Life in Water––#

LIFE IN WATER

1. Introduction
   
   
   1. Water covers 71% of the earth’s surface
      
   2. Also, by weight, living things consist primarily of water
      
   3. Thus, water is crucial to our understanding of life and ecology
      
   4. Here we will survey the water cycle and water ecosystems of the planet
      
      
2. Hydrologic cycle
   
   
   1. Reservoirs of water
      
      
      1. Oceans––97%
         
      2. Polar ice caps and glaciers––2%
         
      3. Freshwater environments––<1%
         
         
   2. Water shifts from one reservoir to another via the hydrologic cycle
      
      
      1. Movement
         
         
         1. Precipitation
            
         2. Evaporation
            
         3. Surface flow
            
         4. Subsurface flow
            
            
      2. Powered by solar energy
         
         
         
         1. Drives winds
            
         2. Causes evaporation
            
            
      3. Turnover times
         
         
         1. Turnover time––Time required for complete turnover of reservoir
            
         2. Vary widely
            
            
            1. Atmosphere––9 days
               
            2. River water––12-20 days
               
            3. Lakes–-Days to centuries
               
            4. Oceans––3,100 years
               
               
3. The oceans
   
   
   1. Oceans cover about 70% of the earth’s surface
      
   2. Three main oceans, all interconnected
      
      
      1. Pacific Ocean––the largest
         
      2. Atlantic Ocean
         
      3. Indian Ocean
         
         
   3. Each ocean is bordered by smaller seas
      
   4. Ocean depths
      
      
      1. Averages
         
         
         1. Pacific Ocean––More than 4000 m
            
         2. Atlantic and Indian oceans––3900 m
            
            
      2. Extremes
         
         
         1. Marianas Trench in the Pacific Ocean––over 10,000 m deep
            
         2. Mauna Loa
            
            
            1. Extends 4000 m above sea level
               
            2. Extends to 6000 m below sea level
               
               
   5. Ocean structure
      
      
      1. Horizontal zones
         
         
         1. Littoral (intertidal) zone
            
            
            1. Shallow, near-shore zone
               
            2. Experiences tides
               
               
         2. Neritic zone––Extends from littoral zone to edge of continental shelf
            
         3. Oceanic zone––Extends beyond continental shelf
            
            
      2. Vertical zones
         
         
         1. Epipelagic zone––0-200 m
            
         2. Mesopelagic zone––200-1000 m
            
         3. Bathypelagic zone––1000-4000 m
            
         4. Abyssal zone––4000-6000 m
            
         5. Hadal zone––Below 6000 m
            
            
      3. Habitats
         
         
         1. Pelagic––Open water of any depth
            
         2. Benthic––Ocean bottom at any depth
            
            
   6. Physical features of oceans
      
      
      1. Light
         
         
         1. Most sunlight––80%––is absorbed by the top 10 m of water, with most UV and infrared removed in the first few meters
            
         2. Longer wavelengths of light––toward the red end of the spectrum––are absorbed more readily than shorter wavelengths
            
         3. Thus, the ocean appears blue
            
         4. Very little light reaches below 50-100 m
            
            
      2. Temperature
         
         
         1. Sunlight warms the ocean surface water––less dense than the cooler, deeper water
            
         2. The less dense, warmer water floats on the cooler water
            
         3. The warm and cold water layers are separated by a thermocline, a zone of rapid temperature change
            
         4. Thermal stratification
            
            
            1. Stratification is a permanent feature of equatorial oceans
               
            2. Stratification is a summer phenomenon in temperate oceans
               
            3. Stratification not even occur in polar regions
               
               
         5. Water temperature ranges over the year
            
            
            1. Surface water
               
               
               1. Equator––1°C
                  
               2. Temperate waters––7°-9°C
                  
                  
            2. Deep water––Little change over the year
               
               
      3. Water movement
         
         
         1. The sea is restless
            
            
            1. Waves
               
               
               1. Created primarily by wind
                  
               2. Represent the flow of energy through water
                  
               3. Waves do not shift large amounts of water from place to place
                  
                  
            2. Surface-water currents
               
               
               1. Currents are also driven by wind
                  
               2. Circulation of surface waters in the form of gyres
                  
                  
                  1. Gyres veer right in the Northern Hemisphere
                     
                  2. Gyres veer left in the Southern Hemisphere
                     
                     
               3. Currents transport great quantities of surface water
                  
               4. Some currents, like the Gulf Stream, are responsible for influencing climate patterns
                  
                  
