Lecture Notes 7 Life in Water (1) PDF

Lecture 3 Life in Water 1. Oceans and seas 1. Contain 97% of earth's water a. Polar ice caps & glaciers = 2% b. All freshwater = 1% (!!) 2. Divided into vertical and horizontal zones c. **[Intertidal]** = shoreline area under tidal influence (a...

Lecture 3 Life in Water 1. Oceans and seas 1. Contain 97% of earth's water a. Polar ice caps & glaciers = 2% b. All freshwater = 1% (!!) 2. Divided into vertical and horizontal zones c. **[Intertidal]** = shoreline area under tidal influence (area between high and low tides) d. **[Neritic]** = shallow area from intertidal zone seaward to edge of continental shelf e. **[Epipelagic]** = area seaward from neritic but only down to 200 m f. **[Mesopelagic]** = 200 m down to 1,000 m g. **[Bathypelagic]** = 1,000 m down to 4,000 m h. **[Abyssal]** = 4,000 -- 6,000 m i. NOTE: 6,000 m = 3.7 miles! i. **[Hadal]** = \> 6,000 m 3. Solar energy decreases w/ depth j. 80% of solar energy is absorbed in upper 10 m k. blue wavelengths (shortest/highest energy) penetrate the deepest 4. Marine productivity generally more associated with proximity to terrestrial habitats -- the source of nutrients -- than latitude (as in terrestrial environments) l. Nutrients in marine environment typically move downward with death of organisms and sinking of their carcasses m. Typically a oneway movement downward for nutrients n. Nutrients can be brought back to surface in neritic zone due to mixing of relatively shallow water of this zone. o. Nutrients can also be brought to surface through "*[upwellings]*" = an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich bottom water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water ii. e.g., Humboldt Current (aka the Peru Current) off western coast of SA creates upwelling and supports major fishery (anchovies, sardines, mackeral) p. Nutrients need to be near enough the surface for light penetration to be able to fuel photosynthesis and growth of **[phytoplankton]** (small, often microscopic photosynthetic organisms) = base of many aquatic food chains q. Phytoplankton eaten by **[zooplankton]** (small, often near microscopic animals like *Daphnia*) r. Zooplankton then eaten by small fish, etc. 5. Open ocean (e.g., epipelagic zone) typically with low productivity due to low nutrient concentrations 6. Likely "birthplace" of life on earth and still where the vast majority of large-scale biodiversity is found s. e.g., \~35 phyla of animals on earth; 34 are found in oceans with \~13 found ONLY in marine environments vs... t. 11 phyla found in terrestrial environments w/ only one (!) restricted to these habitats (Onychophora = 'the velvet worms') 2. Shallow, nearshore marine habitats 7. **[Kelp forests]** u. Dominated by 'kelp' = various species of brown algae some of which can grow \~40 m (\>130 feet!) tall (especially *Macrocystis* spp.) v. Occurs in temperate latitudes w. Habitat for many other species (e.g., many fish, also marine mammals such as sea otter) 8. **[Coral reefs]** x. Dominated by group of Cnidarians known as "corals"; small colonial animals in phylum, Cnidaria iii. Secrete calcium carbonate skeleton that gives the reef its physical structure y. V. high species richness and high productivity z. Primarily limited to tropical and subtropical latitudes (w/in 35° of equator) a. Many stenothermal spp. including reef-building corals leading to negative impacts of global warming (including coral 'bleaching') 3. Shoreline Marine Habitats 9. **[Rocky, intertidal zone]** b. Shoreline area between high and low tides in areas with steeper, rocky coastline c. Many sessile animals such as barnacles and mussels d. Zonation of species depending on tolerance of desiccation (w/ species with greatest tolerance in highest locations) 10. **[Salt Marshes]** e. Dominated by herbaceous (non-woody), euryhaline vegetation like certain grasses (e.g., *Spartina* spp.) and rushes (e.g., *Juncus* spp.) f. Found in relatively flat, low-lying coastal areas w/ sandy or muddy shorelines g. High productivity but low biodiversity 11. **[Mangrove Swamps]** h. Dominated by various species of small, shrubby trees (known collectively as "mangroves") with various adaptations to having roots inundated by water (e.g., aerial/prop roots, etc. and viviparity) i. Found in relatively flat, low-lying coastal areas w/ sandy or muddy shorelines in tropical or subtropical latitudes j. Often serve as "nursery grounds" for reef or offshore marine taxa 12. **[Estuaries]** k. Transition zone where river meets ocean l. Rivers near ocean have fluctuating salinity gradient w/ increasing salinity closer to ocean m. Sessile organisms are typically euryhaline 4. Freshwater habitats *...recall that freshwater makes up 1% of all water...* 13. Terminology n. **[Lotic]** = flowing water (rivers and streams) o. **[Lentic]** = non-flowing water (lakes, reservoirs) p. [Littoral] = shallowest water along shoreline where rooted aquatic plants may grow q. [Limnetic] = open water habitats beyond littoral zone r. **[Eutrophic]** = nutrient-rich habitat s. **[Oligotrophic]** = nutrient-poor habitat t. **[Riparian zone]** = terrestrial habitats bordering rivers and streams u. **[Benthic zone]** = bottom of aquatic habitat iv. Many organisms live here v. Often called "benthos" vi. E.g., corals, clams, mussels, etc. 14. Rivers & streams v. *[River continuum concept]* -- small headwater streams come together to form small rivers which coalesce into large rivers w. Headwater streams usually shaded by riparian vegetation; often contain cool/cold water, high dissolved oxygen; most energy comes from leaves from riparian vegetation which fall into water are colonized by bacteria & fungi, eaten by various stream invertebrates (e.g., larval insects such as mayfly and stonefly nymphs) which are then eaten by cool/coldwater fish like darters, trout, etc. x. Larger streams & rivers are less affected by riparian vegetation, less shaded, much of energy input comes from upstream and from phytoplankton w/in river itself; warmer water w/ less oxygen, warm water fish like catfish, sunfish, carp, etc. 15. Lakes y. Most of world's freshwater resides in a few very large lakes vii. Great Lakes of NA = 20% of worlds freshwater viii. Lake Tanganyika of Africa = 20% ix. Lake Baikal of Siberia = 20% (world's deepest lake w/ average depth of 744 m or 2,442 ft.) z. Thermal stratification (NOTE: this also occurs in ocean) x. Occurs in summer in temperate zone lakes & year-round in tropical lakes xi. Warm surface water (warmed by sun) floats on cooler, denser bottom water xii. Warm surface layer of water = [epilimnion] xiii. Cooler bottom layer of water = [hypolimnion] xiv. Transition zone in which water temperature changes rapidly with depth = [thermocline] xv. Seasonal pattern of temperature change w/ depth in deep, temperate-zone lakes (which are called '**[dimictic lakes]**') xvi. Water densest at 4°C xvii. Get mixing of water (top to bottom) in spring and fall nutrient-rich bottom water brought to surface leads to phytoplankton bloom, etc. xviii. During summer get stratification of water temps. and organisms as well xix. Warmwater fish in epilimnion (e.g., sunfish, largemouth bass) xx. Coldwater fish in hypolimnion (e.g., trout, whitefish)