The rocky shores of the north-east Atlantic have been long studied. Our focus is from Gibraltar to Norway plus the Azores and Iceland. Phylogeographic processes shape biogeographic patterns of biodiversity. Long-term and broadscale studies have shown the responses of biota to past climate fluctuations and more recent anthropogenic climate change. Inter- and intra-specific species interactions along sharp local environmental gradients shape distributions and community structure and hence ecosystem functioning. Shifts in domination by fucoids in shelter to barnacles/mussels in exposure are mediated by grazing by patellid limpets. Further south fucoids become increasingly rare, with species disappearing or restricted to estuarine refuges, caused by greater desiccation and grazing pressure. Mesoscale processes influence bottom-up nutrient forcing and larval supply, hence affecting species abundance and distribution, and can be proximate factors setting range edges (e.g., the English Channel, the Iberian Peninsula). Impacts of invasive non-native species are reviewed. Knowledge gaps such as the work on rockpools and host–parasite dynamics are also outlined.

Introduction

Understanding how changes in biodiversity can lead to changes in the functioning of ecosystems is a critical step for tracing the consequences of human activities through to impacts on ecosystem services. As defined and described in Chapter 1, it is widely recognised that the biodiversity of ecosystems can influence their functioning – the processing of energy and materials – and properties such as stability and total biomass. The relationship between biodiversity and ecosystem functioning has, however, been the subject of extensive and, at times, controversial research over the past two decades, the so-called BEF debate.

The BEF debate rose to prominence in ecology at a conference in Bayreuth in 1992 and has passed through several phases since then, in which the field has expanded in volume, scope, rigour and complexity (Naeem et al., 2009). The first major advances were made in terrestrial ecosystems, particularly grasslands (e.g. Naeem et al., 1994; Tilman et al., 1996). There was, initially, a lag in developing similar levels of understanding for marine ecosystems (Heip et al., 1998), but there is now a substantial body of work covering at least coastal ecosystems (Stachowicz et al., 2007; Naeem et al., 2009). Several authors have described how the structure and functioning of marine systems is different from that of terrestrial systems (e.g. Steele, 1985, 1991; Ormond, 1996; Stachowicz et al., 2007; Naeem, 2012), suggesting that understanding derived from terrestrial systems may not be applicable in a marine context. Indeed, a number of major syntheses have treated the systems separately (e.g. Balvanera et al., 2006; Cardinale et al., 2006). On the other hand, Schmid et al. (2009) argue that because their meta-analysis revealed no differences in the proportion of positive BEF relationships in marine versus terrestrial systems, there is no basis to argue that different mechanisms apply (and see Webb, 2012). An analysis by Crowe et al. (2012) reveals that in general BEF research in marine and terrestrial ecosystems has differed in spatial and temporal scale and approach, making it difficult to draw direct comparisons.

Introduction

Marine ecosystems provide a range of essential benefits to society, including food and other products, waste assimilation, coastal protection and climate regulation as well as less tangible, but no less important cultural and aesthetic benefits (Chapter 2). To a considerable degree, those benefits are underpinned by ecosystem services dependent on the efficient functioning of the ecosystems, although detailed understanding of relationships between particular services and particular functional processes is currently being developed (Chapter 2). In turn, the efficient functioning of ecosystems has been linked to the number and identity of species present, as well as the prevailing environmental conditions (Chapter 5).

Society derives many of its benefits from ecosystems via sectoral activities and industries, such as fishing, construction, energy, shipping, leisure and tourism. These activities can impose pressures on ecosystems, such as removal of biomass, inputs of nutrients and other contaminants and the introduction of artificial structures and non-indigenous species (Chapter 3). Such pressures act through a range of mechanisms affecting different levels of biological organisation to modify biodiversity and ecosystem functioning (Chapters 3 and 4). The chapters in this book have reviewed current knowledge of how the spectrum of human activities and pressures (collectively referred to as stressors) affect biodiversity, ecosystem functioning and the provision of services and benefits to society. A key objective was to provide a synthesis of evidence for policy makers and managers to facilitate trade-offs between sectors of activity based on the benefits they provide weighed against the degree to which they may compromise the delivery of ecosystem services now and into the future (see Chapter 11).

In this chapter, we first synthesise and summarise the inferences presented in the book about the range of impacts of different activities and pressures on biodiversity and ecosystem processes. We then ask how this kind of knowledge can help policy makers and managers, particularly in the achievement of the international targets laid down in the Millennium Development Goals (Chapter 1) and whether the ecosystem approach and the concept of ecosystem services can provide an effective framework for facilitating the achievement of those goals.

Marine ecosystems

The Earth is a blue planet. Seas and oceans cover over 70% of the Earth's surface and, with an average depth of over 3.2 km, the total volume of marine ecosystems is vastly greater than that of terrestrial and fresh-water environments combined, comprising 98% of the total inhabitable space on the planet (Speight and Henderson, 2010). Marine ecosystems contain 31 of the 33 phyla of animals, each of which constitutes a unique and distinctive body plan, with 15 of those phyla occurring only in the sea (Angel, 1993). Approximately 250 000 marine species have been described, with an estimated 750 000 still to be discovered (Census of Marine Life, 2010). Marine creatures include the largest ever to live (blue whales), yet the energy to fuel these giants is mainly captured by microscopic plankton, rather than more substantial plants, one of a number of fundamental differences between marine and terrestrial ecosystems (Steele, 1985, 1991; Webb, 2012). Of the global annual net primary productivity, approximately 104.9 petagrams (1015 grams) of carbon per year, around half is produced by marine ecosystems (Field et al., 1998). Although coral reefs and beds of seaweed are, per unit area, among the most diverse and productive ecosystems on Earth, open oceans have levels of productivity akin to terrestrial deserts because life is so thinly spread, but nevertheless make the single greatest contribution to global productivity because of their size (Whittaker and Likens, 1975).

Archaeological records show that even the earliest humans exploited the marine environment for food, as a medium for transportation and as a repository for waste (Jackson, 2001; Jackson et al., 2001). Today, the marine environment provides approximately 80 million tonnes per year of fish and shellfish from capture fisheries, representing about 3% of our global animal protein supply. Marine aquaculture contributes an additional 20 million tonnes (FAO, 2012). Therefore, marine ecosystems can be seen as having an important role in global food security (Frid and Paramor, 2012).