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Encyclopedia > Intertidal ecology

Intertidal habitats occur on shorelines between the low and high tide lines. At low tide, the intertidal is exposed (or ‘emersed’) whereas at high tide, the intertidal is underwater (or ‘immersed’). Intertidal ecology is the study of the ecology of organisms living in intertidal areas, just as forest and desert ecology are the studies of organisms inhabiting forests and deserts. Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as between different species of intertidal organisms within a particular intertidal community. The most important environmental and species interactions may vary based on the type of intertidal community being studied. The word ecology is often used in common parlance as a synonym for the natural environment or environmentalism. ... Forest ecology is the scientific study of patterns and processes in forests. ... The Earth is made up of distict regions that share unique characteristics of latitude, soil, climate, and plant and animal poplulations that have evolved to adapt to the particular environment of the region. ...


Types of intertidal communities

Intertidal habitats can be characterized as having either hard or soft bottoms or substrates. Rocky intertidal communities occur on rocky shores, such as headlands, cobble beaches, or human-made jetties. Soft-sediment habitats include sandy beaches, mudflats, and salt marshes. These habitats differ in levels of ‘abiotic’, or non-living, environmental factors. Rocky shores tend to have higher wave action, requiring adaptations allowing the inhabitants to cling tightly to the rocks. Soft-bottom habitats are generally protected from large waves but tend to have more variable salinity levels. They also offer a third habitable dimension—depth—thus, many soft-sediment inhabitants are adapted for burrowing. This article is about marsh, a type of wetland. ...


Because intertidal organisms endure regular periods of immersion and emersion, they essentially live both underwater and on land and must be adapted to a large range of climatic conditions. The intensity of climate stressors varies with elevation (or ‘relative tide height’) because organisms living at higher tide heights are emersed for longer periods than those living at lower tide heights. This gradient of climate with tide height leads to patterns of intertidal zonation, with ‘high intertidal’ species being more adapted to emersion stresses than ‘low intertidal’ species. These adaptations may be behavioral (i.e. movements or actions), morphological (i.e. characteristics of external body structure), or physiological (i.e. internal functions of cells and organs)(Ref. 1). In addition, such adaptations generally ‘cost’ the organism in terms of energy (e.g. to move or to grow certain structures), leading to ‘trade-offs’ (i.e. ‘spending’ more energy on deterring predators leaves less energy for other functions like reproduction). // Intertidal Zone (Littoral Zone) (see also intertidal ecology, foreshore, and littoral zone) The intertidal zone, also known as the littoral zone, in marine aquatic environments is the area of the foreshore and seabed that is exposed to the air at low tide and submerged at high tide, ie the area...

Intertidal organisms, especially those in the high intertidal, must cope with a large range of temperatures. While they are underwater, temperatures may only vary by a few degrees over the year. However, at low tide, temperatures may dip to below freezing or may become scaldingly hot, leading to an over 50 degrees Fahrenheit temperature range during a period of a few hours. Many mobile organisms, such as snails and crabs, avoid temperature fluctuations by crawling around and searching for food at high tide and hiding in cool, moist refuges (crevices or burrows) at low tide (Ref. 2). Besides simply living at lower tide heights, non-motile organisms may be relatively more dependent on coping mechanisms. For example, high intertidal organisms have a stronger ‘stress response’, a physiological response of making proteins that help recovery from temperature stress just as the immune response aids in the recovery from infection. Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ...

Intertidal organisms are also especially prone to desiccation (drying out) during periods of emersion. Again, mobile organisms avoid desiccation in the same way as they avoid extreme temperatures: by hunkering down in mild and moist refuges. Many intertidal organisms, including Littorina snails, prevent water loss by having waterproof outer surfaces, pulling completely into their shells, and sealing shut their shell opening. Still other organisms, such as the algae Ulva and Porphyra, are able to rehydrate and recover after periods of severe desiccation.

The level of salinity can also be quite variable. Low salinities can be caused by rainwater or river inputs of freshwater. Estuarine species must be especially ‘euryhaline’, or able to tolerate a wide range of salinities. High salinities occur in locations with high evaporation rates, such as in salt marshes and high intertidal pools. Shading by plants, especially in the salt marsh, can slow evaporation and thus ameliorate salinity stress. In addition, salt marsh plants tolerate high salinities by several physiological mechanisms, including excreting salt through salt glands and preventing salt uptake into the roots. Salinity is the saltiness or dissolved salt content of a body of water. ...

