Sea plants

Sea plants is a gardening heading, not a biological one, and the things filed under it are not one kind of thing. The honest dividing line is plumbing. A seaweed has none: no roots, no vessels, no stem in any working sense, and every cell trades gas and nutrients straight with the water touching it. That is why a seaweed can be thin and flat, why it needs no soil, and why the pad at its base is glue rather than a root. Seagrasses and mangroves are true plants with pipes inside them, and pipes need an anchor and a rooting medium, which is why they grow in sand and mud while the algae grow on rock.

Everything here is governed by one physical fact: light does not last in water, and it does not fade evenly. Red is gone within the first few meters, then orange, then yellow, and what remains at depth is blue. Anything photosynthetic below the shallows needs pigments tuned to catch blue light, which is the real reason the sea's plant life is not uniformly green and why the deepest growth is a thin crust rather than a leafy thing.

This section is where the food on a reef starts. The parrotfish scraping rock, the surgeonfish shoal, the urchin under a ledge, the green turtle in a bay and the dugong on a meadow are all living directly on what grows here, and everything that eats them is living on it one step removed.

On this coast the three are not spread evenly, and none of them is abundant. Algae are everywhere and largely unnoticed, because they are cropped as fast as they grow. Seagrass forms real meadows only in sheltered sandy bays. Mangroves need still water and something more than bare desert shore, so they stand in scattered patches where wadis reach the sea. The 🌊 Red Sea has no rivers and almost no rain, and that shortage sets the ceiling for all of it.