Productivity of coral reefs

Rehana Raj
DFK 1307
I Ph.D
College of Fisheries
Mangalore
jitenderanduat@gmail.com

Introduction
 Productivity- the rate at which new materials are
produced from their precursors by living things; new
tissues, offspring, carbohydrates that leak from a cell
 Productivity of an organism or population- rate at
which it turns resources into more of itself

 Productivity- represents the flux of nutrients from
environment into living organism
 Highly productive environment- organisms won’t
have to travel far to get sufficient food
 Less productive environment- have less food,
support fewer numbers of individual

 Productivity of an ecosystem- net primary
productivity
 The sum of all net production of all species of primary
producers
 Expressed as- dry wt of production in grams of
carbon/m.sq/yr (gm¯²y¯¹)

 Coral reefs- world’s most productive marine ecosystem
 Tiny symbiotic algae (zooxanthellae)-convert sunlight &
nutrients into fuel for coral growth & production
 Provide structural habitats for many different vertebrate
& invertebrates

 Productivity in coral reefs - complex function of light
capture, efficient nutrient recycling, hydrodynamic
process
 Unique mutualism between hermatypic corals &
photosynthetic zooxanthellae-driving force for
settlement, growth & productivity of coral reefs

 Photosynthesis by zooxanthellae- fix large amounts of
‘carbon’; passes on to the host polyp
 Mainly in the form of glycerol or glucose or alanine

 Metabolic products are used by the polyp
 Symbiotic relationship between corals &
zooxanthellae- tight recycling of nutrients back &
forth

Movement of molecules between
coral tissue & zooxanthellae

 Degree to which coral depends on zooxanthellae is
species specific
 Corals are more productive in shallow water bodies

 Major energy is received from sunlight
 Plants, algae & bacteria-capable of capturing the
energy & produce organic matter

 Organisms - Proximate source of energy
 Termed as primary producers

 Zooxanthellae -primary producers in corals
 Belong to the genus Symbiodinium
 Important algae is Symbiodinium microadriaticum

 Zooxanthellae occupies 1-10% of biomass of living
corals
 Density 1-5*10⁶ cells/cm² coral surface area
 Varies with depth and season

 Zooxanthellae translocate upto 90% of their fixed
carbon (C) directly to coral hosts
 Rate at which coral deposits new skeleton (the
calcification rate) – measures production

Products of zooxanthellae are transferred directly to the
coral tissues
Respired, stored or released into environments

 Corals also feeds on tiny other organisms by the mucus
produced by corals
 Prey ranges from zooplankton to even small fishes

 Productivity of coral reef depends on:
a. illumination
b. temperature conditions

 Shallow water coral ecosystem- most productive
ecosystem of the world
 Gross primary productivity-1-15gCm¯²day¯¹

 High level of production- symbiotic algae in reef
building corals & allied invertebrates
 Symbiotic algae accounts-50-70% of the total primary
production

 Excess production from reef- 3% of total primary
production
 <1% of total production is available as harvestable
form

Factors influencing rate of
photosynthesis by zooxanthellaea
 Chief determinants- light & temperature
 Photosynthesis quantified by-flux of O₂ & converted
into units of C
 Availability of light for photosynthesis by
zooxanthellae in corals varies & difficult to measure

 O₂ consumption in the light provides a measure of net
primary production
 Gross primary production-net O₂ production under
illumination & O₂ release by respiration in dark

 Coral growing areas show high primary productivity-
1500-3000gC/m²/yr
 Contributed by zooxanthellae, free living algae,
phytoplankters

 Mucus secreted by coral- due to wave action & grazing
of coral eating animals
 Another source of Carbon available to plankters

Functional groups of coral reefs
-Primary producers
-algae, other plankters
- Planktivores
- fishes & invertebrates, including corals
Predators
-piscivores, corallivores, invertebrate eaters
-Detritivores
-bioeroders – remove coral skeletons
- scrapers – remove algae and sediments
- grazers – remove macroalgae

Main algal groups & their roles in
coral reef ecosystem

Productivity & Diversity
High Productivity
Production (kg Carbon per m2 per year)
Average Oceanic areas 0.1 kg
Rainforest 2 kg
Kelp forest 2 kg
Coral Reef 1.5-5 kg
• high productivity possible because of tight recycling of
nutrients,
photosynthetic fixation of carbon (by corals and algae)
and nitrogen (by blue-green algae)

Coral reef fisheries
 High species diversity compared to temperate &
pelagic systems
 Tropical reef support high standing crop of fishes
 Highest richness of coral reef fisheries-Indo-West
Pacific especially Philippines-2177 species

 A yield of 9 million tonnes annually is possible world wide
 Fish catch with traps on reef vary between 1.37-20 tonnes/km
of coastline
 Production of fish in reefs varies from 25-50 kg*10¯⁴ m¯² y¯¹

Number of Fish species in several
coral reef areas
Geographical area Number of Fish Species
Philippine Islands 2177
New Guinea 1700
Great Barrier Reef 1500
Seychelles Islands 880
Marshall & Marina Islands 669
Bahama Islands 507
Hawaiian Islands 448

 Chaetodontids (butterfly fishes)- dominant species of
coral reef ecosystem
 Great Barrier reef ranks first (50 species)
 The Philippines ranks second
 Indonesia ranks third

Other major inhabitants of coral
ecosystem
 Sponges
 Polychaete worms
 Sea urchins
 Star fish
 Seabirds
 Sea snakes
 Green turtle
 Gastropods
 Giant clam
 White tip reef shark
 Banded coral shrimp
 Spiny lobsters
 Reef crabs
 Carribean reef squid

 More than 25,000 described species from 32 animal
phyla live in reef habitats
 4 times the number of animal phyla found in tropical
rain forests

 Play a crucial role as habitat & nursery grounds for 10-
20% of the world fishery
 Intimately connected to other marine communities
such as mangrove forest, sea grass beds & open seas

 Play significant role in the development of ecosystems-
mangrove & wetlands
 Protect coastline from wave action, erosion, property
damage & loss of life
 Provide livelihood for half a billion people from its
production

Productivity of coral reefs

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