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. (D)</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. (C)</p> Signup and view all the answers

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

<p>Ammonia (A)</p> Signup and view all the answers

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

<p>Phosphorus (D)</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. (C)</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 (A)</p> Signup and view all the answers

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

<p>Phytoplankton (C)</p> Signup and view all the answers

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

<p>Planktivores (B)</p> Signup and view all the answers

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

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

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

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

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

<p>Phytoplankton (B)</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. (B), GPP is always higher than NPP. (C)</p> Signup and view all the answers

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

<p>6500 m (A), 550 m (B)</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% (D)</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. (C)</p> Signup and view all the answers

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

<p>Deep-sea hydrothermal vents (B)</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 (A)</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 (A)</p> Signup and view all the answers

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

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

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

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

What relationship is commonly observed between phytoplankton and zooplankton populations?

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

Why might phytoplankton and zooplankton not coexist abundantly over time?

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

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

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

What effect do phytoplankton like Phaeocystis have on water quality?

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

What happens to zooplankton populations as herbivorous zooplankton numbers increase?

<p>They rapidly decrease in number (A)</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 (A)</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. (D)</p> Signup and view all the answers

Which factor affects the patchiness of phytoplankton?

<p>Grazing by zooplankton. (C)</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. (B)</p> Signup and view all the answers

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

<p>Swarming behavior. (B)</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. (A)</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. (B)</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. (C)</p> Signup and view all the answers

What determines the distribution of meroplankton?

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

Which type of bacteria acts as primary producers through chemosynthesis?

<p>Autotrophic bacteria. (B)</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. (D)</p> Signup and view all the answers

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

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

What role does denitrifying bacteria play in nutrient cycling?

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

How does nutrient accumulation below the euphotic zone primarily occur?

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

Which statement about phytoplankton is true?

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

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

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

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

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

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

<p>Herbivorous zooplankton (B)</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. (B)</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. (A)</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. (B)</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. (A)</p> Signup and view all the answers

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

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

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

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

Why are dark bottles used in the measurement process?

<p>To prevent oxygen production (D)</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 (C)</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 (A)</p> Signup and view all the answers

What assumption is made about respiration when measuring net production?

<p>Respiration is not influenced by light (B)</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 (C)</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 (A)</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 (D)</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) (D)</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 (C)</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. (A)</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 (A)</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. (A)</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. (C)</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) (C)</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 (B)</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. (D)</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 (C)</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. (A)</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 (C)</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. (B)</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. (A)</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. (C)</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. (A)</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 (B)</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 (B)</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 (C)</p> Signup and view all the answers

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

<p>Winter (B)</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 (B)</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 (A)</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 (C)</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 (C)</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. (A)</p> Signup and view all the answers

How does grazing by zooplankton influence phytoplankton distribution?

<p>It creates localized patches of phytoplankton. (B)</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. (C)</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. (B)</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. (B)</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. (A)</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. (C)</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. (D)</p> Signup and view all the answers

Flashcards

Primary Production (Ocean)

The process where autotrophic organisms make organic compounds from seawater.

Gross Primary Production (GPP)

The total amount of organic matter produced during photosynthesis.

Net Primary Production (NPP)

GPP minus losses due to respiration.

Phytoplankton

Microscopic algae that are the major primary producers in the ocean.

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Euphotic Zone

The sunlit surface layer of the ocean where phytoplankton thrive.

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Deep-sea Hydrothermal Vents

Exceptions to the reliance on photosynthesis for energy, using chemical sources from vents.

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Detritus

Organic matter originating from the surface that fuels deep-sea organisms

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Ocean Productivity

The rate at which organic matter is produced by primary producers in oceans.

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Marine nutrient cycle

The continuous process of nutrient regeneration in marine ecosystems, involving the breakdown of organic compounds and the utilization of excretory products by primary producers.

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Dissolved nutrients (e.g., nitrates & phosphates)

Nutrients dissolved in seawater, primarily derived from land runoff and weathering of rocks.

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Primary producers

Photosynthetic organisms (e.g., seagrasses, algae, phytoplankton) that form the base of the marine food web.

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Microbial loop

A part of the food chain involving bacteria and micro-organisms that recycle organic matter.

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Dissolved organic carbon (DOC)

Dissolved organic matter present in water that supports the microbial loop.

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Nutrient excretion

Release of waste products (e.g., ammonia, phosphates) by marine animals.

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Direct regeneration

The immediate use of animal waste products by primary producers.

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Classical food chain

A simplified model that describes the flow of energy (food) from producers to higher trophic levels.

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Nitrogen Fixation in Sea

Certain organisms (Trichodesmium, bacteria) can convert atmospheric nitrogen into usable forms, but this process is likely not significant in the ocean due to high energy demands.

