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Vol. 397: 253–268, 2009 MARINE ECOLOGY PROGRESS SERIES Published December 17
doi: 10.3354/meps08317 Mar Ecol Prog Ser
Contribution to the Theme Section ‘Conservation and management of deep-sea corals and coral reefs’ OPENPEN
ACCCCEESSSS
Distinguishing marine habitat classification
concepts for ecological data management
Mark J. Costello*
Leigh Marine Laboratory, University of Auckland, Box 349, Warkworth, Northland 0941, New Zealand
ABSTRACT: Including ecology in biodiversity data management systems requires classifications of
habitat terms that provide standard definitions and indicate their relationships. In addition to data-
bases, a wide range of intergovernmental, conservation and fishery organizations require classifica-
tions of habitats and ecosystems to enable comparisons between areas and organize information in
maps and reports. However, all of the terms used to describe habitats are concepts whose definition
is context-dependent. This paper reviews the key concepts and ecological perspectives involved in
classifying marine ‘habitats’ and ‘biotopes’ (habitat plus its associated species) so as to advise how
they may be used in data management systems. Classifications of biotopes provide practical mea-
sures of biodiversity at the ecosystem level. As an example the habitat of a benthic invertebrate is
very different in spatial scale to that of a parasite, plankton, tuna or whale. Habitats can be geophys-
ical and/or biogenic, and may operate at different spatial scales. For example, aggregations of deep-
sea coral colonies <1 m in diameter may form km-scale reefs which contain other habitats (e.g. sedi-
ments, sponges). An ecosystem can be physiographically defined as a lagoon, seamount, estuary,
abyssal plain or entire ocean. Different sampling methods will define different regions, such as satel-
lite images of ocean colour, acoustic maps of the seabed, in situ sampling of water or sediment cores
and maps derived from analyses of species distributions that may define biogeographic regions.
Because they are sampled (and thus defined) by different methods and can operate at different spa-
tial scales, separate classifications are recommended for (1) nekton, plankton and benthos and (2)
regions (defined to suit political, geographic or management areas), seascapes (defined by topogra-
phy or water mass), biotopes and guilds (e.g. based on body size, diet or sampling method). Further-
more, it is recommended to record the measurable features used to describe biotopes (e.g. depth,
dominant species, substratum) and to avoid imposing a classification hierarchy where the concepts
and methods of defining them are different. Indeed, one can let users create the most parsimonious
classification for their purposes.
KEY WORDS: Methods · Biogeography · Ocean · Biotope · Seascape · Eco-informatics · Biodiversity
Resale or republication not permitted without written consent of the publisher
INTRODUCTION characteristic species, their benthic or pelagic nature,
intertidal zonation, substratum, salinity, wave action,
Habitat classifications are required for reporting, depth and light penetration, and proposed a classifica-
mapping and comparative analysis of ecological data. tion from the seashore to abyssal plain off the west
Since the early 19th century, they have been devel- coast of Ireland. Such classifications permit: habitats
oped for local and regional surveys to help organise and marine resources (e.g. shellfish beds) to be
and describe the environment and associated assem- mapped at different spatial scales to visualise their dis-
blages of species in a consistent manner (e.g. Pérès & tribution and manage their harvest; ecosystem pro-
Picard 1964, Connor et al. 2004, 2006, Valentine et al. cesses and services to be quantified in space and time;
2005). Southern (1915) reviewed 14 publications since species to be grouped according to their habitat for
1832 that distinguished marine habitats based on their ecological data analysis; and prediction of species
*Email: m.costello@auckland.ac.nz © Inter-Research 2009 · www.int-res.com
254 Mar Ecol Prog Ser 397: 253–268, 2009
occurrence from physical environmental data (e.g. The Group on Earth Observations (GEO) is a partner-
Southern 1915, Zacharias et al. 1999, Costello et al. ship of over 80 countries that plan to create a Global
1990, 1999, Costello 1992, Connor et al. 2004, Andre- Earth Observation System of Systems (GEOSS) that will
fouet et al. 2005, Costello & Emblow 2005, Cattrijsse & require a method of classifying marine ecosystems (An-
Hempel 2006, Redfern et al. 2006, Mumby et al. 2008). drefouet et al. 2008). However, to make these data eco-
Different habitats will require different sampling logically relevant requires classifying the species or their
methods, so habitat classifications also provide a basis locations according to their environment. Classifications
for designing monitoring programmes to assess envi- derived from local studies may not be suitable for appli-
ronmental quality (Diaz et al. 2004). cation to studies from other geographic areas and/or
Environmental management and conservation re- which used different sampling methods. Thus it has been
quires standardised classifications and terminology for unclear how globally applicable databases should clas-
habitats to enable consistent mapping of the environ- sify their data ecologically. This paper describes the key
ment across all possible habitats. This aids ranking of concepts and considerations in designing marine habitat
areas for conservation management, such as in select- classifications, including a short review of terminology. It
ing locations for Marine Protected Areas (MPAs) so then outlines how such data can be organised using exist-
they are representative of the habitats of the country or ing geographic classifications and how each datum could
region. In this instance, habitats are used as a surro- belabelled according to standard habitat descriptors.
