SMITHSONIAN CONTRIBUTIONS TO THE

EARTH SCIENCES

NUMBER 6

Daniel J. Stanley Distribution of

and Noel P. James EchinarachniuS p

(Lamarck) and

Associated Fauna on

Sable Island Bank,

Southeast Canada

ISSUE D

APR 2 7 1971

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1971
ABSTRACT

Stanley. Daniel J., and Noel P. James. Distribution of Echinarachnius parma

(Lamarck) and Associated Fauna on Sable Island Bank, Southeast Canada.

Smithsonian Contributions to the Earth Sciences, number 6, 24 pages, 1971.—A

combined bottom photographic and sampling survey of Sable Island Bank southeast of Nova Scotia, Canada, reveals locally high densities (to 180 individual/m2

)

of the northern sand dollar Echinarachnius parma. Populations of this form are

closely related to texture of the sea floor and generally concentrated on moderately sorted fine to medium sand surfaces. Topography and current regime are

also correlatable factors; depth, time, salinity, and temperature apparently are

not. Sand dollars are second in importance, after current activity, in reworking

surficial sediments, and these organisms modify at least a third of the total Bank

surface in the study area. Bioturbation is particularly intense in the sector north

of Sable Island. Associated epifauna and infauna populations occur in two eastwest trending areas on the Bank north and south of Sable Island. Absence of

conspicuous fauna, save E. parma, in an east-west zone along the crest of the Bank

and near Sable Island results from extremely strong current activity concentrated

in this region.

Official publication date is handstamped in a limited number of initial copies and is recorded in

the Institution's annual report, Smithsonian Year.

UNITED STATES GOVERNMENT PRINTING OFFICE

WASHINGTON: 1971

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 45 cents
Daniel J. Stanley

and Noel P. James

Distribution of

Echinarachnius parma

(Lamarck) and

Associated Fauna on

Sable Island Bank,

Southeast Canada

Introduction

The present study was conducted as an outgrowth

of a sedimentological survey (James and Stanley

1968) of the sand-covered, current-dominated shallow outer banks of the Nova Scotian Shelf off

southeastern Canada. It is an attempt to evaluate

more precisely than heretofore possible the fauna

likely to affect surficial sediments on a shallow

platform, Sable Island Bank, located far from the

present mainland. It is possible as a result of this

investigation to define the regional distribution

pattern and density of the northern sand dollar,

Echinarachnius parma (Lamarck), and associated

fauna commonly encountered on Sable Island Bank.

Previous investigations (James 1966; James and

Stanley 1968) have shown that this circumboreal

echinoderm is particularly abundant on Sable

Island Bank, the largest of the outer banks on the

shelf. Availability of detailed geographic and hydrologic data, together with information on the sediment regimen, suggested that a study of the benthic

fauna of this area would be particularly profitable.

Data evaluated are derived mainly from bottom

photographs, supplemented by surficial samples

collected at numerous stations distributed over

most of Sable Island Bank and immediately adDaniel J. Stanley, Division of Sedimentology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560

Noel P. James, Department of Geological Sciences, McGill

University, Montreal, Quebec, Canada

jacent areas. The present analyses serve, first of all,

to supplement the surprisingly small amount of

quantitative data and field information on this

common sand dollar (Moore 1966). This echinoid

occurs on both margins of northern North America,

in the western North Pacific, and in the western

North Atlantic the known range of E. parma extends from Cape Hatteras to Labrador and Greenland (Mortensen 1948). We relate the distribution

of E. parma to such parameters as time of observation, depth, topography, sediment type, current

regime, and associated fauna. The problem of correlating fauna visually observed on the bottom with

that collected in relatively small bottom grabs is

also considered.

Geographic and Hydrologic Setting of Study Area

MORPHOLOGY.—Sable Island Bank is a sandcovered platform approximately 250 km long with

a maximum width of 115 km. The 90 m (50 fms)

isobath defines the bank margin (Figure 1). Sable

Island, at approximately 60°W longitude and

43°55'N latitude, is located on the eastern margin

of the Bank, 334 km southeast of Halifax on the

Nova Scotian mainland. Topography and sediments

of the island, a low (relief of 1 to 20 m) east-west

trending arcuate bar of sand flats and dunes about

39 km long and 1.5 km wide, have recently been

described by James and Stanley (1967).

Extremely gentle gradients characterize the bank

top east and south of Sable Island (approximately

1
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

1:880 and 1:330 respectively) as well as north

(1:280) of the island. Along its steep northern edge,

the Bank is bounded by the Gully Trough, a depression (90 to 210 m deep) characterized by hummocky and dissected topography. This depression

curves southward around the northeast margin of

the Bank and deepens to form the southeast trending submarine canyon known as The Gully Canyon

(Marlowe 1967). The southeast margin of the Bank

is the boundary between the outer shelf and the

upper continental slope. The outer margin topography and sediments have been detailed elsewhere

(Stanley and Silverberg 1969).

GENERAL WATER MASS PROPERTIES.—Water mass

likely to affect sediments and organisms in the

study area is composed of Atlantic water diluted

by 20% coastal water (Hachey 1961) and covers

the outer banks of the Nova Scotian Shelf, including Sable Island Bank. Between this "shelf water"

and the Gulf Stream to the south lies a band of

"slope water" having intermediate surface salinities

and relatively low temperatures at middepth. Shelf

water is generally well stratified into three layers

during the summer months and less so during the

winter. The upper layer may be as much as 40 fms

(73 m) thick, with temperatures ranging between

5°C and 20°C and salinities less than 32%O. The

intermediate layer ranges between 17 and 80 fms

(31 to 146 m) in thickness, with temperatures from

0°C to 4°C and salinities between 32%o and 33.5%O.

Bottom water, occupying depths of 50 to 110 fms

(91 to 201 m), has a temperature range from 5°C

to 8°C and salinity gradient from 33.5%O to 35%O.

The intermediate layer is most important in

determining the water characteristics of the outer

banks including Sable Island Bank (Hachey 1961).

The presence of this cold water on the shelf is due

to the large volume of water transported from the

east and northeast by the Labrador Current, and

chilling in situ is a continuous feature, at least

during part of the year. Incursions of slope water

(a mixture of surface, coastal, Gulf Stream, Labrador Current, and upwelling deep Atlantic waters,

as described by McLellan et al. 1953) onto the

Nova Scotian Shelf results is salinity variations on

the outer margin of Sable Island Bank ranging from

33%O to 33.5%O and temperature variations from

5°Cto20°C.

CURRENTS, WAVES, AND TIDES.—The regional distribution of benthic organisms whose feeding and

burial habits make them dependent on the texture

of surficial sediments would almost certainly be

controlled to a considerable degree by water-mass

movement affecting Sable Island Bank. There is

ample evidence that bottom currents do, in fact,

modify the sedimentary cover of the bank top. A

circulatory pattern centered around Sable Island

displays an average rate of drift ranging from 0.11

to 0.15 knots (5.6 to 7.7 cm/sec) (Trites 1958).

