Marine food web

marine food chain (typical)
Sun
↓
phytoplankton
↓
herbivorous zooplankton
↓
carnivorous zooplankton
↓
filter feeder
↓
predatory vertebrate

Food webs are built from food chains. All forms of life in the sea have the potential to become food for another life form. In the ocean, a food chain typically starts with energy from the sun powering phytoplankton, and follows a course such as:

phytoplankton → herbivorous zooplankton → carnivorous zooplankton → filter feeder → predatory vertebrate

Phytoplankton don't need other organisms for food, because they have the ability to manufacture their own food directly from inorganic carbon, using sunlight as their energy source. This process is called photosynthesis, and results in the phytoplankton converting naturally occurring carbon into protoplasm. For this reason, phytoplankton are said to be the primary producers at the bottom or the first level of the marine food chain. Since they are at the first level they are said to have a trophic level of 1 (from the Greek trophē meaning food). Phytoplankton are then consumed at the next trophic level in the food chain by microscopic animals called zooplankton.

Zooplankton comprise the second trophic level in the food chain, and include microscopic one-celled organisms called protozoa as well as small crustaceans, such as copepods and krill, and the larva of fish, squid, lobsters and crabs. Organisms at this level can be thought of as primary consumers.

In turn, the smaller herbivorous zooplankton are consumed by larger carnivorous zooplankters, such as larger predatory protozoa and krill, and by forage fish, which are small, schooling, filter-feeding fish. This makes up the third trophic level in the food chain.

A food web is network of food chains, and as such can be represented graphically and analysed using techniques from network theory.[5][6]

Classic food web for grey seals in the Baltic Sea containing several typical marine food chains [7]

The fourth trophic level consists of predatory fish, marine mammals and seabirds that consume forage fish. Examples are swordfish, seals and gannets.

Apex predators, such as orcas, which can consume seals, and shortfin mako sharks, which can consume swordfish, make up a fifth trophic level. Baleen whales can consume zooplankton and krill directly, leading to a food chain with only three or four trophic levels.

In practice, trophic levels are not usually simple integers because the same consumer species often feeds across more than one trophic level.[8][9] For example a large marine vertebrate may eat smaller predatory fish but may also eat filter feeders; the stingray eats crustaceans, but the hammerhead eats both crustaceans and stingrays. Animals can also eat each other; the cod eats smaller cod as well as crayfish, and crayfish eat cod larvae. The feeding habits of a juvenile animal, and, as a consequence, its trophic level, can change as it grows up.

The fisheries scientist Daniel Pauly sets the values of trophic levels to one in primary producers and detritus, two in herbivores and detritivores (primary consumers), three in secondary consumers, and so on. The definition of the trophic level, TL, for any consumer species is:[10]

${\displaystyle TL_{i}=1+\sum _{j}(TL_{j}\cdot DC_{ij})\!}$

where ${\displaystyle TL_{j}}$ is the fractional trophic level of the prey j, and ${\displaystyle DC_{ij}}$ represents the fraction of j in the diet of i. In the case of marine ecosystems, the trophic level of most fish and other marine consumers takes value between 2.0 and 5.0. The upper value, 5.0, is unusual, even for large fish,[11] though it occurs in apex predators of marine mammals, such as polar bears and killer whales.[12] As a point of contrast, humans have a mean trophic level of about 2.21, about the same as a pig or an anchovy.[13][14]

Ocean chlorophyll concentration October 2019

Green indicates where there are a lot of phytoplankton, while blue indicates where there are few phytoplankton. – NASA Earth Observatory 2019.[15]

At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton. Like plants on land, phytoplankton use chlorophyll and other light-harvesting pigments to carry out photosynthesis, absorbing atmospheric carbon dioxide to produce sugars for fuel. Chlorophyll in the water changes the way it reflects and absorbs sunlight, allowing scientists to map the amount and location of phytoplankton. These measurements give scientists valuable insights into the health of the ocean environment, and help scientists study the ocean carbon cycle.[15]

Prochlorococcus, an influential bacterium which produces much of the world's oxygen

