Reproduction corals

1. REPRODUCTION AND LARVAL SETTLEMENT OF CORAL
VIJAYKUMAR, M.E,
DFK – 1304
I PhD, Dept. of FRM
College of Fisheries, Mangalore-02

2. Overview
 Reproduction
 Types of reproduction
 Asexual
 Sexual
 Dispersal
 Settlement

3. PURPOSE OF REPRODUCTION
 To make sure a species can continue.
 Definition: Reproduction is the process by which an
organism produces others of its same kind.
TYPES OF REPRODUCTION
1. Asexual
2. Sexual
Corals can reproduce either asexually by budding or sexually
by releasing gametes (eggs and sperm).

4. ASEXUAL REPRODUCTION
 A new organism (sometimes more than one) is
produced from one organism.
 The offspring will have hereditary material uniform
with the hereditary material of the parent organism.
This means they will be genetically alike.

5. TYPES OF ASEXUAL REPRODUCTION
 Budding
 Regeneration
 Fragmentation

6. BUDDING
 Process by which a new, duplicate plant or animal begins to form at the side
of the parent and enlarges until an individual is created.
 Very common in plants;
 The coral colony expands in size by budding.
 Budding may be intratentacular, in which the new bud forms from the
oral discs of the old polyp, as in Diploria, or extratentacular in which the
new polyp forms from the base of the old polyp, as in Montastraea
cavernosa.

7.  In this form of asexual reproduction, new polyps bud off from
parent polyps to expand or begin new colonies.
 This occurs when the parent polyp reaches a certain size and
divides.
 This process continues throughout the animal's life and
produces polyps that are genetically identical to the parent
polyp

9. REGENERATION
 The ability to restore lost or damaged tissues, organs or limbs.
 It is a common feature in invertebrates, like worms and starfish.

10. FRAGMENTATION
 Corals can also reproduce asexually by fragmentation – that is, when
a portion of the colony (say, a branch), is detached from the rest and
falls in suitable substrate.
This can happen either - naturally,
- wave action
- humans purposely take coral
fragments and place them in other substrate areas
 For instance, if a portion of a larger colony is broken off from the main
colony during a storm or boat grounding, the separated individuals can start
new coral colonies that are genetically identical to the parent colony.
 However, the success of the fragments in establishing a new colony is
dependent upon whether they are exposed to favorable growth conditions.
 For instance, fragments exposed to strong wave action will find it difficult to
settle on a substrate for continued growth.

11.  Broken pieces of corals that land on a suitable substrate may
begin growing and produce a new colony.
 This type of reproduction is common in branching corals like
Acropora cervicornis in which a positive correlation was found
between fragment size and survival.

12. ACCIDENTAL FRAGMENTATION
Turtle Damage

13. ACCIDENTAL
FRAGMENTATION
Wave Damage

14. SEXUAL REPRODUCTION
 Requires two sex cells – egg and sperm
TYPES OF SEXUAL REPRODUCTION
 Broadcast spawning
 Brooding
Gametes (eggs and sperm) develop within the mesenteries of the coral
polyps. These reproductive cells are found on
the mesentery membranes that radiate inward from the layer of tissue
that lines the stomach cavity.
Mature gametes are fertilized either internally or externally, leading to
differences in the location of the subsequent embryonic development
of the planula.

15.  About three-quarters of all stony coral species are broadcast
spawners.
 produce male and/or female gametes that are released into the
water column in massive numbers, enabling them to distribute
their offspring over a broad geographic area.
 The gametes are positively buoyant and float towards the
surface before the eggs and sperm join to form free-floating
larvae called planulae.
 An individual planula floats in the water column until it finds a
suitable space to call home - usually a hard surface to which it
can attach.
Broadcast Spawning

16.  Large numbers of planulae are produced to compensate for the
many hazards, such as predators, that they encounter as they are
carried by water currents.
 The time between planula formation and settlement is a period
of exceptionally high mortality for coral larvae

17. Broadcast spawner

19.  Along many reefs, coral spawning occurs as a synchronized event, when
many coral species in an area release their eggs and sperm at about the same
time.
 The timing of a broadcast spawning event is very important because male
and female corals cannot move to make reproductive contact with each other.
 Because colonies may be separated by wide distances, the release of sperm
and eggs must be precisely timed, and usually occurs in response to multiple
environmental cues.

20.  There are both long-term and short-term controls that affect the timing of
spawning events.
 The long-term control of spawning may be related to temperature, day length,
or rate of temperature change.
 The short-term control is usually based on lunar cues. The final release, or
spawn, is usually based on the time of sunset.
 Broadcast spawning coral species may spawn on only one or a few nights each
year, and though different species may spawn at different times, the spawning
events for any given species happen at the same time.

21. This close-up photo shows rows of
individual brain coral polyps in
different stages of releasing their
eggs.

22.  Whereas three quarters of stony corals are broadcast spawners, the remaining
quarter of coral species are brooders.
 Brooding species generally have high success in recruiting new larvae into
established colonies, but many of these species reach only small colony size
and thus do not contribute much to the overall growth of a reef.
 In this reproduction mode, only male gametes are released into the water
column.
 The male gametes are negatively buoyant and are transported by waves and
current before sinking to the ocean floor.
 If encountered, the male gametes are then taken in by female coral polyps
containing egg cells.
Brooding
Brooding involves internal fertilization, and the development of the planulae
takes place inside the 'parental' polyp before release into the water, a process
known as planulation.

23.  Fertilization occurs inside the female coral and produces a small planula.
 This planula is released later through the mouth of the female coral at an
advanced stage of development so that it is capable of settling onto hard
substrate very soon after its release.
 Thus, brooding species generally disperse their larvae shorter distances from
the mother colony than broadcasters
planula in polyp
Pocillopora damicornis,
a brooder

24. zygote
Sexual Reproduction
planula
larvae
egg
sperm

26. Environmental Stresses Yielding Lower recruits in Corals
• Turbidity & sedimentation
• High temperature
• Low salinity
• Aerial exposure at low tide
• Mechanical damage
• Intraspecific competition
• Oil & fuel oil pollution
• Eutrophication

27. Cleavage - two cell stage
Fertilized egg

28. Early Blastula
Cleavage-four cell stage

29.  Dispersal is primarily by tiny planktonic larvae called planulae produced in
large numbers to compensate for the hazards of passive transportation in
water currents.
 Corals, similar to many benthic animals, reproduce via a larval stage,
which undergoes a dispersal period in the plankton before attaching
to the reef and growing to establish a new colony (recruitment to the
population).
Dispersal

30. Settlement rates and subsequent recruitment are a measure of
reproductive success and it has long been known that variation in
settlement rates is a key determinate in the understanding of how
the abundance and diversity of corals vary in space and time.
With increasing disturbances to coral reefs, both directly through anthropogenic
activities, and indirectly via effects associated with climate change, an
understanding of coral settlement and recruitment rates and the influence of
disturbance on this critical stage of the life cycle of these animals is essential.
However, if larval supply is limited, or conditions are not optimal for coral larval
settlement and new recruit growth, then algae and other invertebrates out-compete
corals and take over these spaces.
Successful larval settlement and recruitment of corals is therefore critical to the
resilience and recovery of coral reefs.
Settlement