OCEANOGRAPHIC PROCESSES OF CORAL REEFS: Physical and Biological Links in the Great Barrier Reef - Chapter 11 potx

Connectivity in the Great
Barrier Reef World
Heritage Area—
An Overview of Pathways
and Processes
Mike Cappo and Russell Kelley
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
The Great Barrier Reef in Time and Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
A Walk around the Great Barrier Reef World Heritage Area . . . . . . . . . . . . . . . . 163
The Cross-Shelf Paradigm and Land-Ocean Processes—
How Far Offshore Does “Land Influence” Extend? . . . . . . . . . . . . . . . . . . . . . . . 168
Cross-Shelf and Inter-Oceanic Connectivity through
Food Chain Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Connectivity amongst Habitats through Larval Dispersal
and Ontogenetic Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
A Case Study of Baitfish–Predator Links. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
INTRODUCTION
The notion of landscape-scale ecosystem “connectivity” is neither new nor a wholly
scientific construct. Australian poet Judith Wright summed up what many scientists
intuitively feel about reefs when she wrote:
Biologists now often talk of the Reef as only the main system of an overall system of
reefs throughout the whole Indo-Pacific region, and suspect that there may be intercon-
nection of all these reefs through the planktonic movement across the ocean. The Reef
cannot be thought of, either, as separate from the mainland coasts, with their many
fringes of great mangrove forests that form a tremendously fertile breeding-ground for
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many species which during part of their lives may enter the waters of the reef proper.
The interlocking and interdependent physical factors which have so long kept the reef
alive and growing, such as water temperatures, freshwater replenishment from streams
and estuaries, the tidal movements which bring deep ocean water in and out of the
calmer and narrower waters within the Barrier, and the winds and weather systems, are
probably all indispensable to the maintenance and dynamics of its living species.
(Wright, 1977)
A broad knowledge base is associated with the Great Barrier Reef (GBR)
province from the earliest navigational survey vessels of the 1800s, subsequent sci-
entific expeditions, and an expanding body of contemporary research literature from
the physical, geological, ecological, and molecular sciences. This has been comple-
mented by an important body of unpublished literature and personal observations col-
lected from the public and reef users, making the GBR one of the most
comprehensively investigated ecosystems on earth. Across these disciplines “con-
nectivity” is a recurrent theme, and here we give an illustrated overview and exam-
ples of some types and scales of ecological connectivity spanning the GBR World
Heritage Area, with an emphasis on fish life-history studies.
THE GREAT BARRIER REEF IN TIME AND SPACE
Geological investigations of the GBR have revealed a “layer cake” cap of modern
(9000 years to present) limestone to overlie an ancient (last interglacial ~120,000-
year-old) body of reefal limestone. This is evidence for a previous incarnation of the
GBR during a past era of high sea level (Davies & Hopley, 1983). In essence the GBR
is only a living ecosystem during phases of high interglacial sea level, for periods less
than 10% of the last 500,000 years (Potts, 1984).
The GBR does not exist as the living system we currently “know” during those
intervals of time when conditions are rendered unfavourable for reef building on the
continental shelf by falling ice-age sea levels (Davies, 1992). During these times the
genetic legacy of GBR must, by inference, lie on the present continental slope or else-
where in the western Indo-Pacific. The early closure during any ice age of the shal-

low Torres Straits seaway to the north of the GBR ensured that the Coral Sea was the
principal connection in spread of larvae derived from inter-stadial reef communities.
The structure and dynamics of present-day GBR communities can be determined
by processes operating in both evolutionary and ecological time and on both local and
larger spatial scales (Bellwood, 1998; Caley, 1995; Veron, 1995). Palaeogeography
determines the chance of an organism occurring at a particular location, and biolog-
ical constraints and physiological tolerances (e.g., to salinity and temperature) will
govern its spread and persistence. The genetic connectivity of populations can occur
at the larger of these scales across oceans and is shaped by sea level changes and for-
mation of physical barriers to dispersal (Veron, 1995; Williams & Benzie, 1998).
Connectivity is visible at progressively larger scales in reef ecosystems, from the
inter-cellular level between coral polyps and zooxanthellae, to symbioses and com-
mensalism amongst species (e.g., Poulin & Grutter, 1996), to tight nutrient capture
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and recycling in food webs on coral reefs (Hamner et al., 1988; Alongi, 1997). Here
we focus on the mesoscale ecological processes and pathways.
A WALK AROUND THE GREAT BARRIER REEF
WORLD HERITAGE AREA
The Great Barrier Reef World Heritage Area (GBRWHA) does not extend to the
coastal plain. However, for this review we broadly define primary habitats, or
“biotopes” linked to the health and integrity of the GBR system, to be catchments and
coastal floodplains, estuaries and bays, shallow and deepwater seagrass beds,
lagoonal and inter-reef “gardens and isolates” of megabenthos, coral reefs, and the
pelagic realm that links them all.
The general ecological framework for the pathways discussed in this chapter are
illustrated in the cross-shelf vista in Figure 1, with a representation of the life cycle
of the red emperor Lutjanus sebae. This species is perhaps the most familiar to the
public of the lutjanid family of fishes, which are known to make ontogenetic migra-
tions (to various degrees) between biotopes. The montage of biotopes at the bottom

of Figure 1, and Figures 2 to 7, summarise the habitats linked in some way to the ecol-
ogy of the lutjanid family (and others) of fish.
Beginning upstream (Figure 2), aquatic species in freshwater wetlands from the
coastal plain have evolved to exploit ephemeral habitats in seasonal or episodic mon-
soon flooding, during which spawning, upstream dispersal, and downstream migra-
tions occur in association with pulses of primary and secondary production (Bayley,
1991). Fish, crustaceans, amphibians, reptiles, and piscivorous and herbivorous birds
move about the landscape and between catchments by migrating upstream, down-
stream, or across floodplains and along riparian corridors.
Between these flood events the degree of shading and litter-fall from riparian
vegetation has profound influence on stream temperatures, light regimes, and stream
metabolism—the balance between primary production and respiration. Healthy
streams are net consumers of organic carbon and respiration exceeds primary pro-
duction, so oxygen concentrations are high (Bunn et al., 1999). Loss of shade and
aquatic weed and pasture grass invasions cause tropical freshwater streams to flip to
net production of carbon, high nocturnal plant respiration and bacterial oxygen con-
sumption, and massive streambed accumulation of decaying matter and sediment in
anoxic conditions (Bunn et al., 1997 and 1998).
The connectivity of disturbances from human uses and impacts is most evident
in the coastal plain and fringes immediately behind the GBRWHA and above the nat-
ural, or artificial, restraints to saline intrusion (see State of the Environment
Queensland, 1999 for reviews). For example, alteration of natural drying and filling
cycles for some tributary lagoons of the Burdekin River has had some positive and
negative effects on wetland birds and fish. Year-round filling has enabled introduced
duckweed (Cabomba caroliniana) and water hyacinth (Eichornia spp.) to flourish
and sometimes completely cover and de-oxygenate entire lagoons. The weed mats
shelter introduced fish (e.g., Tilapia, Oreochromis, Gambusia) from native predators.
Connectivity in the Great Barrier Reef World Heritage Area 163
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Introduced pasture grasses such as para grass (Brachiaria muticum) and hymenachne