Among the phytoplankton are members from a phylum of bacteria called cyanobacteria. Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, Prochlorococcus, is just 0.5 to 0.8 micrometres across.[16] In terms of individual numbers, Prochlorococcus is possibly the most plentiful species on Earth: a single millilitre of surface seawater can contain 100,000 cells or more. Worldwide there are estimated to be several octillion (10²⁷) individuals.[17] Prochlorococcus is ubiquitous between 40°N and 40°S and dominates in the oligotrophic (nutrient poor) regions of the oceans.[18] The bacterium accounts for about 20% of the oxygen in the Earth's atmosphere.[19]

• Phytoplankton form the base of the ocean foodchain
• 
  Phytoplankton
• 
  Dinoflagellate
• 
  Diatoms

In oceans, most primary production is performed by algae. This is a contrast to on land, where most primary production is performed by vascular plants. Algae ranges from single floating cells to attached seaweeds, while vascular plants are represented in the ocean by groups such as the seagrasses. Larger producers, such as seagrasses and seaweeds, are mostly confined to the littoral zone and shallow waters, where they attach to the underlying substrate and are still within the photic zone. But most of the primary production by algae is performed by the phytoplankton.

Thus, in ocean environments, the first bottom trophic level is occupied principally by phytoplankton, microscopic drifting organisms, mostly one-celled algae, that float in the sea. Most phytoplankton are too small to be seen individually with the unaided eye. They can appear as a green discoloration of the water when they are present in high enough numbers. Since they increase their biomass mostly through photosynthesis they live in the sun-lit surface layer (euphotic zone) of the sea.

The most important groups of phytoplankton include the diatoms and dinoflagellates. Diatoms are especially important in oceans, where according to some estimates they contribute up to 45% of the total ocean's primary production.[20] Diatoms are usually microscopic, although some species can reach up to 2 millimetres in length.

The second trophic level (primary consumers) is occupied by zooplankton which feed off the phytoplankton. Together with the phytoplankton, they form the base of the food pyramid that supports most of the world's great fishing grounds. Zooplankton are tiny animals found with the phytoplankton in oceanic surface waters, and include tiny crustaceans, and fish larvae and fry (recently hatched fish). Most zooplankton are filter feeders, and they use appendages to strain the phytoplankton in the water. Some larger zooplankton also feed on smaller zooplankton. Some zooplankton can jump about a bit to avoid predators, but they can't really swim. Like phytoplankton, they float with the currents, tides and winds instead. Zooplanktons can reproduce rapidly, their populations can increase up to thirty percent a day under favourable conditions. Many live short and productive lives and reach maturity quickly.

• Zooplankton form a second level in the ocean food chain
• 
  Segmented worm
• 
  Tiny shrimp-like crustaceans
• 
  Juvenile planktonic squid

Particularly important groups of zooplankton are the copepods and krill. Copepods are a group of small crustaceans found in ocean and freshwater habitats. They are the biggest source of protein in the sea,[21] and are important prey for forage fish. Krill constitute the next biggest source of protein. Krill are particularly large predator zooplankton which feed on smaller zooplankton. This means they really belong to the third trophic level, secondary consumers, along with the forage fish.

Jellyfish are easy to capture and digest and may be more important as food sources than was previously thought.[22]

Together, phytoplankton and zooplankton make up most of the plankton in the sea. Plankton is the term applied to any small drifting organisms that float in the sea (Greek planktos = wanderer or drifter). By definition, organisms classified as plankton are unable to swim against ocean currents; they cannot resist the ambient current and control their position. In ocean environments, the first two trophic levels are occupied mainly by plankton. Plankton are divided into producers and consumers. The producers are the phytoplankton (Greek phyton = plant) and the consumers, who eat the phytoplankton, are the zooplankton (Greek zoon = animal).

Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as trophic dead ends, minor players in the marine food web, gelatinous organisms with a body plan largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the ocean sunfish and the leatherback sea turtle.[23][22] That view has recently been challenged. Jellyfish, and more generally gelatinous zooplankton which include salps and ctenophores, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested.[23] But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of tuna, spearfish and swordfish as well as various birds and invertebrates such as octopus, sea cucumbers, crabs and amphipods.[24][22] "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics."[22]

Predator fish sizing up schooling forage fish

Marine invertebrates

Fish

• Forage fish: Forage fish occupy central positions in the ocean food webs. The organisms it eats are at a lower trophic level, and the organisms that eat it are at a higher trophic level. Forage fish occupy middle levels in the food web, serving as a dominant prey to higher level fish, seabirds and mammals.[25]

• Predator fish

• Ground fish

Other marine vertebrates

In 2010 researchers found whales carry nutrients from the depths of the ocean back to the surface using a process they called the whale pump.[26] Whales feed at deeper levels in the ocean where krill is found, but return regularly to the surface to breathe. There whales defecate a liquid rich in nitrogen and iron. Instead of sinking, the liquid stays at the surface where phytoplankton consume it. In the Gulf of Maine the whale pump provides more nitrogen than the rivers.[27]

• 
  Humpback whales lunge from below to feed on forage fish
• 
  Gannets plunge dive from above to catch forage fish

• 
  Whale pump nutrient cycle

On average there are more than one million microbial cells in every drop of seawater, and their collective metabolisms not only recycle nutrients that can then be used by larger organisms but also catalyze key chemical transformations that maintain Earth’s habitability.[28]

There has been increasing recognition in recent years that marine microorganisms play much bigger roles in marine ecosystems than was previously thought. Developments in metagenomics gives researchers an ability to reveal previously hidden diversities of microscopic life, offering a powerful lens for viewing the microbial world and the potential to revolutionise understanding of the living world.[29] Metabarcoding dietary analysis techniques are being used to reconstruct food webs at higher levels of taxonomic resolution and are revealing deeper complexities in the web of interactions.[30]

Microorganisms play key roles in marine food webs. The viral shunt pathway 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.[31] Viral shunting helps maintain diversity within the microbial ecosystem by preventing a single species of marine microbe from dominating the micro-environment.[32] The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM.[33]

Ocean particulate organic matter (POM)
as imaged by a satellite in 2011

Cycling of marine phytoplankton. Phytoplankton live in the photic zone of the ocean, where photosynthesis is possible. During photosynthesis, they assimilate carbon dioxide and release oxygen. If solar radiation is too high, phytoplankton may fall victim to photodegradation. For growth, phytoplankton cells depend on nutrients, which enter the ocean by rivers, continental weathering, and glacial ice meltwater on the poles. Phytoplankton release dissolved organic carbon (DOC) into the ocean. Since phytoplankton are the basis of marine food webs, they serve as prey for zooplankton, fish larvae and other heterotrophic organisms. They can also be degraded by bacteria or by viral lysis. Although some phytoplankton cells, such as dinoflagellates, are able to migrate vertically, they are still incapable of actively moving against currents, so they slowly sink and ultimately fertilize the seafloor with dead cells and detritus.[34]

DOM, POM and the viral shunt

Connections between the different compartments of the living (bacteria/viruses and phyto−/zooplankton) and the nonliving (DOM/POM and inorganic matter) environment [35]

The viral shunt pathway facilitates the flow of dissolved organic matter (DOM) and particulate organic matter (POM) through the marine food web

The giant virus CroV attacks C.roenbergensis

Cafeteria roenbergensis a bacterivorous marine flagellate

A Mavirus virophage (lower left) lurking alongside a giant CroV [36]

A giant marine virus CroV infects and causes the death by lysis of the marine zooflagellate Cafeteria roenbergensis.[37] This impacts coastal ecology because Cafeteria roenbergensis feeds on bacteria found in the water. When there are low numbers of Cafeteria roenbergensis due to extensive CroV infections, the bacterial populations rise exponentially.[38] The impact of CroV on natural populations of C. roenbergensis remains unknown; however, the virus has been found to be very host specific, and does not infect other closely related organisms.[39] Cafeteria roenbergensis is also infected by a second virus, the Mavirus virophage, which is a satellite virus, meaning it is able to replicate only in the presence of another specific virus, in this case in the presence of CroV.[40] This virus interferes with the replication of CroV, which leads to the survival of C. roenbergensis cells. Mavirus is able to integrate into the genome of cells of C. roenbergensis, and thereby confer immunity to the population.[41]

Diagram of a mycoloop (fungus loop)