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Nitrogen Cycle Input (Sea)

Land plants, bacteria, and microorganisms fix atmospheric nitrogen, and runoff carries it into the sea.

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Nitrate Reduction

Some bacteria in oxygen-poor conditions use organic carbon for energy and release nitrogen by oxidizing organic material, reducing nitrates to nitrogen gas.

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Bacterial Roles in Marine Food Webs

Bacteria break down organic matter to simpler nutrients, useful for plants, and also produce bacterial protoplasm as a direct food source for some animals.

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Sulphur Cycle Regeneration

Bacteria decompose organic sulfur compounds, creating hydrogen sulfide, which gets oxidized to sulfur and then to sulfate.

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Langmuir Vortices

Spiral patterns in the surface water caused by wind action, creating zones of convergence and divergence of water.

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Phytoplankton Patchiness

Uneven distribution of phytoplankton in the water caused by factors like currents, turbulence, and grazing.

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Inverse Phytoplankton-Zooplankton Relationship

A trend where abundant phytoplankton lead to low zooplankton populations, and vice-versa.

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Phytoplankton Grazing

Zooplankton consuming phytoplankton, impacting the abundance of both.

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Phytoplankton Growth Rate

Rate at which phytoplankton populations multiply, influenced by environmental conditions.

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Animal Exclusion Hypothesis

Theory that some phytoplankton species produce substances that make water unpleasant for animals, causing them to avoid it.

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Phaeocystis Blooms

Massive growth of Phaeocystis phytoplankton forming slimy colonies, affecting water quality and deterring some organisms.

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Phytoplankton Secretion

Release of chemicals by phytoplankton, influencing other organisms and water quality.

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Nutrient Loss

Organic matter sinking from the euphotic zone to deeper water, potentially becoming incorporated into sediment.

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Nutrient Regeneration

The decomposition of sinking organic matter in deeper layers, releasing nutrients back into the water.

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Vertical Water Mixing

Upward movement of water from deeper layers, bringing nutrients back to the surface, supporting primary production.

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Upwelling

A process where wind drives nutrient-rich water from deeper levels to the surface, supporting high productivity.

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Chemosynthesis

Production of organic matter using energy derived from chemical reactions, not sunlight.

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Autotrophic Bacteria

Bacteria that produce organic matter through chemosynthesis, playing a role in nutrient cycling.

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N-compounds

Nitrogen compounds, essential nutrients for the growth of organisms in the ocean.

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Nitrogen Fixation

The conversion of atmospheric nitrogen gas into usable forms, essential for marine ecosystem productivity.

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Denitrification

The process where nitrogen compounds are converted back into atmospheric nitrogen gas, removing them from the marine ecosystem.

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Sinking

Gravity-driven downward movement of organic matter from the euphotic zone, transporting nutrients.

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Land Drainage

Nutrients from land sources, like sewage and fertilisers, entering the ocean.

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Dissolved N2

Nitrogen gas dissolved in seawater, largely unusable by organisms.

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Atmospheric N2

Nitrogen gas present in the atmosphere, the largest pool of nitrogen.

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Zooplankton Behaviour

The way zooplankton move and react to different environmental factors, including the presence of phytoplankton.

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Plankton Patchiness

The uneven distribution of plankton, often occurring in concentrated areas or patches.

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Zooplankton Grazing

The consumption of phytoplankton by zooplankton, influencing the distribution and abundance of phytoplankton.

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Vertical Migration

The daily up-and-down movement of plankton, often influenced by light and food availability.

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Swarming Behaviour

The gathering of large numbers of zooplankton in specific areas, often for breeding purposes.

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Meroplankton Distribution

The dispersal of meroplankton (larvae that live in the plankton for a period) is influenced by the distribution of their benthic (bottom-dwelling) parents.

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Plankton Patchiness & Feeding

The uneven distribution of plankton (patchiness) benefits zooplankton because it allows them to efficiently feed in areas of high food concentration.

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Even vs. Patchy Food Distribution

While patchy food distribution allows zooplankton to feed efficiently, even food distribution could lead to starvation if it's too dilute.

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Energy Flow in Food Webs

The movement of energy from one trophic level to the next, with some energy lost as heat at each step.

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Trophic Level Efficiency

The percentage of energy transferred from one trophic level to the next.

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Why is farming herbivores better?

It's more energetically efficient to consume herbivores than carnivores, as less energy is lost through the food chain.

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Organic Matter Cycling

The continuous process of organic material breaking down and being recycled back into the ecosystem.

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Primary Production

The formation of organic matter by producers, primarily through photosynthesis, which forms the base of the food web.

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What's the input in energy flow?

Sunlight is the primary input of energy in marine ecosystems, driving photosynthesis and powering the food web.

