Bioturbation on:  
[Wikipedia]  
[Google]  
[Amazon]
Bioturbation is defined as the reworking of
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
s and
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
s by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and
are thought to be a primary driver of
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
.
The formal study of bioturbation began in the 1800s by
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
experimenting in his garden.
The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant
ecosystem services
Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. Th ...
. These include the alteration of
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.
[Shaler, N. S., 1891, The origin and nature of soils, in Powell, J. W., ed., USGS 12th Annual report 1890-1891: Washington, D.C., Government Printing Office, p. 213-45.]
Bioturbators are deemed
ecosystem engineer
An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem enginee ...
s because they alter resource availability to other species through the physical changes they make to their environments.
This type of ecosystem change affects the evolution of cohabitating species and the environment,
which is evident in
trace fossil
A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s left in marine and terrestrial sediments. Other bioturbation effects include altering the texture of sediments (
diagenesis
Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...
),
bioirrigation
Bioirrigation refers to the process of benthos, benthic organisms flushing their burrows with overlying water. The exchange of dissolved substances between the porewater and overlying seawater that results is an important process in the context o ...
, and displacement of microorganisms and non-living particles. Bioturbation is sometimes confused with the process of bioirrigation, however these processes differ in what they are mixing; bioirrigation refers to the mixing of water and solutes in sediments and is an effect of bioturbation.
Walrus
The walrus (''Odobenus rosmarus'') is a large pinniped, flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living species in ...
es,
salmon
Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
, and
pocket gophers
Pocket gophers, commonly referred to simply as gophers, are burrowing rodents of the family Geomyidae. The roughly 41 speciesSearch results for "Geomyidae" on thASM Mammal Diversity Database are all endemic to North and Central America. They are ...
are examples of large bioturbators.
[Humphreys, G. S., and Mitchell, P. B., 1983, A preliminary assessment of the role of bioturbation and rainwash on sandstone hillslopes in the Sydney Basin, in Australian and New Zealand Geomorphology Group, p. 66-80.] Although the activities of these large macrofaunal bioturbators are more conspicuous, the dominant bioturbators are small invertebrates, such as
earthworm
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...
s,
polychaete
Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...
s,
ghost shrimp, mud shrimp, and
midge larvae.
The activities of these small invertebrates, which include burrowing and ingestion and defecation of sediment grains, contribute to mixing and the alteration of sediment structure.
History of study of bioturbation
Bioturbation's importance for soil processes and
geomorphology
Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...
was first realized by Charles Darwin, who devoted his last scientific book to the subject (''
{{R from other capitalisation ...
'').
Darwin spread chalk dust over a field to observe changes in the depth of the chalk layer over time.
Excavations 30 years after the initial deposit of chalk revealed that the chalk was buried 18 centimeters under the sediment, which indicated a burial rate of 6 millimeters per year.
Darwin attributed this burial to the activity of earthworms in the sediment and determined that these disruptions were important in soil formation.
In 1891, geologist
Nathaniel Shaler
Nathaniel Southgate Shaler (February 20, 1841 – April 10, 1906) was an American paleontologist and geologist who wrote extensively on the theological and scientific implications of the theory of evolution.
Biography
Born to a slave-holding fami ...
expanded Darwin's concept to include soil disruption by ants and trees.
The term "bioturbation" was later coined by Rudolf Richter in 1952 to describe structures in sediment caused by living organisms.
Since the 1980s, the term "bioturbation" has been widely used in soil and geomorphology literature to describe the reworking of soil and sediment by plants and animals.
Evolution and Ecology
Evolution
The onset of bioturbation had a profound effect on the environment and the evolution of other organisms.
Bioturbation is thought to have been an important co-factor of the
Cambrian Explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
, during which most major animal
phyla Phyla, the plural of ''phylum'', may refer to:
* Phylum, a biological taxon between Kingdom and Class
* by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another
Phyl ...
appeared in the fossil record over a short time.
Predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
arose during this time and promoted the development of hard skeletons, for example bristles, spines, and shells, as a form of
armored
Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat
Co ...
protection.
It is hypothesized that bioturbation resulted from this skeleton formation.
