BR22610 Functional and Behavioural Adaptations to Living in Marine Environments

Topics Covered:
- Organismal
- Physical factors
- Ecological aspects
Focus Areas:
- Tides
- Exposure tolerance
- Temperature
- Desiccation
- Gas exchange (considering all marine organisms)
- Predation/herbivory
- Pressure
- Locomotion/buoyancy
- Competition
- Wave exposure
- Feeding
- Larval supply and recruitment
- Salinity
- Reproduction and development
- Facilitation
- Sediments
- Position maintenance
- Bioturbation
- Behavioural rhythms and orientation
- Disturbance
- Deep water adaptation
- Top-down/bottom-up processes
- Communication

Types of Cycles:
- Tidal cycles (approximately 12.4 hours)
- Diurnal cycles (approximately 24 hours)
- Semilunar cycles (approximately 28 days)
- Seasonal cycles (365 days)
Importance of Geophysical Events:
- They dictate the duration and extent of aerial exposure to intertidal organisms, particularly sessile species.
Temperature Range:
- Exposed intertidal shores can experience temperatures from below -22°C to above +40°C (e.g., Modiolus demissus).

Abiotic Stresses:
- Aerial exposure
- Wide ranges of temperature
Thermal Tolerance:
- Intertidal species exhibit higher thermal tolerance limits compared to subtidal species.
- Tropical species show higher thermal tolerance limits than temperate species (example: Petrolisthes violaceous).

Key Points from 2019 Study:
- Dramatic mortality events occur due to direct impacts on individual organisms.
- Increased susceptibility to predators as a secondary effect.
- Sublethal thermal stress reduces overall fitness due to physiological costs for protection and repair of cellular components.

High temperature poses greater problems than low temperature.
Effects include:
- Protein denaturation, leading to compromised cellular processes and integrity.
- Disturbances in membrane functions, including ciliary action.
Q10 Effect:
- The rate of enzyme reactions is temperature-dependent; rates increase with temperature until denaturation occurs.
- In marine science, higher temperatures correlate with rising metabolic costs ( $M_O2$ ).
Desiccation Risk:
- Ionic imbalance may occur.

Homeotherms:
- Mainly mammals and birds that regulate body temperature (Tb) at a constant level (more details provided later).
Ectotherms:
- All invertebrates, plants, and most fish; their metabolic rate (Mr) and behavior are affected by ambient temperature.

Morphology Adaptations:
- High-shore animals tend to exhibit larger body sizes and lower surface area-to-volume ratios (e.g., Littorina littorea).
- Methods to minimize body contact with substrate include:
- Snails attaching to overhangs via mucus threads (only in low energy shores).
- Strategies of Littorinids:
  - Withdrawing foot
  - Perched activities on the shell aperture lip.
Temperature Regulation Examples:
- Tectarius muricata (a tropical gastropod featuring heat-elaborated ridges for air cooling).
- Lighter shell color in snails helps maintain lower temperatures and minimize heat absorption, influencing species distribution.

Evaporative Heat Loss:
- An effective cooling mechanism yet poses a significant risk of desiccation, leading to trade-offs in energy conservation.
- Example: Barnacle Tetraclita rubescens retains water in its thick porous shell, allowing for evaporative cooling while preventing desiccation.

Specific Species Examples:
- Collisella digitalis (fingernail limpet) and Patella vulgata display home scars beneath Fucus patches.
- Gastropods utilize crevices for shelter during extreme temperatures (e.g., Broome, WA: 38°C).
Evidence of Behavioural Strategies:
- Crevice usage providing cooling effects and reducing exposure to solar heating, based on findings from Gray and Hodgeson (2004).

Behavioural Patterns:
- Rhythmic behaviors observed in response to heat stress; e.g., Afruca tangeri displays phototaxis, being photopositive at dawn/dusk and photonegative during peak daytime to mitigate heat exposure.

Intertidal organisms face varied environments, with pronounced challenges for sessile species due to aerial exposure, leading to:
- Thermal stress and desiccation issues requiring various adaptations.
- Morphological, behavioral, and physiological coping strategies emerging in response to extreme thermal conditions.

Importance of Colour:
- Shell color impacts body temperature differentials.
- Behavioural strategies such as foot position and shell orientation can reduce temperatures by 2–4 °C.
Examples: Littorina keenae showcases these colour and behavioural interactions.

When under thermal stress, heat shock factors dissociate from carriers and activate heat shock genes, which increase the production of heat shock proteins (HSPs).
- Function of HSPs:
- Serve as molecular chaperones preventing protein damage, refolding damaged proteins, and maintaining membrane functionality.

Studies on Tegula rugosa reveal HSP70 expression varying by habitat, indicating adaptations to environmental conditions.
- Field temperatures recorded with thermisters showed significant differences based on intertidal versus subtidal living conditions.

Example of Trematomus bernacchii, an Antarctic ice fish, showing a lack of adaptive HSP response due to stable environmental temperatures.

Pompeii Worm (Alvinella pompejana):
- Tolerates extreme temperatures
- Ranges from 22°C to 80°C in differing areas (e.g., holes in black smokers at depths over 2000m).
- Recognized as possibly the most eurythermal metazoan species.

Investigated individual survival against temperature extremes, reflecting stress gene expression patterns and overall adaptability to extreme conditions.

Upcoming topics will cover desiccation and freezing effects in marine organisms.