The relationship of the distribution of the planktonic worm, Poeobius meseres Heath, to the water masses of the North Pacific

The relationship of the distribution of the planktonic worm, Poeoblus meseres Heath, to the water masses of the North Pacific JOHN A. McGOWAN (Received 5 January 1959)

Abstract--The distribution of a planktonic worm, Poeobius meseres HEATH, was determined from an examination of over 1800 quantitative plankton tows taken in the North and South Pacific. This distribution is compared with the distribution of water masses, as defined by temperature-salinity curves. Since the water mass concept involves a three dimensional unit of the ocean, its use in describing the environment of an animal whose distribution is also three dimensional, is preferable to the method of comparing plankton distributions with horizontal isotherms or isohalines. The distribution of Poeobius coincides, for the most part, with that of the Subarctic water mass and the transition region of Subarctic water, the California Current. However, a few specimens were found in the eastern tropical Pacific. A satisfactory explanation for its restricted presence in this latter area is not possible at this time, but there is some evidence to indicate that this southern segment of the population is not endemic but has been carried in from the north. If this is true, then the occurrence of Poeobius here must be accounted for in considering the sources of the Intermediate water of the area. INTRODUCTION TIlE environment o f m o s t oceanic, z o o p l a n k t o n i c species is generally described in terms o f the t e m p e r a t u r e a n d salinity ranges to which the animals seem limited. But because z o o p l a n k t o n is distributed three-dimensionally it is frequently difficult to relate the overall h o r i z o n t a l distributions o f species to the h o r i z o n t a l distributions o f t e m p e r a t u r e o r salinity limits. However, with the d e v e l o p m e n t o f the water mass c o n c e p t (I-[ELLAND-HANSEN 1916, SVERDRUP et al., 1942) it has become possible to relate the distributions o f species to that o f water masses. It is the p u r p o s e o f this p a p e r to present the distribution o f a pelagic organism, Poeobius meseres H~ATH (1930), and to c o m p a r e it with the distribution o f a water mass. Poeobius meseres, a small, transparent, p l a n k t o n i c animal ranging in length up to 27 ram, was originally described by HEATH (1930) from M o n t e r e y Bay, California. He o b t a i n e d specimens from a p l a n k t o n sample taken from a d e p t h o f a p p r o x i m a t e l y 350 m. HEATH suggested that Poeobius was " a connecting link between the A n n e l i d a a n d the E c h i u r o i d a . " A l t h o u g h R e m a n e (see PICKFORD, 1947) considered it to be an echiuroid, FISHER (1946) excluded it from that Phylum. PICKFORD (1947), after an intensive study o f the a n a t o m y a n d histology o f Poeobius, came to the conclusion that it was an a b e r r a n t Polychaete. B o t h HEATH a n d PICKFORD were concerned p r i m a r i l y wth the phylogenetic status o f this strange worm, a n d virtually nothing is k n o w n o f its ecology a n d life history. The only i n f o r m a t i o n available on the distribution o f Poeobius is the statement by PICKFORD (1947) that " Pelagic in habit, it has been t a k e n from m o d e r a t e depths off the coasts o f C a l i f o r n i a and in A l a s k a n waters," the r e p o r t b y BOGOROV (1955) o f its occurrence in the N o r t h - w e s t Pacific (position n o t given) a n d HARTMAN'S 0 9 5 5 ) r e p o r t t h a t " P o e o b i u s meseres is k n o w n only from the n o r t h e r n Pacific." 125

126

JOHN A. McGOWAN

D u r i n g the analysis of over 1800 p l a n k t o n samples taken in the Pacific by the Scripps I n s t i t u t i o n of Oceanography, the occurrence o f Poeobius was recorded. These observations were then c o m p a r e d with hydrographic data which had been taken at the same time a n d place. This c o m p a r i s o n revealed that the distribution of Poeobius generally coincided with the distribution of the Subarctic Water Mass. METHODS The p l a n k t o n samples used in this study came from several different cruises and expeditions (Fig. l, Table 1). The routine sampling done by the California Co-operative Oceanic Fisheries Investigations (C.C.O.F.I.), served as a model for all of these cruises

Table 1.

