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The open ocean - Coggle Diagram
The open ocean
Introduction
-Large sections of the mid oceanic environments are comparable with terrestrial desert environments, as nutrient levels are low, phytoplankton populations very small
and resulting food chains limited.
The conditions
include, amongst others:
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Marine food chains
-west coast experiences regular increases in nutrient supplies and subsequent phytoplankton blooms due to upwelling.
-Off the south coast, nutrient supplies may become restricted by the formation of a thermocline in summer.
-barrier between the warm surface layer and the deeper, nutrient-rich water limits the growth of significant phytoplankton populations to spring,
-east coast has smaller but relatively stable phytoplankton populations. owing to a constant supply of warm, relatively nutrient-poor water all year round.
Planktonic food webs
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-Zooplankton, including radiolarians, foraminifera's and copepods, drift with the
phytoplankton and feed on them.
All are fed on by larger carnivores such as krill, jellies, bluebottles and small fish.
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The Southern ocean
-experiences huge summer productivity, giving rise to
planktonic explosions of krill in particular.
-provide an abundant food supply for
many larger animals, including whales.
Many of these whales, especially the
Southern Right and Humpback whales ,migrate to the South African coastline in winter, to mate and give birth to their calves.
Pelagic fish
-Variable nutrient supplies around our coastline dictate the distribution of open ocean
pelagic fish.
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-generally higher nutrient content of water, at all times, in the
Benguela Current.
-Frequent summer upwelling events along the western shoreline, making the nutrient levels even higher and promoting phytoplankton blooms.
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pelagic schools now regularly extend as far as Mossel Bay and move even
further north during ‘sardine runs’, an annual event linked to the reproductive cycle of
sardines, during which they form massive school.
