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How do seaweeds attach to rocky bottoms in estuaries?

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Diagram showing four main types of estuaries: salt wedge, partially mixed, vertically homogeneous, and fjord. Each panel illustrates river and seawater mixing patterns, with arrows indicating the direction of saltwater and freshwater flow. — estuary Four main types of estuaries: (A) salt wedge estuary, (B) partially mixed estuary, (C) vertically homogeneous estuary, and (D) fjord (black arrows indicate salt water and white arrows fresh).

In estuaries where water movement is strong enough to clear away sediment and expose rocky bottoms, rooted plants are replaced by seaweeds.1

These organisms attach themselves to hard surfaces using a specialized, rootlike structure known as a holdfast. Unlike the roots of higher plants, holdfasts do not function to extract nutrients or water from the substrate. Instead, their sole purpose is to provide a firm anchor, allowing the seaweed to cling to the rocky bottom and resist the force of currents.2134