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Riley, Gordon Arthur

RILEY, GORDON ARTHUR

(b. Webb City, Missouri, 11 June 1911; d. Halifax, Nova Scotia, Canada, 7 October 1985)

quantitative biological oceanography, ecological modeling.

Riley introduced quantitative hypothesis testing and modeling to the study of biological oceanography, first using experimental methods and statistics to determine the causes of biological processes in the sea, an approach fostered by his teacher G. Evelyn Hutchinson. In the 1940s, despite the skepticism of the ecological establishment about mathematical techniques, he began the use of differential equations in modeling biological oceano-graphic processes. Later he made original contributions to regional oceanography, transport and mixing, and particles in seawater, all in a biological context. Late in his career, as an administrator of science, he built a school of oceanography whose graduates carried his influence throughout North America and beyond. He was elected a Fellow of the Royal Society of Canada in 1973, and in 1976 was awarded the American Association for the Advancement of Science’s Rosenstiel Award in Marine Sciences for his innovations in biological oceanography.

From Embryology to Limnology After an undergraduate degree in biology at Drury College (now Drury University), Gordon Riley did research on ascidian (sea squirt) embryology for an MS degree at Washington University, St. Louis, in 1934. He was then accepted at Yale to work toward a PhD with the eminent embryologist Ross G. Harrison. After a few unexciting months with Harrison, Riley was fascinated to discover the world of limnology (study of freshwater lakes), presented in one of his classes by the young Yale faculty member G. Evelyn Hutchinson. Hutchinson soon accepted Riley as his first graduate student and assigned him the problem of investigating the copper cycle of lakes, on the premise that nothing was known of the elements in lakes and their biological effects except for the major nutrients although all might be significant in controlling aquatic production. During his conversion to limnology, Riley also discovered statistics, as taught to him at Yale by the mathematical biologist Oscar W. Richards, and incorporated into his thinking a mathematical, deductive approach to science espoused by Hutchinson and based on the ideas he derived from Harold Jeffreys’s book Scientific Inference (1931). Stimulated by Richards, and with the encouragement of Hutchinson, Riley applied statistics to his limnological work, also using the newly established technique of light and dark bottle incubations of phytoplankton cells (green unicells at the base of aquatic food webs), culminating in his PhD dissertation in 1937. During postdoctoral research soon after, he began to apply the technique of multiple regression analysis to relate ecological factors to their presumed biological effects.

Making the Study of the Sea Quantitative During a cruise in the Gulf of Mexico in 1937, Riley first applied multiple regression analysis to marine ecosystems, showing that phytoplankton standing crop was a quantitative function of nutrient levels. Soon thereafter, appointed to the staff of Yale’s Bingham Oceanographic Laboratory, he began to study the control of production in Long Island Sound, and, in the summer of 1938 in the Dry Tortugas, Florida, finding in the tropical seas at the Tortugas an unexpectedly high level of phytoplankton production. As he continued to refine and expand these studies during the next few years, he established the light and dark bottle technique as a way of isolating natural systems in a way that allowed manipulation of the interacting factors (such as nutrient supply, light, temperature, and gRāzīng by animals) that affected the Abūndance and production of the plants, followed by causal analysis using multiple correlations.

Riley’s quantitative analyses of the factors influencing marine production extended to the western North Atlantic Ocean, first from his base at Yale, and then as a staff member of the Woods Hole Oceanographic Institution (WHOI) from 1942 to 1948. His attention soon turned too to the fisheries-rich Georges Bank, off Cape Cod, which was becoming a focus of interest at Woods Hole. Until they were ended by the United States’s entry into World War II late in 1941, six cruises of the WHOI ketch Atlantis enabled Riley to compare the richness of Georges Bank with the more depauperate western North Atlantic and Gulf of Mexico, focusing especially on the onset of the spring bloom on the bank. Using statistical analyses, he showed that the bloom could be predicted knowing only temperature and nutrient levels. Water motion also played an important role, mixing the cells too deep in the water during the winter to allow net production; only when vertical mixing was limited by surface warming in the spring could the bloom begin. By the middle of 1941, Riley believed that he had developed a sound, quantitative basis for the prediction of seasonally varying production in a wide variety of marine ecosystems ranging from coastal bays to the open oceans.

