In the sea, much of this work is done by microscopic bacteria, who gather waste and dead matter, and break it down into inorganic chemicals that can be reused as mineral nutrients, by zooplankton and other creatures. Image: © Joint Nature Conservation Committee (JCC)/ Alejandra Size/ WISE Marine.
Here is a very simple explanation of the aquatic food web and is only one of several differing versions, depending on which animals and organisms are included. The foundation of the ocean food web is occupied by single-celled algae and other tiny plant-like organisms, who create their own energy out of sunlight.
Collectively known as phytoplankton (Greek for “drifting plant”) these microorganisms are the starting point for the entire marine food. Microscopically small (about 1-5 mm in length), phytoplankton saturate the sunlit near-surface waters around the world in their billions.
Like their terrestrial counterparts, these marine plants use photosynthesis to convert sunlight, carbon dioxide (CO2) and water to create complex carbohydrates, like sugars. Phytoplankton is the “primary producers” of the organic carbon needed by all marine animals in order to live.
The most common type of primary producer (chemoautotrophs) uses the sun’s energy to build carbohydrates. These organisms use chemosynthesis to metabolize chemical compounds emitted from hydrothermal vents, methane seeps, and other geological features.
Mostly filter-feeders, they drift through the water grazing on phytoplankton and bacteria that form the base of the food web, and in turn, are preyed upon by fish, insects and other predatory zooplankton. Cope pods, the biggest source, are crustaceans with a resilient exoskeleton made of calcium carbonate.
In this sense, krill serve as a nutrient bridge from microscopic phytoplankton to larger fish and mammals. Phytoplankton is aquatic plants or bacteria, while zooplankton are tiny fish, crustaceans and other marine animals.
Phytoplankton inhabits the near-surface of the sea (the euphoric zone) in order to photosynthesize sunlight; zooplankton live in the darker and colder depths. Although they vary enormously in size, herbivores share a prodigious appetite for marine vegetation, as well as a common fate.
Almost every other living thing in the marine biosphere “consumes” the energy initially created by phytoplankton. In other words, all marine life depends on phytoplankton creating enough usable energy in their bodies.
According to a 2010 study published in Nature, the numbers of phytoplankton in the ocean had declined substantially over the past century. In a follow-up study, prompted by criticism as to sample sizes and other matters, the authors made use of a larger database of measurements and upgraded their methodology, but ultimately came to similar conclusions.
Studies have found that marine mammals like whales enhance primary productivity through the release of fecal plumes. Traditionally regarded as minor players in the marine food web, due to having a gelatinous, watery body with little nutritional value, jellyfish are now thought to be a major constituent of the diets of swordfish and tuna, as well as octopus and crabs.
Species of forage fish include: anchovies, herrings, Hilda, mackerel, menhaden, sardines, shad, sprats, as well as captain, half beaks, silver sides, squid and smelt. To compensate for their size and to deter predators, forage fish form large shoals which follow regular routes along coastlines, and also across the open sea, pursued by large numbers of marine predators, including whales, seals, tuna, dolphins and seabirds.
Some larger species of whales rely upon forage fish for up to three quarters of their food intake. Marine tertiary consumers include: baleen, humpback and Mike whales; harbor seals, cod, tuna, Chinook salmon, barracuda, dolphins and porpoises, swordfish, penguins and seals, as well as seabirds like pelicans, shear waters, cormorants and gannets.
Unfortunately, removing sharks from the ocean leads to population growth among larger predators, such as groupers. Another study off the southeastern coast of the United States revealed that the loss of large sharks resulted in an increase of the ray population.
The hungry rays ate all the coastal scallops, forcing the closure of the local shellfish industry. Roughly 300-400 million tons of heavy metals, solvents, and other toxic slurry from industrial plants are dumped annually into the world’s oceans.
In addition, millions of tons of nitrogen and phosphorus from agricultural and industrial runoff arrive in the ocean every year, causing more hypoxic ‘dead zones’. If all this wasn’t having a big enough impact on the world’s oceans, we also use them as a dumping ground for plastic, especially microplastic.
