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and their application to pelagic fisheries is not easily foreseen, they have shown that critical constraints in the management of marine fisheries can be overcome. After all,
experimentation, although limited, can be approached in the sea and TURFs present a potential for suitable replication and control in the design of such experiments Castilla
´ and Fernandez, 1999. The challenges are to perfect and expand this direction, to include
the resource users in management, to be more holistic in the approach i.e. to use ecosystem approaches, to use schemes for managing multispecies fisheries and, thereby,
to bridge fisheries management and EME.
4. Conservation and experimental marine ecology
4.1. Marine protected areas MPAs MPAs have been established worldwide as a recognition of the conservation crisis,
over-exploitation of marine resources and the misuse of coastal areas. They have provided an opportunity for studies of ecosystems and for understanding the long-term
dynamics of marine systems. MPAs have been shown to be important tools to protect critical habitats, to provide protection from pollution, to increase the number and size of
individuals of fished species, to serve as ’seeding grounds’ i.e. to supply recruits to fished areas and for ‘‘spillover’’ objectives i.e. the export of biomass; Castilla, 1999.
The increase or decrease, within MPAs, of predator, producer, competitor, engineer species, etc., may have different ecological consequences to the structure, dynamics or
resilience of the community under conservation. The establishment of MPAs can result in different ecological results at the local or regional scale. In essence, the establishment
of MPAs represents a human intervention into marine systems from which humans or some of their activities are totally or partially excluded. MPAs and other conservation
tools preserves, marine parks, marine sanctuaries, isolated islands, coastal areas protected by legal decrees such as shores around yales, military facilities have provided
unique observational and experimental opportunities for EME. An example of this is the test of the ecological role of predators and humans in cascades of species or community
trophic interactions on rocky shores i.e. Estes et al., 1998; Lindberg et al., 1998; Castilla, 1999. Nevertheless, in most cases, because of the MPAs’ locations, number or
extension, the experiments have not been properly designed e.g. there has been no proper replication. Alternative statistical approaches have been used instead. For
instance, comparisons of means between two populations or ’before and after’ paired comparisons MPAs versus outside localities; Underwood, 1991, 1997 or Bayesian
inference concerning the difference between the two means Box and Tiao, 1992. Confounding influences on the results exist and causality needs to be interpreted
carefully. On the other hand, MPAs’ experimental approaches have notable advantages over small-scale experimental plots. They involve large components of an ecosystem and
allow for direct ’exclusion of humans’. Results obtained from MPAs are more readily transferrable into societal issues, such as those of conservation and management
Castilla, 1999.
MPAs fulfill objectives for conservation and management and, at the same time, serve
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.C. Castilla J. Exp. Mar. Biol. Ecol. 250 2000 3 –21
as tools for experimentation. In the future, they may play a critical role in the saga of the ´
resources of the oceans Hockey and Branch, 1997; Castilla and Fernandez, 1999. Nevertheless, at present, most of the MPAs in the world are not under appropriate
scientific scrutiny or regular monitoring. As ‘‘no-take’’ areas, most MPAs are fulfilling only one part of their main role. This is the conservation of a whole or a portion of an
ecosystem. Concurrently, however, critical knowledge on the structure, dynamics and resilience of the preserved ecosystems has not been addressed, due to the lack of
appropriate monitoring.
4.2. Human-exclusion experiments In the marine literature, there are several partial or total manipulations of human
activities MPAs or other areas. These have had different objectives, methodologies and were at variable spatial and time-scales. Three cases involving predators, which are
relevant examples in the EME literature and have had important consequences for conservation and or managerial issues, are highlighted. First is the interactions among
the sea otter, Enhydra lutris, sea urchins and kelp-beds in the Pacific North West and Alaska Estes et al., 1978, 1998; Estes and Duggins, 1995. Second is the interactions
between the rock lobsters Jasus lalandii, whelks and bivalves in South Africa Barkai and Branch, 1988; Barkai and McQuaid, 1988; Castilla et al., 1994. The final example
is that of the muricid snail Concholepas concholepas and its interactions with bivalves and barnacles in Chile Castilla, 1999.
