12

| SECT. ;
O2,Mi/L . “ | mo

Figure 4. Vertical. distribution of salinity and dissolved
woe oxygen, Sections I and. 11: . Shading indicates shelf
water. : a


the 200 m contour is not readily apparent. Possibly they, too,
are diel migrants and find the underlying slope water intolerable.

In future studies of this nature it would be desirable to
sample.in the spring when the temperature contrast. between: shelf
and slope waters is at a maximum and the surface temperature
manifestation of the shelf/slope front is readily discernible from
satellite IR imagery and shipboard observations. In addition, it
would be expedient to employ a discrete depth plankton sampler
such as the MOCNESS (Wiebe et al. 1976) so that the vertical
distribution of larval fishes and associated zooplankton: could be
ascertained and more precise correlations of abundances with
oceanographic features established.


16

78 77 76 75 74 73 72 7\

*5.0
SECT X 02,ML/L

)
["4
w
ro
w
=

79
”
[4
ui
i
Ww
=

Figure 8.

Vertical distribution of salinity ‘and dissolved
oxygen, Sections IX-and X. oF


Vii

ABSTRACT

SS

Appreciable differences existed in water mass distributions
along the edge of the continental shelf as interpreted from_
satellite infrared imagery and shipboard temperature, salinity,
and dissolved oxygen observations. In general, shipboard
indications of water mass distributions based on salinity and
dissolved oxygen values were compatible, but the discontinuities
observed were not as marked as those indicated by satellite
imagery and evidenced a more southerly dispersion of shelf
water. Chlorophyl1 concentrations and zooplankton volumes were
appreciably greater over the continental shelf; (<200 m).

‘Nanoplankton/netplankton ratios were greatest in oceanic waters..—
a

The distributions of neritic and oceanic taxa of ichthyoplankton,
zooplankton, and phytoplankton substantiated previous inferences
as to their geographic range and optimum water type. Although the
precise depth distribution of ichthyoplankton and zooplankton was
not ascertained, oceanic species were restricted to areas of slope
or Gulf Stream water or to areas in which these water types were
readily accessible.

a
| Preceding Page Blank |



13

METERS

oo sect re ©
4 Oz ,ML/AL —

Figure 5.. Vertical distribution ‘of ~ salinity ~and dissolved
oxygen, Sections III and IV. , .


19

SHELF : NO. /M? OCEANIC

1-10 70° 68° 66° 64°.
10-100 42
100-1000
1000-10000
19,000 +

40°

42°

nips ee eb bees

42°

40° 40°

. NASUTUS
+ 42°

42°

40 aoe

°° ©. FINMARCHICUS + P BOREALIS

L L i 1 1 it L L i 1 1 4
70° 68° 66° 70° 68° 66°

Figure 11. Distribution of neritic and oceanic copepod species.


15

100

SECT. UIT * 355
SAL., Yoo, ( L

METERS

100

METERS

Figure 7. Vertical distribution of salinity and dissolved
oxygen, Sections VII and VIII.


10

42° 42°
sor L aoe
4 b
ar La
+ =
aor Lao
200M TEMP,,°C
T T
7 70° oe oe ca
ar Lae
aor | ao

SURFACE SAL.,%o |

T T
72° 70° oe

Figure 2.

T T
66° 64°

Shipboard: observed surface and 200. m temperatures

surface salinities.

and


as based on satellite IR imagery and shipboard hydrographic
observations is consistent with previous observations made during
late summer and early fall (Mooers, Flagg, and Boicort 1978;
Chamberlin 1981; Joyce et al. 1984). It. appears that the
intensity of satellite coverage is such that thermal contrasts are
detected that are not usually observable .from widely spaced
shipboard temperature observations. At -this time of the year
salinity and dissolved oxygen serve as better indices of shelf and
oceanic.water. than does temperature. To further illustrate this
point, we have plotted (Fig. 3) shipboard observed surface
temperature, salinity, and dissolved oxygen values and satellite
IR imagery during a detailed survey of Warm Core Ring 81-D made
just prior to the cruise in question (Albatross IV Cruise 81-11,
23 Sept.-5 Oct. 1981). We have depicted shelf water (shaded) as
having a salinity <34.5°/oo (Wright 1976; Wright and Parker 1976)
and a dissolved oxygen concentration >5.5 m1/1 (McLellan 1957).
The correspondence in the position, area, and form of Warm Core
Ring 81-D based on satellite imagery and surface salinity and to a
lesser extent dissolved oxygen was good. The distribution of
surface temperature did not clearly delineate the warm core ring.