These new hard parts enabled animals to dig into the sediment to seek shelter from predators, which created an incentive for predators to search for prey in the sediment (see
Evolutionary Arms Race
In evolutionary biology, an evolutionary arms race is an ongoing struggle between competing sets of co-evolving genes, phenotypic and behavioral traits that develop escalating adaptations and counter-adaptations against each other, resembling an a ...
).
Burrowing species fed on buried organic matter in the sediment which resulted in the evolution of deposit feeding (consumption of organic matter within sediment).
Prior to the development of bioturbation, laminated
microbial mat
A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...
s were the dominant biological structures of the ocean floor and drove much of the
ecosystem functions.
As bioturbation increased, burrowing animals disturbed the microbial mat system and created a mixed sediment layer with greater biological and chemical diversity.
This greater biological and chemical diversity is thought to have led to the evolution and diversification of seafloor-dwelling species.
An alternate, less widely accepted hypothesis for the origin of bioturbation exists. The
trace fossil
A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
''
Nenoxites
''Nenoxites'' is an extinct genus of Ediacaran ichnofossils described by Mikhail Fedonkin in 1973. The genus is monotypic; the only species to have been described is ''Nenoxites curvus''.
Description
''Nenoxites'' is a repichnia trace of soft ...
'' is thought to be the earliest record of bioturbation, predating the Cambrian Period.
The fossil is dated to 555 million years, which places it in the
Ediacaran Period. The fossil indicates a 5 centimeter depth of bioturbation in muddy sediments by a burrowing worm.
This is consistent with food-seeking behavior, as there tended to be more food resources in the mud than the water column.
However, this hypothesis requires more precise
geological dating to rule out an early Cambrian origin for this specimen.
The evolution of trees during the
Devonian Period
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...
enhanced soil weathering and increased the spread of soil due to bioturbation by tree roots.
Root penetration and uprooting also enhanced soil carbon storage by enabling mineral weathering and the burial of organic matter.
Ecosystem function
Functional Groupings
Bioturbators have been organized by a variety of functional groupings based on either ecological characteristics or biogeochemical effects. While the prevailing categorization is based on the way bioturbators transport and interact with sediments, the various groupings likely stem from the relevance of a categorization mode to a field of study (such as ecology or sediment biogeochemistry) and an attempt to concisely organize the wide variety of bioturbating organisms in classes that describe their function. Examples of categorizations include those based on feeding and motility, feeding and biological interactions, and mobility modes. The most common set of groupings are based on sediment transport and are as follows:
* Gallery-diffusers create complex tube networks within the upper sediment layers and transport sediment through feeding, burrow construction, and general movement throughout their galleries.
Gallery-diffusers are heavily associated with burrowing
polychaete
Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...
s, such as ''
Nereis
''Nereis'' is a genus of polychaete worms in the family Nereididae. It comprises many species, most of which are marine. ''Nereis'' possess setae and parapodia for locomotion and gas exchange. They may have two types of setae, which are found on ...
diversicolor'' and ''Marenzellaria spp.''
*Biodiffusers transport sediment particles randomly over short distances as they move through sediments. Animals mostly attributed to this category include
bivalves
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
such as clams, and
amphipod
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...
species, but can also include larger vertebrates, such as bottom-dwelling fish and rays that feed along the sea floor.
Biodiffusers can be further divided into two subgroups, which include
epifaunal (organisms that live on the surface sediments) biodiffusers and surface biodiffusers.
This subgrouping may also include gallery-diffusers,
reducing the number of functional groups.
*Upward-conveyors are oriented head-down in sediments, where they feed at depth and transport sediment through their guts to the sediment surface.
Major upward-conveyor groups include burrowing
polychaete
Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...
s like the
lugworm
The lugworm or sandworm (''Arenicola marina'') is a large marine worm of the phylum Annelida. Its coiled castings are a familiar sight on a beach at low tide but the animal itself is rarely seen except by those who, from curiosity or to use as f ...
, ''Arenicola marina,'' and
thalassinid shrimps.
*Downward-conveyor species are oriented with their heads towards the
sediment-water interface and defecation occurs at depth.
Their activities transport sediment from the surface to deeper sediment layers as they feed.
