Tropical Coastal Environment processes and hazards

2. Distribution and occurrence of coral reefs and
mangroves
Sources and characteristics of coral reefs sediments
Reef sediment transport and accumulation
Sources and characteristics of mangrove sediments
Management and remediation of coral reef and
mangrove sediments

3. Tropical environment is characterized by average
temperature between 20°C-30°C having warm and humid
climate.
They include wide range of sedimentary environments
such as deltas, lagoons, estuaries, beaches etc. Which are
comparable to the temperate zone but they represent two of
the most beautiful, unique and important environments i.e.,
Coral reefs and Mangroves.
Tropical Costal Environment ?

4. • Corals are two layered invertebrates formed in shallow ocean by algae and calcareous
skeletons of certain coelenterates of which polyps being major ones.
• Polyps within a colony are linked by living tissues and can share their food (Allen &
Steene, 1994).
• The polyp extracts calcium carbonate from the sea and secretes it as a cup providing
anchorage and when the calcium carbonate cups of many billions of these polyps
fuse together, they form coral reefs (Veron, 2000).

5. James & Macintyre (1985)
Types of
Coral Reefs
Fringing
Reefs
Barrier
Reefs
Atoll
Bank
Barrier
Reefs
Patch Reefs

6. Coral reef ,Belize, Caribbean, Central America
Great Barrier Reef, Australia
Photo: Fringing reef of Tahiti, French Polynesia,
Pacific Ocean

7. They are tropical trees and shrubs that thrive in conditions most timber could never tolerate i.e.
Salty, coastal waters, and the interminable ebb and flow of the tide and the first species to
colonize mud and sandbanks flooded by seawater.
They grow in areas with low-oxygen soil, where slow-moving waters allow fine sediments to
accumulate and serve as a buffer zone between marine and terrestrial communities.
Ecologically, they provide diverse habitat for terrestrial organisms, and many species of coastal.
Offshore fish rely on them as their breeding, spawning, and hatching grounds.
 There are confirmed 54 species of mangroves in the world and many more as well.
 Some of the examples are Red, Black, White, and Buttonwood mangroves.

8. Mangroves of Sundarbans,Bangladesh
Aerial view of Sundarban mangrove,Bangladesh &India
Mangroves of Phillipines
Mangrove roots above and below water

9. Distribution and Occurrence of Coral reefs and
Mangroves
 Coral reefs are mostly concentrated to shallow sea(less than 100m).
 where the sea is warm (usually between 25° and 29°C).
 Vastly located within the latitude of 30°N to 30°S i.e., mostly in tropical seas.
 They occupy an estimated area of 255,000km2
 Mangrove ecosystems extend along some 60–75% of tropical and subtropical coastlines (MacGill 1958) and
recent mapping estimates suggest a global coverage of around 190,000 km2 (Spalding et al. 1997).
 The main defining characteristics of mangroves are that they comprise Communities of salt tolerant
tropical/subtropical trees and shrubs, and as such represent tropical equivalents of temperate salt-marsh
communities (Woodroffe 1983).
At the global scale, mangrove distributions exhibit a reasonably close correlation with the mean winter 15°C sea-
surface isotherm (Woodroffe &Grindrod 1991), which equates to a latitudinal range between about 30°N and
30°S.

10. Sources and
characteristics of
coral reef
sediments
Skeletal
sediments
Non- Skeletal
Sediments
Allochthonus
Sediments

11. They are the most abundant reef
sediments which can be subdivided into
sediments produced by:
1.Breakdown of carbonate framework
contributors
2.Those derived from reef-associated
benthic organisms and calcareous algae.
Coral reef which framework is composed of two main constructional components, the skeletons
of hermatypic corals (primary frame builders and a diverse array of associated calcareous
encrusting faunas(secondary frame builders).

12. Breakdown of these primary and secondary framework contributors (and thus framework related sediment production)
is facilitated by physical and biological activity.
 Physical disturbance results in fragmentation and
transport of coral framework, and generation of
coral rubble which in turn can be degraded by
physical reworking to produce fine coral sand/silt.
 Bio erosion is facilitated by a wide range of reef-
associated faunas, including fish and echinoids, and
endolithic forms of sponges, bivalves and worms.
(Adapted from Scoffin 1987.)

13. They occur within reef and reef-related sediments and include carbonate muds, peloids and ooids.
Carbonate silts (grain size< 63 μm)are composed of significant component of lagoon sediments.
Much of this material comprises single aragonite crystals derived from the breakdown of
carbonate secreting marine algae, although some may also result from direct precipitation from
supersaturated sea waters.
Some peloids are also believed to result from phases of chemical precipitation around a central
nucleus.