Plankton samples used in this study

Expeditions Scripps Institution of Oceanography

Date

Mid-Pacific

1950

12

Northern Holiday

1951

55 21 trawls (not used in this study)

Shellback

1952

Capricorn

1953

Number of tows

i

Depth of tows (m)

6

203 15 trawls 35 143 135 38 12 16 4 trawls

0-100 0-1000 or greater 0-140

0-300 0-1000 or greater 0-140; 0-400; 0-1000 0-150 150-300

300-450 450-600 0-1000 0-2000 or greater

Trans-Pacific

1953

Troll

1955

85

0-300

EQUAPAC

1956

89

0-280

1954

14 12 14 13 20 10 12

0-25 25-50 50-75 75-100 100-300 300-500 500-700

PAS

CCOFI

1950 to 1954

532 (used in this study)

0-140

CCOFI

1950

8

0-400

Nor-Pac

1955

162 30 20

0-140 140-280 0-700

162 30 20 12

0-140 140-280 0-560 0-700 or greater

8

0-700 or greater

p

Downwind

1957

Tage (Hopkins

19511952

M a r i n e Sta.)

I ' ~ !

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The relatior~ship of the distribution of the planktonic ~orm, Poeobius meseres Heath

127

and expeditions (AHLsTRoM, 1954). The vertical distribution of Poeobius was determined, for the most part, from the results of hauls made with an openingclosing net, one metre in diameter, adapted from that described by L~AVn'T(1935, 1938). This net may be towed obliquely and opened and closed at any desired depth. Occasionally a number of these nets were used in series along a cable, thus sampling several strata simultaneously (Fig. 2).

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DISTRIBUTION (1)

Geographic distribution

The greatest density of Poeobius was found in the North Pacific in the region of the Oyashio and Subarctic current. Although DALES (1957) did not find it in the surface waters (0-70 m) of the California Current, it does occur at intermediate depths (400 m or greater) in this current and also in the eastern-most part of the tropical Pacific but in greatly decreased numbers (Fig. 3). It is probably present in the Gulf of Alaska but few samples have been taken from that region. Poeobius did not occur in any of the 298 plankton hauls taken from the upper 700 m of the

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600~

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300~

150

II

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The relationship of the distribution of the planktonic worm, Poeobius meseres Heath

129

Eastern or Western North Pacific Central waters, nor did JOHNSON (1956) record it as being present in the Beaufort or Chukchi seas. It apparently does not exist in any other oceans of the world.

140 160

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Fig. 3. The geographical distribution of Poeobius. The numbers of organisms p~r 1000 m a of water filtered by the net are shown for three strata : A, 150-300 m ; B, 300-450 ; C, 450-1600 m. By increasing the depth of tow, the range is extended to the south in the eastern Pacific, and the abundance o f Poeobius decreases.

(II)

Vertical distribution

The opening-closing net tows taken on the Trans-Pacific Expedition show that in its area of greatest abundance in the Oyashio and Subarctic current, Poeobius is most commonly found at depths ranging from 150 to 300 m (Table 2 and Fig. 6). Although no systematic use of the opening-closing net has been made in the California Current, the area has been intensively sampled with open, quantitative, one-metre nets towed at various depths (U.S. Fish and Wildlife Service, 1954). In the northern part of this region (Tables 1 and 3), Poeobius was found only in those tows that went to a depth of 400 m or more ; in the southern part, which was covered by the Pelagic

130

JOHN A. McGOWAN

A r e a Studies (P.A.S.) survey (Fig. 1), Poeobius was f o u n d only at depths o f 700 m o r more. S o u t h o f 20 ° N i n the eastern t r o p i c a l Pacific* it was found, with one

Table 2.

