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Chapter 11

Between the Tides

Coller Marine ScienceIntertidal Ecology

And the Giant Shall Rise with the Moon…

Between The Tides

Intertidal EcologyObjectives:• Compare and contrast the conditions of the intertidal with those of the open ocean.

• Identify the differences in types of intertidal regions. Rocky, soft-bottomed, gravel etc. and explain the relationship between grain size and the conditions in the intertidal.

• Be familiar with nomenclature of grains sizes for substrate and their relative sizes.

• Describe the changes in salinity, temperature, PO2, P CO2, pH and turbidity that affect the intertidal.

• Identify and describe the behavior of waves along the coastline.

• Explain the differences between active and passive margins and how they lead to the formation of the types of coastal regions associated with them.

• Identify at least twenty local intertidal species.

• Describe the physical and behavioral adaptations that intertidal organisms exhibit which allow them to endure the variety of conditions in their environment.

• Be familiar with the role of space as a limiting resource in the rocky intertidal as well as the role of keystone species in the formation of these communities.

• Describe the patterns of zonation and the associated species.

Factors that Impact the Intertidal

• Desiccation: Organisms in the upper intertidal may spend hours out of the water. Thus those organisms in the upper and middle intertidal must have either physical or behavioral adaptations to cope with or better yet prevent the water loss associated with prolonged exposure.

– Clamping down:– Clustering– Shading– Burrowing and Home Scars

• Feeding Restriction: Many organisms can only feed when tide is in and food is available. Others must wait for low tides to expose prey or detritus.

Factors that Impact the Intertidal• Variations in Water Chemistry: Intertidal

waters, particularly isolated tidal pools are subject to high levels of variation in chemistry.– Evaporation leads to higher salinity.– Precipitation and runoff lead to lower salinity.– Runoff and effluent deliver pollutants and excess

nutrients, (eutrophication).– Isolated pools can have fluctuations in [O2],

[CO2], and pH due to photosynthetic activity and cellular respiration.

• Variations in Water Temperature: Intertidal waters being shallower are more susceptible to fluctuations in temperature.– Dependent on ambient temperature.– Water temperature affected by the colligative

properties of the solutes.– Organisms run and hide. Coloration and ridges

can allow for less absorption or more radiation of excess heat.

• Wave Shock: The impact of waves can vary greatly depending upon a variety of conditions from the shape of the coastline to the weather on any given day. The results of wave shock can be either beneficial or devastating depending upon the circumstances. Waves mix the oceans and erode coastal sediments providing both oxygen and nutrients . Waves can also dislodge, displace and even crush organisms.

– Clamp down

– Hard shells with opercula

– Many are flexible with strong attachments to the bottom

– Many have a low profile or shelter in crevices or home scars.

Factors that Impact the Intertidal

Distribution of Wave Energy

Refraction of wave fronts affects the distribution of wave energy along the shore.

Coping With Wave Shock

Shelter: Cracks and crevasses are prime real estate in the rocky intertidal.

Home Scars: Limpets and related species will make their own shelter using their radula to burrow into the substrate.

Coping With Wave Shock

Stay Low and Clamp Down: A low profile and a strong grip enable slow moving organisms to resist wave shock.

Be Rocky: Calcareous deposits in the tissues of many organisms or shells allow them to resist the destructive forces of waves.

Coping With Wave ShockHold on Tight: Byssal threads and holdfasts provide strong attachment to the rocky substrate.

Strong and Flexible: Macroalgae bend with the flow and have tough bodies that do not break. Anemones change their shape to avoid being pulled off of the bottom.

Rocky IntertidalVariations in water chemistry in an isolated tidal pool.

• The variation in tolerances of species gives rise to the vertical zonation found in the intertidal which results in the distinct bands observed in these communities.

Rocky Intertidal: Vertical Zonation

Competition for Space: The Zone WarsRecruitment to Different Sites, Pacific Northwest

These two boulders are located in False Bay, San Juan Island, Washington. They are only about 10 m apart and the boulder sides you see have the same orientation facing away from the shore, yet they have completely different cover (barnacles at left, seaweed at right). Such differences are also found on continuous rocky shores, and it is often not clear why such great differences in dominance are found. Can you suggest some hypotheses to explain the difference?http://life.bio.sunysb.edu/marinebio/rockyshore.html

Adaptations for Life in the Rocky Intertidal

Photo by Peter PetraitisYellow arrows point to byssal threads attached to the dog whelk. Byssal threads are generally used for attachment to the substrate in the intertidal here however they have an alternate function.The dog whelk Nucella lapillus also feeds on the mussel Mytilus edulis on rocky shores of New England. When it mounts a mussel it commences to drill a hole in the shell. Peter Petraitis has found that the mussels can fight back, however, and respond by attaching byssal threads to the snail and ensnare it, which traps them and exposes them to crab predation.

Photo by Lizbeth FrancisHere is a shot of a rocky shore with

large numbers of these anemones. The yellow arrows point to bare zones

between clones, discovered by Lizbeth Francis. Anemones can be identified as

members of given clone by means of similar coloration and sex. The bare

zones are wide enough that limpets can move freely down these inter-clonal

highways.

Combat Between AnemonesLike many anemones, A. elegantissima have well-developed acrorhagi (elongated white tentacle-like structures on left anemone) that bear high concentrations of nematocysts. When two anemones from different clones (and, hence are genetically different) come into contact, one or both anemones rear back and expose the acrorhagi, which are located beneath the tentacles. In the picture at left, the left anemone is about to lower down and attack the right anemone, which is nearly contracted. The small whitish blobs on the right anemone are batteries of nematocysts that were injected in an attack a few minutes before. In the lab, it is possible for the dominant anemone to kill the subordinate (these two anemones were separated before the worst happened), but in the field withdrawal is more common, which explains the origin of the bare zones between clones.

Soft-bottom Intertidal

Grain Size

Vertical Zonationorganisms consist of epifauna (organisms living on the surface) and infauna (organisms living below the surface); primary producers are diatoms

• upper portions are occupied by a few species of burrow-dwelling amphipods or ghost crabs

• middle portions is also populated with amphipods, lugworms (live in U-shaped burrows and eat sediment), isopods, sand crabs, polychaete worms, harpacticoid copepods (live in interstitial spaces between sand grains), gastrotrichs (live in interstitial spaces between sand grains). These forms are generally elongated to fit between sand grains.

• lower portion is populated with polychaetes, amphipods, surf clams, cockles, sand dollars, fiddler crabs

Bioturbator

Epifauna, Infauna and Meiofauna

Substrate Grain Size

Common Intertidal Organisms of S. Cal• Cnidarians

– Aggregating anemone– Giant green anemone– Strawberry anemone

• Macrophyta– Sea Lettuce Ulva– Dead Man’s Fingers Codium fragile– Rockweed Fucus– Lithothamnion– Corallina– Oarweed Laminaria digitata

• Echiura– Fat Innkeeper Worm

Common Intertidal Organisms of S. Cal• Echinodermata

– Bat Star– Ochre Star– Brittle stars

• Striped• Spiny

– Purple sea urchin– Green sea urchin– California sea cucumber– Common sand dollar

• Arthropoda– Purple shore crab– Striped shore crab– Blue footed hermit crab– Common mole crab– Spiny mole crab

Common Intertidal Organisms of S. Cal• Mollusca

– Periwinkle– Black turban snail– Owl limpet– Rough limpet– Giant keyhole limpet– Kellet’s whelk– Wavy top turban snail– Leafy hornmouth– California sea slug– Black abalone– Chestnut cowery– California cone snail

• Osteichthyes– Sculpin