ABSTRACT
A 4.6 kilometer stretch of beach was sampled for poly-
chaete distribution. Analysis shows these beach polychaetes
to be divided into three groups with respect to tidal height.
A high group of 4 species of sand and particle feeders clus-
ters around the mean higher high water (+1.72 meters). A
parallel group of sand and particle feeders occurs on the
low beach (0.0 to +0.73 meters). A smaller group of preda¬
tors spans the area from the low beach to the higher high
water line. It is suggested that the polarization into
high and low groups is caused by a central zone of substrate
disturbance and/or by differing moisture and organic contents.
The area of study contained two gradients. The first was a
vertical gradient of moisture and organic content increasing
with decreasing tidal height. The second was a lateral
gradient of increasing wave action and sand size, decreasing
organic content and water content, and decreasing species
number.
INTRODUCTION
Polychaete worms have often been found to be major consti-
tuents of sandy beach communities (Eltringham, 1971). Histori-
cally, however, their distribution has been studied only in the
most general terms and very little has been learned about their
distribution on specific beaches and how this distribution
relates to environmental factors. This condition is character-
istic of the status of our present understanding of sandy beach
communities. In short, very little is known about intertidal
zonation and ecological relationships in the sand habitat as
compared to the voluminous literature available on the rocky
intertidal.
Many of the organisms of the beach live under the surface
of the sand and therefore the usual vertical gradients, so often
associated with tidal cycles and exposure in the rocky inter-
tidal, are not immediately evident here. Closer examination of
the seemingly homogeneous sandy beach reveals that indeed organ-
isms are distributed relative to tidal height and they also may
show lateral variation in response to changing physical features
along the beach.
Previous studies of polychaetes in the Monterey Bay area
(Moore, 1909; Chamberlain, 1918) have been mostly taxonomic in
nature and have provided little information concerning distri-
bution, physical environmental parameters, or the possible
relations between the two. A few studies (Rote, 1969; Clark
and Haderlie, 1962) have dealt with the biology of single species.
The area chosen for our study, Del Monte Beach, was a
stretch of beach within Monterey Bay which showed apparently
strong gradients of wave action and associated parameters.
This offered us a study area with two sets of cross gradients,
one vertical, related to tidal exposure, and the other hori-
zontal, related to geographical variations.
This investigation was designed to determine the specific
distribution of polychaete species on this stretch of sandy
beach in Monterey Bay and to try and relate this distribution
to gradients of physical factors.
MATERIAL AND METHODS
AREA OF STUDY
The study was conducted on a 4.6 km beach stretching north
from Municipal Wharf 2 in Monterey, California to the southern
border of Fort Ord. Six transects, approximately 900 meters
apart, were established (Fig. 1), each stretching from the berm
to the lowest point that could be reached at lower low tide
(approximately -0.3 meters). Both physical parameters and
polychaete distributions were studied at each transect at lower
low tide either on the same day or on two successive days.
ORGANIC CONTENT DETERMINATION
On each transect sand samples were taken 15 cm below the
beach surface at four equidistant locations reaching from the
berm to the waterline with the exact locations determined by the
length of the transect. The organic content was determined, in
triplicate, using the wet ashing technique of Strickland and
Parsons (1965).
SAND SIZE AND WATER CONTENT
Samples were taken on the surface and 15 cm below at four
or more locations between the berm and the waterline on each
transect. The samples were placed in tared beakers and covered.
In the laboratory the samples were weighed, dried for 24 hours
in an 80° oven and weighed again to constant weight. From
these figures water content of the samples was calculated as
percentage water per gram dry weight of sand. Water content
was determined only for the subsurface samples.
All samples were then analysed for sand size by combining
each pair of surface and below surface samples and sifting
through a set of Standard Tyler screens with mesh sizes of
8, 4, 2, 1, 0.5, 0.25, 0.125, and 0.063 mm. Cumulative per-
centages were calculated and graphed against screen size to
determine md values for each sample. Since the mdQ values
for the samples on any single transect were always very close
(e.g. at Del Monte the mean Q value was 1.16 with a standard
deviation of 0.082), they were averaged to give a single mdo
value for the entire transect.
PERMEABILITY
A constant head permeability device was used after the
methods of Means and Parcher (1971). On each transect three
samples were taken at tidal heights of approximately O, O.6,
and 1.8 meters using a PVC pipe coring device. 60 ml bottle
samples were taken from the top, middle, and bottom of this
core. In the laboratory the core was "reconstructed" by
pouring the sand into the constant head device in the same
sequence as it was collected in the field. The apparatus was
then filled with water and allowed to run for 4.3 hours, after