(Hymenachne amplexicaullis) have invaded the riparian zones and their runners over-
grow the floating weed mats to form concentrated fuel loads for very hot wild fires.
In turn, these fires kill remnants of riparian trees (e.g., Melaleuca spp., Eucalyptus
spp.) and palms (e.g., Pandanus spp., Livistona spp.) that shaded and cooled the
lagoons (J. Tait, personal communication).
Farther downstream, the landward advance and retreat of saline surface and
groundwaters with drought, flood, and tide are a fundamental forcing in the dynam-
ics of floodplain primary production, governing both the distribution and growth of
ephemeral hydrophytes, bulkuru sedgelands (Eleocharis dulcis), and ti-tree
(Melaleuca spp.) stands. The dramatic saline intrusion on the Mary River floodplain
in the Northern Territory (Woodroffe et al., 1993) shows the rapidity of change in
freshwater habitats and creek evolution with tidal influence. A similar advance of
mangroves into freshwater ti-tree swamps has occurred in the Moresby catchment of
the GBRWHA due to expansion of the tidal prism from the deepening of Mourilyan
Harbour mouth (Russell et al., 1996). Both cases may exemplify the effect of rising
sea levels.
The coastal fringe is a geologically young, dynamic zone of diversity, produc-
tion, confusion, and conflict in the forces of nature, culture, and law. Lowlands bear-
ing freshwater lagoons and swamps, salt-flats, marshes, and mangroves are buffered
from sea waves and wind disturbance by dunes and beach ridges, estuaries, and semi-
enclosed bays bearing headlands (Figure 3). Within catchments, slopes decrease
toward the sea allowing the deposition and processing of sediments, minerals, and
nutrients in low energy environments.
Vegetated habitats of the coastal plain and fringe, such as the Melaleuca swamps,
sedgelands, mangrove forests, and seagrass beds (Figures 2 to 4), shelter many
species between wet seasons and episodic flood events. They also serve to trap sedi-
ments and nutrients and kick-start food chains (see Alongi, 1997; Bunn et al., 1999;
Butler & Jernakoff, 1999; Cappo et al., 1998; Robertson & Blaber, 1992). The swamp
habitats, in particular, are known for their effects on the residence time and passage
of raw sediment and nutrients derived from catchments and have become known as

the “kidneys of the coastal zone” (Crossland, 1998). Seagrasses also affect water
movement over the beds of blade-like leaves, and settle and bind sediments (see
Butler & Jernakoff, 1999). In general terms, the structural complexity of freshwater
macrophyte fronds, mangrove prop roots, and seagrass blades provides shelter and
protection for juveniles and their prey, substrata for attachment of palatable epi-
phytes, and the bases of detrital food chains, as well as altering local hydrology
(Wolanski, 1994).
The estuaries may loosely be defined as the zones where there is an interface, or
“salt wedge” between fresh and salt surface waters—but the same interfaces
also occur in groundwater in the poorly recognised “underground estuaries”
(G. Brunskill, personal communication). Chemical reactions at the surface interface
cause re-mineralisation, flocculation, and precipitation of nutrients and sediments
(e.g., Woodroffe, 1992; Wolanski et al., 1992). Upwelling and river discharge account
nearly equally for at least 75 to 80% of total nutrient inputs in the GBRWHA (see
164 Oceanographic Processes of Coral Reefs
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reviews by Wasson, 1997; Rayment & Neil, 1997). Subterranean flow out into the
areas between reefs is also known to occur at certain times and places, but this flux
and the consequences of the nutrients it carries are unknown (P. Ridd, personal com-
munication). Trawlermen report “wonky-holes” where (presumably) freshwater
seeps up into lagoon waters. These are reported not to be active year-round, and can
fill with sediment between outflow events.
Rainfall (or the lack of it) is a prime disturbance in the dynamics and connectiv-
ity of coastal habitats and coral reefs. Flood pulse events naturally carry over into the
estuarine zone, delivering freshwater, sediments, nutrients, and contaminants into the
coastal zone, and triggering both downstream migration of catadromous fish and
prawns to spawn and upstream return of larvae to reach nurseries. Catadromous
species in the GBRWHA include the barramundi (Lates calcarifer), jungle perch
(Kuhlia rupestris), tarpon (Megalops cyprinoides), eels (Anguilla spp.), and fresh-
water prawn (Macrobrachium sp.) (Russell & Garrett, 1985). Bayley (1991) sug-

gested that a “flood pulse advantage” is evident in the amount by which freshwater
fish yield per unit area is increased by flood pulses in tropical fisheries, and that
watercourses are more or less acting as refugia for native freshwater fishes between
flood events when they can access floodplains (the “flood pulse concept”). The most
visible effects of prolonged rainfall events occur in the supra-littoral saltpans nor-
mally encrusted with thick layers of salt. These can become freshwater lagoons in
which bulkuru and hydrophytes flourish from dormant seed or banks of underground
corms. In turn, this primary production attracts migratory magpie geese (Anseranas
semipalmata), black swans (Cygnus atratus), yellow spoonbills (Platalea flavipes),
brolgas (Grus rubicundus), frogs (e.g., Cyclorana novaehollandiae), insects, fish,
and crustacea to feed for various periods (see Australian Nature Conservation
Agency, 1996).
The importance of the “environmental flows” of freshwater in estuaries is poorly
studied (Loneragan & Bunn, 1999). Most widely cited are significant positive or neg-
ative correlations between rainfall, salinity, and river discharge for banana prawns
(Penaeus merguiensis) in some regions (see Staples et al., 1995 for review). Access
to, and persistence and quality of, barramundi nursery habitats in supratidal fresh-
water swamps are also enhanced by episodically high rainfall, sufficient to produce
recognisable signals in the size structure of fishery landings 3 to 4 years after the
event (R. Garrett, personal communication).
The physiology of osmoregulation is limiting at lower temperatures (Dall, 1981),
so the maintenance of a narrow salinity/temperature balance is not so critical in the
tropics, enabling aquatic fauna to cope well with estuarine salt wedges, whereas the
wedge profoundly influences the distribution of temperate species. Surprisingly,
there has been little Australian use of such a fundamental concept (Cappo et al.,
1998), but it fits well the generalisation that there is more plasticity in the life histo-
ries of tropical species. For example, the giant trevally Caranx ignobilis and the big-
eye trevally C. sexfasciatus are found in the tropical Kosi Bay estuary down to about
0.25 ppt—the bare minimum needed for kidney function—but temperature has to be
at optimum level (Whitfield et al., 1981). The same species visit freshwaters of the

