Wrack zone

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Wrack line on a sandy beach Wrack line reveals last high tide mark near the dunes.jpg
Wrack line on a sandy beach

The wrack zone or "wrack line" is a coastal feature where organic material (e.g kelp, seagrass, shells) and other debris is deposited at high tide. This zone acts as a natural input of marine resources into a terrestrial system, providing food and habitat for a variety of coastal organisms.

Tide The periodic change of sea levels caused by the gravitational and inertial effects of the Moon, the Sun and the rotation of the Earth

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.


Physical characteristics

The wrack zone is most commonly associated with a sandy beach habitat but can also be present in rocky shores, mangroves, salt marshes, and other coastal systems. [1] Debris is carried up the intertidal zone as the tide comes in, and is deposited on the sand when the tide goes out. The zone can be recognized as a linear patch of debris toward the upper part of a beach running parallel to the water's edge. The location of the wrack zone varies geographically and temporally. It is found at a higher elevation during spring tides compared to neap tides. The size of a beach and its intertidal zone will influence the location of wrack deposition. Additionally, storms will often increase the volume of debris that is deposited.

Rocky shore An intertidal area of coast where solid rock predominates

A rocky shore is an intertidal area of seacoasts where solid rock predominates. Rocky shores are biologically rich environments, and are a useful "natural laboratory" for studying intertidal ecology and other biological processes. Due to their high accessibility, they have been well studied for a long time and their species are well known.

Mangrove A shrub or small tree that grows in coastal saline or brackish water

A mangrove is a shrub or small tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves occur worldwide in the tropics and subtropics, mainly between latitudes 25° N and 25° S. The total mangrove forest area of the world in 2000 was 137,800 square kilometres (53,200 sq mi), spanning 118 countries and territories.

Salt marsh A coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides

A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.

The wrack zone may be composed of a variety of materials, both organic and inorganic. A common organic component is seaweed, such as kelp, which easily floats to coastal waters after being dislodged by its holdfast or otherwise torn by wave action and animal activity. Other organic components may include seagrasses, terrestrial plants, driftwood, and stranded animal remains. Common inorganic components include plastics, fishing line, and other manmade materials.

Seaweed Macroscopic marine algae

Seaweed or macroalgae refers to several species of macroscopic, multicellular, marine algae. The term includes some types of red, brown, and green macroalgae. Marine algae species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; ocean algae species from seaweeds to planktons play a vital role in carbon capture, producing up to 90 percent of the planet's oxygen. Understanding these roles provides guiding principles for conservation and sustainable use of seaweeds to take precedence over industrial exploitation. Mechanical dredging of kelp, for instance, destroys the resource and dependent fisheries. Certain species of seaweed are valuable for nutrition, biomedicine, bioremediation, and other uses.

Kelp Large brown seaweeds in the order Laminariales

Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera.


A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate.


Sanderling (Calidris alba) feeding in the wrack zone Sanderling (Calidris alba) (6).JPG
Sanderling (Calidris alba) feeding in the wrack zone

Role in coastal food webs

Organic debris that accumulates in the wrack zone is considered a cross-boundary subsidy, linking the marine system to the terrestrial system by providing resources that form the base of coastal food webs. [2] Terrestrial invertebrates such as isopods, amphipods, polychaetes, and shore flies feed on seaweed and other dead material. [3] These invertebrates provide food for shore birds and other predators on the beach. In addition, when organic debris decomposes, it delivers nutrients to the soil, promoting the growth of coastal vegetation. [1]

Cross-boundary subsidy

Cross-boundary subsidies are caused by organisms or materials that cross or traverse habitat patch boundaries, subsidizing the resident populations. The transferred organisms and materials may provide additional predators, prey, or nutrients to resident species, which can affect community and food web structure. Cross-boundary subsidies of materials and organisms occur in landscapes composed of different habitat patch types, and so depend on characteristics of those patches and on the boundaries in between them. Human alteration of the landscape, primarily through fragmentation, has the potential to alter important cross-boundary subsidies to increasingly isolated habitat patches. Understanding how processes that occur outside of habitat patches can affect populations within them may be important to habitat management.

Food web A natural interconnection of food chains

A food web is a natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs. To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter from inorganic substances, including both minerals and gases such as carbon dioxide. These chemical reactions require energy, which mainly comes from the Sun and largely by photosynthesis, although a very small amount comes from hydrothermal vents and hot springs. A gradient exists between trophic levels running from complete autotrophs that obtain their sole source of carbon from the atmosphere, to mixotrophs that are autotrophic organisms that partially obtain organic matter from sources other than the atmosphere, and complete heterotrophs that must feed to obtain organic matter. The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. The food web is a simplified illustration of the various methods of feeding that links an ecosystem into a unified system of exchange. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes - from cyanobacteria to giant redwoods, and from viruses and bdellovibrio to blue whales.