This surface circulation pattern varies seasonally

(Bumpus and Lauzier 1965). The northeasterly

and easterly drift along the outer Bank margin constitutes a general off-the-shelf movement and is

consistent except in spring when there is a westerly

drift east of Sable Island. Bottom-circulation patterns in the study area are modified by marked

topographic features including The Gully Canyon

and Sable Island.

In fall and winter, when the Bank top is most

likely to be affected by storms, the number of

waves over 20 feet or more are reported 5% of the

time (Climatological-Oceanographic A tlas for Mariners 1959). In spring the number and size of waves

decrease (waves less than 4 feet in height account

for over 45% of all waves), and in summer waves

over 5 feet in height are rare. Fall and winter are

times of long period, high waves from the west and

northwest. In spring and summer the direction

changes 90 degrees and the waves set from the open

ocean to the south.

Tidal currents are particularly important in

determining the current circulation around Sable

Island (Cameron 1965) and modifying bed forms

on the shallow Bank surface. Cotidal lines, trending in an ENE-WSW direction across the shelf

(Sverdrup et al. 1942), suggest that the predominant

tidal flow may be NW-SE. Currents do, in fact, tend

to set westward (Canadian Hydrographic Service

1960). The mean range of tides on the bank is 3.7

feet. The ebb stream sets southward at 1.5 to 2

knots (77 to 103 cm/sec) on the submerged terminal bars of Sable Island, and the flood stream runs

0.5 knots (26 cm/sec) less northward {Canadian

Hydrographic Service 1960). Terminal bars of

Sable Island directly affect the flow pattern of tidal

currents in the study area; the morphology of the

terminal bars is, in turn, directly molded by these

currents (James and Stanley 1967).
NUMBER 6
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

TABLE 1. —Sample stations on Sable Island Bank, Nova Scotian Shelf

Sample No.

Depth

(meters)

Position

Longitude Latitude

Composition

^Gravel Colour

Sample Equipment

Phleger core Van Veen grab Camera

1

2

1+

5

6

7

8

9

10

11

12

13

Ik

15

1$

17

18

19

20

21

22

23

21+

<326

27

28

29

30

31

32

27

38

39

1+0

l+l

1+2

1+3

1+1+

1+6

1+8

50

51

52

II

55

56

57

58

59

6o

61

62

P63A

360

39

22

23

28

2

20

52

256

175

286

231

223

63

1+

128

132

73

1+0

187

50

52

53

20

32

1+1+

52

72

128

120

50

38

20

16

20

26

65

139

121

170

51

29

20

15

1+1+

90

37

90

65

37

38

22

33

38

25

36

20

18

18

59*03.0'

59*15.5'

59*23.5'

59*33-5'

59*38.2'

59*^1-5'

59*31.5'

59*2l+.O'

59*18.0'

59*07-5'

59*15.0'

59*23.0'

59*29.0'

59*37-0'

59*39.0'

59*37-5'

59*32.5'

59*26.5'

59*1+3.0'

59*1+3.0'

59*1+2.0'

59*1+2.0'

59*1+2.0'

59*1+8.0'

59*1+7.5'

59*1+8.0'

59*1+7.0'

59*^8.5'

59*1+8.0'

sample

59*51+.0'

59*5^-0'

59*53-5'

59*5^-0'

59*5^.0'

59*51+.0«

60*01.0'

6o°oi.O'

60*00.6'

6o°oi.O'

60*01.0'

60*09.0'

60*07.5'

60*07.5'

60*20.0'

60*07.0'

60*12.0'

60*17.0'

60*20.5'

60*35.0'

60*26.1+'

60*20.0'

60*17.0'

60*11.5'

60*09.5'

60*17.0'

60*32.o«

60*1+3.0*

60*1+7.0'

60*35.0'

60*27.0'

60*19.0'

60*21.0'

i+i+*oo.8f

i+i+*oo.5'

^3*58.5'

l+i+*o6.0'

i+i+*08.0'

l+l+'ll+.O'

l+l+*O2.5'

l+i+*26.5'

l+i+*28.5'

. . — ^ - ^

l+l+*O2.5'

1+3*58.0'

l+l+*00.0'

l+l+*02.0'

l+l+*20.0'

i+i+*O7.5»

i+i+*O3.5'

1+3*59.0'

1+3*57.5'

^3*57.5'

^3*58.5'

l+l+°10.0'

l+l+*05.0'

^3*5? !o*

l+l+*O2.5'

l+l+°01.0'

1+3*59.0'

I4V05.0'

kk*09.0'

1+3*57.0'

1+3*57.2'

1+3*57.0'

1+3*57-0

1+3*51+.5'

small speck mud

0.00 98.7 1.3

0.00 98.8 1.2

0.00 97.9 2.1

0.00 98.7 1.3

0.00 99.0 1.0

0.00 98.3 1.7

0.00 99.1 0.9

0.00 99.1+ 0.6

96.I+ 2.7 0.8

0.00 38.0 62.0

0.00 72.3 27.7

0.00 60.8 39.2

0,00 97.8 2.2

0.00 99/3 0.7

0.00 89.8 10.2

8.5 85.5 6.0

18.3 80.6 1.1

3-3 95-2 1.5

0.00 35.2 61+.8

0.00 91+.9 5.1

0.00 90.2 9.8

0.00 97.3 2.7

1.0 97-7 1.3

2.2 96.3 1.5

00.0 97.8 2.2

00.0 97.5 2.5

3.7 95.I 1.2

0.00 87.9 12.1

00. 0

l+.l

0.7

00.0

00.0

00.0

00.0

00.0

00.0

0.7

10.9

00.0

00.0

1.9

00.0

00.0

1.7

71+.7

00.0

19.1

1.0

2.1

00.0

00.0

00.0

00,0

00.0

00.0

00.0

00.0

00.0

00.0

00.0

52.1

90.3

97.0

98.8

98.5

99.0

99.2

9k. k

77

5.5

2.3

1.2

1.5

1.0

0.8

1.2

1.2

1.3

3 22.0

i

1 5

-2

k 95.6

8 1.

97 A

98.5

99.0

97.5

21+. 1

75.

97-

97.

