Intertidal ecology
Intertidal ecology is the study of
Organisms living in this zone have a highly variable and often hostile environment, and have evolved various
Intertidal regions are
Types of intertidal communities
Intertidal habitats can be characterized as having either hard or soft bottoms substrates.
Environment
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 relative tide height because organisms living in areas with higher tide heights are emersed for longer periods than those living in areas with lower tide heights. This gradient of climate with tide height leads to patterns of
Intertidal organisms, especially those in the high intertidal, must cope with a large range of
Intertidal organisms are also especially prone to
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.
In addition to these exposure stresses (temperature, desiccation, and salinity), intertidal organisms experience strong mechanical stresses, especially in locations of high
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
Food web structure
During tidal immersion, the food supply to intertidal organisms is subsidized by materials carried in seawater, including
, eat dead organic material, including dead producers and consumers.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[13][15] 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.
Although intertidal ecology has traditionally focused on these negative interactions (predation and competition), there is emerging evidence that positive interactions are also important.[17] Facilitation refers to one organism helping another without harming 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.[18] 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[19] 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.
Current topics
Humans are highly dependent on intertidal habitats for food and raw materials,[20] 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 (quickly!) to these new environmental conditions.[20] Due to the global scale of this issue, scientists are mainly working to understand and predict possible changes to intertidal habitats.
2. 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).
3.
See also
References
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- ^ National Academy of Sciences. Marine protected areas: tools for sustaining ocean ecosystems/ Committee on the evaluation, design, and monitoring of marine reserves and protected areas in the United States Ocean Studies Board Commission on Geosciences, Environment, and Resources National Research Council. National Academy Press, Washington, D.C., 2001
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- ^ Ballantine, W.J. (1961). "A Biologically-defined Exposure Scale for the Comparative Description of Rocky Shores". Field Studies Journal. 1 (3).
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- ^ Kelleher, Graeme; Bleakley, Chris; Wells, Sue C. A Global Representative System of Marine Protected Areas: Antarctic, Arctic, Mediterranean, Northwest Atlantic and Baltic (partial document). Vol. I. Washington, D.C.: The International Bank for Reconstruction/The World Bank, 1995.
- PMID 21708776.
- JSTOR 3450442.
- ^ Ricketts, Edward F.; Calvin, Jack; Hedgpeth, Joel W. (1992). Between Pacific Tides (Fifth ed.). Stanford University Press.
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Bibliography
- Bertness, M. D., S. D. Gaines, and M. E. Hay (2001) Marine community ecology. Sinauer Associates, Inc.
- Kozloff E. N. (1973) Seashore life of the northern Pacific coast. University of Washington Press.
- Ricketts E. F., J. Calvin and J. W. Hedgpeth (1939) Between Pacific Tides (5th Ed.) Stanford University Press.