Aquatic food web is formed by the interrelations between organisms like algae, macrophytes, crustaceans, fish, reptiles, amphibians and aquatic mammals that function simultaneously in multiple food chains or linear energy sequences.
This article discusses the aquatic food web, using a series of aquatic food chains and their components, as follows;
1). Aquatic Food Chain 1 (as a component of the Aquatic Food Web)
Trophic Level 1: Seaweed, phytoplankton, mangrove plants
Trophic Level 2: Copepods (zooplankton), rabbitfish, bivalves, aquatic worms
Trophic Level 3: Marine iguana, large crustaceans, seal, barracuda
Trophic Level 4: Great white shark, orca
*Producers in the Aquatic Food Web (from Chain 1)
Seaweed, phytoplankton, and mangrove plants are the primary producers in this food chain.
Seaweed and phytoplankton are photosynthetic organisms that have physiological adaptations enabling them to capture and convert solar radiation (in form of visible light) into biomass and chemical energy .
Mangrove plants refer to shrubs and trees that are salt-tolerant, and have evolved in saline aquatic environments (that is; brackish and marine zones). Like phytoplankton and seaweeds, mangrove plants are able to produce energy photosynthetically.
These autotrophs play an important role in the introduction of bioenergy into aquatic ecosystems; which is a necessary step that precedes the energy-transfer dynamics known as food chains and food webs.
As primary producers, the autotrophs occupy the base of the food chain, from which they provide nutrients and energy directly or indirectly to all heterotrophic organisms in higher trophic levels.
Autotrophs play a major role in establishing complex trophic links that network to form the aquatic food web; because they serve as food sources to various organisms from different food chains in the ecosystem; which are ecologically related through their dependence on the autotrophs.
*Primary Consumers in the Aquatic Food Web (from Chain 1)
Primary consumers in aquatic food chain one (1) are; copepods (zooplankton), rabbitfish, bivalves (such as clams or mussels), and aquatic worms.
Copepods are an example of zooplankton; and may be described as small crustaceans whose food comprises mainly of phytoplankton .
Rabbitfish is a classic example of a herbivorous primary consumer in the aquatic ecosystem. It grazes on plant materials like macroalgae and seaweed .
Bivalves can be described as filter-feeders, whose dietary strategy involves the extraction of nutrients from water using a filtering structure that captures organic particles and phytoplankton.
Aquatic worms are detrivores; and may be classified as primary consumers when their detrital substrate has a high percentage of plant debris. Their activities are essential to facilitate biodegradation and the recycling of nutrients in water bodies.
*Secondary Consumers in the Aquatic Food Web (from Chain 1)
Marine iguana, large crustaceans, seals, and barracuda represent secondary consumers in this food chain.
The marine iguana may be described as a herbivorous reptile, whose main food sources include microalgae and seaweed . However, it is omnivorous and also consumes crustaceans (like copepods) and aquatic insects.
Large crustaceans including some species of crabs and lobsters; consume zooplankton including bivalves and copepods.
Seals are aquatic mammals with carnivorous feeding habits, that consume various invertebrates and fish within their environment.
Barracuda is a predatory (carnivorous) fish whose food sources include crustaceans and smaller fish.
For secondary consumers, energy is obtained mainly from herbivorous primary consumers.
In terms of range of food choices, omnivorous secondary consumers like the marine iguana, are at an advantage, because they can exploit both autotrophic and heterotrophic organisms as part of their diet.
*Tertiary Consumers in the Aquatic Food Web (from Chain 1)
Tertiary consumers at the top of food chain 1 are the great white shark and orca, which may also be referred to here as apex predators.
Great white shark is a large, distinctive and carnivorous fish that can consume other large fish, small fish, and seals among other aquatic animals.
To fulfill their predatory role, these animals have sharp teeth and powerful jaws, used to capture as well as consume prey.
The orca or killer whale, is a social marine mammal that is highly adaptive and intelligent . Its diet consists of sea lions, seals, fish and dolphins, among others.
As an apex predator, the orca is important for regulation of prey population-sizes in lower levels of the food chain.
*Trophic Relationships in Aquatic Food Chain 1, as Building Blocks of the Aquatic Food Web
Food chain 1 vividly illustrates how nutrients and energy are transferred across the various trophic levels of the aquatic ecosystem, and from one class of organisms to another.
