Page 26 - The World About Us

Spot the blenny
1.1.1
2.1.5

How are nutrients recycled within coral reefs?

As we have already seen, coral likes
solar energy as sunlight
solar energy as sunlight fig.XX Nutrient cycling in coral reefs.
to live in clear and clean waters. Too
much sediment, for example at river phytoplankton nutrient transfer
mouths, will kill off the polyps by along food chains
covering them with a layer of silt. Too zooplankton
much ammonia or nitrites in the sea
water is toxic to coral, while too many fish, coral, invertebrates phytoplankton
nitrates allow algae to grow faster than photosynthesis waste containing
by zooxanthellae
coral. This algae can kill the coral as it nitrogen
grows over the surface of the reef.
aerobic bacteria
This is why healthy coral reefs are
not found where there are large
amounts of human sewage deposited Algae
in the sea. Nitrogen
& energy
upwelling of nutrients
Coral from the ocean floor
fig.69 Nutrient cycling in coral reef ecosystems.
are passed directly to the algae which Phytoplankton is then eaten by, o en
use it to build their own ssues. microscopic, zooplankton. This
plankton can be consumed by other
Meanwhile, the Zooxanthellae
creatures, including corals.
algae photosynthesise, turning energy
from the Sun into sugars. Some of these Some zooplankton act as detrivores
sugars are passed onto the coral within the tropic structure of the reef.
fig.70 Coral is given its colour by algae. polyps. The advantage of this These live off dead and decaying
rela onship is that nutrients can be ma er, thus recycling nutrients within
Coral needs nutrient-poor water in
passed back and forth between coral the ecosystem. The ammonia excreted
order to thrive. So in these nutrient-
poor waters, how does coral survive? and algae, without the risk of them by fish is converted first into nitrites,
The answer lies in the symbio c being lost to the vast oceans. and then nitrates, by nitrifying bacteria.
rela onship between the polyp and The corals are also gaining energy These bacteria keep the sea water
chemically-clean for fish and corals, as
the Zooxanthellae algae. The coral and nutrients by catching plankton in
well as providing a food source for
collects floa ng zooplankton and their tentacles. Phytoplankton are the
phytoplankton from the waters. The primary producers of carbohydrates, zooplankton and other animals.
waste products, especially the nitrogen, converted from sunlight, in the ocean. The cycling and recycling of
nutrients and energy within a reef
fig.71 Colonies of coral polyps are the building blocks for coral reefs.
system is highly complex. Beds of sea
grass and the mangrove swamps along
shorelines, help remove lots of
dissolved nutrients from the water.
These areas also provide nursery zones
for many juvenile reef fish.

As fish, crustaceans and other
marine life move onto the reef from
the mangroves, they transfer nutrients
in their bodies. Edible detritus from
these creatures, as well as that being
brought up from the ocean floor on
ocean currents, can be eaten by the
coral.
This cycling helps to keep the en re
ecosystem of the reef, mangrove and
sea grass beds in balance.

26

Biodiverse ecosystems are under threat from human activity.