MINISTRY OF EDUCATION AND TRAINING
NONG LAM UNIVERSITY
FACULTY OF CHEMICAL AND FOOD TECHNOLOGY
----------

ESSAY ON ENVIRONMENTAL SCIENCE
Topic: Today's State of Coral Reef Ecosystems
Throughout The World

January, 2022


Table of contents
Acknowledgment ...........................................................................................................iv
Abstract ...........................................................................................................................v
List of Abbreviations .................................................................................................... vi
List of figures ................................................................................................................vii
List of tables ................................................................................................................ viii
1 Introduction ...................................................................................................................1
2 Distribution of coral reefs and their importance .......................................................... 4
2.1

Mesophilic coral reef ......................................................................................... 4

2.2

Mesophotic coral reef .........................................................................................5

3 Biological responses to a rapid changes .......................................................................7
3.1

The reason behind coral reef deterioration ........................................................8

3.2

The importance of acclimation and adaptability in the face of fast change to

coral survival ..............................................................................................................13
4 Prospects for coral reef recovery from disturbance ................................................... 16
4.1

Natural recovery ...............................................................................................16

4.2

Assisted recovery ............................................................................................. 18

5 Methology for coral reef protection ........................................................................... 19
5.1

Integrated coastal zone management implementation .................................... 19

5.2

Appropriately managed marine protected areas (MPAs) ................................19

5.3

Increase coral reef monitoring ......................................................................... 20

5.4


Capacity development ......................................................................................20

ii


5.5

Stricter control overfishing activities of fishermen, especially those

employing destructive techniques ..............................................................................21
6 Conclusion .................................................................................................................. 23
7 References ...................................................................................................................24

iii


Acknowledgment
First of all, I would like to express my sincere thanks to Nong Lam University for
bringing the subject of Environmental Science into the curriculum. In particular, I
would like to express my deep gratitude to the subject lecturer - Ms. Le Thi Lan Thao
for teaching and imparting valuable knowledge to me during the past study period.
During my time in your class, I have gained a lot of useful knowledge, effective and
serious study spirit. This will definitely be valuable knowledge, luggage for me to be
able to step firmly in the future.
Environmental Science is an interesting, extremely useful, and highly practical subject.
Ensure to provide enough knowledge, associated with the practical needs of students.
However, due to limited knowledge and the ability to absorb reality, there are still
many surprises. Although I have tried my best, surely the essay is hard to avoid errors
and many inaccuracies, I hope you will consider and give suggestions to improve my

essay.
Thank you sincerely!

iv


Abstract
Coral reefs may be found in a variety of habitats, where they offer food and shelter for
a broad variety of creatures, as well as a variety of other ecological goods and services.
Warm-water coral reefs, for example, require shallow, sunny, warm, and alkaline
waters to grow and calcify at the rapid rates required to develop and sustain their
calcium carbonate structures. At deeper depths (40 - 150 m), "mesophotic" (low light)
coral reefs build calcium carbonate at considerably slower rates (if at all in certain
circumstances), yet they nonetheless provide as the home for a diverse range of
species, including some vital to fisheries. Finally, in the dark depths, so-called "coldwater" coral reefs can be discovered at depths of 2,000 m or more. Coral reefs are
among the most prolific and diversified ecosystems on the planet, providing a wide
range of important ecosystem services. Despite their worth, coral reefs are under
severe threat from a variety of sources. This essay offers a quick overview of the state
of the world's coral reefs and the factors contributing to their deterioration. In addition,
this article suggests several viable solutions for promoting the sustainable use of coral
reef resources, to assuring their long-term existence.

v


List of Abbreviations
GCRMN

Global Coral Reef Monitoring Network


ICZM

Integrated coastal zone management

MPA

Marine protected area

SST

Sea surface temperatures

vi


List of figures
Figure 1. Distribution of two types of coral reef ecosystem throughout the world
(Pörtner et al., 2014) ........................................................................................................ 4
Figure 2. Many marine life species find refuge in warm-water coral environments.
(Credit:

James

Watt,

2019,

/>
collections/marine-life/coral-reef-ecosystems) ............................................................... 5
Figure


3.

Mesophotic

coral

ecosystems

(Credit:

L.

