Chapter 13 Primary Productivity Primary productivity rate at which organisms store energy through the formation of organic matter using energy derived from solar radiation during photosynthesis or from chemical reaction during chemosynthesis 99 of the ocean s biomass relies directly or indirectly on organic matter supplied by photosynthetic primary productivity Biological Production The amount of organic matter in an ecosystem measured as amount per surface area is its biomass the total mass of all living things and their products Ecosystem production is measured as biomass energy stored or stored carbon Net production is the change in biomass over a specified time NP B2 B1 or NP GP Respiration Measurement of Primary Productivity plankton nets direct at sea method of measuring primary productivity capture plankton in plankton nets Factors affecting primary productivity Availability of nutrients nitrogen phosphorus iron silica are all needed by phytoplankton Availability of solar radiation photosynthesis needs light energy solar radiation to happen compensation depth for photosynthesis depth at which net photosynthesis becomes zero Light Transmission in Ocean Water Visible light solar energy falls in range of wavelengths Sun affects 3 major components of the ocean o Major wind belts of the world which produce ocean currents and wind driven ocean waves derive their energy from solar radiation o Thin layer of warm water at the ocean surface created by solar heating overlies the great mass of cold water that fills most of the ocean basins o Photosynthesis can occur only where sunlight penetrates the ocean water so phytoplankton and most animals that eat them must live where the light is Electromagnetic spectrum the sun radiates a wide range of wavelengths of electromagnetic radiation The color of objects objects absorb different wavelengths of light making them have different colors Why are the margins of the oceans so rich in life The margins have unstable conditions yet they are rich in life Water depths are shallow allowing much greater seasonal variations in temperature and salinity A water column that varies in thickness Breaking waves release large amounts of energy Areas with large biomass have the lowest water temperatures because cold water contains higher amounts of nutrients than warm water Upwelling a flow of deep water toward the surface that brings water from depths below the euphotic zone the deep water is rich in nutrients Types of Photosynthetic Marine Organisms Seed Bearing Plants Macroscopic Large Algae classified by the color pigment they contain o Brown largest members cold water areas o Green freshwater contain chlorophyll o Red most abundant and widespread rarely found in freshwater Microscopic Algae directly or indirectly the source of food for more than 99 of marine animals most are phytoplankton o Golden consist of diatoms and coccolithophores o Red Tides when a large amount of dinoflagellates exist they color surface waters red Eutrophication the artificial enrichment of waters by a previously scarce nutrient that can trigger an overabundance of algae such as an HAB Thermocline forms a barrier to vertical mixing preventing the resupply of nutrients to the sunlit surface layer Energy Flow in Marine Ecosystems Not a cycle but a unidirectional flow Algae absorb solar radiation photosynthesis converts this solar energy into chemical energy which algae uses for respiration The chemical energy is also passed on to the animals that consume the algae for their growth and other life functions Animals expend mechanical and heat energy the ecosystem relies on a constant input of energy in the form of sunlight Flow of Nutrients in Marine Ecosystems Biogeochemical cycles flow of nutrients depends on this matter does not dissipate but is cycles from one chemical form to another by various member of the biotic community The chemical components of organic matter enter the biological system through photosynthesis These chemical components are passed on to animal populations consumers through feeding When organisms die some of the material is used and reused within the euphotic zone while some sinks as detritus Some of this detritus feeds organisms living in deep water or on the sea floor while some undergoes bacterial or other decomposition processes that convert organic remains into usable nutrients when upwelling hoists these nutrients to the surface again they can be used by algae and plants to begin the cycle anew Trophic levels feeding stages that animals receive energy by Gross ecological efficiency at any trophic level is the ratio of energy passed on to the next higher trophic level divided by the energy received from the trophic level below Marine Fisheries Fisheries no owner but highly capitalized 100M ton y fishery 28m ton aquaculture 90 from continental shelved dominated by a few major fishing nations Repeated failures in recent years e g Pacific sardine Atlantic herring Peruvian anchovy Atlantic cod Fisheries management organized effort directed at regulating fishing activity with the goal of maintaining a long term fishery they assess ecosystem health determine fish stocks analyze fishing practices establish closed areas set and enforce catch limits Fish populations are depleting this is leading to an abundance in lobster because their main predator cod are all being caught The Logistic Curve o Calculated from the logistic growth equation which is based on the premises that small populations with abundant resources grow at exponential rates o Intraspecific competition slows growth rates and competition increases as populations grow thus slowing rates o Populations eventually reach their logistic carrying capacity at which point the growth rate becomes zero Growth and Carrying Capacity o When there is no competition or predating AND plenty of nutrients a species responds with rapid increase Eventually this stabilizes at a carrying capacity o Maximum sustainable yield calculated as that number of individuals added per harvest period to a population that is at exactly one half its carrying capacity o Optimum sustainable population maximum population indefinitely sustainable Fishing methods o Trawling a bag shaped net with long wings is thrown into the water they re catching demersal fish cod shrimp o Purse seining a square net deployed in a circle and pursed at the bottom they re catching pelagic fish for meal and Menhaden which are an important Gulf of Mexico
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