1 l INTRODUCTION TO CORAL REEF

ECOSYSTEM

CORAL REEFS
LEARNING PACKET 1
BACHELOR OF SCIENCE IN MARINE BIOLOGY

Prepared by:

MA. LUNINGNING L. AMPARADO

 1 l INTRODUCTION TO CORAL REEF
ECOSYSTEM

PREFACE

This learning packet deals with the biological and physical interactions that
govern the functional mechanisms of coral reef ecosystem. This learning packet
comprises of discussions on the biology and ecology of corals. It comprises of
evaluations and task for students to understand the role and importance of coral and
coral reef ecosystem.
 1 l INTRODUCTION TO CORAL REEF
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UNIT 1: INTRODUCTION TO CORAL REEF

ECOSYSTEM
1.0 Learning Objectives

a. Identify taxonomically the different coral species (hard and soft corals).
b. Characterize the ecological adaptations of hard and soft corals.
c. Describe the morphology of coral.
d. Explain how corals reproduce.
e. Discuss coral reef distribution.
f. Discuss the reef zonation and biological interaction (invertebrates, vertebrates
and marine plants) in each zone.
g. Create models on the different types of reef formation.
h. Assess the status of corals in the intertidal zone of Punta de Jesus.

Introduction

Coral reefs are important ocean habitats and offer a compelling case of
the risks of climate change. Reefs provide a large fraction of
Earth’s biodiversity—they have been called “the rain forests of the
seas.” Scientists estimate that 25 percent of all marine species live in
and around coral reefs, making them one of the
most diverse habitats in the world. But warmer temperatures brought
by climate change causes a negative impact on corals and coral reef communities by
prompting coral bleaching events and altering ocean chemistry. This subject MarBio 8
Coral Reefs discuss on the biology and ecology of coral communities, that will lead to
understand reef management and conservation.

1.1. Coral biology

Corals

Although they are often mistaken for plants or rock, corals are simple animals,
belonging to a group of invertebrates (spineless animals) called cnidarians. Anemones,
hydroids and jellyfish are also cnidarians. All cnidarians are characterized by a large
stomach cavity and specialized stinging cells called cnidocytes, which they use to
capture prey.

Polyps are the actual coral animals. Thousands of these animals cover one coral branch
or mound. A polyp has a small cylindrical body, with an opening or mouth encircled
by numerous stinging tentacles.
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Corals often grow into huge coral colonies or coral heads. Each coral head can be made
up of hundreds or thousands of individual polyps, which are all linked to their
neighbors by connective tissue — including their stomach.

1.1.1. Hard and Soft Corals

Hard corals, like elkhorn coral and staghorn coral, grow in colonies and are often
referred to as “reef-building corals.” Hard corals have hard, calcium-based skeletons,
a hard substance that eventually becomes rock. Most hard corals -- also called stony
corals -- consist of numerous single polyps living together in colonies. A single polyp
consists of a sea-anemone like organism that secretes the calcium-based structure of
the colony's skeleton. If you look very closely at the polyp, all hard corals' polyps have
rings of six smooth tentacles. Hard corals provide the majority of structure on coral
reefs, with their dead skeletons becoming the anchors for other corals, including both
hard and soft coral.

Genus Acropora

Acropora cervicornis Acropora cytherea

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Genus Isopora

Isopora palifera Isopora crateriformis

Genus Lobophyllia Genus Fungia

Lobophyllia hemprichii Fungia fungites

Photo taken form Google.com

Soft corals, like sea fingers and sea whips, are soft and bendable and often resemble
plants or trees. These corals do not have stony skeletons and are non-reef-building
corals—instead, they grow wood-like cores and fleshy rinds for protection. Like hard
corals, they tend to live in colonies.

