FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
355
However, it was the dramatic results from moored
seabed cameras focusing on bait, or traps baited
with fish or other carcasses, that provided the most
convincing evidence of the role of large carcasses
as a source of food to deep-sea organisms (Isaacs
and Schwartzlose, 1975; Thurston, 1979; Stockton and
DeLaca, 1982). These experiments showed that such
concentrated food sources attract dense aggregations of
a range of scavenging species, ranging from amphipod
crustaceans to large fish, virtually anywhere on the
deep-sea floor. The efficiency and rapidity of the
response, which results in the carcass being reduced
to bone within hours, or days in the case of a large
cetacean, testifies to the high degree of specialization
of scavengers for such food sources. Even if the dead
bodies of fish provide less persistent packages of food
than a large whale, they must be quantitatively more
important on the deep-sea bed. Even the bones are
eventually utilized, as it is unusual to encounter fish
bones in deep-sea sediments, although the hard dentine
of shark teeth is more persistent, and such teeth are well
preserved in abyssal sediment.
The unpredictability in where they fall, and their low
density, makes such concentrated food inputs difficult
to estimate quantitatively. Certain areas underlying
the seasonal migration routes of fish or marine
mammals may experience these inputs more frequently
(Tyler, 1988; C.R. Smith et al., 1989; Tyler et al.,
1993). Another potential source of input is from the
discarded by-catch of trawling in deep-sea fisheries
on the continental slope. Such fisheries are as yet
unregulated and highly selective, meaning that often
a large proportion (up to around 50%) of trawled
biomass re-enters the sea as highly localized, and
relatively massive, dead food falls (Connolly and Kelly,
1996).
Dead whales
I shall deal with whales separately, as such megacarrion
provides the largest amount of biomass from a sinking
carcass, and therefore the most persistent food-fall.
C.R. Smith et al. (1998) have estimated that adults
of the nine largest species will provide in excess of
10 000 kg wet weight of organic matter. Even if the
number of large cetacean food-falls to the deep-sea bed
may have declined greatly since the development of
modern whaling, such food-falls represent a colossal
concentration of organic enrichment in a food-poor
environment. That biological specialization to such
windfalls is well developed is shown from seabed
experiments using autonomous lander vehicles, which
show tissue removal rates by fish and invertebrate
scavengers of between 0.05 and 0.4 kg h
−1 (Jones et al.,
1998). This is a similar rate to that observed with
large fish carcasses (C.R. Smith, 1985), and means
that a small cetacean (50 to 100 kg) may be reduced
to skeleton within 15 days. For larger carcasses,
scavenging and decomposition may remove 1 kg h
−1 ,
equivalent to 9 t yr
−1 , sufficient to skeletonize small
whales within a year (Jones et al., 1998). There is also
a slow loss of particulate and dissolved organics into
the surrounding water and sediment (C.R. Smith et al.,
1998). Such falls may be locally important (Katona
and Whitehead, 1988; Britton and Morton, 1994).
Estimates of carbon input to the deep-sea benthic
system based on whale population size and natural
mortality are 2 to 3 orders of magnitude less than
that provided directly from primary production at the
surface by phytodetritus (Jelmert and Oppen-Berntsen,
1996). At the basin-wide scale in the Northeast
Pacific, the input of dead whale falls is probably of
the order of only 0.1% of published estimates of
detrital sedimentation to the sea floor (C.R. Smith
and R.S. Lampitt, personal communications). Butman
et al. (1994) have given a speculative account of
changes in such effects as inputs to the deep-sea bed
ecosystem caused by changes in whale populations
through whaling.
Whale skeletons located on the deep-sea bed seem
to be persistent features whose large bones typically
contain 10% lipid and 25% protein. In one experiment
a dead dolphin measuring 2.04 m long was put on the
abyssal seabed (4800 m water depth) in the Northeast
Atlantic for 276 days. This was estimated to provide
500 kg of organic carbon from the skeleton, equivalent
to 325 years of average daily background flux per
square metre (Jones et al., 1998). Such a rich substrate
encourages anaerobic decomposition with development
of Beggiatoa bacterial mats over the surface. Sulphide
generated by these microbial processes is utilized by
chemoautotrophic bacterial endosymbionts in a variety
of attached bivalve molluscs, such as the genera
Calyptogena, Vesicomya and species of the families
Lucinomidae and bivalves, hyalinoecid Thyasiridae,
which normally are associated with reducing environments (see Chapter 4) (C.R. Smith et al., 1989; Bennett
et al., 1994; Naganuma et al., 1996).