north Queensland estuaries (V. McCristal, personal communication), and there is an
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increasing awareness of the ability of our tropical serranids and lutjanids (and other
families) to persist in low salinities (e.g., Sheaves, 1996). In contrast, no temperate
carangids enter freshwater, major movement by temperate fish occurs downstream to
escape freshwater flows in southern estuaries, and there are very few euryhaline
species in the south.
Just offshore from the vegetated coastal fringe, the dominance of fine, terrige-
nous sediments has produced an “estuarisation of the shelf” (sensu Longhurst
& Pauly, 1987) that offers alternative nursery habitats in turbid bays to the shelter and
enhanced food supplies in estuaries. Sediment type is a major determinant of habitat
type and fisheries production. In general terms the finer sediments have higher rates
of benthic primary and secondary production with more benthic infauna available as
food for prawns, crabs, fish, and other higher consumers (Alongi, 1997; Robertson
& Blaber, 1992). Seagrass and algal beds in bays (Figure 4) also provide critical nurs-
ery habitat for tiger prawns (Loneragan et al., 1998), and are directly grazed by her-
bivorous dugong (Dugong dugon) and green turtles (Chelonia mydas) (Lanyon et al.,
1989; Preen, 1995). More subtle, but perhaps equally important, is the indirect sup-
port to some coastal fishes and crustaceans given by seagrasses through food chains
based on grazing on epiphytes and seagrass detritus (see reviews in Butler
& Jernakoff, 1999; Watson et al., 1993). A “critical chain of habitats” may best explain
the life history requirements of such species (Cappo et al., 1998) which include the
juveniles of lethrinid emperors found as adults on coral reefs (Wilson, 1998).
Farther offshore, between the mainland and the mid-shelf reef matrix, lies the
“GBR lagoon,” a wide expanse (56 km in the central section) of shallow (15 to 40 m
in the central section) water characterised by changes in sediments and biodiversity.
Sediments nearshore in depths Ͻ15 m generally have high silt and clay fractions of
terrigenous origins (Jones & Derbyshire, 1988), changing to carbonate-based facies
around the 22- to 23-m isobaths (Birtles & Arnold, 1988). Within the lagoon are

patchy assemblages or seafloor “isolates” of invertebrate megabenthos (Figure 5).
Larger communities of these filter feeders develop in “inter-reef gardens” where
directional currents are prevalent (Figure 6). Halimeda bioherms (Drew & Abel,
1988) and deepwater seagrass beds (Figure 7) occur in the shelf lagoon and between
the emergent reefs and support poorly known resources of biodiversity (Lee Long
et al., 1996). Also lying within the outer reef matrix are relatively large, unstudied
areas of corals and other phototrophic reef-building organisms in depths Ͻ50 m
(Birtles & Arnold, 1988).
These continental habitats are connected by flooding and outwelling of material
from the coastal zone, through its food web extensions and by ontogenetic move-
ments and migration of organisms. These fluxes vary on regular tidal and seasonal
time scales, on less regular quasi-decadal, or longer, climate cycles (Lanyon
& Marsh, 1995; Lough, 1998; Jones et al., 1998), and with irregular, intermediate, or
catastrophic disturbances such as floods, cyclones, and “phase shifts” (see Done,
1992; Done et al., 1997; McCook, 1999; Preen et al., 1995; Puotinen et al., 1997).
Toward the mid- and outer-shelf the proportion of reef-related species found in
inter-reefal habitats increases. Reef-derived sediments, rubble, and “hard grounds”
become important sites for patch nucleation of inter-reefal bryozoans, ascidians,
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sponges, corals, and crustose coralline algae, and the effect of reef structures on local
tides and currents becomes an influence on the nature of seafloor communities. In
turn, the skeleton-forming benthos of the lagoonal zone can provide settlement sites
for colonial and solitary megabenthos, such as gorgonians and macro-algae. Farther
offshore an “inter-reef” community of megabenthos can be recognised, on isolates or
attached to Pleistocene surfaces and other areas of calcium carbonate rock pock-
marked with solution holes and overlain by a veneer of carbonate sediment. These
“natural isolates” and “megabenthos gardens” (see Figures 1, 5, and 6) of biological
origin form “islands of hard substrata in a sea of otherwise unstable soft sediments”
(Birtles & Arnold, 1988).

They provide the basis for the rise in diversity deeper than 22 to 23 m in the GBR
lagoon. At shallower depths the isolates cannot form because of the frequent distur-
bance by surface wave action. This link between substratum type and sessile
megabenthos may be a well-recognised feature of our tropical shelves (Long et al.,
1995), but the role of seabed current shear stress in determining the patterns of dis-
tribution of isolates and patches is only now being investigated (Pitcher et al., 1999).
Large sponges (e.g., Xestospongia, Ianthella, Cymbastella), gorgonians (e.g.,
Ctenocella, Subergorgia, Semperina, Echinogorgia), the vase coral Turbinaria, and
patches of macroalgae are characteristic features of the patches. These megabenthos
shelter numerous commensal animals within their internal chambers, and other
macrofauna, such as echinoderms, crustacea, and octopus, shelter within crevices
beneath the megabenthos canopy (Hutchings, 1990; Pitcher, 1997). Hawksbill turtles
(Eretmochelys imbricata) and some pomacanthid angelfish eat sponges. These
diverse and poorly known communities have attracted significant research in pursuit
of natural products of pharmaceutical promise (Hooper et al., 1998).
The provision of this structural complexity shelters a range of fish species which
prey on the organisms living in the patches, or move away at night to consume soft-
bottom invertebrates in the unconsolidated sediments nearby. These fish most notably
include the commercially and recreationally important lutjanids, lethrinids, and ser-
ranids. For example, the “red snappers” (L. sebae, L. malabaricus, L. erythropterus,
and L. argentimaculatus) (see Figure 1) and the “sweetlip emperors” (Lethrinus spp.)
form the major part of the inter-reef line fishery on the GBR (Williams & Russ,
1994). Underwater video has shown the painted sweetlip (Diagramma pictum) to
shelter from the current by sitting motionless inside the cups of large Xestospongia
and Turbinaria spp. The isolates and megabenthos patches may also be very impor-
tant as “stepping stones” for fish such as mangrove jack that move offshore across the
lagoon to deeper habitats. The shelter and trophic roles of production in deep-water
seagrass beds (Lee Long & Coles, 1997) and Halimeda bioherms (see Figures 1 and
7) are also very poorly known, although dugong are known to feed in the deepwater
seagrass beds (W. Lee Long, personal communication).