98.7

99.0

98.8

99.2

98.9

98.7

98.8

99.0

99.0

98.9

.2

0.7

1.5

1.0

0.9

1.2

1.2

5-8

1.6

0.6

l .l

1-3

1.0

1.2

0.8

1.1

1.3

1.2

1.0

1.0

1.1

5Y5/2

2.5Y6.5/1+

2.5Y6.5A

2.5Y6/3

2.5Y6.5/I+

2.5Y7/2

2-5Y7/5

2.5Y6.5/I+

2.5Y6/I+

5Y1+/2

5Y1+/2

5Y6/2

2.5Y 6.5/2

5Y1+/2

5Y5/1+

5Y6/1+

2.5Y6.5/8

5Y1+/2

5Y5-5/2

5Y5/2

5Y6/2

2.5Y6/3

5Y6/2

2.5Y6/1+

5Y5/I+

10YR 6/8

5Y1+/2

5Y5A

5YI+/3

2.5Y6/I+

2.5YU.5/I+

5*5/3.

2.5Y6/3

2.5Y6/3

.5Y6/3

•5Y6/2

.5Y6/1+

2 .• 5Y1+/1+

7-

2.5Y6/1+

2.5Y6/1+

2.5Y6/3

2.5Y6/2

2,5Y6/i+ 5/

2.5Y6/1+

2.5Y1+/2

2.5Y5/I+

2.5Y6/1+

5Y5/2

2.5Y6/3

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+

2.5Y6/1+
NUMBER 6

TABLE 1. — Sample stations on Sable Island Bank, Nova Scotian Shelf— Continued

Sample No.

Depth

(meters)

Position

Longitude Latitude

Composition

^Gravel $Sand $Mud Colour

Sample Equipment

Phleger cure VanVeen grab Camera

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

20

10

38

40

36

62

53

57

36

20

10

45

59

105

175

50

40

18

18

20

27

46

92

320

54

42

37

10

22

40

46

120

440

80

60

42

40

31

23

5

99

732

230

76

54

38

26

20

24

-

102

6o'

6o'

60'

60'

60'

60'

60'

60'

6oc

60*

6o°

60*

60*

60*

60*

60*

60°

60'

60*

60*

60*

6o°

60*

59°

59°

59°

59°

59°

59°

59°

59°

59°

59*

59*

59*

59°

59°

59*

59°

59°

59°

59°

59°

59°

59°

59°

59°

59°

59°

59°

59°

'13-5'

'10.0'

'17.0'

'31-51

'43.2'

'35-O'

'26.2'

'18.5'

'14.0'

11.5'

07.5'

12.5'

17.0*

21.0'

07-5'

08.0'

08.0'

O7.O1

07-5'

01.0'

01.0'

01.0'

01.0'

53-5'

52.0'

53-5'

53-5'

55.0'

48.0'

V7.51

^7-5'

48.0'

42.0'

43.01

43.0'

42.5'

36.5;

42.5'

42.5'

29.01

30.0'

14.0'

24.5'

'29-5'

34.o1

38.0'

00.0'

31.0'

16.01

'06.0'

43 57-51

43*57.0'

43*53.5'

43*50.0'

43*46.5'

43*37.0'

43*43.5'

^49,0 '

]± >t ° c X , ^'

43*56.5'

43*49.5'

43*40.0'

43*30.0'

43*30.6'

43*45.0'

43*50.0'

43*54.0'

43*41.5'

43*54.5-

43*52.5'

43*49.0'

43*37.5'

43*31.5'

43*46.0'

43*49.0'

43*51.5'

l|.x°SS 0'

43*52.0'

43*49.0'

43*37.3'

43*34.0'

43*41.0'

43*46.0'

43*51.0'

43*52.0'

44*55.0'

43*58.0'

43*59.5'

43*43.5'

43*37.5'

^3*40.0'

43*46.5'

43*51.5-

43*55.5'

43*57.2'

43*58.0'

43*58.0'

43*53.5'

43*50.5'

00.0

2.0

00.0

00.0

00.0

00.0

00.0

00.0

00.0

00.0

00.0

0.8

00.0

00.0

00.0

11.8

5.6

00.0

00.0

00.0

00.0

00.0

3.5

/

00.0

00.0

00.0

00.0

1.3

00.0

00.0

0.4

00.0

0.9

00.0

00.0

00.0

00.0

12.4

0.00

00.0

00.0

00.0

20.4

00.0

7.5

00.0

00.0

00.0

00.0

00.0

99.9

97.2

98.8

95.6

98.8

98.0

98.4

98.1

98.8

99.0

98.9

96.7

98.0

97-0

9^.5

87.3

92.8

98.8

99-0

96.4

98.5

97.3

95.3

/

97.8

96.9

98.1

98.9

97.8

98.0

97.1.

95- h

31.8

97.3

96.3

97.5

98.5

98.6

86.5

98.8

80.5

58.6

94.8

72.2

98.0

90.1

99.1

98.7

98.9

98-9

99.2

1.0

0.8

1.2

4.4

1.2

2.0

1.6

1.9

1.2

1.0

1.1

2.5

2.0

3.0

5.5

0.9

1.6

1.2

1.0

3.6

1.5

2.7

1.2

/

2.2

3.1

1.9

1.1

0.9

2.0

2.9

4.2

69.2

1.8

3-7

2.5

1.5

1.4

1.1

1.2

19.5

41.4

5.2

2.0

2.4

0.9

1.3

1.1

1.1

0.8

2.5Y7/4

10YR7/2

2.5Y6/4

2.5Y5/2

2.5Y5A

5Y5/2

5Y5/2

5Y5/2

2.5Y6/2

2.5Y6/3

5Y6/2

5Y5/2

5Y5/2

5Y5/2

5Y5/2

2.5Y6/4

5Y5/2

2.5Y7/2

2.5Y6/2

7-5Y3/2

2.5Y6/2

5Y5/2

5Y5/2

ioyR6/2

7-5Y5/4

5Y5/2

5Y5/1

5Y7/2

2.5Y6.5/4

5Y5/2

5Y5/2

2.5Y5/2

5Y5/1

2.5Y6/4

5Y6/2

5Y5/2

5Y5/2

5*5/2

2.5Y6.5A

2.5Y7/3

5*5/2

5Y5/2

1OY5/1.5

5*5-5/2

5Y6/2

5Y6/2

2.5Y7/3

2.5Y6A

2.5Y6/4

2.5Y6/6
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

SEDIMENT DISPERSAL.—Bottom currents mold the

surface of Sable Island Bank in response to watermass movement of the type described in the previous section. Large sedimentary features, including sand waves and subaqueous dunes in water less

than 40 fms (73 m) deep, show that net current

movement north and south of Sable Island is in

opposite directions: toward the east in the region

north of the island, and toward the west, south of

the island (James and Stanley 1968). Intensity of

current activity increases, as would be expected, in

the shallower water close to the island. This circulatory pattern is confirmed by an independent

examination of the texture and mineralogy of the

sand on the Bank.

Most of the sediment on the Bank surface is

now (or in the recent past) being moved by bottom currents. Winnowing and bypassing of finer

sediment would explain the absence of fine silt and

clay on the Bank surface (Stanley and Cok 1968).

