354
John D. GAGE
western North Pacific suggest that parcels of kelp
such as Macrocystis pyrifera are rapidly consumed by
megafauna (C.R. Smith and Hamilton, 1983).
The pelagic macroalga Sargassum has a wider
recorded distribution on the deep-sea bed than seagrass;
but Sargassum usually occurs in clumps, whereas
seagrass usually occurs as small blade fragments that
may be easily overlooked (personal observations).
Sargassum occurs in considerable quantities out to
abyssal depths in the Northwest Atlantic in the
Sargasso and Caribbean Seas, in the Gulf of Mexico
and in the central Pacific, and less frequently in
the Northwest Atlantic off New England (Grassle
and Morse-Porteous, 1987). Sargassum may be driven
down to depth by storms causing the gas bladders
to collapse so that it sinks to the seabed (Johnson
and Richardson, 1977). Rowe and Staresinic (1979)
estimated that sinking Sargassum might provide up
to 10% of the total organic input to the abyssal
benthos in the Sargasso Sea. Observations of the
author, P.A. Tyler and C.M. Young off the Bahamas
suggest that macroalgae are recycled more rapidly than
seagrass.
Land plant remains
Pieces of plants washed out to sea from the land
may float for some time before becoming sufficiently
waterlogged to sink onto the deep-sea bed far from
land. Not surprisingly, the presence of branches and
twigs, pieces of wood, bark and fruits in deep-sea
trawlings has been regularly noted from the time of
the great oceanographic expeditions right up to the
Danish Galathea Expedition in 1950–52. Results from
the Galathea cruise were discussed by Wolff (1979),
together with earlier records. These inputs seem to be
particularly noticeable in the deep sea near the mouths
of large rivers in the tropics.
Response of deep-sea biota to macroalgae, and
land plant drops
Observations and in situ experiments using a deepdiving submersible show that amphipods and the
echinoid Stylocidaris lineata are able quickly to locate
patches of Thalassia and Sargassum on the bottom. The
results show that algal/seagrass food-falls are rapidly
colonized by animals such as amphipods, while plasticbag controls were not. This indicates that these foodfalls provide a significant energetic imput to the deepsea bed (Lawson et al., 1993; Young et al., 1993). Other
data indicate that benefits to the smaller sedimentdwelling benthic fauna are less direct, and that ‘normal’
macrofauna may even be negatively affected by the
proximity of fresh kelp falls (Levin and C.R. Smith,
1984).
Wolff (1979) recorded various animal species employing sunken wood and other land-plant material as
substratum, shelter or food. Few metazoans are able to
utilize the lignin and cellulose content of wood as food,
but exceptions include the highly specialized, wood
boring bivalve molluscs, and ostracods (Turner, 1973,
1977; Maddocks and Steineck, 1987). The response
of such organisms may be extraordinarily rapid; colonization and population growth of Xylophaga on wood
blocks resulting in extensive utilization within a few
months (Dean, 1993; Romey et al., 1994; R. Harvey
and P.A. Tyler, personal communications).
PASSIVE ORGANIC INPUTS TO THE DEEP-SEA
BENTHIC BOUNDARY – LARGE PACKAGES OF
ANIMAL ORIGIN
The overall significance of large packages of highly
concentrated organic material sinking from the upper
water column in the form of the dead carcasss of
large animals, such as marine mammals, fish and
large invertebrates such as squid, has long been
largely conjectural (Stockton and DeLaca, 1982). In
his early review of the characteristics of the deepsea environment, Bruun (1957) suggested that the
sinking remains of whales and sharks might constitute
an important food source. However, there was little
support for an important role being played by such
large packages of organic material from dead animals
in the nutrition of the deep-sea benthic system until
the 1960s. Nevertheless, the overall importance of
large food falls of animal origin, and the degree of
dependence on scavenging by deep-sea biota, is still far
from clear (Britton and Morton, 1994).
Response by the specialized scavenger community
to large packages of animal origin
There has long been good evidence from analyses
of gut contents demonstrating that the remains of
such carcasses may be important in the diet of many
deep-sea species (see e.g., Litvinova and Sokolova,
1971; Sedberry and Musick, 1978; Tyler et al., 1993).
