Rocky Shores Flashcards

Adaptation to Life on Rocky Shores

Learning Outcomes

• Discuss adaptations to temperature and desiccation stress.

• Discuss adaptations to waves and currents.

• Evaluate whether adaptations are a direct response to abiotic or biotic factors.

Vertical Stress Gradient

• Zonation is a pattern.

• Processes underpinning this pattern:

  • Abiotic: Exposure, temperature, desiccation, topography.

  • Biotic: Competition, predation, settlement.

Temperature Changes & Desiccation: Behavioural Adaptations

• Settlement variations in strategies:

  • Throughout intertidal

  • Low on shore/pools

  • Mid shore

  • High on shore

  • Crevices

• Hiding & night foraging.

Temperature Changes & Desiccation: Physical Adaptations

• High shore species:

  • Paler shells

  • Lower body temperatures

• Mid shore species:

  • Darker shells

  • Higher body temperatures

• Reference: McMahon (1990) Hydrobiologia 193: 241-260

• Shells/tests offer physical advantages.

Temperature Changes & Desiccation: Physiological Adaptations

• Oxygen deficit or build-up of waste during low tide.

• Respiratory organs must be moist to acquire oxygen, and usually withdrawn at low tide.

• Adaptations:

  • Reduce metabolic rate

  • Bind hemoglobin with oxygen

  • Respire in air

  • Air cavity/bubble

• Examples:

  • Turbo castanea with operculum

  • Onchidella celtica

  • Siphonaria spp.

Temperature Changes & Desiccation: Biochemical Adaptations - Water Loss

• Patella vulgata:

  • Distribution: High shore to low shore

  • High shore individuals can lose 60-65% water

  • Low shore individuals can lose 50-55% water

• Patella ulyssiponensis:

  • Distribution: Low shore

  • Low shore individuals can lose 30-35% water

• High shore species/individuals are better adapted to water loss.

Temperature Changes & Desiccation: Biochemical Adaptations - Water Loss

• Pelvetia canaliculata, Fucus spiralis, Fucus vesiculosus

• Experiment measuring condition of thalli after exposure to high temperature (24^{\circ}C) and low humidity (desiccation stress) for 10 days.

• High shore species (e.g., Pelvetia canaliculata) can remain healthy, while low shore species are damaged or dead.
  *Reference: Schonbeck & Norton (1978) JEMBE 31, 303-313

Temperature Changes & Desiccation: Behavioural

• Mushrooming: Williams et al. (2005) Mar Ecol Prog Ser 292: 213-224

• Thermal refuge selection:
  *Winter: Warmer habitat
  *Summer: Cooler habitat
  *Ng et al. (2017) J Exp Mar Biol Ecol 492: 121-131

• Aggregation: Ng et al. (2017) J Exp Mar Biol Ecol 492: 121-131. Displayed as X, Y, Z.

• Shell orientation: Ng et al. (2017) J Exp Mar Biol Ecol 492: 121-131.

• Shell posturing: Miller & Denny (2011) Biol Bull 220: 209-223. Displayed as X, Y, Z.

• Towering: Ng et al. (2017) J Exp Mar Biol Ecol 492: 121-131. Displayed as X, Y, Z.

Horizontal Stress Gradient

• Stresses:

  • Settlement & foraging problems

  • Dislodgement

  • Siltation, smothering & interference with respiration

• Direct forces: Lift & drag (tension/shear)

• Indirect forces: Wave action can mobilize objects (compression)

• Examples: Hook Head, Ireland & Rhosneigr, North Wales

Lift and Drag

• Drag (= a force that lies parallel to direction of flow):

  • Proportional to cross-sectional area of organism

  • Occurs when moving water slows as it moves over an organism

• Lift (= a force that lies perpendicular to flow):

  • Proportional to surface area

  • Occurs when water moves faster over one surface than another

• Both exert forces on intertidal organisms and alter morphologies (e.g., kelp), or hold on tight (e.g., limpet).

• Water molecules are sticky; velocity (U) decreases closer to the bottom.

Waves & Currents: Behavioural Adaptations

• Hiding to prevent dislodgement:

  • In boundary layer

  • In crevices (e.g. Helcion pectunculus)

• Foraging during low water (e.g. Siphonaria capensis)

• Boundary layer has decreasing velocity near the bottom surface.

