Marine Biology 54, 251-260 (1979) MARINE BIOLOGY 9 by Springer-Verlag 1979 Population Dynamics of Euterpina acutifrons (Copepoda: Harpacticoida) from North Inlet, South Carolina, with Reference to Dimorphic Males* LM. D'Apolito** and S.E. Stancyk Belle W. Baruch Institute for Marine Biology and Coastal Research and Department of Biology, University of South Carolina; Columbia, South Carolina 29208, USA Abstract p o p u l a t i o n d y n a m i c s of E u t e r p i n a a c u t i f r o n s (Dana), a pelagic, h a r p a c t i c o i d copepod, are s u m m a r i z e d in a life table b a s e d on field data. H i g h e s t m o r t a l i t y o c c u r r e d in the last n a u p l i a r stage (NVI) and the first c o p e p o d i t e stage (CI). O v e r a l l survival in the field was 0.06% from the first n a u p l i a r stage (NI) to adult (CVI). The net r e p r o d u c t i v e rate (R o = 55.590) and i n t r i n s i c rate of i n c r e a s e (rm = 0.28) w e r e s u f f i c i e n t l y high to m a i n t a i n a p o p u l a t i o n w i t h such a low survival rate in nature. E. a c u t i f r o n s was p r e s e n t and b r e e d i n g in the field from A p r i l t h r o u g h December. Low t e m p e r a t u r e s l i m i t e d breeding, w h i c h b e g a n w h e n the t e m p e r a t u r e r e a c h e d 16.5~ and c e a s e d w h e n it fell to 11~ O p t i m u m t e m p e r a t u r e for N o r t h Inlet E. a c u t i f r o n s was 25~ w i t h a m a x i m u m l a b o r a t o r y survival of 15.3% and a g e n e r a t i o n time of 10.3 days. G e n e r a t i o n time in the field (20~ was 14 days. T e m p e r a t u r e also a f f e c t e d the a b u n d a n c e of d i m o r p h i c males. Small m a l e s w e r e always m o s t abundant, but p e a k e d d u r i n g the c o l d e s t month; large m a l e s became equal in a b u n d a n c e only d u r i n g the w a r m e s t months. The I ntroduction I n v e s t i g a t i o n s of p o p u l a t i o n d y n a m i c s in p l a n k t o n i c o r g a n i s m s have b e e n p r i m a r i l y field studies of f r e s h w a t e r species (Edmondson, 1960; Hall, 1964; Comita, 1972; Allan, 1973). P o p u l a t i o n p a r a m e t e r s have also b e e n e s t i m a t e d for several m a r i n e c a l a n o i d species b a s e d on l a b o r a t o r y c u l t u r e studies (Jacobs, 1961; Heinle, 1969; Katona, 1970; P a f f e n h ~ f e r , 1970). F i e l d studies of m a r i n e c o p e p o d s h a v e not b e e n u t i l i z e d as a source of inform a t i o n in l i f e - h i s t o r y studies. The intent of this study was to cons t r u c t a life table and s u m m a r i z e the p o p u l a t i o n d y n a m i c s of a small m a r i n e copepod, E u t e r p i n a a c u t i f r o n s (Dana), b a s e d p r i m a r i l y on field samples. This p r e d o m i n a n t l y p e l a g i c h a r p a c t i c o i d was selected for study b e c a u s e it has a w o r l d w i d e d i s t r i b u t i o n in coastal, shelf and o c e a n i c w a t e r s (Fanta, 1972) as well as *Contribution No. 298 from the Belle W. Baruch Institute for Marine Biology and Coastal Research. **Present address: Academy of Natural Sciences of Philadelphia, Benedict Estuarine Research Laboratory, Benedict, Maryland 20612, USA. being l o c a l l y a b u n d a n t (Lonsdale and Coull, 1977). Life table i n f o r m a t i o n is a l m o s t n o n - e x i s t e n t for m a r i n e invertebrates, b e c a u s e there are p r o b l e m s w i t h d e t e r m i n i n g j u v e n i l e m o r t a l i t y and rec r u i t m e n t in o r g a n i s m s w i t h p e l a g i c larvae (Strathmann and B r a n s c o m b , in press) as well as w i t h l i f e - h i s t o r y data in g e n e r a l (Stearns, 1977). Since E. acutif r o n s d i s a p p e a r s in the winter, e s t i m a t e s of j u v e n i l e m o r t a l i t y can be m a d e by f o l l o w i n g the first cohorts to appear in the spring, b e f o r e o v e r l a p p i n g g e n e r a tions m a s k effects. The p r i n c i p a l p r o c e d u r e used to predict p o p u l a t i o n g r o w t h rates in the field has been E d m o n d s o n ' s (1960) eggratio t e c h n i q u e or some m o d i f i c a t i o n of this m e t h o d (Edmondson, et al., 1962; Hall, 1964; Comita, 1972). The e g g - r a t i o m e t h od u t i l i z e s eggs per total female population x egg d e v e l o p m e n t time-1 to estim a t e female births female-1 day-1. This e s t i m a t e is the i n s t a n t a n e o u s b i r t h rate, b, w h i c h ignores all m o r t a l i t y of a nonp h y s i o l o g i c a l nature (i.e., predation, c o m p e t i t i o n , etc.), and is the m a x i m u m rate of i n c r e a s e of the p o p u l a t i o n (rm) (Allan, 1976). However, the m e t h o d assumes a c o n s t a n t m o r t a l i t y rate for all 0025-3162/79/0054/0251/S02.00 252 L.M. D'Apolito and S.E. Stancyk: Population Dynamics of Euterpina acutifrons life stages, and i m p o r t a n t i n f o r m a t i o n about a g e - s p e c i f i c c h a r a c t e r i s t i c s is lost. The major a d v a n t a g e of life tables is their a b i l i t y to s u m m a r i z e the vital statistics of a p o p u l a t i o n at a g e - s p e cific intervals. Gehrs and R o b e r t s o n (1975) w e r e the first to use a life table, based on field data, to d e t e r m i n e m o r t a l i t y in all age classes of a natural p o p u l a t i o n of a f r e s h w a t e r c o p e p o d (Diaptomus clavipes). An u n u s u a l c h a r a c t e r i s t i c of Euterpina the males are d i m o r p h i c (Haq, 1965). There