Research study 3

Trochid snails belonging to the genus Calliostoma are generally thought to be consumers of kelp or of organisms, such as bryozoans and diatoms, that grow on kelp.  A study at Friday Harbor Laboratories, Washington discloses that at least 2 species, annulatum and variegatum, mainly eat campanularid and sertularid hydroids. 

Of 56 individuals of annulatum collected and dissected, 54 are noted to have guts filled with hydroid fragments, and observation of about 100 individuals in the field shows that nearly all are eating hydroid polyps along with their eggs. When attacking a hydroid polyp, annulatum makes contact with a tentacle, grabs hold of the stem or hydranth with its jaws, and severs it with its radula.  These pieces of stems, in short segments, can be found in the gut.  This species may also attack sea anemones, most notably, brooding anemones Epiactis prolifera.

Of 8 variegatum specimens examined, 7 have guts filled with hydroids. 

In comparison, all intertidal specimens of ligatum have guts filled with detritus, while subtidal representatives of ligatum have guts filled with unidentifiable debris. This species will, however, eat hydroids when kept in the laboratory, but not apparently in the field.  Perron 1975 Veliger 18: 52. Photograph of C. variegatum courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC. Photos from upper Left, clockwise: C. annulatum, C. variegatum, C. ligatum.

A study on foods of Calliostoma canaliculatum at Hopkins Marine Station, Pacific Grove, California indicates that not only do they feed by scraping diatoms off the surfaces of kelps, but they are likely scavengers on dead flesh as well.  Keen 1975 Veliger 17: 413. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

Calliostoma canaliculatum

Research study 6

What governs feeding preferences of black turban-snails Chlorostoma funebralis?  A study in Santa Cruz, California that assesses preference of the snails for 13 species of common brown algae in pairwise laboratory feeding tests and in field-array tests shows that content of phenolics is the most important determinant of palatability, while other features such a phagostimulants and nutritional content appear to play lesser roles.  High levels of phenolics in brown algae are a generally effective feeding deterrent against a variety of invertebrate herbivores, including sea urchins, crustaceans, and various gastropods. 

Tests of feeding preferences of C. funebralis show stronger preferences for brown algal-species with low amounts of phenolic compounds than for ones with high levels of phenolics.  Specifically, the 6 most preferred algal species contain an average of 0.8% dry-mass phenolics, while the 7 least preferred species conain an average of 4.5% phenolics. The former are mostly Laminariales, while the latter are mostly Fucales.  Interestingly, with the exception of the feather-boa kelp Egregia menziesii, relatively few of the most preferred species are eaten in the field by C. funebralis. Another possible determinant of feeding preference, namely, nitrogen content, seems not to be important.  Thallus toughness also does not appear to be important in determining overall preferences, but may play a role in determining choices among algae low in phenolics.  The author suggests that evolution of feeding preferences in C. funebralis may owe more to avoidance of algal defenses, with positive aspects of food quality such as nitrogen content probably playing a lesser role.  Steinberg 1985 Ecol Monogr 55: 333; see also Steinberg 1984 Science 223: 405.

NOTE  these polymers of the simple phenolic phloroglucinol (1,3,5-trihydroxybenzene) are common components of brown algae

NOTE nitrogen content of the 13 species averages only 1-3% of dry mass.  It actually correlates positively with feeding preferences of C. funebralis, but the author notes that this may actually owe to an indirect effect of a significant negative correlation between algal nitrogen content and phenolic content

In a follow-up article to Research Study 7 above the same author directly tests the deterrent effects of phenolics.  Three invertebrate herbivores, including Chlorostoma funebralis and C. brunnea are presented with agar discs containing different amounts and types of phenolic substances, and the amounts eaten over a 48-h period monitored and compared.  All phenolics deter feeding by Chlorostoma at concentrations of 5mg ^. mg^-1 in the agar discs, but whether the tests are being done at “physiological” levels, in other words, at levels as found naturally in the seaweeds, is not clear (see histogram). Steinberg 1988 J Exp Mar Biol Ecol 120: 221.

NOTE  algal phenolics used include the monomeric phenolic phloroglucinol and other poyphloroglucinols extracted from the brown algae Fucus vesiculosus, Halidrys sp., and Eisenia arborea.  In the data the phenolics are indicated by alga of origin, with 2 extracts from Fucus being used, and also commercial (from terrestrial plants) tannic acid being included.  Fucus vesiculosus inhabits Atlantic shores, but its polyphenolics are thought to be similar to those in west-coast Fucus spp.

NOTE  the third species is the sea urchin Strongylocentrotus purpuratus; only results for C. funebralis are considered here