Selected Trans-Pacific Expedition opening-closing series, showing depth and temperature range o f P o e o b i u s

Station 25 A B

C D 40A B

C D 42 A B

C D 46 A B

C D 48 A B

C D 59 A B

C D

Depth of tow (m)

Numbers per 1000m3

Temperature range (°C)

0-150 150-300 300-450 450-600

0

170 5 5

3.5-11.2 4.0-4.3 3.7-4.0 3-4-3.7

0-150 150-300 300-450 450-600

0 179 120

0

1.4-9.1 3-25-3.6 3.3-3.6 3.1-3.3

0-150 150-300 300-450 450-600

115 29 0

0.6-9.2 0.9-3.6 3.~3-6 3-1-3.4

0-150 150-300 300-450 450-600

0 135 28 17

0.7-9.9 3.1-3.35 3.2-3.4 3.0-3.25

0-25 25-100 35-115 140-320

0 o 0 40

9.2-9-7 1.3-9.3 1.3-7.0 1.7-36

0

0-150 150-300 300-450 450-600

5.6-14.65 4.1-5.55 3.8-4.1 3.55-3.8

exception, only in trawls t h a t reached depths o f 1000 m o r m o r e (Fig. 3). The exception was the c a p t u r e o f two individuals at a d e p t h o f 300 m n e a r Shellback Station 207 (Table 3). WOOSTER a n d CROMWELL (1958, p. 178) have p o i n t e d o u t t h a t this area near the n o r t h e r n b o u n d a r y o f the E q u a t o r i a l C o u n t e r c u r r e n t is c h a r a c t e r i z e d b y very shallow thermoclines.

Relationship o f P o e o b i u s distribution to water masses T h e w a t e r in the t o p 1000 m n o r t h o f 4 5 ° N in the Pacific has been called the Subarctic W a t e r M a s s (Sv~RDRUP et al., 1942, p. 712). It is generally believed that this water originates m o s t l y from the O y a s h i o with some slight mixing with water from the K u r o s h i o Extension. A s this Subarctic water a p p r o a c h e s the N o r t h A m e r i c a n continent it splits, some m o v i n g n o r t h w a r d to form the G u l f o f A l a s k a Gyre, the rest m o v i n g s o u t h w a r d as the California Current. The t e m p e r a t u r e - s a l i n i t y relationship g r a d u a l l y changes as the water moves south a n d b y the time the California C u r r e n t begins to t u r n south-west at a b o u t 25 ° N latitude, b e c o m i n g p a r t o f the N o r t h * WOOSa'ERand CROMWELL(1958) have defined this area as " the region lying between the Tropic of Cancer (23 ° 27' N) and the Tropic of Capricorn (23 ° 27' S) and extending westward from the coast of Central and South America to 130° W.

The relationship of the distribution of the planktonic worm, Poeobius meseres Heath

131

Equatorial Current (Reid et al., 1958), mixing has considerably altered its properties. Ninety-seven per cent of all Poeobius caught were in hauls taken in the area of the Table 3.

All P o e o b i u s records excepting the Trans-Pacific Expedition, the Norpac Expedition, and tho, e reported by PICKFORO (1947) Numbers of organisms caught

Water filtered by net (m3)

0-147

1

444

0-42 I

I

1668

0-423

3

1945

8-51

0-1200

several

Cruise station

Position

CCOFI 5201 137"40

25 ° 00'N 1! 3° 25-5'W

1-52

CCOFI 5004 47"55

40° 04'N 1240 55'W

4-50

CCOFI 5004 60'70

37° 17'N 124° 21'W

4-50

N.H.

Depth of haul

Date

(m)

53° 34.5'N

!

