Learn About Chitons: Feeding, growth, shell repair


Topics on chiton feeding, growth, & shell repair include diets, considered here, and RADULA & FEEDING, GROWTH, and SHELL REPAIR considered in other sections.

Research study 1

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.

Diets of several west-coast chitons from around San Francisco Bay, California are depicted below. Algae, including diatoms are coloured shades of red, green, and brown, while animal matter is indicated in dark grey:

photograph of chiton Mopalia ciliata courtesy Lovell & Libby LangstrothMopalia ciliata. Photograph courtesy Lovell & Libby Langstroth, California and calphotos
pie diagram showing diet of chitons Mopalia ciliata in the San Francisco Bay region
photograph of chiton Mopalia muscosaMopalia muscosa. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.
pie diagram showing diet of chitons Mopalia muscosa in the San Francisco Bay region
photograph of chiton Mopalia hindsii courtesy Linda Schroeder and Northwest Shell ClubMopalia hindsii. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.
pie diagram showing diet of chiton Mopalia hindsii in the San Francisco Bay region
photograph of chiton Mopalia hindsii courtesy Linda Schroeder and Pacific Northwest Shell ClubMopalia hindsii (variety). Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.
pie diagram showing diet of chiton Mopalia hindsii in the San Francisco Bay Region
photograph of a chiton Mopalia hindsii leaving a trail of feces behind as it crawls

The propensity for chitons Mopalia hindsii to eat almost any type of bottom material is shown here. This aquarium-held individual is eating detritus and leaving a trail of feces as it crawls along 0.4X

Research study 2

photograph of veiled chiton Placiphorella velata courtesy Ron Long, Simon Fraser University, Burnaby

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

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.

photograph of a veiled chiton Placiphorella velata from below
Placiphorella velata with mantle raised, waiting for prey to wander by.

Research study 2.1

drawing of veiled chiton Placiphorella velata in prey-capture orientationAn early description of the carnivorous habit in the veiled chiton Placiphorella velata is provided by a researcher at Stanford University, California.  In normal feeding posture the head flap is raised  with the dorsal bristles or setae extended.  The curtain of precephalic tentacles remains pressed to the substratum (see drawing).  At this point any physical stimulation of the bristles or flap causes the veil to clamp down quickly.  Tests with live amphipods, shrimps, small crabs, and polychaetes show that prey of up to 1cm in length may be captured  in this way.  After the flap drops down it curls inward, pushing the prey towards the mouth, the precephalic tentacles are raised, and the mouth extends to meet the prey.  Small prey may be drawn in by the radula and swallowed whole, while larger ones are torn apart before being ingested.  If a prey is missed on the first attempt, a second attempt may be made. Through examination of gut contents and fecal pellets the author determines that amphipods are regularly consumed.  Other dissected individuals reveal remnants of diatoms, sponges, and algae, indicating that while the species is predatory, it also feeds in the manner of a typical chiton.  While other west-coast species of chitons are known to eat bottom-dwelling invertebrates, this is the first report of one taking motile prey.  McLean 1962 J Moll Stud 35 (1): 23.

Research study 3

graphs showing seasonal variations in rate of feeding of a chiton Katharina tunicata and calorific value of various seaweeds in the Port Renfrew area of British ColumbiaIn 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 photograph of chiton Katharina tunicata eating seaweed Hedophyllum sessileBiol Ecol 18: 139.

Research study 4

Diets of several species of chitons at Pacific Grove, California and surrounding regions of the Monterey Peninsula, California are presented below:

photograph of chiton Cyanoplax hartwegii courtesy Jim Watanabe, CaliforniaCyanoplax 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

photograph of chiton Mopalia lignosa courtesy Linda Schroeder, Pacific Northwest Shell Club

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. 

histogram showing dietary components in a chiton Tonicella lineata in Pacific Grove, CaliforniaIn 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 graph showing foraging times of chitons Tonicella lineata in relation to time of day and tidal cyclephotograph of a lined chiton Tonicella lineata with a northern abalone Haliotis katschatkanaperiods 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

Research study 5

schematic showing densities of 6 species of chitons at Deception Pass, WashingtonA 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 histogram showing dieary preferences in several west-coast chiton speciestheir 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

NOTE3percentages 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

Research study 6

photograph of several black leather chitons Katharina tunicata amongst holdfasts and blades of its principal dietary seaweed, the kelp Hedophyllum sessile courtesy Russ Markel, Bamfield Marine Sciences Centre, British ColumbiaThe 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