is a d i s t i n c t size d i f f e r e n c e b e t w e e n the two forms (a "small" m a l e = 0.53 to 0.60 mm, and a "large" m a l e = 0.65 to 0.70 mm) as w e l l as s t r u c t u r a l d i f f e r e n c e s in antennae, a n t e n n u l e s and the s e c o n d pair of legs. I n t r a s e x u a l d i m o r p h i s m has also b e e n described in other species of copepods (Lowndes, 1929; Sewell, 1929; Fleminger, 1967; see Fleminger, 1956, and Haq, 1965 for reviews), but these reports p r i m a r i ly discuss size and m o r p h o l o g i c a l differences and ignore p o p u l a t i o n effects. E. acutifrons is the only species for which the b i o l o g y of the d i m o r p h i c m a l e s has been s t u d i e d (Haq, 1972, 1973), and there is some e v i d e n c e that they p e r f o r m d i f f e r e n t functions in the life h i s t o r y of the species. Haq (1972) s u g g e s t e d that the small m a l e was always m o r e active in b r e e d i n g than the large male. Physiological investigations indicated that the small m a l e was m o r e colda d a p t e d and the large m a l e was m o r e w a r m - a d a p t e d (Moreira and Vernberg, 1968). Haq (1972) and V e r n b e r g and Moreira (1974) s u g g e s t e d that this m a y be an a d a p t a t i o n of the species for successful b r e e d i n g in the c o l d e r areas of its d i s t r i b u t i o n . acutifrons is that (when E. acutifrons first a p p e a r e d after a w i n t e r absence), in an a t t e m p t to follow a c o h o r t t h r o u g h one generation. A single o b l i q u e tow was m a d e on each sample date, w i t h a 0.5 m m o u t h d i a m e t e r n y l o n net (No. 20, 73 ~m) c o n t a i n i n g a d i g i t a l f l o w m e t e r with a l o w - v e l o c i t y propeller. Samples w e r e p r e s e r v e d in the field i m m e d i a t e l y after c o l l e c t i o n w i t h 10% b u f f e r e d formalin. T e m p e r a t u r e and s a l i n i t y of surface w a t e r s (• 0.5 cO; • O.5~) w e r e r e c o r d e d on each sample date. L a b o r a t o r y analysis f o l l o w e d the m e t h o d of F r o l a n d e r (1968), and cons i s t e d of d i l u t i n g the sample to a k n o w n volume, e x t r a c t i n g the s u b s a m p l e w i t h a 2 ml H e n s e n - S t e m p l e pipette, and counting and i d e n t i f y i n g the organisms. Subsamples w e r e d r a w n from each sample until a m i n i m u m of 200 i n d i v i d u a l s of Euterpina acutifrons had b e e n counted. All i n d i v i d u a l s were i d e n t i f i e d to age class, and sex was d e t e r m i n e d in the adults. N a u p l i i were t r a n s f e r r e d by m o u t h - p i p e t t e to a slide, m o u n t e d in glycerin, and m e a s u r e d w i t h a camera lucida. N a u p l i a r size classes corres p o n d e d to the age classes d e f i n e d by Haq (1965) and F a n t a (1972). If nauplii w e r e i n a d v e r t a n t l y lost during transfer, the a b u n d a n c e of each age class was prop o r t i o n a l l y i n c r e a s e d to sum all classes to the o r i g i n a l total number. Adults and c o p e p o d i t e s were t r a n s f e r r e d w i t h fine forceps and m o u n t e d in H o y e r ' s M e d i u m (Galigher and Kozloff, 1971). Age class and sex w e r e d e t e r m i n e d by m o r p h o l o g i c a l characteristics (Haq, 1965). To e s t i m a t e brood size, eggs of o v i g e r o u s females were s e p a r a t e d from u n d i s t u r b e d egg sacs w i t h a fine t u n g s t e n probe and counted. Laboratory Studies Materials and Methods Field Studies P l a n k t o n samples were c o l l e c t e d from May 1976 t h r o u g h April 1977 in N o r t h Inlet Estuary, Georgetown, South Carolina, USA (33o20'N; 79~ This is a Type C e s t u a r y (Pritchard, 1955), 700 to 800 m wide at s m o u t h at low tide and app r o x i m a t e l y 4 to 5 m deep. S a m p l e s w e r e taken during h i g h tide (when h i g h e s t numbers of Euterpina acutifrons (Dana) w e r e r e p o r t e d w i t h r e s p e c t to tidal regime; W. Sikora, p e r s o n a l communication) and at the m o u t h of N o r t h Inlet, w h e r e Lonsdale and Coull (1977) found h i g h e s t numbets of all copepods. S e a s o n a l a b u n d a n c e was d o c u m e n t e d w i t h b i w e e k l y samples, and daily samples were c o l l e c t e d from A p r i l 7, 1977, through A p r i l 24, 1977 L a b o r a t o r y cultures of Euterpina acutifrons were m a i n t a i n e d t h r o u g h the summer of 1977. G r a v i d females w e r e i s o l a t e d from live field samples c o l l e c t e d on June I, 1977. The eggs of 42 o v i g e r o u s females were counted, and the average number of eggs per clutch was determined. F i f t y g r a v i d females were p l a c e d by m o u t h - p i pette into i n d i v i d u a l 9 cm culture dishes (Carolina B i o l o g i c a l Supply) in a p p r o x i m a t e l y 20 ml of 0.45 ~m M i l l i pore-filtered seawater with a constant s a l i n i t y of 32~. Phaeodactylum tricornutum was a d d e d so that a thin d i a t o m layer c o v e r e d the b o t t o m of each dish (Bernard, 1963; Nassogne, 1970; Haq, 1972). Too m u c h P. tricornutum r e s u l t e d in h i g h m o r t a l i t y of nauplii, p r e s u m a b l y b e c a u s e of the t e n d e n c y of the dead d i a t o m cells to c l u m p t o g e t h e r and stick to various L.M. D'Apolito and S.E. Stancyk: Population Dynamics of E u t e r p i n a p a r t s of t h e i r bodies. The m e d i u m was s t i r r e d o c c a s i o n a l l y . C u l t u r e dishes w e r e c o v e r e d a n d p l a c e d in large p l a s t i c pans l i n e d w i t h s e v e r a l layers of w e t a b s o r b e n t paper. T h e s e pans w e r e p l a c e d in i n c u b a t o r s at 20 ~ , 25 ~ and 30~ (2 0 . 