In addition to these ‘exposure’ stresses (temperature, desiccation, and salinity), intertidal organisms experience strong ‘mechanical’ stresses, especially in locations of high wave action. There are myriad ways in which the organisms prevent dislodgement due to waves. Morphologically, many mollusks (such as limpets and chitons) have low-profile, hydrodynamic shells. Types of substrate attachments include mussels’ tethering byssal threads and glues, sea stars’ thousands of suctioning tube feet, and isopods’ hook-like appendages that help them hold onto intertidal kelps. Higher profile organisms, such as kelps, must also avoid breaking in high flow locations, and they do so with their strength and flexibility. Finally, organisms can also avoid high flow environments, such as by seeking out low flow microhabitats. Additional forms of mechanical stresses include ice and sand scour, as well as dislodgment by water-borne rocks, logs, etc. The concept wave is related to a disturbance that propagates through space, often transferring energy. ...

For each of these climate stresses, species exist that are adapted to and thrive in the most stressful of locations. For example, the tiny crustacean copepod Tigriopus thrives in very salty, high intertidal tidepools, and many filter feeders find more to eat in wavier and higher flow locations. Adapting to such challenging environments gives these species competitive edges in such locations. Filter feeders (also known as suspension feeders) are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure, such as the baleen of baleen whales. ...

Food web structure

During tidal immerson, the food supply to intertidal organisms is subsidized by materials carried in seawater, including photosynthesizing phytoplankton and consumer zooplankton. These plankton are eaten by numerous forms of filter feedersmussels, clams, barnacles, sea squirts, and polychaete worms—which filter seawater in their search for planktonic food sources. The adjacent ocean is also a primary source of nutrients for autotrophs, photosynthesizing producers ranging in size from microscopic algae (e.g. benthic diatoms) to huge kelps and other seaweeds. These intertidal producers are eaten by herbivorous grazers, such as limpets that scrape rocks clean of their diatom layer and kelp crabs that creep along blades of the feather boa kelp Egregia eating the tiny leaf-shaped bladelets. Higher up the food web, predatory consumers—especially voracious sea stars—eat other grazers (e.g. snails) and filter feeders (e.g. mussels). Finally, scavengers, including crabs and sand fleas, eat dead organic material, including dead producers and consumers. Figure 1. ... Leaf. ... Diagrams of some typical phytoplankton Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column. ... Photomontage of plankton organisms For the Spongebob SquarePants character, see Sheldon J. Plankton. ... Filter feeders (also known as suspension feeders) are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized structure, such as the baleen of baleen whales. ... Mussels A mussel is a bivalve shellfish that can be found in lakes, rivers, creeks, intertidal areas, and throughout the ocean. ... Categories: Pages needing attention | Animal stubs ... Orders Ascothoracica Acrothoracica Thoracica Rhizocephala A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea and is hence distantly related to crabs and lobsters. ... Classes Ascidiacea Thaliacea Appendicularia Urochordata (sometimes known as tunicata and commonly called urochordates, tunicates or sea squirts) is the subphylum of saclike filter feeders with input and output siphons. ... Orders Amphinomida Capitellida Chaetopterida Cirratulida Cossurida Ctenodrillidae Eunicida Flabelligerida Magelonida Myzostomida Nerillida Opheliida Orbiniida Orweniida Phyllodocida Pisionidae Polygordiida Protodrilida Psammodrilidae Sabellida Spionida Spintheridae Sternaspida Terebellida Tomopteris from plankton The Polychaeta or Polychaetes are a class of annelid worms, generally marine, with a pair of fleshy protrusions on each body segment... An autotroph (in Greek eauton = self and trophe = nutrition) is an organism that produces its own cell mass and organic compounds from carbon dioxide as sole carbon source, using either light or chemical compounds as a source of energy. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Diatoms are the most common of the eukaryotic algae. ... Families Alariaceae Chordaceae Laminariaceae Lessoniaceae Phyllariaceae Pseudochordaceae Kelp are large seaweeds, belonging to the brown algae and classified in the order Laminariales. ... Seaweed covered rocks in the UK Phycologists consider seaweed to refer any of a large number of marine benthic algae that are multicellular, macrothallic (large-bodied), and thus differentiated from most algae that tend towards microscopic size (Smith, 1944). ... This page is a candidate for speedy deletion, because: See article: Limpet If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ... Phthirus pubis Pubic lice (Phthirus pubis), also known as crabs , are one of the many varieties of lice (singular louse) specialized to live on different areas of different animals. ... It has been suggested that this article or section be merged with User:Stellertony/Notepad/Sea_star. ... Giant African Snail (Achatina fulica) The name snail applies to most members of the molluscan Class Gastropoda that have coiled shells. ... Sub-orders Gammaridea Caprellidea Hyperiidea Ingolfiellidea Amphipoda (amphipods) include about 4600 different species of small, shrimp-like crustaceans. ...

