Estuarine, Coastal and Shelf Science (1983) 16, 217- 227

The Abundance and Distribution of Free-living Nematodes from. Two Canadian Pacific Beaches

Jyotsna Sharmaa and John M. Webster Department of Biological Sciences, Simon Fraser University, Burnaby, Vancouver, British Columbia, Canada VJA 15%

Received 22 October 1981 and in revisedform 16 March 1982

Keywords: Xematoda; littoral; distribution environmental conditions; Canada west coast

Free-living marine nematodes at two littoral sites near Vancouver, Canada were studied over a I -year period. Sixty-four species were found at a Belcarra Park site, with a maximum nematode density of 6.7 x lo5 m -a and 24 species at Iona Island, with a maximum density of 1.6 x 10~ m -2. At both sites most of the nematodes occurred in the upper 2 cm of the 6 cm depth of sediment examined, and the vertical distribution of most species remained constant during the year. The distribution of the nematodes in relation to some physical parameters is discussed. The occurrence of certain species suggests that they have a worldwide distribution.

Introduction

Free-living nematodes are the major component of the meiofauna in most marine benthic habitats, from the littoral to the deep sea. In a recent review of their role in the littoral ecosystem, Platt & Warwick (1980) conclude that ‘any general assessment of intertidal habitats is incomplete if the nematode fauna is not taken into consideration’.

Though several publications on the natural history and ecology of the North American Pacific coast are available, there are only a few taxonomic descriptions on free-living nematodes from the Canadian Pacific coast (Nelson et al., 1971, 1972). The taxonomic relationships of two of the cyatholaimids discussed in this paper, Paracyatholaimuspugettensis and P. vancouverensis, are discussed by Sharma & Vincx (1982) and Paracanthonchus caecus is described as P. canadensis n. sp. by Vincx et al. (in press). This paper describes the composition of the nematode fauna over a I-year period at two contrasting sites near Vancouver, British Columbia. The density of nematodes and vertical distribution of the dominant species in the surficial sediment is recorded and discussed in relation to some of the physical parameters.

Materials and methods

Samples were taken during 1976 at two sites in the area of Vancouver, British Columbia, namely Iona Island (49’1o’N, 123’15’W) at 2.13 m above mean tide level and Belcarra Park (49’19’N, 123”56’W) at 0.76 m above mean tide level.

“Present address: Instituut voor Dierkunde, Rijksuniversiteit Gent, K. L. Ledeganckstraat-36, gooc-Gent, Belgium.

2x7 o2?2-7714/83/o20217$-11 $03.00/o ‘G 1983 Academic Press Inc. (London) Limited

218 J. Sharma &‘J. M. Webster

At each site, three replicate samples were taken within a r-m2 quadrat on six occasions during the year using a hand-held plexiglass corer (2.4 cm diameter). In addition, approximately 500 g of sediment were collected from the quadrat for organic carbon measurement and sediment grain size analysis. The upper 6 cm of the core were sliced into 2 cm sections and nematodes extracted in the following way (based on Hopper & Meyers, 1967): the sediment was first passed through a ~.o-mm sieve to remove coarse particles and then through a 44-pm sieve to separate the silt-clay particles. Sediment retained on this sieve was centrifuged twice in a I : I Karo syrup-sea water mixture (x80 g for 2 min) and the supernatant poured through a 44-pm sieve. Organisms retained on the fine sieve were fixed in hot 5% formalin-sea water and the nematodes were processed through glycerin (Seinhorst, 1959) for identification.

Temperature and salinity measurements of the overlying water were taken at the site of sampling using a Yellow Springs Instrument S-C-T meter. The sediment’s grain size was determined by the technique of Buchanan (1971) and the sorting determined by the phi quartile deviation. Organic carbon was measured with a Perkin-Elmer Elemental analyzer.

A three-level nested analysis of variance was performed on the total number of species and log @+I transformed nematode density with the components of site, time and depth. A three-way analysis of variance on the log n+~ transformed data of the 17 dominant species was done with the components of time, depth and developmental stage.