Although much of the Bank is undergoing active

erosion, several zones of probable sediment accumulation are on the Bank margins (shelf-break)

south, east, and northeast of Sable Island (James

and Stanley 1968, their Figure 10).

Methods

A total of 114 bottom grab sample stations were

taken on the Bank and surrounding area during the

period from 5 to 9 May 1965 (Table 1 and Figure

1). The sample grid was planned so that the density

of stations increases toward Sable Island. A Van

Veen type grab sampler, which covers approximately 0.15 m2

 of surface area and when full recovers about 20 kg of sediment, was used on 110 of

these stations. Small Phleger cores were collected

at 4 of the deeper stations. Camera lowerings were

made at 32 of these stations with an EG&G bottom

camera rig, below which was suspended at 7.6-cmdiameter compass for orientation of physical and

biogenic features. The camera was automatically

triggered (not bottom-activated) and photographs

were taken every 12 to 15 seconds while the camera

rig was about 1 to 4 meters above the sea floor. The

camera rig remained near the bottom for approximately 5 to 10 minutes as the ship drifted on station. The direction of drift on station is indicated

by a 25-cm-long vane attached to the compass.

A total of 307 (1 to 30 per station) usable black

and white 35-mm photographs were obtained at

28 of the 32 camera stations. A small clock showing the exact time when photographs were taken

and a number recording the frame sequence, noted

in the data chamber, were also photographed.

Depth of stations ranged from 10 to 250 meters.

Position, water depth, and textural composition of

bottom sediment of each sample station are listed

in Table 1. Complete cruise data and results of

mineralogical analyses of the bottom samples collected at the 114 stations are detailed in James

(1966). Negatives of all photographs are maintained in the bottom-photograph collection in the

Division of Sedimentology, National Museum of

Natural History. Data obtained at each of the 28

camera stations are listed in an extensive table

available from the National Oceanographic Data

Center, Washington, D.C. (NODC Accession number 70-1010). From each usable photograph the

area photographed was calculated and the following information recorded: quality of photographs,

presence of compass in photo frame, presence of

ripple marks, sand waves and other current indicators, mottling, bioturbate structures (tracks and

burrows), and fauna. Where one particular species

was abundant (e.g., E. parma or anemones), the

total number of individuals was counted. In the

case of E. parma, apparently stationary, partially

buried and moving individuals were counted separately. The occasional white, often overturned, sand

dollar was interpreted to be dead. Finally, the number of individuals per square meter was calculated.

Sediment Texture and Evidence of Current Activity

Bottom photographs supplement information obtained from the mineralogical and textural analyses (Figure 5). Distinctly different types of seafloor microtopography and texture were noted

(Plate 1) : clean sand, generally rippled; shelly

sand with granular texture; silt and silty sand bottom; and sea floor completely modified by burrowing organisms (bioturbation). A light and dark

mottled bottom was observed at a number of stations. The dark material is almost certainly organic; the patchy distribution is produced by burrowing organisms and bottom-current activity that

disrupt this bottom veneer.
NUMBE

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'-* o rt rt 5 ° « a IISJ g g & & l a

Illf

S 5 S8 3 i 1-8
8 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

Bottom photographs also provide evidence of

short-term bottom-current activity (Plate 2). Most

useful in detailing current direction are sand ripples noted at 14 camera stations (Figure 2). In one

instance, the predominant orientation of anemones, presumably bending in the current direction

(Station 13), was also noted. The NW-SE trending

crests at Station 82 are those of larger sand waves.

The ripple-crest orientation was recorded at all 14

stations, and the sense of bottom-current movement determined at 8 of these (Figure 2).

In shallow water surrounding Sable Island, the

orientation of ripple marks confirms the circulatory pattern described earlier. Northeast of the

island, at Station 59, a NW trend off the Bank is

suggested. Current directions recorded in the head

of The Gully Canyon (Stations 9 and 13) indicate

a movement seaward, generally parallel to the

canyon axis. A predominant downslope current

movement is also noted at the shelf-break near the

head of Sable Island Canyon (Station 18).

It is noteworthy that areas presenting evidence

of strong current activity and those illustrating

mottled sediment are generally mutually exclusive

(Station 55 is an exception). At Station 9, what

appears to be eroded algal matter has been concentrated in ripple troughs by bottom-current activity.

Echinarachnius parma on Sable Island Bank

POPULATION DENSITY.—The northern sand dollar

Echinarachnius parma (Lamarck) was observed in

13 of 28 camera stations. Where present, the density ranged to as many as 185 individuals per square

meter (at Station 21). The number of photographs

showing this species varied from 5 to 22 at any

one station. The photo-to-photo variation in density at each station is depicted on- the histograms

shown in Figure 3.

Immediately apparent is the irregularity of concentration (Plate 3) caused by clustering of individuals. From comparison of the number of

animals counted within the area covered by the

photograph (shown in black on histograms in

Figure 3), it appears that if the area covered exceeds one square meter, the number counted is

relatively close to the mean for that particular

station (see Stations 8 and 21). Only a few photographs suffice then to give a reasonably close approximation to the overall distribution at any one

position on the bank.

It is noteworthy that correlation between individuals photographed at the surface and individuals

retrieved in a small grab at the same station is

poor (Figure 3). Those areas that contain more

than 50 sand dollars per m2 yielded two or more

individuals in the accompanying small Van Veen

grab sample. This low retrieval reflects the small

area covered by the grab but also suggests that not

many sand dollars were buried at the time of the

survey.

REGIONAL DISTRIBUTION.—A chart showing the

distribution and density of E. parma on Sable Island Bank is given in Figure 4. This chart is compiled from both bottom photographs and grab

samples (the presence of at least 2 individuals or

more retrieved in a grab sample at a station where

no photos are available indicates the probable

abundance of at least 50 individuals/m2). The

northern sand dollar is present over one third of

the total Bank surface. Highest densities are found

in an arcuate trending belt north of Sable Island

as earlier postulated in a sedimentological study

of the Bank (James and Stanley 1968) . Concentrations of up to 180 individuals per m2

 are found

just north of the two terminal submerged bars extending from Sable Island. High densities (>20/

m

2

) are rarely found in water deeper than 30 fms

(55 m).

While a large area of relatively few sand dollars

is found on the Bank southeast of Sable Island,

the crests of the island's two submerged terminal

bars, nearshore stations, and the area southeast of

the island appear devoid of sand dollars as well.

Sand dollars do occur, however, in two restricted

areas southeast of the island: (a) a linear NE-SW

trend in shallow water just south of Sable Island's

eastern submerged bar, and (b) at depths of 100

meters on the eastern margin of the Bank adjacent

to The Gully Canyon.