To more clearly define water mass distributions and
boundaries prevailing at the time of Albatross IV Cruise 81-12,. we
have plotted in Figures 4-8 vertical profiles of salinity and
dissolved oxygen for the 10 north-south sections shown in Figure 1
using the same criteria for differentiating shelf and slope water
as in Figure 3. The agreement between these two criteria in
separating shelf and slope water was fairly good.

In Section I (Fig. 4) salinity values show shelf water
overlying slope water to a position just north of Station 7, while
dissolved oxygen values reveal shelf water overlying slope water
throughout the section. . The Section II salinity values (Fig. 4)
demonstrate a slight surface manifestation of slope water at
Station 11, while dissolved oxygen values indicate that. shelf
water overlays the whole area. Both the Section III salinity and
dissolved oxygen values (Fig. 5) evidence an upper layer of. shelf
water over the whole section, although dissolved oxygen values
show subsurface slope water extending further onto the shelf. The
Section IV salinity values (Fig. 5) show shelf water extending
seaward to Station 26. The dissolved oxygen observations,
although incomplete, indicate a similar distribution. There was
no surface salinity or dissotved oxygen manifestation of the
shelf/slope front in Sections V or VI (Fig. 6). The dissolved
oxygen concentrations in Section VII (Fig. 7) indicate an isolated
surface pool of low dissolved oxygen (slope?) water overlying the
shelf break. This pool is not evidenced in the salinity values.
In Section VIII (Fig. 7) there were two cells of low dissolved
oxygen water, one at the bottom. at 70 m depth and one at the
surface (Sta. 61). The salinity values did not indicate any
isolated pools of slope water in the shelf water layer. The
salinity values in Section IX (Fig. 8) indicate that shelf water
was present at inshore Stations 65-67 while dissolved oxygen
values showed an additional isolated surface pool of shelf. water


7 rs “7

42° 42°
0°

vot ceuis/t_|
Ty] 1-3

3-10
10-30
30-100 140°
100-300
300-1000

40°

42° ra — 42°

104 CELLS/L

| 0.1-0.3
03-1
1-3
3-10
10-30 740°
30-100

40°

: DIATOMS, SURFACE 7]
1 L
72 70° oe - rr 64°

Figure 14. Total phytoplankton and diatom distributions.

YUL S. GOVERNMENT PRINTING OFFICE: 1985--501-658--20,042


ABSTRACT... see eeeeee
LIST OF FIGURES......
INTRODUCTION.........
MATERIALS AND METHODS
RESULTS... ce eeeeeneeee

v

CONTENTS

Temperature, Salinity, and Dissolved Oxygen.............4.

Ichthyoplankton..
Zooplankton......
Phytoplankton....
DISCUSSION.........8
LITERATURE CITED.....

/ Preceding page blank




11

40°F

40°

ape 40. 42°
40°
SLW .
r IR IMAGERY /cs SURFACE SALINITY 14
23 SEP - 5OCT
age 42°
FE sos
| SURFACE TEMP | SURFACE O, 7
23 SEP - 5OCT 23 SEP - 5OCT
i i ! i ! i
68° a ey

Figure 3.

Shipboard observed surface temperature salinity, and
dissolved oxygen during 23 September-5 October 1981
and position of Warm Core Ring 81-D and ‘associated
water masses as determined from satellite imagery on
28 Septemer 1981.


INTRODUCTION

..AsS part of. an effort to determine the extent of seaward
advection of shelf plankton assemblages in the vicinity of a semi-
permanent frontal zone, a survey was conducted in autumn 1981
(Albatross IV Cruise 81-12; 12-23 October 1981). ° This report
examines the changes in ichthyoplankton, zooplankton, and
phytoplankton assemblages across the shelf/slope front in the area
bounded by longitudes 70°00'W and 66°00'W.

