greater at the northern sites than at the southern sites, but there were low densities
of asteroids and holothurians. This may be related to a lack of appropriate substrata
or food availability at the sites. This is in agreement with Roff et al. (2003) and
Edgar et al. (2004) who indicated that, in most cases, abiotic factors such as
salinity, temperature, depth, rock type or sediment particle size are important
factors for biota that act in synchrony with biological process to affect macro and
micro distribution.
Pawson and Ahearn (2001) collected echinoderms from bathyal and abyssal
waters and reported four new records for the Galápagos Islands and eight new
species. The new species included four holothurians (one representing a new
genus), one echinoid, and three asteroids. The cidaroid echinoid Centrocidaris
doederleini that was formerly considered rare occurs in numerous populations,
reaching average densities of 185 ind m
-2 (Pawson and Ahearn 2001). The
ophiuroids Ophiothix spp. and Ophiacantha spp. often occur together in large
aggregations of more than 100 individuals in black sandy areas with negligible
current activity (Pawson and Ahearn 2001). The asteroids Henricia spp. and
Coronoaster sp are fairly common on a variety of habitats, but were found mostly
on rocky substrates; the stalked crinoids Thalassometra agassizii and Calamocrinus
diomedeae are very rare (Pawson and Ahearn 2001).
6.3 Research
6.3.1 Ecology and Population Biology
Sea Cucumbers
Isostichopus fuscus
Distribution and Density
Isostichopus fuscus is a deposit-feeding aspidochirote species distributed from the
Gulf of California to Ecuador, including the Galápagos Islands (Maluf 1991).
The cylindrical, tough and flexible body is brownish with darker warts (Fig. 6.3a).
The color may change to dark brown depending on the color of the substrate. This
species is found mainly on rocky reef areas from 2 to 40 m depth (Hickman 1998)
although it has been seen at 60 m. In Galápagos, its distribution is not continuous.
Therefore there is a high level of uncertainty regarding its population dynamics.
The largest population was concentrated in the western region of the archipelago
along the Bolívar Channel (Murillo et al. 2002a). The average size of the individuals was 20 cm in length and the range in wet weight was 100–410 g (average
271 g) (Sonnenholzner 1997). At this location densities fluctuated between 0.27
and 0.40 ind m
-2 from 1994 to 1997, but decreased to 0.13 ind m
-2 due to an
illegal fishery (Piu 1998, 2000; Martínez 1999; Murillo et al. 2002a, b). In 2003,
196
J. Sonnenholzner et al.
of asteroids and holothurians. This may be related to a lack of appropriate substrata
or food availability at the sites. This is in agreement with Roff et al. (2003) and
Edgar et al. (2004) who indicated that, in most cases, abiotic factors such as
salinity, temperature, depth, rock type or sediment particle size are important
factors for biota that act in synchrony with biological process to affect macro and
micro distribution.
Pawson and Ahearn (2001) collected echinoderms from bathyal and abyssal
waters and reported four new records for the Galápagos Islands and eight new
species. The new species included four holothurians (one representing a new
genus), one echinoid, and three asteroids. The cidaroid echinoid Centrocidaris
doederleini that was formerly considered rare occurs in numerous populations,
reaching average densities of 185 ind m
-2 (Pawson and Ahearn 2001). The
ophiuroids Ophiothix spp. and Ophiacantha spp. often occur together in large
aggregations of more than 100 individuals in black sandy areas with negligible
current activity (Pawson and Ahearn 2001). The asteroids Henricia spp. and
Coronoaster sp are fairly common on a variety of habitats, but were found mostly
on rocky substrates; the stalked crinoids Thalassometra agassizii and Calamocrinus
diomedeae are very rare (Pawson and Ahearn 2001).
6.3 Research
6.3.1 Ecology and Population Biology
Sea Cucumbers
Isostichopus fuscus
Distribution and Density
Isostichopus fuscus is a deposit-feeding aspidochirote species distributed from the
Gulf of California to Ecuador, including the Galápagos Islands (Maluf 1991).
The cylindrical, tough and flexible body is brownish with darker warts (Fig. 6.3a).
The color may change to dark brown depending on the color of the substrate. This
species is found mainly on rocky reef areas from 2 to 40 m depth (Hickman 1998)
although it has been seen at 60 m. In Galápagos, its distribution is not continuous.
Therefore there is a high level of uncertainty regarding its population dynamics.
The largest population was concentrated in the western region of the archipelago
along the Bolívar Channel (Murillo et al. 2002a). The average size of the individuals was 20 cm in length and the range in wet weight was 100–410 g (average
271 g) (Sonnenholzner 1997). At this location densities fluctuated between 0.27
and 0.40 ind m
-2 from 1994 to 1997, but decreased to 0.13 ind m
-2 due to an
illegal fishery (Piu 1998, 2000; Martínez 1999; Murillo et al. 2002a, b). In 2003,
196
J. Sonnenholzner et al.