Soft corals' chief difference from hard corals is structural. While hard corals secrete
calcium-based skeletons, soft corals do not. Instead, soft corals contain structures
within their tissues called spiracles that support their bodies. Additionally, soft corals
have eight fuzzy tentacles for feeding. Aquarium hobbyists often consider zoanthids
to be soft corals. While a biologist would consider zoanthids a type of sea anemone,
for aquarium purposes, their care is identical to true soft corals.
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Nicella sp. (Sea fan) Acanthogorgia sp. (Sea fan)

Dendronephthya hemprichi Sarcophyton glaucum

Photo taken form Google.com

1.1.2. Structure of Corals

Photo taken from coast.noaa.gov

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1.1.3. Reproduction of Corals

Corals can reproduce either asexually or sexually. In fact, most reef-building corals use
both reproduction strategies.

Corals reproduce asexually by either budding or fragmentation. Through budding, new

polyps “bud” off from parent polyps to form new colonies after the parent polyp
reaches a certain size and divides. This produces polyps that are genetically identical to
the parent and continues throughout the coral’s life. In fragmentation, an entire colony
(rather than just a polyp) branches off to form a new colony. This may happen, for
example, if a larger colony is broken off from the main colony. However, the
fragmented colony needs optimal conditions to settle on a substrate and grow.
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In terms of sexual reproduction, coral larvae are either fertilized within the body of a
polyp or in the water, through a process called spawning. In some areas, mass coral
spawning events occur one specific night per year, determined by environmental
cues, such as temperature, day length, and lunar cycles. The corals have to coordinate
both within its species and amongst other species so that hybridization is limited. This
broadcast spawning is an adaptation to the corals’ sedentary lifestyle since corals
cannot move to make contact with one another and may separated by large distances.

Once in the water, larvae ‘swim’ to the ocean surface. If they are not eaten, they
eventually settle to the ocean floor and attach to a hard surface. Once attached, they
metamorphose into a coral polyp and begin to grow, dividing in half. As more and
more polyps are added, a coral colony develops and eventually begins to reproduce.

Some coral species, such as Brain and Star coral, produce both sperm and eggs at the
same time. For other corals, such as Elkhorn and Boulder corals, all of the polyps in a
single colony produce only sperm and all of the polyps in another colony produce
only eggs.

Coral polyp releases gametes

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seaweeds, reed fishes, other invertebrates and vertebrates)

The intertidal zone is where the land meets the ocean, and includes beaches,
mangroves, lagoons and areas where fresh water meets salt water. Beaches are
important for coral reefs, as they filter out runoff and sediments from the land. Much
of the sand on beaches is produced from the natural breakdown of coral fragments.
Mangroves are highly adapted plants that thrive in intertidal waters. They are also
extremely important for coral reefs, filtering mud and sediments from the land, and
acting as nurseries for juvenile reef species. A recent study documented that up to 26
times more fish can be found on reefs near intact mangroves than reefs far from
mangroves.

Lagoons are areas of deeper water (3-10 meters deep) that separate reefs from the coast.
They are generally filled with sand, seagrasses and patch reefs, and are home to a
diverse group of plants and animals. Seagrasses provide habitat and nursery grounds
for many marine animals, and help stabilize the sand and substrate.

The reef flat is the shallow platform that extends outwards from the shore (1 to 2 meters
deep and up to hundreds of meters wide). Exposure to harsh physical conditions limits
coral growth, giving way to sand, rubble and encrusting algae. Many small
invertebrates are found in the reef flat, including mollusks, worms and crustaceans. The
back reef is located where the lagoon rises up towards the shallow waters of the reef
flat.

The back reef gets a lot of sun exposure with generally calm conditions, and is
characterized by a mixture of intricate coral gardens and sandy patches.
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The reef crest or algal ridge is the highest point of the reef facing the ocean, and is
characterized by a line of waves that break along the edge. Often exposed at high tide,
the reef crest ranges from 1-50 meters wide. Constant wave action and exposure limits
coral growth, but some branching corals have adapted to this environment. Coralline
algae dominates (hence the name “algal ridge”), and small crabs, shrimps and cowries
can be found seeking shelter in the nooks and crevices.

The fore reef or reef front is on the seaward side of the reef crest, where the reef slope
falls steeply towards the seabed. Conditions change greatly with depth.