Species interactions

In addition to being shaped by aspects of climate, intertidal habitats—especially intertidal zonation patterns—are strongly influenced by species interactions, such as predation, competition, facilitation, and indirect interactions. Ultimately, these interactions feed into the food web structure, described above. Intertidal habitats have been a model system for many classic ecological studies, including those introduced below, because the resident communities are particularly amenable to experimentation.

One dogma of intertidal ecology—supported by such classic studies—is that species’ lower tide height limits are set by species interactions whereas their upper limits are set by climate variables. Classic studies by Robert Paine (Ref. 3, 4) established that when sea star predators are removed, mussel beds extend to lower tide heights, smothering resident seaweeds. Thus, mussels’ lower limits are set by sea star predation. Conversely, in the presence of sea stars, mussels’ lower limits occur at a tide height at which sea stars are unable to tolerate climate conditions.

Competition, especially for space, is another dominant interaction structuring intertidal communities. Space competition is especially fierce in rocky intertidal habitats, where habitable space is limited compared to soft-sediment habitats in which three-dimensional space is available. As seen with the previous sea star example, mussels are competitively dominant when they are not kept in check by sea star predation. Joseph Connell’s research on two types of high intertidal barnacles, a Balanus and a Chthamalus species, showed that zonation patterns could also be set by competition between closely related organisms (Ref. 5). In this example, Balanus outcompetes Chthamalus at lower tide heights but is unable to survive at higher tide heights. Thus, Balanus conforms to the intertidal ecology dogma introduced above: its lower tide height limit is set by a predatory snail and its higher tide height limit is set by climate. Similarly, Chthamalus, which occurs in a refuge from competition (similar to the temperature refuges discussed above), has a lower tide height limit set by competition with Balanus and a higher tide height limit is set by climate.

Although intertidal ecology has traditionally focused on these negative interactions (predation and competition), there is emerging evidence that positive interactions are also important (Ref. 6). Facilitation refers to one organism ‘helping’ another without harming itself (note: in predation, the prey ‘helps’ the predator, but at great harm to itself!). For example, salt marsh plant species of Juncus and Iva are unable to tolerate the high soil salinities when evaporation rates are high, thus they depend on neighboring plants to shade the sediment, slow evaporation, and help maintain tolerable salinity levels (Ref. 7). In similar examples, many intertidal organisms provide physical structures that are used as refuges by other organisms. Mussels, although they are tough competitors with certain species, are also good facilitators as mussel beds provide a three-dimensional habitat to species of snails, worms, and crustaceans.

All of the examples given so far are of ‘direct’ interactions: Species A eat Species B or Species B eats Species C. Also important are indirect interactions (Ref. 8) where, using the previous example, Species A eats so much of Species B that predation on Species C decreases and Species C increases in number. Thus, Species A indirectly benefits Species C. Pathways of indirect interactions can include all other forms of species interactions. To follow the sea star-mussel relationship, sea stars have an indirect negative effect on the diverse community that lives in the mussel bed because, by preying on mussels and decreasing mussel bed structure, those species that are facilitated by mussels are left homeless. Additional important species interactions include mutualism, which is seen in symbioses between sea anemones and their internal symbiotic algae, and parasitism, which is prevalent but is only beginning to be appreciated for its effects on community structure. In biology, mutualism is an interaction between two species in which both species derive benefit. ... Parasitism is an interaction between two organisms, in which one organism (the parasite) benefits and the other (the host) is harmed. ...

