Download 14 -The Tidelands

14 -The Tidelands
Rocky Shores, Soft-Substratum Shores,
Marshes, Mangroves, and Estuaries
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
ZONATION -universal feature of rocky shores,
also true of soft sediments but not as distinct
(3-dimensional nature, owing to presence of
burrowing organisms and others within the
sediment)
Example of zonation on rocky shore, along a gradient of
wave exposure on a site in the United Kingdom
2 SPATIAL GRADIENTS:
• Vertical
• Horizontal - changing wave exposure
Vertical gradient
•
•
•
•
•
Heat Stress, Desiccation
Gas Exchange - dissolved oxygen
Reduced feeding time
Wave shock
Biological interactions - competition,
predation
Heat Stress/Desiccation
• Varies on small spatial scales
• Body size, shape are both important reduction of surface area/volume reduces
heat gain and water loss
• Evaporative cooling and circulation of body
fluids aids in reduction of heat loss
• Well sealed exoskeletons aid in retarding
water loss (acorn barnacles, bivalves)
Vertical Gradients
• Higher intertidal organisms more resistant to
heat and desiccation stress than lower intertidal
organisms
Vertical Gradients 2
• Higher intertidal organisms more resistant to
heat and desiccation stress than lower intertidal
organisms
• Higher intertidal animals have less time to feed.
Sessile forms therefore grow more slowly than
lower intertidal organisms
Vertical Gradients 3
• Higher intertidal organisms more resistant to
heat and desiccation stress than lower intertidal
organisms
• Higher intertidal animals have less time to feed.
Sessile forms therefore grow more slowly than
lower intertidal organisms
• Mobile carnivores can feed only at high tide,
usually feed more effectively at lower tide
levels, which are immersed a greater
proportion of the day
Oxygen consumption
• Intertidal animals usually cannot respire at
time of low tide
Oxygen consumption 2
• Intertidal animals usually cannot respire at time of
low tide
• Respiratory organs (gills of polychaetes,
bivalves) must be moist to acquire oxygen, and
therefore are usually withdrawn at low tide
Oxygen consumption 3
• Intertidal animals usually cannot respire at time of
low tide
• Respiratory organs (gills of polychaetes, bivalves)
must be moist to acquire oxygen, and therefore are
usually withdrawn at low tide
• Some animals greatly reduce metabolic
rate at time of low tide
Oxygen consumption 4
• Intertidal animals usually cannot respire at time of
low tide
• Respiratory organs (gills of polychaetes, bivalves)
must be moist to acquire oxygen, and therefore are
usually withdrawn at low tide
• Some animals greatly reduce metabolic rate at
time of low tide
• Some high intertidal animals can respire
from air (e.g., some mussels) even at low
tide, as long as air is not too dry
Pacific sand bubbler crab, Scopimera inflata, has membrane
on each leg (shaded green), which exchanges gas from air
into arterial blood
Wave shock 1
• Abrasion - particles in suspension scrape
delicate structures
Wave shock 2
• Abrasion - particles in suspension scrape delicate
structures
• Pressure - hydrostatic pressure of breaking
waves can crush compressible structures
Wave shock 3
• Abrasion - particles in suspension scrape delicate
structures
• Pressure - hydrostatic pressure of breaking waves
can crush compressible structures
• Drag - impact of water can exert drag, which
can pull organisms from their attachments to
surfaces, erode particles from beaches and
carry organisms from their burrows or living
positions
Causes of Vertical Zonation 1
• Physiological tolerance of different species at
different levels of the shore
Causes of Vertical Zonation 2
• Physiological tolerance of different species at
different levels of the shore
• Larval and adult preference - larvae may settle
at time of high tide at high levels, mobile
organisms have a series of behavioral responses
that keep them at certain levels of shore
Causes of Vertical Zonation 3
• Physiological tolerance of different species at
different levels of the shore
• Larval and adult preference - larvae may settle at
time of high tide at high levels, mobile organisms
have a series of behavioral responses that keep
them at certain levels of shore
• Competition - species may be capable of
excluding others from certain levels of the
shore
Causes of Vertical Zonation 4
• Physiological tolerance of different species at
different levels of the shore
• Larval and adult preference - larvae may settle
at time of high tide at high levels, mobile
organisms have a series of behavioral responses
that keep them at certain levels of shore
• Competition - species may be capable of
excluding others from certain levels of the
shore
• Predation - mobile predators more effective
usually on the lower shore: affects distributions
of vulnerable prey species
A rocky shore in the U.K. At the time of low tide on hot dry days, the
gastropod Nucella lapillus retreats into the crack where it is moist and
cool. Note the areas cleared of mussels adjacent to the cracks.
