Pacific Coastal Biome
427
the Gulf of Papua, observations by Robertson et al. indicated inshore chlorophyll concentrations of 025–507 g chl liter
−1 , whereas offshore, they found 032–073 mg chl m
−3 .
Values suggested by SeaWiFS sensors are not—subjectively—greatly different from these
in either of the two gulfs, but Davies (2004) confirms that these data, as we would
expect, overestimate chlorophyll because of interference from CDOM and suspended
particulates.
Investigation of Synechococcus ecology around islands in the Philippines shows that
populations of these cyanobacteria in shelf regions are very sensitive to disturbance of the
coastal ecosystem whether by anthropogenic increases in local siltation or by the episodic
passage of typhoons (Agawin et al., 2003). High biomass is induced near nutrient sources
in river effluents, but significant declines in growth rate and biomass occur in response to
silt content of effluent river water or in coastal water after passage of a typhoon. Changes
due to such factors were found to be greater than the overall seasonal abundance cycle.
Where human population pressure is heavy, in the western part of the province around
the Gulf of Thailand, there is already much evidence of regional eutrophication of coastal
waters with increased frequency of phytoplankton blooms and knock-on consequences
for the benthic ecosystem of the gulf that will be touched on in the next section.
Regional Benthic and Demersal Ecology
Perhaps it is worth noting in passing that the biogeography of SUND does not respond
to the presence of Wallace’s Line, which passes across the province between the Lombok
and Makassar Straits; marine organisms do not obey the same rules as terrestrial species
for whom this line divides an Asiatic from an Australian fauna.
Because this is a region of very heavy monsoon rainfall, major discharge of freshwater
to the shelf regions is to be expected everywhere; because it is also a region of intense
recent expansion of the human population and deforestation, it is also to be expected that
heavy deposition of organic-rich sediments will occur on the shelves. From the coastline
of this province a total of around 3 × 10
9 tons of silt annually is discharged to the shelf:
this amount is twice that of the discharges from the Amazon and Orinoco combined.
Where the topography of the shelf is such as to form isolated basins, these accumulate
very soft muddy deposits, even if relatively far from any estuary. Such is the case in the
fluid-mud bottoms of the central Java Sea that support only a very low biomass of macrofaunal benthic organisms (< 1 g m
−2 ash-free dry weight), mostly of small polychaetes.
These fluid-mud bottoms are the habitat of very large numbers of meiofaunal nematodes
that may reach half-a-million individuals per square meter. Annual productivity of such
assemblages equals about one half of the autotrophic production in the water column
above (De Wilde et al., 1989). In the Gulf of Papua, the silt carried by the Fly River
(see earlier discussion) is deposited as either laminated or bioturbated muds that are
the trawling grounds for a major fishery for penaeid shrimps; here, oxic and suboxic
diagenesis resemble those described for the Amazon shelf, with a very rapid release of
nutrients that satisfies 71% and 35% of the daily N and P requirements of the superjacent
phytoplankton.
Where the accumulation of silt does not occur, as over much of the Gulf of Carpentaria,
sandy and shelly deposits with many coral heads, sand waves and an abundant epifauna
of soft corals and cup sponges. Although there is abundant information on the demersal
fish fauna, I have not located any satisfactory accounts of the invertebrate benthos of
SUND: nevertheless, the surveys reported by Chatananthawej et al. (1987) in the Gulf of
Thailand suggest nothing unusual in the relative composition of the major invertebrate
groups in relation to bottom type.
The fishery potential of the very large shelf areas of this province was sufficiently
self-evident that scientific trawling surveys were initiated during the colonial period, and
427
the Gulf of Papua, observations by Robertson et al. indicated inshore chlorophyll concentrations of 025–507 g chl liter
−1 , whereas offshore, they found 032–073 mg chl m
−3 .
Values suggested by SeaWiFS sensors are not—subjectively—greatly different from these
in either of the two gulfs, but Davies (2004) confirms that these data, as we would
expect, overestimate chlorophyll because of interference from CDOM and suspended
particulates.
Investigation of Synechococcus ecology around islands in the Philippines shows that
populations of these cyanobacteria in shelf regions are very sensitive to disturbance of the
coastal ecosystem whether by anthropogenic increases in local siltation or by the episodic
passage of typhoons (Agawin et al., 2003). High biomass is induced near nutrient sources
in river effluents, but significant declines in growth rate and biomass occur in response to
silt content of effluent river water or in coastal water after passage of a typhoon. Changes
due to such factors were found to be greater than the overall seasonal abundance cycle.
Where human population pressure is heavy, in the western part of the province around
the Gulf of Thailand, there is already much evidence of regional eutrophication of coastal
waters with increased frequency of phytoplankton blooms and knock-on consequences
for the benthic ecosystem of the gulf that will be touched on in the next section.
Regional Benthic and Demersal Ecology
Perhaps it is worth noting in passing that the biogeography of SUND does not respond
to the presence of Wallace’s Line, which passes across the province between the Lombok
and Makassar Straits; marine organisms do not obey the same rules as terrestrial species
for whom this line divides an Asiatic from an Australian fauna.
Because this is a region of very heavy monsoon rainfall, major discharge of freshwater
to the shelf regions is to be expected everywhere; because it is also a region of intense
recent expansion of the human population and deforestation, it is also to be expected that
heavy deposition of organic-rich sediments will occur on the shelves. From the coastline
of this province a total of around 3 × 10
9 tons of silt annually is discharged to the shelf:
this amount is twice that of the discharges from the Amazon and Orinoco combined.
Where the topography of the shelf is such as to form isolated basins, these accumulate
very soft muddy deposits, even if relatively far from any estuary. Such is the case in the
fluid-mud bottoms of the central Java Sea that support only a very low biomass of macrofaunal benthic organisms (< 1 g m
−2 ash-free dry weight), mostly of small polychaetes.
These fluid-mud bottoms are the habitat of very large numbers of meiofaunal nematodes
that may reach half-a-million individuals per square meter. Annual productivity of such
assemblages equals about one half of the autotrophic production in the water column
above (De Wilde et al., 1989). In the Gulf of Papua, the silt carried by the Fly River
(see earlier discussion) is deposited as either laminated or bioturbated muds that are
the trawling grounds for a major fishery for penaeid shrimps; here, oxic and suboxic
diagenesis resemble those described for the Amazon shelf, with a very rapid release of
nutrients that satisfies 71% and 35% of the daily N and P requirements of the superjacent
phytoplankton.
Where the accumulation of silt does not occur, as over much of the Gulf of Carpentaria,
sandy and shelly deposits with many coral heads, sand waves and an abundant epifauna
of soft corals and cup sponges. Although there is abundant information on the demersal
fish fauna, I have not located any satisfactory accounts of the invertebrate benthos of
SUND: nevertheless, the surveys reported by Chatananthawej et al. (1987) in the Gulf of
Thailand suggest nothing unusual in the relative composition of the major invertebrate
groups in relation to bottom type.
The fishery potential of the very large shelf areas of this province was sufficiently
self-evident that scientific trawling surveys were initiated during the colonial period, and