Current topics

Humans are highly dependent on intertidal habitats for food and raw materials (Ref. 9), and over 50% of humans live within 100 km of the coast. Therefore, intertidal habitats are greatly influenced by human impacts to both ocean and land habitats. Some of the conservation issues associated with intertidal habitats and at the head of the agendas of managers and intertidal ecologists are:

1. Climate change: Intertidal species are challenged by several of the effects of global climate change, including increased temperatures, sea level rise, and increased storminess. Ultimately, it has been predicted that the distributions and numbers of species will shift depending on their abilities to adapt (relatively quickly!) to these new environmental conditions (Ref. 9). Due to the global scale of this issue, scientists are mainly working to understand and predict possible changes to intertidal habitats. Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years Climate change refers to the variation in the Earths global climate or regional climates over time. ... Measurement of recent sea level rise from 23 long tide gauge records in geologically stable environments Changes in sea level since the end of the last glacial episode Sea level rise is an increase in sea level. ...

2. Invasive species: Invasive species are especially prevalent in intertidal areas with high volumes of shipping traffic, such as large estuaries, because of the transport of non-native species in ballast water (Ref. 10). San Francisco Bay, in which an invasive [[Spartina]] cordgrass from the east coast is currently transforming mudflat communities into Spartina meadows, is among the most invaded estuaries in the world. Conservation efforts are focused on trying to eradicate some species (like Spartina) in their non-native habitats as well as preventing further species introductions (e.g. by controlling methods of ballast water uptake and release). The term invasive species refers to a subset of those species defined as introduced species or non-indigenous species. ... Ballast may mean: Look up ballast in Wiktionary, the free dictionary. ...

3. Marine protected areas: Many intertidal areas are lightly to heavily exploited by humans for food gathering (e.g. clam digging in soft-sediment habitats and snail, mussel, and algal collecting in rocky intertidal habitats). In some locations, marine protected areas have been established where no collecting is permitted. The benefits of protected areas may spill over to positively impact adjacent unprotected areas. For example, a greater number of larger egg capsules of the edible snail Concholepus in protected vs. non-protected areas in Chile indicates that these protected areas may help replenish snail stocks in areas open to harvesting (Ref. 11). The degree to which collecting is regulated by law differs with the species and habitat.

Links to species lists and photographs:

Rocky intertidal species, Australia <http://www.rockyshores.auz.info/back_info04.htm#>


1. Somero, G. N. 2002. Thermal physiology and vertical zonation of intertidal animals: optima, limits, and cost of living. Integrative and Comparative Biology 42:780-789.

2. Burnaford, J. L. 2004. Habitat modification and refuge from sublethal stress drive a marine plant-herbivore association. Ecology 85:2837-2849.

3. Paine, R. T. 1966. Food web complexity and species diversity. American Naturalist 100:65-75.

4. Paine, R. T. 1974. Intertidal community structure: experimental studies on the relationship between a dominant competitor and its principal predator. Oecologia 15:93-120.

5. Connell, J. H. 1961. The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42:710-723.

6. Bruno, J. F., J. J. Stachowicz, and M. D. Bertness. 2003. Inclusion of facilitation into ecological theory. Trends in Ecology and Evolution 18:119-125.

7. Bertness, M. D., and S. D. Hacker. 1994. Physical stress and positive associations among marsh plants. American Naturalist 144:363-372.

8. Menge, B. A. 1995. Indirect effects in marine rocky intertidal interaction webs: patterns and importance. Ecological Monographs 65:21-74.

9. Harley, C. D. G., A. R. Hughes, K. M. Hultgren, B. G. Miner, C. J. B. Sorte, C. S. Thornber, L. F. Rodriguez, L. Tomanek, and S. L. Williams. 2006. The impacts of climate change in coastal marine systems. Ecology Letters 9:228-241.

10. Cohen, A. N., and J. T. Carlton. 1998. Accelerating invasion rate in a highly invaded estuary. Science 279:555-558.

11. Manriquez, P. H., and J. C. Castilla. 2001. Significance of marine protected areas in central Chile as seeding grounds for the gastropod Concholepus concholepus. Marine Ecology Progress Series 215:201-211.

12. Bertness, M. D., S. D. Gaines, and M. E. Hay. 2001. Marine community ecology. Sinauer Associates, Inc., Sunderland, Massachusetts, USA.

13. Kozloff, E. N. 1973. Seashore life of the northern Pacific coast. University of Washington Press, Seattle, Washington, USA.

14. Ricketts, E. F., J. Calvin, and J. W. Hedgpeth. 1939. Between Pacific tides (5th Ed.). Stanford University Press, Stanford, California, USA.



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