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CHAPTER 3 LIFE IN WATER 1 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. 2 Fig. 3.2 3 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. 4 Fig. 3.5 5 Fig. 3.6 6 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. 7 – Water movement Current transport nutrients, oxygen, and heat. Formation of circulation systems called “gyers” in which winddriven 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. 8 – 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. 9 Fig. 3.9 10 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. 11 Fig. 3.12 12 Fig. 3.13 13 Fig. 3.14 14 – 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. 15 – 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 ????. 16 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. 17 Fig. 3.17 18 – 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. 19 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. 20 Fig. 3.22 21 Fig. 3.24 22 Fig. 3.25 23 Fig. 3.26 24 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. 25 Rivers and streams can be divided vertically into: water surface, the water column and bottom or benthic zone. Hyporheic zone: below the benthic zone as 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. 26 Fig. 3.30 27 – 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. 28 Fig. 3.33 29 Fig. 3.34 30 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. 31 Fig. 3.37 32 Fig. 3.38 33 Fig. 3.39 34