            3. Deep-water currents occur as water cools and drops, followed by movement along benthic surface
               
            4. Upwellings
               
               
               1. Occurs along the west coasts of continents
                  
               2. Off-shore winds blow warm water away from shore
                  
               3. This water is replaced by deeper, cooler water
                  
               4. The resultant circulation patterns bring nutrients to the surface, increasing productivity
                  
                  
   7. Chemical features of oceans
      
      
      1. Salinity
         
         
         1. Usually 34.0 - 36.5 g/kg of water in open ocean
            
         2. Can be as high as 40.0 g/kg water in the Red Sea
            
         3. Lowest near equator and above 40° N and S latitudes due to heavy precipitation
            
         4. Highest at about 30° N and S latitudes where there is little precipitation and high rates of evaporation
            
         5. Major contributors to salinity
            
            
            1. Sodium ion
               
            2. Chloride ion
               
            3. Magnesium ion
               
               
      2. Oxygen
         
         
         1. Concentration of dissolved oxygen is about 0.9% in surface seawater compared to 20% in air
            
         2. Oxygen levels diminish in deeper water
            
         3. Some very deep waters contain little or no oxygen
            
         4. Note that there are no gilled hometherms!
            
            
   8. Biological features of oceans
      
      
      1. Living things occur throughout the ocean waters, no matter how dark or poor in oxygen
         
      2. Oceanic food webs
         
         
         1. Phytoplankton, microscopic photosynthetic organisms, live primarily in the epipelagic (euphotic) zone
            
         2. These form the base of the food web for most sea creatures
            
         3. Zooplankton feed on the phytoplankton, thus forming the second tier of the oceanic food web
            
         4. Zooplankton, in turn, are fed upon by a huge variety of invertebrates and vertebrates
            
            
      3. Life around deep-sea vents
         
      4. Diversity of life
         
         
         1. Freshwater environments
            
            
            1. Contain 14 animal phyla
               
            2. None of these phyla are endemic
               
               
         2. Terrestrial environments
            
            
            1. Contain 11 animal phyla
               
            2. Only 1 of these phyla is endemic
               
            3. There is great terrestrial diversity within phyla
               
               
         3. Saltwater oceans
            
            
            1. Support 28 animal phyla
               
            2. 13 of these phyla are endemic
               
               
   9. Conservation issues
      
      
      1. Pollution
         
      2. Ozone holes
         
      3. Over-harvesting
         
         
4. Shallow marine waters
   
   
   1. Occur at edges of continents and borders of islands
      
   2. Water penetrated by large amounts of light––Lots of photosynthesis
      
   3. High primary productivity in these waters supports great biomass and biodiversity
      
   4. Kelp beds
      
      
      1. Kelp refers to various species of brown algae, which are protists
         
      2. Description
         
         
         1. Photosynthetic
            
         2. Very long stipes and blades
            
         3. Creates forest-like conditions––Kelp canopy up to 25 m above seafloor
            
         4. Holdfasts
            
            
      3. Habitat requirements
         
         
         1. Require plenty of light
            
         2. Temperature––From below 10°C - 20°C+
            
         3. Live in areas of ocean currents which bring in nutrients and wash away wastes
            
         4. Salinity––Varies quite widely
            
         5. Good oxygenation
            
            
   5. Coral reefs
      
      
      1. Also occur at edges of continents and borders of islands
         
      2. Are restricted to tropical areas
         
      3. Coral reefs exhibit the highest levels of productivity known on the planet
         
      4. Coral reefs also exhibit tremendous biodiversity
         
      5. Coral animals are members of Phylum Cnidaria
         
         
         1. Polyps
            
            
            1. Filter feeders
               
            2. Symbiotic algae (zooxanthellae)
               
               
               1. Live within cells of polyps
                  
               2. Provide nutrients to polyps
                  
                  
         2. Corals produce limy, calcium carbonate skeletons
            
         3. These skeletons remain in place even after the animals die
            
         4. New coral growth occurs over the old skeletons––Results in massive reef deposits over time
            
            
      6. Habitat requirements
         
         
         1. Warm salt water
            
            
            1. 18°C - 25°C
               
            2. Equatorial regions
               
               
         2. Stable salinities
            
         3. Good oxygenation
            
         4. Lots of light (for zooxanthellae)
            
         5. Currents for nutrient and waste transport
            
            
      7. Reef structure
         
         
