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CHAPTER 3. LIFE IN WATER. Hydrological Cycle. Over 71% of the earth’s surface is covered with water. Oceans contain over 97% of the water in the biosphere, less than 1% is fresh water. Hydrological Cycle: process of exchange water among various “reservoirs”.
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CHAPTER 3 LIFE IN WATER
Hydrological Cycle • Over 71% of the earth’s surface is covered with water. Oceans contain over 97% of the water in the biosphere, less than 1% is fresh water. • Hydrological Cycle: process of exchange water among various “reservoirs”. • The hydrological cycle is solar driven, with different turnover time for various reservoirs. • Turnover time: Time require for the entire volume of particular reservoirs to be renewed. Size, rates effect Turnover. • Turns over time for atmosphere is about 9 days, renewal time for river water 12 to 20 days, Oceans 3,100 years.
Natural History of aquatic environment • Biology of aquatic environments corresponds broadly to variations in physical factors such as light, temperature, water movement, and chemical factors such as salinity and oxygen. • World oceans covers over 360 million km² and consists of one continuous interconnected mass of water. • Three major ocean basins: Pacific, Atlantic and Indian. Each with several smaller seas along its margins. • Depth of Pacific (Average 4,000 m), Atlantic and Indian (Average 3,900 m). Marianas trench at Pacific (10,000 m), deepest than Mount Everest more than 2 km. • Oceans are divided into vertical and horizontal zones.
Physical Conditions • Light • Approximately 80% of solar energy is absorbed in the first 10 m. • Within the visible range, red, orange, yellow and green are absorbed, while blue wave most likely to scattered, thus color of the sea is blue. • Within 10 m different color is seen, while below 50 to 60 m it is blue color. • Light penetration (see fig.3.6). • Temperature • Sunlight absorbed by water increase kinetic state, or velocity of motion. • Thermocline: a layer of water through which temperature change rapidly. • Thermal stratification: Layering of waters column by temperature. • Lowest temperature -1.5°C around the Antarctic, the highest average surface temperature a bit over 27°C near the equator. • Maximum annual variation in surface temperature approximately 7 to 9°C . • The greatest stability just 100 m depth is less 1°C.
Water movement • Current transport nutrients, oxygen, and heat. • Formation of circulation systems called “gyers” in which wind-driven surface currents. • Circulation system move to right in the Northern Hemisphere, while left in the Southern Hemisphere (Fig 3.5). • Deep water may also moves to the surface in a process called “Upwelling”. • Different density and movement effect behavior and distribution of marine organisms. • Salinity • Salinity: amount of salt dissolved in water. • Salinity varies from 34‰ to 36.5 ‰, with highest in subtropical 20 to 30 N and S altitude. • The relative proportions of major ions Na, Mg and Cl are approximately constant.
Oxygen • Oxygen present in water with various concentation. • 1 Liter of sea water approximately contains a maximum of about 9 ml, comparing to 200 ml in 1 L of air. • Typically oxygen concentration is highest near surface and decrease progressively with depth. • The minimum oxygen concentration is found at 1,000 m. • Biology • Photosynthetic organisms (Phytoplankton) found in euphotic zone. • Zooplankton:small animals drifting with sea current. • Chemosynthetic organisms in deep sea around thermal vents. • Oceans consist the highest animal phyla especially endemic one.
Life in Shallow Marine Water: Kelp Forests and Coral Garden • Shallow waters along the continents and around islands support high marine diversity and biomass. • At temperate latitude and over a solid bottom brown seaweed(Kelp). • Kelp structure(canopy, stems or stipes, and holdfasts) (fig 3.14) • At the equator coral reefs confined between 30° N and S latitude. • Categories of coral reefs : Fringing reefs, Barrier reefs, and atolls. (Fig 3.13). • Distinctive habitats associated with coral reefs including: • reef crest: Corals grow in the surge zone created by waves coming from the open sea, and extend to a depth of about 15 m. • Buttress zone: Coral formation alternate with sand-bottomed canyons. • Lagoon : found behind the reef crest that contains numerous small coral reefs called patch reefs and sea grass beds. • Sea grass : plants found at the bottom of shallow waters.
Physical conditions • Sufficient light penetration is needed for seaweed and reef-building coral. Depth of penetration from few meters to 100m. • Temperature limits the distribution of both kelp and coral. • Kelp : below 10°C in winter and rise above 20°C in summer. • Coral : above 18°C to 20°C (average 23-25°C), sensitive to higher temp, and lethal above 29°C. • Water moves continuously within the coral reefs and kelp by oceanic currents. • Biological productivity of coral and kelp depend on the flushing action of currents. • Corals and kelp depend on flushing action of the current. • Hurricanes could detached current or kelp from their locations, which may effect their long-term survival.
Conditions • Corals grow only in fairly stable salinity, heavy rains or runoff from river reduce salinity below 27% can be lethal. • Kelps forest appears more tolerance to freshwater runoff near shore. • Coral reefs and kelp beds found where water is well oxygenated. • Coral reefs are effected by predatory crownof-thorn sea star, which eat corals. • Algae population compete for space with coral and kelp. • Coral species compete among themselves for space. • High species diversity of corals (over 600) that support tremendous species of marine organisms and fishes. • Human influence and practices on coral reefs ????.