Waves & Currents: Physical Adaptations

• Anchoring against dislodgement:

  • Kelp holdfast

  • Starfish tube feet

  • Mussel byssal threads

• Barnacle glues

• Limpets: suction @ high tide, mucus @ low tide. Reference: Smith (1992) J Exp Mar Biol Ecol, 160: 205-220

Waves & Currents: Physical Adaptations - Shell Morphology

• Reference: Hayward & Ryland (1995)

• Examples: P. ulyssiponensis, P. depressa, P. vulgata

Sessile Animals: Lift and Drag

• Lottia gigantea:

  • Streamlined (majority of force is lift)
    *Lift: 235 N/m^2

• Acmae mitra:

  • Blunt or less streamlined (majority of force is drag)
    *Drag: 207 N/m^2

• Stiff structures (e.g., limpet shells) trade-off between lift and drag.

• A shape that minimizes drag maximizes lift; shape that minimizes lift maximizes drag.

• Limpets hold on to rock via their adhesive muscular foot. Denny (1987). https://doi.org/10.1016/0169-5347(87)90150-9

Waves & Currents: Physical Adaptations - Flexible & Orientation

• Sea Squirt (Styela) altered orientation of siphon.

Waves & Currents: Physical Adaptations - Shape & Size

• Shape and size adaptations for exposed or sheltered conditions.

Waves & Currents: Physiological Adaptations - Growth Strategies & Life Cycles

• Postelsia palmaeformis (sea palm):

  • Sheltered: Can settle and survive if bare space; usually outcompeted

  • Exposed: More space (disturbed patches); settles on mussels (facilitates dislodgement) = bare space

Waves & Currents: Physiological Adaptations - Growth Forms

• Laminaria hyperborea (tangle/cuvie) & Laminaria digitata (oarweed)

• At exposed sites: Longer & more numerous frond digits (sometimes whole length of frond)

• Compared to sheltered sites with shorter and fewer digits (cucullate form)

• Transplant experiments (exposed-sheltered) demonstrate these adaptations.

Other Adaptations

• (No specific information provided on slides 32 and 33)

Useful Resources

• Key resources:

  • Raffaelli & Hawkins (1996) Intertidal Ecology, Kluwer Academic Publishers. Charles Seale-Hayne Library Main (574.52638 RAF)

  • Little, Williams & Trowbridge (2010) The Biology of Rocky Shores, 2nd Ed, Oxford University Press. Charles Seale-Hayne Library Main (578.7699 LIT)

• Papers: Source examples from the primary literature.

Vertical Stress Gradient and Zonation

• Zonation: Distinct horizontal bands of organisms that occur at different tidal heights.

Vertical Distributions: ‘Zonation’

• Adapted from Stephenson & Stephenson (1972)

  • Supralittoral: Rarely covered by water

  • Littoral (intertidal): Divided into upper, mid & low

  • Sublittoral (subtidal): Always covered by water

• Zonation is a pattern underpinned by:

  • Abiotic factors: Exposure, temperature, desiccation, topography

  • Biotic factors: Competition, predation, settlement

Abiotic Factors: Uni-directional Vertical Stress Gradient

• Environmental harshness (abiotic stress) increases up the shore.

• Key gradients and their impacts:

  • Desiccation, temperature & salinity variability: increase upshore

  • Availability of light & air: increases upshore

  • Availability of nutrients & suspended food: increase downshore

  • Abiotic stress tolerance: increases upshore

  • Growth, reproduction & maximum size: increase downshore

  • Importance of facilitation: increases upshore

  • Importance of competition & predation: increases downshore

  • Productivity, biomass & biodiversity: increase downshore

Vertical Stress Gradient: Impacts on Ecology

• High Shore Characteristics:

  • High abiotic stress

  • Low resource availability

  • Unfavorable organismal performance

  • Reduced biological interactions

  • Low ecological attributes (biomass, productivity, species richness)

• Low Shore Characteristics:

  • Low abiotic stress

  • High resource availability

  • Favorable organismal performance

  • Increased biological interactions

  • High ecological attributes (biomass, productivity, species richness)

  • High diversity, productivity, surface cover and structural complexity

• High shore: Low diversity, productivity, surface cover, and surface complexity (at organismal scales).

