Macroalgae are invaluable constituents of marine forest environments and important sources of material for human needs. However, they are currently at risk of severe decline due to global warming and negative anthropogenic factors. Restoration efforts focus on beds where macroalgae previously existed, as well as the creation of new marine forests. Some artificial seaweed reefs (ASRs) have succeeded but others have failed; the contributions of ASRs to marine forest formation have been not fully determined. Here, we review ASRs, the benefits of macroalgal forests, threats to macroalgae, restoration, and marine forest formation to explore the current status of ASRs. The published literature indicates that ASRs have played critical roles in marine forest formation; notably, they support the establishment of submerged aquatic vegetation beds that allow ocean macroalgal afforestation. ASRs have evolved in terms of complexity and the materials used; they can sustainably mitigate marine deforestation. However, continuous reviews of ASR performance are essential, and performance improvements are always possible.

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Oyster reefs are currently at risk of severe decline due to dangerous human interference and its aftermath; hence, artificial oyster reefs (AORs) have been utilized for their restoration. AORs with high vertical reliefs interact with the surrounding flow, constitute a reverse flow, and create a wake region in which concentrated nutrients and food organisms exist. However, the correlations of the structural characteristics of an AOR with its wake regions have not been studied. Thus, we established 96 AOR models, carried out flow analyses, and obtained their wake volumes, considering shell orientation, composition, penetration depth, and growth stage. We found that the growth stage is the most critical parameter for establishing a normalized wake volume. This implies that the number of oyster shells (N) is the most critical factor in securing a normalized wake volume, in which their correlation was linear and significant (R2=0.89). We also found that the correlations of the normalized wake volume with blocking and surface complexity indices were linearly significant, respectively. Additionally, wake volume efficiency increased with the number of oyster shells; specifically, the criterion for wake volume efficiency of EI (efficiency index) ≥ 2.0 was satisfied when N≥50 per 900 cm2.