Deep Coral Sea waters from far offshore also influence the GBR in two main
ways (see Wolanski, 1994 for review). First, tidal “jetting” occurs in narrow passes
separating shelf-edge reefs. This causes periodic local nutrient upwelling correlated
with abundant growth and vast, mound-like seafloor accumulations (bioherms) of the
calcareous algae Halimeda (Wolanski et al., 1988). Second, episodic intrusions of
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high nutrient water move up the continental slope and inshore at a regional scale,
stratifying the summer water column and influencing the abundance and production
of phytoplankton communities. Blooms of the diatom Trichodesmium during this
stratification can cause doubling of carbon fixation rates (Alongi, 1997).
THE CROSS-SHELF PARADIGM AND LAND-OCEAN
PROCESSES—HOW FAR OFFSHORE DOES
“LAND INFLUENCE” EXTEND?
A recent stock-take (Lucas et al., 1998) of the values and biodiversity of the GBR-
WHA showed three common traits in major phyla of fauna and flora—very high
diversity, a lack of knowledge for most groups, and cross-shelf changes in diversity
and abundance. In that report, distinct reefal and inter-reefal faunas and nearshore
communities were reported for the phytoplankton, the mangroves (37 species: Duke,
1992), the seagrasses (15 species), the Halimeda (Drew & Abel, 1988), the corals
(Ͼ360 species: Veron, 1995), the octocorals (80 genera), the flatworms (Ͼ200
species), the molluscs (5000 to 8000 species), zooplankton (McKinnon & Thorrold,
1993), the echinoderms (Birtles & Arnold, 1988), the sponges (Ͼ1500 species),
prawns (Gribble, 1997), cephalopods (Moltschaniwskyj & Doherty, 1994, 1995), and
the fishes (e.g., Newman & Williams, 1996; Newman et al., 1997; Williams
& Hatcher, 1983).
These patterns are connected with major cross-shelf changes in physical factors
around the 22- to 23-m isobaths. These include changes in nutrients, turbidity, wave
action at the seabed, sediment type, and sediment re-suspension rates, which mani-
fest as a progression in the structure and function of pelagic and benthic communi-

ties (see Alongi, 1997 for review). Northward, longshore predominance of water
movement is partially responsible for an abrupt change from well-mixed coastal
waters overlying terrigenous silts, clays, quartz, and silica sands to clear, nutrient-
poor waters overlying sedimentary deposits increasing in carbonate content seaward
(Belperio & Searle, 1988). The discontinuity in biodiversity of a range of benthic
communities in this gradient can sometimes be sharp, with a transition between
“inshore” and “lagoonal” zones occurring in as little as 500 m (Birtles & Arnold,
1988). In other cases the transition is much more gradual (Jones & Derbyshire, 1988;
Watson et al., 1990).
The largest source of modern terrigenous sediment for the GBR shelf is direct
fluvial input during discrete flood events in the wet season. These pulses are most
dramatic—and variable—in the dry tropics. Variability at annual and decadal scales
is linked to the passage of tropical cyclones and the strength and duration of the
summer monsoon caused by ENSO climate variability (Lough, 1998; Mitchell &
Furnas, 1997). For example, the Burdekin River is dominant with mean annual flow
of 9.272 ϫ 10
6
Ml, but this statistic hides the extremes of drought and flood forcing
geological, hydrological, and biological processes in the coastal fringe and reefs. The
range of annual flows is 0.54 ϫ 10
6
to 50.927 ϫ 10
6
Ml, with a coefficient of varia-
tion of 116.7% (Wolanski, 1994).
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Flood plumes enter the GBR lagoon mostly between 17 and 23°S and typically
flow northward, and the residence times of dilute patches inside headlands are in the
order of a few weeks. In the 1981 Burdekin River flood peak, the entire Upstart Bay

was filled with freshwater and a plume of brackish water (Ͻ18 ppt) stretched 100 km
northward along the coast. At this time the surface salinities over the 15- to 20-m iso-
baths off Bowling Green, Cleveland, and Halifax Bays were 15 to 30 ppt, and signif-
icant seawater dilution at the seabed was measured in these depths (Wolanski, 1994).
The plumes can cause coral mortality on coastal fringing reefs and also travel on the
surface to outer-shelf reefs (Furnas et al., 1997; Mitchell & Furnas, 1997) affecting
coral metabolism and calcification rates sufficiently to cause recognisable signatures
in skeletal growth bands (Isdale, 1984).
The ocean interface with these fluvial inputs can occur in a hydrodynamic shear
zone in the general region of the central lagoon that may shift inshore and offshore
from the 22- to 23-m isobaths, or disappear, with prevailing winds. Whilst there is no
evidence that this shear zone causes cross-shelf changes in benthic community com-
position and diversity, its nature demonstrates important connections between phys-
ical oceanography and biology. The poleward flowing East Australian Current pushes
water onto the outer shelf, southward through the reef matrix, and through major pas-
sages (such as Magnetic and Palm Passages). Under typical southeasterly wind con-
ditions that shallow body of water trapped against the coast moves in the opposite
direction, northward (Wolanski, 1994). The result is a velocity shear and a zone of
low residual displacement, found by Moltschaniwskyj and Doherty (1995) in the
middle of the lagoon in the central GBR (24 to 33 km offshore), and marked by gra-
dients in temperature and salinity.
The cross-shelf location of this feature (known as a separation front or “coastal
boundary layer”) is predicted in models to shift seaward with increasing SE wind
strength, and vice-versa (Wolanski, 1994). High secondary productivity (McKinnon
& Thorrold, 1993; Thorrold & McKinnon, 1995) and high densities of juvenile and
larval fish and cephalopods (Thorrold, 1992; Moltschaniwskyj & Doherty, 1995)
indicate that this area is important both biologically and hydrodynamically. The juve-
nile and larval fishes include reef fish taxa found farther offshore as adults, as well as
piscivorous larvae of various mackerels and tunas from inshore (Thorrold, 1993).
These studies suggest juvenile fishes and cephalopods in this low shear zone were