gate for biodiversity because it is impractical to sample
and map all species distributions in a region. However,
as most ecological studies are local to regional in scale, KEY CONCEPTS AND TERMINOLOGY
the scope and structure of their classifications have
been specific to their study areas. The terms habitat, biodiversity, ecosystem and eco-
The classification of biological species creates a phy- tone are concepts, and thus can only be defined in a
logenetic hierarchy that represents a species’ evolu- certain context. This context depends upon the species
tionary history. In contrast, there is no common con- of interest and the sampling methods, thus different
ceptual framework to provide a standard definition methods will provide different definitions of each term.
and classification of habitats, ecosystems and related
concepts (Jax 2006). They are variously defined by fea-
tures such as geography, topography, sediment grain Habitats from perspectives of nekton, plankton and
size, nutrients, salinity, temperature and/or species benthos
composition. Thus, to develop a global classification
that covers all marine biodiversity, benthic and It is generally agreed that a habitat is defined as the
pelagic, shallow and deep sea, at a variety of spatial physical and chemical environment in which a species
scales, is challenging. lives. Researchers considering free-swimming and wide-
During this decade, an increasing amount of marine ranging animals such as birds, mammals, turtles and fish
species distribution data has been published online (nekton) are likely to have different perspectives on
(Costello & Vanden Berghe 2006). For example, the habitat than those studying plankton and benthos. These
Ocean Biogeographic Information System (OBIS) pub- 3 different perspectives also involve completely different
lishes about 19 million records of over 100000 species methods of observation and sampling. Furthermore,
from 600 data sets (www.iobis.org, Costello et al. 2007). these species vary in their spatial distribution on very dif-
The Global Biodiversity Information Facility (GBIF) ferent time scales. Nekton may move significant dis-
contains all the data from OBIS with similar mapping tances within minutes, whereas plankton move little but
tools, plus additional data (http://data.gbif.org). One within a moving water mass, and benthic fauna and flora
of the largest contributors to OBIS, OBIS-SEAMAP, may never move within their lifetime (O’Dor et al. 2009).
enables exploration and analysis of marine mammal, Both the environmental conditions and spatial area will
bird and turtle distributions (Halpin et al. 2006, Best et be different for these different biota. Thus to combine the
al. 2007), while FishBase provides all kinds of informa- 3 perspectives of nekton, plankton and benthos within a
tion on fish (Froese & Pauly 2009). Another OBIS con- single habitat classification seems unnecessary and is
tributor, Hexacorallia, provides a world database on potentially misleading about their relationships.