Rocha.,

2019,

...........................5
Figure 4. Cold-water coral system (Oculina varicos) (Hourigan et al., 2007) ............... 6
Figure 5. Phu Quoc marine reef is damaged by boats mooring (Credit: Thanh Nien
Magazine) .........................................................................................................................8
Figure 6 (A). Relationships between the accumulation of atmospheric CO2 and the
slowdown of coral calcification as a result of ocean acidification (B). Temperature,
[CO2]atm and carbonate-ion concentrations have all been rebuilt during the last
420,000 years. (Credit: IPCC, 2013) ...............................................................................9
Figure 7 The surface ocean's aragonite saturation condition as predicted by the
University of Victoria Earth System Model under different CO2 atmospheric
concentrations. (Pörtner et al., 2014) ............................................................................ 12

vii



List of tables
Table 1. The temperature change of sea areas in 60 years from 1950 to 2009 (Change,
2014) .............................................................................................................................. 10

viii


Introduction
Warm-water and cold-water corals both generate calcium carbonate skeletons, which
accumulate over time to form a three-dimensional reef matrix that offers the home for
thousands of fish and other species. Many warm-water coral reefs produce enough
limestone-like calcium carbonate to form carbonate structures. Calcification rates are
high enough to offset large rates of bioerosion and wave-driven physical erosion.
These structures support the framework of barrier reefs and islands, both of which are
crucial to tropical coasts. Despite occupying less than 0.1% of the ocean floor, tropical
coral reef ecosystems support at least 25% of known marine species, with additional
reef species still to be identified (Molinos et al., 2016). Warm-water coral reef
biological diversity is estimated to have 1 - 9 million species that reside in and around
coral reefs. As light levels decrease, the trend for carbonate-dominated reef structures
decreases in deeper areas of these warm-water reef systems. At low light levels,
erosion and dissolution outweigh calcium carbonate formation, resulting in coral
communities that may be plentiful but lack a three-dimensional calcium carbonate reef
foundation. These "mesophotic" (low light) coral reefs extend from 40 to 150 meters
and provide considerable habitat, with species discovery rates staying relatively high
due to the difficulty of visiting these reefs (Bongaerts et al., 2011). Mesophotic reef
systems are likely to comprise an area equivalent to shallow warm-water coral reefs.
Scleractinian corals that develop symbiosis with dinoflagellate protists from the genus
Symbiodinium dominate both shallow and deeper mesophotic coral reefs. Based on

this symbiosis, their internal symbionts (those that live inside the gastrodermis or
digestive tissues of their coral hosts) may photosynthesize and supply a rich source of
sugars, glycerol, lipids, and other organic compounds to the host coral (Muscatine,
1990). Corals may develop and calcify at a rapid rate under the clear, warm, and
shallow water conditions seen in tropical beaches because of this association. The
number of Scleractinian corals that host Symbiodinium declines with depth beyond 20
- 40 meters, depending on water column clarity. The deepest Scleractinian corals
1


symbiotic with Symbiodinium can be found 100 meters or more below the surface of
tropical seas (Englebert et al., 2015). The capacity of corals to catch and feed on
watery particles and plankton adds to the productivity of this symbiotic relationship
(i.e., polytrophy). The capacity to photosynthesize and feed at the same time is critical
to the development of the extremely prolific coral reef ecosystems that line many
tropical coasts. Scleractinian corals have been symbiotic with Symbiodinium for about
230 million years, according to evidence from isotope traces in fossils (Muscatine et
al., 2005). Most likely, they were driving productive and diversified ecosystems that
were not dissimilar to those found today.
Cold-water coral reefs can reach depths of 3,000 meters, however certain cold-water
corals can flourish in seas as shallow as 50 meters (e.g., Norwegian shelf). There is so
little light below 200 meters deep that photosynthesis is no longer viable. As a result,
cold-water corals do not create a symbiotic relationship with Symbiodinium and must
rely on particle feeding. Advances in underwater surveying and mapping technology
have mostly prompted discoveries of the locations and size of cold-water reefs (Turley
et al., 2007). Cold-water coral reefs have now been identified in every ocean, forming
significant assemblages within the deep ocean that offer crucial habitat for thousands
of other species, including many economically important species.
Coral reefs provide various advantages to human societies, including food, income,
recreation, coastal protection, cultural contexts, and a variety of other ecological

