Table 2. Comparison of average conditions when WCB amoA transcripts were present or absent in Monterey Bay surface waters.

	Temperature† (oC)	Salinity	Chl a (μg l−1)	NH 4 + (μM)	NO 2 − (μM)	NO 3 − (μM)	SiO 4 4− (μM)	PO 4 3− (μM)	O2 (ml l−1)	15NH4+oxidation (nmol l−1 day−1)
Absent
Mean	12.3a	33.5a	10.2	0.24a	0.16a	4.4a	5.6a	0.8a	7.0a	5.2a
s.d.	0.9	0.2	6.9	0.27	0.12	5.1	5.3	0.4	1.1	6.7
N	34	34	34	34	34	34	34	34	34	15
Present
Mean	10.6b	33.7b	8.4	0.81b	0.33b	17.1b	18.5b	1.7b	4.6b	29.4b
s.d.	0.9	0.1	8.0	0.83	0.16	7.3	8.9	0.4	1.4	20.0
N	39	39	39	39	39	39	39	39	39	26

^†Different letters between April and June denote significantly different means (α=0.05), within a variable; when letters are absent, no statistical difference between means was found.