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Where does energy go after a food web?

Energy lost through respiration, excretion, and decomposition eventually becomes dissipated as heat.

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What's the relationship between matter and energy?

Matter is cycled through the ecosystem, while energy flows through it, being lost continuously.

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Net Primary Production

The amount of organic matter produced by photosynthesis in phytoplankton minus the amount lost through respiration.

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Dark Bottle Experiment

A method to measure respiration in phytoplankton samples by comparing oxygen levels in a sealed, dark bottle to the original level.

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Light Bottle Experiment

A method to measure photosynthesis in phytoplankton samples by comparing oxygen levels in a sealed, clear bottle to the original level.

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Photosynthetic Zone

The layer of water where sunlight penetrates and allows phytoplankton to photosynthesize.

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Bacterial Growth in Bottles

A complication in bottle experiments where bacteria can quickly multiply, potentially affecting oxygen measurements.

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Oxygen Conversion

Converting measured oxygen levels into carbon production and loss figures.

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Respiration in Bottles

The process of oxygen consumption by all living organisms, including phytoplankton, zooplankton, and bacteria inside sealed bottles.

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Bottle Suspension

Placing pairs of sealed bottles (light and dark) at the same depth in the sea to mimic natural conditions.

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The 14C method

A technique for measuring primary production based on the uptake of radioactive carbon-14 (14C) by phytoplankton and macroalgae.

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How does the 14C method work?

Samples of seawater with added 14C are incubated, and the amount of 14C incorporated into phytoplankton is measured to determine their carbon fixation rate.

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What are the limitations of the 14C method?

It only measures 14CO2 incorporated into the filtered material, not the soluble organic products released into the water.

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How does the 14C method compare to oxygen determination?

Both provide estimates of primary production, but 14C focuses on phytoplankton specifically, while oxygen determination includes zooplankton.

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What are the sources of inaccuracies in both methods?

Phytoplankton patchiness and the loss of dissolved organic matter during incubation can affect both the 14C and oxygen determination methods.

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Why is the 14C method generally considered more accurate?

It provides a direct measurement of carbon fixation by phytoplankton, unlike oxygen determination, which can be influenced by other organisms.

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

It focuses purely on phytoplankton, as zooplankton don't assimilate the radioactive isotope, providing a clearer picture of primary production.

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What are the main problems affecting the accuracy of assessing production?

Phytoplankton distribution patchiness and the loss of dissolved organic matter during incubation make it difficult to get a true picture overall.

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Compensation Depth

The depth at which the rate of photosynthesis matches the rate of respiration for phytoplankton, resulting in no net gain in organic matter.

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Phytoplankton as 'Shade Plants'

Phytoplankton are often considered 'shade plants' because their own light absorption limits sunlight penetration in the water column, creating a self-shading effect.

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Phytoplankton and Water Mixing

Phytoplankton can be transported to different depths by waves and currents, influencing their primary productivity and respiration rates.

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Effect of Depth on Phytoplankton Production

As phytoplankton are transported deeper, their primary productivity decreases as they enter regions with less light, eventually reaching the compensation depth where they only respire.

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Primary Production Rate

The rate at which organic matter is produced by phytoplankton through photosynthesis, reflecting the overall productivity of the marine ecosystem.

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Generalized Diagram of Primary Production

A diagram that shows the relationship between primary production rate, depth, and the compensation depth, highlighting the factors that influence phytoplankton productivity.

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Respiration vs. Photosynthesis

Respiration occurs when phytoplankton break down organic matter for energy, consuming oxygen. Photosynthesis occurs when they create organic matter from sunlight, releasing oxygen.

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Ocean Seasons

Distinct periods in the ocean marked by variations in temperature, light, and nutrients, significantly impacting plankton populations.

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Seasonal Thermocline

A layer in the ocean where temperature changes rapidly, separating warmer surface water from colder deeper water. Forms during summer in temperate regions.

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Winter in Temperate Seas

Surface water cools down, leading to mixing of the water column. Nutrients from deeper layers are brought to the surface.

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Spring Bloom

A rapid increase in phytoplankton population in spring due to increased sunlight and nutrient availability.

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Summer Stratification

Warmer surface water forms a stable layer on top of colder, nutrient-rich water, limiting mixing and phytoplankton growth.

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Autumn Mixing

Cooling surface water allows for some mixing, bringing nutrients back to the surface, leading to a smaller phytoplankton bloom.

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Plankton Abundance

The number of plankton organisms in a particular area. Varies seasonally due to changes in temperature, light, and nutrients.

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Seasonal Cycle of Copepods

Copepods, a type of zooplankton, exhibit seasonal cycles in abundance, often following patterns related to water temperature and nutrient availability.

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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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