*2.2. Sample Collection*

Two antipatharian species, which were the most abundant species at the sites, the bottle-brush-like *Cupressopathes abies* (Figure 2a) and the whip-like *Stichopathes maldivensis* (Figure 2b), were sampled. Six colonies of each species were sampled at a 20 m depth and five colonies of each at a 40 m depth in November–December 2018 (permit no. 089/19/MESipReS). Colony height ranged between 25 and 35 cm for *C. abies* and 200 and 250 cm in height for *S. maldivensis*. It has been shown that Symbiodiniaceae abundance and clade can vary at the intra-colony level [24]; therefore, three samples 3–4 cm long were taken from each colony at the top, the middle and the base, making a total of 66 samples from 22 separate colonies. Half of every sample was preserved in 100% ethanol for subsequent molecular analysis. The other half was fixed in 3% glutaraldehyde buffered with 0.1 M sodium cacodylate before rinsing and storing them in 70% ethanol for later morphological study. Due to the minute size of their polyps (~0.7 mm, Figure 2a), prior to fixation, samples of *C. abies* were placed in a 5 g/L magnesium chloride solution buffered in filtered sea water in order to relax the polyps and tentacles so as to facilitate further observation.

**Figure 2.** (**a**) The bottle-brush-like *Cupressopathes abies* and (**b**) the whip-like *Stichopathes maldivensis*, with an image showing a section of two individual polyps in the bottom right corner. Scale bars of polyp images = 1 mm.