MATERIALS AND METHODS

Shipboard sampling included standard double oblique. 0.61 cm
Bongo net tows (0.505 and 0.333 mm mesh) to a maximum depth of 200
m. Water samples for salinity, dissolved oxygen, phytoplankton
species composition, and chlorophyll a were obtained at depths of
1, 10; 20, 30,-40,:50, 75 and 100 m. An XBT cast was made midway
between stations. Hydrographic data (temperature, salinity,
dissolved oxygen) were processed and summarized at the NMFS Woods
Hole. Laboratory, ichthyoplankton and zooplankton. species
composition and abundance were ascertained at the NMFS
Narragansett Laboratory, chlorophyll determinations were made at
the. NMFS Sandy Hook Laboratory, and phytoplankton species
composition and abundance were determined at Old Dominion
University, Norfolk, VA. :

- RESULTS
Temperature, Salinity, and Dissolved Oxygen

The station locations and water: mass “distributions as
interpreted from satellite infrared (IR) imagery on 12 and 21
October by the National Earth Satellite Service (NESS) are shown
in Figure 1. Shipboard observed surface and 200 m temperatures
and surface salinities: are plotted in Figure 2. ‘There is’ little
conformance between the location of the shelf/slope boundary as
interpreted from satellite imagery and from the distribution of
shipboard observed surface temperature and salinity values,
although the 14°C and 15°C isotherms and the 33.0°/oo and 33.5°/o0
isohalines roughly encompass the infrared-inferred
discontinuity. Both surface temperatures (>18°C) and salinities
(>36°/o00) demark Gulf Stream water -in the extreme southeast
section of the sampling area. Subsurface temperatures (9°C and
15°C. at 200 m) show that at this depth slope water bordered upon
the..200 m isobath between 72°W and 66°W longitudes and that the
Gulf, Stream north wall was only manifest in the southeast extreme
of the sampling area.

. The poor agreement between the distribution of shelf and
oceanic water masses (esp. the position.of the shelf/slope front)



42°

40°,

38°
42°

40°

7

4 42°
440
“MEAN. WATER COLUMN (75M) [ 7
CHLOROPHYLL, MG/M3
en ae 36
442°

NO. /10m? 140°

1-3

3-10
[}10-30 |
Es) 30-100

& sr:
“oe woviom2 |“
1-3
p 3-0
/ . 7 10-30
MYCTOPHIDAE BOTHUS OCELLATUS.
38° > 1 1 nm 1 1 1 1 1 1 1 L ae _ 1 1 38°
72 70° 68° oor 64° 72° 70° 68° 66° 64°
Figure 9. The distribution of mean water column chlorophyll,

zooplankton displacement volume,

and two shelf and

oceanic taxa of larval fishes, 12-23 October 1981.


‘ty

NOAA Technical Memorandum NMFS-F/NEC-38

The Shelf/Slope Front
South of Nantucket Shoals and Georges Bank
as Delineated by Satellite Infrared Imagery
and Shipboard Hydrographic

and Plankton Observations

U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Woods Hole, Massachusetts

May 1985



Rhincalanus cornutus, R. nasutus, and. Pleuromamma borealis were
restricted for the most-part to waters south of the 200 m contour.

* Phytoplankton

The distribution of integrated chlorophyl1 concentrations to
a maximum depth of 75 m is shown in Figure 9. The highest
integrated chlorophyll] values (1.0-2.0 mg/m?) occurred’ over the
continental. shelf (<200 m) in’ the northwest section of the
sampling: area and where -shelf. water extended. to. the bottom: or
close to the bottom. With few exceptions (Section VII) offshore
(>2000 m) chlorophyll, concentrations were <0.4 mg/m. The
association of high chlorophyl] values with shelf water is
manifest in the chlorophy1] vertical distribution plots shown in
Figure 12.

For total stations the average ratio of nanoplankton (<20 um)
to netplankton (>20 um); on a basis of chlorophyll a values was
4/1... As has been previously noted (cf. Malone 1971; Ryther 1969;
Yentsch and Ryther 1959), percent nanoplankton values were
appreciably higher in oceanic than in neritic waters (Fig. 13).
Areas. of high standing crop (chlorophyll a, Figs. 9 and 12)
coincided with areas over the continental shelf having relatively
high percent netplankton.

