Intertidal Ecology

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

The RI environment Tides Temperature- wide range 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

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

Teahupo'o, Tahiti

Wave Characteristics

Idealized Water Motion Energy Flows, but not the water! Back and forth motion

Swell Height Swell height is the product of 1. Wind Speed 2. Longevity 3. Fetch

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. field has varying direction and strength over the volume of the earth The stress-producing effects of a non-uniform gravitational field acting on an elastic body are called tidal forces. Tidal forces from a gravitating body have a strength that depends in the inverse cube of the distance from that body, F ~ 1/r3.

_ _ Center of Earth BUT… These are very small differences Water flows Tides are a differential force, that is, they result by the difference in the force of gravity between two points. So things need to be BIG to have a difference. change in person’s height is million times smaller than a size of atom! Going upstairs results in a weight change that is about 5 times larger than that produced by the tidal mechanism during a spring tide. Land can move ~14 inches at high tide, but we don’t notice. The Day gets longer by about 2.3 milliseconds every 100 years The Moon recedes by about 3.84 meters/century. After a few Billion Years, this adds up until: The Moon will be ~50% farther away from the Earth The Lunar Sidereal Month will be about 47 days long The Earth's rotation period (the day) will be 47 days long The Earth & Moon will be locked together in a 1:1 Tidal Resonance, and always keep the same face towards each other. Water flows towards forces ___________ _ = _ ___________ = Negative net force Positive net force

Tidal Forces While gravitational forces depend on the inverse square of distance, these tidal forces, being differences in force over lengh, depend on the inverse cube of distance. That's why tidal forces on earth due to the sun are much smaller than those due to the moon, even though the sun's mass is very much greater than the moon's mass. 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.

Spring and Neap Tides Sun is about ½ as strong an influence as the Moon Tides are two LONG waves that the Earth rotates underneath **

Types of Tides *but we are not on Waterworld

Types of Tides

The Rocky Intertidal Smallest of all ocean environments Dominated by Algae and Inverts

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.

Desication Heat Balance

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.

Wave Action High energy Two Biological consequences Structural Physical integrity Thick shells, attachments, etc. Functional Behavioral integrity Foraging patterns, Reproduction

An easily overlooked abiotic issue that organisms need to deal with in the intertidal: Space 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

Zonation Stephenson 1949- based on organisms, not tide height

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…

Competition in the Intertidal J. Connell, 1961. Tried to answer question: “What causes zonation” Realized Niches Fundamental Niches High Tide ? Zone of Competition Low Tide

Keystone Species

Keystone Species Keystone species have a disproportionately larger effect on the environment than expected Presence of starfish = increased species richness and diversity

Other keystones

Impact of Grazers Regulation of algal species (lower levels) Snails, crabs, limpets, chitons, urchins, fish…

Impact of cover

…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!

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

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.

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?

60 years of Change Temperature had… Species had too… Barry et al. 1996 Same area of Hopkins Marine Station Intertidal area was compared in 1933 and in 1993; over 60 years what had changed? Temperature had… Water temperatures increased on average by about 1.3 °F Peak summer temperatures in August rose nearly 4 °F ! Species had too… Warm-adapted Southern species increased Cold-adapted Northern species decreased Cosmopolitan species remained the same

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