Besides surviving what do they contribute? How many varieties are there? Inquiring minds wanna know these things JakobA! That's a beauteous fish. I knew deep beneath the seas much beauty exists. If you do too deep you can't see a thing though. It is very dark way down deep. Isn't it? Thank you for your reply and the video.
Some eat the detritus sinking from near the surface. Those will now provide food for larger fish and on up the chain. They fill a niche. We can only see them in their habitat using undersea drones equipped with bright lights.
Most weeds are flowering plants. Many useful plants are non-flowering. Here is an example of the world's smallest flowering plant: Duckweed. Most people call it pond scum. It's not. The large flower is a lily.
A weed is a plant growing where it is not wanted. A noxious weed is a plant considered harmful to environment or animals. My wife grows rhubarb in the garden to make pies and cakes (rhubarb-strawberry pie is my favorite), However, we visited Chili and found that there (on Pacific coast) it is considered a noxious weed!! One persons weed, is another's flower.
I understand your question, but I don't know how to answer it. "Weed" has a negative connotation and is usually used in that sense, but I had occasion to look this up a few years ago. The following is from Wikipedia.
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place". Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks. Taxonomically, the term "weed" has no botanical significance, because a plant that is a weed in one context is not a weed when growing in a situation where it is in fact wanted, and where one species of plant is a valuable crop plant, another species in the same genus might be a serious weed, such as a wild bramble growing among cultivated loganberries. Many plants that people widely regard as weeds also are intentionally grown in gardens and other cultivated settings, in which case they are sometimes called beneficial weeds. The term weed also is applied to any plant that grows or reproduces aggressively, or is invasive outside its native habitat.
JakobA the unAmerican. 