. The samples contained 273. species of, phytoplankton, in’
addition to. a pico-nanoplankton component composed mainly of
cyanobacteria (1.5-5.0um). Higher surface cell concentrations of
both “total phytoplankton. and diatoms were generally associated
with the cooler and less.saline shelf water (Fig. 14). The pico-
Nnanoplankton fraction represented, 71% of the total cell counts for
all ‘depths, averaging 34.9 x 107 cells/1. . The diatoms were the
next post abundant group at 16% of the total cells, averaging 8.0
x 10% cells/1 for all stations and. depths. Other groups
represented included the Dinophyceae, Haptophyceae,
Euglenophyceae, Cryptophyceae, Chrysophyceae, and cyanobacteria.
The diatoms averaged 16 x 10° cells/1 over the continental shelf
compared to 2:6 x 104 cells/1 at locations seaward. The highest
diatom concentrations were in the northwest portion of «the
sampling area and correspond to sites of high mean chlorophy1]
values. These diatom populations included both small (<20 ym) and
larger cell types. Using cell volume as ‘the basis for determining
phytoplankton biomass of the standing crop, the mean water column
value for diatoms was 78% of the total, followed: by the
Dinophyceans - (14%), with .the pico- nanopTankton contributing less
than 1%.

“The most abundant diatoms over the shelf were colonial and
chainforming species, e.g. Leptocylindrus danicus, Chaetoceros
-sociale, and Rhizosotenia delicatula. These are typically neritic
species, with LC. danfcus and R. delicatula common. dominants in
estuaries along the coast. Regional patches of larger diatoms
(Coscinodiscus spp. and Rhizosolenia spp.) also contributed to



at the two offshore stations (Sta. 69 and 70). The distribution
of shelf water was essentially similar in Section X (Fig. 8) based
on dissolved oxygen and salinity values, being confined to the
area inshore of Station 74, the exception being an isolated patch
of shelf water indicated by dissolved oxygen values at Station
73. Gulf Stream water, as indicated by salinity values >36°/00,
was encountered at the two offshore stations (72 and 71).

With the exception. of the extreme eastern region of the area
of coverage. (Sections IX and X), the surface salinity values
indicated an appreciably. greater offshore extension of shelf water
than did the infrared temperature data. It was only in Sections
I, IX, and X that slope water” (>34.5°/00) was observed in the
surface layer. :

Ichthyoplankton

The distribution of two characteristic shelf and oceanic taxa
of larval fishes are shown in Figure 9. - Scophthalmus -aquosus
(windowpane) and Merluccius bilinearis (silver hake) were
restricted for the most part to the continental shelf (<200 m),
the one exception being the occurrence of silver hake larvae at
Station 23 on Section III. At this station shelf water (salinity
<34.59/00) extended to a depth of 100 m. Seventeen taxa of
Myctophidae were collected. Ceratoscopelus maderensis,
Diogenichthys atlanticus, Benthosema glaciale, and Diaphus sp.
made up the bulk (75%) of the catch. The myctophids were confined
to areas deeper than 200 m and to areas characterized by surface
or -subsurface. slope or Gulf Stream water. The myctophids are
mesopelagic and most species inhabit considerable depth by day
(200-600 m), but are often found at the surface at night. The
night/day ratio in the catch of total myctophids was 5.7. Bothus
ocellatus (eyed flounder), a warm water species which is commonly
carried into northern areas via the Gulf Stream, was also confined
to offshore waters deeper than 200 m, although its distribution
was more limited than that of the Myctophidae. The distribution
patterns of the four larval fish taxa in relation to water mass
type is clearly reflected in the  temperature-salinity-
ichthyoplankton diagrams shown in Figure 10.:.

: Zoop]ankton

Zooplankton displacement volumes tended to be highest over
the continental shelf (Fig. 9), although relatively high values
also occurred in offshore areas (e.g., Sections II, III, IX, and
X). Copepods dominated the zooplankton collections with 60
species being identified (2 Harpacticoida, 3 Cyclopoida, and 55
Calanoida). Examples of the distributions of three neritic and
three oceanic copepod species are shown in Figure 11. Temora
longicornis, Centropages hamatus, and Calanus finmarchicus were
confined almost wholly to continental sheTf waters (<200 m) while



Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure
Figure

10.
ll.
12.