either aggregating there, actively or passively, or had better survivorship—or combi-
nations of all these factors. Increases in zooplankton abundance and in copepod egg
production have been measured in rapid response to both wet season flood plumes
and to episodes of upwelling and cross-shelf intrusion of Coral Sea water (Thorrold
& McKinnon, 1995). These data support the suggestion by Alongi (1997) that some
members of the coastal and offshore zooplankton and benthic communities in the
GBRWHA are “opportunistic, poised to respond quickly to these climatological and
hydrographical events.”
There are also a wide variety of wind-driven surface features that structure the
pelagic environment of the GBR lagoon and act to attract or passively aggregate and
transport pelagic stages of fish, crustaceans and cephalopods, and their prey (see
Kingsford, 1990 and 1995). These include the phenomena of Ekman drift and
Connectivity in the Great Barrier Reef World Heritage Area 169
© 2001 by CRC Press LLC
Langmuir cells, as well as wind-rows of drift algae (e.g., Sargassum) and flotsam (see
Figure 1) that provide food and shelter for pre-settlement stages—or act to transport
them across boundary currents toward shore (Kingsford et al., 1991). Pre-settlement
stages of the tripletail (Lobotes surinamensis) and batfish (Platax spp.) adopt strik-
ing mimicry of the shape, colour, and motion of floating leaves in these slicks. A vari-
ety of large pelagic scombrids and carangids actively feed at the surface on the small
fishes and crustaceans sheltering in these surface features of the GBR lagoon.
In summary we suggest that for some materials and processes, and outside the
occurrence of cyclonic disturbances and flood pulses, the 22- to 23-m isobaths may
represent the general “land–ocean interface” within reef and inter-reef dynamics.
However, far too little is known of bentho-pelagic coupling, carbon and nitrogen
cycling, and interconnections between lagoonal waters and the GBR matrix to elab-
orate sophisticated food web models or nutrient budgets for this tropical shelf
(Alongi, 1997).
CROSS-SHELF AND INTER-OCEANIC CONNECTIVITY
THROUGH FOOD CHAIN LINKS

Obvious transfer of material away from vegetated habitats occurs in the form of float-
ing “litter”—mangrove propagules, leaves, wood and root material, and seagrass
seeds, flowers, blades, and rhizomes. Early overseas studies in Florida established a
paradigm that stressed the importance of mangrove forests in supporting nearshore
secondary production via detrital-based food chains (e.g., Odum & Heald, 1975).
Connections between saltmarsh, mangrove, and seagrass communities and those far-
ther offshore in the GBRWHA have since been examined within the context of “out-
welling”—the export of nutrients or organic detritus from fertile estuarine areas to
support productivity of offshore waters (see Robertson et al., 1992; Alongi, 1997 for
reviews). The amount of material exchanged is influenced not only by rate of primary
and secondary production in vegetated coastal habitats, but also by physical charac-
teristics of geomorphology, exposure to tide and wave energy, heat, light, and rain-
fall—to the extent that each system is unique (Alongi, 1990a, b, and c; Alongi et al.,
1989). However, recent reviews (Butler & Jernakoff, 1999; Alongi, 1997) indicate
few data are available on outwelling from Australian saltmarshes and seagrasses.
Despite their proximity to major coastal nurseries the extent of material connectivity
between mangroves and adjacent seagrass beds and saltmarshes also remains
unknown in Australia (Robertson & Duke, 1987; Robertson et al., 1992).
Surprisingly, in the GBRWHA the “outwelling” of mangrove material is of lim-
ited importance in the coastal zone, since little material (relative to the enormous total
tree production and standing biomass) is exported from the forests—and generally
not more than a few kilometres from the mangrove estuaries (see Robertson et al.,
1992; Alongi, 1997 for reviews). This carbon does have a significant impact on sed-
imentary nutrient cycles, but does not translate into a significant dietary subsidy for
fish and prawns and other coastal macro-organisms outside the forests, despite
170 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
the fact that juveniles of some penaeid prawns feed on mangrove detritus or on
meiofauna that is mangrove dependent (Alongi et al., 1989). These findings have
recently been supported by studies using stable isotopes to trace food chains sup-

porting juvenile penaeid prawns, which showed the primary source of carbon
depended on the location within estuaries (Loneragan et al., 1997). Seagrass and
associated epiphytes were traced as most important in supporting feeding by juvenile
tiger prawns (Penaeus esculentus, P. semisulcatus) in seagrass beds in mangrove-
lined estuaries, despite the proximity to mangroves and the presence of large quanti-
ties of mangrove detritus in the seagrass beds. The considerable amount of mangrove
and terrestrial carbon exported from tropical Australian estuaries during the wet sea-
son was considered to be unlikely to contribute to offshore food webs supporting
adult prawns, with benthic microalgae or seagrass detritus possible sources on the
coastal grounds. Furthermore, the contribution of mangrove/terrestrial sources to the
food of juvenile banana prawns (P. merguiensis) appeared to be limited to small spa-
tial scales, within the mangrove fringe of small creeks and mainly during the wet sea-
son (Loneragan et al., 1997; Vance et al., 1996).
Whilst “outwelling” from the coast has not been measured to be as important as
widely perceived, substantial connectivity does occur through the movement of large
bundles of protein (in the form of prawns, baitfish, and other organisms) across
shelves from coasts to reefs. In the case of mangrove export the early Florida model
of food chains (Odum & Heald, 1975) had as its base mangrove litter, thought to be
flushed into mangrove waterways where microbial decomposition occurred to pro-
mote saprophytes upward to consumers of detritus, and their predators. However,
later work showed that consumption and retention of litter within forests by sesarmid
and ocypodid crabs has profound effects on pathways of energy and carbon flow
within forests, the quantities of material available for export from the forests, and
nitrogen cycling within them (see Robertson et al., 1992; Lee, 1998 for reviews).
In turn, the leaf-burying mangrove crabs provide a fundamental link between
mangrove primary production and coastal food chains (Robertson & Blaber, 1992).
Recruitment of larval fish into mangrove waterways peaks in the Townsville region
during mid-summer (Robertson & Duke, 1990a and b) in coincidence with the out-
flow on ebb tides of vast numbers of crab zoeae, which are consumed by zooplank-
tivorous, juvenile fish (see Robertson et al., 1992). Studies in progress of adult diets

