*2.4. Mortality and Morbidity*

Skin ulceration begins with one or more small white ulcerative spots, followed by the appearance of deep and enlarging ulcerative lesions, resulting in the exposure of the underlying muscles and spicules [24] (Figure 1D). Mortality and morbidity were calculated as follows:

$$M\_t = \frac{D\_\varepsilon}{T} \times 100\%$$

$$M\_b = \frac{D\_i}{T} \times 100\%$$

where *Mt* is the mortality, *Mb* is the morbidity, *De* is the number of dead sea cucumbers, *Di* is the number of diseased sea cucumbers, and T is the total number of sea cucumbers.

#### *2.5. Crawling Behavior*

Crawling behavior of sea cucumbers is composed of five stages (Figure 1G) [25]. A sea cucumber extends its body and then enters the contraction stage. The sea cucumber contracts from the back of the body to the middle and front in sequence. Finally, it returns to a static state [25]. Sea cucumbers complete each crawling cycle as described above, which is counted as one occurrence of crawling behavior. Sea cucumbers were randomly selected from each group and were placed into cubic plastic boxes (length × width × height: 60 mm × 47 mm × 45 mm). Two grams of mixture of sea mud and commercial feed at a ratio of 1:4 was put in the bottom of the box, and the number of occurrences of crawling behavior was counted within 1 h by using a digital camera (FDR-AXP55, Shanghai Suoguang Electronics Co., Ltd., Shanghai, China) (*n* = 6).

#### *2.6. Feeding Behavior*

Feeding behavior refers to the process of sea cucumbers ingesting food through its mouth tentacle activity [26]. Sea cucumbers stretch their tentacles out of their mouths, then extend their tentacles to grab the food, and finally capture the food into their mouths by contracting their tentacles [26]. One occurrence of tentacle activity was counted if sea cucumbers completed one tentacle activity cycle. Sea cucumbers were selected from each group and placed into cubic plastic boxes (length × width × height: 60 mm × 47 mm × 45 mm; Figure 1F). Two grams of mixture of sea mud and commercial feed at a ratio of 1:4 was put in the bottom of the box, and the duration of tentacle activity of all sea cucumbers

within one hour was recorded by using a digital camera (FDR-AXP55, Shanghai Suoguang Electronics Co., Ltd., Shanghai, China) (*n* = 6).
