BIOGEOCHEMICAL BUDGETS I N CORAL REEF SYSTEMS S. V. Smith, P. L. J o k i e l , G . S. Key
INTRODUCTION
The t e r m "model" i n ecosystem a n a l y s i s r e f e r s t o t h e s y s t e m a t i c c o n c e p t u a l i z a t i o n of t h e myriad components w i t h i n a n ecosystem. A h i g h d e g r e e of m a t h e m a t i c a l s o p h i s t i c a t i o n i s d e s i r a b l e a s a n u l t i m a t e g o a l of ecosystem a n a l y s i s . U n t i l t h a t s o p h i s t i c a t i o n c a n a l s o o b t a i n s u f f i c i e n t r e a l i s m , less s o p h i s t i c a t e d c o n s t r u c t s i n t h e form of mass- b a l a n c e b u d g e t s p r o v i d e c o n s i d e r a b l e i n s i g h t i n t o t h e dynamics of eco-
s y s terns.
Budgets, l i k e t h e i r more c o m p l i c a t e d c o u n t e r p a r t s , i n v o l v e t h e i d e n t i f i c a t i o n o f s i m p l e " f u n c t i o n a l u n i t s , " o r "compartments," w i t h i n t h e ecosystem; b u d g e t s a l s o r e q u i r e The i d e n t i f i c a t i o n of l i k e l y p a t h - ways of m a t e r i a l flow through t h e system. However, b u d g e t s do n o t r e q u i r e t h a t m a t h e m a t i c a l f u n c t i o n s d e s c r i b i n g t h e c h a r a c t e r i s t i c s of m a t e r i a l f l u x b e d e v i s e d . Budgets of c a r b o n f l u x have been developed f o r s e v e r a l c o r a l r e e f systems o r p o r t i o n s t h e r e o f , and c a r b o n b u d g e t s f o r h y p o t h e t i c a l r e e f s w i l l b e t h e primary s u b j e c t of t h i s d i s c u s s i o n .
GENERAL BUDGETARY CONSTRUCT
The primary s u b j e c t of d i s c u s s i o n h e r e w i l l b e a c o r a l a t o l l of h y p o t h e t i c a l , b u t r e a l i s t i c , dimensions. Imagine a c i r c u l a r a t o l l w i t h a l a g o o n of 100 km2 a r e a , a r e e f f l a t of 20 km2, and a f o r e - r e e f ( t o a d e p t h of a b o u t 50 m e t e r s ) of 1 0 km2. T h i s a t o l l would have a l a g o o n a b o u t 11 km i n d i a m e t e r , a r e e f f l a t a b o u t 500 meters wide, and f o r e - r e e f a b o u t 250 meters wide. Data g i v e n by Wiens (1962) s u g g e s t t h e s e dimensions t o b e r e a l i s t i c . I n a d d i t i o n t o t r e a t i n g each of t h e above p h y s i o g r a p h i c u n i t s a s compartments i n t h e b u d g e t s , w e w i l l c o n s i d e r t h e
two f u r t h e r compartments of c a r b o n d i o x i d e and f i x e d carbon i n t h e ocean w a t e r . There i s t h u s t h e f o l l o w i n g 5-compartment b u d g e t : o c e a n i c C02
and f i x e d c a r b o n , lagoon, r e e f f l a t , and f o r e - r e e f .
The c o n n e c t i v i t y d e s c r i b e s m a t e r i a l t r a n s f e r from one compartment t o a n o t h e r . For t h e most p a r t i n a p h y s i o g r a p h i c b u d g e t , t h a t connec- t i v i t y i s two-way. That i s , i f m a t e r i a l i s t r a n s p o r t e d from any one compartment A t o compartment B , i t p r o b a b l y c a n a l s o go from B t o A.
Arrows on a compartment diagram show i n t e r p r e t a t i o n s of t h e d i r e c t i o n of n e t f l u x . Probably
any
compartment p a i r can b e connected. The diagram d e s c r i b e s o n l y t h e c o n n e c t i v i t i e s which seem l i k e l y t o b e q u a n t i t a t i v e l y s i g n i f i c a n t.
Hawaii I n s t i t u t e of Marine Biology, U n i v e r s i t y of Hawaii, Kaneohe
,
Hawaii, USAC l e a r l y , t h e r e i s n e t f l u x from o c e a n i c C02 t o a l l t h r e e r e e f compartments i n t h e form of CaC03 p r e c i p i t a t i o n . We assume t h a t n e t o r g a n i c carbon f l u x i s i n t h e same d i r e c t i o n , t h a t i s , t h a t a t o l l s a r e s i t e s of n e t C02 u p t a k e i n t h e form of primary p r o d u c t i o n . T h i s p o i n t w i l l b e d i s c u s s e d i n more d e t a i l l a t e r i n t h e p r e s e n t a t i o n . With r e s p e c t t o CaC03, most of t h e o t h e r a r r o w s a r e f a i r l y obvious. CaC03 i s s t r i p p e d o f f t h e r e e f and is t r a n s p o r t e d e i t h e r t o t h e lagoon o r t o t h e o c e a n i c f i x e d c a r b o n p o o l , and m a t e r i a l i s a l s o l o s t from t h e f o r e - r e e f t o t h a t p o o l . D e p o s i t s of f o r e - r e e f m a t e r i a l p i l e d on r e e f f l a t s a r g u e t h a t t h e r e i s n e t t r a n s f e r from t h e f o r e - r e e f t o t h e r e e f f l a t . I t seems l i k e l y t h a t t h i s d i r e c t i o n of n e t t r a n s f e r i s e q u a l l y v a l i d f o r o r g a n i c carbon. M a t e r i a l c a r r i e d from t h e f o r e - r e e f t o t h e r e e f f l a t o r d e l i v e r e d t o t h e l a g o o n h a s a r e l a t i v e l y good chance of set- t l i n g o u t i n t h e s e environments; m a t e r i a l t r a n s p o r t e d oceanward i s l i k e l y t o d r i f t away from t h e a t o l l . Thus, t h e f o r e - r e e f i s i n h e r e n t l y a n i n e f f e c t u a l t r a p f o r p a r t i c u l a t e m a t e r i a l i n comparison w i t h t h e r e e f f l a t o r l a g o o n .