of predatory estuarine fish showed a predominance of adult sesarmid and other grap-
sid crabs in the diet of spotted-scale sea perch (Lutjanus johnii), mangrove jack
(Robertson et al., 1992), estuary cod (Epinephelus coioides, E. malabaricus), and
other major angling species (M. Sheaves, personal communication). Other major out-
flow of invertebrate protein occurs through spawning swarms of polychaete worms
at the surface of mangrove forest waterways in mid-summer, and sub-littoral swarms
of the sergestid shrimp Acetes sibogae australis (Omundsen et al., 2000). These
shrimp are visibly important to scyphozoan “box” jellyfish (Chironex,
Chiropsalmus), manta rays (Manta spp.), and a variety of other predators. Other
direct links within the mangrove estuaries are visible between mud crabs (Scylla ser-
rata) which eat the large Telescopium and other gastropods (I. Knuckey, personal
Connectivity in the Great Barrier Reef World Heritage Area 171
© 2001 by CRC Press LLC
communication) and barramundi which consume primarily banana and “school”
prawns (Penaeus and Metapenaeus spp.). Both Telescopium and banana prawns are
known to consume directly some mangrove detritus (Robertson et al., 1992).
The cross-shelf connectivity of such fluxes are very difficult to measure, occur
at a variety of spatial and temporal scales, and may be highly significant. For exam-
ple, green turtles that feed on Halodule and Halophila seagrass in coastal bays and
estuaries (Brand-Gardner et al., 1999) migrate seaward across the entire shelf to lay
eggs at major outer-shelf rookeries in the northern and southern GBR (Limpus et al.,
1992). At Moulter Cay, several hundred pairs of Nankeen night herons (Nycticorax
caledonicus) nest and rear young, feeding principally on turtle hatchlings. Enough
adult turtles die on the cay beaches to attract seasonal aggregations of tiger sharks
(Galeocerdo cuvieri) to feed on the carcases that float off from the inter-tidal. It is
unknown if these aggregations of prey, predators, and scavengers occur on some
rhythm or cycle to coincide with turtle nesting or only by local attraction through
scent plumes or other cues. Nevertheless, this annual event provides a direct link
between the inter-tidal and nearshore seagrass beds and outer-shelf reefs.
These links are trans-oceanic for some taxa. Feeding-ground captures of green

and loggerhead turtles (Caretta caretta) tagged while nesting at eastern Australian
rookeries over a 21-year period were summarised by Limpus et al. (1992) and Bowen
et al. (1995). These turtles nest in the GBR region but range widely throughout the
Arafura and Coral Seas. Tag recoveries included many from turtles that live in neigh-
bouring countries and migrate to breed in Australia. The breeding females show a
remarkable fidelity to home feeding grounds as well as to nesting beaches.
Aggregations of other “megafauna” occur in the GBRWHA in aggregation with
seasonally or episodically abundant prey, including whale sharks (Rhincodon typus)
in the Coral Sea “hotspot,” which are encountered in October and November in asso-
ciation with an abundance of spawning lantern fish (Diaphus spp.) (Gunn et al., 1992;
Wilson et al., in press). Yellowfin (Thunnus albacares) and bigeye tuna (T. obesus)
aggregate at the same time and place and feed almost exclusively on Diaphus spp.
there (McPherson, 1991).
A variety of migratory waders and seabirds also rely on the GBRWHA for over-
wintering and feeding grounds (Hulsman et al., 1997). These include several species
which move north from Antarctica, such as the Wilson’s storm petrel (Oceanites
oceanicus) (Simpson & Day, 1993). Seabird feeding at sea and defecation at rook-
eries produce important accumulations of guano, providing one of the few feedback
mechanisms, other than plate tectonic activity, for returning phosphorus to the land
(E. Gyuris, personal communication).
Pisonia trees have root mycorrhiza with a unique adaptation to thrive in guano,
and are major colonisers of sand cays in the southern GBR. In connection with move-
ments of at least 18 species of seabirds the trees are spread long distances when the
very sticky seeds adhere to their feathers (Walker, 1991). Similar, cross-shelf recruit-
ment of rainforest trees to some northern GBR islands occurs when Torresian
Imperial Pigeons (Ducula spilorrhoa) feed on the mainland and fly offshore to roost
(King, 1990).
172 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
CONNECTIVITY AMONGST HABITATS THROUGH

LARVAL DISPERSAL AND ONTOGENETIC MIGRATION
A long-standing idea predicts that dispersal is adaptive in environments subject to
sudden unpredictable change (such as high sea level reefs in the cyclone belt),
because given enough time all populations of non-dispersers go extinct. A wide vari-
ety of fauna and flora have dispersive larvae, seeds (seagrasses), or propagules (man-
groves) which connect habitats across water bodies, but just how far these “juveniles”
normally travel from their natal area is an unanswered question in marine biology
(Jones et al., 1999).
Sometimes extreme physical gradients are crossed, as in the case of eels
(Anguilla australis, A. obscura, and A. reinhardtii), which are spawned in the oceanic
waters of the Coral Sea (Merrick & Schmida, 1984) but migrate as elvers into the
uppermost water bodies in catchments—sometimes overland in wet grass. “Supply-
side ecology” (Caley et al., 1996), “source-sink” modelling (Dight et al., 1990a and
b), and the “recruitment-limitation” hypothesis (Doherty & Williams, 1988) have
been major research themes addressing this major difference between “open” marine
and “closed” terrestrial ecosystems.
In the case of reef fish, Doherty et al. (1985) took the view that the “adaptive-
ness” of larval dispersal is selected for in the patchy pelagic environment of the GBR
water column. This followed observations that fish larvae must have available in
close proximity a relatively high density of appropriately sized food organisms for
survival. These densities are only observed in smaller-scale patches, on the order of
metres or less, and in turn these patches are themselves part of larger patches or pro-
duction systems, whose upper dimensions may be on the order of tens of metres to
hundreds of kilometres (Williams & English, 1992). The problem of placing eggs (or
larvae) into an appropriate (pelagic) environment is the life’s work of a fish. This rea-
soning could be applied equally well to larval retention around oceanic island reefs,
given that coastal waters there are more productive than the nutrient-depleted oceanic
environment.
Early attempts at understanding dispersal had approximated larvae as passive
particles, but Stobutzki and Bellwood (1997 and 1998) showed remarkable swimming

