Physiology of Marine Primary Producers AICE Marine Science A Level

Cambridge Syllabus: (a)Demonstrate an understanding of the ecological importance of primary producers for carbon fixation and shelter. (b)Explain why different types of primary producers are found in different habitats (a)Open ocean (diatoms, dinoflagellates, cyanobacteria, & Sargassum) (b)Shallow waters (zooxanthellae, sea grass [Thalassia], & kelp) (c)Intertidal regions (green, red, & brown algae) (c)Demonstrate an understanding that photosynthesis is the process that nearly all primary producers use to fix carbon (d)Demonstrate an understanding that photosynthesis involves the use of light energy from the sun, pigments including chlorophyll, and a number of enzymes (e)Explain why and how light intensity, light wavelength, and temperature affect the rate of photosynthesis and can act as limiting factors (f)Describe how light of different wavelengths penetrates to different depths in water, and relate this to the presence of accessory pigments, including xanthophylls and phycobilins, in primary producers (g)Use the knowledge and understanding gained in this section in new situations, or to solve related problems

(a) Demonstrate an understanding of the ecological importance of primary producers for carbon fixation & shelter. All photosynthesizers use carbon dioxide, water, & sunlight to produce glucose & oxygen CO 2 = H 2 O  C 6 H 12 O 6 + O 2 EX: phytoplankton, sea grasses, kelp, seaweed, cyanobacteria Base of food chains/webs Seagrasses, such as Thalassia, (flowering plants) grow in sandy & muddy sediment, provide habitat for many organisms (shelter for juvenile fishes), their roots hold sediment in place, & blades reduce water current speed

(a) Demonstrate an understanding of the ecological importance of primary producers for carbon fixation & shelter. Kelp (Laminaria) provides habitat, shelter, & food for many organisms Floating Sargassum provides habitat, shelter, & food

Kelp Forest Ecosystem

Sargassum Ecosystem

Open Ocean: Drifters & floaters Phytoplankton – Diatoms – Dinoflagellates – Cyanobacteria Sargassum (b) Explain why different types of primary producers are found in different habitats Phyto: microscopic, some gas-filled, some form chains/link together Sarg: gas-filled sacs to remain afloat

Phytoplankton Diatoms – Single-celled algae – Possess frustules made of silica – Yellow-brown chloroplasts Dinoflagellates – Single-celled algae – Possess 2 flagella for movement (vertical) Cyanobacteria – Single-celled blue-green bacteria – Build chains – No chloroplasts; photosynthetic pigments are in cytoplasm

Shallow waters: Zooxanthellae – Symbiotic single-celled algae in coral’s tissues – Provide coral with glucose & AAs – Shallow & clear water Thalassia & Zostera – Sea grasses (flowering plants) – Grow in muddy or sandy substrates – Roots hold sediment in place – Shallow water; somewhat sheltered Kelp – Cool, clear – Up to depths of about 40m – Brown macroalgae – Require hard substrate for attachment (algae lacks root systems of plants, has holdfast instead) – Blade (lamina) contains gas-filled sac that allows blade (like leaf) to remain at water’s surface (b) Explain why different types of primary producers are found in different habitats

Intertidal Regions: – Rocky shores – Macro algae has holdfast that attaches to hard rocky surface Green algae – EX: Ulva (sea lettuce) Red algae – EX: Chondrus Brown algae – EX: Fucus vesiculosus (bladder wrack) & Ascophyllum nodosum (egg wrack) (b) Explain why different types of primary producers are found in different habitats

Rocky Shore Factors leading to zonation on the rocky shore: – Resistance to desiccation – Rates of growth – Resistance to grazing by herbivores – Competition between species

Rocky Zonation

(c) Demonstrate an understanding that photosynthesis is the process that nearly all primary producers use to fix carbon CO 2 + H 2 O + sunlight C 6 H 12 O 6 + O 2 Majority is by phytoplankton; productivity varies according to the availability of factors including sunlight & inorganic nutrients

(d) Demonstrate an understanding that photosynthesis involves the use of light energy from the sun, pigments including chlorophyll, and a number of enzymes Original source of energy is the Sun Chlorophyll is a green pigment that absorbs light in red & blue- violet spectrum Carotenoids are yellow or orange pigments which absorb blue- violet light Light-independent stage of photosynthesis is controlled by enzymes; CO 2 fixation is catalyzed by ribulose biphosphate carboxylase (RuBisCO)