Emerging Synthesis for Plants and Sessile Animals (Connell, 1972)

• Proximate causes:

  • Upper limits: Due to direct physical effects (associated with emersion)

  • Lower limits: Due to biological factors (competition, grazing, predation, larval behavior)

• Upper limits set by physical factors: direct observations of damage to Pelvetia in warm weather on upper shore.

Lower Limits Set by Biological Factors: Experimental Manipulations

• Grazing exclusion by caging/fencing experiments (Boaventura et al. (2002), JEMBE). Showed impact of grazing.

• Lower limits generally set by biological factors (e.g., Pelvetia rotting when transplanted lower on shore due to pathogens, but more evidence needed).

Abiotic: Thermal and Desiccation Stress

• Experiment: Exposure to high temperature (24^{\circ}C) and low humidity (desiccation stress).

• Pelvetia canaliculata, Fucus spiralis, Fucus vesiculosus exposed for 10 days (Schonbeck & Norton, 1978).

Abiotic: Microhabitats Modify Vertical Distribution

• Crevices, drainage channels & rock pools: refuge from abiotic stress.

• Upper limits of the distribution of organisms can be extended.

• Large algae, fish and other organisms can persist in pools (Metaxas & Scheibling (1993) Mar Ecol Prog Ser 8, 187-198).

Biotic Factors: Competition

• Rocky Shore Zonation

• Competition in different zones affects the distribution of species.

• Examples: Anemones, Barnacles, Limpets, Hermit Crab, Mussels, Kelp Forest, Periwinkles, Benthic Invertebrates, Spiral Wrack

A Tale of Two Barnacles – Competition for Space

• Chthamalus stellatus

• Semibalanus balanoides

Manipulative Field Experiments

• involve changing one factor, whilst holding other factors constant

• are used to determine the relative importance of different drivers

• are crucial in determining the causes of zonation patterns (and/or other factors)

Biotic Factors: Interspecific Competition - Connell (1961) Ecology 42:710–723

*Interspecific competition between Balanus (+) and Chthamalus, leading to Chthamalus mortality
*Chthamalus survival

Competition in Natural Communities

• Concepts of fundamental and realized niche.

• Chthamalus and Balanus example (Connell, 1961).
  First field-based experimental evidence of interspecific competition.

Larval Settlement and Mortality

• C. montagui (High) and C. stellatus (Mid) (Delany et al. (2003) Mar Ecol Prog Ser 249: 207–214).

• Larval supply/post settlement mortality.

• Proportions settling did not differ between high and mid.

• C. stellatus: high mortality on high shore.

• C. montagui: high mortality on mid shore.

Biotic Factors: Predation

• Rocky Shore Zonation

• Different predators within the zones:
  Examples: Anemones, Barnacles, Limpets, Hermit Crab, Mussels, Kelp Forest, Periwinkles, Benthic Invertebrates, Spiral Wrack.

Species Interactions

• Competition (e.g. for food, space, etc.)

• Predation

• Mutualism
  *Illustrative Diagram showing direct and indirect effects between Algae, Herbivore, and Predator.

Field Studies of Predation - Paine (1974) Oecologia 15: 93–120

• Keystone predation is considered to be an indirect biotic interaction.
  *Classic Example: Pisaster Starfish Predation.

Paine’s 1966 Pisaster Removal Experiment

*Illustrated diagram demonstrating the removal of starfish. Control, Experiment, and Results are indicated. Species involved are Mussels, Goose Barnacles, Acorn Barnacles and Rockweed.

Biotic Factors: Predation

*Illustrating interaction between models, hypothesis, null hypothesis, experiment, interpretation and observations.

Keystone Predation Not Universal

*Menge et al. (1994, Ecological Monographs) investigated variation in interaction strength between the original keystone predator, the seastar Pisaster ochraceus, and its primary prey, mussels (Mytilus californianus and M. trossulus)

Interplay Between Biotic and Abiotic Factors

*Barnacles settle throughout intertidal.
*Nucella and Pisaster are present.
*Nucella consume most young barnacles in midintertidal. Mytilus begins to outcompete barnacles.
*Few B.cariosus become too large for Nucella and persist in midintertidal. B. glandula persists only in high intertidal. Pisaster prevents Mytilus monopolization. Typical situation.

