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Chapter 11: The Pacific Ocean
the gamut of nitrogen-fixing organisms associated with coral and, according to some
budgets, such rates are sufficient to satisfy the nitrogen needs of the reef community.
Regeneration is active and rapid so that with uptake of P during the daytime and release
at night, bottom water becomes enriched over background. Recycling of nutrients occurs
between the gamut of symbionts inhabiting individual coral heads.
It is also a solid generalization that primary productivity of reefs is dominated by
benthic plants, rather than by phytoplankton—usually comprising a large fraction of
nano- and pico-fraction cells. Even during the period June–August, when a general
chlorophyll enhancement occurs over the entire shelf, as discussed earlier, SeaWiFS images
indicate a significantly higher chlorophyll biomass for the Barrier Reef (as well as for the
Capricorn line of reefs north of Sandy Cape) than the clearer water of the inner shelf.
During the dry season during austral summer (December–February) the very clear water
of the lagoon inside the Barrier Reef separates a near-shore zone of high chlorophyll
from that over the reef itself. The latter signal probably emanates at least in part from the
benthic algal mats and other components of the reef flora: such a suggestion is reinforced
by the clear image given by the carbonate shoals of such places as the Bahama Banks,
identifiable in SeaWiFS images as a persistent feature surrounded by water of high clarity.
Perhaps we may assume that this signal represents the benthic autotrophs whose
productivity is far greater than that of phytoplankton over the reef: not only benthic
macroalgae (Sargassum, Halimeda, and Penicillus) and sea grasses (Thalassia and Cymodecea), but also the symbionts of corals contribute to the high productivity associated with
this warm, shallow, and very well-lit environment. Characteristic carbon fixation rates
for reefs are from 1 to 5 kg C m
−2 y
−1 and this is partitioned between different groups
of autotrophs.
This is not the place for a discussion in any detail of the higher trophic-level biota of
the shelf in this province, nor am I equipped to describe adequately the extraordinary
diversity of the Queensland shelf benthic and demersal fauna; suffice it to emphasize
that the long-term stability of the reef ecosystem follows the generalities that we now
accept for the maintenance of dynamic balance of ecosystems: that the balance between
production and consumption can be very easily disturbed by the removal of individual
species or the addition of others. Whether the observed episodic population explosions
of crown-of-thorns starfish (Acanthaster) are natural or induced by human disturbance,
they are testament to the fragility of the ecological balance of reefs, as of other ecosystems.
This province, of course, because its great latitudinal extent, includes both tropical
coral-shelf regions and others of the western and southwestern Tasman Sea that are
characterized by subtropical demersal fish (e.g., Sparidae, Lutjanidae) and benthic communities that follow the Thorson-Petersen model and resemble the New Zealand faunas.
There is evidence here that the low-density plumes of estuarine water that extend out
across the shelf of New South Wales serve actively to aggregate the larvae of demersal fish
spawned on the shelf; those, such as mullet, that pass their juvenile period preferentially
within estuaries are cued to the presence of that habitat by an encounter with a buoyant
plume having estuarine characteristics.
Synopsis
Case 3—Winter-spring production with nutrient limitation—This is perhaps the most
relevant case, but this province has a very large latitudinal extent and is thus very
heterogeneous; for the more northerly parts of the coast, this model is dysfunctional.
Mixed-layer depth undergoes a moderate seasonal excursion (January 20 m, July 80 m)
that is consistent with austral winter mixing, at the season when the coastal eddy field is
also weak. Photic depth responds to the irradiance cycle, varying between 20 and 50 m
seasonally, so that the pycnocline is illuminated only in austral summer (October–April).
Chapter 11: The Pacific Ocean
the gamut of nitrogen-fixing organisms associated with coral and, according to some
budgets, such rates are sufficient to satisfy the nitrogen needs of the reef community.
Regeneration is active and rapid so that with uptake of P during the daytime and release
at night, bottom water becomes enriched over background. Recycling of nutrients occurs
between the gamut of symbionts inhabiting individual coral heads.
It is also a solid generalization that primary productivity of reefs is dominated by
benthic plants, rather than by phytoplankton—usually comprising a large fraction of
nano- and pico-fraction cells. Even during the period June–August, when a general
chlorophyll enhancement occurs over the entire shelf, as discussed earlier, SeaWiFS images
indicate a significantly higher chlorophyll biomass for the Barrier Reef (as well as for the
Capricorn line of reefs north of Sandy Cape) than the clearer water of the inner shelf.
During the dry season during austral summer (December–February) the very clear water
of the lagoon inside the Barrier Reef separates a near-shore zone of high chlorophyll
from that over the reef itself. The latter signal probably emanates at least in part from the
benthic algal mats and other components of the reef flora: such a suggestion is reinforced
by the clear image given by the carbonate shoals of such places as the Bahama Banks,
identifiable in SeaWiFS images as a persistent feature surrounded by water of high clarity.
Perhaps we may assume that this signal represents the benthic autotrophs whose
productivity is far greater than that of phytoplankton over the reef: not only benthic
macroalgae (Sargassum, Halimeda, and Penicillus) and sea grasses (Thalassia and Cymodecea), but also the symbionts of corals contribute to the high productivity associated with
this warm, shallow, and very well-lit environment. Characteristic carbon fixation rates
for reefs are from 1 to 5 kg C m
−2 y
−1 and this is partitioned between different groups
of autotrophs.
This is not the place for a discussion in any detail of the higher trophic-level biota of
the shelf in this province, nor am I equipped to describe adequately the extraordinary
diversity of the Queensland shelf benthic and demersal fauna; suffice it to emphasize
that the long-term stability of the reef ecosystem follows the generalities that we now
accept for the maintenance of dynamic balance of ecosystems: that the balance between
production and consumption can be very easily disturbed by the removal of individual
species or the addition of others. Whether the observed episodic population explosions
of crown-of-thorns starfish (Acanthaster) are natural or induced by human disturbance,
they are testament to the fragility of the ecological balance of reefs, as of other ecosystems.
This province, of course, because its great latitudinal extent, includes both tropical
coral-shelf regions and others of the western and southwestern Tasman Sea that are
characterized by subtropical demersal fish (e.g., Sparidae, Lutjanidae) and benthic communities that follow the Thorson-Petersen model and resemble the New Zealand faunas.
There is evidence here that the low-density plumes of estuarine water that extend out
across the shelf of New South Wales serve actively to aggregate the larvae of demersal fish
spawned on the shelf; those, such as mullet, that pass their juvenile period preferentially
within estuaries are cued to the presence of that habitat by an encounter with a buoyant
plume having estuarine characteristics.
Synopsis
Case 3—Winter-spring production with nutrient limitation—This is perhaps the most
relevant case, but this province has a very large latitudinal extent and is thus very
heterogeneous; for the more northerly parts of the coast, this model is dysfunctional.
Mixed-layer depth undergoes a moderate seasonal excursion (January 20 m, July 80 m)
that is consistent with austral winter mixing, at the season when the coastal eddy field is
also weak. Photic depth responds to the irradiance cycle, varying between 20 and 50 m
seasonally, so that the pycnocline is illuminated only in austral summer (October–April).