A Change of Direction to Mathematical Modeling By the time his active work at sea was curtailed by the onset of war in 1941, Riley believed that he was hot on the trail of a quantitative, ecologically based, predictive theory of plankton growth in the sea. However, after the war years (when he was involved in studies of underwater sound, taught oceanographic techniques to naval officers, studied marine fouling, and was assigned to do follow-up studies of the Bikini Atoll atomic tests in 1946), Riley returned to studies of marine production, but with an enhanced appreciation of the shortcomings of his early work. The immediate stimulus to a new approach was his interest in the effect of gRāzīng animals on the spring phytoplankton bloom, a subject carefully examined by H. W. Harvey and his colleagues at the Plymouth Laboratory in England in a publication in 1935 and characterized mathematically by Richard Fleming of the Scripps Institution of Oceanography in a simple prey–predator equation. This proved to be the stimulus for a wholly new formulation of plankton dynamics, necessary because as the range and number of Riley’s multiple regression analyses increased, the results became harder and harder to interpret and were inconsistent from time to time and place to place. Some kind of new approach was necessary. He was ready to turn his methods on their head, for as he said, “the only way to avoid them [the limitations of the multiple correlation method] is by the opposite approach—that of developing the mathematical relationships on theoretical grounds and then testing them statistically by applying them to observed cases of growth in the natural environment” (Riley, 1946, p. 55). This was to be the core of his modeling technique in biological oceanography for nearly twenty years.

The basis of Riley’s new approach was to develop predictive equations expressing population changes as a function of a number of simple environmental variables such as, for phytoplankton, light intensity, water transparency, nutrients, the depth of the mixed layer, surface temperature, and the Abūndance of grazers. Analogous treatments were developed for the herbivorous zooplankton, and eventually, in his last application of the technique in 1963, for fish, the top members of aquatic food chains. The use of differential equations to express the theoretical relationships involved in marine production systems was based on his belief that only a few biological and physical factors interacted in nature. It was greatly stimulated by the work of biological oceanographers at the Plymouth Laboratory in England, especially Hildebrand W. Harvey, who provided precise information on chemical factors, light and gRāzīng in the English Channel. Added to this was the physical oceanographic approach that Riley learned in Woods Hole, and, to a large extent, taught himself.

After his first modeling attempts in 1946 using differential equations, Riley introduced two new modeling studies of considerable complexity and great originality. The first, published in 1949 in collaboration with Henry Stommel and Dean Bumpus, predicted the distribution of populations of phytoplankton in the western North Atlantic Ocean as a result of changes in the physical environment. The second, in 1951, was a study of biological activity in deep water of the Atlantic, predicting the horizontal and vertical distribution of the nonconservative variables (i.e., variables affected by biological activity) oxygen, phosphate, and nitrate as a result of the interaction of biological and physical processes. These models set a new standard for biological oceanographic analysis and firmly lodged physical oceanographic techniques in biological oceanography. Riley’s approach, using physical oceanographic techniques with chemical and biological data to solve difficult biological problems, provided the form followed by many later analyses, but was even more important in providing an example of how biological oceanography should be pursued as a quantitative science in which physical analysis was essential.

Yale and Long Island Sound Of equal influence was the work that Riley and his graduate students began in Long Island Sound beginning in 1948, when he returned to the Bingham Oceanographic Laboratory from WHOI. The sound became the home sea of Yale oceanography, a testing area for questions dating from the late 1930s about the factors governing levels of production from place to place, the efficiency of material transfers from one group of organisms to another, the relative importance of biological and physical variables, and how to account for variations in fish production. Using quantitative dissection of the biological and physical processes at work, Riley and his students established by the end of the 1950s that Long Island Sound was twice as productive as the English Channel, although less efficient ecologically, and showed a different partition of biological activity than the channel. They noted too that there was a large amount of non-living particulate matter in the sound, an observation that led into a totally new area of research.

