HYDR_SP1112_author_14 1..14

12 In diversity research, the use of survey data appears to have declined in favour of experimental or modeling 13 approaches because direct relationships are difficult to demonstrate. Here we show that use of field data can 14 yield information concerning the mechanisms governing diversity. First, we establish that tintinnids display 15 a global latitudinal pattern of diversity similar to other pelagic organisms; species numbers appear to peak 16 between 20 and 30 north or south. This common large scale spatial trend has been attributed to the 17 gradient in water column structure across the global ocean. We then examine the generality of a rela18 tionship between planktonic diversity and water column structure by considering data from the Mediter19 ranean Sea, in which water column structure changes seasonally. Among populations of foraminifera, 20 tintinnids, and the dinoflagellates of the genus Ceratium, we compare data from trans-Mediterranean 21 sampling conducted at different times and monthly changes in species richness at single sites. We find that 22 water column structure alone appears to be a poor predictor of temporal changes in diversity. Lastly, we 23 present an example of temporal changes in tintinnid diversity based on data from an oceanographic 24 sampling station in the N. W. Mediterranean where resources, as chlorophyll, appear distinctly unrelated to 25 changes in water column structure. We show that short-tem temporal changes in diversity (week to week 26 shifts) can be related to changes in chlorophyll concentration. We conclude that in tintinnids diversity can 27 be directly linked to characteristics of food resources. 28