The answer is:
The author includes information in a list mid way through the article. What the author implying with information about tropical waters and food is as follows:
Tropical waters: Like crocodiles and alligators, plesiosaurs would have needed the warmth of the sun to regulate its own metabolism. The crocodile has the ability to regulate its own metabolism. Being a cold-blooded animal allows the crocodile to survive and adapt. That means Nessie would have to regulate its own metabolism by cooling off in the Loch Ness river or sunbathing for warmth.
Let's now look into food:
The power of the sun helps create algae, algae is then consumed by plankton as the base for marine life.
"If there is a group of Nessies, then even more food would be needed. Because the loch is full of silt (underwater dust) not much light gets into the deepest areas. So the food chain, which depend on plankton, is very weak at its base..." from the BBC 'proves' Nessie does not exist. 27 July, 2003.
The BBC argues that because of suspended particles the light cannot creates sufficient nutrients to support a vast marine life.
Plesiosaurs would need a large quantity of food. As a result, there is probably not enough food to support such a large creature according to the BBC.