Results

Environmental parameters Seawater temperature tended to be lower throughout the year at Iona Island than at Belcarra Park (Table I). Salinity at both sites was highest in February and lowest in the summer especially at Iona Island (Table I). The mean grain size composition of the sediment (Table I) was higher at Belcarra Park than at Iona Island but the sediments at Iona Island were better sorted than those at Belcarra Park. By the scale of Folk & Ward (1957), the Iona Island sediment was in the range of well to moderately sorted while the Belcarra Park sediment was moderately to poorly sorted. The amount of organic carbon associated with sediments was

TABLE I. Temperature and salinity of water overlying sediments and the percentage silt-clay content, mean grain size, sorting and percentage carbon content of sediments at Belcarra Park and Iona Island sites over I year

Belcarra Park 8 Feb. 7 Apr. 20 May 20 Aug. IO Nov. IO Dec.

Temperature (“C) Salinity (x0) o/O silt-clay Mean grain size (mm) Sorting 0/O carbon

IO’0 23’5

-

- 2’1

16.5 ‘4’5 20’0 10’0 6.5 - 19’0 21’0 18.0 14’5 5.6 7.6 15‘2 15.6 12’0

0’574 0.574 0’392 0.709 0.a13

0.81 1’10 0.80 1’90 “55 “3 4’1 I .6 2’2 2’2

Iona Island II Jan. 7 Mar. 19 Apr. 31 May 15 Oct. 20 Dec.

Temperature (“C) Salinity (x0) % silt-clay Mean grain size (mm) Sorting yO carbon

3’0 9’5 - ‘4’5 10’0 1’0

23.0 16.0 - 12.5 7.0’0 I 8.0 4’4 4’4 6.0 8.0 40.0 25’2

0.420 0.483 0.467 0’595 0’234 0.268 0’45 0’55 0.68 0’50 1’00 0.85 0’5 0.8 0’7 I.4 0.8 0.4

TABL

E 2.

Nu

mbe

r of

sp

ecie

s an

d ne

mat

ode

dens

ity

per

18

cm2

at

the

Belca

rra

Park

and

Iona

Isl

and

sites

at

thr

ee

dept

hs

sam

pled

over

I

year

. Ea

ch

value

is

th

e m

ean

of

three

re

plica

te

sam

ples&

s.D.

(mea

n va

lues

rndl

are

in

pare

nthe

ses)

Balca

rra

Park

Dept

h (cm

)

o-2

8 Fe

brua

ry 7

April

20

May

I Au

gust

IO

Nove

mbe

r IO

De

cem

ber

SP.

Dens

ity

SP.

Dens

ity

Sp.

Dens

ity

SP.

Dens

ity

Sp.

Dens

ity

Sp.

Dens

ity

21

51of

253

31

422&

135

3o

38o~

t235

36

85

2f715

29

23

2415

5 27

36

2 +7

4 (2

.83

X 10

~)

(2.3

4 x

IO’)

(2.1

I

x 10

5)

(4’73

x

IO51

(1

.29X

Io5)

(2

.01

x 10

6)

2-4

I2

256&

187

25

257x

t181

22

Io9f

47

26

3o5+

355

22

228

4~ 17

7 I2

16

oh81

(1

.42

X Io

4)

(I.43

x

106)

(6.

10

X IO

”) (1.

69

X 10

~)

(1.27

X

10”)

(8.90

X

IO’)

4-6

IO

70+4

8 22

12

6~t25

23

85

145

15

43

*4r

I2

ro

5f13

o 19

37

xt16

(3;;;

x 104

) (7.

00

x IO

”) (4

.70

x 10

4)

(2.40

X

100

(5.80

x

10~)

(2

.10

x IO

’)

Tota

l 80

5 57

3 11

99

407

560

(4.53

x

107

(4’47

x

107

(3.18

X

10~)

(6.

66

x 10

5)

(2.26

X

IO’)

(3.11

X

Io5)

---~ Iona

Isl

and

II Ja

nuar

y 7

Mar

ch

19

April

31

May

15

Octob

er

20

Dece

mbe

r -

Dept

h (cm

) Sp

. De

nsity

SP

. De

nsity

Sp

. De

nsity

Sp

. De

nsity

Sp

. De

nsity

SP

. De

nsity

o-2 2-4

4-6

Tota

l

8 31

&12

6 43

dz

41

II 59

i26

I4

Io9i3

1 7

193

zt74

IO

197*

5o

(I.70

x

100

(2.40

X

10~)

(3

.30

x 104

) (6.

05

x 10

~)

(1.07

X

10~)

(1.

09

x 10

~)

3 23

*4

3 IS

&II

5 r4

f3 (1.