and sensory abilities of a range of reef fish larvae, to “hold” favourable position in the
pelagic environment and seek out settlement sites on reefs. For example, surgeon-
fish juveniles (Acanthuridae) were able to swim, on average, for 194.3 h continu-
ously, covering the equivalent of 94.4 km, and distances covered by other taxa ranged
from 8.3 to 62.2 km. The late pelagic stages of reef fish also display nocturnal
orientation behaviour, possibly in response to sound, which may aid in their settle-
ment on reefs.
Most recently, these abilities have been recognised in tests of “self-seeding and
larval retention” hypotheses (see Johannes, 1978) in explaining replenishment of off-
shore (and oceanic) island reefs. Jones et al. (1999) employed direct mark and release
of over 10 million damselfish embryos to demonstrate the self-recruitment of a
Lizard Island species. Swearer et al. (1999) used trace element and growth rate
Connectivity in the Great Barrier Reef World Heritage Area 173
© 2001 by CRC Press LLC
signatures in wrasse otoliths to show that recruitment to an island population may
often result from local retention on leeward reefs. Both studies indicate that models
that overemphasise downstream dispersal of passive larvae (to “sinks”) will not pre-
dict the long-term behaviour of populations, inside or outside marine reserves set up
to preserve “sources.”
The life histories of many major reef fish families are poorly known, but there is
an increasing awareness that larval or juvenile dispersal inshore occurs to turbid,
shallow waters and vegetated habitats for some scombrids, lutjanids, serranids, and
lethrinids associated with reefs as adults. This is followed to a greater (e.g., mangrove
jack) or lesser degree (Lutjanus johnii) by offshore ontogenetic migration (e.g.,
Newman & Williams, 1996; Newman et al., 1997) to spawning grounds amongst the
reef matrix or the inter-reef megabenthos. Mangrove jack penetrate nursery areas as
far upstream into freshwater as physical barriers and oxygen concentrations will
allow. The immature fish then move offshore from mangrove habitats (presumably
utilising inter-reef isolates and gardens en route: see Figures 1, 5, and 6) at about
45 to 48 cm length and 6ϩ to 8ϩ years of age to mature in deeper waters (Sheaves,

1995). This cross-shelf movement has been directly demonstrated by increasing
numbers of tag returns from the “AusTag” Sportfish Tagging Program for both man-
grove jacks and black-spot estuary cod (Epinephelus malabaricus) (Sawynok, 1999).
Crustaceans also move offshore to reach spawning grounds—at the edge of the shelf
break in the case of mud crabs (Scylla serrata) (Hill, 1994) and ornate rock lobster
(Panulirus ornatus) (Moore & MacFarlane, 1984) in the GBRWHA.
Fish size generally increases with depth for red emperor Lutjanus sebae, and the
sea-perches L. malabaricus and L. erythropterus (McPherson et al., 1992), indicating
progressive offshore movement, but there are important differences in ontogeny.
Juvenile L. malabaricus and L. erythropterus Ն2.5 cm long occur in large bays of the
Central GBR, especially around sparse seagrass beds (Williams & Russ, 1994;
Newman & Williams, 1996; Newman et al., 1997) and also inside estuaries of the far
northern section (D. Donald, personal communication). They are restricted to
depths Ͻ15 m with high silt and clay fractions in the Central GBR, including sea-
grass beds, whereas juvenile L. sebae have a much wider depth range and can be
found over both terrigenous and carbonate sediments in the range 15 to 62 m (Jones
& Derbyshire, 1988). Red Emperor juveniles can be caught on the same inter-reef
grounds over high-relief shoals and wrecks and exposed Pleistocene reef surfaces as
mature adults, and there is some evidence that they may be less common than L. mal-
abaricus and L. erythropterus in turbid waters of 5 to 15 m (A. Zavodny, personal
communication; Williams & Russ, 1994).
It is also important to recognise that connection of other ecosystems with the
GBRWHA occurs at between-ocean scales, in the case of migrations by humpback
whales (Megaptera novaehollandiae) and other cetaceans, seabirds, black marlin
(Makaira indica), and sea turtles (see Marsh et al., 1997). In the case of black mar-
lin, mature fish congregate in the northwest Coral Sea, in the Cairns–Lizard Island
region, to spawn between September and December. Their piscivorous larvae are
most common within 0.25 nm of the reef crest after this spawning, presumably
in coincidence with high prey abundance (P. Speare, personal communication).
174 Oceanographic Processes of Coral Reefs

© 2001 by CRC Press LLC
A southward migration of young-of-the-year and 2-year-old fish then occurs from
northern Queensland (see below) to central New South Wales in association with the
progression of the East Australian Current. Tagged fish in a wide range of sizes have
moved large distances (up to 7200 km in 359 days) to and from the GBRWHA.
Recaptures of fish near their points of release after 1, 2, 3, or 4 years strongly suggest
annual homing of at least mature parts of the population to the northwest Coral Sea
(Pepperell, 1990).
Long-shore feeding and spawning migrations through various portions of the
GBR lagoon have also been demonstrated for a variety of “lesser” (Scomberomorus
munroi, S. queenslandicus, S. semifasciatus) (Begg et al., 1998) and Spanish (S. com-
merson) mackerels (McPherson, 1987). In the central section during the months of
October and November the Spanish mackerel migration (from perhaps as far south as
New South Wales) culminates in spawning aggregations around Rib reef and other
mid-shelf reefs close to major passages (McPherson, 1997). Numerous carcharhinid
sharks accompany the schools. The currents in these locations may aid larvae in dis-
persal to inshore feeding grounds and nurseries, and these larvae have been caught in
light traps at the “coastal boundary layer” nearby (Jenkins et al., 1984 and 1985;
Thorrold, 1993).
Inshore spawning migrations are also known for at least eight species of whaler
(Carcharhinidae) and hammerhead (Sphyrnidae) sharks, whose adults move into
shallow bays to pup in early –mid-summer. The bull shark (Carcharhinus leucas)
pups inhabit estuaries and the freshwater reaches of suitable wet-tropics rivers. The
bays are communal nursery areas for these sharks, which have similar diets compris-
ing mainly fast-growing, planktivorous engraulid and clupeid baitfish. There is a sea-
sonal coincidence between highest numbers of shark juveniles and highest prey
abundance (Simpfendorfer & Milward, 1993). This temporal coincidence of juvenile
predators and recruitment pulses of prey resources occurs also for the lesser and span-
ish mackerels (see Jenkins et al., 1984 and 1985).
A CASE STUDY OF BAITFISH–PREDATOR LINKS

