View source for Earth:Wrack zone

{{Short description|Coastal area where organic material is deposited at high tide}}
[[File:Wrack line reveals last high tide mark near the dunes.jpg|thumb|260x260px|
Wrack line on a sandy beach adjacent to a sand dune ecosystem
]]
The '''wrack zone''' or '''wrack line''' is a coastal feature where organic material (e.g. kelp, seagrass, driftwood) and other debris are deposited at [[Astronomy:Tide|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.

== Physical characteristics ==
The wrack zone is most commonly associated with a sandy beach habitat but can also be present in [[Earth:Rocky shore|rocky shore]]s, [[Earth:Mangrove|mangrove]]s, [[Earth:Salt marsh|salt marsh]]es, and other coastal systems.<ref name=":0">{{Cite journal|last1=Strain|first1=E.M.A.|last2=Heath|first2=T.|last3=Steinberg|first3=P.D.|last4=Bishop|first4=M.J.|date=March 2018|title=Eco-engineering of modified shorelines recovers wrack subsidies|journal=Ecological Engineering|volume=112|pages=26–33|doi=10.1016/j.ecoleng.2017.12.009|doi-access=free}}</ref> Debris is carried up the [[Earth:Intertidal zone|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.

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

== Ecology ==
[[File:Sanderling (Calidris alba) (6).JPG|thumb|[[Biology:Sanderling|Sanderling]] (''Calidris alba'') feeding in the wrack zone]]

===Role in coastal food webs===
Organic debris that accumulates in the wrack zone is considered a [[Earth:Cross-boundary subsidy|cross-boundary subsidy]], linking the marine system to the terrestrial system by providing resources that form the base of coastal [[Biology:Food web|food web]]s.<ref>{{Cite journal|last1=Schooler|first1=Nicholas K.|last2=Dugan|first2=Jenifer E.|last3=Hubbard|first3=David M.|last4=Straughan|first4=Dale|date=2017-07-01|title=Local scale processes drive long-term change in biodiversity of sandy beach ecosystems|journal=Ecology and Evolution|language=en|volume=7|issue=13|pages=4822–4834|doi=10.1002/ece3.3064|pmid=28690811|issn=2045-7758|pmc=5496535}}</ref> Terrestrial invertebrates such as [[Biology:Isopoda|isopods]], [[Biology:Amphipoda|amphipods]], [[Biology:Polychaete|polychaete]]s, and shore flies feed on seaweed and other dead material.<ref name=":1">{{Cite web|url=http://explorebeaches.msi.ucsb.edu/sandy-beach-life/wrack-community|title=Wrack Community {{!}} Explore Beaches|website=explorebeaches.msi.ucsb.edu|language=en|access-date=2018-03-29}}</ref> 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.<ref name=":0" />

===Role in habitat formation===
The wrack zone adds structure to the beach landscape, providing habitat for animals that live there. For example, [[Biology:Rove beetle|rove beetle]]s burrow in the wet sand below the wrack zone, benefiting from moist conditions and the availability of herbivorous invertebrate prey species.<ref name=":1" /> [[Biology:Kelp fly|Kelp flies]] like ''[[Biology:Coelopa pilipes|Coelopa pilipes]]'' rely on washed up kelp in wrack zones for food, shelter, and [[Biology:Oviparity|oviposition]]. Additionally, the wrack zone plays a role in the formation of [[Earth:Dune|dune]]s by promoting the accumulation of wind-blown sand.<ref name=":2">{{Cite book|title=Restoration of coastal dunes|last1=Martínez|first1=M.L.|last2=Gallego-Fernández|first2=Juan B.|last3=Hesp|first3=P.|publisher=Springer|year=2013|isbn=9783642334450}}</ref>

== Human impacts ==
[[File:Albatross carcass and marine debris.jpg|thumb|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,<ref>{{Cite journal|last=Law|first=Kara Lavender|date=2017-01-03|title=Plastics in the Marine Environment|journal=Annual Review of Marine Science|volume=9|issue=1|pages=205–229|doi=10.1146/annurev-marine-010816-060409|pmid=27620829|bibcode=2017ARMS....9..205L |issn=1941-1405|doi-access=free}}</ref> and it is estimated that 46% of shorebirds ingest plastic in their lifetime while 26% experience entanglement.<ref name=":3">{{Cite journal|last1=Worm|first1=Boris|last2=Lotze|first2=Heike K.|last3=Jubinville|first3=Isabelle|last4=Wilcox|first4=Chris|last5=Jambeck|first5=Jenna|date=2017-10-17|title=Plastic as a Persistent Marine Pollutant|journal=Annual Review of Environment and Resources|volume=42|issue=1|pages=1–26|doi=10.1146/annurev-environ-102016-060700|issn=1543-5938|doi-access=free}}</ref> A variety of effects have been observed in animals that ingest plastic, including reduced reproductive success, changes in immune function, and increased mortality.<ref name=":3" /> 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.<ref name=":3" />

===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, although the deleterious effects are ameliorated by the removal of plastics and the like.<ref name=":2" />

===Shoreline hardening===

[[Earth:Seawall|Sea walls]] and other coastal armoring structures can affect the location of a wrack zone and reduce the accumulation of organic material.<ref name=":0" /> This can negatively affect the structure and diversity of coastal habitats.

== See also ==
{{columns-list|
* {{annotated link|Earth:Intertidal zone}}
* {{annotated link|Earth:Littoral zone}}
* {{annotated link|Earth:Marine debris}}
* {{annotated link|Earth:Sand dune ecology}}
* {{annotated link|Earth:Shingle beach}}
* {{annotated link|Earth:Supralittoral zone}}}}

== References ==
{{Reflist}}


{{coastal geography}}

[[Category:Coastal geography]]

{{Sourceattribution|Wrack zone}}