30X

10~)

(8

.30

x 10

8)

(7.7

0X

103)

I0

54

*45

2 76

f34

3 75

177

(3

’00

x IO

’) (4

.20

X 10

~)

(4’17

X

IO’)

3 II&

IO

2 91

7 4

8zt4

5 12

59

2 26

&s

2 IS

+19

(6.10

X 10

~)

(5’00

x

103)

64

67

(44;

x ro

3)

(6.70

x

10~)

(1.

40x

10~)

(8

.30

x 10

~)

I75

295.

28

7 (3

.60

X ro

4)

(3’70

x

IO’)

(4.50

x

IO’)

(9’70

x

104)

(1.

64x

IO?

(1.59

x IO

51

220 J. Sharma &J. M. Webster

higher at Belcarra Park than at Iona Island (Table I). The high carbon content at Belcarra Park in May was associated with the presence ‘of an abundance of visible detritus and a substantial diatom population. No measurements were made on the redox potential but the redox discontinuity layer was visible at a depth of x*5-3*0 cm at Iona Island and 2-o-3.0 cm at Belcarra Park.

The nematode fauna The nematode density at Belcarra Park was significantly (P<o.og) higher than at Iona Island throughout the year (Table 2). The maximum and minimum densities in the upper 6 cm of the sediment at BeIcarra Park were 6.7 x ro5 mm2 and 2.3 x 10~ mm2 during August and November, respectively. The maximum and minimum at Iona Island, however, were 1.6 x 10~ me2 and 3.6 x 10~ rnp2 during October and February, respectively. At both sites total nematode density was highest in the upper 2 cm of the sediment, and although absolute density changed with time there was no significant change in the relative vertical distribution (Table 2).

The number of species recorded for Belcarra Park (64) was significantly greater than at Iona Island (24) (Table 3). Significantly more species (P<o.og) occurred in the summer at both sites than in the winter (Table 2). The proportional vertical distribution of species in the top 3 cm of sediment (Table 2) did not change during the year. Significantly (P<o.og) more species were found in the top 2 cm of sediment and few species were found below 4 cm, especially at Iona Island.

TABLE 3. List of nematode species occurring at the Belcarra Park and Iona Island sites during the year of sampling

Species Feeding

category” Belcarra

Park Iona

Island

Leptolaimus sp. Areolaimus elegans A. boomerangi Axonolaimus spitwsus Odontophora peritricha Parascolaimus sp. Paraterschellingia sp. Siphonolaimus sp. Solenolaimus sp. Desmolaimus zeelandicus Metalinhomoeus setosus Terschellingia longicaudata Eleutherolaimus stensoma Didelta sp. Linhomoeus sp. L. undulatus Paralinhomoeus buculentus Cylindrotheristus resimus Diplolaimella sp. Mesotheristus circumscriptus Monhystera refringens Paramonhystera mutilus Paramonhystera sp. Steineria gerlachi Theristus modicus Cobbia urinator Sphaerolaimus sp. Aponchium sp.

IA 1A IA IB IB IB IA 2B IA IB IB IA IB IB 2A 2A IB IB IB IB IB IB IB IB IB 2A 2B 2B

+++ +++ +++ +++ +++ ++ ++ +++ + +++ +++ +++ +++ ++ +++ +++ ++ + +++ + t-t+ +++ +++ +++ +++ +++ +++ +

+

+++

+

+++

+++

+

+++

+++

Free-living nematodes at two Canadian Pacific beaches 221

TABLE 3 continued

Species Feeding

category’ Belcarra

Park Iona

Island

Ehynchonema sp. SB Microlaimus dentatus 2A M. texianus ZA Monoposthia costata 2A Sabatieria americana IB S. ancudiana IB S. pulchra IB Chromadorina germanica 2A Euchromadora sp. 2A Denticulella sp. IA Innocuonema clivosum 2A Neochromadora appiana 2A Spilophorella paradoxa 2A Neotonchus sp. 2A Parapomponema websteria 2B Acanthonchus sp. 2A Paracanthonchus caecus 2A Paracyatholaimus pugetten Gs 2A P. vancouverensis 2A Cyatholaimus sp. 2A Hals3oanolaimus sp. 2B Bathylaimus sp. IB Paratripyloides sp. IB Triploides gracilis IB Cytolaimium sp. IA Bhabdocoma sp. 1A Oxystomina sp. IA Halalaimus sp. IA Anticoma pellucida IB Lauratonema pugiunculus IB Mesacanthion sp. 2B Viscosia carnleyensis 2B V. tumidula ZB Oxyonchus sp. 2B Anoplostoma sp. IB Onckolaimus skawensis 2B 0. vesicarius 2B Euystomina sp. 2B Symplocostoma sp. 2B Bhabditis marina IA Bolbella rp. 2B

