UNCORRECTED PROOF 2 Probing diversity in the plankton: using patterns in Tintinnids 3 (planktonic marine ciliates) to identify mechanisms 4 5 John R. Dolan*, Rodolphe Leme´e, Ste´phane Gasparini, Laure Mousseau & Ce´line Heyndrickx Marine Microbial Ecology Group, Laboratoire d’Oce´anographie de Villefranche, CNRS UMR 7093, Station Zoologique, B. P. 28F-06230, Villefranche-Sur-Mer, France (*Author for correspondence: E-mail: dolan@obs-vlfr.fr) 9 10 Key words: biodiversity, zooplankton, Mediterranean, latitudinal gradient, phytoplankton, foraminifera 11 Abstract 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 rela- 18 tionship between planktonic diversity and water column structure by considering data from the Mediter- 19 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 29 Introduction 31 Three major approaches are commonly employed 32 in diversity research: experimentation, modeling, 33 and survey, each of which possesses particular 34 weaknesses. Here, after briefly reviewing the 35 drawbacks of recent experimental and modeling 36 efforts, we will illustrate the major problem in- 37 volved in using survey data – that of distinguishing 38 direct effects on diversity from co-varying or 39 indirect factors. To show the utility of survey data 40 we will begin by establishing the validity of using 41 tintinnid ciliates as an example of a typical 42 planktonic group. Then, we will use survey data to 43 explore factors co-varying with tintinnid diversity 44 to determine if a plausible controlling mechanism 45 influencing diversity can be identified. 46 The experimental approach has been employed 47 most commonly to investigate the relationship 48 between a single ecosystem function (production, 49 nutrient regeneration, etc.) and diversity. Typically 50 experimentation with planktonic communities has 51 involved very simple petri dish or test tube com- 52 munities of a few microbial species (e.g., Naeem & 53 Li, 1998; Naeem et al., 2000) or even strains of the 54 same species (e.g. Buckling et al., 2000; Kassen 55 et al., 2000). Thus, conclusions have been drawn 56 from short-term results with very rudimentary Journal : HYDR Dispatch : 15-6-2005 Pages : 14 h LE h TYPESET MS Code : HYDRSP1112 h CP h DISK 4 4 Hydrobiologia (2005) 00: 1–14 Ó Springer 2005 DOI 10.1007/s10750-005-1112-6 AUTHOR’S PROOF! PDF-OUTPUT