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Summary Article: Hardy, Alister Clavering (1896-1985)
From The Hutchinson Dictionary of Scientific Biography

Place: United Kingdom, England

Subject: biography, biology, religion

English marine biologist who designed the Hardy plankton continuous recorder. His development of methods for ascertaining the numbers and types of minute sea organisms helped to unravel the intricate web of life that exists in the sea.

Hardy was born in Nottingham on 10 February 1896 and was educated at Oundle School and then at Exeter College, Oxford. He served in World War I as a lieutenant and later as a captain 1915-19. The following year he studied at the Stazione Zoologica in Naples and returned to the UK in 1921 to become assistant naturalist in the fisheries department of the Ministry of Agriculture and Fisheries. In 1924 he joined the Discovery expedition to the Antarctic as chief zoologist and on his return in 1928 he was appointed professor of zoology and oceanography at Hull University, where he founded the department of oceanography. In 1942 he was made professor of natural history at the University of Aberdeen and, two years later, became professor of zoology at Oxford. He held this post for 15 years, 1946-61, when he served as professor of field studies at Oxford. In recognition of his achievements in marine biology, he was knighted in 1957. He returned to Aberdeen in 1963 to take up a lectureship at the university.

Before Hardy's investigations, the German zoologist Johannes Müller had towed a conical net of fine-meshed cloth behind a ship and collected enough specimens from the sea to reveal an entirely new sphere for biological research. The really serious study of the sea began in the late 19th century with the voyage of HMS Challenger, the purpose of which was to investigate all kinds of sea life, and it returned to the UK with an enormous wealth of material. A German plankton expedition was led by Victor Hensen in 1899, who coined the word plankton to describe the minute sea creatures that, it has since been established, form the first link in the vital sea food-chain.

Hardy made his special study of plankton on the 1924 Discovery expedition. The aim of quantitative plankton studies is to estimate the numbers or weights of organisms beneath a unit area of sea surface or in a unit volume of water. Müller's original conical net of fine mesh is still the basic requirement in any instrument designed to collect specimens from the sea, but the drawback is that it can be used only from stationary vessels for collections at various depths, or from moving vessels whose speed must not exceed two knots. Faster speeds displace the small organisms by the turbulence created. Hardy developed a net that can be used behind faster-moving vessels and which increases enormously the area in which accurate recordings can be made.

The first of these nets was the Hardy plankton recorder, which, reduced to its simplest terms, is a high-speed net. It consists of a metal tube with a constricted opening, a fixed diving plane instead of a weight, and a stabilizing fin. The net itself is a disc of 60-mesh silk attached to a ring placed inside near the tail. It was designed for easy handling aboard herring-fishing vessels to be towed when the skipper was near the grounds chosen for the night's fishing. If the disc showed plenty of herring food, the chances of a good catch were high. The indicator is no longer used for this purpose, having been superseded by more modern echo-sounding equipment, but it served as the basis for Hardy's second invention, which is still used and through which it has been possible to map the sea life in the oceans of the world.

This improved instrument is known as the Hardy continuous plankton recorder, and was first developed at the oceanographic department that Hardy himself founded at the University of Hull in 1931. The instrument can be used by unskilled personnel aboard ship after being suitably prepared by scientists ashore and is later returned to the laboratory where scientific observations can be made under more ideal conditions.

While the ship tows it along at normal cruising speed the instrument continuously samples the plankton. As the instrument is towed, the water flowing through it drives a small propeller that, acting through a gearbox, slowly winds a long length of plankton silk mesh and draws it across the path of the incoming water. As the mesh, which is graduated in numbered divisions, collects the plankton, it is slowly wound round a spool. This roll of silk mesh is then met by another roll and both are wound together in sandwich form, with the plankton collected by the first roll safely trapped between the two. The whole is stored in a small tank filled with a solution that preserves the plankton for later detailed study in the laboratory.

The recorder can be used at a depth of 10 m/33 ft and at speeds ranging from 8-16 knots/15-30 kph. Regular surveys, initiated at Hull and developed in Edinburgh, now annually cover many thousands of kilometres in the Atlantic, North Sea, and Icelandic waters. The knowledge of plankton distribution, which is continuously being updated, is of major importance to the fishing industry because there is a vitally close relationship between the occurrence of plankton and the movements of plankton-feeding fish used for human consumption.

Hardy suggested that if just 25% of the pests that exist in the sea can be eliminated and fish can be allowed to have some 20% of the potential food supply instead of the 2% they have now, then any given area could support ten times the amount of fish it supports at present. Hardy's methods have therefore not only added to our overall knowledge of sea life but have also indicated ways in which it could be put to better use.

© RM, 2018. All rights reserved.

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