Particulate Organic Matter and a Change of Direction In the early 1960s Riley and some of his coworkers began to study the distribution and formation of particulate organic matter, showing that it was widespread in the oceans, was of ecological significance, and could be formed by bubbling seawater. This research came with him from Yale to Dalhousie University in 1965, when, as a result of an administrative decision at Yale to abandon plans for a department of oceanography, Riley left to direct the Institute of Oceanography (founded in 1959) at Dalhousie and to direct its transition into a graduate department of oceanography. This move, along with his program on Long Island Sound at Yale during the 1950s, resulted in a school of oceanographers, some of them initially Yale undergraduates or graduate students, later an active group of graduate students at Dalhousie University. Many of these got their degrees just when oceanography began to expand in the late 1950s and 1960s, and by the 1970s Riley’s influence had made the Dalhousie graduate program one of the best on the continent, providing faculty members and scientists to the University of Rhode Island, WHOI, Oregon State University, Dalhousie University, the Bedford Institute of Oceanography, and many other institutions. By the time of his retirement in 1976 he considered himself an administrator, but the effect of his scientific work and graduate teaching was still profound.

Riley’s approach to biological oceanography, using physical oceanographic techniques to solve biological problems, provided a new practical and conceptual framework for the field. It was widely influential in providing a new esprit de corps as well as a new modus operandi for biological oceanographers. His approach to scientific investigation recognized that the simpler patterns found in nature could be analyzed or modeled mathematically. The more complex ones required detailed observational or experimental work before mathematical modeling became possible. Modeling was never Riley’s only route to understanding: the pattern of nature required a sophistication of approach equal to the varieties of pattern in nature. Working largely alone, and often unappreciated (he was never elected a member of the U.S. National Academy of Sciences), Riley’s influence came to pervade biological oceanography when the uniqueness of his work was appreciated and as the influence of his students spread throughout the marine sciences.

BIBLIOGRAPHY

WORKS BY RILEY

“Correlations in Aquatic Ecology.” Journal of Marine Research 2 (1939): 56–73. Use of the correlation and multiple correlations techniques.

“Factors Controlling Phytoplankton Populations on Georges Bank.” Journal of Marine Research 6 (1946): 54–73. Introduction of differential equations to modeling in biological oceanography.

With Dean Bumpus and Henry Stommel. “Quantitative Ecology of the Plankton of the Western North Atlantic.” Bulletin of the Bingham Oceanographic Collection 12, no. 3 (1949): 1–169.

“Oxygen, Phosphate, and Nitrate in the Atlantic Ocean.” Bulletin of the Bingham Oceanographic Collection 13, no. 1 (1951): 1–126. Innovative physical analysis of the oxygen use and nutrient regeneration in deep ocean waters.

“Review of the Oceanography of Long Island Sound.” Papers in Marine Biology and Oceanography, supplement to Deep-Sea Research 3 (1955): 224–238. Summary of the work of Riley and his students in the home sea of the Yale oceanographers.

“Organic Aggregates in Seawater and the Dynamics of Their Formation and Utilization.” Limnology and Oceanography 8 (1963): 372–381.

“Theory of Food Chain Relations in the Ocean.” In The Sea, vol. 2, The Composition of Sea-Water: Comparative and Descriptive Oceanography, edited by Maurice Neville Hill. New York: Interscience, 1963. Extension of Riley’s modeling technique to the whole food chain.

“Reminiscences of an Oceanographer.” Papers. Halifax, NS, Department of Oceanography, Dalhousie University, 1984. The best single source of biographical information and information on the background of Riley’s work.

OTHER SOURCES

Hutchinson, G. Evelyn. “Reminiscences and Notes on Some Otherwise Undiscussed Papers.” In Selected Works of Gordon A. Riley, edited by J. S. Wroblewski. Halifax, NS: Dalhousie University, 1982. Includes information on Riley’s student days at Yale.

Jeffreys, Harold. Scientific Inference. Cambridge, U.K.: Cambridge University Press, 1931.

Mills, Eric L. Biological Oceanography: An Early History, 1870–1960. Ithaca, NY: Cornell University Press, 1989. See especially chapters 10 and 11 for a detailed account of Riley’s career and work.

Wroblewski, J. S., ed. Collected Works of Gordon A. Riley. Halifax, NS: Dalhousie University, 1982. Reprints of many publications, along with interpretive essays by colleagues.

Eric L. Mills

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