Download May 2011 Oceanography Ch # 13 Biological Productivity and

May 2011
Oceanography Ch # 13
Biological Productivity and Energy Transfer.
Producers – Plants and Algae. Plankton makes up the major mass in the marine Envir.
In total darkness, bacteria like organisms make their food by oxidizing H2S or methane to
support self in the deep ocean (Benthos).
13 -1. Primary Productivity is the amount of carbon fixed thru photosynthesis of organic matter
Photosynthesis productivity. – A chemical reaction in which energy from the sun is stored in
organic molecules.
New production brought in from the outside by upwelling.
Regenerated production is recycled nutrients from within the system.
Measuring Primary Productivity.
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Pulling a cone shaped sock at certain depths to collect the plankton
Gran method. Use of bottles to measure the O2 produced by photosynthesis. (Light
and Dark Bottle method)
Radioactive carbon isotope
Satellite color scan. Measure of chlorophyll
Factors affecting Primary Productivity
Availability of nutrients – generally sourced from land. Iron is very important and necessary for
productivity.
Availability of Solar Radiation. Max penetration of sunlight is 1 km. The Euphotic zone
Habitat : The ocean margin. Has the richest concentration of organisms where conditions are
most unstable , such as : unstable water depth, temp and salinity. Waves release energy.
Conditions which stress organisms. They adjust to the environment so long as nutrients are
available.
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The distribution of life is uneven as a result of : Upwelling – nutrient supply; Surface currents
moving towards the equator. Ekman transport – moves sfc waters away from the coast and
nutrient-rich water constantly rises to replace the surface water.
Light transmission in the water.
See Electromagnetic Spectrum (p.391)
Color of Objects. Different wavelengths are absorbed at different depths. No light below
1000 meters.
Water color and life in the Ocean.
Color is influenced by turbidity and photosynthetic pigment. Coastal waters and
upwelling areas are very productive. Water in the open ocean is clear blue and has lower
productivity and turbidity.
13 -2. Photosynthetic Marine Organisms.
Mostly microscopic algae, some seed bearing plants and larger algae.
The seed bearing plants are exclusively in shallow coastal water – grasses in tidal zones, salt
marshes, mangrove swamps
Macroscopic, algae such as sea weeds attached to the bottom, except for a few floating species.
Brown algae – largest in cold waters to depths of 30 met +Green Algae , mostly in fresh waters
Red algae is the most abd and widespread. In warm and cold waters.
Microscopic algae produce food for most of the marine organisms (99%)
Golden algae (diatoms) tests composed of opaline silica
Coccolithophores , small calcareous plates cover in temperate and warmer waters.
Dinoflagellates made of cellulose and sometimes produce red tide.
Photosynthetic bacteria – extremely small.
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13 -3. Regional Productivity
Varies from place to place. Most productive zones are :
Coral reefs
Estuaries
Upwelling zones
Productivity in Polar Oceans. Experiences 3 months darkness. Diatoms peak in May;
Zooplankton in June; Whales migrate so as to be in the right place at the right time.
Productivity in Tropical oceans. It is low, because there is no mixing of waters.
Productivity is low but constant, except in equatorial upwelling , coastal up welling and coral
reefs.
Productivity in Temperate Oceans. Limiting factors are available sunlight and nutrient
supply.
Winter – most sunlight is reflected. Low
Spring- Limited by lack of nutrients. Phytoplankton is decreased and consumed by the
Zooplankton.
Summer - Thermo cline prevents mixing and nutrients cannot be replaced by deeper
waters. Low productivity
Fall - Nutrients return to the surface and productivity returns
13 -4. Energy Flow.
Not a cycle but a unidirectional flow begins with solar energy and ends with a high level
of entropy in the Marine Ecosystem.
How Energy flows in the Marine Ecosystem.
Unidirectional - Sunlight absorbed by Algae and converted to chemical energy, which
Organisms consume. Producers (Autotrophic); Consumers (heterotrophic = different
nourishment) are herbivores, Carnivores, Omnivores and Bacteriovores ; Decomposers
(heterotrophic) feed on detritus and waste products.
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Nutrient Flow.
Depends on Biogeochemical cycles. Chemical components enter the biological system
through photosynthesis or chemosynthesis in feeding.
13 -5. What Oceanic feeding Relationships exist?
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Active Predation
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Cruisers
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Filtering – (suspension)
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Locating on sea floor – detritus organic matter in sediments (arenicola); on
sediments (orchestoidea)
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Carnivorous
Trophic levels. Each feeding stage is a trophic level. Generally, individual members of a feeding
population are larger than the organisms consumed (see p. 393 & 394).
Transfer efficiency; Very inefficient between trophic levels. (a) Only 2% of light absorbed by
algae is synthesized into food. (b) 10% (6 to 15%) of food consumed , is available to the next
trophic level.
Food Chains, Individuals of a feeding population are generally larger and less numerous than
their prey. A sequence of organisms through which energy is transferred starting with the
primary producer and culminating with the “top” carnivore.
Food Web – Carnivores feeding on a number of different animals. Carnivores which feed
through the web are most likely to survive.
The Biomass Pyramid. The number of individuals and total biomass decrease at successive
trophic levels because the amount of energy available decreases.
13 -6. Issues affecting Marine Fisheries
Fisheries supply between 20 and 27% protein intake. Best Harvest in * non-Tropical shelves,
followed by * Tropical shelves,* Upwelling areas, * Coastal and Reef Systems, and last * Open
Oceans.
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Over fishing. – Harvesting of fish stocks so rapidly that the majority of the population is sexually
immature and unable to reproduce. The consequences are : (1) A decrease in max. sustainable
yield. (2) smaller fish- big fishes disappear, which allows prey fish to florish. Research indicates
that sport fishing is a major contributor to over fishing.
Incidental Catch (bycatch) – any organism that are caught incidentally, while seeking
commercial species. Est. 20 MMmetric Tons/year or 25% of harvest. Example: Yellow Fin Tuna
is known to swim below dolphins and when Purse Seine nets are used , the dolphins are
trapped.
The Marine Mammals Protection Act modifies these Purse Seine nets. Drift nets made with
material that is invisible to the fish are now banned.
13 -7. Fisheries Management
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Includes assessing ecosystem health.
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Determining fish stocks
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Analyzing fishing practices
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Modifying gear
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Establishing closed areas
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Setting and enforcing catch limits.
The issues are : some fisheries encompass the waters of different countries and various
ecosystems.
Regulations of Vessels – The world’s fleet has about 4 MM of which 1.3 MM are engine
powered, and mechanized decked. Their nets can catch up to 60,000 #/ haul.
NW Atlantic – Canada and US rxtend their EEZ to 200 Nautical miles.
Deep Water Fisheries – Industry changes species names, and or move to different areas.
Ecosystem- based-fishery Management goal is to ensure sustainable fisheries. – Starts with AN
Ecosystem rather than a target species and to rebuild stocks.
13 – 8. Sea food Choices.
Demand has driven some fish populations to near extinction.
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