Beaches and Wave Action
• Exposed beaches - strong erosion and sediment
transport
• Difficult environment for macrobenthos to survive
and maintain living position
• Swash riding - means of moving up and down
with rising and falling tide - maintain position in
wet but relatively non-eroded tidal level
Swash Riding - found in Mole Crab Emerita, some species
of the bivalve Donax
The mole crab, Emerita talpoida, burrowing into
an exposed beach in North Carolina
Interspecific Interactions and
Zonation
• Why are there vertical zones, with
dominance often of single sessile species
within a zone?
Interspecific Interactions and
Zonation 2
• Why are there vertical zones, with
dominance often of single sessile species
within a zone?
• Possible explanations: (1) Differences in
tolerance of species at different tidal
heights (2) Competitive interactions (3)
other factors
Investigation by Field
Manipulation Experiments
• Classic experiments of Joseph Connell
• Studied factors controlling vertical zonation
by selective inclusion and exclusion of
hypothesized interacting species
Rocky Shores of Scotland - Key
Species in Connell’s study
• Chthamalus stellatus - acorn barnacle, ranging
from subtropical latitudes to northern British
isles
• Semibalanus balanoides - acorn barnacle,
ranging from Arctic to southern British isles,
overlapping in range with C. stellatus
• Nucella lapillus - carnivorous gastropod, drills
and preys on barnacles
Connell Field Experiment
• transplant newly settled Chthamalus
to all tidal levels
• caged some transplants, excluded
Nucella
• allow Semibalanus to settle and
cleaned Semibalanus cyprids off
some rocks
Results of Connell
Experiment
• Chthamalus survival poorer in presence of
Semibalanus
• Chthamalus survival decreased where
Semibalanus grew the fastest
• Chthamalus survival increased in high
intertidal due to its resistance to
desiccation
Conclusions from Connell
Experiments
• Predation important in lower intertidal
• Biological factors control lower limit of
species occurrence
• Physical factors control upper limit
• Community structure a function of very
local processes (larval recruitment not
taken into account as a factor)
Desiccation
MHW spring
MHW neap
Mean tide
MLW neap
MLW spring
Physical
factors
Interspecific effects
Adult density
Settlement of cyprids
Soft Sediments
• Zonation not as distinct as on rocky
shores
• Competition - demonstrated by
experiments
Dense population of the barnacle
Semibalanus balanoides
Mud Flat Field Experiments by
Sarah Woodin
• burrowing Armandia brevis versus tube
builders
• Cage placed on sediment with top screen:
tube builders settled on screen, Armandia
burrowed through and reached higher
densities than when screen was absent and
tube builders settled directly in sediment
and established tubes
Soft Sediments - Vertical
Stratification
• Dominant species found at different levels
below sediment-water interface
• Experimentally reduce density of deepdwelling clams, remaining individuals grow
faster - demonstrates effect of density
• Removal of shallow dwelling species of
bivalves has no effect on growth of deeperdwelling species
Occurrence of various bivalves at different burrowing
depths in a sand flat in southern California
Predation and Species
Interactions
• Predators reduce prey density
• Prey species compete
• Conclude: predation may promote
coexistence of competing prey species
Field Experiment of Robert Paine
• Rocky shores of outer coast of Washington
State
• Principle predator - starfish Pisaster
ochraceus
• Pisaster preys on a wide variety of sessile
prey species, including barnacles, mussels,
brachiopods, gastropods
Pacific coast starfish Pisaster ochraceus, flipped over
Left: eating a mussel, Right: eating barnacles
Paine Experiment and Results 1
• Removal of Pisaster ochraceus
Paine Experiment and Results 2
• Removal of Pisaster ochraceus
• Successful settlement of recruits of mussel
Mytilus californianus
Paine Experiment and Results 3
• Removal of Pisaster ochraceus
• Successful settlement of recruits of mussel Mytilus
californianus
• Other species greatly reduced in abundance,
Mytilus californianus became dominant
Paine Experiment and Results 4
• Removal of Pisaster ochraceus
• Successful settlement of recruits of mussel Mytilus
californianus
• Other species greatly reduced in abundance,
Mytilus californianus became dominant
• Conclude: Pisaster ochraceus is a keystone
species, a species whose presence has strong
effects on community organization mediated by
factors such as competition and predation
Larval Recruitment Exerts
Strong Effects 1
• Results from manipulative experiments usually
depend upon steady recruitment of larvae of
competing species
Larval Recruitment Exerts
Strong Effects 2
• Results from manipulative experiments usually
depend upon steady recruitment of larvae of
competing species
• What if recruitment is variable?