Potential Issues with Zonation

• 3 zones an over simplification.

• Defined in biological terms.

• Usually conspicuous species.
  *Often not evenly distributed
  *Spatial relationships vary

• Although caveats these zones are still broadly apparent & useful.
  *But how real are zones? Underwood (1978) JEMBE 33: 261-276. Could zonation be… “the visible overlapping patterns of distribution of individual, abundant & conspicuous species, such as barnacles, laminarian algae, or lichens”?
  Diagram displaying % emersion of different species.

Exceptions to Abiotic/Biotic Control

• Grazing controls upper limit of algae (Boaventura et al. (2002))

• Competition controls upper limit of fucoids (Hawkins and Hartnoll (1985))

• Light limitation determines lower limit of algae (E.g. murky Mersey Estuary)

• But… There are always exceptions. Abiotic (high), biotic (low) ……?

What About the Role of Disturbance?

*OSTERA CRESC - THE UNIVERSITY OF MELBOURNE

Effects of Disturbance

• Hypothetical relationships (Connell (1978) Science 199: 1302- 1310) illustrate the impact of disturbance on diversity.

• Disturbance: Abiotic (wave action, heat wave) / Biotic (predation, herbivory, human perturbation)

• Low diversity due to high levels of mortality, dominated by pioneer species in recently disturbed areas.

• Disturbance rare/long time ago/small = Diversity low. Competitively dominant (climax) species exclude those with low competitive ability.

Effects of Disturbance

*Disturbance - Littorina littorea grazing activity
*Context dependent: Grazers feed on competitive dominants in pools / Grazers do not feed on competitive dominants on rock.
*Lubchenco (1978) American Naturalist 112: 23-39.

Will Climate Change Modify Zonation Patterns?

• A warming climate reorganise the outcomes of competitive interactions between organisms in the intertidal zone?

• A warming climate remove historically dominant, but thermally sensitive, species?
  *Climate change may tip the balance of biological interactions, changing the structure of intertidal communities.
  *Induced by environmental changes.

Disturbance and Succession in The Intertidal

• Disturbance is frequent on intertidal shores.

• Disturbance, e.g., storms, marine heatwaves, human trampling, can occur at any time.

• Disturbance can create ‘patchiness’.

• Patches where different species dominate, despite predictable competitive outcomes.

• Establishment of new individuals (settlers, recruits) – offspring from individuals at same, or different, site.

• Recovery of existing individuals – growth

• Survival, growth, reproduction may vary with the intensity, duration, frequency of disturbance (Wethey (2002). https://doi.org/10.1093/icb/42.4.872).

Disturbance and Succession in The Intertidal

• Demonstration on how interaction between Hormosira, Morula, barnacles can be disturbed.

• Morula finds refuges within Hormosira canopy at low tide

• Mortality of barnacles (suspension feeder) is typically high within and near seaweeds
  *Severe storm in 1974 tore *Hormosira* away. No Hormosira cover for Morula, with no predators, barnacles became very abundant
  *Intertidal shores switched from *Hormosira-* to barnacle-dominated for 5 years
  *Effect persisted at some sites, due to barnacles occupying space (& limpet grazing); few *Hormosira* recruits, limited Hormosira growth, explained by R. Hull

Spatial Scale of Disturbance Affects Community Composition

• Paine’s early work emphasised the importance of keystone predators (e.g., Pisaster maintains diverse communities of invertebrates (northern hemisphere rocky shores)).

• Later, the role of disturbance became apparent – disturbance can make habitat available, creating ‘patches’
  *Storm events can remove mussels from mussel beds. Patches provide space for settlers of other species,

Spatial Scale of Disturbance Affects Community Composition

*The size of open habitat patches affects patch future, mussels recolonise small patches by pulling themselves (very slowly!). Large patches are too far for mussels to recolonise; instead, algae colonises the patch centre

Recap

• Zonation as a pattern

• Physical factors controlling upper limits

• Biotic factors controlling lower limits

• Role of microhabitats on rocky shores

• Interspecific interactions: Competition for space

• Interspecific interactions: Predation

• Classic rocky shore experiments and concepts

• Role of disturbance in shaping intertidal diversity

Further Reading

*Levinton JS. Marine Biology. Chapter 14. The tidelands: Rocky shores, soft- substratum, marches, mangroves, and estuaries. pp 355 – 412.
*Underwood & Chapman. 2007. In: Marine Ecology (Eds: Connell & Gillanders) Chapter 15. Intertidal Temperate Rocky Shores.

