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Intertidal Ecology

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Best understood marine environment

• Easy to get to

• Don’t need to get wet (at least not very)

• Amenable to terrestrial methods

• Dominated by sessile organisms

• Classic studies of Paine, Connell and others

• However, poorly understood when submerged

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The RI environment

• Tides– Duration, time, drastically changes environment

• Temperature- wide range• Salinity-rain and evaporation• Substrate-

– Rocks: Basalt and sandstone-soft ; Granites are hard

– Pilings, docks, etc

• Wave Action– Mechanical forces, erosion of substrate; importance of

spray extension

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Waves• Waves are moving energy

• Waves begin as a disturbance- some energy that is put into the system– Think of throwing a rock into a quiet pond

• Wind is the cause of most of the disturbances we are concerned with to form Ocean waves

5Teahupo'o, Tahiti

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Wave Characteristics

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Idealized Water Motion

Energy Flows, but not the water!

Back and forth motion

8 Swell Height

Swell height is the product of

1. Wind Speed

2. Longevity

3. Fetch

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Tides

• What is a tide?– Periodic raising and lowering of average sea

level– Tides are basically very long, shallow waves

that wrap around the earth.

• Waves are caused by a disturbance, so what is the disturbance here?– Differential Gravitational interactions of Earth,

Sun and Moon.• Acts on land and water, but water can move, so it

piles up on itself.

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Center of Earth

____________

=___________

_

=Positive net force

Negative net force

Water flowstowards forces

BUT…These are very small differences

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Tidal Forces

Water flows horizontally toward the Earth-Moon line on each side, due to the differential gravity and resulting tidal forces on each side of the globe.

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Spring and Neap Tides

Sun is about ½ as strong an influence as the MoonTides are two LONG waves that the Earth rotates underneath**

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Types of Tides *but we are not on Waterworld

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Types of Tides

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The Rocky Intertidal

• Smallest of all ocean environments

• Dominated by Algae and Inverts

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Adaptation to Water Loss

• Loss dependent on Duration and Timing– How long exposed, magnitude of tide, time of

day (or night), local weather (fog, etc.)– Critical tide levels and decade lunar variations

• Adaptations:– Mobility and microhabitats-Move or settle into

less stressful areas (cracks, overhangs, under algae etc.)

– Tolerance-many species can loose tremendous amounts of tissue water

• Avoid: Shells, home scars, Mucus, • Deal: many algae-just dry out and wait.

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DesicationHeat Balance

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Salinity Changes

• Can vary from full seawater to full fresh

• Evaporation can bring tide pools up to 100 ppt! Hypersaline 3x as salty as normal seawater.

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Wave Action• High energy

• Two Biological consequences– Structural

• Physical integrity

• Thick shells, attachments, etc.

– Functional• Behavioral integrity

– Foraging patterns, Reproduction

20An easily overlooked abiotic issue that

organisms need to deal with in the intertidal:

SpaceSpace• The rocky intertidal is mostly a 2-D world

• Little infaunal space, organisms are epifaunal

Therefore, organisms often are in a battle for the limited available substrate

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ZonationStephenson 1949-

based on organisms, not tide height

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What causes zonation?

• Physical (probably main player in upper limits)

– Tidal height, spray zone, max exposure time (and everything that goes with it)

– Critical tide levels- the average is not necessarily as important as extremes

– Temp, Sunlight (UV)

• Biological– Competition, grazing, and larval recruitment

– Many of the classic studies were trying to answer these questions…

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Competition in the Intertidal

High Tide

Low Tide

Realized Niches

Fundamental Niches

Zone of Competition

J. Connell, 1961. Tried to answer question: “What causes zonation”

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Keystone Species

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Keystone Species

• Keystone species have a disproportionately larger effect on the environment than expected

• Presence of starfish = increased species richness and diversity

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Other keystones

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Impact of Grazers• Regulation of algal species (lower levels)

– Snails, crabs, limpets, chitons, urchins, fish…

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Impact of cover

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…are there any larvae?

• Reproductive behaviors of species are important for larval supply

• Reproductive isolation:– If numbers get too low,

many species have trouble finding a “mate”

•May 2001, the white abalone became the first marine invertebrate to receive federal protection as an endangered species •“Mates” need to be within about three feet of a member of the opposite sex for success!

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Choosy Larvae- recruitment

• Larval settlement is not Larval settlement is not random. The multitude of random. The multitude of cues in a large way define cues in a large way define the adult distribution of the adult distribution of many species and therefore many species and therefore determined by larval choice determined by larval choice and not solely by predation, and not solely by predation, competition and grazing.competition and grazing.

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Disturbance• Maximum species richness is found in areas with

intermediate levels of disturbance• Disturbance resets the successional clock

– Pioneer (few)---Intermediate (many)---climax (few)

• Sousa (1979)- Intermediate Disturbance Hypothesis– Algal richness determined by boulder stability in intertidal– Small- easy overturn– Large- infrequent overturn

•Disturbance must occur at some intermediate frequency or severity that allows species to accumulate within the patch, but prevents one or a few of them from monopolizing its resources, but disturbance must not occur so often or with such severity that many species are eliminated.

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So…what causes zonation in the Intertidal?

• Physical (main player in setting upper limits)– tides, waves, temp, salinity, sunlight…other abiotic

factors

• Biological (main player in setting lower limits)– competition, predation/grazing, symbiosis, and larval

recruitment• Much time was spent trying to find the one answer to the

question, but the more researchers have looked, the more apparent is the notion of the thoroughly dynamic nature of the oceans

Ecology is indeed the interaction of the abiotic and biotic worlds

So what happens to communities when the physical world changes?

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60 years of Change

• Same area of Hopkins Marine Station Intertidal area was compared in 1933 and in 1993; over 60 years what had changed?

Barry et al. 1996

Species had too…Species had too…Temperature had…Temperature had…

Water temperatures increased on average by about 1.3 °F

Peak summer temperatures in August rose nearly 4 °F !

Warm-adapted Southern species increasedCold-adapted Northern species decreasedCosmopolitan species remained the same

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Summary• Both physical and biological interactions determine the

distributions and zonation of intertidal life

• Predation, competition, and larval supply are important biological determinants of distribution

• Historical perspective: intertidal ecology is the best studied of all marine habitats, but it is still in its infancy (toddler?), it’s only been studied for ~50 years

• The physical environment is changing in many ways due to human impact that will elicit biological changes, both in species range, health, and behavior. This makes it all the more important to understand this important system now, before it changes forever