1. Primary producers (seaweed, phytoplankton, and mangrove plants) introduce food resources into the system by capturing electromagnetic waves from the Sun and converting this energy to biomass (which contains chemical energy for living organisms)
2. Primary consumers (copepods, rabbitfish, bivalves, and aquatic worms) obtain their energy by feeding on the primary producers
3. Secondary consumers (marine iguana, large crustaceans, seals, and barracuda) consume mostly primary consumers to obtain energy
4. Tertiary consumers/apex predators (great white shark and orca) prey on primary and secondary consumers
*Importance of Organic/Trophic Groups in Chain 1
Each trophic level and organism in the food chain, is important to the dynamics of energy in the ecosystem.
Primary producers are crucial as the foundation of the food chain, through their photosynthetic function.
Primary consumers are vital for regulating primary producer population-sizes, and facilitating energy-transfer to higher levels of the food chain.
Secondary consumers play a key role in controlling primary consumer population, adaptation and spatial distribution.
Apex predators contribute to ecologic sustainability by influencing distribution, species richness, and abundance of other consumers.
*Adaptations of Organisms in Food Chain 1
There are various adaptive characteristics possessed by organisms in food chain 1; which vary according to their trophic positions and roles.
Adaptations of primary producers include photosynthetic pigments and tissues for efficient underwater-gas exchange; as well as specialized structures for obtaining nutrients from water.
Herbivores like marine iguana and rabbitfish have specialized digestive tracts, and dentition for consuming and digesting plant matter.
Large carnivores like orcas and great white shark have keen sensory capabilities, social-behavioral adaptations, streamlined morphology, and powerful jaws that help them in hunting, capture, and consumption of prey.
In playing their respective ecological roles, organisms in this food chain (1) form trophic relational links with each other and other aquatic organisms that are actively contributing to other feeding sequences/chains. These links as the components that establish aquatic food webs.
2). Aquatic Food Chain 2 (as a component of the Aquatic Food Web)
Trophic Level 1: Macroalgae, phytoplankton, macrophytes
Trophic Level 2: Mbuna, pleco, shrimp, aquatic worms
Trophic Level 3: Heron, catfish, large crab
Trophic Level 4: Aquatic monitor, crocodile
*Primary Producers in the Aquatic Food Web (from Chain 2)
The primary producers in this food chain are; macroalgae, phytoplankton, and macrophytes (aquatic plants).
Macroalgae can be described as algae with multicellular composition and macroscopic dimensions, that occur in freshwater and marine terrains.
These organisms are autotrophic and can convert sunlight to biomass and chemical energy.
Macrophytes are plants like cattails, coontails and lilies, among others that grow either partly or entirely submerged in water .
Primary producers constitute the foundation of food chain 2, and are responsible for providing both nutrients and energy to organisms in other levels.
*Primary Consumers in the Aquatic Food Web (from Chain 2)
Mbuna (a herbivorous cichlid fish), plecos (a catfish with suction-cup-shaped mouth), shrimp, and aquatic worms are the primary consumers in food chain 2.
Mbuna primarily consumes macroalgae, and may also graze on biofilms that grow on rocks within their environment.
Similarly, plecos feed by scraping algae of rock surfaces in water, using their specialized mouth-parts.
Food for the shrimp consists of organic matter in the water column, and detritus on the sedimentary bed.
Aquatic worms facilitate biodegradation by feeding on organic litter, which is usually dominated by plant material.
For all organisms in trophic level 2, producers serve as a direct source of food. Some of these organisms are solely herbivorous, while others are omnivorous or detrivorous.
*Secondary Consumers in the Aquatic Food Web (from Chain 2)
The secondary consumers in food chain 2 are; heron, catfish, and large crabs.
Heron can be described as a semi-aquatic bird that wades through shallow areas in water bodies, and feeds on aquatic organisms like amphibians, crustaceans, and fish.
Catfish is an opportunistic feeder that is known to consume a broad variety of food sources including shrimp, smaller fish, aquatic worms, and other invertebrates.
Large crabs are usually omnivorous, and may scavenge through detritus to consume animal and plant matter. They may also prey on smaller aquatic organisms.
*Tertiary Consumers in the Aquatic Food Web (from Chain 2)
Tertiary consumers occupy the top of food chain 2, and include aquatic monitor and crocodile, both of which serve here as apex predators.