Isopoda order of arthropods

Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and five pairs of branching appendages on the abdomen that are used in respiration. Females brood their young in a pouch under their thorax. Isopods have various feeding methods: some eat dead or decaying plant and animal matter, others are grazers, or filter feeders, a few are predators, and some are internal or external parasites, mostly of fishes. Aquatic species mostly live on the seabed or bottom of freshwater bodies of water, but some taxa can swim for a short distance. Terrestrial forms move around by crawling and tend to be found in cool, moist places. Some species are able to roll themselves into a ball as a defence mechanism or to conserve moisture. There are over 10,000 species of isopod worldwide, with around 4,500 species found in marine environments, mostly on the seabed, 500 species in fresh water, and another 5,000 species on land. The order is divided into eleven suborders. The fossil record of isopods dates back to the Carboniferous period, at least 300 million years ago, when isopods lived in shallow seas. The name Isopoda is derived from the Greek roots iso- and -pod.

Role in habitat formation

The wrack zone adds structure to the beach landscape, providing habitat for animals that live there. For example, rove beetles burrow in the wet sand below the wrack zone, benefiting from moist conditions and the availability of herbivorous invertebrate prey species [3] . Additionally, the wrack zone plays a role in the formation of dunes by promoting the accumulation of wind-blown sand. [4]

Rove beetle family of insects

The rove beetles are a family (Staphylinidae) of beetles, primarily distinguished by their short elytra that typically leave more than half of their abdomens exposed. With roughly 63,000 species in thousands of genera, the group is currently recognized as the largest extant family of beetles. It is an ancient group, with fossilized rove beetles known from the Triassic, 200 million years ago, and possibly even earlier if the genus Leehermania proves to be a member of this family. They are an ecologically and morphologically diverse group of beetles, and commonly encountered in terrestrial ecosystems.

Dune A hill of loose sand built by aeolian processes or the flow of water

In physical geography, a dune is a hill of loose sand built by aeolian processes (wind) or the flow of water. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have a shorter "slip face" in the lee side. The valley or trough between dunes is called a slack. A "dune field" or erg is an area covered by extensive dunes.

Human impacts

Albatross carcass with marine debris at Eastern Island, Midway Atoll Albatross carcass and marine debris.jpg
Albatross carcass with marine debris at Eastern Island, Midway Atoll

Inorganic debris

Manmade objects are often washed ashore in the wrack zone, posing a threat to coastal animals. Plastics in particular are the most common form of litter found on beaches, [5] and it is estimated that 46% of shorebirds ingest plastic in their lifetime while 26% experience entanglement. [6] A variety of effects have been observed in animals that ingest plastic, including reduced reproductive success, changes in immune function, and increased mortality. [6] There is also growing evidence suggesting that plastic bioaccumulates through the food web, so predators may be affected by the accumulation of plastic in their prey's diet. [6]

Bioaccumulation is the accumulation of substances, such as pesticides, or other chemicals in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost by catabolism and excretion. Thus, the longer the biological half-life of a toxic substance, the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high. Bioaccumulation, for example in fish, can be predicted by models. Hypotheses for molecular size cutoff criteria for use as bioaccumulation potential indicators are not supported by data. Biotransformation can strongly modify bioaccumulation of chemicals in an organism.

Beach raking

Sandy beaches are often groomed for aesthetic and recreational value. The removal of organic debris limits habitat and food availability for wrack-associated animals and inhibits the formation of dunes. [4]

Shoreline hardening

Sea walls and other coastal armoring structures can affect the location of a wrack zone and reduce the accumulation of organic material. [1] This can negatively impact the structure and diversity of coastal habitats.

See also

Related Research Articles

Beach Area of loose particles at the edge of the sea or other body of water

A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles. The particles can also be biological in origin, such as mollusc shells or coralline algae.

Mudflat coastal wetlands

Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

Littoral zone Part of a sea, lake or river that is close to the shore

The littoral zone or nearshore is the part of a sea, lake or river which is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to mean the same as the intertidal zone. However, the meaning of "littoral zone" can extend well beyond the intertidal zone.

Benthic zone the region at the lowest level of a body of water including the sediment surface and some sub-surface layers

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention.

Marine debris Human-created solid waste in the sea or ocean

Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a lake, sea, ocean, or waterway. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood, are also present.

Intertidal zone The area of coast between low and high tide marks

The intertidal zone, also known as the foreshore and seashore and sometimes referred to as the littoral zone, is the area that is above water at low tide and underwater at high tide. This area can include many different types of habitats, with many types of animals, such as starfish, sea urchins, and numerous species of coral.

Intertidal ecology

Intertidal ecology is the study of intertidal ecosystems, where organisms live between the low and high tide lines. At low tide, the intertidal is exposed whereas at high tide, the intertidal is underwater. 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 broadest of classifications being based on substrates—rocky shore and soft bottom communities.