Parasitic chytrids can transfer material from large inedible phytoplankton to zooplankton. Chytrids zoospores are excellent food for zooplankton in terms of size (2–5 μm in diameter), shape, nutritional quality (rich in polyunsaturated fatty acids and cholesterols). Large colonies of host phytoplankton may also be fragmented by chytrid infections and become edible to zooplankton.[42]

• Amend, A., Burgaud, G., Cunliffe, M., Edgcomb, V.P., Ettinger, C.L., Gutiérrez, M.H., Heitman, J., Hom, E.F., Ianiri, G., Jones, A.C. and Kagami, M. (2019) "Fungi in the marine environment: Open questions and unsolved problems". MBio, 10(2): e01189-18. doi:10.1128/mBio.01189-18.

Roles of fungi in the marine carbon cycle [43]

Giant kelp is a foundation species for many kelp forests.[82]

The ochre starfish is a keystone predator

California mussels displace most other species unless ochre starfish control their numbers

  How starfish changed modern ecology – Nature on PBS  

Foundation species are species that have a dominant role structuring an ecological community, shaping its environment and defining its ecosystem. Such ecosystems are often named after the foundation species, such as seagrass meadows, oyster beds, coral reefs, kelp forests and mangrove forests.[83] For example, the red mangrove is a common foundation species in mangrove forests. The mangrove’s root provides nursery grounds for young fish, such as snapper.[84] A foundation species can occupy any trophic level in a food web but tend to be a producer. [85]

The term was coined in 1972 by Paul K. Dayton,[86] who applied it to certain members of marine invertebrate and algae communities. It was clear from studies in several locations that there were a small handful of species whose activities had a disproportionate effect on the rest of the marine community and they were therefore key to the resilience of the community. Dayton’s view was that focusing on foundation species would allow for a simplified approach to more rapidly understand how a community as a whole would react to disturbances, such as pollution, instead of attempting the extremely difficult task of tracking the responses of all community members simultaneously.

Sea otters predate sea urchins, making them a keystone species for kelp forests

Sea urchins damage kelp forests by chewing through kelp holdfasts

                    Sea otters versus urchins – Pew                    

Keystone species are species that have large effects, disproportionate to their numbers, within ecosystem food webs.[87] An ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.[88]

The concept of the keystone species was introduced in 1969 by the zoologist Robert T. Paine.[89][90] Paine developed the concept to explain his observations and experiments on the relationships between marine invertebrates of the intertidal zone (between the high and low tide lines), including starfish and mussels. Some sea stars prey on sea urchins, mussels, and other shellfish that have no other natural predators. If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species.[91]

Sea otters limit the damage sea urchins inflict on kelp forests. When the sea otters of the North American west coast were hunted commercially for their fur, their numbers fell to such low levels that they were unable to control the sea urchin population. The urchins in turn grazed the holdfasts of kelp so heavily that the kelp forests largely disappeared, along with all the species that depended on them. Reintroducing the sea otters has enabled the kelp ecosystem to be restored.[92][93]

Cryptic interactions in the marine food web

Illustration of the material fluxes, populations, and molecular pools that are impacted by five cryptic interactions (red: mixotrophy; green: ontogenetic and species differences; purple: microbial cross‐feeding; orange: auxotrophy; blue: cellular carbon partitioning). In fact, these interactions may have synergistic effects as the regions of the food web that they impact overlap. For example, cellular carbon partition in phytoplankton may affect both downstream pools of organic matter utilized in microbial cross‐feeding and exchanged in cases of auxotrophy, as well as prey selection based on ontogenetic and species differences.[94]

Cryptic interactions, interactions which are "hidden in plain sight", occur throughout the marine planktonic foodweb but are currently largely overlooked by established methods, which mean large‐scale data collection for these interactions is limited. Despite this, current evidence suggests some of these interactions may have perceptible impacts on foodweb dynamics and model results. Incorporation of cryptic interactions into models is especially important for those interactions involving the transport of nutrients or energy.[94]