13.
14.

vi

LIST OF FIGURES

Albatross IV Cruise 81-12 station locations

(12-23 October, 1981) and water mass distribu-

tions based on satellite infrared imagery on
12 October and 21 October 1981.........eeeeeeeeeee 9

Shipboard observed surface and 200 m tempera
tures and surface salinities........seeeeeeeeeeeee 10

Shipboard observed surface temperature salinity,

and dissolved oxygen during 23 September-5

October 1981 and position of warm core ring

81-D and associated water masses as determined

from satellite imagery on 28 September 1981....... ll

Vertical distribution of salinity and dissolved
oxygen, Sections I and II, shading indicates
SHELF Water... cece cc cceeneeeereeeeceeeeeeteeere 12

Vertical distribution of salinity and dissolved
oxygen, Sections II and IV......eccceeeeeceeeeeeee 13

Vertical distribution of salinity and dissolved
oxygen, Sections V and VI.....eceeeeeeeeeseeeeeeee 14

Vertical distribution of salinity and dissolved
oxygen, Sections VII and VIII.....sceeeeeeeseeneee 15

Vertical distribution of salinity and dissolved
oxygen, Sections IX and X...ccccccccccevcceneecece 16

The distribution of mean water column chlorophyll,
zooplankton displacement volume and two shelf and
oceanic taxa of larval fishes, 12-23 October

LOBL cece cece t eee cree eee e eter cence eeeeeeneaee 17

Ichthyoplankton abundance in relation to tem-
perature and salinity

Distribution of neritic and oceanic copepod

SPOCTOS. .eceeece cence ce cee eeeceneeneeeeceeeeetens 19
Vertical distribution of chlorophy11, Sections

TeXe cc cccc cece cece cece eer e eee e nen eeeteeeeeeeeneeee 20
Percent nanoplankton.........sseeeees eeceweeeeees 21

Total phytoplankton and diatom distributions...... 22


2)

a

Ww

te

w

=

)

[4

ud

HF
200

= "0
100

Figure. 6.

; 355
4 secraz .
4 SAL, %eo
J i L _l i
J : 60 |

| SECT IZ
Op ML/L

TTT YT

Vertical distribution of
oxygen, Sections V and VI.

salinity and dissolved


20

SECT .
4 CHL,MG/MF

METERS

100

-|secr ©
cH, MG/M

Figure 12.

Vertical distribution

48 47°« «460: «45 A ABD
6 | J I | |
“ho ft Ket ecenr ot :
T° fob acoer TINS og

4-0

4 a on
4 OT . .

1004 “SECU + .
7 CHL, MG/M?
52 53 54 S55 56

* SECT.» WI

qj CHL, MG/M
65 66 67 «68 «66970
otort + | | \
4 pe 0 :7i 0
Sa
4 ° +01
10044 “SECT IK .
4 CHL, MG/M

SECT ZX + . :
CHL, MG/M?

of chlorophy11, Sections I-X.




7
LITERATURE CITED

CHAMBERLIN, J. L. :
1981. Application of satellite infrared data to analysis of
ocean frontal movements and water mass interactions off the
northeast coast. NAFO SCR Doc. 81/1X/123, 15 p.

COLEBROOK, J. M., R. S. GLOVER, and G. A. ROBINSON.

1961. Continous Plankton Records, 1946-1956: Contributions
towards a plankton atlas of the north-eastern Atlantic and
the North Sea--General Introduction. Bull. Mar. ‘col.
5(42) :67-80.

COLTON, J. B., Jr., and R. R. BYRON.
1977. Gulf of Maine--Georges Bank ichthyoplankton collected
on ICNAF larval herring surveys September 1971-February
1975. NOAA Tech. Rep. SSRF-717, 35 p.

HEDGPETH, J. W. (Ed).
1957. Treatise on marine ecology and paleoecology. Vol. 1
Ecology. Mem. Geol. Soc. Amer., No. 67:1-1296.

JOYCE, T., R. BACKUS, K. BAKER, P. BLACKWELDER, 0. BROWN, T.
COWLES, R. EVANS, G. FRYWELL, D. MOUNTAIN, D. OLSON, R. SCHLITZ,
R. SCHMITT, P. SMITH, R. SMITH, and P. WIEBE.

1984. Rapid evolution of a Gulf Stream warm-core ring.
Nature 308 :837-840.

MALONE, T. C.