Useful References

*Several references are listed on slide 78.

Key Players and Physical Gradients

*OSTERA CRESC - THE UNIVERSITY OF MELBOURNE

Primary Producers

Diagram displays:
*Ulva lactuca Foliose
*Corallina spp. Articulated calcareous
*Lithothamnia Crustose
*Pelvetia canaliculata Leathery macrophyte - Fucoid
*Fucus spiralis Leathery macrophyte - Fucoid
*Laminaria digitata Leathery macrophyte - Kelp
*Cladophora spp. Filamentous

Vertical Distribution of Fucoid Algae

Channeled wrack (Pelvetia canaliculata)
Spiral wrack (Fucus spiralis)
Bladder wrack (Fucus vesiculosus)
Serrated/toothed wrack (Fucus serratus)
Oarweed (Laminaria digitata)

Grazers

Gibbula umbilicalis Topshell
Littorina saxatilis, Littorina littorea Winkles
Patella vulgata Common limpet
Idotea spp. Isopod
Archidoris pseudoargus Nudibranch
Asterina gibbosa Cushion star

Keystone Grazers

Boaventura et al. (2002) J. Exp. Mar. Biol. Ecol, 267: 185-206.

Suspension Feeders

Mytilus spp. Mussels
Semibalanus balanoides / Chthamalus montagui / Chthamalus stellatus Barnacles
Sabellaria alveolata Polychaete worm
Botryllus schlosseri / Dendrodoa grossularia Ascidians
Halichondria panicea Sponge:

Competition in Natural Communities

Fundamental niche / Realised niche
Diagram displayed with Chthamalus / Balanus - Connell (1961) Ecology 42:710–723

Predators

Nucella lapillus Whelk
Eledone cirrhosa Octopus
Cancer pagurus Crab
Asterias rubens Starfish
Actinia equina Anemone

Field Studies of Predation / Keystone Predation

Paine (1974) Oecologia 15: 93–120 - Diagram displayed

Omnivores & Detritivores

Talitrus saltator Amphipod Detritivore
Carcinus maenas Green shore crab Omnivore
Anurida maritima Springtail Detritivore
Palaemon serratus Common prawn Omnivore

Physical Gradients

1. Particle size gradient

2. Salinity gradient (freshwater to marine)

3. Horizontal gradient (exposure to wave action)

4. Vertical gradient (tidal elevation or emersion)

Particle Size Gradient and Kinds of Coastal Habitats

Raffaelli & Hawkins (1999) - Mangroves, seagrasses, sandy beaches (and salt marshes) - Unstable & lifeless

Particle Size Gradient and Kinds of Coastal Habitats

Image credit: WildSingapore/Ria Tan - Pulau Hantu, Singapore / Changi, Singapore

Particle Size Gradient and Kinds of Coastal Habitats

Shingle beach at Camano Island State Park, Washington: Image credit: Dana Hunter

Particle Size Gradient and Kinds of Coastal Habitats

Raffaelli & Hawkins (1999) - Mangroves, seagrasses, sandy beaches (and salt marshes) / Rocky shores - Unstable & lifeless

Rocky Shores

Post St. Mary Ledges, Isle of Man, UK (LB Firth) / Lorne, Victoria, Australia (L. Loke)

Rocky Shores

St John’s Island, Singapore (L. Loke) / Sentosa Island, Singapore (L. Loke)

Physical Gradients

1. Particle size gradient

2. Salinity gradient (freshwater to marine)

3. Vertical gradient (tidal elevation or emersion)

4. Horizontal gradient (exposure to wave action)

Salinity Gradient

Chesapeake Bay, summer surface salinity Dark green: salinity < 10 psu. Fully marine salinity 35 psu Can also use ppt Coastal areas affected by river input & precipitation 10 / 10 / 20 / 20 / 30 mm - Sea water / Fully stratified / Moderately stratified (wind, tide mixing) / Vertically homogenous

Physical Gradients

1. Particle size gradient

2. Salinity gradient (freshwater to marine)

3. Vertical gradient (tidal elevation or emersion)

4. Horizontal gradient (exposure to wave action)

Vertical Gradient

Tidal cycle overriding factor controlling distribution of species on the shore
Cycle of submersion (covered by water) & emersion (exposed to air)
Intertidal organisms are of marine origin Tolerances & adaptations
Periods of submersion and emersion dependant on location on the shore
Timing of emersion dependent on geographic location High tide / Ebbing / Low tide / Flooding
90% of the world’s coasts have semidiurnal tides:
Two high & two low tides in 24 hr separated by ~6.4 hours.

