168 Producti vity and Benthic Organisms
The vagile benthos on the rocky substrate - starfish, sea urchins, gastropods,
ostracods - feeds on epibenthic organisms, for example, by scraping off algae, or
preying on sessile animals. It protects itself from storms and predators by hiding in
nooks and crannies, growing thick shells, or by clinging to the rock, as do the chitons
and patellas using their strong sucker foot. On soft bottom (in less agitated environments), most vagile benthic animals ingest sediment, especially surface detritus (deposit feeders). Others hunt for prey.
We see that life in the bottom is greatly influenced by the type of the substrate,
which, like the organisms themselves, reflects environmental factors: temperature,
salinity, oxygen content, currents, microtopography. Thus, sedimentary processes and
life on the sea floor are intimately associated. The remains of organisms within their
habitat yield valuable clues to conditions of both growth and sedimentation, therefore. In fact, benthic organisms may produce much or all of the substrate, in places.
One aspect of ecology which is of great interest to geology is the production rate
of hard parts, that is, carbonate (Fig. 6.7). Off Miami, the macrobenthos produces
annually about lOOO g carbonate per m 2 in the tidal zone, between 1 and 400 g per
m 2 in the deeper water offshore. On shallow areas of the Persian Gulf, a single
species of foraminifer, Heterostegina depressa (Fig. 6.10), delivers annually 150 g
carbonate per m 2 . This protist lives in symbiosis with photosynthesizing algae, as do
corals. Questions regarding type and rate of mineralization are obviously of importance to paleoecology; here biological and geological research are closely intertwined. Benthic foraminifera whose shells provide a lasting record are ideally suited
to define the limits of many of these conditions (Figs. 6.9 and 6.10.).
For an appreciation of the relationships between organisms and environment of
deposition, let us have a closer look at benthic organisms and their substrates, hard
and soft.
6.3 Organisms and Rocky Substrate
Rocks in the ocean floor outcrop where currents or waves keep the floor free from
sediments, or in areas of active erosion. Steep-sided walls in fracture zones and other
rugged topography are also likely places for rock outcrops.
A great number of different materials can be called rock: ancient sandstones and
limestones of wave-cut platforms or along submarine canyons, basalt scarps or manganese pavements, submerged dead coral and cemented beach sand (beach rock),
boulders dropped from icebergs or left in the shelf in moraines, sunken ships, and
other man-made objects. All such substrates can be densely covered by benthic
organisms under the right conditions, in some cases (drop-stones, ships) forming
epibenthic "oases" on an otherwise rather empty muddy sea floor. The most abundant
type of rocky substrate undoubtedly is provided by the pillow basalts of the MidOcean Ridge. These basalt outcrops are commonly rather barren, except in local spots
of hydrothermal exhalation (see Sect. 6.9).
In shallow areas, rocky bottoms are commonly covered by algae. The algae can be
microscopic diatoms (many of these move about on the rock), or up to several-
The vagile benthos on the rocky substrate - starfish, sea urchins, gastropods,
ostracods - feeds on epibenthic organisms, for example, by scraping off algae, or
preying on sessile animals. It protects itself from storms and predators by hiding in
nooks and crannies, growing thick shells, or by clinging to the rock, as do the chitons
and patellas using their strong sucker foot. On soft bottom (in less agitated environments), most vagile benthic animals ingest sediment, especially surface detritus (deposit feeders). Others hunt for prey.
We see that life in the bottom is greatly influenced by the type of the substrate,
which, like the organisms themselves, reflects environmental factors: temperature,
salinity, oxygen content, currents, microtopography. Thus, sedimentary processes and
life on the sea floor are intimately associated. The remains of organisms within their
habitat yield valuable clues to conditions of both growth and sedimentation, therefore. In fact, benthic organisms may produce much or all of the substrate, in places.
One aspect of ecology which is of great interest to geology is the production rate
of hard parts, that is, carbonate (Fig. 6.7). Off Miami, the macrobenthos produces
annually about lOOO g carbonate per m 2 in the tidal zone, between 1 and 400 g per
m 2 in the deeper water offshore. On shallow areas of the Persian Gulf, a single
species of foraminifer, Heterostegina depressa (Fig. 6.10), delivers annually 150 g
carbonate per m 2 . This protist lives in symbiosis with photosynthesizing algae, as do
corals. Questions regarding type and rate of mineralization are obviously of importance to paleoecology; here biological and geological research are closely intertwined. Benthic foraminifera whose shells provide a lasting record are ideally suited
to define the limits of many of these conditions (Figs. 6.9 and 6.10.).
For an appreciation of the relationships between organisms and environment of
deposition, let us have a closer look at benthic organisms and their substrates, hard
and soft.
6.3 Organisms and Rocky Substrate
Rocks in the ocean floor outcrop where currents or waves keep the floor free from
sediments, or in areas of active erosion. Steep-sided walls in fracture zones and other
rugged topography are also likely places for rock outcrops.
A great number of different materials can be called rock: ancient sandstones and
limestones of wave-cut platforms or along submarine canyons, basalt scarps or manganese pavements, submerged dead coral and cemented beach sand (beach rock),
boulders dropped from icebergs or left in the shelf in moraines, sunken ships, and
other man-made objects. All such substrates can be densely covered by benthic
organisms under the right conditions, in some cases (drop-stones, ships) forming
epibenthic "oases" on an otherwise rather empty muddy sea floor. The most abundant
type of rocky substrate undoubtedly is provided by the pillow basalts of the MidOcean Ridge. These basalt outcrops are commonly rather barren, except in local spots
of hydrothermal exhalation (see Sect. 6.9).
In shallow areas, rocky bottoms are commonly covered by algae. The algae can be
microscopic diatoms (many of these move about on the rock), or up to several-