Marine Nitrogen Cycle and Nutrient Dynamics
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Questions and Answers

What is the role of Trichodesmium and certain bacteria in the nitrogen cycle?

  • They produce sulphate from organic sulphur.
  • They primarily convert nitrogenous compounds into carbon.
  • They decompose dead organic matter into its gaseous forms.
  • They fix dissolved elemental nitrogen. (correct)

    • How do bacteria in anaerobic conditions contribute to the nitrogen cycle?

  • By fixing nitrogen from the atmosphere and converting it into soluble forms.
  • By reducing nitrate to elemental nitrogen for energy. (correct)
  • By increasing the dissolved oxygen levels in the water.
  • By converting ammonia to nitrate through oxidation.

    • What major functions do bacteria serve in marine food cycles?

  • Synthesizing proteins from inorganic materials.
  • Converting carbon dioxide into organic matter.
  • Producing methane from decaying matter.
  • Breaking down dead organic matter and transforming it into bacterial protoplasm. (correct)

    • How are sulphur-containing compounds primarily regenerated in the marine environment?

    <p>By bacterial decomposition yielding hydrogen sulphide.</p> Signup and view all the answers

    What is the likely limitation of nitrogen fixation by Trichodesmium and bacteria in marine environments?

    <p>High energy requirements for the fixation reaction.</p> Signup and view all the answers

    What form of nitrogen is primarily excreted by most marine animals?

    <p>Ammonia</p> Signup and view all the answers

    Which nutrient is mainly excreted by marine animals in the form of phosphate?

    <p>Phosphorus</p> Signup and view all the answers

    What role do seabirds and pinnipeds play in the nutrient cycle between land and sea?

    <p>They cycle nutrients between land and sea.</p> Signup and view all the answers

    What is the source of dissolved nutrients like nitrates and phosphates entering the marine environment?

    <p>Land runoff</p> Signup and view all the answers

    Which group of organisms utilizes the products released by animal metabolism directly?

    <p>Phytoplankton</p> Signup and view all the answers

    In the classical food chain, which organisms are directly consumed by piscivores?

    <p>Planktivores</p> Signup and view all the answers

    What process allows nutrients to be recycled in the marine environment?

    <p>Complex processes degrading organic compounds</p> Signup and view all the answers

    What is dissolved organic carbon (DOC) primarily associated with in the microbial loop?

    <p>Heterotrophic nanoflagellates</p> Signup and view all the answers

    Which organisms are primarily responsible for primary production in the ocean?

    <p>Phytoplankton</p> Signup and view all the answers

    What is the difference between gross primary production (GPP) and net primary production (NPP)?

    <p>NPP accounts for losses due to respiration.</p> Signup and view all the answers

    At what depths did early biologists believe life could not exist in the ocean?

    <p>6500 m</p> Signup and view all the answers

    What percentage of net primary production (NPP) is attributed to phytoplankton in the euphotic zone?

    <p>Over 90%</p> Signup and view all the answers

    Which of the following statements about seaweeds and seagrasses is true?

    <p>They are less productive than phytoplankton overall.</p> Signup and view all the answers

    Which type of community derives energy from chemical sources rather than photosynthesis?

    <p>Deep-sea hydrothermal vents</p> Signup and view all the answers

    How quickly can phytoplankton produce its own weight of new organic material under favorable conditions?

    <p>Within 24 hours</p> Signup and view all the answers

    What are the habitats described as exceptions to the dependence on photosynthetic primary producers?

    <p>Deep-sea hydrothermal vents and cold seep communities</p> Signup and view all the answers

    What phenomenon is created by wind action in the uppermost layers of water?

    <p>Langmuir vortices</p> Signup and view all the answers

    What is a significant factor influencing the distribution of organisms in upward-swimming organisms?

    <p>Localized turbulence</p> Signup and view all the answers

    What relationship is commonly observed between phytoplankton and zooplankton populations?