The deepest stations where individuals are encountered are near the heads of Sable Island Canyon (Station 78, 175 m) and The Gully Canyon

(Station 9, 256 m).

A number of trends were observed in the detailed

photographic analysis. Comparison of sand dollars

with the known compass diameter indicates that the
NUMBER 6

08:17

19:00

(5)

200

100

200

100

11:25

15:16

1

10:10

12:30

(it)

12^25

(111)

. . . Station number

100

Sequenc e

of photo

it* /

E. parma retrieved in grab

LEGEN D

FIGURE 3.—Histograms showing photo-to-photo variation in concentration of the northern sand

dollar Echinarachnius parma (Lamarck) (density in m2) as observed at camera and grab stations

on Sable Island Bank. The area covered in each photograph and time of sampling is also

shown.
10 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

"a

u

&

Ia * •

.S -o

O M

It

1 8

.2 *-
NUMBER 6 11

6100 30 6000 59°00

S100 5900

SABLE ISLAND BANK

MEAM GRAIN SIZE (M7 )

(After Folk ond Ward , I957)

 z

I I <O- 0 COARSE

\JZZ'i\ 1.0 - 2. 0 MEDIUM SAND

|-.•.'.•[ 2. 0 - 3.0 FINE SAND IN J UMTS

f-~-1 ^>3. 0 VERY PINE SAND

FICURE 5.—Distribution of mean grain size (in <f> units) on Sable Island Bank (after James

and Stanley 1968). Note close relation between the presence of E. parma (see Figure 4) and that

of fine to medium sand grade.

predominant size of E. parma observed in photos

is between 5 and 6 cm. This is in close agreement

with dimensions of this form found off New England (Lohavanijaya and Swan 1965). It is difficult

to estimate the amount of movement of individuals

in some photographs due to the absence of reworked sand markings. In many cases, however,

partially buried forms and those having left a trail

are noted (Plate 4).

There appears to be no relation between numbers

of individuals and time of day or in the tidal cycle

(Figure 3). Only in a few cases were individuals

found in concentrations such as those observed by

Zenkevitch (1963) in the northwest Pacific. With

the possible exception of Station 56 (Plate 4) individuals appear to be moving in a random pattern,

confirming the observations of Weihe and Gray

(1968) and Boehmer (1970) on southern United

States species of sand dollars. In areas of high density this movement is responsible for modifying

physically produced bottom structures, and the

effect of this bioturbation can be seen on Plate 4.

The movement, by rotation and progression, as

described by Parker (1927) in response to feeding

and burying, modifies both rippled and nonrippled

surfaces. The broad, flat, generally arcuate tracks

made by the sand dollars are characteristic and may

be recognized in the fossil record.

At Station 9 (256 m) located in the head of The

Gully Canyon, sand dollars were observed on a

rippled sand bottom in which organic matter, probably algal detritus, was noted in ripple troughs

(Plate 2f).

Other Epifauna

In addition to E. parma the presence of other organisms living on the sea floor as noted in bottom

camera stations and grab recoveries include starfish, brittle stars, anemones, gastropods, and fish

(hake and cod). Their distribution is shown in

Figure 6 and examples are illustrated in Plate 5.

Starfish [Henricia sanguinolenta (O. F. Miiller)

and others] are found at 8 camera stations from

depths of 20 to over 200 m and appear more numerous north of Sable Island. Brittle stars (Ophi-
12 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

« 5

° S

o

 c

a, >~

.2 a,
NUMBE

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13

-s

w O ^ s H l e3 o 3 | §1

> 2 am

, "3

1

8

So .2

3 o
14

6100 6000

SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

30 5S[00

61 00 5900

SABLE ISLAND BANK

SORTING

(After Folk and Word,1957)

I I <0.35 V.WELL

0.35-0.5 WELL SORTED

0.5 - 0.71 MODERATar WELL

>0.71 MODERATELY

FIGURE 8.—Regional distribution of sorting of sand on Sable Island Bank. The zones generally

devoid of fauna north and south of Sable Island are very well sorted sands coinciding with

areas of high current activity (Figure 2).

omusium lymani Wyville Thomson at 2 camera

stations and in 3 grab samples), on the other hand,

were not recorded above 90 m. These ophiuroids

appear not to be restricted geographically but are

rather limited to deeper water (for example, Gully

Trough, The Gully Canyon, and outer shelf near

the shelfbreak).

Numerous attached anemones were observed at

6 deep water camera stations (>90 m); north

of Sable Island, at Station 33 (50 m), several anemones were attached to shells. At Station 51 in the

Gully Trough (depth of 146 m) as many as 98

(26/m2) were counted in a single photograph.

Gastropods, including the species Aporrhais occidentalis, were recognized at 8 camera stations and

recovered in 7 grab samples. These mollusks are

more common north of Sable Island. Gastropods

occur in water deeper than 55 m on the southern

part of the Bank, while north of Sable Island they

are found in depths over 35 m and in even shallower water in the lee of the submerged terminal

bars of the island.

The organisms cited above generally occur together. The regional distribution of this epifaunal

assemblage occurs in east-west trending zones as

depicted in Figure 4. A belt 34 to 40 km wide that

parallels the shallow crestal axis of the Bank is

generally devoid of conspicuous epifauna.

Infauna

The regional distribution of organisms living

within the surficial sediments cover of Sable Island Bank, evaluated from both photographs and

grab recoveries, is shown in Figure 7. Included in

this assemblage are tubes and polychaetes from

grab recoveries and burrows and tubes observed

in photos. Actual examples are shown in Plate

6. The regional distribution pattern of this assemblage is similar to that of the epifauna (Figure

6). The zone devoid of infauna, however, is narrower (12 to 22 km) than that devoid of epifauna

and is more symmetrically oriented along the crest

of the Bank.

Infauna is generally associated with a mottled

sediment surface. Small mounds of light-colored
NUMBER 6 15

sand surrounding burrow openings (Plate 6) are

separated by darker areas, suggesting that this

patchy coloring results, in some cases, from bioturbation (i.e., disruption of an originally continuous dark veneer).

Recognizable pelecypod shells, including Cyrtodaria siliqua, Pecten magellanicus, and Arctica

islandica, are observed in bottom photographs.

Fragments of shell, or shell hash, are ubiquitous.

Bottom photographs are generally unreliable in

estimating the density of pelecypods because of the

large number of buried individuals. Bottom grab

samples reveal a concentration of shell fragments

in southeast, northeast, and northwest belts trending away from Sable Island toward deeper water

on the Bank (in James and Stanley 1968, their

Figure 6B) . Shells are also abundant near the south

shore of the island, at ends of both bars, and in

shallow water surrounding submerged offshore

terminal bars.