155 ~ 00'W

Tage 248-B

Monterey Bay

9-52

0-740

25

4721

Tage 242-B

Monterey Bay

3-52

0-910

12

4904

Tage 144-B

Monterey Bay

12-51

0-980

3

4941

26° 12'N

4-54

0-900

209

PAS 120"90

118 ° 30'W

PAS 130"150

22° 30'N 121 ° 15'W

4-54

0-700

2160

PAS 140.180

19o 40'N 122° 15'W

4-54

0-700

3475

SB 186-187

1° l'5'N 91 ° 45'7'W

8-52

0-938

SB 108-109

4 ° 04'S 82° 14'W

7-52

0-1640

12° 13"5'N 106° 07'W

8-52

0-300

06 ° 58'S 88° 35'W

7-52

0-1463

SB 207 SB 101-102

Subarctic W a t e r Mass (Fig. 4). Temperature-salinity curves based on data taken at these stations where the d e p th o f Poeobius capture was known, fell generally within the range o f curves characteristic o f this water mass (Fig. 5). Th o se few curves which fell outside this range were f r o m stations on the edge o f the Poeobius distribution, an d even these curves indicate the presence o f a certain a m o u n t o f Subarctic water. F u r t h e r evidence that Poeobius resides primarily in Subarctic W a t e r is the finding, based on the results o f the Trans-Pacific Expedition, that Poeobius disappeared abruptly f r o m the p l a n k t o n when the relatively sharp physical boundaries were crossed f r o m Subarctic to C e nt r al waters (Figs. 6 and 7). O n the o t h e r hand, in the areas where there is a gradual change o f properties f r o m the Subarctic W a t e r to the California Current, the n u m b er s o f Poeobius decreased gradually (Fig. 3).

132

JOHN A. McGOWAN

There is some reason to believe that Poeobius might occur in the Intermediate Water o f the eastern and western north-central Pacific. UDA (1938), SWRDRUP et aL (1942, p. 716) and others have described a convergence zone at about 41 ° N ,between 150 ° and 160 ° E, where mixed Oyashio and Kuroshio water sinks and spreads out

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Fig. 4. All known records of Poeobius. Circles indicate net tows that reached a depth of 400 m or more, triangles indicate tows that reached a depth of 700 m or more. Those circles and triangles shown in solid black indicate stations where Poeobius were captured. Open circles and triangles indicate that no Poeobius were found at that station. The hatched portion of the chart is the boundary area of Subarctic and Transition Region water (SvERDRtrPet al., 1942, p. 740). in a clockwise circulation over most o f the North Pacific at depths ranging from 200 to 900 m. Although the shallower strata (0-300 m) o f this area have been fairly well sampled (Fig. 1), only 21, widely spaced tows reached a depth o f 700 m or more in the eastern half o f this region (Fig. 4). Poeobius was not found in any o f these tows. If it is assumed that the animal would be randomly distributed at low densities, the failure to find it in these tows can be used to set an upper 95 per cent confidence level o f 1 animal per 11,548 m 3 o f water for its density in this region (FisrmR and YATES, 1938, p.1). This may be compared with an average density o f 1 animal per 17 m 3 in the Subarctic Water Mass.

The relationship of the distribution of the planktonic worm, Poeobius meseres Heath

13 3

I f there were no further records of Poeobius, its distribution could be simply related to that of the .Subarctic Water Mass. However, seven individuals were found in the Intermediate Water of the eastern equatorial Pacific. There is little doubt that some mixing does occur between this water mass and the southern portion of the California Current, but this does not seem sufficient to account for the numbers of Poeobius caught here. The source of the Intermediate water of the eastern tropical

l(

33

34 SALINITY

35

(%.)

Fig. 5. Temperature-salinity curves from stations where Poeobius was taken on the Trans-Pacifie Expedition, compared with SVERDRUP'SSubarctic and Western North Pacific water. Station numbers axe indicated on the fine lines. Only that segment of the curve within the depth range of Poeobius is plotted. Pacific is not really known, but SVERDRUP suggests that it is " formed off the coast of South America by the gradual transformation of Subantarctic w a t e r " (SVERDRUP et al., 1942, p. 706). I f this is true, the presence of Poeobius might indicate that it is an antitropical species (HUBBS, 1952) as are several other pelagic organisms in the Pacific Ocean. However, plankton samples taken on the Scripps Downwind Expedition (Fig. 1) and reports of the Dana (Wesenburg-Lund, personal communication) and Discovery expeditions (MONRO, 1936) indicate that it is not present in either the Central Water or the Subantarctic water of the South Pacific, and TEBBLE (1958) did not find it in the Antarctic or Subantarctic waters of the South Atlantic. It seems therefore that this explanation cannot be used to account for the occurrence of Poeobius in the eastern tropical Pacific. Another possible explanation for the presence of Poeobius in this area is that these seven individuals represent a second and hitherto undescribed species with different ecological requirements. There are however, only slight morphological bases for this

134

JOHN A. McGOW^N

STATION NO. I

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Fig. 6. Trans-Pacific sampling programme, Stations 1 to 44, showing tbe vertical distribution of Poeobius. The numbers to the right of the vertical bars indicate the numbers of organisms per 1000 m s. The specimens from the de~pest tows on Stations 25 and 42 might have come from the shallower depths.

