Although one thinks of chitons as being herbivores, some species ingest a fair bit of animal matter during their foraging.  This is shown in gut analyses of 4 Mopalia species collected around San Francisco Bay, California.  Diets of the 4 range from 15-59% animal matter by volume, with M. hindsii being the most carnivorous.  Animals eaten are mostly encrusting types such as bryozoans, sponges, and hydroids, but small barnacles and mussels may be taken in, as well as barnacle cyprids and other larvae.  Barnawell 1960 Veliger 2: 85.

Another animal-eating species is the veiled chiton Placiphorella velata but, unlike the mopaliids featured in Research Study 1 above, Placiphorella is predatory. It feeds by trapping small crustaceans and other invertebrates under its raised veil.  The veil is fringed with sensory tentacles and is often quite colorful.  When a prey is sensed within the canopy of the veil, the chiton drops it quickly down, trapping the prey between the veil and the substratum.  Feeding is by radular scraping. No research seems to have been done specifically on the diet or feeding behaviour of veiled chitons. Photograph on Left courtesy Ron Long, Simon Fraser University, Burnaby, British Columbia.

NOTE a deep water species P. pacifica (= ushakovi) lives on the west coast from Alaska to Mexico.  Smith 1974 Veliger 17: 159

These 2 photographs, both of aquarium-held specimens,
show the arrangement of foot, mouth, sensory tentacles,
and veil in Placiphorella velata. 1X for each

In the Port Renfrew area of British Columbia, black-leather chitons Katharina tunicata feed principally on the brown alga Hedophyllum sessile.  Feeding rates vary during the year, with seasonal lows occurring during autumn and winter (see graph upper Right).  Interestingly, the seaweed varies seasonally in energy content, with values during autumn and winter being almost twice as high as at other times of the year.  Thus, overall energy intake of Katharina remains steady during the course of the year.  Locomotory and other activities are much less during the winter season but, as Katharina and other chitons in this area spawn in the early springtime, perhaps the extra energy is used in building gonads.  Himmelman & Carefoot 1975 J Exp Mar Biol Ecol 18: 139.

Cyanoplax hartwegii eats at least 24 different algal species, along with diatoms, surfgrass Phylospadix sp., and sponges.  In Silvetia-compressa beds, 80% of the diet is made up of this algal species.  In crevices, the red algae Hildenbrandia sp. and the green alga Cladophora sp. comprise most of the diet.  In high-level tidepools the red algae Condracanthus spp. and Hildenbrandia sp. comprise 40% of the diet.  Robb 1975 Veliger 18(Suppl): 34. Photo courtesy Jim Watanabe, Hopkins Marine Station, Pacific Grove, California (photo is 1.2X life size) and calphotos.

NOTE  although expressed by the author in this way, it is not a true interpretion of the data.  The author’s data show only that identifiable bits of Silvetia are present in gut contents of 80% of 65 individuals dissected

Mopalia lignosa include a variety of macro-algae (13 species of red algae, 7 species of green, and 3 species of brown) in their diets.  Analysis of gut matter in individuals from 3 different sites show the following %-volume components: 16% diatoms, 16% Ulva , 29% rocks and sand, <5% other algae. Fulton 1975 Veliger 18 (Suppl): 38. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

Nuttallina californica in areas around Monterey, California eat a variety of red and green algae.  A comparison of what is eaten with what is available in the habitat suggests a preference for the erect, branching coralline alga Corallina sp. and an avoidance of crustose corallines (e.g., Lithothamnion spp.).  The author suggests that this may owe to the adaptive morphology of Nuttallina’s radula, but does not provide details.  Nishi 1975 Veliger (Suppl) 18: 30.

During juvenile and adult life, lined chitons Tonicella lineata are commonly associated with coralline algae, and it is likely that this substratum acts to induce settlement in the larvae.  A survey of 3 sites on the Montery Peninsula occupied by T. lineata shows that corallines comprise 65-90% of algal cover. 

