Table 3.
Bottom surface area of the study systems was coarsely divided into three substrate classes: “hard” (gravel, stones, boulders and base rock), “soft” (silt, clay and mud) and “sand”. The average proportion of these substrate classes in the different depth intervals used in this study was derived from the Swedish (EU Interreg IVA-funded projects “ULTRA” and “SUPERB”, County Administrative Board of Västerbotten) and Finnish [The Finnish Inventory Program for the Underwater Marine Environment (VELMU)] monitoring programmes. An average of the Swedish and Finnish data was used for the Bothnian Bay, whereas only the data from Sweden were used for the Öre estuary. Macroalgal cover was only available from Sweden (EU Interreg IVA-funded projects “ULTRA” and “SUPERB”, County Administrative Board of Västerbotten), but is assumed to be valid also for the Finnish coastline. There are a few percent of the Finnish bottom surface area that are “unclassified” (not shown)
| Depth interval (m) | Bottom substrate, Sweden | Bottom substrate, Finland | Macroalgal cover | |||||
|---|---|---|---|---|---|---|---|---|
| Hard | Soft | Sand | Hard | Soft | Sand | Soft and sand | Hard | |
| (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | |
| 0–1 | 39.2 | 29.4 | 31.4 | 25.5 | 33.9 | 36.1 | 24.9 | 4.4 |
| 1–3 | 46.0 | 25.7 | 28.3 | 42.1 | 27.0 | 29.8 | 17.2 | 3.5 |
| 3–6 | 60.5 | 20.1 | 19.4 | 52.9 | 23.6 | 22.8 | 5.1 | 1.3 |
| 6–10 | 68.1 | 19.5 | 12.4 | 53.6 | 28.0 | 17.8 | 0.8 | 0.2 |