1971. The relative importance of nannoplankton and
netplankton as primary producers in tropical oceanic and
neritic phytoplankton communities. Limnol. Oceanogr.
16 :633-639.

MCLELLAN, H. J.
1957. On the distinctness and origin of the Slope Water off
the Scotian Shelf and its easterly flow south of the Grand
Banks. J. Fish. Res. Board Can. 14(2) :213-239.

MOOERS, C. N. K., C. N. FLAGG, and W. C. BOICORT.

1978. Prograde and retrograde fronts. In Oceanic fronts in
coastal processes. Malcolm J. Bowman and Wayne E. Esaias
(Eds.). Proceedings of a Workshop held at the Marine
Sciences Research Center, Stony Brook, N. Y., May 23-27,
1977. Springer-Verlag, New York.

RYTHER, J. H.
1969. Photosynthesis and fish production in the sea. Science
166 :72-76.

WIEBE, P. H., K. H. BORT, S. H. BOYD, and A. F. MORTON.
1976. A multiple opening/closing net and environmental system
for sampling zooplankton. J. Mar. Res. 34:313-326.


L 42°

L 40°

L 38°

tL 42°

L 40°

38°

72 70° 68° 66° 64°

Figure 1. Albatross IV Cruise 81-12 station locations (12-23
Uctober, I981) and water mass distributions based on
satellite infrared imagery on 12 October and 21
October 1981. ‘


NOAA Technical Memorandum NMFS-F/NEC-38

This TM series is used for documentation and timely communication of
preliminary results. interim reports, or special purpose information, and
has not received complete formal review, editorial control, or detailed
editing.

The Shelf/Slope Front
South of Nantucket Shoals and Georges Bank
as Delineated by Satellite Infrared Imagery
and Shipboard Hydrographic
and Plankton Observations

J.B. Colton, Jr.1, J.L. Anderson’, J.E. O’Reilly?,
C.A. Evans-Zetlin?, and H.G. Marshall?

‘Narragansett Lab., National Marine Fisheries Serv., Narragansett, RI 02882
? Sandy Hook Lab., National Marine Fisheries Serv., Highlands, NJ 07732
3Dept. of Biological Sciences, Old Dominion Univ., Norfolk, VA 23508

U.S. DEPARTMENT OF COMMERCE
Malcolm Baldridge, Secretary

National Oceanic and Atmospheric Administration
Anthony J, Calio, Acting Administrator

National Marine Fisheries Service
William G. Gordon, Assistant Administrator for Fisheries

Northeast Fisheries Center
Woods Hole, Massachusetts

May 1985

n


18

37 Fs es CC SO CS CS NG CS NS CN
| BOTHUS OCELLATUS” , | MYCTOPHIDAE *
364 +
. o °
a.) | + 58
354 ° + °
ate . ois) .
= 4 . L ca
8 oe 7 oe
S aa. . 1, .
> Jo: Lo:
a . .
Z 334 . 7 +o.
Ss vo Se tea
qo4 a “ :
(vp) . .
324 : + .
a a rer
<q _| SCOPHTHALMUS «+ MERLUCCIUS .
0 AQUOSUS BILINEARIS
O36 +
Ee 4 a L “3
Zz J ° .
— 35 eo + _-
—e | ot J oa
) ot + ot
QR wf. . + oe .
4 : + NOHO?
° ° + ABSENT
34. 7 +o. 7-3
tO Lao. Oy ° 3-10
4 2 Sone + sT Re | 0 0-30
an . |e 30-100
324 3 4 . | + 100-300
T T T T qT TT TT T T T T TT TT T qT T
0 12 14 6B lo 12 14 1B

200m INTEGRATED TEMPERATURE (°C)

Figure 10. Ichchtyoplankton abundance in relation to temperature
and salinity.


NOAA TECHNICAL MEMORANDUM NMFS-F/NEC

Under the National Marine Fisheries Service's mission to "Achieve a
continued optimum utilization of living resources for the benefit of the
Nation," the Northeast Fisheries Center (NEFC) is responsible for planning,
developing, and managing multidisciplinary programs of basic and applied
research to: (1) better understand the living marine resources (including
marine mammals) of the Northwest Atlantic, and the environmental quality
essential for their existence and continued productivity; and (2) describe and
provide to management, industry, and the public, options for the utilization
and conservation of living marine resources and maintenance of environmental
quality which are consistent with national and regional goals and needs, and
with international commitments.