Notable downward-conveyors include those in the
peanut worm family,
Sipunculidae
Sipunculidae is a family of peanut worms.
Species ''Phascolopsis''
* ''Phascolopsis gouldii'' (De Pourtalés, 1851)
''Siphonomecus''
* ''Siphonomecus multicinctus'' Fisher 1947
''Siphonosoma''
* ''Siphonosoma arcassonense'' (Cuenot, 1902)
* '' ...
.
![Arenicola marina 2010](https://upload.wikimedia.org/wikipedia/commons/e/e7/Arenicola_marina_2010.JPG)
* Regenerators are categorized by their ability to release sediment to the overlying water column, which is then dispersed as they burrow.
After regenerators abandon their burrows, water flow at the sediment surface can push in and collapse the burrow.
Examples of regenerator species include
fiddler
A fiddle is a Bow (music), bowed String instrument, string musical instrument, most often a violin. It is a colloquial term for the violin, used by players in all genres, including European classical music, classical music. Although in many ...
and
ghost
A ghost is the soul or spirit of a dead person or animal that is believed to be able to appear to the living. In ghostlore, descriptions of ghosts vary widely from an invisible presence to translucent or barely visible wispy shapes, to rea ...
crabs.
Ecological Roles
The evaluation of the ecological role of bioturbators has largely been species-specific.
However, their ability to transport solutes, such as dissolved oxygen, enhance organic matter decomposition and diagenesis, and alter sediment structure has made them important for the survival and colonization by other macrofaunal and microbial communities.
Microbial communities are greatly influenced by bioturbator activities, as increased transport of more
energetically favorable oxidants
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...
, such as oxygen, to typically highly reduced sediments at depth alters the
microbial metabolic processes occurring around burrows.
As bioturbators burrow, they also increase the surface area of sediments across which oxidized and reduced solutes can be exchanged, thereby increasing the overall sediment metabolism. This increase in sediment metabolism and microbial activity further results in enhanced organic matter decomposition and sediment oxygen uptake.
In addition to the effects of burrowing activity on microbial communities, studies suggest that bioturbator fecal matter provides a highly nutritious food source for microbes and other macrofauna, thus enhancing benthic microbial activity.
This increased microbial activity by bioturbators can contribute to increased nutrient release to the overlying water column.
Nutrients released from enhanced microbial decomposition of organic matter, notably limiting nutrients, such as ammonium, can have bottom-up effects on ecosystems and result in increased growth of phytoplankton and bacterioplankton.
![Goby fish with shrimp](https://upload.wikimedia.org/wikipedia/commons/0/04/Goby_fish_with_shrimp.jpg)
Burrows offer protection from predation and harsh environmental conditions.
For example, termites ''(
Macrotermes bellicosus
''Macrotermes bellicosus'' is a species of ''Macrotermes''. It is the largest termite known, with queens measuring about long, workers about and soldiers are slightly larger. ' means "combative" in Latin. The species is a member of a genus indi ...
)'' burrow and create mounds that have a complex system of air ducts and evaporation devices that create a suitable microclimate in an unfavorable physical environment.
Many species are attracted to bioturbator burrows because of their protective capabilities.
The shared use of burrows has enabled the evolution of
symbiotic relationships
Symbiosis (from Ancient Greek, Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different Organism, biological organisms, be it Mutualism (biolog ...
between bioturbators and the many species that utilize their burrows. For example, gobies, scale-worms, and crabs live in the burrows made by innkeeper worms. Social interactions provide evidence of co-evolution between hosts and their burrow symbionts.
This is exemplified by shrimp-goby associations.
Shrimp burrows provide shelter for gobies and gobies serve as a scout at the mouth of the burrow, signaling the presence of potential danger.
In contrast, the blind goby ''
Typhlogobius californiensis'' lives within the deep portion of ''
Callianassa
''Callianassa'' is a genus of mud shrimps, in the family Callianassidae. Three of the species in this genus ('' C. candida'', '' C. tyrrhena'' and '' C. whitei'') have been split off into a new genus, '' Pestarella'', while others such as '' C ...
'' shrimp burrows where there is not much light.
The blind goby is an example of a species that is an obligate
commensalist, meaning their existence depends on the host bioturbator and its burrow.
