Macro-algae functional groups as an assessment tool of biodiversity

Chalk sea-stack near Flamborough Head on the north-east coast of England

Traditionally, seaweed ecology has relied on the study of individual species and the identification of assemblages. Alternatives to ecological groups are functional groups. In 1975, a simple classification system, using three morphological groups of algae, was proposed by Dayton. Based on more detailed categories, Littler and Littler (1980) proposed a functional form model to study trends in the successional status of seaweeds. The model they developed integrated the morphological attributes of the thallus in relation to the productivity and the survival of benthic macroalgae. They applied the groups to a subtropical rocky intertidal system and were able to relate the various groups to the stability of the substratum (Littler & Littler, 1984). Steneck & Watling (1982) confirmed that polyphyletic groups based on the anatomical and morphological characteristics of the thallus could be grouped to reflect ecological characteristics. More recently, Steneck and Dethier (1994) studied sites from three biogeographical regions. They suggested that the use of functional groups could provide insight into the structure of communities and could be used to make comparisons in space and time. Such studies have concentrated on the use of functional groups for assessing the response of complex algal communities to disturbances in subtidal environments (Lavorel et al., 1997).

Rocky shores

Such a functional group approach has ecological application on intertidal rocky shores (Tobin et al., 1998; Tobin, 2000). In a preliminary survey of the Yorkshire coast (England), the authors were confronted to the fact that the identification of seaweeds at species level in such complex habitats requires a high level of taxonomic expertise and is time consuming. Moreover, it was sometimes difficult or even impossible to identify species in the field. Using several sampling sites in North-East England, they showed that these difficulties can be overcome by dividing the biota into functional groups They compared species based and group based descriptions of algal-dominated shores. They demonstrated that, on temperate rocky shores, the functional group approach could help identifying large-scale factors affecting the distribution and survival of marine macrophytes. They further showed the utility of the functional group approach in temporal studies. Patterns in community structure could be detected and a degree of stability undetectable at species level could be highlighted.

Recolonisation

Following a land-slide which affected the intertidal rock platform, functional groups were used for understanding recolonisation processes of a degraded ecosystem. Looking for a simple protocol, Ducrotoy & Pickaert (2001) suggested that the approach could rely on a simple sampling strategy, including a reduced sampling effort, but could describe recolonisation forces and help assessing progress in recovery. The hypothesis to be tested was that, rather than occurring as a uniform and progressive process, recolonisation would happen step by step and imply successive attempts from plants to reinstall. 

Extensive chalk cliffs at Flamborough Head, BIOMARE European Marine Biodiversity site.

Experiment

An experimental approach to this problem was made possible because a large-scale disturbance took place in the intertidal area of a wave cut platform where the hypothesis could be tested. In May 1993, the wave cut platform at Holbeck, Scarborough (North Yorkshire, United Kingdom) was impacted by a land slide from the overhanging cliff. Twenty thousand tonnes of clay were deposited on the rocky shores within minutes. The engineering works that took place over the following year resulted in a complete removal of intertidal organisms over about a 1 ha area.

The simple groupings proposed by Dayton (1975) were adapted to the situation found on the coast of North-East England. Because of its simplicity and the confidence in assigning species to groups, results could easily fit the model of the recolonisation (Sylvand & Ducrotoy, 1998).

Digital photographs

In order to meet the requirements for monitoring the European Natura 2000 site at Flamborough Head, Ducrotoy & Simpson (2001) have developed techniques based on the use of computer processed digital photographs (Malone, 1997; Strong, 1998; Simpson, 1999). Such techniques are now being used at other similar sites throughout Europe, notably SAC and SPA designated under the European Directives (IECS unpublished). 

Flamborough Head is a candidate marine SAC. It was designated for the chalk cliffs and sea caves under the EU Habitats and Species Directive, a SPA under the EU Wild Birds Directive, a Heritage Coast, a Sensitive Marine Area (SMA), a Site of Special Scientific Interest, and a Ramsar Site. Recently, it was selected as a Flagship Site for intensive research on biodiversity, in the framework of the European Concerted Action BIOMARE.

Bibliography

Dayton, P.K., 1975. Experimental evaluation of ecological dominance in a rocky intertidal algal community. Ecological Monographs, 45: 137-159.

Ducrotoy, J.P. & Pickaert C., 2000. A functional group approach to seaweed recolonisation of a wave cut platform. Journal de Recherche Oceanographiques, 26: 43-56.

Ducrotoy, J.P. & Simpson S.D., 2001. Developments in the application of photography to ecological monitoring, with reference to alga beds. Aquatic Conservation: Marine and Freshwater Ecosystems, 11: 123-135.

Lavorel, S., McIntyre, S., Landsberg, J. & Forbes, T.D.A., 1997. Plant functional classification: from general groups to specific groups based on response to disturbance. TREE, 12, (12): 474-477.

Littler, M.M. & Littler, D.S., 1980. The evolution of thallus form and survival strategies in benthic marine alga: Field and laboratory tests of a functional form model. American Naturalist, 116 (1): 25-44.

Littler, M.M & Littler, D.S., 1984. Relationships between macroalgal functional form groups and substrata stability in subtropical rocky intertidal systems. Journal of Experimental Marine Biology and Ecology, 74: 13-34.

Malone, R., 1997. A proposed methodolgy for the long-term monitoring of the intertidal macroalgae on a wave-cut platform, with specific reference to Selwicks Bay, Flamborough Headland, North Humberside. Heritage Coast Report: 26 pp.

Simpson, S.D., 1999. A long-term monitoring strategy for the algal beds at Selwicks Bay, Flamborough, England: Unpublished Mres thesis, University of York.

Steneck R.S. & Watling L., 1982. Feeding capabilities and limitation of herbivorous molluscs: a functional group approach. Marine Biology, 68: 299-319.

Steneck, R.S. & Dethier, M.N., 1994. A functional group approach to the structure of algal-dominated communities. Oikos, 69: 476-498

Strong, E., 1998. Broad scale monitoring of a macroalgal community at Selwicks Bay, Flamborough Head. Unpublished Mres thesis, University of York.

Sylvand, B. & Ducrotoy, J.-P., 1998. Monitoring coastal and estuarine systems: The need for an integrated approach. In: With rivers to the Sea: Interaction of Land Activities, Fresh Water and Enclosed Coastal Sea, Falkenmark M. (ed.), Stockholm International Water Institute, Stockholm: 189-204.

Tobin, M., 2000. Applications of a functional group approach to the study of temperate algal communities. Unpublished Dphil Thesis, University of York.

Tobin, M.L., Scott, G.W. & Ducrotoy, J.-P., 1998. Applications of a functional group approach to algal community ecology. In: Changes in the marine flora of the North Sea, Scott G.W. & Titley I. (eds.), CERCI, University College Scarborough: 135-147.