*3.2. 1st Mariculture Trial: Testing Materials and Attachment Procedures*

The air concrete material was found to be unsuitable for further experimentation, as none of the explants attached to it (Table 1 (a)). In addition, the material was positively buoyant in seawater, which hampered easy handling. There was no difference in preference between white and black PVC (80% survival for both plates), as sponges attached equally well to both substrates without showing any signs of disparity (Supplementary Figure S1a,b, Table 1 (a)). Cable-ties gave a better recovery percentage than super glue (80% vs. 60%), but, in addition to increasing handling time, cable-ties also triggered the dispersion of *C. renifomis* explants into two parts for both black and white PVC's (fission; Supplementary Figure S1b). The combinations PVC/chicken wire and cemented PVC/cable-tie were the most successful methods in terms of recovery percentage (all sponges survived on plate). However, the cost of material, plate weight, and handling time were factors favoring the PVC/chicken wire method (Table 1 (a)). Accordingly, PVC/chicken wire method was selected for the 2nd trial.

#### *3.3. 2nd Mariculture Trial: Testing Culture Plate Orientation and Site*

The explants at the polluted site (Supplementary Figure S1c) and pristine site (Supplementary Figure S1d) showed signs of bacterial infections and decay within a week after initiation of the cultures, causing initial losses at both sites (4.8% and 2% of explants deteriorated in the polluted and pristine sites, respectively). Among the explants that survived the initial deterioration, overall survival after six months was slightly better at the polluted site (79% of 238 explants survived at the polluted site and 63% of 245 explants survived at the pristine site; Table 1 (b)). The culture frame at the pristine site was found to be demolished, when revisited in May 2012. It was found 50 m away from the culture site. As a consequence, it was not possible to deduce annual survival and growth rates for the culture at the pristine site. At the polluted site, survival was highest among sponges that were put at an angle of 90◦ or higher (Figure 4). Growth rates were highly variable among treatments (Figure 5), but the average growth at "light" angles of 0–90◦ (−41 ± 38%; negative values points to loss of WW biomass) was significantly lower than the average growth at "shade" angles of 90–180◦ (39 ± 36%; Student's *t*-Test *z* = −3.4, *p* < 0.01, *n* = 5). The 90◦ plate was selected as the preferred culture orientation in Trial 3, based on the survival rate and the ease of operation (photography, measurements, and handling; see Table 1 (b) for details). Photographic measurement of growth was found to be impossible with the

PVC-chicken wire method as a result of continuous movement, splitting, and fusing of *C. reniformis* explants, and epibiont growth. In addition, chicken wire compressed the explants, which may not be beneficial for their development. Also, installing the large 50 × 50 cm PVC plates was time consuming. Therefore, smaller (25 × 25 cm) PVC plates were used in Trial 3 and superglue was selected as the attachment method.

**Figure 4.** 2nd mariculture trial, polluted site, June 2011–June 2012; survival percentage of *C. reniformis* explants on PVC plates with various angles (0–90◦ light represents PVC plates with greater light

exposure and 90◦ shade −180◦ plates receiving less light exposure).

**Figure 5.** 2nd mariculture trial, polluted site June 2011–June 2012; growth rate as percentage wet weight increase of *C. reniformis* explants on PVC plates with various angles (0–90 light represents PVC plates with greater light exposure and 90 shade −180 plates receiving less light exposure; 25 explants for each plate).
