Marine Ecosystems
Types of Marine Ecosystems
| More Articles on Wildlife: |
|
|
The types of marine ecosystems are: coastal waters (including
estuaries and lagoons), coral reefs, soft bottom continental
shelves, upwelling continental shelves, open oceans and
polar oceans.
Coastal waters - constitute the interface between
the marine and the freshwater environments, and between
the continents and the oceans.
Estuaries - are broad portions of rivers or streams
near their outlet, influenced by the marine water body
into which they flow. As such, estuaries are semi-enclosed
coastal bodies of brackish water with free connection
to the open sea. The demarcation between an estuary and
the sea is generally the mean tidal level.
Lagoons - similar to coastal ponds or lakes, are
shallow brackish water bodies with one or more restricted
outlets to the sea.
Estuaries and most lagoons receive water from land and
therefore can be heavily impacted by land-based sources
of pollution through inland runoffs. Coastal waters are
the main area of development for artisanal fisheries and
play a key role as nursery grounds for a wide range of
marine species as well as being the principle cause of
conflict between artisanal and industrial fisheries.
Coral reefs - are the dominant type of ecosystems
in tropical areas with low upwelling or freshwater inputs.
Coral reef ecosystems occur in areas where sunlight can
reach reef-building corals on solid surfaces and stable
sediments. They are fragile, vital for island countries,
richest in biodiversity and heavily impacted by inland
runoffs and inland activities (e.g. deforestation or inappropriate
agricultural practices). Coral reefs are particularly
sensitive to destructive fishing methods using explosives
and poisons. They are mainly used by artisanal fisheries.
Soft-bottom continental shelves - occur in front
of major river systems and deltas from which they receive
their characteristic fine sediments (e.g. gravel, sand
and mud). Extending up to a depth of 200 metres, they
are usually strongly influenced by the riverine effluents
from which they draw their high productivity and which
govern their natural variability. These ecosystems are
exploited with a variety of fishing methods and are particularly
suitable for bottom trawling. Artisanal fisheries are
generally restricted to the shallower areas of these shelves,
while semi-industrial and industrial fleets (with which
artisanal fisheries often conflict) can exploit both the
nearshore and offshore areas.
Upwelling continental shelves - are very productive
continental shelves found mostly at the eastern boundaries
of the oceans, often in front of arid zones or deserts.
The usually wind-driven, upwelling process brings cold,
nutrient-rich water from deep layers into the euphotic
zone where photosynthesis uses sunlight and the upwelled
nutrients to produce the organic matter that is the basis
of the marine food chain. These ecosystems are affected
by strong inter-annual variability (e.g. El Niño
and La Niña, off Peru-Chile). They represent areas
of especially high concentrations of small pelagic species
usually exploited by surface fisheries using purse seiners
and mid-water trawls.
Open oceans - represent the largest area and volume
of marine ecosystems, although their biological and fisheries
production per unit of area is far less than the other
ecosystems. The depth of open oceans varies from about
200m, where in theory the continental shelf ends and the
continental slope starts, to 11 500m in the deepest trenches.
Seamounts are noticeable elements of the open ocean ecosystem
and host some long-living and fragile deep-sea resources
(e.g. orange roughies) on which fisheries have recently
expanded - causing concern for the conservation of these
poorly-known ecosystems. Upper layers are exploited mainly
with wide opening midwater trawls (e.g. for horse mackerel)
and longlines (e.g. for tuna, billfishes and sharks).
Polar oceans - are particular, highly-productive
ecosystems with great seasonality, characterized by active,
current-driven, enrichment processes that sustain important
fishery resources (e.g. fish, krill, whales, small cetaceans)
and other species (e.g. seabirds, seals). |
|
|
