12.1 | Introduction Coral and shellfish reefs can reduce flooding and erosion in coastal areas, but not all reefs provide significant coastal protection benefits. This chapter provides an overview of the coastal protection benefits of reefs (e.g., reducing flooding, storm damage, and erosion) and discusses the suite of co-benefits that reefs can also provide (e.g., fisheries production, habitat and biodiversity, recreation and tourism revenue, and improved water quality). For many reef-lined coasts around the world, reefs act as the first line of defense against flooding, storm damage, and erosion. However, the various ways in which reefs provide coastal protection are not always fully recognized and accounted for, in part, due to the historical focus on understanding and predicting flooding and erosion impacts for certain open-coast sandy shorelines lacking reefs. Yet, understanding the coastal protection services of reefs and assessing how they can reduce risk are critical because reefs will need to be effectively incorporated into climate adaptation programs, hazard mitigation strategies, and coastal development and management decisions (see Chapter 6). This chapter is not intended to be a comprehensive reference on reef restoration, which in many cases can be closely related to the use of reefs for coastal defense. There are other sources that provide detailed information (e.g., reefresilience.org 2020a; public.tableau.com, n.d.). Instead, this chapter focuses on describing the key aspects relevant to the use of reefs for flood and erosion risk management.
12.2 | Defining the Feature, Its Values, and Contexts for Application 12.2.1 Introduction Reef is a general term that describes shallow, submerged structures in the ocean. Natural reefs are formed by a variety of marine organisms, and often have a profound influence on coastal hydrodynamics, sediment transport, and morphological changes. The shallow nature and morphological complexity of reefs support some of the world’s most productive marine ecosystems and provide habitats for large portions of marine species. As such, the broad ecosystem services that reefs provide worldwide are widely recognized and valued. Reef ecosystems are influenced by environmental characteristics (e.g., sea surface temperature, nutrients, and turbidity) that define the habitat requirements that govern their geographic distributions. Coral reefs mostly occur within warm (i.e., 20°C to 30°C), oligotrophic, clear waters that are optimal for coral growth. Organisms living within coral reefs
12 | Reefs
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