products and services. Despite their biological variety, productivity, and human value,
both warm and cold-water coral reefs are being severely damaged by global factors
(Burke et al., 2011). As a result, numerous coral reefs throughout the world are fast
deteriorating. While local factors such as pollution, overfishing, and physical reef
destruction can have a significant impact on coral reefs, changes in ocean temperature
and chemistry caused by anthropogenic activities are dramatically reducing the
distribution, abundance, and survival of entire coral reef ecosystems (Hoegh-Guldberg
et al., 2002). Given these hazards, as well as the importance of coral reefs to humans
and marine biodiversity, this essay focuses on the issues that coral reef ecosystems
2


and associated human communities face, particularly those posed by stressors
increasingly.

3


Distribution of coral reefs and their importance
2.1 Mesophilic coral reef
Warm-water coral reefs are significant ecosystems throughout the Pacific, Indian, and
Atlantic oceans' coasts (Figures 1), where they are often found in a broadband (30°S
to 30°N) of warm, sunny, alkaline, transparent, and rather nutrient-deficient ocean
waters. Scleractinian or reef-building corals thrive in this environment, depositing vast
quantities of calcium carbonate. When corals die, their dead skeletons accumulate
over time and are "glued" together by the actions of other species like encrusting red
coralline algae. Other creatures, such as calcifying green algae, invertebrates, and
phytoplankton, contribute to the total carbonate budget of warm-water coral reefs,
resulting in three-dimensional calcium carbonate structures that accumulate over
hundreds of thousands of years. In turn, the three-dimensional structures (Figure 2)

inside warm-water reef systems provide habitat for hundreds of thousands of species,
many of which provide food, income, and other ecological goods and services such as
coastal protection to coastal human communities. Coral reefs are also crucial for bioprospecting and the creation of new medications. The asset value of coral reefs has
been estimated to be close to $1 trillion (Hoegh-Guldberg, 2015), with the economic
worth of coral reef goods and services reaching $375 billion yearly, benefiting
approximately 500 million people in at least 90 countries globally (Burke et al., 2011).

Figure 1. Distribution of two types of coral reef ecosystem throughout the world (Pörtner et al., 2014)

4


Figure 2. Many marine life species find refuge in warm-water coral environments. (Credit: James Watt,
2019, />
2.2 Mesophotic coral reef
As light levels fall with depth, decalcification takes hold, and the overall carbonate
balance of reef ecosystems moves to the negative. Scleractinian corals and their
symbionts survive in these circumstances, and reefs are referred to as "mesophotic."
Scleractinian coral colonies in these settings are frequently platelike in form, orienting
themselves to maximum light gathering under these low-light circumstances (Figure
3). Mesophotic reef systems are likewise predominantly limited to locations with high
water clarity, carbonate ion concentrations, and temperatures. Mesophotic reef
systems, like their shallower counterparts, serve a vital role in maintaining fisheries
and hence human livelihoods. Many species remain unknown due to the difficulties of
operating at depths greater than 30 meters.

Figure 3. Mesophotic coral ecosystems (Credit: L. Rocha., 2019,
/>
5



Cold-water corals often form reefs at considerably larger depths ranging from 200 to
2,000 meters. However, they can also be found at shorter depths in some areas. Deepwater corals are not light-dependent since they are not symbiotic with Symbiodinium.
Deep-water corals grow slower than warm-water corals due to the colder and more
CO2-rich (and hence less alkaline) waters, producing aggregations known as patches,
banks, thickets, bioherms, mounds, gardens, and massifs. In the absence of strong
wave action, these fragile and slow-growing reefs form aggregations that can span
extensive swaths of the seafloor and include almost mono-specific stands of
Scleractinian corals like Lophelia pertusa and Oculina varicosa (Figure 4). In addition
to Scleractinian corals, they frequently have a plethora of coral-like animals, such as
soft corals, gorgonians, and Alcyonaceans.

