Notes for Marine Biology: Function, Biodiversity, Ecology 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low tide Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide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low tide Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide Some animals greatly reduce metabolic rate at time of low tide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 Chthamalus MHW spring MHW neap Mean tide MLW neap MLW spring Competition Chthamalus Semibalanus Semibalanus Wave Shock Predation 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 deep-dwelling clams, remaining individuals grow faster - demonstrates effect of density Removal of shallow dwelling species of bivalves has no effect on growth of deeper-dwelling 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

The effects of variation of tidal flushing on larval recruitment in Higher phytoplankton Higher suspension feeder Growth Higher recruitment Lower phytoplankton Lower suspension feeder Growth Lower recruitment High freshwater flow, tidal flushing 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

Disturbance and spatial scale: events following the 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

Subhabitats of the Spartina salt marsh environment Short S. alterniflora Spartina patens Tall S. alterniflora MHW Eroding creek edge Peat Geukensia demissa Peat Peat Ilyanassa obsoleta MLW Creek Fundulus heteroclitus 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

Roots types, leaves, fruits and seedlings of a mangrove 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