         1. Fringing reefs––Along island rims
            
         2. Barrier reefs (following island subsidance)
            
            
            1. Offshore from island
               
            2. Lagoon between reef and island
               
               
         3. Atolls
            
            
            1. Form rings above total subsided islands
               
            2. Lagoon inside ring
               
               
      8. Human impact
         
         
         1. Exploited for organisms
            
            
            1. Harvesting of corals for decoration
               
            2. Netting, dynamiting, and poisoning to collect stunned tropical fish
               
               
         2. Silt from runoff due to agriculture and development cause coral polyps to die
            
            
   6. Intertidal zones
      
      
      1. Occur along coastlines throughout the world
         
      2. Different circumstances create conditions favorable for different ecological communities
         
         
         1. Exposed vs sheltered
            
         2. Rocky vs sandy
            
            
      3. Tides
         
         
         1. Local periodic rise and fall of the ocean
            
         2. Causes of tides
            
            
            1. Gravitational pull of sun and moon
               
            2. Highest tides occur when sun and moon are aligned––at full and new moons
               
            3. Tidal cycles preserved in the sediments
               
               
         3. Everything in the intertidal zone is affected by tidal fluctuations
            
            
      4. Structure
         
         
         1. Supratidal (splash) zone
            
            
            1. Organisms not immersed
               
            2. Often wetted by waves
               
               
         2. Upper intertidal zone––Covered by only the highest tides
            
         3. Middle intertidal zone––Covered and uncovered during average tides
            
         4. Lower intertidal zone––Uncovered only during lowest tides
            
         5. Subtidal zone––Below the lower intertidal zone
            
            
      5. Tidepools form at low tides
         
      6. Habitat conditions
         
         
         1. Light––High levels but fluctuating
            
         2. Temperature––Fluctuates greatly
            
         3. Water movements
            
            
            1. Waves
               
            2. Tides
               
            3. Currents
               
               
         4. Salinity––Varies greatly, especially in tidepools
            
         5. Oxygen––Levels generally quite high
            
            
      7. Organisms
         
         
         1. Rocky intertidal areas
            
            
            1. Sea stars
               
            2. Sea urchins
               
            3. Sea anemones
               
            4. Limpets
               
            5. Chitins
               
            6. Mussels
               
            7. Barnacles
               
            8. Crabs
               
            9. Some fish like sculpins
               
               
         2. Sandy intertidal areas––Fewer organisms
            
            
            1. Clams
               
            2. Marine worms
               
               
   7. Estuaries
      
      
      1. Occur where freshwater rivers join saltwater seas
         
      2. Estuaries experience tidal effects
         
      3. Habitat conditions
         
         
         1. Highly variable light and temperature
            
         2. River flow and tides play important roles
            
         3. Salinity varies greatly––Influenced by
            
            
            1. Distance from mouth of river
               
            2. Level of tide
               
               
         4. Oxygen variable
            
            
            1. High water movement
               
            2. High levels of decomposition
               
               
      4. Organisms
         
         
         1. Low biodiversity (unlike many other shallow marine habitats)
            
         2. High productivity
            
         3. Many young organisms
            
            
            1. Estuaries serve as nesting grounds
               
            2. Estuaries are of major importance to the health of commercial fisheries
               
               
      5. Human impact
         
         
   8. Salt marshes
      
      
      1. Transition zones between terrestrial and saltwater habitats where there are sandy shores
         
      2. Occur mainly in temperate latitudes
         
      3. Contain primary herbaceous vegetation––e.g., saltgrass and pickleweed
         
      4. Habitat conditions––Similar as for estuaries
         
      5. Highly productive
         
      6. Human impact
         
         
   9. Mangrove swamps
      
      
      1. Also transition zones between terrestrial and saltwater habitats where there are sandy shores
         
      2. Occurs mainly in tropical latitudes
         
      3. Contains mangrove trees of different species, distributed according to intertidal levels
         
      4. Human impact
         
         
5. Rivers and streams
   
   
   1. Account for part of the <1% of water that is freshwater on the earth’s surface
      
   2. Characterized by continuously flowing water
      
   3. Serve important roles in the hydrologic cycle by draining the world’s landscapes
      