Marine Shores: Life between high and low tides • The shores are most dynamic environments (tides, waves, light, splashes, erosion, depositions… ect). • Intertidal zone: area covered by waves at high tide and exposed to air at low tides. • Intertidal zone can be divided into several vertical zones (Supratidal fringe or splash zone, upper intertidal zone, middle, lower, and subtidal) Fig. 3.17. • Intertidal zone exposed to air temperature, especially supratidal and upper, thus extremes temperatures(0-40 °C) effect organisms living in tide pools. • Most two water movements effecting organisms are : • Semidiurnal (two high tides each day) • Diurnal (Single high and low tide each day) • Spring tides (High tide at full moon) • Neap tides (High tide when moon and sun aligned ) • Organisms effected by exposed frequently to air, currents, splashes.
Conditions • Salinity is varied especially at isolated pools within intertidal zone. • Oxygen does not generally limit the distribution of organisms because: • Organisms exposed to air at low tide. • Waves mixes oxygen thoroughly. • Interstatial water within the sediment maybe low along the muddy, sandy shores. • Zonation of species: Distribution of species within the intertidal zone according to their adaptations to exposed environmental conditions. • Substrates effect on distributions (muddy, sandy and rocky) as organisms adapt to live in it. • Human used the intertidal zone as source of food, recreation, education , and research.
Estuaries, Salt Marshes, and Mangrove Forest • Estuaries: area where sea meet the river. • Mangroves forest: low laying area with mangrove trees. Fig. 3.22, 3.25 • Salt marshes: area of low-lying cost usually dominated by herbaceous plants and concentrated in sandy shores, and found from temperate to high latitude. Fig 3.24 • Conditions • Currents is the heart of the estuaries and mangrove forest. • Since salt marshes and mangrove effected by tide fluctuations. Hence, organisms in these environments are exposed to high variations of light. • Water is turbid, suspended fine organic and inorganic matters. • Temperature is varies within the water, as it is shallow and could reach 40°C. • Salinity fluctuate widely, evaporation and fresh water vs. sea. • Fluctuation of salinity according to distance sea. Fig 3.26. • Human influence, discharge of sewage, heavy metals, and oxygen depletion.
Rivers and Streams: Life Blood and Pulse of the Continents • Human history, ecology, and economy. (Nile, Tigris, …ect). • Nonequilibrial theory, one of the newest branches of theoretical ecology: focuses on the river dynamic. • Rivers drain most of the landscapes of the world (rain-river basin, drainage net work). • River and streams can be divided along three dimensions. Fig 3.30. • They can be divided along their lengths into: pools, runs, riffle and rapid. • River can be divided across their width into: wetted channels and active channels. • A wetted channel contain water even during low conditions. • Active channel which extends out from one or both sides of wetted channel, may be dry during part of the year but is inundated annually during high flows. • Riparian zone: a transition between the aquatic environment of the river and upland terrestrial environment.
Rivers and streams can be divided vertically into: water surface, the water column and bottom or benthic zone. • Hyporheiczone: below the benthiczoneas it is transition between areas of surface water flow and groundwater. • Phreatic zone: area below the hyporheic zone which contain groundwater. • Each parts of a river or stream is physically and chemically distinctive environments supporting different organisms. Conditions • Streams Light influence according to: penetration and light intensity. • Generally streams are more turbid than lakes because • Rivers are more contacts with landscape (washing materials). • Erode bottoms and suspend bottom sediments. • Temperature is close to air temperatures (0-30°C). • River is continuous movement of water. Different flow according to the zones (pool, riffle….). • River discharge: amount of water carried by river. • Streams and rivers could be “flashy” in arid and semiarid regions. • Industrial discharge effect river or stream organisms.
Salinity in the rivers influenced by annual rainfall and leached soluble materials from the basin. Salinity ranges 10-100 folds. Fig 3.33. • Oxygen is inversely with temperature. • Organisms tolerate oxygen deficiencies are varied and distribution is based on that along the river or the stream. • Number of fish species in tropical rivers is much higher than in temperate rivers. • The organisms in the river changes from head-waters to mouth. • River continuum concept: Concept in which suggest that in temperate regions, leaves and other plant parts are often the major source of energy available to the stream ecosystem. • According to this concept : Coarse particulate organic matter (CPOM) attacked by microbes, then shredded by invertebrates, to form fine particulate organic matter (FPOM). • In large rivers the major source of energy is FPOM, and in some rivers phytoplankton. • Most of invertebrates of streams and rivers live or in the sediments. Fig 3.34 . • Human influence on pollution, irrigation, transportation and recovery.
Lakes: Small Seas • Lakes are simply basins in the landscape that collect water. • 20% of fresh water is in lake Baikal. • Littoral zone: Shallowest water along the lake shore where rooted aquatic plant may grow. • Limnetic zone: Zone beyond the littoral zone in the open lake. • Lakes are generally divided vertically into three main depth zones: • Epilimnion: the warm surface layer • Thermocline or metalimnion: a layer which temperature substantially with depth, generally about 1°C per meter of depth. • Hypolimnion: lower layer below thermocline where water is cold and dark. Conditions • Color of the lake depend on light absorption within the lake. • Lakes becomes thermally stratified as they heated. Fig 3.38 • Wind-driven mixing process through seasons. • Oxygen depletion when decomposition occurs. • Oligotrophic: well mixed lake with low biological productivity. • Eutrophic: low oxygen with high biological productivity.