which large changes in permeability due to packing had ceased.
After measuring the core length and water head a quantity of
water was taken in a beaker over a period of 20 seconds and the
permeability determined by the equation:
pin cm secL where
hAt
L = length of core in cm, Q = volume of water collected in co,
h = length of water head in cm, A = cross sectional area of core
in cm, and t = time in seconds.
SALINITY
Salinity of interstitial water was sampled along each
transect at the four points used for sand size. Determination
was accomplished with an AO refractometer which reads salinity
directly in parts per thousand.
POPULATION SAMPLING
Samples were taken along each transect at 3 meter intervals,
starting at the berm. 1.5 meters on each side of the transect a
quarter meter cubic corer (1/64 m2) was driven into the beach and
the enclosed sand troweled into a bucket. The sample was then
wet sifted on the beach simultaneously through two screens of
mesh sizes 6 and 1 mm respectively. All organisms were collected
and returned to the laboratory for counting and identification.
In addition qualitative samplings were often taken to determine
boundaries of populations and to assure that no major polychaete
populations were overlooked.
RESULTS
I. PHYSICAL FACTORS
WAVE ACTION AND SLOPE OF BEACH
A definite gradient of increasing wave action from south
to north was observed with slight wave action occuring at Del
Monte increasing to relatively heavy wave action at Sand City.
Wave size increased at a moderate rate between Del Monte and
Holiday Inn and then showed a large increase at Seaside and
Sand City. Although wave action varied greatly from day to day
over the entire area, the same general gradient was apparently
maintained.
Due to daily degradation and accumulation of sand on the
beach, the slope of each transect could not be easily determined.
However a gradient much like that seen with wave action was
observed. The beach was relatively flat at Del Monte, increas-
ing in slope toward Holiday Inn. At Holiday Inn there was a
rapid increase in beach slope corresponding very closely to the
observed rise in wave action. Although not quantified it was
noted that large areas, especially in the central portions of
the beach between mean higherhigh water and mean lower low water
were often eroded and then refilled within two days o l
PARTICLE SIZE
Particle size distribution again showed a gradient parallel
to that of wave action with sand size ranging from a median o
value of 1.16 at Del Monte to -0.06 at Sand City (Fig. 1). Sand
size increased slowly over the first three transects and then
rapidly increased between Townhouse and Holiday Inn. Sand size
increased moderately toward Seaside where there was a large jump
in grain size. Within each transect the sand size stayed
relatively constant between the upper and lower limits of the
beach. Most samples on any one transect showed no statistical
difference to a 95% confidence level. The greatest differences
to be found were at Seaside and Sand City but even these differ-
ences were not significant when the confidence level was dropped
to 688.
ORGANIC CONTENT
Organic content was inversely related to wave action. The
highest organic content was 409 ug Carbon/g dry sand at Del
Monte and the lowest was 202 at Seaside (Fig. 1). The biggest
change in organic content was the decrease between USNPGS and
Holiday Inn where the level dropped from 403 to 244 ug Carbon/
g dry sand. The mean organic contents exhibited a gradient
between the two extremes but due to the great randomness of
values on any one transect (Fig. 2) the variations between some
individual transects were not statistically apparent. There is
a difference between Del Monte and Seaside to a 95% significance
level using a t distribution. Using a Mann-Whitney U test with
a 90 level of significance the values from Del Monte and Holi-
day Inn are also found to be statistically different. Our
data also suggested that the organic content of the upper beach
was less than that of the lower beach (Table 1).
WATER CONTENT
The volume of interstitial water decreases along a vert-
ical gradient from the lower to the upper beach and along a
horizontal gradient from Del Monte to Sand City (Fig.1). Lower
water content higher on the beach is probably due to desic-
cation during low tides when these measurements were made.
This would mean that the water content would vary most in the
zone between lower high water and higher high water. Interstitial
water content decreases slowly and evenly from 18.8% water/g
dry sand to 10.3% between Del Monte and Sand City.
SALINITY
Salinity readings were taken on both interstitial and sur
face water at various levels on the beach and consistently
gave readings between 32°/00 and 340/00.
PERMEABILITY
Permeability measurements suggest an increasing gradient
from Del Monte to Sand City, but the high value obtained at
USNPGS and low value at Seaside are inconsistent with such an
interpretation. It is believed that the method of determination
produced conditions of packing different from those in the
natural state and this caused the apparently inconsistent results.
II. RELATIONSHIPS OF PHYSICAL GRADIENTS
The common factor associated with the demonstrated gradients
seems to be wave action. It controls sand movement and distri-
bution and slope of the beach which in turn affects permeability,
10