Although newly hatched blind gobies have fully developed eyes, their eyes become withdrawn and covered by skin as they develop.
They show evidence of commensal
morphological evolution because it is hypothesized that the lack of light in the burrows where the blind gobies reside is responsible for the evolutionary loss of functional eyes.
Bioturbators can also inhibit the presence of other benthic organisms by smothering, exposing other organisms to predators, or resource competition.
While thalassinidean shrimps can provide shelter for some organisms and cultivate interspecies relationships within burrows, they have also been shown to have strong negative effects on other species, especially those of bivalves and surface-grazing
gastropods
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...
, because thalassinidean shrimps can smother bivalves when they resuspend sediment. They have also been shown to exclude or inhibit polychaetes,
cumacea
Cumacea is an order of small marine crustaceans of the superorder Peracarida, occasionally called hooded shrimp or comma shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans. They live in so ...
ns, and
amphipods
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
.
This has become a serious issue in the northwestern United States, as ghost and mud shrimp (thalasinidean shrimp) are considered pests to bivalve
aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
operations. The presence of bioturbators can have both negative and positive effects on the
recruitment
Recruitment is the overall process of identifying, sourcing, screening, shortlisting, and interviewing candidates for jobs (either permanent or temporary) within an organization. Recruitment also is the processes involved in choosing individual ...
of larvae of conspecifics (those of the same species) and those of other species, as the resuspension of sediments and alteration of flow at the sediment-water interface can affect the ability of larvae to burrow and remain in sediments.
This effect is largely species-specific, as species differences in resuspension and burrowing modes have variable effects on fluid dynamics at the sediment-water interface.
Deposit-feeding bioturbators may also hamper recruitment by consuming recently settled larvae.
Biogeochemical effects of bioturbation
Since its onset around 539 million years ago, bioturbation has been responsible for changes in
ocean chemistry
Marine chemistry, also known as ocean chemistry or chemical oceanography, is influenced by plate tectonics and seafloor spreading, turbidity currents, sediments, pH levels, atmospheric constituents, metamorphic activity, and ecology. The fiel ...
, primarily through nutrient cycling.
Bioturbators played, and continue to play, an important role in nutrient transport across sediments.
For example, bioturbating animals are hypothesized to have affected the cycling of sulfur in the early oceans. According to this hypothesis, bioturbating activities had a large effect on the sulfate concentration in the ocean. Around the Cambrian-Precambrian boundary (539 million years ago), animals begin to mix reduced sulfur from
ocean sediment
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and rocks and have been transported from the land to the sea, mainly ...
s to overlying water causing sulfide to oxidize, which increased the sulfate composition in the ocean. During large extinction events, the sulfate concentration in the ocean was reduced. Although this is difficult to measure directly, seawater sulfur isotope compositions during these times indicates bioturbators influenced the sulfur cycling in the early Earth.
Bioturbators have also altered phosphorus cycling on geologic scales.
Bioturbators mix readily available particulate organic phosphorus (P) deeper into ocean sediment layers which prevents the precipitation of phosphorus
(mineralization) by increasing the sequestration of phosphorus above normal chemical rates. The sequestration of phosphorus limits oxygen concentrations by decreasing production on a geologic time scale.
This decrease in production results in an overall decrease in oxygen levels, and it has been proposed that the rise of bioturbation corresponds to a decrease in oxygen levels of that time.
The negative feedback of animals sequestering phosphorus in the sediments and subsequently reducing oxygen concentrations in the environment limits the intensity of bioturbation in this early environment.
Nutrient cycling is still affected by bioturbation in the modern Earth. Some examples in the aquatic and terrestrial ecosystems are below.
Aquatic
Terrestrial freshwater ecosystems
Important sources of bioturbation in freshwater ecosystems include
benthivorous (bottom-dwelling) fish, macroinvertebrates such as worms, insect larvae, crustaceans and molluscs, and seasonal influences from
anadromous
Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...
(migrating) fish such as salmon. Anadromous fish migrate from the sea into fresh-water rivers and streams to spawn. Macroinvertebrates act as biological pumps for moving material between the sediments and water column, feeding on sediment organic matter and transporting mineralized nutrients into the water column.
