Introduction

Marine environments encompass some of the most diverse ecosystems on Earth. For example, marine habitats harbour 28 animal phyla and 13 of these are endemic to marine systems. In contrast, terrestrial environments contain 11 animal phyla, of which only one is endemic. The relative strength and importance of drivers of broad-scale diversity patterns vary among taxa and habitats, though in the upper ocean the temperature appears to be consistently linked to biodiversity across taxa (Tittensor et al. 2010). These drivers of pattern have inspired efforts to describe biogeographical provinces (e.g. the recent effort by Spalding et al., 2013)) that divide the ocean into distinct regions characterized by distinct biogeochemical and physical combinations). Biogeographers such as Briggs (1974) examined broad-scale pattern in marine environments in historical treatises and although many of the patterns described therein hold true today, the volume and diversity of data available to address the question have increased substantially in recent decades. We therefore focus our chapter on more recent analyses that build on those early perspectives. The International Census of Marine Life programme that ran from 2000-2010 provided significant new data and analyses of such patterns that continue to emerge today (McIntyre, 2011; Snelgrove, 2010). Indeed, many of our co-authors were part of that initiative and that influence is evident in the summary below. In the few years since that programme ended, some new perspectives have emerged which we include where space permits, noting that we cannot be exhaustive in coverage and also that the large data sets necessary to infer broad-scale patterns do not accumulate quickly.

Not surprisingly, the different scales, at which many organisms live, from ambits of microns for microbes to ocean basins for migratory fishes and marine mammals, along with variation in the drivers and patterns of diversity, render a single analysis impossible. In order to assess gradients in marine biodiversity we use a taxonomic framework for some groups of organisms and a habitat framework for others.