+-t +-I+ ++ +t-+ +++ +++ +++ +++ +-t+ +++ +-I +++ + + +++ +++ +++ +++ ++ +++ +++ +++

t+t +-I-+ +++ +++ +++ ++ + ++ ++ +++ +++ t +++ ++

t +++ ++ +++

+++ +++ +++ + ++ +

+++

++ ++

+ +++

f, occurred in one sampling period; + -t, occurred in two sampling periods; + + +, occurred in more than two sampling periods. “Categorized as described by Wieser (1952) (see text).

Those species which typically comprised over 10% of the samples at each site (25 at Belcarra and six at Iona) were examined in detail. The remaining species were excluded from this analysis as they occurred in too low numbers. The mean number of the most abundant species and their prevalence in the fauna was determined (Table 4). All species are categorized (Table 3) according to the feeding categories proposed by Wieser (1952), namely: IA, selective deposit feeders; IB, non-selective deposit feeders; 2A, epigrowth feeders; 2B, predators and omnivores. At Iona Island the six dominant species were non-selective deposit feeders (xB) and epigrowth feeders (2B) and the 25 dominant nematode species at Belcarra Park represented all four of Wieser’s feeding categories.

TABL

E 4.

Nu

mbe

r an

d pe

rcen

tage

ab

unda

nce

(in

pare

nthe

ses)

at

Be

lcarra

Pa

rk an

d Io

na

Islan

d sit

es

of

the

dom

inant

ne

mat

ode

spec

ies

in

the

uppe

r 6

cm

of

sedim

ent

(18.0

9 cm

*) ov

er

I ye

ar

(fkS.

D.

of

three

re

plica

tes)

. Th

e sig

nific

ance

lev

el of

th

e co

mpo

nent

s of

tim

e (T

), de

pth

(D)

and

deve

lopm

ent

stage

s (S

) ar

e al

so

given

’

Belca

rra

Park

8 Fe

b. 7

Apr.

20

May

I Au

g.

IO

Nov.

zo

Dec.

T D

S TD

Areo

laim

us

elega

ns

Desm

olaim

us

zeela

ndicu

s

Met

alinh

omoe

us

seto

sus

Ters

chel

lingi

a lon

gicau

data

Eleu

ther

olaim

us

steno

som

a

Para

linho

moe

us

bucu

lentu

s

Linho

moe

us

sp.

L.

undu

latus

Para

mon

ohys

tera

sp.

P.

mut

ila

Cobb

ia ur

inato

r

Ther

istus

m

odicu

s

Saba

tieria

sp

.

S.

ancu

diana

S.

amer

icana

S.

pulch

ra

11+8

(I.

4 98

zt43

(13.5)

0 24*12

(3.

2) 2If

I4 (2.8

) 0 2058

(3.3)

0 0 25*34

58

+21

(3.0)

(8.2

) IfI

41

*3I

(0.2

) (5.

6) 0

0

309f3

Io 21

*21

(34.8)

(3.

1) 0

0

0 0

ZIfI9

(1

.1)

4&s (043

) 30

*40

(3.3)

78f74

(8.

4) 12

*18 (1W

41

8 (0.

4) 9+

4 (1.2

) Ii2

(0.

3) 0 0 0

II&IO

(1.2

) II*

10

(1.8

) 7*3

(1

4)

108f9

6 (2

1.0)

51

f28

(9.0)

2Ozt2

7 W

I 29

1-24

(5.9)

27k-2

1 (5

.0)

6+x0

(1.7)

29i21

(4.

4) 7+

6 (0.

9) 31

4 (0

.5)

37zt2

9 (6.

4) IfI

(0.1

)

2f3

(0.4)

IIztI7

(1

.5)

46h5

3 (4.

4) 44

561

(2.8

) 9f7

(1

.0)

209*2

02

(15’

0)

28+2

0 (3'

1) 48

143

(3'9) 1z

.t2

(0.1

) 28

511~

390

(15.4)

30

f41

(3.0)

srf38

(5

’1)

33f33

(3.