Both benthivorous and anadromous fish can affect ecosystems by decreasing primary production through sediment re-suspension,
the subsequent displacement of benthic primary producers, and recycling nutrients from the sediment back into the water column.
Lakes and ponds
![Chironomidae](https://upload.wikimedia.org/wikipedia/commons/0/0e/Chironomidae.jpg)
The sediments of lake and pond ecosystems are rich in organic matter, with higher organic matter and nutrient contents in the sediments than in the overlying water.
Nutrient re-regeneration through sediment bioturbation moves nutrients into the water column, thereby enhancing the growth of aquatic plants and phytoplankton (
primary producers
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
).
The major nutrients of interest in this flux are nitrogen and phosphorus, which often limit the levels of primary production in an ecosystem.
Bioturbation increases the flux of mineralized (inorganic) forms of these elements, which can be directly used by primary producers. In addition, bioturbation increases the water column concentrations of nitrogen and phosphorus-containing organic matter, which can then be consumed by fauna and mineralized.
Lake and pond sediments often transition from the aerobic (oxygen containing) character of the overlaying water to the anaerobic (without oxygen) conditions of the lower sediment over sediment depths of only a few millimeters, therefore, even bioturbators of modest size can affect this transition of the chemical characteristics of sediments.
By mixing anaerobic sediments into the water column, bioturbators allow aerobic processes to interact with the re-suspended sediments and the newly exposed bottom sediment surfaces.
Macroinvertebrates including
chironomid
The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many species ...
(non-biting midges) larvae and
tubificed worms (detritus worms) are important agents of bioturbation in these ecosystems and have different effects based on their respective feeding habits. Tubificed worms do not form burrows, they are upward conveyors. Chironomids, on the other hand, form burrows in the sediment, acting as bioirrigators and aerating the sediments and are downward conveyors. This activity, combined with chironomid's respiration within their burrows, decrease available oxygen in the sediment and increase the loss of nitrates through enhanced rates of
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
.
The increased oxygen input to sediments by macroinvertebrate bioirrigation coupled with bioturbation at the sediment-water interface complicates the total flux of phosphorus . While bioturbation results in a net flux of phosphorus into the water column, the bio-irrigation of the sediments with oxygenated water enhances the adsorption of phosphorus onto iron-oxide compounds, thereby reducing the total flux of phosphorus into the water column.
The presence of macroinvertebrates in sediment can initiate bioturbation due to their status as an important food source for benthivorous fish such as
carp
Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...
.
Of the bioturbating, benthivorous fish species, carp in particular are important ecosystem engineers and their foraging and burrowing activities can alter the water quality characteristics of ponds and lakes.
Carp increase water
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids can ...
by the re-suspension of benthic sediments. This increased turbidity limits light penetration and coupled with increased nutrient flux from the sediment into the water column, inhibits the growth of macrophytes (aquatic plants) favoring the growth of phytoplankton in the surface waters. Surface phytoplankton colonies benefit from both increased suspended nutrients and from recruitment of buried phytoplankton cells released from the sediments by the fish bioturbation.
Macrophyte growth has also been shown to be inhibited by displacement from the bottom sediments due to fish burrowing.
Rivers and streams
River and stream ecosystems show similar responses to bioturbation activities, with chironomid larvae and tubificid worm macroinvertebrates remaining as important benthic agents of bioturbation. These environments can also be subject to strong season bioturbation effects from anadromous fish.
Salmon function as bioturbators on both gravel to sand-sized sediment and a nutrient scale, by moving and re-working sediments in the construction of redds (gravel depressions or "nests" containing eggs buried under a thin layer of sediment) in rivers and streams
and by mobilization of nutrients.
The construction of salmon redds functions to increase the ease of fluid movement (
hydraulic conductivity
Hydraulic conductivity, symbolically represented as (unit: m/s), is a property of porous materials, soils and rocks, that describes the ease with which a fluid (usually water) can move through the pore space, or fractures network. It depends on th ...
) and porosity of the stream bed.
In select rivers, if salmon congregate in large enough concentrations in a given area of the river, the total sediment transport from redd construction can equal or exceed the sediment transport from flood events.
