Regulation of sea urchin populations also depends on certain trophic interactions. Experimental studies have identified key fish species that successfully prey
upon D. africana and have the potential to control their populations (Clemente
2007; Clemente et al. 2011). This has important implications for coastal management. By controlling herbivore densities, and thus the amount of intact macroalgal cover, predatory fish indirectly aid in preserving ecosystems service or
capacity to provide locally important fishing resources and coastal productivity in
sublittoral rocky reefs. The predatory fish observed are mainly species very susceptible to fishing (Clemente 2007). Consequently increased fishing activities have
been associated with lower numbers of these predatory species and higher urchin
densities in the Canary Islands (Clemente et al. 2009; 2011) and elsewhere (Sala
et al. 1998; Guidetti 2006; Guidetti and Dulc ˇic ´ 2007). Additionally, fishing
decreases the mean size of fish. This adds to the loss of species capable of consuming large sea urchins and resulting in a smaller escape by size from predation
that favour their proliferation. The removal of fish predators by severe overfishing
in most areas of the Canarian Archipelago have led to an urchin population outbreak driven only by settlement and recruitment in the absence of any kind of
predatory or top-down control (Hernández 2006; Clemente 2007). This ecological
disequilibrium, mediated by trophic cascade processes, has major consequences
for the structure and function of the entire benthic community.
Because top-down effects on D. africana at the eastern Atlantic archipelagos
depend on specific predatory species and their abundances within the food web,
preserving the diversity of fish predators must be a priority of conservation efforts
(Clemente et al. 2010). However, at this time this scientific knowledge has not
been fully taken into consideration by policy makers and no protection measures
have been directly applied to key predators of the sea urchin. There is only one
kind of effective management tool in force that can indirectly contribute to the
control of sea urchin populations. This is marine protected areas in which fishing
restriction measures are implemented to allow fishing stocks to recover (Hernández et al. 2008a). As elsewhere around the world (Sala et al. 1998; Babcock
et al. 1999; McClanahan et al. 1999; Guidetti 2006), studies in the Canary Islands
have stressed the value of marine protected areas as a tool for ecosystem restoration; not only for fishes and fishing resources that increases predation on urchins
and indirectly aids regeneration of benthic communities (Hernández et al. 2008a;
Clemente et al. 2009). In fact, the three marine protected areas within the Canary
support higher densities of fish predators and higher levels of predation intensity
on D. africana compared to equivalent non-protected locations (Clemente 2007;
Clemente et al. 2011).
Regardless of the complexity of factors involved in regulation of overpopulations of D. africana may be achieved by aiding the recovery of the predatory fish
community with appropriate fishing bans and protection measures. Current
knowledge about the species’ population dynamics has critical implications for the
conservation of rocky reef ecosystems in the eastern Atlantic Islands. They add to
a growing body of research suggesting that the incidence of barrens and their
associated impacts are related to human disturbance (Steneck 1998; Jackson et al.
498
J. C. Hernández et al.
upon D. africana and have the potential to control their populations (Clemente
2007; Clemente et al. 2011). This has important implications for coastal management. By controlling herbivore densities, and thus the amount of intact macroalgal cover, predatory fish indirectly aid in preserving ecosystems service or
capacity to provide locally important fishing resources and coastal productivity in
sublittoral rocky reefs. The predatory fish observed are mainly species very susceptible to fishing (Clemente 2007). Consequently increased fishing activities have
been associated with lower numbers of these predatory species and higher urchin
densities in the Canary Islands (Clemente et al. 2009; 2011) and elsewhere (Sala
et al. 1998; Guidetti 2006; Guidetti and Dulc ˇic ´ 2007). Additionally, fishing
decreases the mean size of fish. This adds to the loss of species capable of consuming large sea urchins and resulting in a smaller escape by size from predation
that favour their proliferation. The removal of fish predators by severe overfishing
in most areas of the Canarian Archipelago have led to an urchin population outbreak driven only by settlement and recruitment in the absence of any kind of
predatory or top-down control (Hernández 2006; Clemente 2007). This ecological
disequilibrium, mediated by trophic cascade processes, has major consequences
for the structure and function of the entire benthic community.
Because top-down effects on D. africana at the eastern Atlantic archipelagos
depend on specific predatory species and their abundances within the food web,
preserving the diversity of fish predators must be a priority of conservation efforts
(Clemente et al. 2010). However, at this time this scientific knowledge has not
been fully taken into consideration by policy makers and no protection measures
have been directly applied to key predators of the sea urchin. There is only one
kind of effective management tool in force that can indirectly contribute to the
control of sea urchin populations. This is marine protected areas in which fishing
restriction measures are implemented to allow fishing stocks to recover (Hernández et al. 2008a). As elsewhere around the world (Sala et al. 1998; Babcock
et al. 1999; McClanahan et al. 1999; Guidetti 2006), studies in the Canary Islands
have stressed the value of marine protected areas as a tool for ecosystem restoration; not only for fishes and fishing resources that increases predation on urchins
and indirectly aids regeneration of benthic communities (Hernández et al. 2008a;
Clemente et al. 2009). In fact, the three marine protected areas within the Canary
support higher densities of fish predators and higher levels of predation intensity
on D. africana compared to equivalent non-protected locations (Clemente 2007;
Clemente et al. 2011).
Regardless of the complexity of factors involved in regulation of overpopulations of D. africana may be achieved by aiding the recovery of the predatory fish
community with appropriate fishing bans and protection measures. Current
knowledge about the species’ population dynamics has critical implications for the
conservation of rocky reef ecosystems in the eastern Atlantic Islands. They add to
a growing body of research suggesting that the incidence of barrens and their
associated impacts are related to human disturbance (Steneck 1998; Jackson et al.
498
J. C. Hernández et al.