Aquatic monitor is a reptile semi-aquatic behavior, which is known to prey on smaller reptiles, fish, small mammals, and amphibians within their surroundings.
Adaptations of this reptile for its role include sharp claws and teeth, as well as swimming capability .
Crocodiles are also semi-aquatic reptiles, which are much larger than aquatic monitor and consume mainly fish, which they supplement with mammals and birds.
They are known for possessing strong muscles and powerful jaws, and are skilled hunters.
*Trophic Relationships in Food Chain 2
1. The primary producers (macroalgae, phytoplankton, and macrophytes) produce food from solar energy and inorganic materials, through photosynthesis
2. primary consumers (mbuna, plecos, shrimp, and aquatic worms) feed on primary consumers for survival
3. Secondary consumers (heron, catfish, and large crabs) acquire energy from primary consumers which they consume
4. Tertiary consumers (aquatic monitor lizard and crocodile) prey on primary and secondary consumers, thereby contributing to the flow of energy
Phytoplankton appears as a producer in both food chains 1 and 2.
In both chains, they produce biomass that is consumed by other organisms (directly or indirectly) as a food and nutrient source.
Aquatic worms are primary consumers in both chains 1 and 2; where they consume plant remains and contribute to decomposition as well as nutrient-cycling.
Crustaceans occur in both food chains (1, 2). In chain 1, they are addressed largely as 'crustaceans', while chain 2 specifies them as shrimp (a primary consumer) and large crabs (as secondary consumers).
These recurrences and multi-trophic level appearances in food chains are the foundation and essence of the aquatic food web; which is built from such complex ecologic loops and trophic relations.
*Importance of Organisms in Food Chain 2
An important role is played by each organism mentioned in this food chain.
Primary consumers supply food and energy from sunlight, in a form that is usable for the sustenance of life in the aquatic biome. They also influence carbon sequestration, oxygen production, and regional climatic conditions.
The primary consumers help regulate the growth of primary consumers, preventing excessive growth that could deplete oxygen and nutrients in water bodies. At the same time, they help relay energy from primary producers to non-heterotrophic consumers in higher trophic levels.
Secondary consumers help regulate primary consumer populations, thereby contributing to nutrient cycling.
The overall equilibrium of food resources is established by apex predators, which feed on all consumers (and in some cases, on producers as well) beneath them in the food chain.
Organic adaptations in this food chain, vary from one individual to another.
Herbivorous fish like plecos and mbuna are equipped with specialized structures like distinctive oral morphology and dentition, that enable them maintain their plant-based diet.
In shrimps, filter-feeding adaptations occur, such as appendages for capturing particulate organic matter.
Adaptations of aquatic worms include specialized mouth-parts that aid detrivorous feeding.
Herons have elongate necks and equally-long beaks for extracting prey from water or mud, while crocodiles have powerful jaws for prey capture and consumption.
Large crabs and catfish have both physiological features and adaptive behaviors that enable them exploit a broad range of food sources.
3). Aquatic Food Chain 3 (as a component of the Aquatic Food Web)
Trophic Level 1: Mangrove plants, seaweed, macrophytes
Trophic Level 2: Krill, shrimp, copepods, sponges
Trophic Level 3: Large crab, bass, pike, barracuda
Trophic Level 4: Dolphin, kingfisher, seal
Trophic Level 5: Polar bear, orca
*Primary Producers in the Aquatic Food Web (from Chain 3)
Mangrove plants, seaweed, and macrophytes (aquatic plants) play the role of primary producers in this food chain.
The mangrove plants include trees that are specially adapted to grow in saline estuaries and coastal areas.
These plants help create micro-habitats, and provide food for several organisms in their environment.
Seaweed may be described as a type of marine algae. It functions alongside macrophtic plants like seagrass, to contribute to aquatic primary production, through photosynthesis.
*Primary Consumers in the Aquatic Food Web (from Chain 3)
Krill, shrimp, copepods, and sponges are the primary consumers occupying trophic level 2 of food chain 3.
Krill are crustaceans with a small form, and significant resemblance to shrimps, which feed on detritus and phytoplankton.
Shrimp are scavengers with omnivorous feeding habits, that also feed on detritus and plant matter .
