Re: Re: What is a carnivorous plant?

Liane Cochran-Stafira (
Tue, 20 Jun 1995 10:00:20 -0500

> Geez, you've never heard of an algae bloom that used up all
>the oxygen and killed off all the fish?
>> Ah, but only red marine algae - I've encountered the argument
>> before, but I find it a little too spurious even for me :) even
>> with the supposed nutritional benefit to the algae. I guess the
>> main objection is that there appears to be no attraction or trapping
>> of prey, just blanket poisoning/suffocation.
>Hi guys,
> I read in Discover last year that these are indeed very carnivous.
>after the alge kills the fish and ect they change their morphology
>to become animal like. They give up using chlorophyll move under their
>own power similar to amoeba and eat the dead. I forget the whole of
>how this was found but after the red tides researchers weren't finding
>anywhere the number of alge they were expecting and started looking.
>Reading this really shocked me... it still doesn't sound possible.
>I guess we are going to have to add algae to our collections. I
>beleive there is some debate as to whether these are really plants or
>not though.

Hi Dave,

A number of the algal groups resort to heterotrophic means of acquiring
carbon when grown under reduced light. Some resort to feeding on bacteria,
while others can capture small protozoans. Some even just absorb dissolved
nutrients. The example you cite is the first reference I've heard of that
lists algae as consumers of animal matter, although there are some examples
of algae as parasites in animals. I haven't seen this Discover article and
would really like to read it. Do you remember which issue it was in?

A carnivore usually refers to an organism that has some morphological or
behavioral adaptation for capturing and consuming prey. Thus, Sarracenia,
whether they produce enzymes or not, have special leaf adaptations for
capturing prey, and would be considered carnivorous. Likewise, if it can
be shown that some of the other plants mentioned in this discussion have
the beginnings of such capture mechanisms, it could be that they represent
species evolving towards carnivory. For the algae example, if it's true
that the toxins produced by the various dinoflagellates and other red tide
algae are produced to kill fish so they can be consumed, I don't suppose
it's too far fetched to consider them carnivorous also. If the toxins have
some other function, and the fish kills and subsequent consumption of the
dead material are incidental, then I would consider the algae to be
decomposers or saprophytes rather than carnivores.

Also, on the topic of "algae as plants" - they are *NOT* considered to be
members of the kingdom Plantae. Algae are a rather messed up group in
terms of their phylogeny. Although placed in the kingdom Protista (in the
old 5 kingdom system), many species have very little relationship to other
members of the kingdom such as the protozoa or even to other algal groups.
The only algae that have any real relationship to higher plants are members
of the Characeae, which are believed to be ancestral to higher plants.

My $.02 worth,
Liane Cochran-Stafira