The Intertidal Zone

1
The Intertidal Zone

• Lecture 11
• Marine Biology

2
Review of Mid-Term Exam

• Technicalities - spelling
• - It is Arctic, not Artic. This was even
  spelled for you elsewhere on the exam, so
  there is really no excuse.
• - The element is chlorine, not chloride.
  Chloride is chemical nomenclature for a
  salt, usually a metal- salt, as in sodium
  chloride (yes, this was even wrong on our
  answer key!)
• Point to be made
• leniency was the rule this time, even in cases
  where spelling resulted in a literally wrong
  answer rather than just a misspelled word. Next
  time, partial credit will result where the wrong
  term or wrong word is used.

3
Review, cont.

• 2. Technicalities - grammar
• Short answer questions are to be answered in a
  few words or sentences only. More is okay, but
  not required.
• Short essay questions are, unless otherwise
  requested, to be answered in complete
  sentences. Scratching down words and partial
  phrases for answers, even if correct, will result
  in partial credit.
• The instructions were on the exam, and they are
  to be followed. If there are questions, please
  ask.

4
Review, cont.
3. Instructions This exam sometimes asked you to
list and describe certain things. Most of you
simply listed them. Most of you received nearly
full credit, despite a lack of description. This
will not be the case on the final exam. Point to
be made Read what the question is asking you to
answer carefully. Your grade is based on very
few scores, and each weighs heavily in your
final grade. There is little room for error
from this point forward.
5
Review, cont.

• Results of Mid-term Exam
• Overall, the results were normally distributed
  and performance was good to excellent.
• Raw scores were scaled to a 70-100 point
  distribution, with one outlying low score scaled
  seperately.
• High Score (raw) 93, two others above 90.
• Everyone received two points to their raw score
  for question 19 which no one answered correctly.

6
Review, cont.

• Question 12. What is the best explanation for the
  presence of high diversity in the deep benthos?
• Answers
• greater area higher diversity (area
  hypothesis)
• lack of competition/predation (cropper or
  disturbance theory)
• long times in stable conditions (stability-time
  hypothesis)
• Common answer greater surface area high
  diversity
• The deep ocean is below the surface, hence no
  surface area

7
Review, cont.
Question 19. Where do we find the highest sea
surface temperatures in the ocean, geographically
speaking? Answer Red Sea. It is a shallow
oceanic basin without much turnover. Common
answer on exam tropical and equatorial regions.
The tropics are a latitudinal region, typically
defined as the region between about 23.5N and
23.5S between the Tropics of Cancer and
Capricorn. But, as we saw, upwellings and
circulation patterns can result in very cool
surface seawaters even in tropical equatorial
regions.
8
Review, cont.

• Question 20. Why is the ocean blue?
• Answer Blue wavelengths penetrate the farthest
  in seawater.
• Almost everyone answered this correctly - or
  close.
• Question 30. Which wavelength penetrates the
  deepest in clear seawater? a) red b) yellow c)
  green d) blue e) violet
• Answer d) blue, of course!
• Almost everyone got this question wrong???!!!
  WHY?

9
Review, cont.

• Question 28. Which answer describes the vertical
  zonation of the oceans from shallowest to
  deepest?
• a) Continental shelf, bathyal, abyssal, hadal,
• deep sea trench
• b) Continental shelf, abyssal, bathyal, hadal,
• deep sea trench
• c) Photic, aphotic, bathyal, abyssal, hadal
• d) Continental shelf, photic, aphotic, abyssal,
• bathyal
• e) Continental shelf, continental slope,
• continental rise, deep ocean floor

10
Review, cont.

• Question 30. Which seawater sample would have the
  highest density?
• 17C, 35ppt, 0m depth
• 17C, 32 ppt, om depth
• 25C, 35ppt, 0m depth
• 17C, 35 ppt, 1000m depth
• 25C, 32ppt, 1000m depth
• Density increases with depth, salinity.
• Density decreases with temperature.
• Therefore, the deepest, most saline, coldest
  water is the most dense.

11
Review, cont.
Question 36. Describe the major features of a
wave and how they break.
Part 1 Major features of a wave
12
Review, cont.
Part 2 How waves break

• Periods remain same, other parameters change
• Wavelength and velocity decrease in shallow
  water
• When water depth 1/2 wavelength, height
  increases,
• water piles up, and particle velocity at wave
  crest
• exceeds wave velocity, and it tumbles forward

13
The Intertidal Zone
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General Intertidal
The intertidal constitutes the smallest area of
the oceans - narrow coastal fringe between high
and low tides - well studied because of
access - greatest environmental variation of all
oceanic zones - very high diversity
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Environmental Conditions

• 1. Tides - the periodic rise and fall of sealevel
  over a time interval
• diurnal tides, semidiurnal tides,
• mixed tides
• duration of aerial exposure
• most important to intertidal
• communities.

16
Intertidal at Low Tide
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The origin of tides
18
Tidal Curves
19
Tidal Curves, cont.
20
Environmental Conditions, cont.

• 2. Temperature
• affects intertidal by temperature
• extremes and variations
• also impacts communities through
• increasing dessication effects

21
Adaptations to dessication
22
Mollusk adaptations to the intertidal
23
Environmental Conditions, cont.
3. Wave Action - shear physical force influences
communities more in intertidal than any other
zone. 4. Salinity - large variations in salinity
occur and shape communities
24
Waves as structuring forces
25
Algae adaptations to the intertidal
26
Factors affecting zonation patterns
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Structuring forces of the intertidal
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Vertical Zonation

• Competition is a major structuring force in
  intertidal vertical zonation patterns
• Dayton
• Kelp are competitively dominant over other algae.
  
