Temperature Effects on Marine Animals P.1

Temperature Effects on Marine Animals (Part 1)

Context:
- Follows lectures on respiration, circulation, nitrogen excretion, osmoregulation, and buoyancy.
- Leads into two more lectures on temperature effects, focusing on enzymes, proteins, and membranes and cold-temperature adaptations.
Focus:
- Temperature variability in the marine environment.
- How temperature affects physiological processes.
- The Q10 concept and metabolic rate responses.

Among all abiotic factors, temperature has the greatest impact on physiology.
Affects metabolism, enzyme activity, growth, locomotion, reproduction, and distribution of species.
Temperature effects on physiological processes follow the Q10 rule (explained later).

More stable than terrestrial environments due to water’s high specific heat capacity.
Deep ocean (~80% of marine habitat) remains cold (~2–4°C) year-round.
Surface waters and coastal regions experience more variation:
- Tropics: Warm year-round (small seasonal variation).
- Temperate waters: Large seasonal variation (~15°C difference annually).
- Polar regions: Cold, with some variation due to seasonal ice melt.
- Intertidal zones: Extreme fluctuations (exposure to air & sun).
Special cases:
- Antarctic waters: Can drop to -1.9°C (seawater freezing point).
- Hydrothermal vents: Can reach 350°C (but rapidly cools with distance from the vent).
- Geothermal hot springs: Some species tolerate >50°C (e.g., Pompeii worm).

Theoretical range for life: -1.9°C to ~350°C.
Observed range for metazoan animals: -1.9°C to ~50°C.
- Hottest animal: Pompeii worm (~50–70°C tolerance).
- Coldest animals: Antarctic icefish survive at sub-zero temperatures.

Term	Definition	Examples
Endotherms	Maintain stable internal temperature via metabolic heat production.	Mammals, birds, Opah (only fully endothermic fish).
Ectotherms	Body temperature varies with the environment.	Most fish, reptiles, amphibians, invertebrates.

Endothermic marine animals (e.g., mammals, seabirds) use insulation (fur, blubber) to retain heat.
Some fish (e.g., tuna, sharks) show regional endothermy, maintaining warmer core temperatures than surroundings.

Species must either adapt, migrate, or face extinction.
Range shifts observed:
- Many species moving poleward to stay within preferred temperature ranges.
- Some species moving deeper to find cooler waters.
- Polar species (e.g., Antarctic fish) face high extinction risk due to lack of colder habitats.

Thermocline Type	Description	Where Found?
Permanent Thermocline	Exists year-round	Tropics & subtropics
Seasonal Thermocline	Forms in summer, disappears in winter	Temperate regions
Diurnal Thermocline	Daily fluctuations due to sunlight	Shallow coastal waters

As temperature increases, metabolic rate generally increases.
Q10 Concept (Van’t Hoff Rule):
- Q10 measures how much a process speeds up with a 10°C temperature increase.
- Q10 = 2: The rate doubles with a 10°C increase.
- Q10 = 3: The rate triples with a 10°C increase.

Response Type	Description	Example
Acute Response	Immediate physiological change with sudden temperature shifts.	Metabolic rate spike when a fish is transferred from 5°C to 25°C.
Acclimated Response	Long-term physiological adjustment over days/weeks.	Fish at 25°C reduces metabolic rate over time as it acclimates.

Acclimation involves changes in enzyme expression and metabolic compensation.

Marine organisms experience different temperature regimes based on depth, latitude, and habitat.
Deep waters are cold and stable, while surface waters & coastal regions vary more.

Metabolic rate increases with temperature (Q10 rule).
Beyond optimal temperatures, enzyme activity declines and organisms experience stress.