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Chapter 3

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Biology 2F03: Fundamental and Applied Ecology Chapter 3: Life in Water 3.1 The Hydrologic Cycle - 71% of the earth’s surface is covered by water - Oceans contain over 97% of water in the biosphere, polar ice caps and glaciers contain 2% and less than 1% is freshwater in rivers, lakes, and actively exchanged groundwater - 20% of the planet’s freshwater is found in Canada - Across earth, over 65% of freshwater us found in glaciers and ice fields and 30% is groundwater - Ex.: Alberta - Because of changes to freshwater supplies and demands, the distribution of water across the biosphere is dynamic - Hydrologic cycle: exchanges of water among reservoirs - During the hydrologic cycle, water enters each reservoir either as precipitation or surface/subsurface flow and exits as evaporation or flow - Hydrologic cycle is powered by solar energy, which drives the winds and evaporates water - Water vapour cools as it rises and condenses, forming clouds - Clouds are then blown by solar-driven winds across the planet, eventually yielding to rain or snow, the majority of which falls back on the oceans and some of which falls on land - Reservoirs will be replenished at different rates, and ecologists of measure turnover times, the time required for the entire volume of a particular reservoir to be renewed - Reservoir size and rates are two of the main determinants of turnover time - Water in the atmosphere turns over every 9 days, river water 12 to 20, lake renewal are longer, oceans 3,100 years 3.2 Life in Water and the Natural History of Aquatic Environments - The biology of aquatic environments corresponds broadly to variations in physical factors such as light, temperature and water movements and to chemical factors such as salinity and oxygen - The Ocean:  Geography:  Covers over 360 million km of earth’s surface (70%), and consists of one continuous, interconnected mass of water  Arctic, Atlantic, Indian, Pacific, and Southern 2ceans  Largest and deepest: Pacific (180 million km , depth 4km)  Structure:  Intertidal zone: shallow shoreline under the influence of the rise and fall of the tides  Neritic zone: extends from the coast to the margin of the continental shelf, where the ocean is about 200m deep  Oceanic zone: beyond the continental shelf  Epipelagic zone: surface layer of the oceans that extends to a depth of 200m  Mesopelagic zone: extends from 200 to 1,000m  Bathypelagic zone: extends from 1,000 to 4,000m  Abyssal zone: from 4,000 to 6,000m  Hadal zone: deepest parts of the ocean  Benthic: habitats on the bottom of the ocean and other aquatic environments  Pelagic: habitats off the bottom regardless of depth  Physical conditions:  Light: o Approximately 80% of the solar energy striking the ocean is absorbed in the first 10m o Most ultraviolet and infrared light is absorbed in the first few meters blue light is absorbed less rapidly o In the open ocean algae are at low concentrations and very little of the blue light available is used in photosynthesis, which is why the ocean appears blue  Temperature: o Sunlight absorbed by water increases the kinetic state, of water molecules o Because more rapid molecular motion decreases water density, warm water floats on cold water o Warm and cold layers are separated by thermocline, a layer of water in which temperature changes with depth o Thermal stratification: layering of water column by temperature o Temperate oceans are stratified only in summer, and the thermocline breaks down as surface waters cool during fall and winter o Lowest oceanic temperature, -1.5 C, highest 27 C o o Annual variation in surface temperature: 7 C-9 C o o At 100m depth, annual variation in temperature is less o than 1 C  Water movements: o Prevailing winds drive currents that transport nutrients, oxygen and heat, as well as organisms across the globe o Currents moderate climates, fertilize surface waters off the continents, stimulate photosynthesis, and promote gene flow among populations of marine organisms o Wind-driven surface currents sweep across vast expanses of open ocean to create great circulation systems called gyres o Oceanic gyres transport warm water from equatorial regions towards the poles o Deepwater currents produced as cooled, high-density water sinks and then moves along the ocean floor o Upwelling: winds blow surface water offshore, allowing colder water to rise to surface  Chemical conditions:  Salinity: o When an organism’s internal salinity differs from the salinity of the surrounding