5 c~ v a l u e b a s e d on the n u m b e r of eggs per female, w h i c h was b a c k - c a l c u l a t e d from the n u m b e r of NI, u s i n g a 56% s u r v i v a l rate from egg to NI (see "Results"). R esu Its All d i s h e s w e r e e x a m i n e d daily. A f t e r each h a t c h o c c u r r e d , the o r i g i n a l female was t r a n s f e r r e d to a new c u l t u r e dish and n e w l y - h a t c h e d n a u p l i i w e r e counted. Time of a p p e a r a n c e of the first c o p e p o dite stage, p r e s e n c e of a d u l t females and fist egg sac w e r e noted. G e n e r a t i o n time was c a l c u l a t e d as time from egg to a p p e a r a n c e of the f i r s t egg sac. B e c a u s e the c u l t u r e s w e r e e x a m i n e d o n l y once daily, all times are ~ I day. F e c u n d i t y was e s t i m a t e d from the total n u m b e r of b r o o d s per female. E g g m o r t a l i t y was e s t i m a t e d by c o m p a r i n g the a v e r a g e number of eggs per b r o o d w i t h the a v e r a g e n u m b e r of n a u p l i i hatched. O v e r a l l labor a t o r y s u r v i v a l was c a l c u l a t e d from the p r o p o r t i o n of n a u p l i i s u r v i v i n g to m a t u rity. Life Table U s i n g e s t i m a t e s of d u r a t i o n of each age class r e p o r t e d from the l a b o r a t o r y by Haq (1972), a g e - s p e c i f i c m o r t a l i t y was c a l c u l a t e d from the a g e - c l a s s d i s t r i b u tions in the d a i l y field s a m p l e s in April. A life table and s u r v i v o r s h i p c u r v e w e r e c o n s t r u c t e d u s i n g the m e t h o d s of M e r t z (1970) and P i a n k a (1974). Life table p a r a m e t e r s i n c l u d e s u r v i v o r s h i p or the n u m b e r of i n d i v i d u a l s living at the b e g i n n i n g of each age interval, i x ; the n u m b e r of i n d i v i d u a l s dying d u r i n g each age i n t e r v a l , dx; m o r t a l i t y rate per 1,0OO a l i v e at the b e g i n n i n g of each age interval, qx; the m e a n n u m b e r a l i v e or the n u m b e r a l i v e at the m i d d l e of e a c h age interval, L~; the total life e x p e c tancy in days, Tx; and the m e a n l i f e t i m e r e m a i n i n g for those a t t a i n i n g each age interval, e x. V a l u e s for m x , a g e - s p e c i f i c f e c u n d i t y (number of f e m a l e o f f s p r i n g per female), are not i n c l u d e d in the life table, since only one a g e - c l a s s in the s p e c i e s (the adult, CVI) is r e p r o ductive. A v a l u e for m x was o b t a i n e d from the l a b o r a t o r y data (assuming a 1:1 sex ratio) by d i v i d i n g the n u m b e r of NI p r o d u c e d by a s i n g l e female by 2. The i n t r i n s i c rate of increase, r m , and the net r e p r o d u c t i v e rate, Re, w e r e c a l c u lated from the life t a b l e data u s i n g the Euler equation e -rmx iXinx=l x=O (Lotka, 1907, for R o and r m 253 acutifrons 1913). A d d i t i o n a l v a l u e s w e r e o b t a i n e d u s i n g an m x Field Studies S u r f a c e - w a t e r t e m p e r a t u r e s r a n g e d from 7 ~ to 29~ (Fig. I), w i t h a m a x i m u m in A u g u s t 1976, and a m i n i m u m in J a n u a r y 1977. S a l i n i t y r a n g e d from 30 to 36~ (Fig. I); the w i d e s t s a l i n i t y f l u c t u a tions o c c u r r e d d u r i n g the c o l d e s t m o n t h s of the y e a r (October to F e b r u a r y ) . Six d i s t i n c t peaks in E u t e r p i n a a c u t i f r o n s a b u n d a n c e (Fig. 2) w e r e o b s e r v e d from May 1976 to May 1977. In late June there was a large i n c r e a s e in the total population, n a u p l i a r stages w e r e e x t r e m e l y a b u n d a n t (9,045 m -3) and c o p e p o d i t e numbers i n c r e a s e d and r e m a i n e d h i g h t h r o u g h August. N a u p l i a r stages then d e c l i n e d s l i g h t l y and p e a k e d a g a i n in July, foll o w e d by an a d u l t peak in e a r l y August. T u r n o v e r times of the p o p u l a t i o n app e a r e d to be q u i t e r a p i d at t h e s e temp e r a t u r e s (26 ~ to 29~ making delineation of g e n e r a t i o n s in the field impossible (note the p r o l o n g e d peak of abund a n c e of c o p e p o d i t e stages w i t h i s o l a t e d p e a k s of n a u p l i i and adults, Fig. 2). In early S e p t e m b e r (field t e m p e r a t u r e , 25~ n a u p l i i a g a i n i n c r e a s e d in n u m b e r w i t h a s u b s e q u e n t i n c r e a s e in c o p e p o dites and adults in late S e p t e m b e r . A d i s t i n c t g e n e r a t i o n c o u l d be f o l l o w e d t h r o u g h O c t o b e r and N o v e m b e r (Fig. 2) (when t e m p e r a t u r e d e c r e a s e d from 17 ~ to 15~ A d e c l i n e in the total p o p u l a t i o n was i m m e d i a t e l y f o l l o w e d by an i n c r e a s e 30 39 o0 , "J /"... ,,,2o o,.o" o,d ' d~ cc < o ~o \~ # fi- i ~- ~ i 15 9 i" i\ 9 ~ i " ~- i \ i o i 09 ....". i > 1~ \ -< q ~ t t7 uJ t'-- 10 5 3s t- ==.~ 31 [M I IjI IjI IAI ISI Ioi MONTHS NI IDI IjI IF; IMI IAI I 29 1976-77 Fig. I. Temperature (continuous line) and saiinity (dotted line) in the mouth of North Inlet, South Carolina, USA, from May 22, 1976 to April 23, 1977 954 L.M. D'Apolito and S.E. Stancyk: Population Dynamics of Euterpina acutifrons 1500 11i1{/ "I00, / l l l I I l l l t / l l l l l l / I i I i i i i I i I f I I ~ J I l I 45 tn I-CI < fi 500 ~ 2500 i ! ! ! ,, oo n f l l l l l l l l l l l l l l l [ l l l l l > < i it/ '.