The rela.tionship of the distribution of the planktonic worm, Poeobius meseres Heath

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Fig. 7. The Trans-Pacific Expedition sampling programme, Stations 45 to 70 and 115 to 125, showing the vertical distribution of Poeobius. The specimens from the deepest tows on Stations 49 and 59 might have come from the shallower depths.

136

Jom~ A. McGOWAN

suggestion. All specimens from this area were rather larger than the average of those collected in pure Subarctic water, but despite the large size of these animals, their gonads were either missing or greatly reduced in size (Table 4). These differences do not necessarily indicate that they represent a new species for the resorption of gonads and other internal organs is a well known phenomenon in invertebrates living under unfavourable conditions. One might, therefore, expect to find such a condition in Poeobius that had been carried out of their normal environment. I f this explanation is correct and the Poeobius in this area are sterile expatriates from the north, our ideas on the sources of the Intermediate water of the eastern tropical Pacific will have to be reconsidered. DISCUSSION Few attempts have been made to relate the entire distribution of a pelagic planktonic organism to the distribution of water mass*. RUSSELL (1935 and 1939), FRASER (1939 and 1952), PmRCE (1939) and others have shown that the distributions of chaetognaths and certain other organisms in the vicinity of the British Isles are related to the movements of waters from different sources and according to FRASER (1952) " it has now been established that the various species of Chaetognatha are associated each with a more or less specific hydrographical environment, making the group one of the foremost of the biological indicators." JOHNSON (1956) has shown that copepods also may be used as an aid in tracing the water movements in the Chukchi and Beaufort seas. It should be pointed out, however, that most of the species considered by these authors are more widely distributed than the limited areas they have investigated and that until all of the boundaries of their distributions are well known, it will be difficult to define in physical terms the regimen to which they are limited, or to show whether or not their overall ranges coincide with the concept of a physical water mass. HAEFNER'S (1952) study on Chauliodus is perhaps more extensive, but because he does not have accurate data on depth of capture, it is not certain that his species are really limited to the depth ranges to which he asssign them. Further, his technique of using a single temperature-salinity measurement at the presumed depth of capture is probably not sufficient to identify a water mass, for SVERDRUP et al. (1942, p. 143) have pointed out that this may be done only in exceptional cases and that a T-S curve is usually required to define a water mass. TEaBLE (1958) has reported that certain pelagic polychaetes in the South Atlantic and Antarctic oceans are limited to particular water masses, but at the time of this writing his detailed information has not been published. In a recent study on the chaetognaths of the Antarctic regions, DAVID (1958) has shown that the boundaries of the ranges of some specimens do, indeed, coincide with hydrographic boundaries and that some of these species are endemic to the Antarctic water. While T-S relationships are used to identify water masses, this does not necessarily mean that the organisms limited to these water masses are limited by temperature and salinity alone. Water having characteristics that would fit certain points of the Subarctic T-S curve may be found in many parts of the world, and yet, so far as is known at present, Poeobius meseres occurs only in Pacific Subarctic water or in waters which may have Subarctic components. There are many possible explanations but until more is known of the biology of the animal, they can only be considered * As defined by SVERDRUI"et al. (1942, p. 143).

The relationship of the distribution of the planktonic worn%

Table 4.

PoeobiusmeseresHeath

137

Size and gonad condition of P o e o b i u s from the Subarctic and Eastern Equatorial regions

Station TP 40B

T P 36C

TP 41B

Zone

Size of specimens

Month

Condition of Gonads

Aug.

ovary ovary ovary ovary

Subarctic

18 m m 20 m m I t mm 15 mm

Subarctic

17rnm 9ram 12 m m 10 m m 9 mm 16 mm 15 mm 10 mm 10 m m 10mm 13 m m

Aug.