0) 14

zt8

(1%

68

ct39

(89)

26

k36

(1.4)

II&

IO

(0.5

) 0

~&IO

(1.8

) 85

5 (1

.8)

11*1

6 (2.5

) 12

5*12

8

(17-J)

IIz

ti’

(2.5

) 2O

zk-13

(3.

8) Ii2

(0.1

) 2I

f20 (2.7)

x0*1

6

(2.4)

28*18

(6.5)

29zk

-28

(3.8)

IOk7

(1

.8)

94f62

(19

.0)

I7fI4 (2

.5)

15+2

(6

.1)

0

8zt6

(1.

9) 42

*24

(7.3)

0 3954

4 (6.

4) 3*3

(0

.5)

241tI

I (4'

5) Ii2

(0.1

)

2lltI

(0

.5)

IIt1

(0.1

)

715 (1.4)

0 4*2

(0.7)

147+

67

(19.2)

0 0 8414

3 I

I (15

'71

+++

+++

+++

++-t

+++

+++

+++

+++

+--

+ 4.

.

+++

+++

n.s.

n.s.

n.s.

n.s.

n.s.

i i-

+

n.s.

+++

+++

+++

++i

+++

+++

+++

is+

i+i

+++

+++ KS

.

t-t+

+++

+++

+++

+++

-+-

S.

jubat

a

Neoc

hrom

ador

a ap

piana

Para

cyat

holai

mus

pu

gette

nsis

P.

vanc

ouve

rens

is

Neot

onch

us

sp.

Spilo

phor

ella

para

doxa

Tripy

loide

s gr

acilis

Visc

osia

ca

rnley

ensis

V.

tum

idula

0

39z!z

I4 (5.

9) 12

7+x2

0 (21

.0)

0 0 0 0 0 0

0

21xtI

3 (8

4 22

f21 (2.3)

31+3

6 (3.

3) 17

f20

(3.1)

56f5

2 (6

.0)

5zt6

(0

.6)

48h7

3 (4.

5) 8rk

I3 (1

’4

9ir2

(0.4) 6zt8

(1

.8)

22f32

(3.3)

6zt9 (043

) If1

(0

4 6f3

(1

’0)

0

241t1

6

(4.6)

51

f46

(9.0)

0 3rt2

(0.5

) 24

i26

(3-I)

26

+23

(x-7)

IIr

t5

(2’9)

9rt4

(0.7)

0

4Orfr3

4 (2.

7) 4x

*29

(4.8)

0 18&1

8

(4’3) ZjcI

(0

.5)

0 7f9

(1.0

) IO

*10 (2

.5)

2It:I

(0.

5) 18

lk25

(2

’1)

I9lfI2

(4.

6)

n.s.

+++

n.s.

+++

0 4613

2 (7.

9) 21

f23

++

+ ILS

.

(3.4)

0 ++

+ n.

s.

0 IfI (0.2

) 0 6+

4 n.

s. n.

s. n.

s. ++

i (1

.1)

14fIO

it-+

n.

s. ++

+ ++

i (2.

7)

Iona

Isl

and

II Ja

n.

7 Ma

r. 19

Apr

. 31

Ma

y 15

Oc

t. 20

De

c. T

D S

TD

Para

scola

imus

sp

. 74

8 3*2

7f6

3i2

0

0

@+2

(6

.0)

(6.4)

(1’4)

Ther

istus

sp

. 8=

t4 2f4

22

f9 IO

f17

0 5=

tfr8

+++

n.s.

++

+ n.

s. (13

.9)

(5.5

) (26

.2)

(6.1

) (2

.6)

Saba

tieria

pu

lchra

33

0 40

*41

IffIO

42

ytII

253fI

IO

209f2

3 ++

+ n.

s.

+++

+++

(48.0)

(50

.0)

(27.4)

(31

.3)

(84.0)

(73

.9)

Neoc

hrom

ador

a sp

. 3f

I If2

2&

I 16

-f14

0 If1

++

+ n.

s.

n.s.

n.

s.

(5.1

) (4.

7) (2.

3) (5

’4

(1-J

Pa

raca

ntho

nchu

s ca

nade

trtis

7*x

1418

X9

*12

2841

8 32

16

3813

n.

s. n.

s. ++

+ n.

s. (12

.0)

(22.4)

(8

.1)

0-w

(12.0)

(13

.1)

Tripy

loide

s gr

acilis

2*3

3f4

0

IIf

452

16f13

n.

s.

n.s.

n.

s. n.

s.