The net effect on sediment movement is the downstream transfer of gravel, sand and finer materials and enhancement of water mixing within the river substrate.
The construction of salmon redds increases sediment and nutrient fluxes through the
hyporheic zone
The hyporheic zone is the region of sediment and porous space beneath and alongside a stream bed, where there is mixing of shallow groundwater and surface water. The flow dynamics and behavior in this zone (termed hyporheic flow or underflow) is re ...
(area between surface water and groundwater) of rivers and effects the dispersion and retention of marine derived nutrients (MDN) within the river ecosystem.
MDN are delivered to river and stream ecosystems by the fecal matter of spawning salmon and the decaying carcasses of salmon that have completed spawning and died.
Numerical modeling suggests that residence time of MDN within a salmon spawning reach is inversely proportional to the amount of redd construction within the river.
Measurements of respiration within a salmon-bearing river in Alaska further suggest that salmon bioturbation of the river bed plays a significant role in mobilizing MDN and limiting primary productivity while salmon spawning is active.
The river ecosystem was found to switch from a net
autotroph
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...
ic to
heterotroph
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
ic system in response to decreased primary production and increased respiration.
The decreased primary production in this study was attributed to the loss of benthic primary producers who were dislodged due to bioturbation, while increased respiration was thought to be due to increased respiration of organic carbon, also attributed to sediment mobilization from salmon redd construction.
While marine derived nutrients are generally thought to increase productivity in riparian and freshwater ecosystems, several studies have suggested that temporal effects of bioturbation should be considered when characterizing salmon influences on nutrient cycles.
Marine environments
Major marine bioturbators range from small
infaunal
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...
invertebrates to fish and marine mammals.
In most marine sediments, however, they are dominated by small invertebrates, including polychaetes, bivalves, burrowing shrimp, and amphipods.
= Shallow and Coastal
=
![Benthic bioturbation and bioirrigation](https://upload.wikimedia.org/wikipedia/commons/c/c3/Benthic_bioturbation_and_bioirrigation.jpg)
Coastal ecosystems, such as estuaries, are generally highly productive, which results in the accumulation of large quantities of
detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
(organic waste). These large quantities, in addition to typically small sediment grain size and dense populations, make bioturbators important in estuarine respiration.
Bioturbators enhance the transport of oxygen into sediments through irrigation and increase the surface area of oxygenated sediments through burrow construction.
Bioturbators also transport organic matter deeper into sediments through general reworking activities and production of fecal matter.
This ability to replenish oxygen and other solutes at sediment depth allows for enhanced respiration by both bioturbators as well as the microbial community, thus altering estuarine elemental cycling.
![Marine Nitrogen Cycle](https://upload.wikimedia.org/wikipedia/commons/4/4f/Marine_Nitrogen_Cycle.jpg)
The effects of bioturbation on the nitrogen cycle are well-documented.
Coupled denitrification and nitrification are enhanced due to increased oxygen and nitrate delivery to deep sediments and increased surface area across which oxygen and nitrate can be exchanged.
The enhanced nitrification-denitrification coupling contributes to greater removal of biologically available nitrogen in shallow and coastal environments, which can be further enhanced by the excretion of ammonium by bioturbators and other organisms residing in bioturbator burrows.
While both nitrification and denitrification are enhanced by bioturbation, the effects of bioturbators on denitrification rates have been found to be greater than that on rates of nitrification, further promoting the removal of biologically available nitrogen. This increased removal of biologically available nitrogen has been suggested to be linked to increased rates of nitrogen fixation in microenvironments within burrows, as indicated by evidence of nitrogen fixation by sulfate-reducing bacteria via the presence of ''nif''H (nitrogenase) genes.
Bioturbation by walrus feeding is a significant source of sediment and biological community structure and nutrient flux in the Bering Sea.
Walruses feed by digging their muzzles into the sediment and extracting clams through powerful suction.
By digging through the sediment, walruses rapidly release large amounts of organic material and nutrients, especially ammonium, from the sediment to the water column.
Additionally, walrus feeding behavior mixes and oxygenates the sediment and creates pits in the sediment which serve as new habitat structures for invertebrate larvae.