Tides: Lunar Cycle

Earth / Neap / Spring / Neap / Spring / Neap - New moon / Half moon / Full moon / Half moon
Tides are produced by the gravitational pull of moon & sun. Highest at equinoxes (21 March & 23 Sept). Lowest at solstices (21 June & 22 Dec)

Tidal Prediction and Terminology

Hawkins & Jones (1992) Percentage exposure to air. MHWS (mean high water of spring tides) / MHWN (mean high water of neap tides) / MTL (mean tide level) / MLWN (mean low water of neap tides) / MLWS (mean low water of spring tides) - Percentage exposure to air. Tidal heights measured in relation to a reference low level on shore (“Chart Datum” or “CD”) / Tide table, Williamstown, 2025 EHWS (extreme high water of spring tides) ELWS (extreme low water of spring tides)

Differences In Nomenclature

Lewis 1964, Stephenson & Stephenson 1972 EHWS Verrucaria/Littorina limit / Barnacles/Pelvetia limit / ELWS Laminaria limit - Supralittoral/Littoral/Sublittoral

Vertical Gradient (Tidal Elevation)

Raffaelli & Hawkins (1999) Highest high tide (EHWS) / Lowest low tide (ELWS)
Most shore species have marine origins increased shore level = increased stress

Vertical Stress Gradient Leads to Species Zonation

Diagram to demonstrate the zones.

Horizontal Gradient (Wave Exposure)

Dynamic balance between grazers and macroalgae very different assemblages; shores can look quite different

4. Horizontal gradient (wave exposure)

Horizontal Gradient (Wave Exposure)

Exposed shore - Experiences heavy wave action/energy / Dominated by sessile organisms e.g. barnacles, limpets Stresses: Settlement & foraging problems, Dislodgement / Benefits: Larval supply/retention?? Hook Head, Ireland
Sheltered shore - Experiences little wave action/energy / Dominated by algae e.g. canopy algae (Ascophyllum nodosum) Stresses: Siltation, smothering & interference with respiration Benefits: Nutrients, Oxygen, food for suspension feeders Rhosneigr, North Wales

Ballantine’s Exposure Scale

Hawkins & Jones (1992, modified from Ballantine 1961)
Scheme uses biology of the shore itself to define wave exposure. 8-point scale: 1 = highly exposed / 8 = very sheltered. Represent an integration of exposure conditions over long time scales.

Communities Along Exposure Gradient

Temperate rocky shores Sheltered Exposed - Fucus vesiculosus evesiculosus / Melaraphe neritoides / Littorina saxatilis / Patella vulgata / Patella ulyssiponensis / Mytilus edulis / Laminaria digitata / Saccharina latissima / Alaria esculenta / Pelvetia canaliculata / Fucus spiralis / Ascophyllum nodosum / Fucus serratus / Himanthalia elongata / Porphyra umbilicalis/ Mastocarpus Stellatus /Chthamalus setllatus / Semibalanus balanoides/ Chthamalus montagui / Verrucaria spp., MID SHORE DOMINATED BY SESSILE ANIMALS.

Temperate Rocky Shores

MID SHORE DOMINATED BY ALGAE

Interactive Effects of The Horizontal (Exposure) and Particle Size Gradients

Raffaelli & Hawkins (1999) - Mangroves, salt marshes / Macrophyte dominated by large seaweeds

Where Do Rocky Shores Occur?

