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Chapter 2: Adaptations to Aquatic Environments (Vocabulary Flashcards)

Chapter 2: Adaptations to Aquatic Environments

  • Acknowledgment context and Indigenous land acknowledgment: University of Arizona on Indigenous lands; reflects on sustainable relationships with Native Nations and Indigenous communities (education, partnerships, service).
  • Learning context: Ecological systems are hierarchical, governed by physical and biological principles, involve diverse roles of organisms, employ multiple study approaches, and are influenced by humans.

Earth as the Blue Planet

  • Approximately 71\% of Earth’s surface is covered by water.
  • Of this water: 97\% is Oceans, 2\% is in Glaciers/Ice Caps, and 1\% is Freshwater.
  • This distribution motivates widespread freshwater challenges and opportunities for life and human use.

Water Use: Millennium Ecosystem Assessment

  • Global freshwater use that exceeds long-term accessible water: 5-25\%.
  • Irrigation withdrawals that exceed supply rates: 15-35\%.
  • Concept: When demand equals supply, interpretation often relies on spatial or temporal context (e.g., maps showing demand vs. supply). See synthesis resource: http://www.millenniumassessment.org/en/Synthesis.html

Properties of Water

1) High absorption of light energy
2) Thermal: High specific heat capacity (energy required to raise temperature by 1^\circ C)
3) Density: Water is about 800+ times as dense as air
4) Viscosity: Water about 55\times more viscous than air
5) Important solvent for inorganic nutrients

Life in Water: Photic Zone

  • Most solar radiation absorbed within the upper meters of water; less than 1\% of light reaches deeper layers.
  • Surface waters are heated; deep waters remain cold, even in tropical regions.
  • Photosynthesis is largely restricted to the photic zone near the surface.

Adaptations to Water: Viscosity

  • Viscosity is the thickness of a fluid and causes resistance to movement.
  • Water’s high viscosity has driven evolution of streamlined bodies to reduce drag.
  • Some tiny marine organisms have evolved long, filamentous appendages that increase drag to enhance certain functions (e.g., feeding, suspension).

Water as a Powerful Solvent

  • Water is polar; the negative oxygen end of one molecule is attracted to the positive hydrogen end of another (hydrogen bonds).
  • Water dissolves many substances by solvating ions (e.g., NaCl) due to its polarity.

Precipitation, Solubility, and Inorganic Nutrients

  • Rainwater dissolves minerals from rocks/soils and transports them via streams to the ocean.
  • Oceans have higher dissolved mineral concentrations than streams and lakes.
  • Each mineral has an upper solubility limit in water, termed saturation; beyond saturation, minerals precipitate out.
  • Example: Calcium carbonate (CaCO3) precipitates to form limestone.
  • Water serves as a vehicle for inorganic nutrients essential for life.

Hydrogen Ions in Water (pH)

  • Water can dissociate into H+ and OH−; acidity is the concentration of H+ in solution.
  • pH is defined as \mathrm{pH} = -\log_{10}([\mathrm{H^+}]).
  • pH scale: lower values indicate acidity; neutral around 7; higher values indicate basic/alkaline conditions.

Acid Rain: Threats to Freshwater

  • SO2 and NO2 react with water in the atmosphere to form \mathrm{H2SO4} and \mathrm{HNO_3} (acid rain).
  • Acid rain dissolves aluminum (Al) from soils in watersheds; pH decreases (more acidic); Al concentrations rise in water.
  • Direct toxicity to fish and invertebrate reproduction; enzymes inhibited or altered.

Acid Rain: Legacy and Spatial Patterns

  • Since the 1960s, acid rain has decreased, yet its effects linger.
  • In some regions (e.g., 2/3 of 97 rivers in the Northeast USA), rivers tend to be more alkaline (basic) due to legacy effects.
  • Discussion prompt: How can legacy acid rain lead to higher alkalinity downstream? (link to article for deeper reading: http://pubs.acs.org/doi/abs/10.1021/es401046s)

Chapter 2 Learning Objectives (Recap)

  • Adaptations to aquatic environments.
  • Water has properties favorable to life.
  • Aquatic environments challenge the balance of water and salt in animals.
  • Uptake of gases from water is limited by diffusion.
  • Temperature limits the occurrence of aquatic life.

Solutes, Osmosis, and Salt Balance in Aquatic Animals

  • Solutes: dissolved substances in water; intracellular and extracellular solute concentrations may differ.
  • Water moves to equalize solute concentrations across locations.
  • Semipermeable membranes allow only certain solutes to pass, reducing free movement.
  • Osmosis: movement of water across a semipermeable membrane to balance solute concentrations.
  • Salt balance in aquatic animals emerges from these osmotic processes.