(z-6

) (5

.1)

(1243

) (1.

9) (5.

3)

“+

+ +

= PC

o.05

; n.

s. =

not

signi

fican

t.

224 J. Sharna &‘J. M. Webster

IO 0

o- 6 o- 6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6

-6 O-6 Oe60-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6

IO

0 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6

O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 Fob 8 Apr 7 May20 Aq I Now IO Des 20 Rb8 Apr7 May2OAugl NovlOOa20 hb 8 APT 7 May 20 Auq I NW IO 0% 20

Parocanthonchus caecus

IO 0 Depth

O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 o - 6 bn)

Jonll Mor7 AprlS May31 Ocfl5 0.~20 Jonll Mar7 AprlS Mey 3, OsfI5 hc20 Jon II Mar 7 Apr 19 May 31 Od I3 Dee 20

Figure I. Vertical distribution of males (m), females (0) and juveniles (illl) of nine dominant species at Belcarra Park (top three rows) and three dominant species at Iona Island (bottom row) over I year.

Some nematode species were lumped into a single species descriptor in the early samples

listed in Table 4. They are Sabatieria pukhra (including Sabatieria sp. females and juveniles), Paracyatholaimus pugettensis (includes P. vancouverensis) and Viscosia spp. (identified initially as oncholaimids). The vertical distribution of 12 of the most abundant species (nine from Belcarra Park and three from Iona Island) that show obvious changes in age structure over time, as expressed by the number of males, females and juveniles are shown in Figure I.

At Belcarra Park, large numbers of certain species were recorded only at certain times, e.g. Linhomoeus undulata, Desmolaimus zeelandicus and Eleutherolaimus stensbma (Table 4, Figure I). At Iona Island, S. pulchra occurred in larger numbers in the autumn months. Relatively high population densities were maintained over several months by Viscosik tumidula at Belcarra Park and by Paracanthonchus canadensis at Iona Island. There was a

Free-living nematodes at two Canadian Pacific beaches 225

significant difference in the variance of density over time of all species examined (Table 4) except V. carnleyensis, P. canadensis and Tripyloides gracilis.

There was a significant difference in the variance of the life stages of all species examined except P. pugettensis, P. vancouverensis, V. car&yen.&, Neochromadora sp. and T. gracilis. Large numbers of juveniles were found during a restricted period of the year for Paralinhomoeus buculentus, L. undulatus and S. pulchra, while similar numbers of juveniles were found throughout several months for V. carnleyensis, P. pugettensis, P. vancouverensis, P. mutila, Cobbia urinator and P. canadensis.

None of the species was evenly distributed throughout the top 6 cm, and their vertical distribution remained fairly constant with the exception of Terschellingia longicaudata and Sabatieria sp. For example, during February and August most individuals of D. zeelandicus were found in the z-4-cm layer whilst they were dispersed more evenly throughout the top 6 cm for the remainder of the year. There was a significant difference in the variance of density at various depths for Areolaimus elegans. T. longicaudata and Theristus modicus.

A significant interaction between time and depth occurred for all species except E. stenosoma, Theristus sp., Neochromadora sp., P. canadensis and T. gracilis. A significant interaction between time and stage of development was recorded for Sabatieria sp. and S. pulchra but a significant interaction between depth and stage (but not between time, depth and stage of development) was seen for P. vancouverensis.

Discussion

The nematode faunas at Iona Island and Belcarra Park differ in terms of composition, numbers of individuals and number of species and this is probably partly attributable to the physicochemical nature of the substrate at the two sites.

The extreme variability noted in replicate samples at both sites is characteristic of the patchiness seen in littoral habitats. Sibert et al. (1977) reported standard deviations as large as 858 for a mean of 1943 nematodes from a mudflat in the Cowichan River estuary, British Columbia. Such patchy distribution is common among meiofaunal organisms and may often be due to the selective attraction of nematode species to scattered, dead and decaying organisms on a beach (Gerlach, 1978).

The large difference in nematode densities between the two sites and their association with grain size (Tables I and z) corroborates data from other studies. For example, densities of a.44 X 10~ m-* from an intertidal sandy beach (McIntyre & Murison, 1973), o-5 X IO’ m-’ from a fine sandflat (Ott, 1972) and 3.5 x 106 m--B from well sorted, medium size sediments (Platt, 1977a) have been reported. A study of the littoral benthic fauna at Iona Island referred to nematode densities on the north part of the causeway of 8.7 x 10~ m--2 (Anon., 1975) which is a similar order of magnitude to our records for the summer months (Table 2).