Plastic pollution, which has skyrocketed since 1980, is now found in all parts of the ocean, from shallow coastal waters to the bottom of the 36,000-foot Mariana Trench. Microplastic waste is ingested by almost every creature in the sea, and so far has been found to block the digestive tracts of at least 267 different species.
European countries, such France, Germany and the UK, had the lowest contamination rate (72 percent). A recent study published in Science magazine suggests the long-term viability of half the killer whale population around the globe is now in question, due to their ingestion of poly chlorinated biphenyls, or PCs.
These highly toxic pollutants, now banned, damage the ovaries of female orcas, limiting their ability to breed. It also absorbs 93 percent of the excess heat produced by global warming, whose impact on water temperature, oxygen and pH levels, and marine life, is intensifying.
The effects of global warming on the oceans are also becoming noticeable throughout the marine food chain, which acts as a barometer of change. Species are becoming disoriented and damaged by marine heatwaves, ocean warming, acidification and oxygenation.
Here are two specific instances of how global warming is forecast to impact on the ocean food web. • A new study published in Los Biology suggests that levels of commercial fish stocks could fall as rising sea temperatures affect their source of food.
• Predicted increases in greenhouse gas emissions might suppress oceanic biological productivity for an entire millennium. Because as the climate warms, westerly winds in the Southern Hemisphere are likely to strengthen and shift towards the pole.
As a result, surface waters will warm, sea ice will disappear, and upwelling of thermohaline circulation currents will increase around Antarctica. Ultimately, the net effect of these changes will be a major decrease in marine biological productivity.
It has taken over three years for the bloodstock at Tropic Seafood, Ltd., to be conditioned to spawn naturally in captivity. During the most recent series of spawning events at Tropic Seafood, Ltd., fertilized eggs were transferred to incubators in order to produce Nassau grouper larvae.
Newly hatched larvae (called yolk-sac larvae, because they carry a yolk sac that contains a single drop of bio-lipid oil) can live off their yolk sacs for nourishment, for about four days after hatching, before their mouth parts become large enough and strong enough to accommodate live food (prey) such as zooplankton. Efforts to culture the Nassau grouper larvae are ongoing with very favorable results.
Zooplankton is small animals that live in the water column of almost all water bodies, including oceans, lakes and ponds, although they mostly cannot survive in rivers and streams. In lakes and ponds, the most common groups of zooplankton include Caldera and Cope pods (which are both micro-crustaceans), conifers and protozoans. They eat bacteria and algae that form the base of the food web and, in turn, are heavily preyed upon by fish, insects and other zooplankton.
Some zooplankton, like many Caldera, is indiscriminate grazers, using their feeding appendages like rakes to filter particles from the water. As a result of their central position in lake food webs, zooplankton can strongly affect water quality, algal densities, fish production, and nutrient and contaminant cycling.
Zooplankton are commonly included in biomonitoring programs because their densities and species composition can be sensitive to changes in environmental conditions. In recent years, many species of zooplankton have been accidentally introduced to Canadian lakes and rivers from Europe and elsewhere, including the spiny water flea (Bythotrephes) and the larval stages of zebra mussels.
Occasionally, some species of zooplankton, such as My sis, have been deliberately introduced to lakes to enhance fish production. ELA was originally founded in 1968 to address problems associated with excessive algal blooms, which are unsightly, may cause fish kills and can result in the development of toxins.
This process, known as eutrophication, is caused by high inputs of nutrients and plagues millions of lakes globally. Because zooplankton eat algae, it has been proposed that it may be possible to control algal blooms by increasing zooplankton grazing.
We tested the effectiveness of the latter method (commonly used in Europe) in the 1990s by adding pike to eutrophic Lake 227. Unfortunately, algal densities remained low for only one year and the lake rapidly rebounded to its former eutrophic state.
Following the pike introduction, minnows were extirpated, densities of a zooplankton called Mafia increased dramatically and algal densities decreased. This research, in conjunction with other studies, suggested that bio manipulation can effectively reduce algae in the short term, but may be less effective as a long-term solution for eutrophication. Mercury (especially methyl mercury) is by far the most important contaminant of freshwater fish and high exposures can have harmful effects on humans who consume it.
For example, in a series of artificially created reservoirs at the site, we found that concentrations of methyl mercury in zooplankton increased by five times or more following impoundment.