355
However, it was the dramatic results from moored
seabed cameras focusing on bait, or traps baited
with fish or other carcasses, that provided the most
convincing evidence of the role of large carcasses
as a source of food to deep-sea organisms (Isaacs
and Schwartzlose, 1975; Thurston, 1979; Stockton and
DeLaca, 1982). These experiments showed that such
concentrated food sources attract dense aggregations of
a range of scavenging species, ranging from amphipod
crustaceans to large fish, virtually anywhere on the
deep-sea floor. The efficiency and rapidity of the
response, which results in the carcass being reduced
to bone within hours, or days in the case of a large
cetacean, testifies to the high degree of specialization
of scavengers for such food sources. Even if the dead
bodies of fish provide less persistent packages of food
than a large whale, they must be quantitatively more
important on the deep-sea bed. Even the bones are
eventually utilized, as it is unusual to encounter fish
bones in deep-sea sediments, although the hard dentine
of shark teeth is more persistent, and such teeth are well
preserved in abyssal sediment.
The unpredictability in where they fall, and their low
density, makes such concentrated food inputs difficult
to estimate quantitatively. Certain areas underlying
the seasonal migration routes of fish or marine
mammals may experience these inputs more frequently
(Tyler, 1988; C.R. Smith et al., 1989; Tyler et al.,
1993). Another potential source of input is from the
discarded by-catch of trawling in deep-sea fisheries
on the continental slope. Such fisheries are as yet
unregulated and highly selective, meaning that often
a large proportion (up to around 50%) of trawled
biomass re-enters the sea as highly localized, and
relatively massive, dead food falls (Connolly and Kelly,
1996).
Dead whales
I shall deal with whales separately, as such megacarrion
provides the largest amount of biomass from a sinking
carcass, and therefore the most persistent food-fall.
C.R. Smith et al. (1998) have estimated that adults
of the nine largest species will provide in excess of
10 000 kg wet weight of organic matter. Even if the
number of large cetacean food-falls to the deep-sea bed
may have declined greatly since the development of
modern whaling, such food-falls represent a colossal
concentration of organic enrichment in a food-poor
environment. That biological specialization to such
windfalls is well developed is shown from seabed
experiments using autonomous lander vehicles, which
show tissue removal rates by fish and invertebrate
scavengers of between 0.05 and 0.4 kg h
−1 (Jones et al.,
1998). This is a similar rate to that observed with
large fish carcasses (C.R. Smith, 1985), and means
that a small cetacean (50 to 100 kg) may be reduced
to skeleton within 15 days. For larger carcasses,
scavenging and decomposition may remove 1 kg h
−1 ,
equivalent to 9 t yr
−1 , sufficient to skeletonize small
whales within a year (Jones et al., 1998). There is also
a slow loss of particulate and dissolved organics into
the surrounding water and sediment (C.R. Smith et al.,
1998). Such falls may be locally important (Katona
and Whitehead, 1988; Britton and Morton, 1994).
Estimates of carbon input to the deep-sea benthic
system based on whale population size and natural
mortality are 2 to 3 orders of magnitude less than
that provided directly from primary production at the
surface by phytodetritus (Jelmert and Oppen-Berntsen,
1996). At the basin-wide scale in the Northeast
Pacific, the input of dead whale falls is probably of
the order of only 0.1% of published estimates of
detrital sedimentation to the sea floor (C.R. Smith
and R.S. Lampitt, personal communications). Butman
et al. (1994) have given a speculative account of
changes in such effects as inputs to the deep-sea bed
ecosystem caused by changes in whale populations
through whaling.
Whale skeletons located on the deep-sea bed seem
to be persistent features whose large bones typically
contain 10% lipid and 25% protein. In one experiment
a dead dolphin measuring 2.04 m long was put on the
abyssal seabed (4800 m water depth) in the Northeast
Atlantic for 276 days. This was estimated to provide
500 kg of organic carbon from the skeleton, equivalent
to 325 years of average daily background flux per
square metre (Jones et al., 1998). Such a rich substrate
encourages anaerobic decomposition with development
of Beggiatoa bacterial mats over the surface. Sulphide
generated by these microbial processes is utilized by
chemoautotrophic bacterial endosymbionts in a variety
of attached bivalve molluscs, such as the genera
Calyptogena, Vesicomya and species of the families
Lucinomidae and bivalves, hyalinoecid Thyasiridae,
which normally are associated with reducing environments (see Chapter 4) (C.R. Smith et al., 1989; Bennett
et al., 1994; Naganuma et al., 1996).