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| Benthos Benthic zone Benthopelagic (coupling) Seabed |
Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs. [1]
The benthic and pelagic zones are interconnected through nutrient (nitrogen, phosphorus, and silicate) exchange from the sediment that help fuel phytoplankton primary production in the water column, which in turn, provide organic substrate for regeneration in sediments by microbes and macrofauna. [2] These exchanges have seasonal variability as temperature and light conditions that drive primary production and sedimentation patterns change. Accumulation of nutrients during winter months generally results in a strong peak in phytoplankton production in spring followed by a peak in sedimentation. In the summer, pelagic recycling of primary production is more efficient and sedimentation generally lower. [3]
The depth of an aquatic ecosystem is a key factor for benthic-pelagic exchanges because it determines the proximity and degree of interactions between the two environments. Coupling is stronger in shallow waters, such as in lakes and in coastal areas because primary productivity is generally higher in these areas where a higher amount of fresh organic matter from either photosynthesis or fecal matter can reach the bottom to fuel benthic fauna, which in turn remineralize and respire organic matter that supplies essential nutrients for primary production at the surface. Stratification of the water column, whether by temperature or salinity, also regulates the degree of exchange between benthic and pelagic habitats. [4]
Oxygen concentrations and biological interactions, such as predation and competition, will also influence benthic community structure and biomass. For example, benthic macrofauna, such as polychaetes and bivalves, are important food sources for demersal fish, including commercially important species such as flatfish and cod. [3]
Diel vertical migrations (DVM) of fishes, zooplankton, and larger invertebrates, such as cephalopods and jellyfish, from the surface to the bottom can transfer nutrients and detritus from the pelagic zone to the benthos. [5] Zooplankton, for example, vertically transport items such as organic carbon, nutrients, parasites, and food resources throughout the water column. [6] Particulates (fecal pellets) and dissolved organic carbon produced by these organisms in the water column constitute marine snow, which supports microbial production at the benthos in what is known as the 'biological pump.' [7]
These daily migrations are along a vertical gradient were movements are typically downward by day and an upward at night in response to several factors, such as predator avoidance, [8] food availability, [9] and light intensity. [4]
Movement driven by life-history stages and feeding patterns also plays a role in benthic-pelagic coupling. Many aquatic organisms inhabit have both pelagic and benthic life stages, such as benthic macrofauna that have pelagic larval stages before settling on the sediment. [10] Organisms who occupy both benthic and pelagic habitats as part of their life history help maintain adult populations and community structure, and serve as inputs essential for ecological interactions such as predation, competition, and parasitism. [4]
Sediment-dwelling organisms are also involved in benthic-pelagic coupling by disturbing the sediment to feed on organic matter trapped between sediment grains or to hide from predators. This is known as bioturbation, which stimulates mineralization of organic matter and the release of nutrients (Hansen et al. 1998; Lohrer et al. 2004; D’Andrea and DeWitt 2009), thereby affecting the growth of phytoplankton in the pelagic zone (Welsh 2003). Bioturbation by macrofauna affects sediment permeability and water content, destabilizes chemical gradients, subducts organic matter, and influences rates of remineralization and inorganic nutrient flux. [11]
Collectively, these outcomes are essential to habitat productivity and overall ecosystem function. [4]
How organisms interact will also determine the degree of benthic-pelagic coupling. These interactions will differ based largely on the species involved. In both freshwater and marine ecosystems, there are benthic organisms that are preyed upon by both demersal and pelagic fish during various life stages. Benthic organisms can also prey upon pelagic species. Benthic suspension feeders, such as bivalves, can exert considerable grazing pressure on phytoplankton and microzooplankton. [12] Thus, benthic and pelagic fauna can act as habitat couplers by consuming resources originating from either the water column or the sediment. [4]
On rocky intertidal shores, the effects of nearshore currents on phytoplankton and sea star propagules influence the benthic community structure of mussels and predation pressure by sea stars. [13]
Detritivores inhabiting benthic areas derive energy from sinking pelagic detritus and are then consumed by either benthic or pelagic predators, impacting community structure. [4]
Benthic and pelagic domains are further linked by pelagic predators such as tuna and swordfish feeding also on demersal resources, while pelagic preys such as sardines and anchovies may feed demersal predators. [14]
The benthic biogeochemical processes are essentially driven by pelagic processes, fueled by the deposition of pelagic material (e.g., organic matter, calcium carbonate). In response, sediments transform the deposited material (such as through degradation and dissolution) back into nutrients available for uptake in the water column. [4] Part of those products becomes available for bacterial and phytoplankton production that ultimately may sink to the seafloor to fuel the benthic communities again. [15]
Anthropogenic pressures regulate benthic–pelagic coupling directly and indirectly through their effects on the physical (e.g., salinity, oxygen, temperature) and biological (e.g., species, communities, functional traits) components of ecosystems. In coastal and estuarine ecosystems, climate change, nutrient loading, and fishing have been shown to have direct effects on benthic–pelagic coupling with clear consequences for ecosystem function. For example, increased water temperatures in Narragansett Bay have caused shifts in the timing and a decrease in the magnitude of phytoplankton blooms. This has decreased the deposition of organic material to the benthos and ultimately reduced inorganic nutrient release from the sediment. [16] [4]
Projected changes in nutrients and salinity could have negative effects on the distribution and productivity of mussels and diminish their role in benthic–pelagic exchange. [17] Overall, eutrophication results in an increase in phytoplankton biomass and blooms, altered phytoplankton community structure, and a decrease in benthic primary production. [4]
Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish, and baleen whales.