Copepods are yet another group of small crustaceans that consume phytoplankton and detrital organic materials.
Sponges are filter-feeders, and survive by extracting organic materials (including autotrophic matter) from the water column.
*Secondary Consumers in the Aquatic Food Web (from Chain 3)
Large crabs, bass, pike, and barracuda represent secondary consumers in food chain 3, which is part of the aquatic food web being discussed in this article.
Large crabs are scavenging crustaceans that have an opportunistic approach to feeding, and can prey on smaller crustaceans like copepods and krill, as well as fish and other invertebrates.
Bass, pike, and barracuda, alongside others like Spanish mackerel, are carnivorous fish that prey on smaller fish as well as invertebrates . Through their feeding, secondary consumers play a vital role in the regulation of population sizes, of organic groups in lower trophic levels.
*Tertiary Consumers in the Aquatic Food Web (from Chain 3)
The fourth trophic level is occupied by; dolphins, kingfishers, and seals, which serve as tertiary consumers.
Dolphins are highly adaptable and intelligent mammals that occur in marine water bodies, and consume crustaceans, fish and squids among other organisms .
The kingfisher can be considered an aquatic raptor, whose location around water bodies has caused it to develop specialized physiological features and behaviors that enable it catch fish efficiently.
Seals are predatory aquatic mammals that occur in oceans and on coasts; where they consume squid, birds and fish, among others.
*Quaternary Consumers in the Aquatic Food Web (from Chain 3)
Tropic level five is the highest and final level in this food chain, and is occupied by the polar bear and orca, both of which are apex predators within their respective territories.
Polar bear is an apex predator in the Arctic region, where it feeds mainly on seals .
Orca or killer whale consumes marine mammals like sea lions and seals, crustaceans and fish, among others, for its survival. Its sheer size compared to other marine consumers places it as one of the biome's most powerful predators.
*Trophic Relationships in Food Chain 3 of the Aquatic Food Web
Food chain 3 is illustrative of the pattern of flow, of nutrients and energy across the aquatic environment, from producers at the basal level, to apex predators at the top of the energy pyramid.
Primary producers (mangrove plants, seaweed, macrophytes) contribute to the energy dynamic by producing biomass from solar energy, water, nutrients and carbon dioxide.
The primary consumers (krill, shrimp, copepods, sponges) feed on primary producers to obtain energy and nutrients.
Secondary consumers (large crabs, bass, pike, barracuda) survive by preying on primary consumers.
The tertiary consumers (dolphins, kingfishers, seals) feed on primary and secondary consumers, while apex predators (polar bear, orca) feed on all consumers beneath them in the trophic hierarchy.
*Recurring Organisms from other Food Chains
Some organisms in chain 3 are also occurring in preceding food chains.
Macrophytes and seaweed occur in chains 2 and 1 respectively as producers, alongside mangrove plants which are also found in chain 1.
These presence of these autotrophs in other food chains within the aquatic ecosystem, indicates that these different food chains are linked through the simultaneous contribution of shared producers. Such links are building blocks for the food web.
It must be noticed, also, that food chain 2 exclusively represents a freshwater aquatic ecosystem, based on its organic assemblage.
In spite of this, it shares some organisms with chain 3 (which is a marine/brackish chain) such as large crabs (as secondary consumers in level 3) and shrimp (as primary consumers in level 2).
These trophic relationships show how complex the aquatic ecosystem is, with some freshwater bodies occurring as distant tributaries, and extracts from saltwater bodies, and sharing many species that migrate from saline to freshwater zones.
Another recurring organic group in chain 3 is the copepods; which reappear in chain 1 also as primary consumers.
*Importance and Adaptations of Organisms in Chain 3, of the Aquatic Food Web
Organisms in food chain, each have an important role to play toward the maintenance of ecological balance, and the transfer of energy across trophic levels.
Primary producers are essential for their photosynthetic function, in the capture and transformation of solar energy to organic bioenergy/matter.
Consumers in this food chain have developed various adaptations and feeding strategies that allow then play their roles and occupy their trophic positions effectively.
Seals, for example; have streamlined body morphology and specialized dentition for capturing prey (which consists mainly of fish). Dolphins are highly-sensitive and can track their prey using echolocation mechanisms .
