30
David THISTLE
than rates measured on similar shallow-water, lowtemperature fishes (Smith and Hessler, 1974). These
low rates appear to be necessary because of low
food availability and are achieved by minimization
of locomotion and accompanying economies at the
cellular level, e.g., lower enzyme concentrations in
muscles than in comparable, shallow-water species
(Siebenaller and Somero, 1982). In contrast, the
weight-specific oxygen consumption of bathyal brittle
stars (three species) and a bathyal holothuroid (Scotoplanes globosa) were similar to those in shallow water
(Smith, 1983).
The collective metabolism of the organisms (bacteria, protozoa, meiofauna, and macrofauna) resident in
the sediment has been estimated by measurements of
sediment-community oxygen consumption (SCOC) per
unit area. Smith and Teal (1973) found that the SCOC
at a station at 1850 m was two orders of magnitude
less than that at several shallow-water stations. Further
work (Smith, 1987) has shown that SCOC decreases
with increasing depth in the deep sea. On a unitbiomass basis, the 1850-m station had a tenth the
SCOC of the shallow-water stations (Smith and Teal,
1973). In contrast, there was no trend in SCOC per
unit biomass with depth among the deep-sea stations
(Smith and Hinga, 1983; Smith, 1987). If one assumes
that the relative metabolic rate among the component
groups of organisms does not change markedly as depth
increases, these results imply that the metabolic rate of
the sediment-dwelling organisms is lower in the deep
sea than in shallow water, but within the deep sea, there
is no trend with depth.
Bioturbation
Bioturbation occurs when organisms (primarily the
infauna) move sediment. Bioturbation rates decrease
with increasing depth in the deep sea, but when
bioturbation rates are normalized by the number of
animals per unit area, which also decreases with
increasing depth, the rate does not change with depth
(Gage, 1991). Individual deep-sea animals mix the
sediment at about the same rate as shallow-water
animals, suggesting that movement rates and metabolic
rates of infauna may not be too dissimilar to such rates
in shallow water.
Growth
The growth of demersal fishes appears to be slow in the
deep sea (Beamish and Chilton, 1982; Merrett, 1989),
as might be expected from their low metabolic rate.
The rate of growth of the deep-sea infauna is less clear.
Turekian et al. (1975) used a radioisotope technique to
study the growth rate of a deep-sea clam. Their best
estimate was that the largest size class (8 mm) was
about 100 years old and that reproductive maturity was
reached in 50–60 years. Although the confidence limits
around these estimates were large, the report has been
very influential because it supported preconceptions
that growth rates would be low and life spans long in
the deep sea.
The disparity between the results of Turekian et al.
(1975) and those from shallow water are not as great
as originally thought. For example, the growth rates of
some deep-sea bivalve species are comparable to those
of shallow-water bivalves (Gage, 1991). Following the
work of Turekian et al. (1975), the growth rates of deepsea benthic organisms have been estimated by other
indirect methods. If the assumptions made are correct,
the growth rates of deep-sea invertebrates are lower
than, but not markedly different from, growth rates
of shallow-water species (Gage, 1991). Direct measurements from time-lapse photographs have shown
that the growth of a deep-sea hard-bottom barnacle
was almost as rapid as that of similar, shallow-water
barnacles (Lampitt, 1990) and that the volume of three
xenophyophore individuals increased by a factor of 3–
10 in 8 months; during these 8 months, periods of rapid
growth were interspersed with periods of no growth
(Gooday et al., 1993) (Fig. 2.23). Colonization studies
suggest that an aplacophoran mollusk can reach adult
size in two months (Scheltema, 1987).
Food availability appears to be a leading variable
in the control of the growth rate of deep-sea animals;
where food is abundant, growth is rapid compared
to that where food is scarce. For example, food is
abundant for tube worms (Vestimentifera) at hydrothermal vents, and their length can increase by tens of
centimeters per year (Lutz et al., 1994). Similarly,
pieces of wood (e.g., tree trunks) that wash offshore
and sink are a rich source of food for wood-boring
bivalves (Xylophaginidae), which reach adult size
within months of settlement (Turner, 1973). The growth
rate of a gooseneck barnacle increased several-fold
when phytodetritus, a likely source of food for this
suspension feeder, was present (Lampitt, 1990). It
appears that growth rates in the deep sea are limited,
not by the physiological challenges of the physical
David THISTLE
than rates measured on similar shallow-water, lowtemperature fishes (Smith and Hessler, 1974). These
low rates appear to be necessary because of low
food availability and are achieved by minimization
of locomotion and accompanying economies at the
cellular level, e.g., lower enzyme concentrations in
muscles than in comparable, shallow-water species
(Siebenaller and Somero, 1982). In contrast, the
weight-specific oxygen consumption of bathyal brittle
stars (three species) and a bathyal holothuroid (Scotoplanes globosa) were similar to those in shallow water
(Smith, 1983).