water content, and settling of organic matter. The gradient of
increasing wave action in this stretch of beach brings with it
proportional increases in sand size, beach slope, and possibly
permeability, while at the same time inversely affecting the
interstitial water content and organic content of the sand.
Gradients along individual transects are probably more
affected by the tidal cycle than by wave action. The amount
of water brought in as well as the amount of time each day a
certain level is covered is dependent upon the tides. This
leads to three zones, an upper dry zone, a central zone of
change, and a low covered zone. Tidal cycles also affect
organic content in that more organic material can settle out
in the lower zones, especially in calm areas.
III. POLYCHAETE DISTRIBUTION
The vertical and lateral distributions as well as
average densities are shown in Figures 3 and 4 and Table II.
VERTICAL DISTRIBUTIONS IN RELATION TO TIDAL HEIGHT
The polychaetes found can be divided into three groups
relative to tidal height. An upper group is clustered on and
above the mean higherhigh water line (1.72 meters, Doty, 1946).
A lower group is found on and below the mean higher low water line
(+0.73 meters). A third group straddles the area inbetween
and reaches into the upper and lower groups.
The upper beach population is dominated by two species;
an Ophellid, Euzonus dillonensis (Hartman, 1938),and the
Spionid, Pygospio californica (Hartman, 1936). Both of these
occur in dense bands 20 to 30 feet wide with a lower border
corresponding very closely to the mean higher high water line.
The members of this group are either sand or detrital feeders.
E. dillonensis has a maximum density at USNPGS with much
smaller densities on the transects to the north and south.
A closely related specie, Euzonus mucronata (Treadwell, 1914),
is found with E, dillonensis only at Del Monte. P. californica
has a maximum vertical range at the USNPGS, but is not found
at Del Monte. Moving north its density drops slightly at
Townhouse and much more severely at Holiday Inn where the
density drop is accompanied by a small downward shift in the
population to a lower tidal height. The fourth member of the
upper beach group is a Phylodocid, Eteone dilatae (Hartman,
1936) which is found on the southern two transects in low num-
bers.
The lower beach group is analogous to the upper group in
that it is composed mainly of sand feeders. Average densities
are much lower on the lower beach and in contrast to the bands
of organisms found in the upper beach, distribution is spotty,
The dominant species of the lower beach is the Orbiniid,
Scoloplos armiger (Muller, 1776) which is found from Del Monte
to Holiday Inn with a maximum density at Holiday Inn. Other
species in the lower group were Travisia gigas (Hartman, 1938),
Euzonus williamsi (Hartman, 1938), and Glycera convoluta
(Keferstein, 1882).
The only major polychaete population in the straddling
group is Nephtys californiensis (Hartman, 1938), found on the
12
southern three transects. At these transects N. californiensis
ranges from just below mean higher high water to below mean lower
low water. At Holiday Inn and Seaside its range is restricted,
especially in its upper limits. One other polychaete, the
Glycerid Hemipodus borealis (Johnson, 1901) may also inhabit
a large portion of the straddling zone. Our data shows their
range at Sand City to be very small, but recent studies of that
beach show a much wider range (Wells, 1972). This suggests that
H. borealis may be replacing N. californiensis at the northern
two transects.
LATERAL DISTRIBUTION TRENDS
One of the most obvious trends over the range between Del
Monte and Sand City is the decrease in total number of species
from 7 to 1 as one progresses to the north. There is a drop
from 7 to 4 species between Del Monte and Holiday Inn (a dis-
tance of 2.8 km) and a drop from 4 to 1 species between Holiday
Inn and Sand City (1.8 km). The largest densities for all
polychaetes are found at USNPGS with 12.3 polychaetes per
core (a core = 1/64 m2) and at Townhouse with 5.7 polychaetes
per core. There is a smaller density at Del Monte (2.1) and
very small densities on the northern three transects (1.4,
0.7, and 0.1) (Fig. 4).
The number of species found on the upper beach decreases
steadily over the four southern transects and drops out entirely
on the two northern transects. The mid tidal range shows a single
species, N. Californiensis, in the three southern transects, but
13
E
because its upper limits are depressed it is found only in the
e proport:
lower beach at Holiday Inn and Seaside. T
n of
reases in moving
species that belongs to the lower group ir
north until Holiday Inn where all species are in the low beach
area (Fig. 5).
14
DISCUSSION
The results showed a gradient of decreasing number of
species and individuals with increasing sand size and
decreasing organic content across the 4.6 km beach moving
north from Del Monte to Sand City. Several explanations for
this are possible.
Since many of the species found were typical sand feeders,
the possibility of the sand reaching sizes prohibitive to inges-
tion was considered. Euzonus dillonensis was used as an exam-
ple of a sand feeder whose distribution was sharply diminished
along the gradient and its ability to ingest sand of larger
size was tested. E. dillonensis was placed in the larger sand
from Sand City where it is not usually found. Analysis of gut
