refugium good or bad?

Did a search for “Chaetomorpha Toxins” and didn’t find anything bad about Chaeto so far. Did find this paper that states that catches of moluscs and fish increased in areas where Chaeto presumably absorbed toxins in a polluted bay:

http://www.ifremer.fr/docelec/doc/2005/publication-2131.pdf

Consequences to the Ecosystem

The effects of seaweed proliferation and accumulation on

the biotope and the environment are both numerous and varied.

First, the seaweed biomass plays an important role in purifying

the medium by absorbing excess nutrients and by accumulating

some toxins (BRAULT, 1983). A primary function

of excessive macroalgal development appears, therefore, to be

the abatement of pollution in coastal ecosystems. Taking into

consideration the entire cycle of growth and decay of the seaweed,

the Venice Lagoon, for example, acts as an important

denitrifying reactor (SFRISO and MARCOMINI, 1994).

Ulva concentrates several metals from water and is sometimes

used to assess the level of this type of pollutants (MALEA

and HARITONIDIS, 2000).

Associations between macrophytes and marine animals are

often considered to be positive. In some cases, seaweed proliferations

provide a supplementary food source which can

have a favourable effect on the development of herbivores.

Another significant ecological role of excessive growths of algae

is the provision of habitats and refuges against predators.

For instance, LENANTON et al. (1985) noted that an increase

in fish catches followed an increase in the biomass of Cladophora

and Chaetomorpha, while VIRNSTEIN and CARBONARA

(1985) reported high densities of small animals (peracarid

crustaceans, gastropod molluscs, etc.) in Gracilaria drift

beds. These proliferations do, however, pose significant fouling

problems in aquacultural areas.

Moreover, the seaweeds involved in the proliferations appear

not to be very numerous in terms of species, but represent

a stronger proportion of the algal community, with the

growth being selective according to their degree of tolerance

of pollution and to their affinity for the nutrients. The most

sensitive species regress in quantity or disappear in favour

of more tolerant species.

So even though Chaeto can harm coastal regions by shading the organisms underneath, it also helps to clean polluted coastal waters. I'll keep reading the search results, but as of now I haven't seen anything about Chaetomorpha being toxic.