Two of these predators, Jasus and Concholepas, eat competitively dominant mussels, Choromytilus and Perumytilus. Enhydra eats herbivorous sea urchins. Jasus, Con-
cholepas and Enhydra are, or have been, overfished or overhunted. The experimental reduction of fishing hunting pressure, through legal decrees or the establishment of
MPAs, has permitted the evaluation of their roles in the structure and dynamics of marine communities. It has also allowed evaluation of the roles of humans. For the sea
otter, a recent change of biological interactions, probably triggered by large anthro- pogenic influences in oceanic ecosystems in the Northern Pacific by offshore fisheries,
has resulted in the increase of predation on otters by the top-level killer whales, Orcinus orca. This has cascaded into an increment of the populations of urchins and in
macroalgal deforestation in Alaska Estes et al., 1998; see Hairston et al., 1960 - HSS hypothesis, but see Polis 1999 for terrestrial ecosystems. This represents a classic
example of a trophic cascade throughout a community. For C
. concholepas, predation by humans and the cascading effects in the intertidal community where humans were
excluded were studied at the Las Cruces MPA in central Chile. The knowledge acquired on ecosystem functioning and the rate of replenishment of resources i.e. gastropods, sea
urchins and crabs inside the MPA have been used for conservation and management of fisheries. Based on these results, the government of Chile regulated access to benthic
resources by divers through the establishment of TURFs, called Management and
´ Exploitation Areas MEAs Castilla et al., 1998; Castilla and Fernandez, 1998, Castilla,
1999. They can be accessed exclusively by small-scale artisanal fisher communities and forced the end of management under open access schemes. The research has permitted
the implementation of TURFs, co-management and legislation for marine conservation
J .C. Castilla J. Exp. Mar. Biol. Ecol. 250 2000 3 –21
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in the country Castilla, 1994, 1999. This case represents an example from which the results from a long-term EME protocol led to the creation of new tools for management,
conservation and legislation.
4.3. Key-stone species and strength of interactions among species In ecology, conservation and management, the concept of predatory key-stone species
Paine, 1966, 1969 has been widely used, cited, popularized, but also attacked. It has been misused when associated with that of a ’key-stone prey’, ’key-stone host’ and
’key-stone modifier’ species Power et al., 1996. This has produced confusion in the ecological literature. Hurlbert 1997 considered that key-stone is not an ecological
concept, but ’a casual metaphor’. It is a fact, however, that, in the past 30 years, few ecological concepts metaphors such as the key-stone species have been so frequently
used in EME, exported to other systems and applied in conservation and management. It is known that dominant species by abundance or biomass are critical for the
maintenance of the structure and dynamics of communities. They provide most of the energy-flow as primary producers, or, as in the case of engineer species Jones et al.,
1994, habitat for other organisms. In contrast, a key-stone species is defined as one whose impact on its community or ecosystem is disproportionately large relative to its
abundance Power et al., 1996. Starfishes, sea otters, gastropods and humans can serve as examples see review by Castilla, 1999. Mills et al. 1993 suggested that dropping
of the key-stone species concept may ’be compensated by the development of management and policy guidelines that more explicitly account for the complexity of
interactions in natural systems’. The conservation of natural ecosystems depends on our understanding of their structure, dynamics and resilience. I do not see how the dropping
of a concept will enhance the development of wise conservation policies. Conversely, if an ecological concept, such as key-stone, is used in its proper context in conservation
and management, it may produce useful results Castilla et al., 1994; Estes et al., 1998; Castilla, 1999.
Recently, the issue of variation in the strengths of interactions among species, a theme related to key-stone species, has been reviewed Berlow et al., 1999. According to these
authors this is a key variable in most dynamic models of food-webs. Understanding it may guide management of natural resources and conservation. For example, it will help
to predict the potential consequences in a community due to loss or severe reductions in density of species i.e. in situations of over-fishing. This could enhance communication
between empiricists and theoreticians, ecologists and fishery managers.
Last but not least, Power et al. 1996 argued that ‘‘community importance’’ and interaction strength, and therefore the status of species as key-stones, are context-
dependent. Ecology is a context-dependent science. Scientists, managers and or conservationists should keep that in mind. There is no doubt that key-stone is not a
simple word applied to an object or concept that it denotes literally. Perhaps the concept needs to be perfected, contextualized or not used as loosely as it has been in the past.
Certainly, it has not had a ’ridiculous effect on ecological thought or arguments’ Hurlbert, 1997.
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5. Bridging experimental marine ecology, conservation and management