Larval Recruitment Exerts
Strong Effects 3
• Results from manipulative experiments usually
depend upon steady recruitment of larvae of
competing species
• What if recruitment is variable?
• Competitively superior species might not take
over, owing to low rates of recruitment
Larval Recruitment Exerts
Strong Effects 4
• Results from manipulative experiments usually
depend upon steady recruitment of larvae of
competing species
• What if recruitment is variable?
• Competitively superior species might not take
over, owing to low rates of recruitment
• Recruitment might be reduced if currents are
not favorable, high water flow results in
flushing of larvae from inshore habitates, poor
year for phytoplankton results in poor year for
success of plankton-feeding larvae
Lower phytoplankton
Lower suspension feeder
Growth
Lower recruitment
High freshwater flow,
tidal flushing
Higher phytoplankton
Higher suspension feeder
Growth
Higher recruitment
Low freshwater flow,
tidal flushing
The effects of variation of tidal flushing on larval recruitment in
a semi-enclosed coastal area, such as a bay
Disturbance as a Factor in
Intertidal Community Structure 1
• Disturbances are physical events that
influence the distribution and abundance of
organisms
Disturbance as a Factor in
Intertidal Community Structure 2
• Disturbances are physical events that
influence the distribution and abundance of
organisms
• Disturbances may reduce abundance of
competing species
Disturbance as a Factor in
Intertidal Community Structure 3
• Disturbances are physical events that
influence the distribution and abundance of
organisms
• Disturbances may reduce abundance of
competing species
• Disturbances may therefore allow
coexistence of competitively inferior species,
or may allow colonization of species adapted
to disturbance
Postelsia palmaeformis, the palm seaweed, invades
rocks that have been severely disturbed by storms, Spores are
released and travel just a few cm fromthe plant, allowing local
spread of a colonizing individual
Spatial Scale of Disturbance is Crucial
in Subsequent Colonization events 1
• A very small scale disturbance in a mussel
bed might just result in the mussels moving
and sealing off the opened patch
Spatial Scale of Disturbance is Crucial
in Subsequent Colonization events 2
• A very small scale disturbance in a mussel bed
might just result in the mussels moving and
sealing off the opened patch
• Larger patches might be colonized by other
species and the patch might last many
months or even indefinitely
Spatial Scale of Disturbance is Crucial in
Subsequent Colonization events 3
• A very small scale disturbance in a mussel bed
might just result in the mussels moving and
sealing off the opened patch
• Larger patches might be colonized by other
species and the patch might last many months
or even indefinitely
• Therefore, spatial scale of disturbance
might affect the spatial pattern of
dominance of species, creating a mosaic of
long-lived patches
California mussels California mussels
California mussels
Small
Newly
Opened
Patch
California mussels California mussels
California mussels
Bay
Mussels
And
Seaweeds
Large
California mussels
California mussels
California mussels
Disturbance and spatial scale: events following the
opening of a small and large patch in a Pacific coast
mussel bed
Estuaries
• Geologically ephemeral but biologically
rich
• Biodiversity declines with decreasing
salinity, especially in so-called critical
salnity range of 3-8 o/oo
• Estuarine flow tends to wash species
toward ocean - larval vertical migration
can retard loss
Estuaries 2
• Species in estuaries often have expanded
range of resource exploitation, owing to
elimination of species from open coast.
Usually estuarine species also occur on
open coast, although there are some
species found only in low salinity
estuarine conditions
Estuaries - Biodiversity
• Diversity of marine-related estuarine
species declines as you move up the
estuary, towards areas of declining
salinity
Estuaries - Biodiversity 2
• There is a critical salinity range, ca. 3-8
o/oo, where diversity is at a minimum
Estuaries - Biodiversity 3
• At lower salinities, biodiversity increases
again, and typical freshwater species are
encountered
Estuaries - Biodiversity 4
• It is believed that the critical salinity range is so
species-poor because normal marine species
cannot survive there very well, nor can
freshwater species, which lack adaptations for
dealing with salt, can survive well here either.
• It has been also suggested that the critical
salinity range has very unusual ratios of
common inorganic elements (e.g., Cl, Na),
which creates further physiological difficulties
Biodiversity along a salinity gradient in the Randerfjord, Denmark
Salt Marshes dominated by
Spartina spp.
