Biodiversity–ecosystem function

This chapter looks at the links between biodiversity and ecosystem function in soft sediments to help understand the implications of biodiversity loss on ecosystem services. The chapter contains a focus on the challenges in developing real-world tests of biodiversity–ecosystem function (BEF) relationships. The various forms of BEF relationships, their implications and the different elements of biodiversity that link to function are described. Given the multiple functions that occur in soft-sediment ecosystems, this has important implications for the assessment and implications of BEF relationships and functional performance in the up-scaling of BEF relationships. The role of BEF in underpinning many ecosystem services and the interconnections in biodiversity and ecosystem service relationships close out the chapter.

Temporal variations in benthic assemblages and processes

Demonstrating changes over time in soft-sediment ecosystems is critical to understanding ecosystem dynamics and predicting how they may change. Monitoring is thus an essential process providing insight into how complex ecological systems change and has important implications in adaptive management, impact assessment and stewardship. The chapter describes how both slow and fast processes operate in soft sediments and drive changes across multiple time scales. The role of time series data in helping to understand detailed short-term studies is discussed. The interactions between space and time have important implications in study design, interpretation and accounting for inconsistency in results. The chapter finishes by discussing two types of temporal change of significant concern these days due to their implications for resilience and ecosystem dynamics: tipping points and hysteresis.

Ecosystem functions and the work of soft sediments

This chapter describes various aspects of how we can define ecosystem function and situations ecosystem function in a continuum from ecosystem processes to services. Illustrating that functions are about connections, the chapter uses examples of productivity, organic matter decomposition, ecosystem metabolism, habitat creation and foodwebs. Changes in the contributions of function to ecosystem dynamics are considered. Sedimentary ecosystems are multifunctional, requiring the development of new methods to assess this aspect of sediments and trait-based approaches are discussed. The role of ecosystem functions in underpinning ecosystem services is described to ensure that valuation and mapping exercises do not lose sight of the foundational role of ecosystem functions.

Data collection methods and statistical analyses

This chapter highlights the questions to ask of data collection methods and statistical analyses before you plunge into their use. It discusses data collection methods within the context of study design, focussing on the resolution and size (in area or time) that methods collect over. The methods covered are those that help explain patterns and processes produced by plants and animals interacting with the sediment and the water column. Similarly, statistical analyses that increase the interpretation of data and allow understanding of interacting processes are highlighted. The need to balance information, replication and costs associated with statistical power is also discussed. As this chapter provides a brief overview only on subjects that have been the subjects of entire books, it also contains references to more extensive coverage.

Disturbance, patches and mosaics

This chapter introduces the range of biological and physical processes that disturb soft sediment. It introduces the concept of disturbance regimes that connect the extent, frequency and magnitude of disturbance. Post-disturbance recovery processes are described in terms of processes that occur within the disturbed patch and processes that influence recovery from outside the patch. Moving on from the patch scale, the chapter introduces the concept of patch dynamics and the concept of the seafloor as a mosaic of patches at different stages of recovery from disturbance. Connectivity between patches is a critical factor linking local recovery processes to landscape-scale processes. This mosaic perspective leads to the introduction of metacommunity dynamics and the potential for heterogeneous landscapes to fragment and eventually homogenise seafloor communities as a consequence of the loss of large habitat-defining species.

Biotic interactions

This chapter addresses the biological processes that influence community composition and dynamics, highlighting the multi-trophic and multi-functional nature of soft-sediment communities. Characterising the biological interactions into competition, predation, adult–juvenile interaction, facilitation, parasitism and disease, the chapter initially focusses on what we know about these processes, their effect on other biological components and their importance in different benthic habitats. It then extends to consider how they, in conjunction with mobility of species, can influence the broader-scale spatial structure and temporal dynamics connecting communities and functions. The chapter recognises the importance of differences in strength of interaction and the potential for weak interactions to affect community dynamics. This is framed around the concept of self-organisation as an emergent characteristic of ecosystem interaction networks and how meta-communities may be constructed.

Restoration of soft-sediment habitats

The final chapter addresses positive interventions that can help reverse the decline in soft-sediment ecosystems. Restoration draws on our understanding of ecosystem processes and the natural history of soft-sediment organisms. The chapter describes how active restoration can be designed to overcome bottlenecks that slow natural recovery processes and to form a critical part of integrative management strategies, such as ecosystem-based management. The chapter describes the what, why, where and how of active restoration, with a focus on the restoration of shellfish reefs, one of the most impacted soft-sediment habitats. Links between restoration and remediation are made to emphasise the importance of ecosystem function in generating positive changes in soft-sediment habitats. As restoration is likely to involve different elements of society in trying to fix problems, it is important that we develop effective ways of measuring success. The chapter ends by touching on the potential to generate new restoration economies, recognising that restoring nature can be at least as economically beneficial as developing more grey infrastructure.

Describing assemblages and biodiversity of sediment-living organisms

This chapter provides insight into the biodiversity of soft sediments, and how it can be measured using a range of univariate, bivariate and multivariate techniques. It highlights that biodiversity can be described across a range of organisational scales and includes the extension of diversity to cover habitats, behavioural characteristics (biological traits) and functional traits. Scale is an important characterisation of biodiversity and the chapter discusses scale both in its effect on the measurement of biodiversity and also for how it links the components of α‎-, β‎- and γ‎-diversity. These linkages are crucial to help us understand the roles of heterogeneity, species turnover and the ecological connections between local species richness and regional species pools. Most species are rare and thus any description of biodiversity would not be complete without consideration of rarity and its contribution to community structure and dynamics.

The sedimentary environment

This chapter introduces the roles of sediment properties and hydrodynamic conditions in influencing soft-sediment communities. It identifies environmental factors that are commonly used to characterise soft-sediment habitats and used to tease out the role of habitat variation from other factors that influence populations and communities. The differences between cohesive and non-cohesive sediments that profoundly influence ecosystem functions are described. Hydrodynamics particularly at the sediment–water interface are introduced as a critical factor affecting many ecosystem processes. The chapter introduces the differences in laminar and turbulent flows. Coastal soft sediments in particular are places of high organic matter remineralisation and thus critical for the recycling of primary nutrients and primary production, particularly by microphytobenthos. These factors underpin the important role of marine sediments in biogeochemistry and earth system processes.

Benthic animals and plants and what they do to sediments

This chapter explores the interactions of plants and animals with their immediate sedimentary environment. Plants and animals fundamentally change the physical and chemical characteristics of their sedimentary environment. The changes they effect are dependent on their size, living position, feeding mode and mobility. The types of changes are discussed as well as the resultant ability of plants and animals to actually create seafloor habitats and contribute to sediment heterogeneity at both small and large scales. Seafloor habitats are therefore best defined by a mix of physical and biology rather than physical descriptors alone. But the differences between how different animals feed and move and their ability to create structures such as tubes and burrows that influence the flows of oxygen and porewater within the sediments and across the sediment–water interface mean that there are not only a variety of vegetated seafloor habitats but a variety of non-vegetated ones.