-..i i Ii olii 4o ~o 211 CO O I E ~ 15oo O9 7-, " < 2w C3 o 20 -r 15 1- > M J A S O N D J F M A MONTHS 1976-77 5oo z 2500 I I 9,O45 I I I I I I I I I I I I I I I I 3272 Fig. 3. Euterpina acutifrons. Percent of gravid females in total population (continuous line) and mean number of eggs per clutch (dotted line) in mouth of North Inlet, May 1976 to April 1977. Vertical bars represent standard errors of means 1500 d s_ z 500 M d d A S MONTHS 0 N D d F M 1976-77 Fig. 2. Euterpina acutifrons. Abundance of nauplii, copepodites and adults in mouth of North Inlet, May 1976 to April 1977 in nauplii and copepodites, w i t h adults r e a c h i n g a peak 2 weeks later (November 20). All age c l a s s e s s h o w e d a final peak in numbers in December, w h e n the field t e m p e r a t u r e was If~ however, by January 12 (temperature = 8~ the p o p u l a tion had d i s a p p e a r e d from the w a t e r column. E. acutifrons r e m a i n e d a b s e n t from the e s t u a r y until April. Adults first r e a p p e a r e d w h e n the t e m p e r a t u r e r e a c h e d 16.5oc; 2 weeks later, the p o p u l a t i o n was d o m i n a t e d by n a u p l i a r stages (Fig. 2). The p e r c e n t a g e of females c a r r y i n g egg sacs v a r i e d over time, w i t h peaks in the p r o p o r t i o n of g r a v i d females (Fig. 3) c o i n c i d i n g w i t h p e r i o d s of p o p u l a t i o n increase. P e r c e n t a g e s are b a s e d only on number of females c a r r y i n g u n d i s t u r b e d egg sacs and, therefore, r e p r e s e n t minim u m e s t i m a t e s of the true p r o p o r t i o n of g r a v i d females. C l u t c h size also v a r i e d over time (Fig. 3), r a n g i n g from 17 to 41 eggs per b r o o d (~ = 34.25 • 11.O2, n = 81). The h i g h e s t numbers of eggs per brood o c c u r r e d w h e n n a u p l i a r numbers were lowest (July, O c t o b e r and December; Figs. 2 and 3). The a b u n d a n c e of adult females and d i m o r p h i c m a l e s is shown in Table I. Females d o m i n a t e d the p o p u l a t i o n throughout m o s t of the year. Small m a l e s always o u t n u m b e r e d large males, and w e r e m o s t a b u n d a n t during b r e e d i n g peaks in the p o p u l a t i o n and during the c o l d e s t months (November and April peaks, t e m p e r a t u r e = 15 ~ to 17~ Large males a p p r o a c h e d small males in a b u n d a n c e only during the w a r m e s t part of the year (August and September). A g e - c l a s s e s h i s t o g r a m s (Fig. 4) were c o n s t r u c t e d from daily samples taken in April 1977 (temperature = 16 ~ to 20~ The i n i t i a l p o p u l a t i o n c o n s i s t e d of cop e p o d i t e s and adults, w i t h adults comp r i s i n g 60 to 80% of the p o p u l a t i o n for the first 7 days. F e m a l e s c a r r y i n g egg sacs w e r e p r e s e n t d u r i n g the first 10 days but, after Day 7, a d u l t numbers g r a d u a l l y d e c r e a s e d and n a u p l i a r stages a p p e a r e d and were a b u n d a n t from Days 7 t h r o u g h 18. At no time were c o p e p o d i t e stages m o s t abundant. The number of adults b e g a n to i n c r e a s e again from Day 14 t h r o u g h Day 18, the last s a m p l i n g date. Laboratory Studies D e v e l o p m e n t of Euterpina acutifrons occurs in 12 stages; 6 n a u p l i a r and 6 copepodite stages, the last c o p e p o d i t e stage (CVI) b e i n g the adult (Haq, 1965). In this paper these d e v e l o p m e n t a l stages are d e s i g n a t e d N a u p l i u s I (NI) t h r o u g h N a u p l i u s VI (NVI) and C o p e p o d i t e I (CI) L.M. D'Apolito and S.E. Stancyk: Population Dynamics Euterpina acutifrons of 955 Table i. Euterpina acutifrons. Numbers m -3 of each age class and sex (in adults) of copepods in mouth of North Inlet, South Carolina, May [976 to April 1977. L ~ and So" indicate large and small males, respectively. Stages are after Haq (1965). -: no sample taken Date 60f Age class N1 N2 N3 1976 May June June July July July Aug. Aug. Sep. Sep. Oct. Oct. Nov. Nov. Dec. Dec. 22 9 25 6 18 31 13 27 Ii 26 iO 24 2 20 4 13 71 57 55 22 21 108 O . 35 0 0 O O O 0 26 18 143 107 14 109 28 276 496 938 ii 143 176 O 207 372 126 325 415 O 98 98 . . . 43 199 259 42 42 O 0 0 2 7 13 37 8 84 84 O 32 5 2 6 16 17 138 249 1977 Jan. Jan. Feb. Feb. Mar. Mar. Apr. Apr. 12 29 9 26 12 28 9 23 O O O O O 0 O 280 O O O O O 0 9 641 100 03 < 2O I-. Z uJ L) CE ILl CL I 16.51~ DAY N6 cl C2 C3 C4 C5 C6 ~ L~ S~ Total 244 33 5,956 353 581 325 56 113 5 1,324 77 166 90 28 320 75 O 81 117 32 40 318 35 42 O 77 217 50 66 258 36 9 165 121 290 234 223 72 121 iOO O 27 142 136 26 112 36 19 551 265 415 451 70 186 52 iO0 2 30 250 132 13 112 18 9 221 386 477 523 530 64 35 176 33 27 409 95 5 163 36 28 O 243 477 270 251 64 104 126 15 17 334 68 8 103 24 28 165 143 373 288 432 57 138 285 46 13 267 150 14 138 381 567 938 386 747 775 1,059 336 432 787 357 50 225 291 28 163 268 364 607 276 518 541 808 136 190 419 287 20 134 73 Ii 77 O 61 iiO O 21 O 28 64 104 126 9 iO 8 14 O O 113 142 221 110 207 234 223 136 138 243 61 20 84 205 17 86 1,227 906 11,O85 2,326 4,126 3,930 2,845 1,445 1,773 1,775 455 379 2,137 991 224 1,797 O 0 O 0 O 0 0 543 O O O O O O O 197 O O O O O O 0 115 O O 0 O O 0 0 0 O O O O O O 0 33 O 0 0 O O O O 0 0 O O O O 0 O 66 0 0 0 O O 4 264 99 0 O O 0 O 3 91 99 0 O O O O O 36 O O O 0 O O i 136 0 O O O O O 4 273 3,585 O 0 O O O 0 O 641 DAY8 through adult (CVI). All results are ported as means • standard deviations (Z • S D ) . DAY9 20 F I ~ _ 7 19~ DAYlO DAY3 20 16~ 60 60 0 O O 0 O O 0 970 N5 20 I ~ 1 9 ~ 20 W 0 Z < s Z N4 F ~ F-l 20 19~ DAY4 17~ DAY14 20 UJ > I-. < _J LLI CE .... I/Ay 16 2O 20 LI ~ c D 19oC A Y 17 DAY18 19~ 2O r~']N2N3N4N5N6CIC2C3C4C5C6 AGE CLASS Fig. 4. Euterpina acutifrons. A g e - c l a s s b u t i o n (as p e r c e n t of t o t a l p o p u l a t i o n ) ly s a m p l e s t a k e n A p r i l 7, 1977 to A p r i l distrifor dai24, 1977 re- Egg sacs of 90% of the gravid females (n = 10) p l a c e d at 20~ hatched within 2 days of isolation, with 25 • 4 NI produced per clutch (Table 2). In 33% of the cultures that hatched, development was arrested in the naupliar stages and all individuals died within 13 d a y s of hatching. First-stage copepodites (CI) appeared in the other 67% of these cultures and development time from NI to CI was 7.6 • 1.3 days (Table 2). A t 2 0 ~ no copepodites survived to the adult stage and all individuals died within 11 t o 13 d a y s of hatching. Cultures raised at 25~ were the most successful in the temperature range tested. Nauplii hatched within I to 2 days of isolation of the gravid female. The mean number of NI produced per egg sac was 16 • 3, a n d d i d n o t s i g n i f i c a n t ly decrease even after a single female produced 6 egg sacs (Tabie 2). Survival from egg to NI was 56% and overall survival from NI to CVI was 4.13%. Based on the total offspring of an individual female, maximum survival was 15.3%. Seventy-two percent of these offspring were females, 22% small males and 6% large males. Generation time at 25~ was 10.3 • 0.98 days. Development time from NI to 256 L.M. D'Apolito and S.E. CI was 5.7 • 0.84 days and from CI CVI was 6 • 1.9 days (Table 2). At 30~ egg sacs of all females 20) h a t c h e d after I day; 19 • 5 N I hatched per egg sac. In 55% of the Stancyk: to (n = cul- Table 2. E u t e r p i n a acutifrons. Laboratory fecundity of females: No. ~ = numfoer of females at each temperature; NI/cl = NI per clutch, ~ • SD; NI/~ = total NI per female. Development time of laboratory cultures at 20~ , 25~ and 30~ is also shown Clutch No. Temperature 2oOc 25Oc 30~ Population Dynamics of E u t e r p i n a acutifrons tures, copepodites appeared after 5 • 1.2 days, but in the other 45% nauplii never reached the copepodite stage and died within 8 days of hatching. Individuals that reached copepodite (CI) w e r e all dead within 10 d a y s o f h a t c h i n g . Forty percent of the original females produced a second clutch which hatched in I day, with a mean number of NI per clutch o f 11 • 4 i n t h e s e c o n d brood (Table 2). T h e n a u p l i i all died 5 to 6 days after hatching without reaching the copepodite stage. One female produced a third clutch, but died 3 days after producing the egg sac which never hatched. I No. ~ NI/cl iO 25 • 4 20 17 • 5 20 19 ~ 5 Life 2 No. ~ NI/cl NI/? O - 16 12 • 3 29 8 ii • 4 30 ia - 8 16 + 5 45 5 20 ~ 7 65 - A life table (Table 3) w a s c o n s t r u c t e d acutifrons based on the daily for Euterpina field samples. Except for the adult stage, when every individual entering the age class eventually dies, highest mortalities occurred in the NVI interval (qx = 0.725 and 0.860, reand CI stage spectively). This high mortality reduced the mean life expectancy (e x) a t S t a g e s NVI and CI. Greatest life expectancy beyond the first naupliar stages was in the CIV stage, and copepods reaching this stage had a high probability of becoming adults. Fecundity (mx), n e t r e p r o d u c t i v e rate (r m) (R o) a n d i n t r i n s i c rate of increase are shown in Table 4. ( T h e v a l u e of m x was calculated from the number of eggs produced per female and again from the number of NI actually produced per female.) Based on the number of eggs per female, m x = 85.0; R O = 55.590 and r m = 0.28. Using the number of NI produced per female, m x = 47.5; R 0 = 31.065 and rm = 0.24. No. ~ NI/cl N~/~ No. ~ NI/cl N~/~ No. ~ NI/cl - 2 15 8o - I 15 95 NI/~ No. ~ NI/cl N~/~ - Development time (days) Egg-NI i.O 1.O-2.0 2.0 NI-CI 7.6 + 1.3 5.7 + 0.84 5.0 + 1.2 0 6.0 _+ 1.9 0 CI-adult Generation time (days) 10.3 • 0.98 aDied carrying egg sac. Table 3. E u t e r p i n a acutifrons. 1977 in North Inlet Age class No. alive at beginning of age interval, i x Life table, based on daily field samples taken from April 7-24, No. dying during age interval, Age-specific mortality, qx dx NI,II NIII NIV NV NVI CI CII CIII CIV CV CVI 1.0OOOO 0.61500 0.46125 0.35978 0.32380 0.08904 0.01246 0.00449 0.00081 0.00081 0.00065 .38500 .[5375 .10148 .O3598 .23475 .07658 .oo798 .00367 .OOOOO .OOO15 .00065 Table Mean no. alive Total life at middle of expectancy each age interval, (days), T x Lx 0.385 0.250 0.220 O. iOO 0.725 0.860 0.640 O.819 O.OOO O. 189 i.O00 .80750 .53813 .41051 .34178 .20642 .05076 .00848 .00265 .00081 .00073 .00033 2.36809 1.56059 1.02246 0.61195 0.27017 0.06374 0.01299 0.00451 0.00187 0.00106 0.00033 Mean lifetime remaining for those attaining age interval, e x 2.368 2.538 2.217 1.7OO 0.834 O.716 i.O42 1.OO6 2.311 1.311 0.500 L.M. D'Apolito and S.E. Stancyk: Population Dynamics of Euterpina acutifrons 257 Table 4. Euterpina acutifrons. Reproductive parameters for copepods from North Inlet -- fecundity, net reproductive rate, and intrinsic rate of increase Fecundity Net Intrinsic (mx) reproductiverate rate of increase (Ro ) (rm) Total no. of female 85 eggs produced per female (56% survival from egg to NI) 55.590 0.28 Total no. of female offspring (Ns produced