contents showed it was able to feed by selecting only the
smaller particles. This, coupled with the observation that
such sand feeding polychaetes as Scoloplos armiger and Euzonus
williamsi occupied positions on beaches of larger sand size,
pointed to the probability that factors other than sand size
caused the species limitations noted.
Factors associated with sand size such as water content
and permeability were considered next. Both show gradients that
suggest higher desiccation on the northern beaches of the study
area. Moisture is essential both in respiratory considerations
and feeding (Dales, 1963) and the problems presented by sand
that quickly loses its water may be insurmountable.
A gradient of increasing wave action caused greater beach
15
contour changes such that on the northern beaches large quant¬
ities of sand could be removed in a single tidal cycle. This
factor would place most burrowing forms in danger of being
washed up into the surf. It is interesting to note that the
one species present on the most northern beach was an inter-
stitial form, the Glycerid, Hemipodus borealis.
The drop in number of species and individuals closely
parallels the drop in organic content. Since the sand and
detrital feeding polychaetes use organic material in the sand
as a nutrient source it is possible that this is the limiting
factor on the northern beaches.
The above suggestions deal with tolerances of the adult
polychaete forms, but it should be remembered that these ani-
mals have a pelagic larval stage that could be controlling the
observed distributions. Even if random oceanic input is con-
ceded this randomness is lost upon consideration of settlement.
Wilson (1952), in studying the bottom dwelling polychaete
Ophelia bicornis found them to choose a substratum appropriate
to a successful adult stage. A similar perception of sand
size, interstitial size, and organic content by beaching larvae
could keep them from settling the more rigorous northern beaches
of the study area. An even more basic consideration would be
that if the larvae act like small sand grains or bits of organic
detritus they might remain in suspension in the heavy surf on
the steeply sloped northern beaches and never settle out while
to the south the milder wave action would permit such settling.
Figure 3 shows that the populations sampled over the 4.6 km
16
beach could be grouped into three categories according to tidal
height. The first clusters around the mean higher high water
line and consists of Euzonus dillonensis, Euzonus mucronata,
Eteone dilatae, and Pygospio californica, which are all sand or
particle feeders. The second group, Travisia gigas, Scoloplos
armiger, and Euzonus williamsi, extend down from the mean higher
low water line and are also sand feeders. The third group,
Nephtys californiensis and Hemipodus borealis, both predators,
ranges over the entire distance between the upper and lower
groups mentioned above.
Of the physical parameters studied only two, organic content
and water content show differences between upper and lower beach
consistent with the zonation observed. The upper group exper-
iences relatively dry conditions being mostly affected by wave
wash at higher tides, while the lower group is more often sub-
merged than not (Doty, 1946). Concerning organic content, the
data is only suggestive (Table 1), but it appears that the lower
beach contains more organic material. It has been shown (Fox.
Crane, McConnaugh, 1948) that E. mucronata needs only small
amounts of organic material absorbed on sand to meet its food
needs. This possibly accounts for its high position on the
beach in the area of less organic content. Differential needs
such as these could account for the upper and lower grouping
noted.
A more complete understanding of what is involved in this
grouping can be obtained by following the groups across the
beach from Del Monte to Sand City. The upper group, which
17
represents a large proportion of the worms on the three southern
beaches, is sharply reduced at Holiday Inn and disappears alto¬
gether at the Seaside transect (Fig. 5). This is paralleled by
a drop in water content and organic content. It is interesting
to note that there is a cross gradient present. From south to
north the water content and organic content go down, and from
upper beach to lower beach they go up. This means that for an
organism to inhabit an area of comparable moisture and nutrient
conditions as it moves in a northerly direction, it would also
have to move down to a lower tidal height. This is exactly
what is found in the positioning of the remnant of the Pygospio
californica population at Holiday Inn. The Euzonus dillonensis
population was sampled quantitatively between Townhouse and
Holiday Inn and found to decrease in numbers gradually. It
would be interesting to sample more carefully taking tidal
heights and seeing if E. dillonensis follows the same trend as
P. californica.
The middle beach group inhabits an area which is more
rigorous than the upper and lower extremes. It is more rigorous
because it is an area over which the tides rush twice a day
whereas the upper and lower beach regions are affected only
once a day, the upper at higher high water and the lower at
lower low water. This représents a stressful condition as each
tide deposits or removes sand and generally churns up the sub-
stratum (Dr. Warren Thompson, personal communication). Even