The collective metabolism of the organisms (bacteria, protozoa, meiofauna, and macrofauna) resident in
the sediment has been estimated by measurements of
sediment-community oxygen consumption (SCOC) per
unit area. Smith and Teal (1973) found that the SCOC
at a station at 1850 m was two orders of magnitude
less than that at several shallow-water stations. Further
work (Smith, 1987) has shown that SCOC decreases
with increasing depth in the deep sea. On a unitbiomass basis, the 1850-m station had a tenth the
SCOC of the shallow-water stations (Smith and Teal,
1973). In contrast, there was no trend in SCOC per
unit biomass with depth among the deep-sea stations
(Smith and Hinga, 1983; Smith, 1987). If one assumes
that the relative metabolic rate among the component
groups of organisms does not change markedly as depth
increases, these results imply that the metabolic rate of
the sediment-dwelling organisms is lower in the deep
sea than in shallow water, but within the deep sea, there
is no trend with depth.
Bioturbation
Bioturbation occurs when organisms (primarily the
infauna) move sediment. Bioturbation rates decrease
with increasing depth in the deep sea, but when
bioturbation rates are normalized by the number of
animals per unit area, which also decreases with
increasing depth, the rate does not change with depth
(Gage, 1991). Individual deep-sea animals mix the
sediment at about the same rate as shallow-water
animals, suggesting that movement rates and metabolic
rates of infauna may not be too dissimilar to such rates
in shallow water.
Growth
The growth of demersal fishes appears to be slow in the
deep sea (Beamish and Chilton, 1982; Merrett, 1989),
as might be expected from their low metabolic rate.
The rate of growth of the deep-sea infauna is less clear.
Turekian et al. (1975) used a radioisotope technique to
study the growth rate of a deep-sea clam. Their best
estimate was that the largest size class (8 mm) was
about 100 years old and that reproductive maturity was
reached in 50–60 years. Although the confidence limits
around these estimates were large, the report has been
very influential because it supported preconceptions
that growth rates would be low and life spans long in
the deep sea.
The disparity between the results of Turekian et al.
(1975) and those from shallow water are not as great
as originally thought. For example, the growth rates of
some deep-sea bivalve species are comparable to those
of shallow-water bivalves (Gage, 1991). Following the
work of Turekian et al. (1975), the growth rates of deepsea benthic organisms have been estimated by other
indirect methods. If the assumptions made are correct,
the growth rates of deep-sea invertebrates are lower
than, but not markedly different from, growth rates
of shallow-water species (Gage, 1991). Direct measurements from time-lapse photographs have shown
that the growth of a deep-sea hard-bottom barnacle
was almost as rapid as that of similar, shallow-water
barnacles (Lampitt, 1990) and that the volume of three
xenophyophore individuals increased by a factor of 3–
10 in 8 months; during these 8 months, periods of rapid
growth were interspersed with periods of no growth
(Gooday et al., 1993) (Fig. 2.23). Colonization studies
suggest that an aplacophoran mollusk can reach adult
size in two months (Scheltema, 1987).
Food availability appears to be a leading variable
in the control of the growth rate of deep-sea animals;
where food is abundant, growth is rapid compared
to that where food is scarce. For example, food is
abundant for tube worms (Vestimentifera) at hydrothermal vents, and their length can increase by tens of
centimeters per year (Lutz et al., 1994). Similarly,
pieces of wood (e.g., tree trunks) that wash offshore
and sink are a rich source of food for wood-boring
bivalves (Xylophaginidae), which reach adult size
within months of settlement (Turner, 1973). The growth
rate of a gooseneck barnacle increased several-fold
when phytodetritus, a likely source of food for this
suspension feeder, was present (Lampitt, 1990). It
appears that growth rates in the deep sea are limited,
not by the physiological challenges of the physical