per female 31.O65 0.24 47.5 Discussion Field densities of Euterpina acutifrons a p p e a r e d to be w e a k l y c o r r e l a t e d w i t h t e m perature (correlation coefficient r = 0.6395). Salinity fluctuation did not affect abundance because the species has a wide salinity tolerance (Moreira, 1975) a n d the s a l i n i t y f l u c t u a t i o n s in t h e f i e l d w e r e s m a l l (Fig. 2). E. acutifrons w a s m o s t a b u n d a n t f r o m J u n e to O c t o b e r w h e n the t e m p e r a t u r e r a n g e w a s 23 ~ to 29~ and completely absent from the water column when temperatures w e r e 11~ or below. Adults and copepodites reapp e a r e d in t h e e s t u a r y w h e n f i e l d t e m p e r a t u r e r e a c h e d 16.5~ This suggests that water temperature closely influe n c e s t h e p r e s e n c e of E. acutifrons in t h e e s t u a r y , b u t is l e s s i m p o r t a n t in r e g u lating abundance. H a q (1972) r e p o r t e d t h a t E. a c u t i f r o n s w a s f i r s t n o t e d in t h e Menai Straits, Anglesey (UK), w h e n w a t e r temperature h a d r i s e n to 16~ and disappeared when temperatures fell below 9Oc. N a u p l i i w e r e t h e f i r s t s t a g e s to a p p e a r in t h e M e n a i S t r a i t s b u t in N o r t h Inlet initial recruitment o c c u r r e d in the adult and late copepodite stages. Preliminary evidence s u g g e s t s t h a t E. acutifrons overwinters in t h e s e d i m e n t in N o r t h I n l e t (S.S. Bell, u n p u b l i s h e d data). The phenomenon of o v e r w i n t e r i n g or resting stages has been documented in several copepod species (Zillioux and Gonzalez, 1972; G r i c e a n d G i b s o n , 1975, 1977; L a n d r y , 1975). Temperature is an i m p o r t a n t v a r i a b l e regulating development t i m e s in c o p e p o d s (Muus, 1967; R o s e n f i e l d a n d C o u l l , i974; a n d H e l p a n d Smol, 1976; a n d T a b l e 5 of t h i s s t u d y ) . In t h e p r e s e n t s t u d y , l a b o ratory cultures at 25~ had a generation t i m e of 10.3 d a y s (Table 2) a n d t h e highest survival of all temperatures tested. Field data from October-November and April indicated the generation time at 2 O O C to b e a p p r o x i m a t e l y 14 d a y s (Fig. 2). H a q (1972) f o u n d 4 d i s t i n c t g e n e r a - Table 5. Euterpina acutifrons. Generation times at various temperatures, based on literature and present study Temperature Generation time Source (~ (days) Io 15-17 16 16 18 18 20 20 23 25 25 55 14 (field data) 25 13 17.5 Haq (1972) This study Bernard (1963) Haq (1972) Neunes and Pongolini (1965) 14-16 Zurlini et al. (1978) 14 (field data) This study 12-14 Haq (1963) 15 Bernard (1963) 9 Hag (1972) 10.3 This study t i o n s o f Euterpina acutifrons in the field, In N o r t h I n l e t , t h e r e a p p e a r e d to b e 6, possibly 7 generations in a year. B a s e d on g e n e r a t i o n times and laboratory surv i v a l r a t e s , the o p t i m u m t e m p e r a t u r e for E. a c u t i f r o n s i n N o r t h I n l e t w a s 25~ although breeding a l s o o c c u r r e d in t h e f i e l d a t 15 ~ a n d 30~ H a q (1972) r e ported 20~ as the o p t i m u m t e m p e r a t u r e f o r t h i s s p e c i e s in t h e w a t e r s n e a r A n glesey, where the average water temperat u r e w a s m u c h l o w e r t h a n in S o u t h C a r o lina waters. A l s o , t h e a b u n d a n c e of d i m o r p h i c m a l e s a p p e a r e d to b e t e m p e r a t u r e - r e l a t e d . Small males were most common during b r e e d i n g p e a k s of t h e p o p u l a t i o n in l a t e spring and early autumn, when field temperatures were lowest. The high abundance of small males during the initial appearance and increase of the populat i o n in A p r i l (Table I) s u p p o r t s b o t h H a q ' s (1972) h y p o t h e s i s that small males a r e m o s t i m p o r t a n t in b r e e d i n g a n d M o reira and Vernberg's (1968) f i n d i n g s that small males are more cold-adapted. L i f e t a b l e d a t a a r e v a l u a b l e in p o p u lation studies because they summarize the a g e - s p e c i f i c mortality and reproduc- 958 L.M. D'Apolito and S.E. Stancyk: Population Dynamics of Euterpina acutifrons tion c a p a c i t y of a p o p u l a t i o n . M o s t zooplankton population studies dealing with age-specific mortality report highest m o r t a l i t y in the e a r l y n a u p l i a r stages (McLaren, 1963; G e h r s and R o b e r t s o n , 1975; C o n f e r and Cooley, 1977). A l t h o u g h some m o r t a l i t y o c c u r r e d in the e a r l i e r n a u p l i a r s t a g e s of Euterpina acutifrons (Table 3), h i g h e s t m o r t a l i t i e s and lowest m e a n l i f e - e x p e c t a n c i e s w e r e in the NVI and CI stages. This m a y i n d i c a t e some e n e r g y c o s t a s s o c i a t e d w i t h the m o l t from n a u p l i u s to c o p e p o d i t e (also n o t e d by Gehrs and R o b e r t s o n , 1975) or s i z e - s e l e c t i v e p r e d a t i o n as n o t e d by A n d e r s o n (1970). L o n s d a ! e et al. (1979) f o u n d that Acartia tonsa s e l e c t i v e l y p r e y e d on Scottolana canadensis n a u p l i i (mean l e n g t h O.199 ~m for S t a g e s IV-VI) w h e n o f f e r e d a v a r i e t y of d i f f e r e n t s i z e d p r e y items. P o s s i b l y , a s i m i l a r s i t u a t i o n o c c u r s in N o r t h Inlet, w h e r e A. tonsa is a d o m i n a n t c o p e p o d y e a r - r o u n d (Lonsdale and Coull, 1977) and the m e a n length of NVI E. acutifrons is 0 . 