at Del Monte, the transect with smallest wave action, large
gouges were often taken out of the mid beach area by the action
18
of the water. The upper and lower regions also represent more
stable conditions of dry or submerged states due to the oscil-
lations of the tides. It is possible that this harsh central
region creates the polarity of polychaete populations and pre-
vents a smooth continuum of species moving down the beach in
tidal height.
The species that does inhabit the central region, Nephtys
californiensis, is clearly the best swimmer and fastest bur-
rower of all the species we sampled. Dales (1963) notes its
swimming and burrowing abilities and attributes these to an
effective parapodial stroke. As the wave action increases
from Townhouse to Holiday Inn to Seaside even N. californiensis
is restricted and it moves out of the more rigorous central
beach area. Moving north from Holiday Inn a similar downward
shift is shown in the distribution of Euzonus williamsi, the
highest member of the lower group.
N. Californiensis disappears at Sand City in accordance
with Clark and Haderlies (1962) findings that Nephtys is not
found on beaches with larger (1 to 0.3 mm) sand size and heavy
wave action. It appears that another predator, Hemipodus
borealis takes over the area vacated by the N. californiensis.
Observations during the time of lower low water on beaches
with light wave activity show that N. californiensis had a
definite limit in its distribution in terms of tidal height,
Consistently over the three southern beaches the mean higher
high water line marked its upper boundary. This is possibly
due to the desiccation problems presented by the upper beach,
19
for without such a physical limit it would only seem natural for
N. californiensis to extend upward into the rich food source pre-
sented by the upper group species. Nephtys feeds on polychaetes
in general, including other Nephtys (Clark, 1962). It is pos-
sible that at high tide the water content is sufficient for
N. Californiensis to range above this boundary.
The fact that N. californiensis and E. dillonensis popu-
lations are co-terminal poses some very interesting questions.
Differences in moisture requirements of the two species could
be causing the sharp break. Their boundary coincides with the
highest point of the beach that is completely submerged (the
mean higher high water line). But there is also the biotic
consideration. N. californiensis is a predator and E. dillon-
ensis a possible prey. Analysis of gut content of N. californ-
iensis found at the higher end of their range suggested that they
were feeding on Euzonus. As in the case of the barnacles
Chthamalus stellatus and Balanus balanoides documented by J.H.
Connell (1961) we seem to have two intertidal populations with
a sharp vertical boundary. It is possible that problems of
desiccation prohibit higher N. californiensis encroachment
while N. californiensis predation marks the lower limitof E.
dillonensis. Such suggestions could easily be tested with
appropriate analysis of N. californiensis desiccation toler-
ances and E. dillonensis distribution in the absence of N.
californiensis. It is interesting to note that the popula-
tions of sand and detritus feeders that exist in the absence
of N. californiensis (P. californica, E. dillonensis, E.
20
mucronata, and Eteone dilatae) exhibit much larger numbers than
those lower beach species that live with it (Scoloplos armiger,
Travisia gigas, etc.).
Generally it is apparent that wave action is of primary
importance to the beach polychaete populations. Not only does
it control such important factors as sand size, water content,
and nutrient levels, but its physical presence seems to create
distinct grouping of species. More work is needed in this area
to isolate the individual aspects of the beach environment and
interpret their specific effect on polychaete distribution.
21
1.
2.
3.
4.
5.
FIGURE CAPTIONS
Map of southern Monterey Bay indicates location of the six
transects studied. Graphs of sand size and organic content
show mean value, standard deviation, and range of values at
each transect. Water content graph shows mean values and
ranges. Curve is plotted along mean values. Boxes show
limits of standard deviation.
Variability of sampling sites and corresponding organic
content values found on the Del Monte transect on one day.
Vertical distribution of polychaetes at the six transects.
shown in order with northernmost transect on extreme right.
Verticalscale represents tidal height in meters. Kites
show relative abundance and tidal range.
Average density of polychaetes per core (1/64 m2) for each
of the six transects, in order with northernmost on extreme
right. Lightly shaded bar represents density above mean
lower high water. Darker shaded bar across mean lower
high water. White bar below mean lower high water. Black
bar represents total average density of polychaetes on transect,
Number of species in relation to mean lower high water
(+1.3 meters). Transects shown in order with northern-
most on extreme right. Lightly shaded bar represents
number of species above mean lower high water. Darker
shaded bar across mean lower high water. White bar below
mean lower high water. Black bar represents total species
number on transect.
22
HMSS
MONTEREY BAY
MONTEREY
1.00.
50
SAND SIZE
Ma
.50
1.00.
—
40.
WATER
30.
CONTENT
20.
100
g dry sand
10
500.
ORGANIC 400.
CONTENT
ugC/g dry sand 300.
200.
001

