2.
R. Nishi
Diet and Feeding Habits of N. californica
Introduction
Individuals of Nuttallina californica (Reeve, 1847) are widely distri-
buted along the western coast of the United States (the Straits of Juan de
Fuca, Washington to San Diego, California (Burghardt and Burghardt, 1969)).
yet information on their diet and feeding habits is largely speculative.
According to MacGinitie and MacGinitie (1919, pg. 386) Nuttallina are largely
sedentary animals, found in deep, form-fitting depressions in the hard
substratum, and seldom or never venture out to feed. MacGinitie and MacGinitie
suggest that such animals have forsaken the grazing habit and subsist on
algal debris which settles in the depressions. The absence of detailed studies
supporting or contradicting this view motivated the present study.
Mussel Point, Pacific Grove, California provides several kinds of habitats.
of which two were selected for study. One consists of crevices in vertical
rocky surfaces at the +3.0 to +.0 foot tidal level, exposed to heavy surf
action, and on the western portion of the Point. Here animals commonly found
with Nuttallina are the barnacles Tetraclita squamosa Darwin, 1851 and
Chthalmalus spp., and the mussel Mytilus californianus Conrad, 1837. The
second habitat consists of beds of calcareous tubes formed by the colonial
cirratulid worm Dodecaceria fistulicola Ehlers, 1901. Here Nuttallina
are found in depressions 1 to 2 cm. deep on the mostly horizontal surface
ane
of the beds at about the +1.0 foot tidal level, exposed to moderate surf.
3.
R. Nishi
Diet and Feeding Habits of N. californica
The Dodecaceria beds were located on the
eastern portion of the Point. Few other animals are found upon
the Dodecaceria bed itself but neighboring it (on the exposed rocky substratum)
are Tegula funebralis Adams, 1854, Phragmatopoma californica Fewkes, 1889
and Anthopleura xanthogrammica Brandt, 1835.
The objective of this study was to compare the diet and feeding habits
of Nuttallina californica in these two habitats. Specifically to
define their diet, determine the sources of the food eaten, and compare the
foods eaten with those apparently available in the microhabitat.
Methods
A specific site at each of the two study areas as well as one site at
Carmel Beach were chosen. At each site food resources inthe vicinity of
Nuttallina californica were determined by randomly placing a 25 X 25 cm.
grid overthe site and measuring the area covered by each macroscopic alga.
This was done four times at each location. The relative abundance or avail¬
ability of each alga was taken asthe area covered by that alga divided by
the total area covered by all of the algae present. At each location all of
the N. californica found within the areas surveyed for algal cover were
R. Nishi
Diet and Feeding Habits of N. californica
collected. This included a total of 25 animals from rocky crevices at
Mussel Point and Carmel Beach and 26 animals from a Dodecaceria bed at
Mussel Point. The specimens were immediately preserved in a 10% formalde¬
hyde solution to stop further digestion. Gut contents were analysed by
removing the digestive tract from the stomach to the small intestine and
squeezing out its contents on to a microscope slide. This was
examined
under a dissecting scope and the macroscopic pieces of algae identified,
counted, and removed. A compound microscope was used to identify the
smaller pieces of algae on the basis of color, cell structure and size.
Relative abundance of each type of alga within the guts was estimated by
counting the number of pieces of each alga found (with rough attempts to
correct for gross differences in size), and dividing bythe total number of
pieces of algae found.
Results and Discussion
From preliminary gut content analyses it was immediately apparent that
instead of merely scraping at algae with its radula, Nuttallina was taking
in large pieces. Length of the largest piece in the gut of each of 31 animals
was measured and the number standardized to the size of the chiton by
expressing it as the percent of body length. These figures show N. californica
is capable of consuming pieces of algae up to 20% of its body length, although
5.
R. Nishi
Diet and Feeding Habits of N. californica
the average size was 12% of the body length. No appreciable difference m
alel m
Abetween Nuttallina of the different habitats could be seen. Microscopic
algae such as diatoms and blue-greens were also found in all of the
animals, yet the abundance of large algal pieces comes from macroscopic
algae. The frequency of occurrence of various macro-algae in the guts of
different individuals is shown in Fig. 1. The most frequently occurring
algae in the animals from rocky crevice communities are Corallina spp.
(80% of the individuals examined), Endocladia muricata (Postels & Ruprecht)
J.G. Agardh (60%), and Cladophora trichotoma (C.A. Agardh) Kützing (188);
the most frequently consumed algae by Dodecaceria bed animals were
Gelidium spp. (53%) and Cladophora trichotoma (76%). These figures correspond
roughly to the relative frequency with which these algae are found in the
habitats from which these animals came.
relar
The of the algal distribution in the habitat vs. average
diet at the three field sites is shown in Fig. 2. Corallina spp. make up
a much higher percentage of the gut contents of Nuttallina collected at
all three locations than would be expected by the composition of the flora
in these habitats. In addition crustose corallines are found in considerably
omallr
fewer amounts in the guts than expected by their presence in the habitat.