• Following storms that damage the dominant kelp,
  smaller algae rapidly invade. They persist for a
  while until dominants again recruit and grow.
  Subordinates are referred to as refuge species or
  opportunistic species.

29
Zonation, cont.

• Predation is also a major structuring force on
  intertidal zonation
• Dayton and Paine
• Mytilus is the dominant space competitor if freed
  from predation (by starfish) and will outcompete
  all other species.
• However, it is slow at settlement and this allows
  other organisms, such as barnacles, to invade
  when predation exists.
• Predatory snails relegate barnacles to the
  highest zone, mussels then invade, and within 2
  years, a sharp vertical zonation pattern appears.

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Interactions in the Intertidal
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Zonation, cont.
How common is this pattern? Chile, Washington,
and New Zealand also conditions where mussels
dominate, predatory seastar present Experiment
For 14-17 years, seastars were removed, and then
added to system Results in Washington and New
Zealand persistence of mussels Why? Mussels had
reached a refuge from predation in large sizes
too large for the predators to significantly
impact. Results in Chile mussels did not persist
as dominants Why? Chilean mussels do not grow to
a large size where they are immune to seastar
atttack.
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Zonation, cont.
Menge and Lubchenko work in the New England
rocky intertidal found that wave exposed shores
have competitive hierarchy mussels gt barnacles gt
algae mussels controlled by seastars and
gastropods
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Factors Affecting Zonation
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Effects of Predation
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Famous study Carefoot
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Famous study Bertness
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Patterns of zonation, cont.
Petriatus Found that mussels and barnacles
dominate lower intertidal in protected areas,
and that algae are rare in exposed areas but
predators are abundant. Why? Uncertain,
but suspected that dessication limits the ability
of seastars to effectively attack prey.
38
Zonation, cont.
General axiom Where predation is low,
competition is high, and vice-versa.
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Algae and Herbivory
Grazers are important in setting limits to algal
growth, and accounts for predominance of
calcified algae, particularly in the
tropics. Also important are chemical defenses
(eg. Kelp produces sulfuric acid to erode the
teeth of sea urchins) Alternative strategies for
algae 1)high investment in chemical defenses
are costly 2) slow growth, low reproduction vs.
high growth, rapid reproduction (but high
mortality from vulnerability to grazers
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Algae Distribution Summary
High Intertidal Zone (supralittoral) grazers
are uncommon except Littorina, but have little
time to graze because of exposure to dessication
(PHYSICAL FACTOR) Mid
Intertidal Zone (midlittoral) barnacles and
mussels compete for space, grazers common
(COMPETITION) Low Intertidal Zoan (sub
littoral) predators of grazers common, algae can
flourish (PREDATION)
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Population Control
Paradigm Population abundance and distribution
in the intertidal is controlled primarily by
biological interactions and post-settlement
effects. Recent challenge Populations limited
by recruitment, Gaines and Roughgarden (1985,
1987) In a study on barnacles, they proposed that
rates of settlement may be more important in some
locations. They found sites with low larval
settlement, low abundance of adults within tears
but high variance between years.
Why? Differences due to variation in settlement.
If settlement is high, adult abundances are also
high.
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Population control, cont.
Also found with high settlement, mortality in
intertidal zone is density dependent with respect
to barnacle populations (due to
seastars) However, with low settlement, mortality
is density independent with mortality due
primarily to physical factors.
43
Population control, cont.
Density dependence implies crowded conditions
with proportionately more mortality at higher
densities. Caveat to paradigm Highest
diversity in rocky intertidal is found at
locations with intermediate levels of disturbance
and competition. Causes of zonation (predation,
competition, etc.) appear to only apply to areas
where there are high rates of settlement. If
settlement is low, there may not be a pattern of
pronounced zonation.
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Population control, cont.
What controls variation in settlement? - maybe
variation in reproductive output - maybe
variation in water column Gaines and Roughgarden
found that subtidal kelp beds just offshore of
rocky intertidal shores harbor fish and
invertebrate populations that feed on incoming
larvae- limits recruitment potential Also showed
that during ENSO events when kelp communities are
diminished that there was a higher recruitment of
barnacles to the shoreline and, vice-versa, that
cold years promoted algal growth and concomitant
low recruitment of barnacles.
45
Tropical Rocky Intertidal
Tropics have a harsher physical environment
compared to temperate shorelines - exposure to
intense solar radiation (dessication problem) -
exposure to periods of intense rainfall
(freshwater stress) - results in low densities
of organisms in the upper intertidal
reaches - also harsher for algae (lots of
grazers!)
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Tropical Algae Adaptations

• Chemical
• Morphological (unpalatable structures)
• Life history attributes
• 2 main forms
• Leafy fast growing, competitively dominant, low
  reproductive rates, high susceptibility to
  grazers
• Crustose slow growing, low competitive ability,
  high reproductive rates, low susceptibility to
  grazers

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Geographic patterns in grazing
Temperate Atlantic (Europe) and Pacific (North
America) limpets, crabs, sea urchins contol
community algae structure Temperate Atlantic
(North America) and Pacific (Austalia, N.
Z.) periwinkles and a high diversity of grazers
contol structure Tropical Pacific
(Panama) 3-dimensional space provides refuge for
sessile species
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Next week
Continuation of the Intertidal Sandy Shores and
Meiofauna