• Salt marshes are accretionary environments
• Colonization of sediment by salt marsh
plants is followed by trapping of fine
particles, accretion of sediments
• Marsh Spartina spp. plants spread by means
of a rhizome system - plants are
interconnected and often consist of broad
stands of the same genotype
As initial colonization of Spartina alterniflora results in spread and
trapping of sediment, marsh sediment surface rises, creating a higher
intertidal environment, which favors colonization of a shorter form
Of Spartina alterniflora distant from the water (SAS) and higher marsh
Species, Spartina patens (SP).
Spartina sediment and
adaptations
• Sediment is often anoxic
• Aerenchymal tissue allows Spartina to
exchange gases, even when surrounded by
anoxic soil
• Presence of fiddler crab burrows enhances
Spartina growth, perhaps owing to aeration
of the soil
Fiddler crab, Uca pugilator, in a Spartina salt marsh.
Crab burrows enhance Spartina growth
The ribbed marsh mussel, Geukensia demissa,
lives semi-infaunally in marsh sediments. Its
presence also enhances Spartina growth, perhaps
owing to deposition of nutrient rich feces and
pseudofeces.
Wrack on the surface of a salt marsh. The
role of this material in the nutrient dynamics
of salt marsh ecosystems is controversial.
Cross-section of Spartina below sediment - note
aerenchymal tissue - allows gas exchange
Grazing on Spartina spp.
• Grazing by invertebrates appears to be
relatively slight
• This may be a response to the tough leaves, rich
in cellulose, which also has silica
• Grazing on flowers, however, may be far
greater, resulting in frequent failures of seed set
Grazing on Spartina spp. 2
• Recent research suggests that the
presence of the snail Littorina irrorata
(found in SE USA) does damage to leaves.
This species rises onto the leaves at the
time of high tide to avoid predation by
crabs
Salt Marsh Creeks
• Older, mature salt marshes consist of
meadows with interspersed creeks
• The creeks have high nutrient input,
support large populations of
invertebrates and are often nursery
grounds for juvenile fishes and
crustaceans
Short S.
Spartina patens alterniflora
Tall S. alterniflora
MHW
Peat
Eroding
creek
edge
Creek
Geukensia
demissa
Peat
Peat
Fundulus
heteroclitus
Ilyanassa
obsoleta
MLW
Subhabitats of the Spartina salt marsh environment
Vertical zonation
• Salt marshes exhibit the intertidal
phenomenon of vertical zonation
• From low to high intertidal one often
finds: S. alterniflora, S. patens, Distichlis
spicata, and Juncus gerardi
• The borders between zones are often
quite sharp
Vertical zonation 2
• Lower intertidal species such as Spartina
alterniflora, are more salt tolerant than high
intertidal forms, but low intertidal forms are
not physiologically limited from growing in
high intertidal area
• High intertidal species are competitively
superior to lower intertidal forms, but are not
able to survive the longer exposure lower down
to salt
The border between the Spartina alterniflora zone
And the Spartina patens zone, in West Meadow Creek,
Long Island, New York
Salt Pans
• Accumulations of wrack on the
upper shore may kill salt marsh
grass beneath
Salt Pans 2
• If wrack is carried away by currents,
evaporation may result in high
concentrations of salt, which kills
seedlings and prevents
recolonization of salt marsh grass
species
Salt Pans 3
• Recolonization quite difficult unless there
are heavy rains, dissolving the salt, or an
incursion of grass, which creates shade
and traps moisture, thus enhancing
dissolution of salt
A salt marsh salt pan, at a high intertidal
site in Rhode Island
Mangrove Forests
• Dominated by species of mangroves,
common in subtropical and tropical
protected shores around the world
• Mangroves broadly rooted but only to
shallow depth, in quite anoxic soils
• Underground roots have projections into
air that allow gathering of oxygen
leaves
fruits
Aerial
roots
Pneumatophores
seedling
Anchoring roots
Roots types, leaves, fruits and seedlings of a mangrove
Salt gland
Mangroves are very salt-rolerant plants, and leaves have
a salt gland (left), which can excrete salt from cell cytosol to the
leaf surfaces (right)
Mangrove Forests: Important
Features
• High primary productivity
• High supply of particulate organic
matter, especially falling leaves, which
subsidize animal growth
• Zonation of mangrove species
• Roots support a rich assemblage of sessile
marine invertebrates
Mangrove forest along a salt creek in Mexico
The End