The large number of nematodes at Belcarra Park during the summer (Table 2) follows a pattern established for other locations (Tietjen, 1969; Skoolmun & Gerlach, 1971; Juario, 1975 ; Platt, 19773). Unfortunately, the summer samples are missing at Iona Island but the large number of nematodes occurring in October and December probably reflect the end of a summer peak population and also the considerably higher silt-clay composition of the October-December samples at this site (Table I). Such an environment is associated with large numbers of S. pulchra (Figure I) and Ward (1973) also found a greater abundance of Sabatieria sp. in areas of silty-clay sediments.

Though sandy habitats generally have higher diversity (McIntyre & Murison, 1973 ; 40

species), the high silt content of the fine grained Iona Island sediments coupled with their

226 J. Sharma &f J. M. Webster

relative impoverishment, as shown by their low organic carbon content, results in low species diversity. The larger number of species found at Belcarra Park could be attributed to the heterogeneity of the sediments which have more interstitial niches available for the greater food content as reflected in the higher organic carbon than at Iona Island (Table I).

The variation in abundance of nematode species follows that described by Juario (1975)

from the German Bight with both epigrowth and deposit feeders found at Belcarra Park during the peak nematode population in spring and summer. In contrast, Tietjen (1969) found a large number of epigrowth feeders during spring and summer and a large number of deposit feeders and omnivores during fall and winter. The presence of different feeding types in the same microhabitat at the same time reflects the ability of nematode species to partition the available food (Lee et al., 1977). The peak abundance of several species in this study was associated with the presence of a large number of juveniles. This is also the case in the studies of Skoolmun & Gerlach (1971), Lorenzen (1974) and Juario (1975).

Most nematodes occurred in the upper 4 cm and significantly fewer at 4-6 cm below the surface (Table 2), which agrees with other reports for comparable habitats (Wieser & Kanwisher, 1961; Tietjen, 1969; Platt, 1977b). Occasional reports refer to free-living nematodes occurring at greater depths especially where the sediment is well organized: e.g. 12 cm in the summer and up to 32 cm in the winter on an intertidal, sandy beach (McIntyre & Murison, 1973), 12-13 cm in a Georgia salt marsh (Teal & Wieser, 1966) and 9 cm on a sandy beach in Hong Kong (Wormald, 1976). Although we detected no pattern in the seasonal fluctuations of total numbers of nematodes at different depths, Platt (1977b)

found that the number of nematodes in the deeper sediments was greater in winter than in the summer. He attributed this variation to the presence of a deeper redox discontinuity layer in winter. Though fluctuations were observed in the density of individual species and their life stages the patchiness of the environment coupled with infrequent sampling failed to give any significant interaction between fluctuations in density over time of the life stages and the depth.

Certain species have been shown to be characteristic of a deeper sulfide layer (Ott, 1972). In the present study the distribution of species such as T. longicaudata, S. pulchra and P. mutila below 2 cm (Figure I) may suggest that they have a greater tolerance of the anoxic conditions found in the deeper sediments. The near absence of species such as Neochromadora appiana and P. caecus below 2 cm could be an indication of their intolerance of oxygen- deficient sediments.

Finally, the occurrence and distribution of certain nematode species in the littoral sediments on the Canadian Pacific coast parallels that occurring in similar habitats in the eastern (Skoolmun and Gerlach, 1971; Platt, 1977a) and western (Tietjen, 1969) Atlantic Ocean and on the oriental coast of the Pacific Ocean (Wormald, 1976). A worldwide distribution of many of these nematode species is, therefore, becoming apparent.

Acknowledgements

We are grateful to Bruce E. Hopper (Canada Department of Agriculture, Ottawa) for his confirmation of species identification, to Nit Smol and Magda Vincx (Instituut voor Dierkunde, Gent) for comments on the manuscript and Carlo Heip (Instituut voor Dierkunde) for suggestions and help with the analysis of the distribution of dominant species.

The research was partly supported by an operating grant (No. A4679) from the Natural Sciences and Engineering Research Council of Canada.

Free-living nematodes at two Canadian Pacific beaches 227

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