4). Aquatic Food Chain 4 (as a component of the Aquatic Food Web)
Trophic Level 1: Phytoplankton, marsh vegetation, seaweed
Trophic Level 2: Copepods, crab, rabbitfish
Trophic Level 3: Dragonfly larva, pelican, pike, heron, barracuda
Trophic Level 4: Shark, large dolphin
Trophic Level 5: Orca, blue whale
*Producers in the Aquatic Food Web (from Chain 4)
Phytoplankton, marsh vegetation, and seaweed are the primary producers in this food chain.
Phytoplankton are photosynthetic and microscopic organisms that occur in the upper segment of the water column as floaters, and serve as the nutritional foundation of the ecosystem through photosynthesis.
Marsh vegetation comprises of reeds, cattails and other plants that thrive in wetlands.
Seaweed refers to macroscopic algae that grows in coastal areas.
*Primary Consumers in the Aquatic Food Web (from Chain 4)
Copepods, crabs, and rabbitfish represent the primary consumers in trophic level 2 of aquatic food chain 4.
Copepods are small crustaceans and tend to consume detritus, as well as phytoplankton.
Crabs are also crustaceans, with omnivorous feeding habits, which can be classified as primary consumers in several contexts, due to the large proportion of vegetative material in their diet.
Rabbitfish is a herbivorous fish that feeds on aquatic plants and algae.
*Secondary Consumers in the Aquatic Food Web (from Chain 4)
Dragonfly larvae, pelicans, pike, herons, and barracudas represent the secondary consumers in this food chain.
The dragonfly larva is an aquatic insect that is carnivorous and preys on other invertebrates in the water column , especially those smaller in size than itself, such as some copepods.
Pike is a predatory fish with sharp teeth and efficient hunting skills, both of which enable it prey on smaller fish.
Heron is a semi-aquatic bird that consumes invertebrates like crustaceans, as well as amphibians and fish.
Like pike, the barracuda is a predatory fish that is well-adapted to its habitat, where it consumes smaller fish and invertebrates.
*Secondary Consumers in the Aquatic Food Web (from Chain 4)
Sharks and large dolphins occupy the fourth trophic level where they function as tertiary consumers.
The shark is an apex predators whose food sources include fish like the pike and rabbitfish, as well as smaller sharks and seals.
Distinctively large dolphins compete effectively with sharks and killer whales at the top of the food chain; consuming a variety of prey that include squid, marine mammals and fish.
These tertiary consumers have developed sensory and communicative capabilities, as well as hunting strategies to help them thrive in their role.
*Quaternary Consumers in the Aquatic Food Web (from Chain 4)
The fifth trophic level is occupied by the orca and the blue whale, serving as apex predators.
Orca exploits a diverse diet due to its adaptive nature; and is known to prey on mammals like seal, smaller whales; fish like pike, as well as other large predators like shark and dolphins.
Blue whales are considered the largest known animals on Earth , and are one of the most imposing aquatic predators.
The blue whale is a filter feeder that uses its baleen plates to extract crustaceans like krill in large numbers, from the water column.
The performance of apex predators like blue whales can be monitored and analyzed as an indicator of the health-status, and productivity of their aquatic habitat.
*Trophic Relationships of Organisms in Food Chain 4
1. Primary producers (phytoplankton, marsh vegetation, seaweed) serve as a direct or indirect food source for other organisms
2. Secondary consumers (pelicans, pike, herons, barracudas) feed directly on the primary consumers
3. Tertiary consumers (sharks, large dolphins) prey on the secondary consumers such as barracuda and pike
4. Apex predators (orca, blue whale) occupy the highest trophic level and exert top-down influence over the entire food chain by preying on consumers beneath them
*Recurring Organisms that Link Out to Form the Aquatic Food Web
1. Phytoplankton can be found in chains 1 and 2, just as they occur in food chain 4 as producers
2. Seaweed occurs in chains 1 and 3
3. Copepods are shared (by chain 4) with chains 1 and 3
4. Shark also occurs in chain 1
5. Dolphin is found also in chain 3
6. Orca is a tertiary consumer in chain 1 (where level 4 is the apex level), and a quaternary consumer in level 5 of chain 4
5). Aquatic Food Chain 5 (as a component of the Aquatic Food Web)
Trophic Level 1: Macrophytes, seaweed, phytoplankton
Trophic Level 2: Aquatic worms, krill, sponges, bivalves
Trophic Level 3: Barracuda; marine iguana, sea lion
Trophic Level 4: Orca, polar bear
*Producers in the Aquatic Food Web (from Chain 5)
Macrophytes, seaweed, and phytoplankton represent the primary producers in this food chain.
