At a local level, the different threats on echinoderm biodiversity can be divided
according to their origin, as natural threats and those generated by human intervention. Considering the natural threats, during El Niño years most parts of
Venezuela showed a delay in the onset of the rainy season and a reduction in the
amount of precipitation (Lozada 2002). This can produce an increase in salinity of
coastal waters in some zones. However, the direct effect of El Niño-Southern
Oscillation phenomena upon echinoderm populations has not been described.
Other threats, like hurricanes, are relatively infrequent in Venezuela in comparison
with the rest of the Caribbean Sea due to the geographical position of the country
(Díaz-Martín 1995). There are no current records of their direct effects on populations of echinoderms. From a geological point of view, Venezuela is located
above a major fault zone, which produces relatively frequent earthquakes. In spite
of this, ‘‘tsunamis’’ have been rare (Grasses 1994). However, identification of a
series of submarine displacements in the Lesser Antilles reveal the vulnerability of
the Venezuelan coasts to this type of phenomenon (Theilen-Willige 2006).
It has been estimated that the most important potential natural threat to echinoderms in Venezuela is the large load of sediments carried by rivers during the
rainy season (May–November). This phenomenon can generate mass mortalities of
marine organisms (Goodbody 1961) and causes losses in the diversity of echinoderms, particularly in coral reefs (Vázquez-Domínguez 2003). In this sense, it is
important to emphasize the influence of the Orinoco River on the patterns of
salinity, currents, nutrient concentration and suspended material in the Atlantic
coast of the country and the eastern Caribbean Sea whose fluctuations are directly
related to the dry-rainy season regime (Penchaszadeh et al. 2000).
Regarding threats by diseases, there are reports that epidemics and the number
of emergent diseases are rising worldwide in corals and other marine organisms
(Richardson et al. 1998; Harvell et al. 1999; Green and Bruckner 2000). In
Venezuela, the echinoid D. antillarum did not escape from the mass mortality
registered in the general Caribbean Sea between 1983 and 1984 (Lessios et al.
1984; Hunte et al. 1986; Lessios 1988). The abundances of D. antillarum recorded
between 2002 and 2003 in different localities of the country show that they have
not reached yet the population density levels reported before the mortality period
of 1984 (Noriega et al. 2006), although our own observations in Mochima Bay and
the Gulf of Cariaco show a high density of individuals with signals of recovery of
the populations.
In addition to disease, an 80 % reduction in the coralline cover has been
reported in the Caribbean Sea (Gardner et al. 2003). In Venezuela coral cover has
decreased at Sombrero Key in Morrocoy National Park (Cróquer and Bone 2003).
This could also compromise the abundance of echinoderms like the echinoid
E. lucunter, generally associated with the terrace and the reef crest (Abbott et al.
1974) and D. antillarum which also occur in these types of environments.
Regarding anthropogenic threats, it is important to show that intense petroleum
exploitation and processing in Venezuela, with a heavy traffic of vessels and a
network of oil pipes, the chances for spills of oil and other derivatives represent a
latent and constant threat. This is particularly serious during the phase of
262
C. Lodeiros et al.
according to their origin, as natural threats and those generated by human intervention. Considering the natural threats, during El Niño years most parts of
Venezuela showed a delay in the onset of the rainy season and a reduction in the
amount of precipitation (Lozada 2002). This can produce an increase in salinity of
coastal waters in some zones. However, the direct effect of El Niño-Southern
Oscillation phenomena upon echinoderm populations has not been described.
Other threats, like hurricanes, are relatively infrequent in Venezuela in comparison
with the rest of the Caribbean Sea due to the geographical position of the country
(Díaz-Martín 1995). There are no current records of their direct effects on populations of echinoderms. From a geological point of view, Venezuela is located
above a major fault zone, which produces relatively frequent earthquakes. In spite
of this, ‘‘tsunamis’’ have been rare (Grasses 1994). However, identification of a
series of submarine displacements in the Lesser Antilles reveal the vulnerability of
the Venezuelan coasts to this type of phenomenon (Theilen-Willige 2006).
It has been estimated that the most important potential natural threat to echinoderms in Venezuela is the large load of sediments carried by rivers during the
rainy season (May–November). This phenomenon can generate mass mortalities of
marine organisms (Goodbody 1961) and causes losses in the diversity of echinoderms, particularly in coral reefs (Vázquez-Domínguez 2003). In this sense, it is
important to emphasize the influence of the Orinoco River on the patterns of
salinity, currents, nutrient concentration and suspended material in the Atlantic
coast of the country and the eastern Caribbean Sea whose fluctuations are directly
related to the dry-rainy season regime (Penchaszadeh et al. 2000).
Regarding threats by diseases, there are reports that epidemics and the number
of emergent diseases are rising worldwide in corals and other marine organisms
(Richardson et al. 1998; Harvell et al. 1999; Green and Bruckner 2000). In
Venezuela, the echinoid D. antillarum did not escape from the mass mortality
registered in the general Caribbean Sea between 1983 and 1984 (Lessios et al.
1984; Hunte et al. 1986; Lessios 1988). The abundances of D. antillarum recorded
between 2002 and 2003 in different localities of the country show that they have
not reached yet the population density levels reported before the mortality period
of 1984 (Noriega et al. 2006), although our own observations in Mochima Bay and
the Gulf of Cariaco show a high density of individuals with signals of recovery of
the populations.
In addition to disease, an 80 % reduction in the coralline cover has been
reported in the Caribbean Sea (Gardner et al. 2003). In Venezuela coral cover has
decreased at Sombrero Key in Morrocoy National Park (Cróquer and Bone 2003).
This could also compromise the abundance of echinoderms like the echinoid
E. lucunter, generally associated with the terrace and the reef crest (Abbott et al.
1974) and D. antillarum which also occur in these types of environments.
Regarding anthropogenic threats, it is important to show that intense petroleum
exploitation and processing in Venezuela, with a heavy traffic of vessels and a
network of oil pipes, the chances for spills of oil and other derivatives represent a
latent and constant threat. This is particularly serious during the phase of
262
C. Lodeiros et al.