Flowering Plants
Very few of the true flowering plants have moved back into the sea. A notable exception is Marine Eelgrass (Zostera spp.) which is particularly widespread in estuarine conditions. This plant is extremely important to many coastal animals, providing safe shelter for some and nutritious grazing for others - it is one of the favourite food plants of the Dugong for example. The ecological importance of the eelgrasses has been widely studied, see: A Study of Eelgrass in Buzzards Bay.
Algae
Seaweeds look plant-like, but they are not very closely related to the flowering plants. They come in red, brown and green varieties and are usually fixed to the seabed in shallow coastal habitats and on the seashore. (A notable exception is Sargassum which sometimes establishes populations that float in the open ocean, e.g. The Sargasso Sea).
Diatoms and Dinoflagellates
Far and away the most important plants in the sea are small to microscopic. There are many different types of organism found in the phytoplankton, but the Diatoms and Dinoflagellates are arguably the most important. Most people will never get to see a diatom because they are too small, but although they might be almost invisible they manage to feed vast numbers of marine animals.
Size Matters
We are used to the idea that you need a lot of plants to feed a relatively small number of grazing animals, and that is often true on land. In the sea, however, we find that a relatively small number of tiny plants can feed vast numbers of much larger animals. This is maybe best explained by imagining that you have two different ways to feed yourself and all your friends – one way is to buy entire cows, the other to feed them on hamburgers which have the amazing ability to reproduce themselves every half-hour. You would need to keep a lot of cattle to supply everyone with enough meat, but only a few of the ‘magic’ hamburgers would be enough. (The total weight of all the cows would be enormous compared to the weight of a few hamburgers!). It is rather like that in the sea – the small phytoplanktonic plants grow and reproduce at a phenomenal rate, so relatively few of them suffice.
Black Smokers
Hydrothermal Vents in the deep ocean sustain chemosynthetic bacteria which effectively replace plants as the ultimate food source in these unique locations. Entire ecosystems exist around these volcanic outpourings which owe nothing at all to photosynthesis. This is one of the very few examples of a food chain that does not begin with plants which get their energy from the sun.
Other articles by John Blatchford
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