Between 10-20 meters is the greatest diversity and abundance of life on the reef. Massive
corals prevail, and extensive spur and groove formations — sections of a reef found
seaward from the reef flat and made of high ridges of corals (spurs) that are separated
by sandy bottom channels (grooves) — often develop in the buttress zone (the zone of
deep channels separated by high ridges or buttresses). Many animals inhabit the holes
and crevices, and large fish, including sharks, jacks, barracudas and tunas patrol the
buttress zone in search of food.

1.1.4. Structure of Coral Reefs

Scientists generally divide coral reefs into five main classes: fringing, barrier, atolls,
bank or platform, and patch reefs.

Fringing reefs lie around islands and continents, and are separated from the shore by
narrow, shallow lagoons. They usually parallel the coastline and at their shallowest
point can reach the water’s surface.

 It lies close to the shore.

 The reef may extend to a distance of 200 metres from the shore into the sea. Its
active growing region is called reef front.
 It is facing the sea.
 The narrow shallow water channel between shore and reef is called reef flat.
 This reef is largely composed of calcium carbonate, sand, dead, and living coral
colonies and other organisms.
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Barrier reefs also grow parallel to the coastline, but are separated by deep, wide
lagoons. At their shallowest point, they can reach the water’s surface, forming a
“barrier” to navigation. The Great Barrier Reef in Australia is the most famous example,
and is the largest barrier reef in the world.

 This type of coral reef is located some distance from the shore.
 The reef front is facing the sea.
 The reef and shore are separated by a deep stretch of water called lagoon. This
lagoon is suitable for navigation.
 The best example for barrier reef is "Great barrier reef of north eastern Australia.
 It is 15 to 250 km away from shore. It extends up to 2000 km in length

Atolls are rings of coral that create protected lagoons and are often located in the middle
of the sea. Atolls usually form when islands surrounded by fringing reefs sink into the
sea or the sea level rises around them (they are often the tops of underwater volcanoes).
The fringing reefs continue to grow and eventually form circles with lagoons inside.
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 It is also called coral island.

 It is a ring like or horse-shoe shaped reef that encircles a lagoon.
 The lagoon is very deep and is suitable for navigation.
 The ring like reef may be broken by a number of channels.
 This is called atoll.
 The biggest Atoll in the world is seen in the form of Suva diva of Maldives.

Bank or platform reefs are open ocean reefs that are simple structures with many
different origins, yet no clear attachment to the coastline. Most of these reefs have an
area that is exposed to wind and a sheltered side where lagoons and small reef patches
can be found. Larger and slightly submerged reefs of this type are also called shoals.

Patch reefs are small areas of reef that occur in shallow waters and lagoons.

Reef zonation (reef flat, crest, slope) and component of coral reef (seagrass bed,

Environmental Conditions Necessary for a Healthy Coral Reef

Abundant Sunlight
Reef-building corals cannot survive without sunlight, since zooxanthellae, their
symbiotic algae, require sunlight for photosynthesis. The majority of zooxanthellae
reef-building corals do not grow below 45m (150ft).

Warm Temperatures
Corals can only live within a narrow temperature range from around 16°C - 29°C (62°F
- 85°F). This explains why corals thrive in the warmer waters of the tropics.

Low Nutrient Levels

Corals are adapted to live in ocean water, which contains very low levels of nutrients.
Nutrients, which are needed by all living organisms, are found in food and dissolved
in water. Too many nutrients can upset the natural balance of life on the reef, creating
conditions that favor other fast growing organisms such as marine plants and sponges.

Clear Sediment-Free
Water Corals prefer clear water with low levels of sediments (small particles of earth,
rock and sand). Sediments can bury corals, blocking out needed sunlight and killing
them. Corals tend to live in areas with some wave action as this helps supply them with
food and oxygen as well as keeping corals free of sediment.
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Salty Water
Corals are marine animals adapted to live in seawater with a salinity of around 35 parts
per thousand. In areas that are too salty, or not salty enough, corals cannot survive.

Hard Substrate
Corals need a hard substrate or surface to attach to and cannot successfully colonize
loose substrates such as rubble or sand. If the substrate is unstable, young coral colonies
will be crushed and killed by wave action and storms.
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Acknowledgement

Disclaimer: all images was downloaded from google.com.