Osmoregulation: Hyposmotic and Hyperosmotic States

  • Hyposmotic: tissue solute concentrations are lower than surrounding water; net osmotic loss of water; organisms drink and retain water to compensate.
  • Hyperosmotic: tissue solute concentrations are higher than surrounding water; net osmotic gain of water; active uptake of minerals helps balance.

High Salt Concentrations: Toxicity and Anthropogenic Impacts

  • High salt concentrations can be fatal to aquatic organisms.
  • Road salt (soil and water runoff) increases salinity in nearby streams and ponds.
  • Elevated salinity (measured in microsiemens) has been linked to amphibian larval mortality.

Salt Balance in Plants

  • Plants in saline environments face salt balance challenges (e.g., root water uptake).
  • Mangrove trees on coastal mudflats: maintain high concentrations of organic solutes in roots to increase osmotic potential; exclude salts from roots via active transport; can secrete salt from leaves.

Diffusion of Carbon Dioxide in Water

  • CO2 is required for photosynthesis by plants and cyanobacteria.
  • CO2 diffuses slowly through water; plants consume CO2 faster than it diffuses into leaf tissues.
  • CO2 is rapidly converted to bicarbonate (HCO3−) or carbonate (CO3^{2−}) ions, which can accumulate and be used for photosynthesis.

Slow Diffusion of CO2 Limits Growth

  • Even with abundant CO2/HCO3−, diffusion is slow, limiting carbon availability to aquatic plants.
  • Boundary layer: a region of unstirred air or water surrounding a surface where gas exchange is slow due to limited mixing.

Adaptations to Low Oxygen

  • Oxygen in air is ~21% by volume; in water, O2 is ~1% by volume.
  • In deep oceans, many organisms have low metabolic rates, reducing O2 demand.
  • Spotted salamander eggs exhibit a mutualistic relationship with algae: eggs provide CO2 to algae; algae provide O2 to eggs; hatch earlier and larger, conferring fitness benefits.

Anaerobic Conditions

  • In oxygen-depleted environments (anoxic), such as waterlogged sediments or deep waters with no photosynthesis, O2 is depleted.
  • Microbes thrive by using alternative energy sources (e.g., sulfur from deep-sea hydrothermal vents).

Eutrophication: Nutrient Enrichment and Hypoxia

  • Excess nitrogen (N) and phosphorus (P) promote algal blooms in the photic zone.
  • When blooms die and decompose, O2 is depleted, causing hypoxic or anoxic conditions.
  • Hypoxia is toxic/fatal for fish and invertebrates; overall microbe and plant diversity declines.
  • Some algae produce neurotoxins that pose ecosystem and drinking water risks.
  • Case in point: Toxic algae and drinking-water contamination (Toledo, Ohio, Aug 2014).

Chapter 2 Learning Objectives (Continued)

  • Reiteration of the climate-influenced factors that shape aquatic adaptation: temperature, diffusion, solute balance, and oxygen availability.

Heat and Biology: Temperature Effects on Biological Processes

  • Heat can disrupt molecular structure and accelerate chemical reactions by increasing molecular movement.
  • Q10 value: the ratio of a physiological process rate at one temperature to the rate at the same process when the temperature is 10°C cooler; typical ranges are 2\le Q_{10} \le 4.
  • Biological implications: higher temperatures can increase metabolic rates but may reduce stability of biomolecules; organisms have thermal tolerances.

Heat and Biological Molecules

  • Proteins and other biomolecules become less stable at higher temperatures and may denature (lose function).
  • Lipids: membranes become more fluid with heat and more stiff with cold.
  • Thermal pollution: human discharges can alter water temperature and affect ecosystems (e.g., effluent from power plants).
  • Some archaea are thermophiles, thriving at temperatures up to 110^{\circ}\mathrm{C}.

Cold Temperatures and Freezing

  • Ice crystal formation can damage cells; organisms have strategies to cope.
  • In seawater, freezing point is lowered to about -1.9^{\circ}\mathrm{C} due to dissolved salts.
  • Marine vertebrates face freezing challenges; some animals use solutes like glycerol and glycoproteins to prevent freezing or enable supercooling (ice-seed coating) (e.g., Arctic cod).

Thermal Optima

  • Thermal optima define the temperature range in which an organism performs best; determined by enzymes, lipids, cellular/tissue structures, and body form.
  • Example: Arctic cod can function in cold waters with activity and oxygen consumption similar to tropical fish in warmer water.
  • Inappropriate temperatures lead to reduced performance and potential mortality for non-adapted species.

Thermal Optima: Current Threats to Aquatic Life

  • Global coral bleaching crisis driven by elevated temperatures: corals expel their symbiotic algae when water is just ~1°C warmer than average.
  • Coral reefs are effectively being 'cooked' by climate warming; bleaching signals ecosystem stress and potential collapse if temperatures remain elevated.

Additional Notes and References

  • A brief on media resource: a video link is provided for supplementary context: https://www.youtube.com/watch?v=mQ10xBl8XMQ