Aquatic Adaptations Study Notes 2

Organism Adaptations

• Organisms adapt to water, land, and changes in climate, life history, sex, and sociality.
• Populations exhibit structure, growth, and dynamics.
• Communities show species interactions, structure, succession, and biogeography.
• Ecosystems cycle energy and nutrients.
• The biosphere undergoes anthropogenic change and requires conservation.

Adaptations to Aquatic Environments

• Properties of water influence aquatic life.
• Water and salt balance are crucial for aquatic organisms.
• Light availability affects photosynthesis in aquatic environments.
• Bioluminescence is a significant adaptation in the deep sea.

Properties of Water

• Water is liquid over a wide temperature range:
  • Water: Melting point $0 °C$, Boiling point $100 °C$, Range $100 °C$
  • Ammonia: Melting point $-78 °C$, Boiling point $-33 °C$, Range $45 °C$
  • Methane: Melting point $-182 °C$, Boiling point $-164 °C$, Range $18 °C$
  • Ethane: Melting point $-183 °C$, Boiling point $-89 °C$, Range $94 °C$
• Adhesion-cohesion-tension:
  • Emergent adaptation from physics enables transpiration.
  • Osmosis: $H_2O$ enters the root.
  • Polarity: $H_2O$ attracted to polar xylem walls, allowing it to creep up.
  • H-bonding: $H_2O$ molecules attract each other, pulling each other up in xylem.
  • Evaporation occurs out of leaves.
• Surface tension allows pond life to thrive on top of the water.

Density and Buoyancy

• Water has high density.
• Adaptations for buoyancy include:
  • Floating at or near the surface.
  • Maintaining position in the water column at a specific depth.
• Examples include: Water-dispersed seeds, macro- and microalgae (e.g., Sargassum spp.), swim bladders in ray-finned fishes.

Density and Temperature

• Maximum density of water occurs at $4°C$.
• The density of water and ice varies with temperature.
• Density is measured in $\frac{g}{cm^3}$.

Life Under Sea Ice

• Various organisms thrive under sea ice, including ice algae, Arctic cod, jellyfish, detritus, sea stars, urchins, and bowhead whales.
• Antarctic krill (Euphausia superba) feed on ice algae.

Antarctic Ice Shelf Loss

• The collapse of the Larsen B ice shelf occurred in Jan-Mar 2002.
• This ice shelf had been stable for over 10,000 years.

Water as a Polar Solvent

• Water dissolves salt ($NaCl → Na^+ + Cl^−$).
• It also dissolves other minerals like carbonate ($CO<em>3^{-2}$) and silicate ($SiO</em>4^{-2}$).

pH

• pH is measured using a log scale.
• pH affects physiology.
• Ocean acidification is linked to increasing seawater $CO_2$ levels and decreasing seawater pH.
• Ocean acidification can lead to decalcification in plankton, coralline algae, reef corals, and mollusks.
• Buffering systems, such as bicarbonate and carbonate, are important in maintaining pH.

Water and Salt Balance

• Aquatic animals are either osmoconformers or osmoregulators.

Osmoconformers

• Marine invertebrates are typically osmoconformers.

Osmoregulators

• Marine ray-finned fishes are osmoregulators.
• Osmoregulation differs in freshwater vs. saltwater teleosts.
• Cells isolate solutes but allow water to pass through osmosis.
• Water movement is from areas of high concentration to low concentration.
• Marine teleosts are hypoosmotic, excreting salt and conserving water.
• Freshwater teleosts are hyperosmotic.
• Mangroves exhibit adaptations for water and salt balance, including salt excretion, tolerance to high sugar concentrations, salt exclusion, and salt storage.

Light and Photosynthesis

• Light penetration varies in marine waters, with less penetration in coastal waters.
• Photosynthesis action spectra differ among marine algae, such as Ulva (shallow) and Porphyra (deep benthic).
• Gas exchange is difficult underwater due to low solubility and slow diffusion.
• Seagrasses utilize both $CO<em>2$ and $HCO</em>3^−$ for photosynthesis.
• They transport oxygen via air tubes for root respiration.

Bioluminescence

• Bioluminescence is common in deep-sea organisms.
• Examples include anglerfish, firefly squid, lanternfish, and certain shrimp species.
• It is hypothesized that 76% of deep-sea animal species use bioluminescence.
• In summary, adaptations to aquatic environments include properties of water, water and salt balance, light and photosynthesis, and bioluminescence.

Marine Ray-Finned Fish Osmoregulation

• Marine ray-finned fishes are hypoosmotic compared to their environment, excreting salt and conserving water.

Phylogeny of Ray-Finned Fishes

• The MRCA (most recent common ancestor) of extant ray-finned fishes likely lived in freshwater.
• The transition to freshwater occurred after the first ray-finned fishes, which were marine.
• Following adaptation to freshwater, some descendants returned to the sea and became hypoosmotic.
• A mass extinction event in the ocean affected ancestral marine ray-finned fishes.

Mangrove Adaptations

• Red mangroves and black mangroves employ different strategies for water and salt balance.
  • Red mangroves exclude salt and tolerate high sugar concentrations in their roots.
  • Black mangroves excrete salt from their leaves.
• Some mangroves are osmoregulators, while others are not.