of native species, and space provided by the spread of artificial marine structures such as coastal defences, human-made reefs and wind turbines. Seagrasses are also predicted to be winners as they can benefit from increased carbon availability under future ocean conditions. Seagrasses will likely expand their range in all regions of the north-eastern Atlantic, provided they can withstand competition from invasive seaweeds and are protected from other human impacts such as dredging. However, their epiphytic cover of crustose calcified seaweeds is predicted to reduce or disappear, while diatoms may well proliferate in their place. Whilst less is known about them, diatoms are again predicted to increase in abundance based on evidence of these communities from CO2 seeps. Compared to the seaweeds and seagrasses, we require a much deeper understanding of the tinier organisms in life. Crucially, the impact of high CO2 on toxic dinoflagellates needs to be given more consideration as there is some evidence that they may become more toxic under future conditions.

On the whole, the predictions provide a clarion call for action on two fronts. Firstly, urgent reductions in greenhouse gas emissions are needed to curb runaway warming and ocean acidification; this is a global phenomenon that is having real-time impacts on our coastal systems and requires global action to prevent future catastrophe. Secondly, careful monitoring of the changes occurring along our shores is required to allow a clear assessment of the consequences of these changes. Our future coastal marine communities will be very different to what we see today, and we need a greater understanding of what this means for the human communities that rely on these important resources.

Images from top to bottom: Kelp at extreme low tide, Combe Martin, Devon, southwest England. Image: Juliet Brodie; Juvenile scallop on maerl off Falmouth, southwest England. Image: Jason Hall-Spencer; Eelgrass at Studland on England’s south coast. Image: Paul Naylor www.marinephoto.co.uk; Kelp forest and animals. Image: Paul Naylor www.marinephoto.co.uk

Juliet Brodie1 (j.brodie@nhm.ac.uk) Chris Williamson1 (williamsoncj@cardiff.ac.uk) and Jason HallSpencer2 (jason.hall-spencer@plymouth.ac.uk)

1. Life Sciences Department, Genomics and Microbial Biodiversity Division at the Natural History Museum.

2. School of Marine Science and Engineering (Faculty of Science & Environment), Plymouth University.

Further Reading

Brodie J., Williamson C.J., Smale D.A., Kamenos N.A., Mieszkowska N., Santos R., Cunliffe M., Steinke M., Yesson Y., Anderson K.M., Asnaghi V., Brownlee C., Burdett H.L., Burrows M., Collins S., Donohughe P., Harvey B., Foggo A., Noisette F., Nunes J., Raggazola F., Raven J.A., Schmidt D.N., Suggett D., Teichberg M. and Hall-Spencer J.M. (2014) The future of the NE Atlantic benthic flora in a high CO2 world. Ecology and Evolution. Volume 4, Issue 13, pages 2787–2798, July 2014.

Author

Juliet Brodie, Chris Williamson and Jason Hall-Spencer

Category