The Sheldon spectrum is an empirically-observed feature of

marine life Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...

by which the size of an organism is inversely correlated with its abundance in the ocean. The spectrum is named after Ray Sheldon, a marine ecologist at Canada’s

Bedford Institute of Oceanography The Bedford Institute of Oceanography (BIO) is a major Government of Canada ocean research facility located in Dartmouth, Nova Scotia. BIO is the largest ocean research station in Canada. Established in 1962 as Canada's first, and currently la ...

in Dartmouth,

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

. Sheldon and colleagues first suggested the existence of the inverse correlation based on seagoing measurements of

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

made with a

Coulter counter A Coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. The Coulter counter is the commercial term for the technique known as resistive pulse sensing or electrical zone sensing, the apparatus is based on T ...

in the late 1960s, most notably during the first circum-navigation of the Americas aboard the

CCGS Hudson CCGS ''Hudson'' was an offshore oceanographic and hydrographic survey vessel operated by the Canadian Coast Guard. The ship entered service in 1963 with the Canadian Oceanographic Service, stationed at the Bedford Institute of Oceanography, call ...

. The inverse correlation implies that

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

density as a function of logarithmic body mass is approximately constant over many

orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...

. For example, when Sheldon and his colleagues analyzed a plankton sample in a bucket of seawater, they would tend to find that one third of the plankton mass was between 1 and 10

micrometers The micrometre (American and British English spelling differences#-re, -er, international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American and British English spelling differences# ...

, another third was between 10 and 100 micrometers, and a third was between 100 micrometers and 1 millimeter. To make up for the differences of size, there must be a remarkably accurate mathematically correlative decrease in number of organisms as they become larger, in order for the biomass to remain constant. Thus, the rule predicts that

krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in n ...

which are a million times smaller than

tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...

are a million times more abundant in the ocean, a prediction which appears to be true. There is strong evidence that human behavior, particularly

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in th ...

and

whaling Whaling is the process of hunting of whales for their usable products such as meat and blubber, which can be turned into a type of oil that became increasingly important in the Industrial Revolution. It was practiced as an organized industry ...

, have modified the Sheldon spectrum for larger species, and it is unknown what long term effects such global alteration may have.Hatton IA, et al
The global ocean size spectrum from bacteria to whales
''Science Advances'' 2021;7(46)

References

{{reflist Marine organisms Planktology Marine biology