The term “marine flowers” often brings to mind plant-like organisms swaying in ocean currents, but it doesn’t represent a formal scientific classification. This phrase describes two distinct groups of marine life. One group consists of the ocean’s only true flowering plants, while the other includes a variety of invertebrate animals that bear a striking resemblance to flowers.
The True Flowering Plants of the Sea
The only true flowering plants, or angiosperms, that live entirely in marine environments are seagrasses. Unlike seaweed, which is a type of algae, seagrasses possess the same fundamental structures as terrestrial plants: roots, stems, and leaves. They are more closely related to lilies than to land grasses and evolved from terrestrial plants that recolonized the ocean millions of years ago. These plants anchor themselves in the seafloor sediment with rhizomes, which are horizontal stems that help them spread and form underwater meadows.
Seagrasses reproduce while fully submerged in seawater. Most species are dioecious, meaning individual plants are either male or female. To reproduce sexually, the male flowers release pollen into the water, which is then carried by currents to fertilize the female flowers. This underwater pollination is a unique adaptation among flowering plants. Common examples include Turtle Grass, a primary food source for green sea turtles, and Eelgrass, which thrives in cooler, temperate waters.
These plants also reproduce asexually through their rhizome systems. The rhizomes spread horizontally beneath the sediment, sending up new shoots and expanding the meadow. This method can create genetically identical clones covering large areas; one known clone of Neptune grass in the Mediterranean Sea spans 15 kilometers. While efficient, this clonal spread can make meadows vulnerable to diseases and environmental changes.
Marine Animals That Resemble Flowers
A group of marine invertebrates is often mistaken for flowers due to their appearance and sedentary nature. These animals, which include sea anemones, corals, and feather duster worms, are part of a group sometimes called “anthozoans,” meaning “flower animals.” Their petal-like structures are actually tentacles or specialized gills used for capturing food. Unlike plants that produce their own food through photosynthesis, these animals are consumers.
Sea anemones anchor themselves to rocks and extend tentacles armed with stinging cells to catch small fish and crustaceans. Coral polyps, which are related to anemones, are small animals that build the structures known as coral reefs. Each polyp has a circle of tentacles for feeding, and together, millions of polyps form a colonial organism. Their colors and collective shape often give the impression of a field of flowers.
Other animal mimics include feather duster worms, which live in tubes attached to rocks or coral. The “flower” part of these organisms is a crown of feathery appendages called radioles, used for both breathing and filtering plankton from the water. If disturbed, these worms can retract their colorful crowns into their tubes.
Ecological Roles of Marine “Flowers”
Both seagrasses and their animal counterparts perform foundational roles in their respective ecosystems. Seagrass meadows are productive habitats that offer food and shelter to a wide array of marine life. They serve as nursery grounds for many juvenile fish, providing protection from predators. Animals like manatees and dugongs graze on the seagrass, making these meadows a food source for large herbivores. The root systems of seagrasses also stabilize the seabed, preventing erosion and improving water clarity by trapping sediments.
The flower-like animals, particularly coral polyps, are ecosystem engineers that construct the frameworks of coral reefs. These reefs house a high level of biodiversity, offering habitats for thousands of species of fish, invertebrates, and algae. The structure of the reef provides shelter and hunting grounds, supporting food webs.
Vulnerability of Marine Habitats
The ecosystems that support marine “flowers” face threats from human activities and climate change. Seagrass meadows are susceptible to coastal development and pollution. Runoff containing excess nutrients and sediments can cloud the water, reducing the light available for photosynthesis and suffocating the plants. Damage from boat propellers and dredging also destroys these habitats by uprooting the plants and their rhizome systems.
Coral reefs are sensitive to changes in ocean temperature and chemistry. Rising sea temperatures caused by climate change can lead to coral bleaching, where corals expel the symbiotic algae living in their tissues, causing them to turn white and starve. Ocean acidification, a consequence of increased atmospheric carbon dioxide, hinders the ability of coral polyps to build their calcium carbonate skeletons. The degradation of these habitats threatens the flower-like animals and the countless other species that depend on them.