    <p>Inverse relationship</p> Signup and view all the answers

    Why might phytoplankton and zooplankton not coexist abundantly over time?

    <p>Rapid removal of phytoplankton</p> Signup and view all the answers

    What hypothesis suggests that zooplankton avoid phytoplankton-rich waters due to water quality?

    <p>Animal exclusion hypothesis</p> Signup and view all the answers

    What effect do phytoplankton like Phaeocystis have on water quality?

    <p>Create a slimy texture</p> Signup and view all the answers

    What happens to zooplankton populations as herbivorous zooplankton numbers increase?

    <p>They rapidly decrease in number</p> Signup and view all the answers

    What is one possible reason for zooplankton to control their depth in the water column?

    <p>To avoid less favorable water quality</p> Signup and view all the answers

    What did Bainbridge conclude about the occurrence of exclusion in natural conditions?

    <p>Exclusion is quite restricted in natural conditions.</p> Signup and view all the answers

    Which factor affects the patchiness of phytoplankton?

    <p>Grazing by zooplankton.</p> Signup and view all the answers

    How do differences in multiplication rates of phytoplankton and zooplankton affect their populations?

    <p>They may have seesaw effects on their relative abundance.</p> Signup and view all the answers

    What behavior is mainly associated with localized patches of adults and larvae?

    <p>Swarming behavior.</p> Signup and view all the answers

    What does the patchiness of plankton imply for the feeding strategies of animals?

    <p>Animals can feed more economically in areas where food is abundant.</p> Signup and view all the answers

    What might cause certain species of plankton to appear or disappear in particular places?

    <p>Attractive or repellent effects influencing behavior.</p> Signup and view all the answers

    What is a consequence of concentrating in patches of the best food supply for animals?

    <p>Efficient feeding and recovery of depleted food stocks.</p> Signup and view all the answers

    What determines the distribution of meroplankton?

    <p>Patchiness in the distribution of the benthos.</p> Signup and view all the answers

    What happens to most of the organic material that moves away from the euphotic zone?

    <p>It accumulates below the euphotic zone as nutrients.</p> Signup and view all the answers

    What process is crucial for restoring nutrients from deep waters to surface layers?

    <p>Vertical water mixing or upwelling.</p> Signup and view all the answers

    Which type of bacteria acts as primary producers through chemosynthesis?

    <p>Autotrophic bacteria.</p> Signup and view all the answers

    Most organic material that sinks to deeper levels may eventually end up where?

    <p>Being permanently incorporated into sediments.</p> Signup and view all the answers

    What is NOT a source of nutrient compounds for animal tissues?

    <p>Nitrogen fixation by bacteria.</p> Signup and view all the answers

    What role does denitrifying bacteria play in nutrient cycling?

    <p>They convert nitrates into nitrogen gas.</p> Signup and view all the answers

    How does nutrient accumulation below the euphotic zone primarily occur?

    <p>From the decay of organic matter.</p> Signup and view all the answers

    Which of the following best describes the euphotic zone?

    <p>The upper layer of water where sufficient sunlight penetrates for photosynthesis.</p> Signup and view all the answers

    What is one effect of animal movements after feeding in the euphotic zone?

    <p>Increased organic material sinking.</p> Signup and view all the answers

    Which statement about phytoplankton is true?

    <p>They are primary producers capable of photosynthesis.</p> Signup and view all the answers

    What is the primary result of nutrient mixing from deep water to the surface?

    <p>Support of primary production.</p> Signup and view all the answers

    What process do autotrophic bacteria perform that is essential for the ocean's nutrient cycle?

    <p>Chemosynthesis.</p> Signup and view all the answers

    What is a consequence of permanent incorporation of organic material in sediments?

    <p>Long-term loss of organic carbon from the cycle.</p> Signup and view all the answers

    What is the gross conversion efficiency of organic matter transfer from each trophic level?