sea anemones with tools for mapping species against
environmental data (Guinotte et al. 2006), and Aqua-
Maps provides predicted and editable species range Ecosystems
maps (Kaschner et al. 2008). However, at present none
of these resources has a habitat classification to place Ecosystems are the combination of one or more habi-
these species distribution data in an ecological context. tats with communities of species that can be consid-
255
Costello: Marine habitat classification
ered a functional unit (Jax 2006). They are connected marine and freshwater environments and, like fronts
in their use of space, food or other resources at the between water masses, have high plankton biomass
same time, even though the ecosystem will exchange and productivity. Because these ecotones have uniquely
materials and individuals of its species with external different species abundances compared to adjacent
ecosystems. Ecosystems are thus comprised of physical habitats, I suggest that they are habitats and biotopes
habitats, species and biogeochemical processes (e.g. in their own right. At one level an ecotone is a bound-
nutrient cycles). Sometimes habitat and ecosystem are ary, but on closer examination it may contain several
incorrectly defined as a geographic place where spe- habitats within it. Thus for the purpose of this paper,
cies live. However, both terms are normally applied to ecotones are considered a useful concept to illustrate
a set of physical environments that can occur repeat- new habitats that arise from the interface between
edly in space and time, such as estuarine ecosystems or habitats. Whether they are presented as habitats or
seagrass beds. Thus they are recurrent ecological fea- ecotones is likely to reflect the spatial scale of a study.
tures. While the concept of ecosystem has heuristic The IMCRA Technical Group (1998) discussed the
value, it has been applied so loosely in the literature presence of biotones, transition zones between biogeo-
(Jax 2006) that it is thus difficult to standardise for data graphic regions, and that they may be larger in area
management purposes. than some regions. While it is clear that there are major
differences in species composition at geographic scales
that are due to evolution over geological time scales,
Biodiversity and biotopes whether the regional biota change over boundaries or
gradients is less clear (Southern 1915, van der Spoel
The Convention of Biological Diversity definition of 1994, Semina 1997). Thus the utility of biotones is less
biodiversity comprises 3 levels: (1) the population evident than that of ecotones.
(genetic), (2) the community of species and (3) the
ecosystem and its interactions (Costello 2001). Biodi-
versity is always measured by the use of surrogates Methods of defining habitats: remote sensing, in situ
because of the cost and practicality of recording all sampling and expert opinion
species in any place repeatedly. The question is thus
how appropriate are the surrogates at the population, There are 3 general methods of mapping where
community and ecosystem levels of biodiversity? habitats occur in the environment, namely remote
Whether the available data are representative of sensing, in situ sampling and expert opinion (Table 1).
marine biodiversity is uncertain because they only Remotely sensed (satellite, aerial and acoustic) data
include a small proportion of the known species in an provides different information at different spatial
area, usually the larger and more conspicuous species scales to in situ sampling (e.g. visual, gabs, cores,
that are easier to sample and identify. Furthermore, the dredges, nets and traps) of the water column and
proportion of species known to science varies from 10 seabed. The first may use satellites to map sea surface
to 90% in different geographic areas and taxonomic colour, and thus the distribution of phytoplankton bio-
groups (M. J. Costello unpubl. data). The use of semi- mass as chlorophyll across entire oceans. Satellite
quantitative data on the dominant species with a list images and aerial photography can also be used to
of associated species in a defined physical habitat map shallow-water coral reefs, seagrass beds and
(i.e. mapping biotopes) provides practical measures probably other habitats (Andrefouet et al. 2008, Wright
of biodiversity at all 3 levels. Additional data on the & Heyman 2008). Satellite-derived gravitational anom-
community structure and ecosystem interactions can aly data have been used to produce world bathy-
be reasonably inferred from these data. Thus classifi- metries (Smith & Sandwell 1997, Becker 2008, Becker
cations that include biotopes can be used as ecosys- et al. 2009) that could be used to identify large seabed
tem-level measures of biodiversity. features (M. J. Costello & A. Cheung unpubl. data).
Acoustic mapping has become the best way of provid-
ing terrain maps of the seabed at all depths (e.g.