The timely need for such information by decision makers often precludes
publication in formal journals. The NOAA Technical Memorandwn NMFS-F/NEC
series provides a relatively quick and highly visible outlet for documents
prepared by NEFC authors, or similar material prepared by others for NEFC
purposes, where formal review and editorial processing are not appropriate or
feasible. However, documents within this series reflect sound professional
work and can be referenced in formal journals. Any use of trade names within
this series does not imply endorsement.

Copies of this and other NOAA Technical Memorandums are available from
the National Technical Information Service, 5285 Port Royal Rd., Springfield,
VA 22161. Recent issues of NOAA Technical Memorandum NMFS-F/NEC are noted
‘below:


METERS

al

Ae

Jae

40°

a2

90 |
40° 140°
a 90
b MEAN WATER
r COLUMN (75M) ~|
1 1 Ll
72° 66° 64°

Figure 13. Percent .nanoplankton.


elevated biomass levels -at several stations. In. contrast, the
pico-nanoplankton: cyanobacteria: were ubiquitous in both shelf and
slope waters, with highest concentrations at the surface. There
was also a tropical and sub-tropical phytoplankton component that
was more evident in, but not limited to slope water. There were
25 of these species, representing 9% of the total phytoplankters,
although none of these were numerically dominant.

There was generally.a positive relationship .between. a more
diverse and abundant phytoplankton assemblage and shelf waters.
This phytoplankton community contained an abundant: diatom: flora
that included as dominants Leptocylindrus danicus, L. minimus,
Thalassionema nitzschoides, Nitzschia pungens, Cylindrotheca
closterium, and Rhizosolenia deTicatula. In contrast, the slope

water was dominated by phytoflagellates and cyanobacteria, with
most of the shelf water species either absent or in low
concentrations.

DISCUSSION

The majority of ichthyoplankton, zooplankton, and
phytoplankton taxa were confined to either a neritic or oceanic
province, at least in a biogeographic sense. Species generally
considered neritic were found in areas shoaler than 200 m and
oceanic species occurred in regions deeper than 200 m. Hedgpeth
(1957) and Colebrook et al. (1961) have commented on the fact that
the edge of the continental shelf (200 m contour) frequently
marked the boundary between oceanic and neritic plankton
communities and that a feature of the distribution of many species
of ichthyoplankton, phytoplankton, and zooplankton was the close
correspondence between the contours of abundance and the edge of
the continental shelf. Our information on the vertical
distribution of the various taxa is inadequate, however, for us to
ascertain if these spatial patterns. of species distributions were
controlled by environmental conditions (water mass properties).
The fact that few neritic species were found south of the. 200 m
contour suggests that factors other than temperature and salinity
are involved in determining distribution patterns. As has been
noted previously (Colton and Byron 1977), a conspicuous. aspect of
the larval fish distribution in the area of concern is the almost
total segregation of shelf (boreal) and oceanic (tropical and
subtropical) species of. larval fishes north and south of the shelf
break (200 m contour). This division appears to be linked in part
to water mass. distribution, as the 200 m isobath coincided with
the subsurface manifestation of the shelf/slope front (9°C at 200
m). Although surface shelf water extended a considerable distance
south of the 200 m contour and in some sections to the southerly
extreme of the. sampling area, diel migrants such as the myctophids
would have. ready access to Slope water at all locations south of
the 200 m contour. Why shelf species. such as windowpane and
silver hake did -not occur in the overlying shelf water south of


WRIGHT, W. R. ‘
1976. The limits of shelf water south of Cape Cod, 1941 to
1972. J. Mar. Res. 34(1):1-14. ,

WRIGHT, W: R:, and'C.°E. PARKER. ws
1976. A volumetric temperature/sal inity census for the widdle
Atlantic Bight. Limnol. Oceanogr. 21(4):563-571.

YENTSCH, C..S., and-J. H:: RYTHER. : .
1959. Relative significance of. the netphytoplankton and
nannoplankton in the waters of. Vineyard Sound. J. Cons.
Perm. Int. Explor. Mer 24:231- 238. ~