They are responsible for the photosynthetic production of energy and biomass, which are the most essential resources for the ecosystem.
The primary consumers of food chain 5 are; aquatic worms, krill, sponges, and bivalves; which occupy the second trophic level.
They range from solely herbivorous to omnivorous and detrivorous feeding habits; and include grazers like krill, and filter-feeders like sponges and bivalves (including clams and mussels).
*Secondary and Tertiary Consumers
Barracudas, marine iguanas, and sea lions represent the secondary consumers in this food chain.
They range from mammals and reptiles to fish in terms of biological classification, and may be solely carnivorous (like barracuda) or omnivorous (like marine iguana) that feed on both algae and invertebrates.
The fourth trophic level is occupied by apex predators, namely orcas and polar bears.
These are both mammals, and range from fully aquatic (orca) to terrestrial/semi-aquatic (polar bear). Food for apex predators here, includes seals and fish like the barracuda.
1. The autotrophic primary producers (macrophytes, seaweed, phytoplankton) convert carbon dioxide, water and sunlight into organic matter that can be consumed as food by heterotrophs
2. Primary consumers (aquatic worms, krill, sponges, bivalves) feed on primary producers to obtain nutrients and energy
3. The secondary consumers (barracudas, marine iguanas, sea lions) feed mostly on the primary consumers
4. Apex predators (orcas, polar bears) depend on lower consumers for nutrition
*Recurring Organisms that Build Out to Form the Aquatic Food Web
1. Seaweed is also found in chains 1, 3, and 4 as a producer
2. Macrophytes occur in chains 2 and 3
3. Phytoplankton occur in chains 1, 2, and 4
4. Aquatic worms occur in chains 1 and 2
5. Krill occurs in chain 3
6. Sponges may be found also in chain 3
7. Bivalves occur in chain 1
8. Barracuda is a secondary consumer also in chains 1, 3 and 4
9. Marine iguana occurs in chain 1
10. Seal; a close relative of the sea lion from the Otariidae taxonomic family , is found in chains 1 and 3
11. Orca and polar bear are also the apex predators in chain 3. Orca can be found in chains 1 and 4
The trophic links highlighted above, like those shown in other food chains that are discussed in this article; form complex interconnections in the aquatic ecosystem, that ultimately result in food webs.
The aquatic food web is a complex network of interconnections that result from trophic relationships between organisms in various trophic levels, functioning simultaneously in multiple food chains.
Examples of food chains whose components link out-ward to form aquatic food webs, are;
*Food Chain 1: Seaweed, phytoplankton, mangrove plants (Trophic Level 1)→copepods (zooplanlton), rabbitfish, bivalves, aquatic worms (Trophic Level 2)→marine iguana, large crustaceans, seal, barracuda (Trophic Level 3)→great white shark, orca (Trophic Level 4)
*Food Chain 2: Macroalgae, phytoplankton, macrophytes (Trophic Level 1)→mbuna, pleco, shrimp, aquatic worms (Trophic Level 2)→heron, catfish, large crab (Trophic Level 3)→aquatic monitor, crocodile (Trophic Level 4)
*Food Chain 3: Mangrove plants, seaweed, macrophytes (Trophic Level 1)→krill, shrimp, copepods, sponges (Trophic Level 2)→large crab, bass, pike, barracuda (Trophic Level 3)→ dolphin, kingfisher, seal (Trophic Level 4)→polar bear, orca (Trophic Level 5)
*Food Chain 4: Phytoplankton, marsh vegetation, seaweed (Trophic Level 1)→copepods, crab, rabbitfish (Trophic Level 2)→dragonfly larva, pelican, pike, heron, barracuda (Trophic Level 3)→shark, large dolphin (Trophic Level 4)→orca, blue whale (Trophic Level 5)
*Food Chain 5:
Macrophytes, seaweed, phytoplankton (Trophic Level 1)→aquatic worms, krill, sponges, bivalves (Trophic Level 2)→barracuda; marine iguana, sea lion (Trophic Level 3)→orca, polar bear (Trophic Level 4)
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