    <p>10%</p> Signup and view all the answers

    Which group of organisms typically demonstrates higher efficiencies in organic matter transfer?

    <p>Herbivorous zooplankton</p> Signup and view all the answers

    Which of the following statements is true regarding farming fish for human consumption?

    <p>Farming herbivorous fish is more efficient due to their position in the food chain.</p> Signup and view all the answers

    What happens to organic materials as a result of respiration, excretion, and decomposition?

    <p>They are broken down and returned as simpler substances.</p> Signup and view all the answers

    What role does sunlight play in the cycling of organic materials?

    <p>It provides the initial energy for organic material synthesis.</p> Signup and view all the answers

    What proportion of organisms at each trophic level typically die and decompose without being consumed?

    <p>A significant proportion die and decompose.</p> Signup and view all the answers

    What is a primary consequence of energy loss in trophic transfers?

    <p>Dissipation of energy as heat.</p> Signup and view all the answers

    Why is certain larval stages noted for having a better efficiency in organic matter transfer?

    <p>They have specialized feeding mechanisms.</p> Signup and view all the answers

    What is measured to determine the net production figure in photosynthesis?

    <p>Oxygen produced</p> Signup and view all the answers

    Why are dark bottles used in the measurement process?

    <p>To prevent oxygen production</p> Signup and view all the answers

    What is a common complication in experiments using sealed seawater bottles?

    <p>Bacterial growth can rapidly affect results</p> Signup and view all the answers

    What must be done to maintain the plants in the bottles during the experiment?

    <p>Keep them in constant motion</p> Signup and view all the answers

    What assumption is made about respiration when measuring net production?

    <p>Respiration is not influenced by light</p> Signup and view all the answers

    What is the primary purpose of immersing bottles in tanks during the experiment?

    <p>To mimic natural light and temperature conditions</p> Signup and view all the answers

    How is the difference in oxygen content between light and dark bottles interpreted?

    <p>It is attributed to oxygen production by photosynthesis</p> Signup and view all the answers

    What happens to the oxygen content in dark bottles after a period of time?

    <p>It decreases due to respiration processes</p> Signup and view all the answers

    What is the main radioactive isotope used in the 14C method for measuring carbon dioxide uptake?

    <p>Carbon-14 (14C)</p> Signup and view all the answers

    Which of the following steps is NOT part of the 14C method for measuring primary production?

    <p>Measuring the oxygen levels in the water</p> Signup and view all the answers

    What is a significant advantage of the 14C method over the oxygen determination method?

    <p>It exclusively measures phytoplankton assimilation.</p> Signup and view all the answers

    Which factor contributes to the challenges of interpreting results from the 14C method?

    <p>Rapid loss of organic products of photosynthesis</p> Signup and view all the answers

    Why is phytoplankton mainly categorized as 'shade plants'?

    <p>They absorb light and reduce its penetration in water.</p> Signup and view all the answers

    What happens to phytoplankton that are carried below the compensation depth?

    <p>They will continue to respire without photosynthetic gains.</p> Signup and view all the answers

    Which component is added to seawater samples to trace carbon fixation in the 14C method?

    <p>Sodium bicarbonate containing carbon-14 (NaH14CO3)</p> Signup and view all the answers

    What does the 14C method measure to estimate total carbon fixation?

    <p>The amount of 14CO2 and total CO2</p> Signup and view all the answers

    How does the population increase of phytoplankton typically affect the compensation depth?

    <p>It leads to a decrease in the compensation depth.</p> Signup and view all the answers

    Why might results from the 14C method yield uncertainties about net primary production?

    <p>Difficulties in accommodating for dissolved organic material losses</p> Signup and view all the answers

    What primarily influences the mixing depth of phytoplankton within the water column?

    <p>Water movements from waves and currents.</p> Signup and view all the answers

    What aspect of phytoplankton distribution can affect the accuracy of measurements in the 14C method?

