EVSC20004 Lecture Notes - Lecture 6: Rocky Shore, Bioerosion, Geomorphology
18 May 2018
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LECTURE 6: ROCKY SHORES – PHYSICAL ENVIRONMENT
• Rocky shores are section of coast composed of consolidated material - majority of coastline is
rocky
• Formed by erosive processes - rate of erosion changes
• Focus on intertidal part of rocky shores - shoreward fringe of the sea-bed between the
highest and lowest extent of the tides - rock platform - intermittently wet and dry
• Coastal geomorphology: study of the development and evolution of a coast as it acts under
the influence of interacting physical processes
• Include winds, wave, currents and sea-level changes, as well as geology - influence
erosion and deposition
• Rocky shore evolution as a question of scale, affecting the components of habitat form and
process
• Drivers of habitat form can interact and determine a range of key physical gradients, together,
affecting biota
Habitat Form and Process
• Geology: the hardness of rock determines erodibility
o Colour of rock determines how hot rock gets - thermal stress for organisms can affect
growth and survival
• Sea level: determines where coastline is at a given time, and thus what rocks are exposed for
erosion
o Large changes in sea level result in massive changes in rocky short habitat
• Rocky shore geomorphology: the morphology of a rocky coast is driven by erosive processes
o Exact form of a rocky coast is dependent on the relative importance of wind, waves,
tides, sea level and how these interact with rock type
o Honeycombing: weathering of rocks, salt crystal expand and pry apart individual grains
that are then removed by wind and water
• Bio-erosion: organisms that can erode rock can be small or large scale
o Limpets - tracks seen on rock
o Neptune's necklace - dense mats, prevents erosion - act as a protected blanket
• Waves: operate on scale of minutes - exert massive mechanical stress on intertidal
organisms: need to be well attached and built tough
Key Physical Gradients
• Desiccation, temp and salinity - increase up the shore and vertically
• Orientation of rock import: horizontal or vertical - temperature consistently hotter on
horizontal rocks
• Wave shock - decreases down the shore and vertically
• Biological zonation is typical in the intertidal zone
• Bands of organisms can be seen on shore lines
• Hydrodynamic forces: drag & lift - both exert unwanted forces on intertidal organisms, limit
water displacement for drag (orient into flow and reduce cross-sectional area to limit
pressure gradient, homogenise water velocity for lift (top and bottom surface provide similar
water distance travels, therefore no pressure gradient) - ALTER MORPHOLOGIES - effect of
water movement
DRAG
Drag: the rate of removal of momentum from a moving fluid by an immersed body
• Is caused by pressure gradients and because of water viscosity (water molecules are sticky)
• Pressure inversely related to water velocity - faster water = lower pressure, slower water =
higher pressure, high velocity = low pressure
• Greater water velocity gradient - greater drag