Ecotones Legendre et al. 2002, Freitas et al. 2006, Wright & Hey-
man 2008), and can be used to map tubeworm distrib-
Boundaries between habitats may be narrow or utions (Degraer et al. 2008).
broad, and play important functional roles in ecosys- The various sampling methods, from satellites to
tems in terms of nutrient flow and dispersal corridors acoustic, video and spot samples, are suitable at differ-
(Risser 1995). The seashore is such an ecotone (be- ent spatial scales (Kenny et al. 2003, Diaz et al. 2004).
tween land and sea), as is the reef edge (between reef However, knowing what species are present almost
and sediment habitats). Estuaries are ecotones between always requires in situ samples taken at point locations
256 Mar Ecol Prog Ser 397: 253–268, 2009
Table 1. Comparison of how 5 key concepts associated with marine habitats are defined and the sampling methods used to collect
information about them
Concept Defined by Sampling method
Habitat Physical environment in which a species, or assemblage of species, Dependent on the species of
lives interest
Region Expert opinion based on biogeography, oceanography and practical Only sampled as seascapes or
management area habitats
Seascape Topography, physiography and hydrography Acoustic mapping, aerial photo-
graphy, spectrophotometric sensing
Biotope Biological community and its physical habitat Visual observation, photography,
samples of substrata and biota
Guild Habitat, body size, sampling method (e.g. net or sieve mesh), diet, habit As for biotopes
or along transects (Wright & Heyman 2008). Whether using management criteria and expert opinion, ‘sea-
recorded by scuba diver, video, photographs or identi- scapes’ by topographic (physiographic) features, ‘bio-
fied in the laboratory from seabed or water samples, topes’ by the assemblage of species in a particular
this data provides a more accurate report of the spe- physical environment and ecological communities as
cies–habitat relationship than remotely sensed meth- ‘guilds’ (Table 1).
ods. However, the latter enable extrapolation of the
extent of the habitat and likely species distributions. In
both these cases the habitat definition is based on ver- Regions
ifiable physical and/or biological data. Where such
data are not available, or a mixture of data is available, The boundaries of regions may be based on political
habitat maps may be drawn by experts based on their history, physiographic features, depth zones and/or
opinion of available data. biogeographic knowledge. Recently, 3 biogeographic
Using expert opinion has the advantage of rapidly classifications have been proposed that collectively
producing maps based on individuals’ knowledge at cover the epipelagic, coastal and deep-sea benthic
low cost. The fact that different experts will have dif- environments: namely Longhurst (1998), Marine Eco-
ferent experiences and perceptions may be helpful, systems of the World (MEOW) (Spalding et al. 2007)
especially if this is brought together to produce a stan- and Global Open Oceans and Deep Sea (GOODS)
dardised methodology. The fact that leading scientists (UNESCO 2009). While many scientific publications,
produced the consequent maps may be an advantage from textbooks to journal articles, refer to biogeo-
and result in their acceptance by the scientific com- graphic regions at oceanic to global scales, they pro-
munity. However, this sidesteps a more objective vide very limited or no species data to support these
approach based on empirical data, and it may conceal regions. In some cases, their boundaries may be pri-
data gaps. If the experts’ focus is on a map produced by marily based on geography and politics, with species
consensus rather than a common methodology, then distributions playing a minor role (Vinogradova 1997,
the outcome may be a mix of different weightings of Spalding et al. 2007). There is a danger that in using
physical or ecological data and/or socioeconomic and maps, readers may not appreciate the limited empirical
political considerations. This particularly applies to support for such regions, and the intermingling of dif-
maps of biogeographic regions as discussed below. ferent types of information used to produce them. It
may be better to think of maps derived from expert
opinion alone as a hypothesis, and data-derived maps
PRACTICAL CONCEPTS FOR HABITAT as models, of biogeographic regions.
CLASSIFICATION The only global regions consistently based on a stan-
dard set of empirical data are those detailed in Long-
Four key concepts: regions, seascapes, biotopes and hurst (1998) for the open-ocean surface (epipelagic)
guilds waters. They provide the best estimate of ocean sur-
face biogeographic regions for the world at present
The physical environment that is used to circum- because they are based on environmental profile and
scribe a species’ habitat can vary greatly depending on ocean-colour satellite data as reasonable surrogates
the ecological perspectives and methods used to define for phytoplankton biomass and ecosystem processes
habitats. Thus ‘regions’ of the ocean may be mapped (Pauly 1999). While the Longhurst (1998) classification
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