John D. GAGE
western North Pacific suggest that parcels of kelp
such as Macrocystis pyrifera are rapidly consumed by
megafauna (C.R. Smith and Hamilton, 1983).
The pelagic macroalga Sargassum has a wider
recorded distribution on the deep-sea bed than seagrass;
but Sargassum usually occurs in clumps, whereas
seagrass usually occurs as small blade fragments that
may be easily overlooked (personal observations).
Sargassum occurs in considerable quantities out to
abyssal depths in the Northwest Atlantic in the
Sargasso and Caribbean Seas, in the Gulf of Mexico
and in the central Pacific, and less frequently in
the Northwest Atlantic off New England (Grassle
and Morse-Porteous, 1987). Sargassum may be driven
down to depth by storms causing the gas bladders
to collapse so that it sinks to the seabed (Johnson
and Richardson, 1977). Rowe and Staresinic (1979)
estimated that sinking Sargassum might provide up
to 10% of the total organic input to the abyssal
benthos in the Sargasso Sea. Observations of the
author, P.A. Tyler and C.M. Young off the Bahamas
suggest that macroalgae are recycled more rapidly than
seagrass.
Land plant remains
Pieces of plants washed out to sea from the land
may float for some time before becoming sufficiently
waterlogged to sink onto the deep-sea bed far from
land. Not surprisingly, the presence of branches and
twigs, pieces of wood, bark and fruits in deep-sea
trawlings has been regularly noted from the time of
the great oceanographic expeditions right up to the
Danish Galathea Expedition in 1950–52. Results from
the Galathea cruise were discussed by Wolff (1979),
together with earlier records. These inputs seem to be
particularly noticeable in the deep sea near the mouths
of large rivers in the tropics.
Response of deep-sea biota to macroalgae, and
land plant drops
Observations and in situ experiments using a deepdiving submersible show that amphipods and the
echinoid Stylocidaris lineata are able quickly to locate
patches of Thalassia and Sargassum on the bottom. The
results show that algal/seagrass food-falls are rapidly
colonized by animals such as amphipods, while plasticbag controls were not. This indicates that these foodfalls provide a significant energetic imput to the deepsea bed (Lawson et al., 1993; Young et al., 1993). Other
data indicate that benefits to the smaller sedimentdwelling benthic fauna are less direct, and that ‘normal’
macrofauna may even be negatively affected by the
proximity of fresh kelp falls (Levin and C.R. Smith,
1984).
Wolff (1979) recorded various animal species employing sunken wood and other land-plant material as
substratum, shelter or food. Few metazoans are able to
utilize the lignin and cellulose content of wood as food,
but exceptions include the highly specialized, wood
boring bivalve molluscs, and ostracods (Turner, 1973,
1977; Maddocks and Steineck, 1987). The response
of such organisms may be extraordinarily rapid; colonization and population growth of Xylophaga on wood
blocks resulting in extensive utilization within a few
months (Dean, 1993; Romey et al., 1994; R. Harvey
and P.A. Tyler, personal communications).
PASSIVE ORGANIC INPUTS TO THE DEEP-SEA
BENTHIC BOUNDARY – LARGE PACKAGES OF
ANIMAL ORIGIN
The overall significance of large packages of highly
concentrated organic material sinking from the upper
water column in the form of the dead carcasss of
large animals, such as marine mammals, fish and
large invertebrates such as squid, has long been
largely conjectural (Stockton and DeLaca, 1982). In
his early review of the characteristics of the deepsea environment, Bruun (1957) suggested that the
sinking remains of whales and sharks might constitute
an important food source. However, there was little
support for an important role being played by such
large packages of organic material from dead animals
in the nutrition of the deep-sea benthic system until
the 1960s. Nevertheless, the overall importance of
large food falls of animal origin, and the degree of
dependence on scavenging by deep-sea biota, is still far
from clear (Britton and Morton, 1994).
Response by the specialized scavenger community
to large packages of animal origin
There has long been good evidence from analyses
of gut contents demonstrating that the remains of
such carcasses may be important in the diet of many
deep-sea species (see e.g., Litvinova and Sokolova,
1971; Sedberry and Musick, 1978; Tyler et al., 1993).