Marine defaunation: Animal loss in
the global ocean
Douglas J. McCauley,1 Malin L. Pinsky,2 Stephen R. Palumbi,3 James A. Estes,4
Francis H. Joyce,1 Robert R. Warner1
Marine defaunation, or human-caused animal loss in the oceans, emerged forcefully only
hundreds of years ago, whereas terrestrial defaunation has been occurring far longer.
Though humans have caused few global marine extinctions, we have profoundly affected
marine wildlife, altering the functioning and provisioning of services in every ocean.
Current ocean trends, coupled with terrestrial defaunation lessons, suggest that marine
defaunation rates will rapidly intensify as human use of the oceans industrializes. Though
protected areas are a powerful tool to harness ocean productivity, especially when designed
with future climate in mind, additional management strategies will be required. Overall,
habitat degradation is likely to intensify as a major driver of marine wildlife loss. Proactive
intervention can avert a marine defaunation disaster of the magnitude observed on land.
Several decades of research on defaunation in terrestrial habitats have revealed a serial oss of mammals, birds, reptiles, and inver- tebrates that previously played important ecological roles (1). Here, we review the
major advancements that have been made in
understanding the historical and contemporary
processes of similar defaunation in marine environments. We highlight patterns of similarity
and difference between marine and terrestrial
defaunation profiles to identify better ways to
understand, manage, and anticipate the effects of
future defaunation in our Anthropocene oceans.
Patterns of marine defaunation
Delayed defaunation in the oceans
Defaunation on land began 10,000 to 100,000 years
ago as humans were expanding their range and
coming into first contact with novel faunal
assemblages (2–4). By contrast, the physical properties of the marine environment limited our
capacity early on to access and eliminate marine
animal species. This difficulty notwithstanding,
humans began harvesting marine animals at least
40,000 years ago, a development that some have
suggested was a defining feature in becoming
“fully modern humans” (5). Even this early harvest
affected local marine fauna (6). However, global
rates of marine defaunation only intensified in
the last century with the advent of industrial
fishing and the rapid expansion of coastal popu-
lations (7). As a result, extant global marine faunal
assemblages remain today more Pleistocene-like,
at least with respect to species composition, than
terrestrial fauna. The delayed onset of intensive
global marine defaunation is most visible in a
comparative chronology of faunal extinctions in
which humans are likely to have directly or in-
directly played a role (8) (Fig. 1).
Comparing rates of animal extinction
Despite the recent acceleration of marine defaunation, rates of outright marine extinction have
been relatively low. The International Union for
Conservation of Nature (IUCN) records only 15
global extinctions of marine animal species in
the past 514 years (i.e., limit of IUCN temporal
coverage) and none in the past five decades (8, 9).
By contrast, the IUCN recognizes 514 extinctions
of terrestrial animals during the same period
(Fig. 1). While approximately six times more animal species have been cataloged on land than in
the oceans (10), this imbalance does not explain
the 36-fold difference between terrestrial and
marine animal extinctions.
It is important to note that the status of only a
small fraction of described marine animal species have been evaluated by the IUCN, and many
assessed species were determined to be data deficient (11) (Fig. 2). This lack of information necessitates that officially reported numbers of extinct
and endangered marine fauna be considered as
minimum estimates (11). There remain, however,
a number of data-independent explanations for
the lower extinction rates of marine fauna. Marine species, for instance, tend to be more widespread, exhibit less endemism, and have higher
dispersal (12, 13).
Complacency about the magnitude of contemporary marine extinctions is, however, ill-advised.
If we disregard the >50,000-year head start of
intense terrestrial defaunation (Fig. 1) and compare only contemporary rates of extinction on land
and in the sea, a cautionary lesson emerges. Marine extinction rates today look similar to the
moderate levels of terrestrial extinction observed
before the industrial revolution (fig. S1). Rates of
extinction on land increased dramatically after this
period, and we may now be sitting at the precipice
of a similar extinction transition in the oceans.
Three other kinds of extinction
The small number of species known to be permanently lost from the world’s oceans inadequately
SCIENCE sciencemag.org 16 JANUARY 2015 • VOL 347 ISSUE 6219 1255641-1
1Department of Ecology, Evolution, and Marine Biology,
University of California, Santa Barbara, CA 93106, USA.
2Department of Ecology, Evolution, and Natural Resources,
Institute of Marine and Coastal Sciences, Rutgers University,
New Brunswick, NJ 08901, USA. 3Department of Biology,
Stanford University, Hopkins Marine Station, Pacific Grove,
CA 93950, USA. 4Department of Ecology and Evolutionary
Biology, University of California, Santa Cruz, CA 95060, USA.
*Corresponding author. E-mail: firstname.lastname@example.org
Fig. 1. Comparative chronology of human-associated
terrestrial and marine animal extinctions. Green bars
indicate animal extinctions that occurred on land, and blue
bars indicate marine animal extinctions. Timeline measures years before 2014 CE. Only extinctions occurring less than 55,000 years ago are depicted.
Defaunation has ancient origins on land but has intensified only within the last several hundred years in the
oceans. See details in (8).