This suggests that Nuttallina may preferentially seek out erect corallines
R. Nishi
Diet and Feeding Habits of N. californica
over crustose forms. This may be due to limitations imposed upon their
feeding habits by the manner in which their radulas work. The radula
in these chitons appears to be best adapted for use in consuming large
bushy algae by tearing them into pieces or swallowing them whole if they
are small enough. The radula does not appear to function as a scraping
organ, which would be best suited in consuming crusts.
Plant
According to Dr. I.A. Abbott (personal communication), the ae most
commonly found in the study areas in terms of biomass and therefore to
be expected in drift feeders are: the flowering plant Phyllospadix sp.,
the brown alga Macrocystis pyrifera (Linnaeus) C.A. Agardh, and red algae
of Lheganera Rhodymenia sp; Botryoglossum farlowianum (J.G. Agardh)
DeToni, Botryocladia pseudodichotoma (Farlow) Kylin, and Gigartina
corymbifera (Kützing) J.G. Agardh. None of these was found within the
guts of the Nuttallina californica examined. Thus it is highly unlikely
Dant
that the Nuttallina studied were feeding upon drift aigae.
7.
R. Nishi
Diet and Feeding Habits of N. californica
Since the diet of N. californica indicates feeding by grazing on larger
algae, and these are not available within deep depressions in the
Dodecaceria bed, feeding acitivity must occur when animals emerge from
their shelters at high tide. Preliminary studies support this hypothesis.
Numerous Nuttallina were observed crawling out of their depressions when
the bed was awash on an incoming tide; however, further studies need to
be done in order to determine whether this movement is correlated with
feeding activity.
8.
R. Nishi
Diet and Feeding Habits of N. californica
Natural History Notes on the Two Populations of Nuttallina californica
The populations of Nuttallina californica studied in the two contrasting
habitats differed markedly in their external appearances. N. californica
from the Dodecaceria bed possessed valves so worn that species-characteristic
markings were erased. The shells of these chitons were beige in color and
pitted by a blue-green alga, Entophysalis deusta (Meneghini) Drouet &
Daily. This coloration exactly matched that of the Dodecaceria bed. In
addition, the girdle bristles were predominantly white with scattered
reddish brown ones. In contrast the rocky crevice Nuttallina possessed
black valves with occasional white stripes down either side of a shiny
dorsal ridge. The girdle bristles were primarily reddish-brown with more
white ones towards the outer edge of the girdle. These Nuttallina were
often found with a profuse growth of algae on both valves and girdle. These
included Endocladia muricata (Postels & Ruprecht) J.G. Agardh, Corallina spp.,
Polysiphonia hendryi Gardner, Cladophora trichotoma (C.A. Agardh) Kützing,
Rhodoglossum affine (Harvey) Kylin, Peyssonnelia sp., and Microcladia sp.
Representative specimens collected from the Dodecaceria bed were
positively identified as N. californica by Mr. Allyn G. Smith of the
California Academy of Sciences.
R. Nishi
Diet and Feeding Habits of N. californica
Acknowledgements
I would like to thank Dr. Donald P. Abbott and Dr. Robin Burnett for
their helpful comments in aiding me to write this paper, James Watanabe.
Stuart Seiff, and Betsy Lyman in assisting me in collecting animals, and
Allyn G. Smith for identification of the Nuttallina. My deepest and
most profound thanks go to Dr. Isabella A. Abbott for her patient aid
in identifying gut contents, her constant encouragement throughout this
study, and her advice in writing this paper.
R. Nishi
Diet and Feeding Habits of N. californica
Literature Cited
Burghardt, Glenn E. and Laura E. Burghardt
1969 A collector's guide to West Coast chitons. 15 pp.; h plts.
San Francisco, Calif. (San Francisco Aquarium Society, Inc.)
MacGinitie, George Eber and Nettie MacGinitie
1949. Natural history of marine animals. xii + 173 pp.; illus.
New York, N.Y. (McGraw-Hill Book Co., Inc.)
10.
11.
R. Nishi
Diet and Feeding Habits of N. californica
Figure Explanations
Figure 1:
Comparison of the frequency of occurence of macroscopic algae in
the guts of Nuttallina californica from rocky crevices (n-25, with full
guts) with those from Dodecaceria beds (n-26, of which 9 contained no
food. Percentages were calculated on the basis of the 17 animals with
full guts).
Figure 2:
Comparison of algal composition in terms of percent of total algal cover
at study sites with corresponding relative abundance of the algae in
the gut contents of N. californica collected from each area at the time of
the survey. From Carmel rocky crevices n-8; from Mussel Point rocky crevices
n-6; and from Mussel Point Dodecaceria beds n-17.
101
80—
—
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FIGURE 1.
R. Nisn
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