Simplifications such as “zooplankton consume phytoplankton,” “phytoplankton take up inorganic nutrients,” “gross primary production determines the amount of carbon available to the foodweb,” etc. have helped scientists explain and model general interactions in the aquatic environment. Traditional methods have focused on quantifying and qualifying these generalizations, but rapid advancements in genomics, sensor detection limits, experimental methods, and other technologies in recent years have shown that generalization of interactions within the plankton community may be too simple. These enhancements in technology have exposed a number of interactions which appear as cryptic because bulk sampling efforts and experimental methods are biased against them.[94]

Schematic representation of the changes in abundance between trophic groups in a temperate rocky reef ecosystem. (a) Interactions at equilibrium. (b) Trophic cascade following disturbance. In this case, the otter is the dominant predator and the macroalgae are kelp. Arrows with positive (green, +) signs indicate positive effects on abundance while those with negative (red, -) indicate negative effects on abundance. The size of the bubbles represents the change in population abundance and associated altered interaction strength following disturbance.[95][96]

Food webs provide a framework within which a complex network of predator–prey interactions can be organised. A food web model is a network of food chains. Each food chain starts with a primary producer or autotroph, an organism, such as an alga or a plant, which is able to manufacture its own food. Next in the chain is an organism that feeds on the primary producer, and the chain continues in this way as a string of successive predators. The organisms in each chain are grouped into trophic levels, based on how many links they are removed from the primary producers. The length of the chain, or trophic level, is a measure of the number of species encountered as energy or nutrients move from plants to top predators.[97] Food energy flows from one organism to the next and to the next and so on, with some energy being lost at each level. At a given trophic level there may be one species or a group of species with the same predators and prey.[98]

In 1927, Charles Elton published an influential synthesis on the use of food webs, which resulted in them becoming a central concept in ecology.[99] In 1966, interest in food webs increased after Robert Paine's experimental and descriptive study of intertidal shores, suggesting that food web complexity was key to maintaining species diversity and ecological stability.[100] Many theoretical ecologists, including Robert May and Stuart Pimm, were prompted by this discovery and others to examine the mathematical properties of food webs. According to their analyses, complex food webs should be less stable than simple food webs.[101]^:75–77[102]^:64 The apparent paradox between the complexity of food webs observed in nature and the mathematical fragility of food web models is currently an area of intensive study and debate. The paradox may be due partially to conceptual differences between persistence of a food web and equilibrial stability of a food web.[101][102]

A trophic cascade can occur in a food web if a trophic level in the web is suppressed.

For example, a top-down cascade can occur if predators are effective enough in predation to reduce the abundance, or alter the behavior, of their prey, thereby releasing the next lower trophic level from predation. A top-down cascade is a trophic cascade where the top consumer/predator controls the primary consumer population. In turn, the primary producer population thrives. The removal of the top predator can alter the food web dynamics. In this case, the primary consumers would overpopulate and exploit the primary producers. Eventually there would not be enough primary producers to sustain the consumer population. Top-down food web stability depends on competition and predation in the higher trophic levels. Invasive species can also alter this cascade by removing or becoming a top predator. This interaction may not always be negative. Studies have shown that certain invasive species have begun to shift cascades; and as a consequence, ecosystem degradation has been repaired.[103][104] An example of a cascade in a complex, open-ocean ecosystem occurred in the northwest Atlantic during the 1980s and 1990s. The removal of Atlantic cod (Gadus morhua) and other ground fishes by sustained overfishing resulted in increases in the abundance of the prey species for these ground fishes, particularly smaller forage fishes and invertebrates such as the northern snow crab (Chionoecetes opilio) and northern shrimp (Pandalus borealis). The increased abundance of these prey species altered the community of zooplankton that serve as food for smaller fishes and invertebrates as an indirect effect.[105] Top-down cascades can be important for understanding the knock-on effects of removing top predators from food webs, as humans have done in many places through hunting and fishing.

In a bottom-up cascade, the population of primary producers will always control the increase/decrease of the energy in the higher trophic levels. Primary producers are plants, phytoplankton and zooplankton that require photosynthesis. Although light is important, primary producer populations are altered by the amount of nutrients in the system. This food web relies on the availability and limitation of resources. All populations will experience growth if there is initially a large amount of nutrients.[106][107]

Biomass pyramids
Compared to terrestrial biomass pyramids, aquatic pyramids are generally inverted at the base

Marine producers use less biomass than terrestrial producers

The minute but ubiquitous and highly active bacterium Prochlorococcus runs through its life cycle in one day, yet collectively generates about 20% of all global oxygen.