Raffaelli & Hawkins (1999)
INCREASING EXPOSURE - no such habitat / seaweeds / grasses & trees - cliff
INCREASING PARTICLE SIZE - shelter / mud/ OSTERA CRESC THE UNIVERSITY OF MELBOURNE

Introduction to Rocky Shores

Distribution of coastal landforms (Denny & Gaines (2007) Encyclopedia of Tidepools & Rocky Shores) - Based on geology & tectonic history, coastlines can be broken into four general geomorphic environments: 1. Steep coastal mountains & sea cliffs 2. Uplifted marine terraces & sea cliffs 3. Low-relief coastal plains, deltas or lowlands with beaches, dunes, bays & lagoons, sand bars & barrier islands 4. Coasts formed by organisms (e.g., coral reefs, mangroves)

Coastal Systems and Gradients

Distribution patterns influenced by four main environmental gradients: 1. Particle size 2. Salinity 3. Vertical: emersion 4. Horizontal: exposure Subject to wide variation in:
Temperature (immersion/emersion, latitudinal gradient, time of tide), Disturbance (wave action, substratum particle size), Salinity (rainfall, evaporation from rock pools)

Global Extent of Rocky Shores

• ~33% Johnson (1988) The Journal of Geology 96: 469-480

Local Rocky Shores

-Examples indicated such as Wurrung/Bunurong Country / Pt Gellibrand / Willamstown / Eagles Nest / Jawbone Marine Sanctuary

Rocky Shores

Sections of the coast composed of consolidated material, such as rock Formed by erosive processes
Erosion rates can vary widely, from negligible amounts to tens of meters per year. Cf. coral reefs: ‘growth’, estuaries: ‘deposition’ Intertidal rocky shores: part of the coast between the highest and lowest tides.

Considering Time Scales in Rocky Shore Development

Coastal geomorphology Understanding the physical processes shaping rocky shores is crucial for explaining their structure and characteristics. Coastal geomorphology examines how rocky shores develop and change over time. Key physical processes, such as waves, tides, currents, wetting and drying, and sea-level changes, drive the formation and evolution of rocky shores. Geology, particularly rock type, is a fundamental factor influencing rocky shore systems and their resilience.

Introduction to Time Scales

Habitats are constantly changing in response to physical processes (Timescale: millions of years to seconds).
Tides and waves are important drivers of erosion and key physical gradients on rocky shores
Habitat components rock type + tides (Physical gradient temperature - Biota distribution) - Tides and other processes erode rocks, determining rocky shore form (geomorphology)

Geology

Rock type and hardness of rock determines how easily it is eroded by waves and wind (Rock fractures accelerate erosion)
Rock colour determines the temperature of the rock. Thermal stress can affect growth and survival (darker rocks (e.g., basalt) absorb more heat than lighter rocks (e.g., granite). Lathlean & Minchinton 2012 Geology - Black settlement plates on rocky shore up to 5.8 oC hotter than white plates

Sea Level

Determines where a coastline is at a given time, and thus what type of rocks are exposed for erosion. Large changes in sea level result in changes to rocky shore habitat

Geomorphology Can Vary with Geology

Different examples of Bays and Coastlines / Bunurong Country/ 13th Beach/Queenscliff
Description: Basalt boulders: Short platforms – high wave energy / Undulating sandstone - Tidal pools and Crevices / Mostly continuous sandstone - Wide platforms – low wave energy - The different geology determines their variance

Rocky Shore Geomorphic Forms

Erosive processes: Operate on small or large scales - drive the morphology of rocky coasts - Form of a rocky coast depends on the relative importance of physical processes (e.g., wind, waves, tides, sea level) and their interaction with rock type ‘Honeycomb’ weathering of rock – salt crystals expand and pry apart individual grains that are then removed by wind and water.

Cornwall, England

Example displayed showing cliff collapse. Erosion.

Bioerosion

Organisms may also play a role in erosion - Grazing track of limpet (limpets rasp at rock using their radula) ‘home’ scars
There are smaller and larger scales. Organisms can erode rock: smaller (microns per year) to larger (metres) scales
https://portphillipmarinelife.net.au/species/5690 - Examples given

Biota Can Prevent Erosion

Algae can dissipate waves, limiting erosion -> example: Neptune’s necklace, Hormosira banksii, explained by R. Hull. Examples given.

Variety of Habitats

Geomorphic processes can result in complex habitats (tidal pools; Crevices; Rock platforms
Short platforms / Wide platforms – low wave energy ) Also shown is diagram demonstrating highly variable dynamic habitat. Lots of microhabitats