Prickly Seaweed

Overview

Prickly seaweed (Acanthophora spicifera) is a highly adaptable red alga found throughout tropical and subtropical marine environments worldwide. It is well-known for its success as an invasive species in regions like Hawaii, where it frequently outcompetes native reef algae.

Appearance

This alga features erect, cartilaginous, and solid cylindrical branches that typically reach up to 40 cm in height. Its color is highly variable, ranging from shades of red and purple to yellow, orange, or brown, often appearing darker in high-energy intertidal zones. The main branches are characterized by numerous, radially arranged, spine-like branchlets, while the tips of the branches are pyramidal with incurved, hair-like structures called trichoblasts. The plant attaches to hard surfaces via an irregularly shaped, discoid holdfast.

Distribution & habitat

Acanthophora spicifera has a nearly continuous global distribution across tropical and subtropical seas, including the Atlantic, Indian, and Pacific Oceans. It thrives in shallow, calm reef flats, tidepools, and rocky intertidal benches. While it typically anchors to hard substrates like rocks, basalt ledges, or dead coral, its brittle nature often leads to it being found as free-floating drift algae.

Biology & behavior

This species exhibits significant morphological plasticity, allowing it to adjust its growth form based on environmental conditions such as water motion. It reproduces both sexually and through vegetative fragmentation. Because the thalli are brittle and break easily, these fragments can disperse and establish new colonies, contributing to its status as a highly successful and widespread invasive organism in certain non-native regions.