2 0 3 ~m. N u m e r o u s l a r v a l fish are also p r e s e n t in the e s t u a r y in s p r i n g and s u m m e r a n d are k n o w n to feed on o r g a n i s m s in this size r a n g e (J. Dean, p e r s o n a l c o m m u n i c a t i o n ) . T h e o r e t i c a l m o d e l s c o n c e r n i n g the e v o l u t i o n of l i f e - h i s t o r y p a t t e r n s gene r a l l y lack e m p i r i c a l s u p p o r t (Stearns, 1976). S t e a r n s (1977) lists n u m e r o u s int r a c t a b l e p r o b l e m s w h i c h p r e v e n t the p r o p e r c o l l e c t i o n of l i f e - h i s t o r y data a n d c o n s t r u c t i o n of life tables. Such i n f o r m a t i o n is e v e n m o r e d i f f i c u l t to o b t a i n in m a r i n e e c o s y s t e m s , and t h e r e are few a d e q u a t e f i e l d - b a s e d life tables for m a r i n e i n v e r t e b r a t e s i n c l u d i n g zoop l a n k t o n (e.g. Hines, in press). I n a b i l ity to d e t e r m i n e p o p u l a t i o n size in a p e l a g i c m a r i n e e n v i r o n m e n t is one p r o b lem. E v e n m o r e i n s u r m o u n t a b l e , is the p r o b l e m of d e t e r m i n i n g j u v e n i l e m o r t a l i ty a n d r e c r u i t m e n t in s p e c i e s w h i c h h a v e l a r v a l s t a g e s ( S t r a t h m a n n and B r a n s c o m b , in press. Acknowledgements. The authors wish to extend their sincere gratitude to S.S. Bell for her advice and encouragement throughout the study, and to Dr. M.J. Youngbluth of Harbor Branch Foundation, Inc. for helpful comments on the original manuscript. Literature Cited Two v a l u e s of net r e p r o d u c t i v e rate (Ro) a n d the i n t r i n s i c rate of i n c r e a s e (rm) w e r e c a l c u l a t e d (Table 4), b u t values b a s e d on the n u m b e r of eggs per fem a l e are h i g h e r and are d i s c u s s e d h e r e b e c a u s e any m x v a l u e s b a s e d on g r a v i d females t a k e n from the f i e l d are n e c e s s a r i l y low. In a p o p u l a t i o n w i t h ext r e m e l y h i g h m o r t a l i t y (0~ survival from NI to adult), the net r e p r o d u c t i v e rate m u s t be v e r y h i g h to m a i n t a i n the p o p u l a t i o n in nature. The R o for Euterpina acutifrons f r o m N o r t h I n l e t was 55. 590 and the i n t r i n s i c rate of i n c r e a s e (rm) was 0.28, i n d i c a t i n g r e l a t i v e l y low m o r t a l i t y a n d a h i g h rate of r e p r o d u c t i o n in the a d u l t stage. Z u r l i n i et al. (1978) r e p o r t v a l u e s of a o a n d rm of 7 0 . 8 9 0 and 0.161, r e s p e c t i v e l y , for E. acutifrons in the l a b o r a t o r y . O u r e s t i m a t e of m x (fecundity) was b a s e d on g r a v i d females b r o u g h t in from the field, and it is l i k e l y t h a t t h e s e f e m a l e s p r o d u c e d prev i o u s u n r e c o r d e d egg sacs. Also, Z u r l i n i et al. o b t a i n e d as m a n y as 16 egg cases f r o m a s i n g l e female, i n d i c a t i n g e i t h e r that p o p u l a t i o n s f r o m the M e d i t e r r a n e a n and N o r t h I n l e t are v e r y d i f f e r e n t , or t h a t our c u l t u r e m e t h o d s a f f e c t e d surv i v a l a n d egg p r o d u c t i o n by females. T h i s is the f i r s t r e p o r t of rm for a mar i n e c o p e p o d from f i e l d d a t a r a t h e r t h a n l a b o r a t o r y cultures, and the h i g h e r value m a y i n d i c a t e that j u v e n i l e m o r t a l i t y r a t e s or a d u l t l o n g e v i t y h a v e b e e n und e r e s t i m a t e d in l a b o r a t o r y cultures. Allan, J.D.: Competition and the relative abundance of two cladocerans. Ecology 54, 484-498 (1973) - Life history patterns in zooplankton. Am. Nat. 110, 165-180 (1976) Anderson , R.S.: Predator-prey relationships and predation rates for crustacean zooplankters from some lakes in western Canada. Can. J. Zool. 48, 1229-1240 (1970) Bernard, M.: Le cycle vital en laboratoire d'un cop@pode p&lagique de M~diterran~e Euterpina acutifrons Claus. P~lagos, Bull. Inst. oc~anogr. Alger i, 35-48 (1963) Comita, G.W.: The seasonal zooplankton cycles, production and transformation of energy in Severson Lake, Minnesota. Arch. Hydrobiol. 70, 14-66 (1972) Confer, J.L. and J.M. Cooley: Copepod instar survival and predation by zooplankton. J. Fish. Res. Bd Can. 34, 703-706 (1977) Edmondson, W.T.: Reproductive rates of rotifers in natural populations. Memorie Ist. ital. Idrobiol. 12, 21-77 (1960) -, G.W. Comita and G.C. Anderson: Reproductive rate of copepods in nature and its relation to phytoplankton population. Ecology 43, 625634 (1962) Fanta, E.S.: Anatomy of the nauplii of Euterpina acutifrons (Dana). Crustaceana 23, 165-181 (1972) Fleminger, A.: Taxonomic and distributional studies on the epiplanktonic calanoid copepods (Crustacea) of the Gulf of Mexico, 317 pp. Ph.D. dissertation, Harvard University, Cambridge, Mass. 1956 L.M. D'Apolito and S.E. Stancyk: - Population Dynamics of Euterpina Taxonomy, distribution, and polymorphism in the Labidocera jollae group, with remarks on evolution within the group (Copepoda: Calanoida). Proc. U.S. natn. Mus. 120, 1-61 (1967) Frolander, H.F.: Statistical variation in zooplankton numbers from subsampling with a Stemple pipette. J. Wat. Pollut. Control Fed. 40, R82-88 (1968) Galigher, A.E. and E.N. Kozloff: Essentials of practical microtechnique, 531 pp. Philadelphia: Lea & Febiger 1971 Gehrs, G.W. and A. Robertson: Use of life tables in analysing the dynamics of copepod populations. Ecology 56, 665-672 (1975) Grice, G.D. and