In 1922, she took a job at the Marine Biological Station in Millport on the Isle of Cumbrae where she worked for the rest of her life.[5][6] From 1928 to 1929 Marshall travelled with Frederick Stratten Russell and J. S. Colman on the Great Barrier Reef Expedition led by Maurice Yonge.[7]
Marshall studied the marine food chain, in particular copepods. This became her life's work. She collaborated for almost 40 years with the chemist, Andrew Picken Orr. Together they studied the plankton and phytoplankton in and around the river Clyde and Loch Striven. They authored several books and many papers together.[5]
In 1934 Marshall received a DSc from the University of Glasgow.[4][6]
In the 1940s she worked with Lillie Newton and Elsie Conway as well as Orr to develop seaweeds from around the United Kingdom as a source of agar for pharmaceutical purposes since imports from traditional sources in the Middle East were prevented by the Second World War.[8] She also examined the effect of fertilizers on marine productivity at Loch Craiglin.[5]
She retired as Deputy Director of the Station in 1964 (having been appointed to this post on the death of Orr, the previous post-holder, in 1962). She continued research there as an Honorary Fellow.[6]
Sheina Marshall was born on 20 April 1896 in Rothesay, Scotland, the second daughter of three, to Jean Colville (née Binnie, born 1861/2) and John Nairn Marshall (born 1860) of Mount Stuart House.[5][10] Marshall's father, a general practitioner, had an interest in natural history and encouraged his daughters' interest in the subject.
Outside her work she enjoyed walking, foreign travel, needlework, poetry and music. She was considered hospitable, dignified and generous.[11]
She died of a heart attack at Lady Margaret Hospital, Millport, Cumbrae on 7 April 1977.[5] She bequeathed her house at Millport to the Directors of Millport.[11]
^Marshall, Sheina M; University Marine Biological Station (1 January 1987). An account of the Marine Station at Millport. University Marine Biological Station. OCLC60305763.
Elizabeth Ewan, Sue Innes, Sian Reynolds, Rose Pipes, eds., The Biographical Dictionary of Scottish Women
'Marshall, Sheina Macalister', in Catherine M. C. Haines, ed., International women in science: a biographical dictionary to 1950, ABC-CLIO, 2001, pp. 201–2