Figure 4. Cold-water coral system (Oculina varicos) (Hourigan et al., 2007)

6


Biological responses to a rapid changes
The decline in the number and community structure of reef-building corals will have
far-reaching consequences for the function that corals play in generating habitat for
the numerous species that live in and near coral reefs. While the influence on a few
groups of coral reef creatures, such as coral reef fishes, is becoming obvious, the
consequences for the overwhelming majority of coral reef organisms remain unknown.
Climate change is likely to drive major changes in the community composition of
many reef-associated species, according to studies of fish on reefs with varying
amounts of damage from coral removed from them as a result of Crown of Thorns
starfish (Acanthaster planci) infestations and mass coral bleaching. (Wilson et al.,
2006),for example, examined data from 17 independent studies conducted over the
last decade and discovered that 62% of fish species on coral-dominated reefs dropped
in abundance within 3 years following disturbances that resulted in a larger than 10%

decline in coral cover. An examination of the fish species that vanished as coral
quantity declined indicated that those that either consume coral directly or require
living coral as a settlement queue is among the first to go from reefs affected by
widespread coral bleaching and death. Fish that consume invertebrates or graze the
epilithic algal matrix exhibited either no change or an increase in abundance in certain
situations. Clearly, we need to understand more about how climate change may affect
species like corals and calcareous algae's capacity to sustain the three-dimensional
structures that serve as fish homes. It is also apparent that, like other creatures,
changes in water temperatures and pH have a number of direct effects on fish. Early
indications indicate that these changes will also play key roles in determining the
health of coral reef fish, particularly in the way variables and responses combine
synergistically (Wilson et al., 2006). Our understanding of the biological
consequences of global warming and ocean acidification remained incomplete.
However, given the vast array of processes that are anticipated to be influenced by the
physical and chemical changes wrought on tropical/subtropical oceans by global
7


warming and ocean acidification, coral reefs are likely to be altered in complicated
and often surprising ways in the future.
3.1 The reason behind coral reef deterioration
3.1.1 Impacts of Anthropogenic stresses
Coral reefs are under increasing threats as a result of the local to global consequences
of human activity. Human activities have fundamentally altered coastlines,
overexploited resources such as fish supplies, and contaminated coastal seas to the
point that many coral reef ecosystems are quickly declining. Warm-water coral reefs,
for example, have fallen by at least 50% in broad areas of the world's tropical regions
during the last 30-50 years (De’Ath et al., 2012). Similar findings have been found for
cold-water reefs, where human activities have increased strain on these systems since
the mid-1980s. Commercial bottom trawling, hydrocarbon exploration and production,

deep-sea mining, cable and pipeline deployment, pollution, waste dumping, coral
exploitation and trade, and damaging scientific sampling are all major causes of coldwater reef degradation (Roberts & Cairns, 2014). The fast advancement of tools for
observing and utilizing the biological and mineral resources of deep-sea ecosystems
has resulted in a rise in human effects.

Figure 5. Phu Quoc marine reef is damaged by boats mooring (Credit: Thanh Nien Magazine)

Many deep-sea coral populations (Scleractinians, gorgonians) have extremely slow
turnover rates and can persist for decades, with some species, such as black corals
8


(Antipatharians), lasting for thousands of years. Because of their longevity and modest
growth rates, these species will need a long time to recover from anthropogenic
stresses. Deep-sea reef habitats are also a "resource frontier" for hydrocarbon
extraction and mining of high-value and "high-tech" metals (Roberts & Cairns, 2014).
As a result, anthropogenic impacts on these reefs are projected to worsen.
Understanding and addressing both local and global risks to coral reefs will be vital if
they are to survive some of the most rapid rates of environmental change in Earth's
recent history
3.1.2 Impacts of Planetary warming and ocean acidification
3.1.2.1 Planetary warming
These declines are also associated with ocean warming and acidification (Figure 6A),
both of which constitute a growing and substantial threats to coral reef ecosystems.
Since the early 1980s, the direct impact of these changes on coral reefs has been
escalating. The latter is a direct outcome of the combustion of fossil fuels and have
been having an increasing influence on warm water coral reefs since the early 1980s.

