INTRODUCTION
Connectivity is a concept shared in landscape and metapopulation ecology that is used to describe the movement or exchange of organisms between habitats on various temporal and spatial scales (Gilpin and Hanski 1991; Hanksi and Gilpin 1997; Crooks and Sanjayan Chapter 1; Taylor et al. Chapter 2; Moilanen and Hanski Chapter 3) and its population and community consequences. Many marine habitats, such as kelp forests, estuaries, wetlands, seagrass beds, coral and rocky reefs, and deep-sea hydrothermal vents, are naturally fragmented and patchy. As a result, many scientists working with marine populations and associated systems adopt a metapopulation-based interpretation of connectivity where landscapes are viewed as a network of habitat patches or fragments in which species occur as discrete local populations connected by the passive and active migration of individuals. In marine systems, connectivity may be generated by movements of early life stages such as larvae or spores (hereafter referred to as propagules), juveniles, or adults.
The majority of marine organisms, including benthic (living on or in the bottom), demersal (living near and in close association with the bottom), and holoplanktonic (living in the plankton) species, have a complex life cycle characterized by planktonic stages of development (e.g., larvae, spores). In the case of marine invertebrates and fishes, propagules exhibit a diversity of nutritional modes, development sites, planktonic durations, and morphological development patterns that can affect patterns of connectivity (Table 8.1).