   4. Rivers have played significant roles in the history of peoples, e.g.:
      
      
      1. Mississippi River
         
      2. Rhine River
         
      3. Nile River
         
         
   5. Rivers and streams may flow into
      
      
      1. Lakes/ponds
         
      2. Oceans
         
         
   6. Habitat conditions
      
      
      1. Variable light
         
         
         1. Water generally quite turbid––Lot’s of suspended material
            
         2. Shading by riparian vegetation may be considerable
            
            
      2. Variable temperature
         
         
         1. Temperature varies somewhat with air temperature
            
         2. Generally between 0°C and 30°C worldwide
            
            
      3. Variable salinity––Contain dissolved materials from terrestrial runoff
         
      4. Oxygen
         
         
         1. Generally quite high due to movement and mixing of water
            
         2. Oxygen levels are highest in the coldest waters
            
            
      5. Organisms
         
         
         1. Swimming––e.g., trout, salmon
            
         2. Benthic
            
            
            1. Generally with means to hold to substrate
               
            2. e.g., caddis fly larvae
               
               
         3. Sediment dwellers––Large numbers and high biodiversity
            
            
      6. Human impact
         
         
6. Lakes
   
   
   1. Collections of non-flowing (or only very slowly flowing) water
      
   2. Lakes form in basin areas created by
      
      
      1. Mountain building
         
      2. Volcanism
         
      3. Glaciation
         
         
   3. Our Great Lakes contain 20% of the earth’s freshwater
      
   4. Lake structure
      
      
      1. Horizontal zonation
         
         
         1. Littoral zone––Where aquatic plants grow in shallow water
            
         2. Limnetic zone––Open, deep water
            
            
      2. Vertical zonation
         
         
         1. Epilimnion
            
            
            1. Warm surface layer
               
            2. Light penetrates this level well
               
               
         2. Metalimnion (thermocline)
            
            
            1. Constitutes a narrow vertical zone
               
            2. Physical factors such as light and temperature change rapidly in the metalimnion
               
               
         3. Hypolimnion
            
            
            1. Cold
               
            2. Dark
               
               
      3. Habitat conditions
         
         
         1. Light varies according to
            
            
            1. Dissolved substances
               
            2. Productivity
               
            3. Depth
               
               
         2. Temperature
            
            
            1. Thermal stratification
               
               
               1. Tropical lakes are continuously thermally stratified
                  
               2. Temperate lakes are stratified in the summer
                  
                  
                  1. Fall and spring are turnover times driven by winds
                     
                  2. In winter, top of lake is colder than deeper water
                     
                     
            2. Water movement
               
               
               1. Inflow and outflow
                  
               2. Turnovers
                  
               3. Wind waves
                  
                  
            3. Salinity varies widely
               
               
               1. Generally very low––120 mg/liter
                  
               2. Can be very high––Great Salt Lake (200 g/liter)
                  
                  
            4. Oxygen
               
               
               1. Oligotrophic lakes
                  
                  
                  1. Low in nutrients
                     
                  2. Low productivity
                     
                  3. High in oxygen
                     
                  4. Lots of fish and other animals
                     
                     
               2. Eutrophic lakes
                  
                  
                  1. High in nutrients
                     
                  2. High productivity
                     
                  3. Low in oxygen (due to decomposition)
                     
                  4. Few fish and other animals
                     
                     
   5. Human impact
      
      
      1. Agricultural and sewage input––eutrophic lakes
         
      2. Dams
         
      3. Introduced species
         
      4. Thermal pollution
         
         
7. Conclusions
   
   
   1. Bodies of water are crucial to human well being
      
      
      1. They serve a sources of water for drinking, bathing, and irrigation
         
      2. They function as transportation pathways
         
      3. They act as moderators of climate
         
      4. They perform as CO₂ buffers
         
         
   2. Because water areas are vast and unsuitable habitats for human colonization, we have tended to overlook their importance
      
      
      1. We have dumped our sewage and chemical wastes into the waters
         
      2. We have dammed the rivers
         
      3. We have destroyed coastal salt marshes, estuaries, and coral reefs in exchange for luxury hotels and beach houses
         
         
   3. Thankfully, we are beginning to appreciate the natural bounty provided by water habitats and we are learning to protect them