Table 1. Physico-chemical conditions at different locations in the tubeworm clump from which individual tubeworms were subsequently collected for the proteomic work.

Location of probe	(1) Among Tevnia tubes and plumes	(2) At Riftia plume	(3) At base of Riftia and Tevnia tubes	(4) Close to Tevnia plumes
Date	2007/12/30	2008/01/01	2008/01/01	2008/01/01
Temperature (°C)	19.8	2.6	65.9	19.4
±	1.1	0.5	1.5	0.8
pH	5.5	7.4	4.9	5.4
±	<0.1	0.1	0.2	<0.1
Free sulfide (m)	0.7	<0.01	1.7	2.1
±	0.06	<0.01	0.8	0.5
Total no. of measurements (n)	31	48	29	49

Average values and s.d. obtained for 3–5 min scans combining temperature, pH and free sulfide ([H₂S] + [HS⁻]) are given. These data sets represent a few discrete positions and illustrate the strong chemical and thermal gradients experienced at the scale of the tubeworm aggregation. Owing to the position of the worm plumes in this gradient, systematic differences in the habitat conditions of the two species can be hypothesized. These observations are consistent with the more complete measurement series previously presented by Nees et al. (2009). A rather large s.d. for sulfide reflects the limited precision of sulfide potentiometric measurements at low pH and high sulfide.