18 m m 16 m m 13 mm

Aug.

ovary large 2 rrLm ovary 1,5 mm ovary 1.75 mm

Sept,

ovary 1 mm ovary ruptured, eggs diffuse in body cavity ovary 1 mm ovary ruptured, eggs diffuse in body cavity

Subarctic

Oyashio

18 m m 19 mm

Subarctic

13 m m 9 mm 14 m m 10 m m 6,5ram

6 mm

TP 25B

t0 mm t6 mm I0 mm 8 mm 12 mm 12 mm 15 mm 16 mm 12 m m

TP 66E

Oyashio

SB 101-2

Tropical Pacific

20mm

SB t08-9

E.T.P.

l0 mm

SB 207

E.T,P.

Eastern

Aug,

Sept,

21 mm Aug.

July

10 mm Aug, 15 m m SB 186-7

E.T.P.

10rnm 10ram

2 mm 2 mm 2 mm 2 mm

ovary large 2-3 mm ovary large 2 mm ovary large 2 mm ovary large 2 m m ovary large 2 mm specimen opaque ovary large 2 m m ovary large 2 m m specimen damaged ovary large 3 m m

13 m m 12 m m TP 47D

large large large large

.......... July

body opaque body watt ruptured ovary t-25 mm body opaque ovary !,25 m m body opaque body opaque ovary large 2,5 mm ovary large 2,5 mm ovary 1"5 mm ovary ruptured ovary large 3 mm ovary large 2 mm ovary large 2.5 m m entire posterior half is ovary viscera gonads viscera gonads

degenerate, missing degenerate, missing

much of viscera missing, gonads missing viscera partially gone, gonads missing ovary present 1"5 m m gonads missing gonads mis.sing

138

JOHN A. McGOWAN

theoretical. One factor which may be of importance is the higher productivity and standing crop of the Subarctic, California Current, and eastern tropical Pacific areas (HOLMr~s, 1958) compared with that of the Central and Equatorial Pacific water masses (STF_m,IANN-NmLsEN, 1957). Thus the southward extension of the range of Poeobius from the Subarctic water mass to the California Current to the eastern tropical Pacific may have a simple relationship to the availability of food. From the foregoing discussion it appears that water masses, as defined by hydrographers, may also exist as biological entities. The water mass concept, which defines a three-dimensional unit of the ocean, thus provides us with an opportunity to compare plankton distributions with that of circumscribed volumes of water, each of which has a unique set of physical properties.

Acknowledgements--The author wishes to thank Mr. JOHN KNAUSSfor his suggestions and assistance. DIS. WARRENWOOSTERand E. W. FAGERalso gave valuable help. This study was done under the direction of Professor M. W. JOHNSON,Scripps Institution of Oceanography. Dr. ERIc BARrIAM,workingunder the Officeof Naval Research Contract N6onr 25127, provided the information on the Monterey Bay Poeobius catches. Scripps Institution o f Oceanography California, U.S.A. Contribution from the Scripps Institution of Oceanography, New Series. REFERENCES AHLSTROME. H. (1954) Distribution and abundance of egg and larval populations of the Pacific sardine. Fish and Wildlife Service, Fishery Bull. 93, (56), 83-140. BOC_,oRov B. G. (1955) Regularities of plankton distribution in the North-West Pacific. Proc. UNESCO Symp. Phys. Oceanogr. Tokyo, 1955. pp. 260-276. DALES R. P. (1957) Pelagic polychaetes of the Pacific ocean. Scripps Inst. Oceanog. Bull. 7 (2), 99-168. DAVIDP. M. (1958) The distribution of the Chaetognatha of the Southern ocean. 'Discovery' Rep. 29, 199-228. FISrlER R. A. and YATESF. (1938) Statistical Tables for Biological, Agricultural and Medical Research. Oliver and Boyd. Flsm~R W. K. (1946) Eehiuroid worms of the North Pacific Ocean. Proc. U.S. Nat. Mus. 96, 215-292. FRASERJ. H. (1939) The distribution of Chaetognatha in Scottish waters in 1937. J. Cons. Int. Explor. Met., 14, 25-34. FRASER J. H. (1952) The Chaetognatha and other zooplankton of the Scottish area and their value as biological indications of hydrological conditions. Scottish Home Department, Marine Research (2), 1-52. HArra~ER R. E. (1952) Zoogeography of the bathypelagic fish Chauliodus. System. ZooL 1, 113-133. HARXMANO. (1955) Endemism in the North Pacific with emphasis on the distribution of marine annelids, and descriptions of new or little known species. Essays in the Natural Sciences in Honor of Captain Allan Hancock pp. 39-61. University of South California Press, Los Angeles. HEATH H. (1930) A connecting link between the Annelida and the Echiuroidea (Gephyrea armata). J. Morph. PhysioL 49, 223-249. HELLAND-HANs~N B. (1916) Nogen hydrografiske metoder. Forh.' Skand. Naturf. Mote 16, 357-359. HOLMESR. W. (1958) Surface chlorophyll "A," surface production, and zooplankton volumes in the eastern Pacific ocean. Cons. Int. Explor. Mer, Rapp. Proc.-Verb. 144 109-116. HtJBBS C. L. (1952) Antitropieal distribution of fishes and other organisms. Proc. 7th Pacif. Sci. Congr. Paeif. Sci. Assoc., 3, Meteorology and Oceanography 324-330.