In one low-intertidal habitat where corallines make up 65% of the cover, diets of Tonicella are 60% by volume corallines (see histogram on Left).  In a nearby subtidal habitat where corallines comprise 100% of the algal cover, 66% of the gut volumes of Tonicella are corallines.

Tonicella lineata in subtidal habitats tend to feed nocturnally.  Daytime is spent digesting.  In intertidal habitats, however, this nocturnal cycle may be interupted by periods of low tide.  Note in the graph on bottom Left that locomotory activity, equated here with feeding, is initiated in late afternoon but interupted just after midnight by the ebbing tide.  Return of the tide around dawn is accompanied by even greater locomotory/feeding activity, possibly a late-stage attempt by the chitons to fill their guts before the onset of full daylight.  Demopulos 1975 Veliger 18 (Suppl): 42.

 

 

 

 

 

 

 

A lined chiton Tonicella lineata and a northern abalone
Haliotis kamtschatkana frequent a coralline-alga
area in Barkley Sound, British Columbia 0.5X

A detailed study of habitats occupied and diets of 6 sympatric species of chitons at Deception Island near Anacortes, Washington shows a degree of resource partitioning by the chitons.  The figure on the Left shows densities of the chitons on a rocky outcropping measuring about 8x5m in area.  The 3 most populous species Katharina tunicata, Tonicella lineata, and Mopalia ciliata tend to be broadly distributed throughout the low intertidal and shallow subtidal regions.  The other 3 species, M. hindsii, M. muscosa, and Lepidochitona dentiens, however, have more restricted intertidal distributions¹.  Nonetheless, there is considerable vertical overlap of several of the species.

Analyses of gut contents show that Katharina has the most generalist-type diet², with diatoms, Ulva, filamentous algae, macrophytes, and some animal matter being present (see histogram on the Right).  Lepidochitona’s diet is primarily diatoms (94% of stomach contents³).  The 3 Mopalia species have comparatively high contents of animal matter⁴ present in their guts (4-25%).  The most notable finding is a general preference for diatoms by all species. 

By comparing % of a foodstuff in the diet with % cover in the species’ habitats, representing an index of selectivity, the author shows preferences for diatoms ranging from 2-5. The selectivity values are indicated by the large-size numbers within each histogram pair for each species, rounded off for visual clarity, with any value significantly over 1 indicating a preference.  The highest selectivity for diatoms (5) is shown by Lepidochitona dentiens, which lives highest on the shore and is the smallest species.  Tonicella lineata exhibits fairly strong preferences for diatoms and invertebrates. The author attributes the high diversity of chitons in the area, in part, to microhabitat resource partitioning.  Piercy 1987 Veliger 29: 388.

NOTE¹  numbers collected of these last 3 species are much less than for the other species, so the data should be interpreted with this in mind

NOTE²  identification of algae, especially macroalgae, is made difficult in the stomachs of herbivores owing to radular maceration and the typical digestive slurry of the contents.  In this respect, the author’s most convincing data may be observations on diatoms because of their relative ease of identification in the gut contents

NOTE³  percentages determined in the study represent the extent of area that a certain food type occupies when the gut contents are spread out on microscope slides

NOTE⁴  this includes bryozoa, hydroids, barnacles, bivalves, gastropods, polychaetes, and some larvae

The diet of black leather chitons Katharina tunicata in the Pile-Point area of San Juan Island, Washington consists of about 50% brown alga Hedophyllum sessile, with the remainder being made up of ephemeral algae such as Ulva and diatoms.  Burnaford 2001 Dissertation Oregon State Univ, Corvallis, Oregon.  Photograph courtesy Russ Markel, Bamfield Marine Science Centre, British Columbia. 

Several black leather chitons Katharina tunicata
crawl amongst the holdfasts and fronds of their
principal food alga, the kelp Hedophyllum sessile 0.4X