Photosynthetic pigments Chlorophylls (a, b, & c): All plants, algae, & cyanobacteria; absorb red & blue-violet Carotenoids: Fucoxanthin (yellow-brown found in brown algae & diatoms); absorb blue- green Phycobilins: Present in red algae & cyanobacteria; absorb blue- green

(e) Explain why and how light intensity, light wavelength and temperature affect the rate of photosynthesis and can act as limiting factors Light intensity Direct relationship: as light intensity increases, so does the rate of photosynthesis Light intensity decreases as depth of water increases; upper regions of oceans therefore have the highest photosynthetic productivity

In low light, the rate at which the products of the light dependent rxns are formed will affect the rate at which the CO 2 is fixed (in the second rxn – light independent) In this case – light would be the limiting factor – and increase in light intensity would increase photosynthesis until another factor (such as availability of CO 2 ) becomes limiting

In the absence of light, no photosynthesis occurs, but respiration continues – Light compensation point occurs at a light intensity where the volume of CO 2 produced in respiration is the same as the volume of CO 2 used in photosynthesis – As light intensity increases further, the rate of photosynthesis exceeds the rate of respiration and there is a net uptake of CO 2 Eventually the rate of photosynthesis levels out and reaches a plateau – At this point, another factor has become limiting At very high light intensities, the rate of photosynthesis may actually decrease, due to adverse effects of the intense light

Light wavelength Each pigment absorbs a narrow range of the spectrum Most plants, algae, & cyanobacteria have multiple pigments Chlorophyll-a: 420 & 660 nm (all plants, not bacteria) Chlorophyll-b: 453 & 643 nm (all plants & green algae) Chlorophyll-c: 445 & 625 nm (diatoms & brown algae) Chlorophyll-d: 450 & 690 nm (some red algae) α-Carotene: 420, 440, 470 nm (red algae & some green) β-Carotene: 425, 450, 480 nm (all other plants) γ-Carotene: 440, 460, 495 nm (green sulfur bacteria, traces in some plants) Fucoxanthol: 425, 450, 475 nm (diatoms & brown algae) Phycoerythrins: 490, 546, 576 nm (main pigment of red algae & some cyanobacteria) Phycocyanins: 618 nm (main pigment of cyanobacteria & red algae) (e) Explain why and how light intensity, light wavelength and temperature affect the rate of photosynthesis and can act as limiting factors

Concentration of CO 2 & other nutrients: – Availability of CO 2 can act as a limiting factor on rate of photosynthesis – More CO 2 available, the (potentially) higher the rate of photosynthesis – More minerals (nitrogen, phosphorus, etc) = increased rate of photosynthesis – Too many nutrients can cause plankton bloom (& some release toxins) Temperature: – Affects that rate of enzyme-controlled rxns & therefore has an effect on the light-dependent stage of photosynthesis – In general: Increased temperature = increased rate of photosynthesis (to a point, then it decreases) (e) Explain why and how light intensity, light wavelength and temperature affect the rate of photosynthesis and can act as limiting factors

(f) Describe how light of different wavelengths penetrates to different depths in water, and relate this to the presence of accessory pigments, including xanthophylls and phycobilins, in marine primary producers For algae living in deeper waters, the deficiencies of chlorophyll as a light absorber become critical because light reaching these depths has been filtered through thick greenish-blue layers of water (dissolved salts, and organisms living in the surface layers, contribute to the absorption of red & blue- violet); plants here have evolved auxiliary pigments that absorb green light (phycobilins)

Fucoxanthol has a broad absorption band; it absorbs all of the blue and green spectrums. Blue absorption band of fucoxanthol declines slowly, covering much of the gap left by chlorophyll in the green. Xanthophylls (yellow pigment) prevents damage to chlorophyll when exposed to high solar radiation (f) Describe how light of different wavelengths penetrates to different depths in water, and relate this to the presence of accessory pigments, including xanthophylls and phycobilins, in marine primary producers

Graph: Absorption Spectrum

Graph: Action Spectrum

NOAA This diagram offers a basic illustration of the depth at which different colors of light penetrate ocean waters. Water absorbs warm colors like reds and oranges (known as long wavelength light) and scatters the cooler colors (known as short wavelength light). Image courtesy of Kyle Carothers, NOAA-OE

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