Figure 6 (A). Relationships between the accumulation of atmospheric CO2 and the slowdown of coral
calcification as a result of ocean acidification (B). Temperature, [CO2]atm and carbonate-ion concentrations

have all been rebuilt during the last 420,000 years. (Credit: IPCC, 2013)

Even with very large swings in average global temperature and atmospheric CO2
concentrations over the glacial cycle, warm-water coral reef ecosystems have
9


experienced a substantial change in temperature and carbonate ion concentrations
(Figure 6B). Warm-water coral reefs shrunk toward the equator during glacial eras
and re-expanded along the world's tropical and subtropical coasts during warm periods
(Hubbard, 2015). While these changes were quick in geological time frames, they
happened across 10,000 years or more and are sluggish in comparison to climate
changes since pre-industrial times.
During the period 1950 - 2009, the average sea surface temperatures (SST) of the
Indian, Atlantic, and Pacific seas increased by 0.65, 0.41, and 0.31°C, respectively
(Table 1). Long-term patterns of climate variability, such as the Pacific Decadal
Oscillation (PDO), contribute to regional variability and complicate efforts to identify
and link regional changes to anthropogenic greenhouse gas emissions (Change, 2014).
Nonetheless, an assessment of Hadley Centre data spanning 60 years (1950 - 2009)
finds strong warming trends in SST for numerous ocean sub-regions (Table 1). With
the exception of the Gulf of Mexico/Caribbean Sea area, significant changes are
plainly seen among the six main warm-water coral reef zones. The rates of rising SST
in warm-water coral reef zones range from 0.07°C (west Pacific Ocean) to 0.13°C
(Coral Triangle and southeast Asia) each decade, resulting in an overall increase in the
regions of 0.44 to 0.79°C between 1950 and 2009.

Table 1. The temperature change of sea areas in 60 years from 1950 to 2009 (Change, 2014)

10



3.1.2.2 Ocean acidification
Changes in the pH of the surface waters have also happened during the last 100 years,
a phenomenon known as ocean acidification. As CO2 enters the ocean, it combines
with water, increasing the concentration of hydrogen ions (therefore reducing ocean
pH) and decreasing the concentration of carbonate ions. While the overall change in
ocean pH appears to be minor (0.1 pH units over the last 150 years), this represents a
26% rise in hydrogen ion concentration. Experimental research indicates that a
decrease in carbonate ions associated with ocean acidification is ecologically relevant
since it can impact the pace at which marine organisms such as corals produce their
calcareous structures (Comeau et al., 2017). These changes in ocean chemistry are
temperature dependent, with CO2 absorption and, as a result, acidification being
greatest when waters are colder. The aragonite (calcium carbonate) saturation state
(Ωarag) is simply the ratio of calcium and carbonate ion concentrations. The ocean's
surface waters are often supersaturated in terms of aragonite (Ωarag > 1). However, the
saturation state of aragonite has a similar distribution to that of sea surface
temperature, with Ωarag being highest in the hottest ocean areas and lowest in the polar
regions, in warmer temperatures where Ωarag is not expected to decrease below 1 (thus
undersaturated with regard to aragonite), significant repercussions on calcifying
organisms are still anticipated. Carbonate accretion on warm-water coral reefs
approaches nil or becomes negative when Ωarag drops below 3.3 (Chan & Connolly,
2013), a threshold that is projected to be achieved in tropical surface seas over the
next few decades at present greenhouse gas emission rates.

11


Figure 7 The surface ocean's aragonite saturation condition as predicted by the University of Victoria Earth
System Model under different CO2 atmospheric concentrations. (Pörtner et al., 2014)


The depth of the aragonite saturation horizon, Ωarag = 1.0, limits the global spread of
cold-water corals. The saturation state of aragonite decreases with depth, thanks to
hydrostatic pressure and decreased temperature, with distinct aragonite "saturation
horizon" below which fluids become under-saturated for aragonite (Ωarag < 1). The
saturation horizon is a complicated result of ocean circulation, temperature, CO2
concentrations, salinity, metabolic activity, and organic compound concentrations, and
it occurs at depths ranging from 200 to 3,500 meters, depending on latitude and ocean
(Jiang et al., 2015). Surface waters and waters at 50 meters depth are largely
supersaturated throughout the global ocean, however in western Arctic waters, the
area of under-saturated waters in the top 250 m north of 70°N grew from 5% to 31%
between 1990 and 2010 (Qi et al., 2017). Large patches of undersaturated Ωarag water
may be observed at 500 meters in the northern and equatorial Pacific oceans. At 1,000
meters, Ωarag = 1.8 throughout all ocean basins, while at 2,000 m, Ωarag = 1.0 across the
Pacific, Indian, and Atlantic Oceans. High latitudes are experiencing faster rates of
ocean acidification than lower latitudes, resulting in a shoaling of the aragonite
saturation horizon. Evidence currently suggests that the aragonite saturation horizon
12