Discussion

INTERPRETATION OF E. parma DISTRIBUTION.—

There does not appear to be any recognizable correlation between density and regional distribution

of E. parma and time of observation or depth of

water on the Bank. The tolerance of this species

to significantly large seasonal variations of temperature and salinities cited earlier is apparent. The

salinity and temperature of bottom water north and

south of Sable Island are not significantly different

and cannot explain the remarkable faunal difference in these two regions (i.e., extremely large

number of sand dollars north of the island as opposed to low densities south of the island). Predators that may affect regional distribution are unknown. The distribution pattern of the northern

sand dollar (Figure 4) can, on the other hand, be

closely related to that of the mean grain size of

sand (Figure 5) which in turn reflects local conditions of bottom current agitation and topography.

The most abundant faunas appear in the fine

(2.0 to 3.0 <f>) and medium (1.0 to 2.0 <£) sand

grades. An exception is Station 8 on the northeastern margin of the Bank where high densities

occur on a coarse sand base. Sand dollars are absent

in a large area southeast of Sable Island, an area

covered by very fine (3.0 <£) sand. Sand dollars also

tend to be absent from regions of very well sorted

sand (Figure 8). Areas of well sorted sand on the

Bank crest and shallow region adjacent to Sable

Island coincide with zones of most intense current

activity as shown in Figure 2. Although sand dollars do occur in rippled areas (such as Stations 54,

55, 111) reflecting moderate to intense water movement above the bottom, they are more commonly

encountered on mottled covered bottoms indicative

of somewhat less intense current activity.

The preference for clean sand by E. parma

(Parker 1927) and other species of sand dollars

(Kier and Grant 1965; Bell and Frey 1969) is well

known. The preference for a distinct sand size related to its burrowing behavior, by Mellita quinquiesperforata (Salsman and Tolbert 1965; Bell

and Frey 1969) is also clearly exhibited by E.

parma. This selection of sand that is frequently

mottled and not very well sorted is undoubtedly

related to the detrital feeding habit of E. parma, a

detritus feeder. The apparent relationship of population density with intense current agitation should

not be overlooked. As has been suggested by others

(Sokolova and Kuznetsov 1960; Zenkevitch 1963;

Reese 1966), E. parma may obtain some of its food

from suspension. Strong current activity like that

near Sable Island would not be conducive to either

substrate stability or successful suspension feeding.

Furthermore, there is some relation between density and topography. Like the species Mellita quinquiesperforata (Weihe and Gray 1968), E. parma

aggregates in the lee of sand bars, in this case the

large terminal bars of Sable Island. Similarly, the

"clumping" response of this species is similar to

that reported for M. quinquiesperforata (Weihe

and Gray 1968).

Population densities calculated in the study

area are somewhat less variable than those of M.

quinquiesperforata whose concentrations range

from 44 to 821 per m2 (Salsman and Tolbert 1965).

Concentrations of the northern sand dollar on the

Bank are also less dense than those depicted by

Sokolova and Kuznetsov (1960) and Zenkevitch

(1963), whose photographs show extremely high

densities of E. parma, with individuals actually

overlapping.

The observation by Emery et al. (1965, their

Figure 9) that more sand dollars were recovered in

grab samples than were counted in bottom photo-
16 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

graphs on the continental shelf southwest of the

study area (suggesting that most forms are buried

and not detectable) is not confirmed by the present

study. Our investigation shows that by far more

individuals occur on the surface (as revealed in

bottom photographs) than in grab samples, indicating that most individual sand dollars were

living on or just at the surface at the time of the

survey (May 1965), and that photographs in this

instance are a more valid means of estimating

population (Figure 3).

The distribution of medium and fine moderately

sorted sand bottom selected by E. parma is closely

related to the present near-bottom current regime

on Sable Island Bank. This texture probably traps

an optimum amount of paniculate matter and

grains covered by organic films that tend to sustain high populations. Coarser grain sizes, representing lag deposits in stronger eroded regimens, are

probably depleted of sufficient organic matter by

abrasion. Finer grain sizes, on the other hand, trap

perhaps too much organic matter thus producing

conditions unsuitable to E. parma. The high number of sand dollars on the surface may, in fact, be

due to higher concentrations of organic matter in

the sand just below the sediment-water interface.

It has been suggested that the dislike by E. parma

of "foul" (lacking oxygen) sand due to decomposition of organic matter causes it to remain on

the surface (Parker 1927). At Station 21, an area

containing as many as 180 individuals per m2 on

the surface, a dark malodorous layer of organic

matter was recovered just below the thin lightcolored sand veneer.

The importance of sand dollars as modifiers of

the surficial sediment of Sable Island Bank is clearly

evident. Mellita quinquiesperforata has been

known to level completely a rippled field 6 to 10

cm in height in a single night (Salsman and Tolbert 1965). As the activity of E. parma is the same

as this southern species, bioturbation must be

regarded as almost as important as current activity

in molding the microtopography and reworking the

sediment of at least one third of the Bank surface.

DISTRIBUTION OF ASSOCIATED FAUNA.—Other organisms living on the sea floor show a dominant

distribution pattern that, like that of E. parma,

displays a predominant east-west trend. When abundant, the epifaunal and infaunal associations resemble faunas on other shallow outer banks of the

continental shelves of northeastern North America (Wigley 1961; Emery et al. 1965). The area

barren of epifauna (except E. parma) appears independent of mean grain size (Figure 5) but coincides with the well to very well sorted sand (Figure 8) and areas of abundant sand ripples and

waves. This would suggest that currents are too

strong in this area for typical northern shelf bottom dwellers. The general absence of Foraminifera

in this barren east-west area adjacent to Sable Island

(James and Stanley 1968) tends to confirm the

above conclusion.

Organisms living within the sediment also require

a reasonably stable bottom and consequently are

not found on the crest of the bank or close to Sable

Island, areas of strongest current activity and moving sediment. The close association of conspicuous

infauna and mottling (the latter suggesting a more

tranquil current regime) is significant in this

respect.

The northern limit of the infauna zone south of

Sable Island is located closer to the island than that

of the epifauna zone. The narrower barren zone

of infauna would suggest that buried or partially

buried organisms are, as a group, somewhat more

tolerant to current activity than those living on the

Bank surface.

Summary of Observations

This investigation of faunal associations on Sable

Island Bank on the outer margin of the Nova

Scotian Shelf shows the following:

1. The distribution of Echinarachnius parma is

more closely associated with mean grain size and

sorting of the surficial sand cover (in response to

current activity) and with local topography than

with any other measured factors.

2. Densities of E. parma reach to a maximum of 180

individuals per m2 and are highest in moderately

sorted fine- to medium-grained sand.

3. After current activity, sorting and bioturbation

as a result of feeding and movement by E.

parma are the most important factors modifying

the surficial sediment cover of the Bank (more

than one third of the total Bank surface area

including the entire sector north of Sable Island) .
NUMBER 6 17

4. Absence of E. parma from regions of strongest

current activity and also from areas of well

sorted and very fine sand grades is probably related to feeding and burial habits.