kilometers


A DEL MIONTE
B U.S. IAVAL POSTGRADUATE
SCHOOL (USHPGS)
C TOWMHOUSES
D HOLIDAY INN
E SEASIDE
F SAND CITY
23
TIDAL
HEIGH
(meters)
291
483
gCg dry sand
324
345
404
349
486
HORIZONTAL DISTANCE (meters)
saa-
saaa

5
—
Szade
Le=-


32
S

2
kaa

3
zruuo
OOL



s-




1


(Siajau



L
-
L
L

jusia

25
LE
a





Above MLHW E
AcrOSS MLHW
Below MLHW
Total Average Density □

11
Del Monte USNPGS Townhouse Holiday inn Seaside Sand City
TRANSECT
IEDE


L
oo
L

o


o

L
L
SL
ZO


m
.
.



.
.

.

.

L





L







S

L




27
II.
TABLE CAPTIONS
1., Organic content of sand at each transect in ug C/g dry
sand. Mean values are given for samples taken above
and below a tidal height of +1.3 meters (mean lower high
water) and for the total of all samples taken at each
transect.
Tidal ranges in meters and densities per core (1/64 m3)
over observed vertical ranges of species found at the
six transects.
O
BEACH
DEL MONTE
USHPGS
TOWNHOUSES
HOLIDAY INN
SEASIDE
SAND CITY
ABOVE
384
276
265
174
150
203
BELOW
486
530
380
315
246
200
TOTAL
410
403
351
244
222
202
29
a



2
9

38
89
NO
10 —

+ +
8



5

1 1
1 1
DA
O
27
1

-
8
O
-
Q
+
—
10
a-

—.
+ +




29
1.
0
oo
1

20 0
2 9

6
19
ION
o

0
o
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32
ACKNOWLEDGEMENTS
We would especially like to thank Dr. Welton Lee of the
Hopkins Marine Station for his great amounts of assistance,
insight, and enthusiasm. We also wish to acknowledge Dr.
Donald Abbott and Dr. John Phillips of the Hopkins Marine
Station and Dr. Warren Thompson of the U.S. Naval Post
Graduate School for their help. Finally, we wish to thank
Fred Johnson for aiding us in our study.