Table 2.

Frequencies and percentages of interaction classes by interaction type summarizing 170 studies manipulating two or more stressors in marine and coastal systems reclassified from Crain et al. (2008). Directional interaction classes are additive (AD), +synergistic (+S), −synergistic (−S), +antagonistic (+A), and –antagonistic (−A). (X) indicates an interaction class is not applicable for the interaction type. Full details of each study/interaction are given in the Table S1

Interaction Type	Classification	Frequency	%
Double negative	AD	15	21
(70 instances)	−S	19	27
(41% of Total)	+S	0	0
	−A	36	51
	+A	X	X
Double positive	AD	14	37
(38 instances)	−S	4	11
(22% of Total)	+S	9	24
	−A	X	X
	+A	11	29
Opposing	AD	12	24
(49 instances)	−S	10	20
(29% of Total)	+S	3	6
	−A	11	22
	+A	13	27
Negative neutral	AD	3	33
(nine instances)	−S	6	67
(5% of Total)	+S	0	0
	−A	0	0
	+A	X	X
Positive neutral	AD	0	0
(three instances)	−S	1	33
(2% of Total)	+S	0	0
	−A	X	X
	+A	2	67
Double neutral	AD	0	0
(one instance)	−S	1	100
(1% of Total)	+S	0	0
	−A	X	X
	+A	X	X
Total	AD	44	26
(170 instances)	−S	41	24
(100%)	+S	12	7
	−A	47	28
	+A	26	15
Total (w/o direction)	Synergism	53	31
(170 instances)	Antagonism	73	43
(100%)	Additive	44	26