H uman history has noted the disappearance of five seabirds, three marine mammals, and four gas- tropods from the world’s oceans. According to a recent review of marine extinctions, another 18 species may have gone extinct globally, although their taxonomic sta- tus is uncertain, while 103 species have been lost from substantial portions of their ranges (Dulvy et al. 2003). Despite evidence of marine extinctions, fewer marine than terrestrial species have been flagged as vulnerable under the US Endangered Species Act (ESA), the World Conservation Union (IUCN) Red List, or the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, the number of marine species on these lists has grown recently and is expected to continue to rise with mounting threats and increased attention to the status of marine popula- tions and ecosystems (International Institute for Sustainable Development 2002; Baillie et al. 2004; Armsworth et al. in press a; Figure 1). In part, the increase in listings represents growing recog- nition that marine species may be as vulnerable to extinc- tion risk as terrestrial species, despite commonly held per- ceptions to the contrary (Roberts and Hawkins 1999; Dulvy et al. 2003; Hutchings and Reynolds 2004). In 1996, IUCN sparked a debate in the scientific literature by listing several commercially important species, includ- ing southern bluefin tuna, Atlantic cod, and North Sea haddock. Although some scientists and managers objected to the “one size fits all” decline threshold (IUCN Criterion A) that triggered the listing of these species (eg Matsuda et al. 1997), others have argued that there is no convincing evidence that marine species are less vulnera- ble to extinction than terrestrial species, and that high fecundity, naturally variable populations, and large disper- sal potential do not necessarily confer resistance to over- exploitation (Hutchings 2001; Dulvy et al. 2003; Hutchings and Reynolds 2004). Many recent papers have pointed to overfishing as a major cause of declines in marine populations (Pauly et al. 1998; Musick et al. 2000; Jackson et al. 2001; Myers and Worm 2003). Dulvy et al. (2003) found that 55% of known local to global marine extinctions were attribut- able to exploitation. However, to date no one has looked in a quantitative way at threats to the full list of vulnera- ble marine species. On land, the most common threat to vulnerable species is habitat loss, rather than overex- ploitation (Wilcove et al. 1998). This difference may rep- resent, at least in part, a temporal lag in exploitation of the seas. We have long since abandoned the harvest of substantial numbers of wild land animals or plants for human consumption, and instead have turned to domesti- cated biomass and industrial agriculture, which is a pri- mary contributor to terrestrial habitat degradation (Wilcove et al. 1998). However, each year, over 80 x 10 6 tons of wild biomass are harvested from the oceans (FAO 275 © The Ecological Society of America www.frontiersinecology.org REVIEWS REVIEWS REVIEWS Losing pieces of the puzzle: threats to marine, estuarine, and diadromous species Carrie V Kappel The number of marine species at risk of extinction is rising. Understanding the threats that contribute to extinction risk in the seas is thus critical to conservation. When major threats to marine, estuarine, and diadromous species on the US Endangered Species Act and IUCN Red lists were ranked according to the number of species they affect, strong consensus in the ranking of threats across species and between institu- tions emerged. Overexploitation is the most frequent threat to vulnerable marine species, with approxi- mately half of threatened species caught as bycatch in fisheries. Habitat degradation, the primary threat to terrestrial species, ranks second in impact on marine species. Loss of listed marine species would probably affect ecosystem function and delivery of ecosystem services because many of these species are strong inter- actors, including ecosystem engineers, taxa that provide important nutrient links between terrestrial and marine ecosystems, and a disproportionate number of high trophic-level predators. Front Ecol Environ 2005; 3(5): 275–282 Hopkins Marine Station, Stanford University, 100 Oceanview Boulevard, Pacific Grove, CA 93950 (ckappel@stanford.edu) In a nutshell: • Most marine species face multiple threats • Overexploitation is the most pervasive of these threats, affect- ing commercial and non-commercial species alike • Bycatch is comparable in impact to targeted harvest and threatens approximately half of the listed marine species • Habitat degradation, the second greatest threat, is particularly problematic for coastal species affected by land-based impacts • By assessing the relative impacts of different threats and build- ing understanding of species’ ecological roles, we can develop conservation priorities