    <p>Patchy distribution of phytoplankton</p> Signup and view all the answers

    Which of the following statements is true regarding the contrasted depth relationships in primary production?

    <p>Respiration exceeds production at depths below compensation.</p> Signup and view all the answers

    What is the potential consequence of the increase in phytoplankton populating the upper layers of water?

    <p>Increased shading affects deeper phytoplankton.</p> Signup and view all the answers

    What does the compensation depth represent in the context of phytoplankton?

    <p>The depth where photosynthesis equals respiration.</p> Signup and view all the answers

    How does increasing phytoplankton density affect the euphotic zone?

    <p>It reduces the light penetration, decreasing the effective depth.</p> Signup and view all the answers

    What primarily influences the seasonal cycle of plankton production in temperate latitudes?

    <p>Variations in seasonal temperature and nutrient availability</p> Signup and view all the answers

    How does the concentration of inorganic nutrients in the photosynthetic zone change throughout the seasons?

    <p>Decreases during winter and increases in spring</p> Signup and view all the answers

    What describes the seasonal changes in temperature at a depth of 70 meters in temperate seas?

    <p>Temperature shows a predictable seasonal pattern</p> Signup and view all the answers

    During which season does the surface water of the sea typically become progressively colder?

    <p>Winter</p> Signup and view all the answers

    Which factor causes the seasonal differences in the standing stock of diatoms and dinoflagellates?

    <p>Changes in the availability of light and nutrients</p> Signup and view all the answers

    What is the relationship between seasonal temperature stratification and ocean mixing processes?

    <p>Seasonal temperature variations influence the timing and intensity of mixing</p> Signup and view all the answers

    What impact do geographical features have on the seasonal cycle of plankton in different regions?

    <p>They can delay or advance seasonal patterns in plankton abundance</p> Signup and view all the answers

    What seasonal effect on nutrient concentrations contributes to phytoplankton growth in spring?

    <p>Increased availability of inorganic nutrients following winter mixing</p> Signup and view all the answers

    What conclusion did Bainbridge reach about the process of exclusion in natural conditions?

    <p>It is of quite restricted occurrence.</p> Signup and view all the answers

    How does grazing by zooplankton influence phytoplankton distribution?

    <p>It creates localized patches of phytoplankton.</p> Signup and view all the answers

    What effect does the patchiness of plankton have on animal feeding strategies?

    <p>Animals can feed more efficiently where food is abundant.</p> Signup and view all the answers

    What factor contributes to the differences in abundance of grazers and their food?

    <p>Differences in multiplication rates.</p> Signup and view all the answers

    What behavior is primarily associated with the emergence of localized patches of eggs and larvae?

    <p>Swarming behavior linked to reproduction.</p> Signup and view all the answers

    Which of the following statements about the relationship between zooplankton and phytoplankton is true?

    <p>Zooplankton behavior can influence the distribution of phytoplankton.</p> Signup and view all the answers

    What does the appearance or disappearance of certain plankton species indicate?

    <p>The influence of attractive or repellent effects between species.</p> Signup and view all the answers

    What advantage does concentrating in patches of abundant food supply provide for animals?

    <p>More efficient feeding and recovery of food stocks in depleted areas.</p> Signup and view all the answers

    Study Notes

    Organic Production and Cycling in the Ocean

    • Early biologists believed deep ocean life was impossible.
    • Life exists in the deepest ocean depths, drawing energy from chemical sources.
    • Energy (food) is available throughout the ocean.
    • Photosynthetic organisms are the basis of energy in the euphotic zone (sunlit).
    • Deep-sea hydrothermal vents and "cold seeps" are exceptions, drawing energy from chemicals.
    • Ocean ecosystems also depend on energy from chemical sources (e.g., hydrothermal vents).