A prime example of the temporal, spatial, and ontogenetic scales we have sought to
portray occurs annually in striking circumstances between the 20- to 40-m isobaths
offshore from mangrove-lined bays in the Cairns, Dunk Island, and Bowling Green
Bay regions. Each winter, aggregations of clupeid, carangid, and scombrid baitfish
and teleost, elasmobranch, avian, and cetacean predators occur in “billfish grounds”
in the middle of the GBR lagoon (Williams, 1990). These aggregations represent
food chain connectivity across-shelf in the movement of baitfish (Williams & Cappo,
1990), and along-shore, in the southward movement of juvenile black marlin
(Pepperell, 1990; Speare, 1994) and the northward movement of maturing Spanish
mackerel (McPherson, 1987 and 1997) and spotted mackerel (Begg et al., 1998).
Off Cape Bowling Green (see Figure 8), the baitfish species school in large sur-
face aggregations and are hunted from below by schools of young-of-the-year black
marlin, pods of adult sailfish (Istiophorus platypterus) and dolphins (Tursiops
Connectivity in the Great Barrier Reef World Heritage Area 175
© 2001 by CRC Press LLC
truncatus), tunas, and sharks, and pursued from above by diving brown booby birds
(Sula leucogaster) and frigate birds (Fregata minor). Studies of the multi-species
aggregations showed that northern pilchards (Amblygaster sirm) and golden-lined
sardines (Sardinella gibbosa) were major components, together with small, fusiform
carangids and scombrids (Selaroides leptolepis, Decapterus russelli, D. macrosoma,
Rastrelliger kanagurta, Cybiosarda elegans) (Cappo, 1995a and b). Northern
pilchards and sardines occurred in 85% of black marlin stomachs, and comprised
93% of prey items. Sailfish diets were more varied, including larval triggerfishes and
leatherjackets, but the northern pilchard occurred in 57% of the sailfish examined.
Later in summer (see Figure 8) the adult pilchards and sardines were detected in
smaller schools and were generally very large, suggesting that they were the old rem-
nants of the winter population. The predators on the grounds were also different, with
small numbers of migrating spotted mackerel (Scomberomorus munroi) appearing,
and with surface activity being dominated by schools of tuna (Thunnus tonggol and
Euthynnus affinis) feeding on small, juvenile northern pilchards and other fish larvae.

The birds above the fish-feeding activity also changed to abundant flocks of sev-
eral species of terns, including the little tern (Sterna albifrons) and the crested terns
(S. bergii, S. bengalensis). Later, in autumn, large numbers of Spanish mackerel in
the 5- to 9-kg range were seen on the grounds. By June or July, the schools of small
black marlin (15 to 40 kg) usually arrived in numbers, but each year was different in
terms of timing of arrival, numbers, and size. These seasonal changes in bait, birds,
and billfish are generally best explained by the changeover periods from southeast
trade winds bringing cooler water in April, to the northwest monsoons in October
bringing down warmer waters from the north.
The prevailing hypothesis is that the bays adjacent to the GBR lagoon billfish
grounds are exceptional nursery areas for baitfish and, as they grow, these fish
migrate progressively out to the grounds (Williams & Cappo, 1990). An abundance
of suitable food for these early life history stages has been documented in the shal-
low bays, especially near mangrove river mouths, in the form of zooplankton
(McKinnon & Klumpp, 1998a and b; Robertson et al., 1988; Williams et al., 1988).
Aerial survey in summer 1990 over the four major capes in the Central GBR spotted
over 320 schools of juvenile baitfish along a 230-km stretch of coast. Over 90% of
these schools were aggregated around river mouths, but a key uncertainty concerns
the role of mangrove crab zoeae in the diets of these fish.
Pulses of juvenile golden-lined sardines appeared within 100 m of shore in
October to December in Bowling Green Bay, and by April had moved offshore into
deeper bay waters toward the billfish grounds. During April to May, the sub-adult sar-
dines were passing the Cape Bowling Green sand spit, and by September they were
in spawning condition on the billfish grounds (Williams & Cappo, 1990; Cappo,
1995a). These nearshore schools of juvenile sardines and pilchards are heavily
preyed upon by grey mackerel (Scomberomorus semifasciatus) and other fish and
sharks (Simpfendorfer, 1998) around pinnacles and rocky headlands. The northern
pilchard showed a much different life cycle to the sardines and all life stages of the
pilchards—from larvae to juveniles, sub-adults, and spawning adults—were found
offshore in the vicinity of the billfish grounds.

176 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
CONCLUSION
The conventional “coral reef paradigm” highlights nutrient trapping and recycling
and close co-evolution of species in symbiotic and commensal relationships to accu-
mulate biomass in otherwise nutrient-poor tropical oceans. This has encouraged a
popular view of reefs as somewhat self-contained biological islands, which are linked
through episodes of larval dispersal with other reef systems. Our conceptual model
extends this to reflect current appreciation of the GBRWHA as a profoundly inter-
connected system in which the non-reef communities are important “load bearing”
elements in terms of the integrity and health of the larger system. The extent and
nature of the seaward influence of human activities in the coastal plains and fringe
are under study, but understanding is complicated by the nature and connectivity of
natural disturbances. Clear gradients and links can readily be shown between
biotopes, in “places, processes, and protein,” but the strengths of these links and the
implications of their disruption are not yet sufficiently known to fully predict human
impacts. Landscape-scale research and management of the GBRWHA is needed,
especially in the poorly known “inter-reef” and through the coastal fringe into the
catchments.
ACKNOWLEDGMENTS
In developing the themes presented here we gratefully acknowledge the contributions
of the Australian Coral Reef Society, V. Veitch and our many other informants, and
G. Ryan for the artwork. We also thank E. Wolanski for the invitation to contribute
this chapter, and especially D. Williams and an anonymous referee for “connecting”
the components of a rough first draft.
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