The relationship of the distribution of the planktonic worm, Poeobius meseresHeath

139

JOHNSON M. W. (1956) The plankton of the Beaufort and Chukchi Sea areas of the Arctic and its relation to the hydrography. Arctic Inst. N.Amer. Tech. Pap. No. 1. LEAvrrr B. B. (1935) A quantitative study of the vertical distribution of the large zooplankton in deep water. Biol. Bull. 68 (1), 115-130. LEAVIX'r B. B. (1938) The quantitative vertical distribution of macrozooplankton in the Atlantic Ocean basin. Biol. Bull. 74 (3), 376-394. MONRO C. C. A. (1936) Polychaete worms (II). 'Discovery' Rep. 12, 59-198. PICKFORD G. E. (1947) Histological and histochemical observations upon an aberrant annelid Poeobius meseres Heath. J. Morph. 80 (3), 287-319. PmRCE E. L. and ORTON J. H. (1939) Sagitta as an indication of water movements in the Irish Sea. Nature, Lend. 144, p. 784. REID J. L., RODEN G. I. and WVLLm J. G. (1958) Studies on the California Current system. Progr. Rep. Calif. Oceanic Fish. Invest., 1 July 1956-1 Jan. 1958, 27-57. RUSSELL F. S. (1935) On the value of certain plankton animals as indicators of water movements in the English Channel and North Sea. Mar. Biol. Ass. 20, 309-332. RUSSELLF. S. (1939) Hydrographical and biological conditions in the North Sea as indicated by plankton organisms. J. Cons. Int. Explor. Met. 14, 171-192. STEEMANN-NIELSEN E. and JENSEN E. A. (1957) Primary oceanic production, the autotrophie production of organic matter in the oceans. 'Galathea' Rep. 1, 49-136. SV~RDRUF H. U., JOHNSON M. W. and FLEMING R. H. (1942) The Qceans, Prentice-Hall, New York. TEnBLE N. (1958, July) Distribution of Pelagic Polychaetes in the South Atlantic Ocean. Nature, Lend. 182 (4629), 166-167. UDA M. (1938) Hydrographical fluctuation in the north-eastern sea region adjacent to Japan of North Pacific Ocean. Jap. Imp. Fisheries Exp. Sta. J. (9), 64-85 (English Abstract). Zooplankton volumes off the Pacific Coast, 1949-50. Special Scientific Report: Fisheries No. 125. U.S. Fish and WildliJe Service (1954). WOOSTER W. S. and CROMWELLT. (1958) An oceanographic description of the Eastern Tropical Pacific. Scripps Inst. Oceanogr. Bull. 7 (3), 169-282.