Marine and Aquatic Ecosystems
Differences between aquatic/marine and terrestrial systems
 One hundred times more inhabitable space
 More stable temperature regime
 No water shortage, but light or nutrients may be limiting
 Primary producers are mostly microscopic and have quick turnover
 Most aquatic grazers are ectotherms and have low metabolic costs = large
relative population sizes
Marine and aquatic ecosystems
 Aquatic/marine ecosystems are influenced by local characteristics of climate,
soil, water chemistry and water depth and also by adjacent terrestrial
ecosystems
 Aquatic/marine systems are very productive
 There is less oxygen in water than in air
– Colder water can hold more oxygen
– Oxygen depletion can be an issues in warm areas
Aquatic habitats
 Life depends on oxygen availability
– Oxygen per liter is only 5% of that in the atmosphere
 Oxygen added by photosynthesis and aeration from the atmosphere
 Oxygen is removed by animal and detritivores respiration, and through
decaying organic matter
Zonation
 In both marine and aquatic systems, habitat is set up into zones
 Both have a photic zone (where light penetrates) and an aphotic zone (too
deep for light to penetrate)
– Depth of penetration varies with water clarity
Marine ecosystems
 Saltwater ecosystems cover vastly more total area and contain much greater
volume of water than all freshwater bodies combined
Ocean productivity
 Open ocean is not productive
 Upwelling and coastal areas are productive
Marine ecosystems
 Vertical stratification is an important aspect of many aquatic ecosystems
– Organisms tend to form distinctive vertical sub-communities
 Neritic – Coastal shallow waters over continental shelves
 Benthic - Bottom sub-community
– Low oxygen levels
 Pelagic - Water column
Neritic zone
 Coral Reefs - Accumulated calcareous skeletons of colonial organisms (coral)
– Depth limited by light penetration
– Among most endangered communities
Georges Banks
Intertidal region
 Part of the neritic zone that is exposed due to tides
 Also called littoral zone
 Rocky intertidal zones are well-studied
Mangroves
 Mangrove trees grow in salt water
– Occur along calm, shallow, tropical coastline
Other coastal habitats
 Barrier Islands - Low, narrow, sandy islands that form offshore from a coastline
– Protect inland shores from surf
– Prized for human development
 Loss of vegetation triggers erosion
Estuaries
 Estuaries - Bays or semi-enclosed bodies of brackish water that form where
rivers enter the ocean
 Important for fish and shellfish reproduction
Pelagic zone
 Consists mostly of plankton
– Small animals, algae, bacteria, etc.
– Photosynthetic plankton account for 40% of all photosynthesis on earth
– Photosynthetic plankton live in top 100 m of ocean where light penetrates
 Nekton are larger organisms
Nekton
Benthic zone
 Benthic zone in coastal areas
 Benthic zone in open ocean is a stressful environment
– Rely on food scraps from world above
– Seasonless, 2-5˚C, pressure of 400-500 atms
– Some are chemoautotrophic –hydrothermal vents with sulfur oxidizing
bacteria
Freshwater habitats
 Strongly connected to terrestrial systems
 Large amount of material enters water from surrounding land
 Small water bodies are ponds (shallow enough for rooted vegetation
throughout), larger water bodies are lakes – but line between them is not
definitive
Freshwater ecosystems
 Lakes
– Non-flowing water
– Freshwater lakes have distinct vertical zones separated by temperature
 Rivers
– Flowing water
Lakes
 Lakes have three zones that depend on depth and distance from shore
– Littoral zone
– Limnetic zone
– Profundal zone
Lake stratification
 Lakes form layers in summer due to temperature differences and lack of
circulation
– Water is most dense at 4˚C and least dense at 0˚C
 These two zones are called the epilimnion (warmer surface water) and the
hypolimnion (colder deep water)
 The thermocline, an abrupt change in temperature, separates these two layers


Nutrients accumulate in hypolimnion
Thermal stratification tends to cut off the oxygen supply to bottom waters
leading to anoxia in oxygen depleted waters
Turnover
 Turnover mixes these two stagnant layers
Lake productivity
 Lakes can be classified based on their levels of productivity
– Eutrophic – lots of nutrients and organic matter
– Oligotrophic – nutrients and organic matter are scarce
Plant nutrients and cultural eutrophication

Eutrophication - Process of increasing nutrient levels and biological
productivity
– Some amount of eutrophication is normal
 Cultural eutrophication - Increase in biological productivity and ecosystem
succession caused by human activities
Eutrophication
Eutrophication
Wetlands
 Land surface is saturated or covered with water at least part of the year
– Swamps, bogs, marshes, etc.
 One of most productive ecosystems on earth
 Trap and filter water - “nature’s kidney’s”
 Provide flood control
Wetlands