Why aren´t there any plantimals on land?

The idea of finding a use for waste from industrial production is of course a great way of increasing ones profits. In Sweden, the paper industry fuels itself to a large extent by using waste products from the plant fiber extraction, and copper refineries nowadays make loads of money on impurities in the copper ore.

Acropora coral

Acropora coral with bands of zooxanthellae

This was not invented by 20ieth century economists, but rather has been the base for the huge success corals have had in shallow, tropical marine areas during several hundreds of millions of years. Basically animals such as corals have waste products consisting of carbon dioxide and nitrogenous and phosphorous compounds. Most animals just get rid of their waste without cashing in on the value such waste can have for other organisms. Plants generally are limited in their growth mainly by limited access to nitrogen and phosphorous and to a lesser but in many cases significant level carbon dioxide. Corals exploit that by in a symbiosis between animal and plant growing small plants, so called zooxanthellae, in compartments just under the skin of the corals. In the extremely nitrogen and phosphorous deficient environment of shallow tropical waters, the waste products of the corals fertilize the environment of the zooxanthellae, leading to the highest production of biomass we know of. Many other marine animals such as jellyfish, anemones, sponges and nudibranchs have this kind of symbiosis, guaranteeing the animal a high availability of energy without investing a lot other than waste products.

 Solarpowered nudibranch

Given that this is a very successful strategy in shallow tropical waters, one would think that some terrestrial animals would have made the same transition and included plants in their bodies as energy providers. It is possible to do such a thing on land, which the success of lichens in many ecosystems bear witness of. However, to my knowledge, no terrestrial animal has such a symbiosis. And, to be honest, it is kind of frustrating that there does not seem to be any good reason for it. Alligators symbiotic with plants would only have to kill a small percentage of what they kill now if they were green and could use plant energy directly rather than first let it go through fish.


Alligator. Wouldn´t it be great to be an alligator with zooxanthellaee?

Also, the very docile daily activity plan of an alligator would be very well suited for a photosynthetic predator.  Maybe, given time, evolution will figure it out. When that happens, remember where you first read about land living plantimals!

Acropora coral

Another Acropora coral with bands of zooxanthellae