5. Underwater photography applied to northern

sand dollar population studies in environments

such as broad, shallow outer banks proves to be

considerably more reliable than bottom sampling

surveys.

6. The shallow, east-west trending axis of Sable

Island Bank, subjected to intense current actiyity, is devoid of the typical neritic northwest

Atlantic epifauna and infauna. Population of

typical shelf benthic organisms (other than E.

parma) appear in the deeper, somewhat less

agitated waters beyond this shallow axis and,

consequently, their regional distribution shows

a good correlation with sorting independent of

mean grain size.

7. The regional population distribution shows that

conspicuous infaunal assemblages on Sable Island Bank are somewhat more tolerant of strong

near-bottom current agitation and related sediment movement than are epifauna.

Acknowledgments

Funds to conduct a survey on Sable Island Bank

were provided by the Institute of Oceanography,

Dalhousie University, Halifax, Nova Scotia. We

would like to thank the Captain, officers, and men

of the CNAV Sackville, Dr. F. Medioli, and Dalhousie University graduate students in the Oceanography Program for their help in collecting bottom samples and photographing the study area.

Our appreciation is also expressed to Drs. D. L.

Pawson and P. M. Kier, Smithsonian Institution,

for critically reading the manuscript. Financial

support to complete this investigation was provided

by Smithsonian Institution Research Foundation

Grant 436330.

Literature Cited

Anonymous

1959. Climatological-Oceanographic Atlas for Manners,

182 pages. United States Office of Climatology and

Division of Oceanography.

Anonymous

1960. Canadian Hydrographic Service, pages 10-11. Nova

Scotia (S.E. Coast) and Bay of Fundy Pilot. Ottawa.

Bell, B. M., and R. W. Frey

1969. Observations on Ecology and the Feeding and Burrowing Mechanisms of Mellita quinquiesperforata

(Leske) . Journal of Paleontology 43 (2) :553-560.

Boehmer, W. R.

1970. Erasure of Sediment Surface Features by Mellita

quinquiesperforata (Leske) . Unpublished Masters

dissertation, Old Dominion University, Norfolk.

Bumpus, D. F., and L. M. Lauzier

1965. Surface Circulation on the Continental Shelf Off

Eastern North America between Newfoundland and

Florida. Serial Atlas of the Marine Environment

Folio 7. New York: American Geographical Society.

Cameron, H. L.

1965. The Shifting Sands of Sable Island. The Geographical Review 55 (4) :463-476.

Emery, K. O., A. S. Merrill, and J. V. A. Trumbull

1965. Geology and Biology of the Sea Floor as Deduced

from Simultaneous Photographs and Samples. Limnology and Oceanography 10(1): 1-21.

Hachey, H. B.

1961. Oceanography and Canadian Atlantic Waters. Fisheries Research Board of Canada Bulletin 134:61-65.

James, N. P.

1966. Sediment Distribution and Dispersal Patterns on

Sable Island and Sable Island Bank. Master of Science Thesis, Dalhousie University, Halifax. 254 pages.

James, N. P., and D. J. Stanley

1967. Sediment Transport on Sable Island, Nova Scotia.

Smithsonian Miscellaneous Collections 152(7) :33

pages.

1968. Sable Island Bank Off Nova Scotia: Sediment Dispersal and Recent History. The American Association of Petroleum Geologists Bulletin 52(11) :2208-

2230.

Kier, P. M., and R. E. Grant

1965. Echinoid Distribution and Habits, Key Largo Coral

Reef Preserve, Florida. Smithsonian Miscellaneous

Collections 149 (6):68 pages.

Lohavanijaya, P., and E. F. Swan

1965. The Separation of Post-Basicoronal Areas from the

Basicoronal Plates in the Interambulacra of the

Sand Dollar, Echinarachnius parma (Lamarck).

Biological Bulletin 129(1) : 167-180.

Marlowe, J. I.

1967. The Geology of Part of the Continental Slope Near

Sable Island, Nova Scotia. Geological Survey of

Canada Paper 65-38:30 pages.

McLellan, H. J., L. Lauzier, and W. B. Bailey

1953. The Slope Water Off the Scotian Shelf. Journal of

the Fisheries Research Board of Canada 10:155-176.

Moore, H. G.

1966. Ecology of Echinoids, pages 73-85, in Physiology of

Echinodermata, edited by R. A. Boolootian. New

York: Interscience Publishers, John Wiley & Sons.
18 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

Mortensen, T.

1948. A Monograph of the Echinoidea, Clypeastroida.

4.2:1-471, 258 figures. Copenhagen: C. A. Reitzel.

Parker, G. H.

1927. Locomotion and Righting Movements in Echinoderms, Especially in Echinarachnius. American

Journal of Psychology 39:167-180.

Reese, E. S.

1966. The Complex Behavior of Echinoderms, pages 157—

218, in Physiology of Echinodermata, edited by R.

A. Boolootian. New York: Interscience Publisher,

John Wiley & Sons.

Salsman, G. G., and W. H. Tolbert

1965. Observations on the Sand Dollar Mellita quinquiesperforata. Limnology and Oceanography 10(1):

152-155.

Sokolova, M. N., and A. P. Kuznetsov

1960. On the Feeding Character and on the Role Played

by Trophic Factor in the Distribution of the Hedgehog Echinarachnius parma Lam. Akademia NAUK

SSSR, Zoologischeskii Zhurnal, 39(8) : 1253-1256.

Stanley, D. J., and A. E. Cok

1968. Sediment Transport by Ice on the Nova Scotian

Shelf, pages 109-125, in Ocean Sciences and Engineering of the Atlantic Shelf. Transactions of the

National Symposium, Marine Technology Society,

Delaware Section, Philadelphia.

Stanley, D. J., and N. Silverberg

1969. Recent Slumping on the Continental Slope Off

Sable Island Bank, Southeast Canada. Earth and

Planetary Science Letters 6:123-133.

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1942. The Oceans, Their Physics, Chemistry, and General

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Trites, R. W.

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York: Wiley.
NUMBER 6 19

PLATE 1.—Variation of sediment texture and microtopography

on Sable Island Bank: a. Station 59, on northwest margin of

Bank, depth 25 m. Coarse, sinuously rippled sand with granules in trough. Some granular material in ripple troughs

may be organic in origin. Wave length of ripple approximately 6 to 12 cm. b. Station 9, in head of The Gully Canyon, 256 m. Dark patchy nature of sand bottom referred to

as mottling in text. Unlike the sea floor at this station,

mottling and current activity are generally mutually exclusive (see Figure 2). c. Station 8, on northeast margin of Bank,

52 m. Echinarachnius parma (Lamarck) on a shelly granular sand bottom. Individual and articulated valves and current

concentrated shell hash are noted, d. Station 13, on eastern

part of Gully Trough, 223 m. Silty sandy sea floor completely

modified (bioturbation) by benthic organisms. Note worm

tube in upper-right corner of photo, e. Station 78, on southern margin of Bank near head of Sable Island Canyon, 175

m. Silty sandy (note cloud produced by compass striking

bottom) sediment covered by old rounded ripples, indicating

past current activity. Ripple crests are oriented NNE-SSW.