has shoaled since the Pre-industrial Period (Chu et al., 2016). For example, in the
northeast Pacific (between 33.5°N and 50.0°N), the aragonite saturation horizon has
shoaled by 19.6 meters in 11 years (2001 - 2012), and at this rate, the whole water
column in this region's northern part is expected to become undersaturated within 50 90 years (Chu et al., 2016).
3.2 The importance of acclimation and adaptability in the face of fast change to
coral survival
Climate change has repercussions for ecosystems, some of which may be
transformational in terms of their influence on primary productivity, food web
dynamics, habitat building species, disease ecology, and a variety of other factors. The
recent fall in the number of warm-water coral reefs, on the other hand, demonstrates
the complicated yet fundamental ways in which marine ecosystems are altering as a

result of high rates of ocean warming and acidification. The ecological consequences
of fast global change for mesophotic coral reefs are less well recognized and
understood than for warm-water shallow reef systems. Threats to cold-water coral
reefs, on the other hand, are less well known and certainly entail a diverse
combination of local and global causes. The current rate of climate change is several
orders of magnitude faster than the fastest rates of environmental change experienced
over the previous million years or more during the ice age transition. This warrants
special attention since ice age transitions, even at slower rates of change, inflict
significant disturbance and alteration to the earth's ecosystem. Meanwhile, corals are
extremely sensitive to slight changes in temperature, light, and a variety of other
environmental factors, and they respond by detaching from the flagellate symbionts
that live in their tissues (i.e. is bleaching). Small temperature changes are slowing
growth and reproduction and increasing coral mortality in many parts of the world,
changes that are likely to result in populations and communities that are more resistant
to heat but have all the negative characteristics of populations and communities with
reduced genetic diversity disability (e.g. greater vulnerability to other factors such as
disease). The possibility that corals might exchange their symbionts for completely
13


unique forms within an ecological time frame, as proposed by the adaptive bleaching
hypothesis, is one of the ecological reactions. While some reefs have returned over the
last 30 years or more, many others have not. Regional variations in resilience are
connected with the presence or lack of other variables impacting the resilience of reefbuilding corals and other reef-associated species such as herbivores, macroscopic
cover, and coral recruitment rates (Baker et al., 2008). The resilience of reef-building
corals weakened by heat stress may be worsened by rising ocean acidification, thereby
limiting their capacity to grow, calcify, and recover. While it is difficult to discern
between the impacts of rising temperature and increased ocean acidification, both heat
stress and acidity have the potential to impair coral resistance to stress. This might
explain why stressors like tornadoes, which do not appear to have risen in frequency

over the last 30 years, appear to have a longer-lasting influence on coral ecosystems
on the Great Barrier Reef (De’Ath et al., 2012). Corals suffer physiological harm as a
result of mass bleaching because it limits the amount of energy available to them.
Warm water corals, for example, exude mucus rich in excess carbohydrates, which
feed a variety of mollusks, crabs, worms, ciliates, fish, and other species (Wild et al.,
2011). It does, however, serve a critical function in avoiding the colonization of
fouling and disease organisms. In addition, several studies have revealed the
intriguing behavior of multi-vesicle symbionts, in which coral-flawless relationships
include two or more distinct types of symbiotic diatom symbionts. the same
organization that may respond to environmental change by promoting the dominance
of certain symbionts over others. The evolution of multicellular symbionts, for
example, will ultimately harmonize with their environment, much as the expression of
different types of enzymes is regulated by an organism's surroundings. As a result, the
shift in dominance of one symbiotic group over another is a kind of physiological
adaptation and hence lacks the key quality of being vulnerable to ongoing change as
`the climate grows into undetermined "territory”. There are also more reasons why
changing the symbiotic structure of the flagellate coral association is unlikely to result
in the high rate of change in the thermal threshold required to keep up with climate
14


