## 4 Discussion
### Effect of Bio-Attachment on the Degradation of Shard DL  
The attachment of marine organisms is a significant factor influencing the degradation of ceramics salvaged from water. The marine organisms attached to the surface of DL mainly included unitary organisms (Serpulids and solitary coral) and modular organisms (coralline algae, red coral, and Bryozoans). The unitary organisms were firmly bound to the defective surface of the sample, likely due to the bio-calcification and bio-mineralization processes. When the Serpulids built their attached tubes, the larvae would push the tube material away from their bodies, thus ensuring maximum attachment to the sample surface [44; 45]. The epidermal cells of the coral larval ectoderm first attached to the sample surface, which served as the bio-mineralization site for secreting calcareous skeletons. The formation of skeletons began with the generation of the bottom; the firm bond between the bottom and the pits on the matrix surface facilitates the solid, long-term attachment of the single coral [46]. After the bottom walls of unitary organisms and the defective surface formed a mechanical lock-key interlocking structure, the hard calcareous skeletons firmly attached to the surface could alleviate the abrasion caused by sea wave-borne debris and the impact of water flow fluctuations on the local surface of the sample [47]. Unitary organisms' compact skeletons could seal open pores and cracks, reducing the deposition of insoluble pollutants and decreasing the permeability of soluble salts like chlorates and sulfates [48; 49]. If mechanical methods alone, such as scalpels, were used to remove these organisms, the underlying surface could suffer irreversible damage. Hence, it is recommended to first soak the sample in dilute acids, such as oxalic acid or EDTA disodium salt solutions, to weaken the bond before mechanical removal [5]. Modular organisms' group skeletons covered extensive areas and reinforced surfaces damaged by mechanical action, thereby withstanding ongoing scouring by sea debris. However, interspace suggests weaker bonding between modular organisms and the stoneware surface compared to unitary organisms, due to the variability in spatial growth among individuals and genetic variations affecting the group skeleton arrangement [15]. The open cellular structure of coralline algae and the net-like structure of red coral did not effectively block inorganic pollutants, which could thus infiltrate and deposit in the stoneware body and pore channels, possibly contributing to chemical alterations of the glaze [13]. The remains of modular organisms could generally be removed by simple mechanical methods. Previous studies have shown that the adhesives and acidic secretions of macro-foulers can erode various materials, including concrete [38; 50], metals [34; 51], and stone relics [12; 43]. Acidic carboxyls generated during metabolism can complex with metal ions, such as Fe, Ti, and Ca, causing bio-erosion phenomena such as pitting and micro-boring. However, no significant bio-erosion was observed on DL, which could be attributed to the material properties of the shard itself. Figure 12 illustrates the degradation process of Shard DL. Initially, the outer wall of DL was glazed and smooth, while the unglazed inner wall was rough with defects. In the marine environment, a biological film less than 1000 nm thick formed on the surface. Mechanical abrasion by sea debris roughened the outer wall glaze, creating pores and cracks. Coralline algae attached to the roughened surface, forming mineralized skeletons and secreting substances that attracted macrofouler larvae such as red coral larvae. As a result, the remaining glaze fell off, exposing the body. The unglazed inner wall attracted macrofouler larvae earlier, leading to their firm attachment and growth. Foreign pollutants deposited on both the inner and outer wall surfaces, filling the skeletons of red coral and coralline algae.