Each type of seaweed has a fixed tidal level, primarily related to the types and proportions of pigments it contains. Different pigments require different wavelengths of light, and the distribution of algae is affected by changes in light intensity and quality. Generally, in darker areas or the deep sea, phycoerythrin and phycocyanin absorb blue and green light more effectively than chlorophyll. Therefore, green algae containing only chlorophyll and carotene tend to inhabit shallower waters. Red algae are more common near the low tide line and in the deep sea. Furthermore, factors such as topography, seabed composition, temperature, humidity, salinity, tides, waves, ocean currents, pollutants, animal foraging, and competition among algae also influence seaweed growth and distribution.
Taking common seaweed along the coast of Taiwan as an example, in the spray zone where seawater doesn't reach but waves can, from late autumn to early spring, the northern and northeastern coasts are mainly covered with seaweeds such as laver, nori, sea lettuce, and sea lettuce, while the southern and eastern coasts are dominated by slender twig algae, sheath algae, and sea lettuce. These seaweeds have a protective gelatinous layer, allowing them to withstand prolonged drought and intense heat. They can often be exposed to sunlight for three to five days without withering, demonstrating their remarkable resilience. However, in summer, the spray zone is completely bare.
The intertidal zone is divided into three sections: Upper, middle, and lower, depending on the tidal changes (spring and neap tides). In the upper intertidal zone, green algae are predominant, commonly including membranous Ulva, tubular Lithocarpus, or filamentous Cladosporium. These algae can withstand strong sunlight and the daily changes in moisture caused by the two ebb and flow of the tides, especially in winter and spring, often forming a lush, verdant "green carpet" on the sea-eroded platforms. In summer, like the spray zone, the rocks in this area are mostly bare, but they can still be found in tidal pools or shaded areas.
These colorful algae in the intertidal zone gradually disappear in summer, but in the subtidal zone below the intertidal zone, which is covered by seawater year-round, various algae can be seen flourishing all year round. Common ones include Sargassum, Pine seaweed, Pteridophyta, Seaweed, Gracilaria, Celosia cristata, Eucheuma, Seaweed, and Centipede seaweed, etc. Sargassum, in particular, often grows in large quantities in June and July, forming small Sargassum seas.