White-fronted plover Species of shorebird of the family Charadriidae from Sub-Saharan Africa and Madagascar

The white-fronted plover or white-fronted sandplover is a small shorebird of the family Charadriidae that inhabits sandy beaches, dunes, mudflats and the shores of rivers and lakes in sub-saharan Africa and Madagascar. It nests in small shallow scrapes in the ground and lays clutches of 1-3 eggs. The species is monogamous and long-lived, with a life expectancy of approximately 11 years. The vast majority of pairs that mate together stay together during the following years of breeding and retain the same territory. The white-fronted plover has a similar appearance to the Kentish plover, with a white fore crown and dark bands connecting the eyes to the bill.

Seal Beach National Wildlife Refuge

The Seal Beach National Wildlife Refuge is a wildlife refuge encompassing 965 acres (3.91 km2) located in the California coastal community of Seal Beach. Although it is located in Orange County it is included as part of the San Diego National Wildlife Refuge Complex. It was established in 1972.

Wild fisheries

A fishery is an area with an associated fish or aquatic population which is harvested for its commercial value. Fisheries can be marine (saltwater) or freshwater. They can also be wild or farmed.

Seashore wildlife

Seashore wildlife habitats exist from the Tropics to the Arctic and Antarctic. Seashores and beaches provide varied habitats in different parts of the world, and even within the same beach. Phytoplankton is at the bottom of some food chains, while zooplankton and other organisms eat phytoplankton. Kelp is also autotrophic and at the bottom of many food chains. Coastal areas are stressed through rapid changes, for example due to tides.

Sea foam Foam created by the agitation of seawater

Sea foam, ocean foam, beach foam, or spume is a type of foam created by the agitation of seawater, particularly when it contains higher concentrations of dissolved organic matter derived from sources such as the offshore breakdown of algal blooms. These compounds can act as surfactants or foaming agents. As the seawater is churned by breaking waves in the surf zone adjacent to the shore, the surfactants under these turbulent conditions trap air, forming persistent bubbles that stick to each other through surface tension. Sea foam is a global phenomenon and it varies depending on location and the potential influence of the surrounding marine, freshwater, and/or terrestrial environments. Due to its low density and persistence, foam can be blown by strong on-shore winds from the beach face inland.

Marine habitats A habitat that supports marine life

The marine environment supplies many kinds of habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species.

Plastic pollution accumulation of plastic products in the environment

Plastic pollution is the accumulation of plastic objects in the Earth's environment that adversely affects wildlife, wildlife habitat, and humans. Plastics that act as pollutants are categorized into micro-, meso-, or macro debris, based on size. Plastics are inexpensive and durable, and as a result levels of plastic production by humans are high. However, the chemical structure of most plastics renders them resistant to many natural processes of degradation and as a result they are slow to degrade. Together, these two factors have led to a high prominence of plastic pollution in the environment.

Dana Point State Marine Conservation Area

Dana Point State Marine Conservation Area (SMCA) is one of four adjoining marine protected areas off the coast of Orange County, CA, on California’s South Coast. By itself, the SMCA measures 3.45 square miles. The SMCA protects marine life by limiting the removal of marine wildlife from within its borders, including tide pools. Dana Point SMCA prohibits take of living marine resources except: only the following species may be taken recreationally below the mean lower low tide line only: finfish by hook-and-line or by spearfishing, and lobster and sea urchin. The commercial take of coastal pelagic species by round haul net, and spiny lobster and sea urchin only is allowed.

Microbead-Free Waters Act 2015

The Microbead-Free Waters Act of 2015 is a United States law that prohibits the addition of plastic microbeads in the manufacturing of certain personal care products, such as toothpaste. The purpose of the law is to reduce water pollution caused by these products. Manufacture of the microbead-containing products was prohibited in July 2017, and retail sales are prohibited as of July 2018.

Helderberg Marine Protected Area A marine conservation area in the Western Cape in South Africa

The Helderberg Marine Protected Area is a small marine conservation area on the north-eastern side of False Bay in the Western Cape province of South Africa, It lies between the mouths of the Lourens River in the Strand, and the Eerste River in Macassar.

Namaqua National Park Marine Protected Area A marine conservation area in Namaqualand in the Northern Cape, in South Africa

The Namaqua National Park Marine Protected Area is an inshore conservation region in Namaqualand in the Northern Cape province the territorial waters of South Africa. It is closely associated with the Namaqua National Park, with which it has a common border and management.

Langebaan Lagoon Marine Protected Area A marine conservation area in the Langebaan lagoon in the Western Cape province of South Africa

The Langebaan Lagoon Marine Protected Area is an inshore conservation region in the territorial waters of South Africa


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  2. Schooler, Nicholas K.; Dugan, Jenifer E.; Hubbard, David M.; Straughan, Dale (2017-07-01). "Local scale processes drive long-term change in biodiversity of sandy beach ecosystems". Ecology and Evolution. 7 (13): 4822–4834. doi:10.1002/ece3.3064. ISSN   2045-7758.
  3. 1 2 "Wrack Community | Explore Beaches". explorebeaches.msi.ucsb.edu. Retrieved 2018-03-29.
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