Compass is 7.6 cm in diameter; compass vane is 25 cm in

length. /. Station 51, in Gully Trough between Middle and

Sable Island Banks, 146 m. Boulders (arrow) on a silty

shelly sand bottom. Note profusion of anemones and other

benthic organisms at this locality. Boulders are glacially

transported (Stanley and Cok 1968).
20 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

PLATE 2.—Evidence of current activity on Sable Island Bank:

a. Station 8, on northeast margin of Bank, 52 m. Sand waves

(scale provided by Echinarachnius parma) with shell hash

granules and organic detritus concentrated in linear troughs.

b. Station 82, on Bank just south of the western tip of Sable

Island, 18 m. Two sets of current ripples on an essentially

sand bottom: predominant sand wave crest orientation of

NW-SE; secondary ripple crests oriented NE-SW. c. Station

59, on northwest margin of Bank, 25 m. Straight asymmetric

sand ripples showing predominant current direction toward

the southeast. Compass and E. parma provide scale, d. Station

9, in head of The Gully Canyon, 256 m. Sinuous and interference sand ripples showing somewhat variable current directions, e. Station 78, on southern margin of Bank near head

of Sable Island Canyon, 175 m. Somewhat vague "relict"

ripples veneered with silt indicative of current activity sometime in recent past. /. Station 9, in head of The Gully Canyon, 256 m. Dark material, possibly of algal origin, concentrated in ripple troughs.
NUMBER 6 21

PLATE 3.—Distribution pattern of the northern sand dollar

Echinarachnius parma (Lamarck) on Sable Island Bank:

a. Station 21, on Bank north of eastern margin of Sable

Island, 50 m. High density of northern sand dollar covering

nearly entire sandy sea floor surface. Note starfish below

compass. See also Station 21 in Figure 3. b. Station 21, same

as Figure 1. Much lower concentration of E. parma. c. Station

8, on northeast margin of the Bank, 52 m. Tendency of sand

dollars to cluster on sand wave crests is shown. Shelly and

organic matter and granules are concentrated in troughs.

d. Station 8, same as in Figure 3. Clustering of E. parma in

linear belts trending parallel with sand wave crests, e. Station 9, in the head of The Gully Canyon, 256 m. Relatively

low sand dollar population on an asymmetrically rippled

sand bottom. Sand is moving parallel with the major downslope trend of canyon. /. Station 33, on margin of Bank north

of Sable Island, 50 m. Population of E. parma on a mottled

and burrowed sand bottom, suggesting tranquil bottom conditions. Note articulated pelecypod valves concave down and

gastropod shell in upper center.
22 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

PLATE 4.—Bottom markings produced by Echinarachnius

parma on the sandy surface of Sable Island Bank: a. Station

21, on margin of Bank north of the eastern sector of Sable

Island, 50 m. Evidence of bioturbation produced by the

northern sand dollars on a mottled sand surface. Evidence

of markings produced by rotation and by progression and

combinations of both are noted. Partially buried forms are

visible, b. Station 56, on the Bank adjacent to the submerged

western terminal bar of Sable Island, 22 m. Sand dollars

completely modifying sand surface of Bank. A possible preferential orientation of individuals moving toward the lower

part of photograph is suggested, c. Station 88, on Bank south

of Sable Island, 54 m. Close view of shallow parallel track

made by moving E. parma on sand surface, d. Station 48,

near margin of Bank north of western sector of Sable Island,

44 m. Close view of partially buried individuals indicating

movement by rotation. Note starfish Henricia sanguinolenta

(O. F. Muller) in right of photograph, and also in a. e. Station

54, on Bank northwest of Sable Island, 37 m. Bioturbation

by E. parma on rippled sand bottom. Note curved parallel

track of individual in lower center part of photograph.

/. Station 22, on Bank north of east terminal bar of Sable

Island, 52 m. Sand dollars on silty bottom covered by dark

organic film. Evidence of burrowing also present.
NUMBER 6 23

PLATE 5.—Association of organisms living on the surface of

Sable Island Bank: a. Station 8, on northeast margin of the

Bank, 52 m. Benthic fish resting on sand wave trough. Note

clustering pattern of E. parma. b. Station 48, near margin

of Bank north of western part of Sable Island, 44 m. Large

starfish in upper part of photograph. Note abundant individual valves of pelecypods concave up and partially buried.

c. Station 86, on margin of Bank south of Sable Island, 92 m.

Abundant brittle star (probably Ophiomusium lymani

Wyville Thomson) on mottled sand surface. Sand dollars

give scale, d. Station 16, in Gully Trough north of Sable

Island, 128 m. Gastropod (see arrow) on a bioturbate silty

sand bottom. Granular texture is probably organic in origin.

e. Station 51, in Gully Trough, 146 m. Large population of

small anemones on gravely silty sand bottom. /. Station 78,

on southern margin of Bank near head of Sable Island Canyon, 175 m. Large anemones on gently rippled sand. g. Station 13, in Gully Trough near the head of The Gully Canyon, 223 m. Close-up of small anemone on sandy silt bottom.
24 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES

PLATE 6.—Association of organisms living within and on the

sediment on Sable Island Bank: a. Station 13, in Gully

Trough near the head of The Gully Canyon, 223 m. High

concentration of worm tubes on a sandy silt bottom, b. Station 13, same as Figure 1. Large number of worm tubes and

anemones on a burrowed sandy silt bottom, c. Station 13,

same as Figures 1 and 2. Trails of benthic organisms, probably worms, on burrowed sandy silt bottom, d. Station 33,

on margin of Bank north of Sable Island, 50 m. Small raised

burrows on a mottled shelly sand bottom covered with E.

parma. Reworking by wormlike organisms probably resulted

in patchy dark and light-colored bottom. Sand dollars provide scale. The associated features suggest relatively tranquil

condition on the sea floor, e. Station 8, on northeast margin

of the Bank, 52 m. Partially buried shell, for the most part

individual valves concave down, concentrated in troughs of

sand waves. /. Station 77, on southern margin of Bank, 105

m. Large individual valves concave up and partially buried.

Mottled surface produced by burrowing organisms.

•ft U.S. GOVERNMENT PRINTING OFFICE: 1971 O 4II-33O