14.  Although mostly influenced by sediments from the within environments of corals it is as well influenced by the
terrigenous sediments mainly from fluvial derived sediment inputs with influx and outflux of the sediments from the
environment.
 A detailed sediment budget of a carbonate embayment at hanalei bay, hawaii, influenced by terrigenous sediment
input (calhoun et al.2002), found that significant proportions of fluvially derived suspended sediments were exported
offshore, and the bay was also subject to inputs of carbonate sediment derived from adjacent coastal areas.
 Also increasingly associated with terrigenous sediment inputs are a range of dissolved and particulate contaminants
linked to anthropogenic (industrial or agricultural) discharges. These include heavy metal and hydrocarbon
contaminants .

15. Although local environmental
factors influence the composition
and abundance of individual
sediment contributors, the
accumulation of carbonate
sediment in reef environments is
influenced by a wide range of
physical and biogenic processes.
These influence sediment
transport, reworking, trapping and
stabilization.
Coral reef
sediment Transport
and Accumulation
Reef Sediment
Transport
Reef sediment
Trapping and
stabilization
Reef Sediment
reworking

16. Sediment transport and deposition are determined by two main factors:
• Shear stress and
• Settling velocity
The former relates to the velocities required to move or entrain sediment particles of a specific size, the latter
to the difference between the gravitational and buoyancy forces acting on the particle.
Grain transport and deposition in carbonate sediments, however, are complicated by differences in grain
skeletal structure (and hence density) and by grain size, shape and texture.
Grains with plate-like morphologies will settle at a slower rate than block or rod-shaped grains and hence
such parameters influence grain transport and deposition (kench & mclean 1996).

17. Transportation of grains vastly depends on the
physical properties of the grains though various
biogenic components and physio-chemical
processes act to trap and stabilize reef sediments.
Examples: Seagrass and green algae.
The long blades of seagrasses, such as Thalassia
and Syringodium, locally reduce current speeds
and promote sediment settling (Scoffin 1970).
In the long-term, such processes can lead to the
development of carbonate mud banks (Bosenceet
al. 1985),which depends upon local rates of
carbonate mud production (Perry& Beavington-
Penney 2005). Photo: Sea grass and Sedimentation

18.  Sediment reworking is mainly dominated by wave and
current action of the water in the costal environment as
well as the intensity of bioturbation and surface feeders
such as crabs, holothurians, shrimps etc.
 Holothurians, for example, are estimated to ingest and
excrete up to 250g of sediment per day and produce a
highly homogenized surficial sediment layer, the
ingestion process may also result in chemical grain
dissolution (Hammond 1981).
 Extensive sediment reworking (with volumes of sediment
turnover in excess of 11 kg m−2 yr−1)may occur
associated with infaunal organisms such as the
Callianassa shrimp (Bradshaw 1997).
 Because of such working of sediments by the organisms
increases the probability of resuspension, re transportation
and instability of the top most sediment layer. Photo: Sea cucumber munching on

19. Mangroves are found diversely in different costal environments , so their sources of sediments are diverse as
well.

20. Mangrove
sediment
Transport and
Accumulation
Mangrove
Sediment
Transport
Mangrove
sediment
Trapping and
stabilization
Mangrove
Sediment
reworking

21. The rate of mechanism and rate depends
upon the circulation pattern influenced by
freshwater runoff ,evapotranspiration and
tidal regime.
The major factors are the alluvial and tidal
interference in the sediments.
Tidal circulation being the primary cause of
water movement and causes the ebb-phase
typically shorter and characterizedby
stronger current speeds of 1 m s−1.
(Wolanskiet al. 1980) while current speeds
on the flats often lessthan 0.1 m s−1.

22. The trapping and stabilization of sediments is
influenced by the types of roots and
pneumatophore density, which modifies current
velocities and flow regimes (Woodroffe 1992).
As currents pass through the dense mangrove
root networks on the mangrove flats, the
vegetation induces micro turbulent flow
(eddies, jets, stagnation zones),which maintains
sediment in suspension.
This material is typically transported
landward and settles out around slack high tide
as flow turbulence reduces (Furukawa &
Wolanski 1996).

23. There is small-scale effects of physical sediment reworking
and transport for the influence grain transport, biological
factors are also involved.
Much of this is attributed to the activities of crabs, which
rework sediment during feeding and burrow construction.
Grapsidae crabs feed primarily on leaf litter, whereas
Ocypodidae (fiddler crabs) are detritivores and ingest sand
grains in order to remove organic material.

24. Management
and
remediation of
coral reef and
mangrove
sediments
Managing
sediments
contaminants
Managing
resource
extraction and
exploitation
Managing
natural costal
hazards

25. For Corals and Mangroves
Education programs
Coral nurseries and
Mangrove nurseries
Plastic pollution control
Development of marine protected area
Responsible stewardship by marine park tourism organizations
Renewable energy development
Strict implementation of laws and regulations

26. Photo: Study and Plantation of corals in Great Barrier Reef, Photo: Coral Plantation in Florida, USA.