= Deep-sea
=
Bioturbation is important in the deep sea because deep-sea ecosystem functioning depends on the use and recycling of nutrients and organic inputs from the
photic zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
.
In low energy regions (areas with relatively still water), bioturbation is the only force creating
heterogeneity
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
in solute concentration and mineral distribution in the sediment.
It has been suggested that higher benthic diversity in the deep sea could lead to more bioturbation which, in turn, would increase the transport of organic matter and nutrients to benthic sediments.
Through the consumption of surface-derived organic matter, animals living on the sediment surface facilitate the incorporation of particulate organic carbon (POC) into the sediment where it is consumed by sediment dwelling animals and bacteria.
Incorporation of POC into the food webs of sediment dwelling animals promotes carbon sequestration by removing carbon from the water column and burying it in the sediment.
In some deep-sea sediments, intense bioturbation enhances manganese and nitrogen cycling.
Role in Organic Contaminant Flux
Bioturbation can either enhance or reduce the
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
of contaminants from the sediment to the water column, depending on the mechanism of sediment transport.
In polluted sediments, bioturbating animals can mix the surface layer and cause the release of sequestered contaminants into the water column.
Upward-conveyor species, like polychaete worms, are efficient at moving contaminated particles to the surface.
Invasive animals can remobilize contaminants previously considered to be buried at a safe depth. In the
Baltic Sea
The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain.
The sea stretches from 53°N to 66°N latitude and from ...
, the invasive ''Marenzelleria'' species of
polychaete worms
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...
can burrow to 35-50 centimeters which is deeper than native animals, thereby releasing previously sequestered contaminants.
However, bioturbating animals that live in the sediment (
infauna
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...
) can also reduce the flux of contaminants to the water column by burying
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
organic contaminants into the sediment.
Burial of uncontaminated particles by bioturbating organisms provides more absorptive surfaces to sequester chemical pollutants in the sediments.
Terrestrial
![Camas pocket gopher mounds](https://upload.wikimedia.org/wikipedia/commons/f/ff/Camas_pocket_gopher_mounds.JPG)
Plants and animals utilize soil for food and shelter, disturbing the upper soil layers and transporting chemically weathered rock called
saprolite
Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widespread o ...
from the lower soil depths to the surface.
Terrestrial bioturbation is important in soil production, burial, organic matter content, and downslope transport. Tree roots are sources of
soil organic matter Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous b ...
, with root growth and stump decay also contributing to soil transport and mixing.
Death and decay of tree roots first delivers organic matter to the soil and then creates voids, decreasing soil density. Tree uprooting causes considerable soil displacement by producing mounds, mixing the soil, or inverting
vertical sections of soil.
Burrowing animals, such as earth worms and small mammals form passageways for air and water transport which changes the soil properties, such as the vertical particle-size distribution, soil
porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
, and nutrient content.
Invertebrates that burrow and consume plant detritus help produce an organic-rich
topsoil
Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.
Description
Topsoil is composed of mineral particles and organic matt ...
known as the
soil biomantle The soil biomantle can be described and defined in several ways. Most simply, the soil biomantle is the organic-rich bioturbated upper part of the soil, including the topsoil where most biota live, reproduce, die, and become assimilated. The biomant ...
, and thus contribute to the formation of
soil horizons. Small mammals such as
pocket gophers
Pocket gophers, commonly referred to simply as gophers, are burrowing rodents of the family Geomyidae. The roughly 41 speciesSearch results for "Geomyidae" on thASM Mammal Diversity Database are all endemic to North and Central America. They are ...
also play an important role in the production of soil, possibly with an equal magnitude to abiotic processes.
Pocket gophers form above-ground mounds, which moves soil from the lower soil horizons to the surface, exposing minimally weathered rock to surface erosion processes, speeding soil formation.
Pocket gophers are thought to play an important role in the downslope transport of soil, as the soil that forms their mounds is more susceptible to erosion and subsequent transport. Similar to tree root effects, the construction of burrows-even when backfilled- decreases soil density.
The formation of surface mounds also buries surface vegetation, creating nutrient hotspots when the vegetation decomposes, increasing soil organic matter. Due to the high metabolic demands of their burrow-excavating subterranean lifestyle, pocket gophers must consume large amounts of plant material.