V.R. Gibson: Occurrence, viability and significance of resting eggs of the calanoid copepod Labidocera aestiva. Mar. Biol. 31, 335-337 (1975) - Resting eggs in Pontella meadi (Copepoda, Calanoida). J. Fish. Res. Bd Can. 34, 410-412 (1977) Hall, D.J.: An experimental approach to the dynamics of a natural population of Daphnia galeata mendotae. Ecology 45, 94-112 (1964) Haq, S.M.: Development of the copepod Euterpina acutifrons with special reference to dimorphism in the male. Proc. zool. Soc. Lond. 144, 175-201 (1965) - Breeding of Euterpina acutifrons, a harpacticid copepod, with special reference to dimorphic males. Mar. Biol. 15, 221-235 (1972) - Factors affecting production of dimorphic males of Euterpina acutifrons. Mar. Biol. 19, 23-26 (1973) Heinle, D.R.: Effects of temperature on the population dynamics of estuarine copepods, 132 pp. Ph.D. dissertation, University of Maryland, College Park, Md 1969 Help, C. and N. Smol: Influence of temperature on the reproductive potential of two brackishwater harpacticoids (Crustacea: Copepoda). Mar. Biol. 35, 327-334 (1976) Hines, A.H.: The comparative reproductive ecology of three species of intertidal barnacles. In: Reproductive ecology of marine invertebrates, Vol. 9. Ed. by S.E. Stancyk. Columbia, S. Carolina: Belle W. Baruch Library in Marine Science, University of South Carolina Press (In press) Jacobs, J.: Laboratory cultivation of the marine copepod Pseudodiaptomus coronatus Williams. Limnol. Oceanogr. 6, 443-446 (1961) Katona, S.K.: Growth characteristics of the copepods Eurytemora affinis and E. herdmani in laboratory cultures. Helgol&nder wiss. Meeresunters. 20, 373-384 (1970) Landry, M.R.: Dark inhibition of egg hatching of the marine copepod Acartia clausi. J. exp. mar. Biol. Ecol. 20, 43-47 (1975) Lonsdale, D.J. and B.C. Coull: Composition and seasonality of the North Inlet, South Carolina zooplankton. Chesapeake Sci. 18, 272-283 (1977) -, D.R. Heinle and C. Siegfried: Carnivorous feeding behavior of the adult calanoid cope- acutifrons 259 pod Acartia tonsa Dana. J. exp. mar. Biol. Ecol. 36, 235-248 (1979) Lotka, A.J.: Studies on the mode of growth of material aggregates. Am. J. Sci. 24, 199-216 (1907) A natural population norm. J. Wash. Acad. Sci. 3, 241-248, 289-293 (1913) Lowndes, A.G.: Results of breeding experiments and other observations on Cyclops vernalis Fischer and Cyclops robustus Sara. Int. Revue ges. Hydrobiol. Hydrogr. 21, 171-188 (1929) McLaren, I.A.: Effects of temperature on the growth of zooplankton and the adaptive value of vertical migration. J. Fish. Res. Bd Can. 20, 685-727 (1963) Mertz, D.B.: Notes on the methods used in lifehistory studies. In: Readings in ecology and ecological genetics, pp 4-17. Ed. by J.H. Conneil, D.B. Mertz and W.W. Murdock. New York: Harper & Row 1970 Moreira, G.S.: Studies on the salinity resistance of the copepod Euterpina acutifrons (Dana). In: Physiological ecology of estuafine organisms, pp 73-79. Ed. by F.J. Vernberg. Columbia, S.C.: University of South Carolina Press 1975 and W.H. Vernberg: Comparative thermal metabolic patterns in Euterpina acutifrons dimorphic males. Mar. Biol. i, 282-284 (1968) Muus, B.J.: The fauna of Danish estuaries and lagoons: distribution and ecology of dominating species in the shallow reaches of the mesohaline zone. Meddr Danm. Fisk.-og Havunders. (N.S.) 5, 3-316 (1967) Nassogne, A.: Influence of food organisms on the development and culture of pelagic copepods. Helgol~nder wiss. Meeresunters. 20, 333-345 (1970) Neunes, H.W. and G.F. Pongolini: Breeding a pelagic copepod, Euterpina acutifrons (Dana) in the laboratory. Nature, Lond. 208, 571-573 (1965) Paffenh6fer, G.A.: Cultivation of Calanus helgolandicus under controlled conditions. Helgolander wiss. Meeresunters. 20, 346-359 (1970) Pianka, E.R.: Evolutionary ecology, 356 pp. New York: Harper & Row 1974 Pritchard, D.V.: Estuarine circulation patterns. Proc. Am. Soc. cir. Engrs 81, 717/i-717/11 - (1955) Rosenfield, D.C. and B.C. Coull: Adult morphology and larval development of Paramphiascella fulvofasciata n. sp. (Copepoda, Harpacticoida). Cah. Biol. mar. 15, 295-317 (1974) Sewell, R.B.S.: The Copepoda of Indian seas (Calanoida). Mem. Indian Mus. 10, 1-407 (1929) Stearns, S.C.: Life history tactics: a review of the ideas. Q. Rev. Biol. 51, 3-47 (1976) - The evolution of life history traits: a critique of the theory and a review of the data. A. Rev. Ecol. Syst. 8, 145-171 (1977) Strathmann, R.R. and E.S. Branscomb: Adequacy of cues to favorable sites used by settling larvae: relation to cause of death and dispersal 260 L.M. D'Apolito and S.E. Stancyk: Population Dynamics of Euterpina acutifrons in two intertidal barnacles. In: Reproductive ecology of marine invertebrates, Vol. 9. Ed. by S.E. Stancyk~ Columbia, S. Carolina: Belle W. Baruch Library in Marine Science, University of South Carolina Press (In press) Vernberg, W.B. and G.S. Moreira: Metabolic-temperature responses of the copepod Euterpina acutifrons (Dana) from Brazil. Comp. Biochem. Physiol. 49A, 757-761 (1974) Zillioux, E.J. and J.G. Gonzalez: Egg dormancy in a neritic calanoid copepod and its implications to overwintering in boreal waters. In: Fifth European Marine Biology Symposium, pp 217-230. Ed. by B. Battaglia. Padova, Italy: Piccin Editore 1972 Zurlini, G., I. Ferrari and A. Nassogne: Reproduction and growth of Euterpina acutifrons (Copepoda: Harpacticoida) under experimental conditions. Mar. Biol. 46, 59-64 (1978) Date of final manuscript acceptance: July 6, 1979. communicated by I. Morris, West Boothbay Harbor