change. First, adaptation to heat stress is only one of the numerous causes, and no
evidence of adaptation to lower carbonate ion concentrations has been found yet.
Second, it would be exceedingly rare for the heat tolerance of reef-forming corals to
be dictated simply by the physiological performance of the bicellular symbionts, given
temperature, pH, and carbonate ion concentrations in coral hosts are expected to
impact many other processes. Third, the fact that the number of coral communities
appears to be declining contradicts the reverse, implying that corals are not getting
more tolerant than previously. Finally, any study of adaptation as a process must
recognize the difficulty of adapting to a continually changing environment. That is,

the environment does not change in a single step (from one environmental state to
another), but rather changes continually (and rapidly) as atmospheric carbon dioxide
accumulates in the atmosphere. This exerts enormous and persistent strain on coral
biomes, making comprehensive evolutionary progression in ecological time
impossible.

15


Prospects for coral reef recovery from disturbance
4.1 Natural recovery
Today, as human activities increase and economic activities accelerate, the threat to
the existence of coral reefs is growing. As a result, the rate at which coral reefs
recover will be determined by the kind and degree of the disturbance, as well as the
reef's community structure and composition. It is impossible to forecast how the reef
will recover from a disturbance and how long it will take. Several aspects, however,
can be recognized as vital for the natural regeneration of the reef:
4.1.1 The existence of disturbances (for example: pollution, sedimentation,
removal of keystone species)
If coral reefs suffer as a result of anthropogenic disturbances, their recovery will be
hampered. An inflow of nutrients in the form of untreated sewage, for example, might
result in an algal bloom that prevents light from reaching the coral. Without light,
coral development is slowed, compromising the coral's capacity to resist disturbance
and compete with other benthic creatures. If the nutrient persists, benthic macroalgae
growth may rise, allowing them to overgrow and suffocate the coral, resulting in a
shift in community composition.
4.1.2 Coral larvae influx from other reefs
The inflow of coral larvae that settle and develop is essential for the rehabilitation and
regeneration of damaged reef regions. The quantity of larvae that a damaged reef will
get is determined by its proximity to neighboring undisturbed reefs. If, for example,

the reef is isolated, larval intake may be restricted, resulting in slower rates of larval
settling and longer durations of recovery (Wilkinson et al., 1999). If, on the other hand,
the reef is part of a collection of reefs, such as the Great Barrier Reef, then recovery
will be controlled by other criteria such as the severity and area of the disturbance
rather than recruitment.

16


4.1.3 The magnitude of the disturbance
If the disturbance is only local, there is a better chance of larval input from nearby
reefs as well as unaffected areas of the damaged reef, resulting in a reasonably quick
recovery. If the damage is regional, other factors such as larval dispersion, the length
of time larvae remain competent to settle, and patterns of local extinction become
major drivers of how long it takes for a reef to recover to its pre-disturbed form.
4.1.4 The timing of the disturbance
Most corals reproduce sexually just once a year when the water temperature is near its
maximum. As a result, an inflow of larvae into the system happens just once a year. If
the disruption happens soon after this reproductive phase, it will take nearly a year for
prospective new recruits to settle. This may allow other benthic organisms that
reproduce more often to settle and occupy the substrate, restricting future coral
colonization. Furthermore, a disruption during this reproductive phase might result in
any corals failing to settle that year, further slowing recovery.
4.1.5 The community's species diversity
Fast-growing corals will swiftly expand into space produced by a disturbance if the
substrate condition allows. As a result, a community dominated by fast-growing corals
may be anticipated to recover from disturbance faster than one dominated by slowgrowing, persistent species. Local extinction of particular coral species
4.1.6 Some polyps survive in the colony
When corals bleach, only the polyps on the colony's top surfaces discharge their
zooxanthellae. This is due to the substantial effect that high light intensities play in

contributing to bleaching, as well as variances in the quantity of light absorbed by
polyps on the colony's top and bottom surfaces. If polyps on the colony's shaded
underside survive, they can renew and develop over the injured area, assisting in
healing.

17