Though this has a detrimental effect on individual plants, the net effect of pocket gophers is increased plant growth from their positive effects on soil nutrient content and physical soil properties.
In the fossil record
In the sediment record
Patterns or traces of bioturbation are preserved in
lithified
Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...
rock. The study of such patterns is called
ichnology, or the study of "trace fossils", which, in the case of bioturbators, are fossils left behind by digging or burrowing animals. This can be compared to the footprint left behind by these animals. In some cases bioturbation is so pervasive that it completely obliterates
sedimentary structures
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.
Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different partic ...
, such as laminated layers or
cross-bedding
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...
. Thus, it affects the disciplines of
sedimentology
Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of mo ...
and
stratigraphy
Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks.
Stratigrap ...
within geology. The study of bioturbator ichnofabrics uses the depth of the fossils, the cross-cutting of fossils, and the sharpness (or how well defined) of the fossil
to assess the activity that occurred in old sediments. Typically the deeper the fossil, the better preserved and well defined the specimen.
Important
trace fossil
A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s from bioturbation have been found in marine sediments from tidal, coastal and deep sea sediments. In addition sand dune, or
Eolian, sediments are important for preserving a wide variety of fossils.
Evidence of bioturbation has been found in deep-sea sediment cores including into long records, although the act extracting the core can disturb the signs of bioturbation, especially at shallower depths.
Arthropods, in particular are important to the geologic record of bioturbation of Eolian sediments. Dune records show traces of burrowing animals as far back as the lower Mesozoic (250 Million years ago),
although bioturbation in other sediments has been seen as far back as 550 Ma.
Mathematical Models
The role of bioturbators in sediment biogeochemistry makes bioturbation a common parameter in sediment biogeochemical models, which are often
numerical models built using
ordinary
Ordinary or The Ordinary often refer to:
Music
* ''Ordinary'' (EP) (2015), by South Korean group Beast
* ''Ordinary'' (Every Little Thing album) (2011)
* "Ordinary" (Two Door Cinema Club song) (2016)
* "Ordinary" (Wayne Brady song) (2008)
* ...
and
partial differential equation
In mathematics, a partial differential equation (PDE) is an equation which imposes relations between the various partial derivatives of a Multivariable calculus, multivariable function.
The function is often thought of as an "unknown" to be sol ...
s.
Bioturbation is typically represented as D
B, or the biodiffusion coefficient, and is described by a
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
and, sometimes, an
advective term.
This representation and subsequent variations account for the different modes of mixing by functional groups and bioirrigation that results from them. The biodiffusion coefficient is usually measured using
radioactive tracer
A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by ...
s such as Pb
210,
radioisotopes
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
from nuclear fallout, introduced particles including glass beads tagged with radioisotopes or inert fluorescent particles, and chlorophyll a. Biodiffusion models are then fit to vertical distributions (profiles) of tracers in sediments to provide values for D
B.
Parameterization of bioturbation, however, can vary, as newer and more complex models can be used to fit tracer profiles. Unlike the standard biodiffusion model, these more complex models, such as expanded versions of the biodiffusion model, random walk, and particle-tracking models, can provide more accuracy, incorporate different modes of sediment transport, and account for more spatial heterogeneity.
See also
*
Argillipedoturbation Argillipedoturbation, sometimes referred to as self-mulching, is a process of soil mixing caused by the shrinking and swelling of the smectite clays contained in the soil. It is an effect specific to soils of the vertisolic variety, and is triggered ...
*
Bioirrigation
Bioirrigation refers to the process of benthos, benthic organisms flushing their burrows with overlying water. The exchange of dissolved substances between the porewater and overlying seawater that results is an important process in the context o ...
*
Zoophycos
''Zoophycos'' is a somewhat cosmopolitan ichnogenus thought to be produced by moving and feeding polychaete worms.
Appearance
''Zoophycos'' occurs in two forms, one planar, and one which resembles a corkscrew. In the latter helicoidal form, ...
References
{{reflist, 28em
External links
Nereis Park (the World of Bioturbation)Worm Cam
Biological oceanography
Aquatic ecology
Limnology
Pedology
Physical oceanography
Sedimentology