water, that organism will be under osmotic stress o Salinity varies with latitude, and among the seas that fringe the oceans o In the open ocean, it varies from 34g/kg-36.5g/kg o Lowest salinities occur near the equator and above 40 N and S latitudes o Highest salinities occur in the subtropics o Salinity varies a great deal more in the small, enclosed basins along the margins of the major ocean+ 2+ o Relative proportions of the major ions [Na ], [Mg ], and [Cl ] remain constant from one part of the ocean to another  Oxygen: o Present in far lower concentrations and varies much more in the oceans o Litre of water contains a maximum of 9mL of oxygen o Concentrations are highest near the ocean surface, and decrease with depth o Below 1,000m oxygen concentrations increase as one travels deeper in the ocean  Biology:  Correspondence between physical and chemical conditions and the diversity, composition, and abundance of oceanic organisms  Photosynthetic inhabitants in the photic zone: phytoplankton and zooplankton  Most deep-sea organisms are nourished by organic matter fixed by photosynthesis near the surface  Biological communities on the seafloor that are nourished by chemosynthesis on the ocean floor  The open ocean is an area nearly devoid of life  Contribute to one-fourth of total photosynthesis in the biosphere  Most fish are found along the coasts  Open ocean is home for thousands of organisms with no counterparts on land  Marine environment supports 28 phyla, 13 of which are endemic to the marine environment  Human influences:  Overfishing  Dumping of wastes  Deep ocean petroleum extraction - Shallow marine waters – kelp forests and coral gardens:  Geography:  In temperate to subpolar regions there are growths of kelp  As you get closer to the equator, kelp forests are replaced by coral reefs, occurring in relatively shallow water  Some corals may live more than 4,000 years  Structure:  Fringing reefs: hug the shore of a continent or island  Barrier reefs: stand some distance offshore, between the open sea and lagoons  Coral atolls: coral islets that have built up from a submerged oceanic island and ring a lagoon  Reef crest: corals grow in the surge zone created by waves coming from the open sea  Below the reef crest in a buttress zone, where coral formations alternate with sand-bottomed canyons  Behind the reef crest lies the lagoon, which contains numerous small coral reefs called patch reefs and sea grass beds  Beds of kelp have structural features similar to terrestrial forests  At the water’s surface is the canopy, the stems of kelp extend from the canopy to the bottom and are anchored with structures called holdfasts  Physical conditions:  Light: o Seaweeds and reef-building corals grow only in surface waters, where there is sufficient light to support photosynthesis  Temperature: o Most kelp are limited to temperate shores, 10 C in o winter, 20 C in summer o Reef-building corals are restricted to warm waters (20 C-29 C)  Water movements: o Continuously washed by oceanic currents delivering oxygen and nutrients and removing waste o Biological productivity may depend upon the flushing action of these currents  Chemical conditions:  Salinity: o Coral reefs grow in waters with stable salinity o Kelp beds appear to be more tolerant of freshwater runoff and grow well along temperate showers  Oxygen: o Occur where waters are well oxygenated  Biology:  Coral reefs face intense biological disturbance  Coral reefs and kelp beds are among the most productive and diverse of all ecological systems in the biosphere  Human influences:  Kelp are harvested for use as a food additive or for fertilizer, and are replaced by rapid kelp growth  Corals are harvested and bleached for decorations, do not grow quickly  Fish and shellfish of kelp forests and coral reefs have also been exploited  Coral reefs buffer the effects of waves  Increased temperatures, light, and pollution, can lead to coral bleaching - Where waves meet rocks – intertidal zones:  Geography:  Thousands of kilometers of coastline around the world have intertidal zones  Exposed and sheltered shores  Rocky and sandy shores  Structure:  Supreatidal fringe: highest zones, covered by high tides but is often wetted by waves  Below fringe is the intertidal zone proper  Upper intertidal zone is covered only during the highest tides, and the lower intertidal zone is uncovered only during the lowest tides  Middle intertidal zone is covered and uncovered during average tides  Subtidal zone: remains covered by water even during the lowest tides 
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