    Primary Production in the Ocean

    • Seaweeds, seagrasses, algae, and especially phytoplankton are primary producers.
    • They carry out photosynthesis, creating organic compounds from seawater.
    • Gross Primary Production (GPP): Total production.
    • Net Primary Production (NPP): GPP minus respiration losses.
    • Phytoplankton is the most significant contributor to ocean productivity (over 90% of NPP in the euphotic zone).
    • Phytoplankton can create its own weight in new organic matter within 24 hours, a rate faster than land plants.
    • Bacterial chemosynthesis also plays a role in primary production, especially in deep-sea environments.

    Food Webs and Trophic Levels

    • Primary producers (autotrophs) are used for food by other organisms.
    • Herbivorous animals (primary consumers) eat primary producers, converting them into animal tissue (secondary production)
    • Carnivorous animals (secondary/tertiary consumers) eat herbivores, creating a food web.
    • Trophic levels show the feeding relationships and transfer of energy.
    • Food chains interconnect to form intricate food webs.
    • Energy loss occurs at each trophic level through respiration.

    Microbial Loop and Dissolved Organic Matter

    • Dissolved organic matter (DOM) is a crucial marine component.
    • DOM serves as a nutrient source for microorganisms.
    • Microbial food webs include ultra-small picoplankton and nanoplankton.
    • These microorganisms carry out photosynthesis and/or ingest bacteria, playing a role in cycling organic matter.
    • DOM recycles major nutrients for photosynthetic organisms.
    • Microbial loop returns energy to the larger food web.

    Regeneration and Nutrient Recycling

    • Primary production requires nutrients like phosphorus and nitrogen.
    • Organic compounds are recycled through bacterial and fungal activity (decomposition).
    • Bacteria convert organic material into soluble inorganic ions usable by plants (regeneration).
    • Nitrogen is recycled through bacterial decomposition.
    • Sulphur compounds regenerate as sulphate via bacterial decomposition.
    • Nutrients released from dead organisms or excrete from marine animals are cycled between land and sea.

    Measurement of Primary Production

    • Methods include laboratory analysis of samples (e.g., oxygen, 14C, chlorophyll) and remote sensing (e.g., satellites).
    • Standing stock measures the total amount of organisms in a given area or volume.
    • Chlorophyll estimations, direct counts, and carbohydrate estimations are common methods to determine primary production.
    • 14C method traces inorganic carbon uptake by phytoplankton to measure production rates.
    • Oxygen determination measures oxygen levels to estimate net production.
    • Remote sensing provides large-scale production estimates.

    Factors Regulating Organic Production

    • Photosynthetic pigments (chlorophyll) absorb light energy for photosynthesis.
    • Compensation depth: depth where photosynthetic gain equals respiration loss.
    • Factors such as light penetration, nutrient availability, temperature, and grazing affect primary productivity.
    • Patchiness of plankton: uneven distribution of plankton in the ocean.
    • Oceanic currents and mixing influence distribution and quantity.

    Ocean Seasons

    • Seasonal variations in temperature, illumination, and nutrient availability affect primary production patterns.
    • Winter: Low productivity, due to low light and cold temperatures.
    • Spring: Increased light and nutrients trigger phytoplankton blooms.
    • Summer: High productivity, light and optimal temperatures.
    • Autumn: Reduced productivity, as the water cools and light diminishes.

    Geographical Differences in Fertility

    • Coastal areas often have high productivity due to nutrient inputs and mixing.
    • Open ocean (high latitudes) have less productivity due to lower nutrient levels.
    • Upwelling zones bring nutrient-rich deep water to the surface, increasing productivity.
    • Mixing and water currents affect nutrient distribution.
    • Global distribution of productivity varies depending on different factors, including coastal upwelling zones.

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    Organic Production and Cycling in the Ocean PDF

    Description

    Explore the intricate balance of the marine nitrogen cycle and the crucial roles played by organisms like Trichodesmium, certain bacteria, and marine animals. This quiz delves into nutrient regeneration processes and the interactions between land and sea ecosystems, highlighting the importance of these functions in maintaining marine biodiversity.

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