Zooplankton are the animal component of the planktonic community, having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments. In other words, it is a biologically mediated process which results in the sequestering of carbon in the deep ocean away from the atmosphere and the land. The biological pump is the biological component of the "marine carbon pump" which contains both a physical and biological component. It is the part of the broader oceanic carbon cycle responsible for the cycling of organic matter formed mainly by phytoplankton during photosynthesis (soft-tissue pump), as well as the cycling of calcium carbonate (CaCO3) formed into shells by certain organisms such as plankton and mollusks (carbonate pump).
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. The name comes from ancient Greek, βένθος (bénthos), meaning "the depths." 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.
Bioturbation is defined as the reworking of soils and sediments 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. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients 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.
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems, which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two ecosystems are examples of freshwater ecosystems.
Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs:
Gelatinous zooplankton are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zooplankton, but not all gelatinous zooplankton are jellyfish. The most commonly encountered organisms include ctenophores, medusae, salps, and Chaetognatha in coastal waters. However, almost all marine phyla, including Annelida, Mollusca and Arthropoda, contain gelatinous species, but many of those odd species live in the open ocean and the deep sea and are less available to the casual ocean observer. Many gelatinous plankters utilize mucous structures in order to filter feed. Gelatinous zooplankton have also been called Gelata.
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below, which is referred to as the biological pump. Export production is the amount of organic matter produced in the ocean by primary production that is not recycled (remineralised) before it sinks into the aphotic zone. Because of the role of export production in the ocean's biological pump, it is typically measured in units of carbon. The term was coined by explorer William Beebe as observed from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms that live very deep in the water column.
Bacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word πλανκτος, meaning "wanderer" or "drifter", and bacterium, a Latin term coined in the 19th century by Christian Gottfried Ehrenberg. They are found in both seawater and freshwater.
The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere caused by the Coriolis Effect. They generally form in large open ocean areas that lie between land masses.
The benthic boundary layer (BBL) is the layer of water directly above the sediment at the bottom of a body of water. Through specific sedimentation processes, certain organisms are able to live in this deep layer of water. The BBL is generated by the friction of the water moving over the surface of the substrate, which decrease the water current significantly in this layer. The thickness of this zone is determined by many factors, including the Coriolis force. The benthic organisms and processes in this boundary layer echo the water column above them.
A marine habitat is a habitat that supports 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. The marine environment supports many kinds of these habitats.
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and in the past billion years; basking sharks and copepods are just two examples of giant and microscopic organisms that feed upon plankton. Planktivory can be an important mechanism of top-down control that contributes to trophic cascades in aquatic and marine systems. There is a tremendous diversity of feeding strategies and behaviors that planktivores utilize to capture prey. Some planktivores utilize tides and currents to migrate between estuaries and coastal waters; other aquatic planktivores reside in lakes or reservoirs where diverse assemblages of plankton are present, or migrate vertically in the water column searching for prey. Planktivore populations can impact the abundance and community composition of planktonic species through their predation pressure, and planktivore migrations facilitate nutrient transport between benthic and pelagic habitats.
Mycoplankton are saprotrophic members of the plankton communities of marine and freshwater ecosystems. They are composed of filamentous free-living fungi and yeasts that are associated with planktonic particles or phytoplankton. Similar to bacterioplankton, these aquatic fungi play a significant role in heterotrophicmineralization and nutrient cycling. Mycoplankton can be up to 20 mm in diameter and over 50 mm in length.
Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 millimeters (53 μm) to 2 millimeters.
Alan Reece Longhurst was a British-born Canadian oceanographer who invented the Longhurst-Hardy Plankton Recorder, and is widely known for his contributions to the primary scientific literature, together with his numerous monographs, most notably the "Ecological Geography of the Sea". He led an effort that produced the first estimate of global primary production in the oceans using satellite imagery, and also quantified vertical carbon flux through the planktonic ecosystem via the biological pump. In later life he offered several critical reviews of several aspects of fishery management science and climate change science.
The viral shunt is a mechanism that prevents marine microbial particulate organic matter (POM) from migrating up trophic levels by recycling them into dissolved organic matter (DOM), which can be readily taken up by microorganisms. The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.
Lake metabolism represents a lake's balance between carbon fixation and biological carbon oxidation. Whole-lake metabolism includes the carbon fixation and oxidation from all organism within the lake, from bacteria to fishes, and is typically estimated by measuring changes in dissolved oxygen or carbon dioxide throughout the day.
Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, many significant terrestrial primary producers, such as mature forests, grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.