By contrast, a single bristlecone pine can tie up a lot of relatively inert biomass for thousands of years with little photosynthetic activity.[108]

Marine environments can have inversions in their biomass pyramids. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is generally larger than the biomass of primary producers. This happens because the ocean's primary producers are mostly tiny phytoplankton which have r-strategist traits of growing and reproducing rapidly, so a small mass can have a fast rate of primary production. In contrast, many terrestrial primary producers, such as mature forests, have K-strategist traits of growing and reproducing slowly, so a much larger mass is needed to achieve the same rate of primary production.

Examples: The bristlecone pine can live for thousands of years, and has a very low production/biomass ratio. The cyanobacterium Prochlorococcus lives for about 24 hours, and has a very high production/biomass ratio.

Mature forests have a lot of biomass invested in secondary growth which has low productivity

Ocean or marine biomass, in a reversal of terrestrial biomass, can increase at higher trophic levels.[109]

In oceans, most primary production is performed by algae. This is a contrast to on land, where most primary production is performed by vascular plants.

Aquatic producers, such as planktonic algae or aquatic plants, lack the large accumulation of secondary growth that exists in the woody trees of terrestrial ecosystems. However, they are able to reproduce quickly enough to support a larger biomass of grazers. This inverts the pyramid. Primary consumers have longer lifespans and slower growth rates that accumulates more biomass than the producers they consume. Phytoplankton live just a few days, whereas the zooplankton eating the phytoplankton live for several weeks and the fish eating the zooplankton live for several consecutive years.[110] Aquatic predators also tend to have a lower death rate than the smaller consumers, which contributes to the inverted pyramidal pattern. Population structure, migration rates, and environmental refuge for prey are other possible causes for pyramids with biomass inverted. Energy pyramids, however, will always have an upright pyramid shape if all sources of food energy are included, since this is dictated by the second law of thermodynamics."[111][112]

Fishing down the food web [114]

Overfishing

Acidification

Pteropods and brittle stars together form the base of the Arctic food webs and both are seriously damaged by acidification. Pteropods shells dissolve with increasing acidification and brittle stars lose muscle mass when re-growing appendages.[115] Additionally the brittle star's eggs die within a few days when exposed to expected conditions resulting from Arctic acidification.[116] Acidification threatens to destroy Arctic food webs from the base up. Arctic waters are changing rapidly and are advanced in the process of becoming undersaturated with aragonite.[117] Arctic food webs are considered simple, meaning there are few steps in the food chain from small organisms to larger predators. For example, pteropods are "a key prey item of a number of higher predators – larger plankton, fish, seabirds, whales".[118]

Effects of ocean acidification

Unhealthy pteropod showing effects of ocean acidification

Ocean acidification causes brittle stars to lose muscle mass

      Pteropods and brittle stars form the base of Arctic food webs

Climate change

"Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer–consumer dynamics, both of which have important implications for the structuring of benthic communities."[119][120]

"...increased temperatures reduce the vital flow of energy from the primary food producers at the bottom (e.g. algae), to intermediate consumers (herbivores), to predators at the top of marine food webs. Such disturbances in energy transfer can potentially lead to a decrease in food availability for top predators, which in turn, can lead to negative impacts for many marine species within these food webs... "Whilst climate change increased the productivity of plants, this was mainly due to an expansion of cyanobacteria (small blue-green algae)," said Mr Ullah. "This increased primary productivity does not support food webs, however, because these cyanobacteria are largely unpalatable and they are not consumed by herbivores. Understanding how ecosystems function under the effects of global warming is a challenge in ecological research. Most research on ocean warming involves simplified, short-term experiments based on only one or a few species."[120]

The distribution of anthropogenic stressors faced by marine species threatened with extinction in various marine regions of the world. Numbers in the pie charts indicate the percentage contribution of an anthropogenic stressors’ impact in a specific marine region.[95][121]

Anthropogenic stressors to marine species threatened with extinction [95]