CaC03 BUDGET
The n e x t s t e p i s t o q u a n t i f y t h e t r a n s f e r r a t e s a s s o c i a t e d w i t h t h e a r r o w s and t h e a c c u m u l a t i o n ( o r l o s s ) r a t e s i n t h e boxes. F i r s t c o n s i d e r CaC03-C ( F i g u r e 1 ) . Lagoon CaC03 p r o d u c t i o n r a t e s have b e e n measured between a b o u t 5 and 1 0 moles m-2yr-1 (Smith and P e s r e t , 1974;
Smith and J o k i e l , 1 9 7 5 ) . The h i g h e r v a l u e i s used h e r e . Thus, t h e h y p o t h e t i c a l l a g o o n produces 1 0 X
l o 8
moles C/yr. The p r o d u c t i o n r a t e i n s h a l l o w , w e l l - f l u s h e d environments s u c h a s r e e f f l a t s h a s beenmeasured t o b e a b o u t 40 t o 50 moles m - 2 y r - l (Smith, 1973; Kinsey, 1 9 7 2 ) . Again, t h e h i g h e r v a l u e i s t a k e n f o r a t o t a l r e e f - f l a t p r o d u c t i o n of 1 0 X 108 moles C/yr. No CaC03 p r o d u c t i o n r a t e d a t a a r e a v a i l a b l e f o r f o r e - r e e f s . Such environments have h i g h s t a n d i n g c r o p s o f c a l c a r e o u s o r g a n i s m s , s o a p r o d u c t i o n r a t e comparable t o t h a t of t h e r e e f f l a t i s assumed--a t o t a l p r o d u c t i o n of 5 X 1 0 moles C/yr. 8 CaC03-mediated l o s s from t h e C02 p o o l i s simply t h e sum of t h e f l u x e s t o t h e r e e f compart- ments, o r 25 X
l o 8
moles C/yr.Of m a t e r i a l e n t e r i n g t h e f o r e - r e e f compartment, we assume a s u f - f i c i e n t amount remains t o a c c o u n t f o r a n e t v e r t i c a l a c c r e t i o n of a b o u t 1 nun/yr. T h i s is e q u i v a l e n t t o a b o u t 1 X
l o 8
moles C / y r . T h i s f i g u r e i s b a s e d p r i m a r i l y on14c
a g e d a t i n g t o o b t a i n d e p o s i t i o n r a t e s on t h e f o r e - r e e f i n Jamaica (Land, 1 9 7 4 ) . I t t h u s a p p e a r s t h a t 4 xl o 8
moles/y r , o r 80% of t h e m a t e r i a l produced i n t h e f o r e - r e e f i s l o s t from t h a t environment. We assume t h a t 75% of t h i s l o s s i s t o t h e ocean and t h e remainder i s t o t h e r e e f f l a t .
T r a n s p o r t from t h e f o r e - r e e f p l u s CaC03 p r o d u c t i o n on t h e r e e f f l a t a c c o u n t f o r 11 X 1 0 moles C/yr i n p u t t o t h e r e e f f l a t . The upward 8 growth of th.e r e e f f l a t i s o b v i o u s l y l i m i t e d by s e a l e v e l , and long-term world-wide s e a l e v e l p r e s e n t l y does n o t show a change of more t h a n a b o u t
FIXED CARBON
10.00
CaCO,- C 6.09 8
2
moles x 1 0 - ~ / ~ r
Lagoon m
7 2 Reef Flat '2x10 m
7 2
Fore-Reef4~10 m
L A G O O N
15.91
F i g u r e 1. Compartment d i a g r a m of CaC03-C f l u x i n a c o r a l a t o l l .
2.25
f 1
,6.75 . REEF FLAT
2.00 , 1.00 . FORE-REEF
1.00
f
1 mm/yr. For t h e b u d g e t , we assume t h a t t h e r e i s a 1 m / y r d e p o s i - t i o n r a t e on t h e r e e f f l a t , o r 2 X 1 0 moles C/yr. 8 We f u r t h e r assume t h a t 75% o f t h e l o s s from t h e r e e f f l a t i s t o t h e l a g o o n , and t h a t t h e remainder i s e x p o r t e d t o t h e ocean.D e p o s i t i o n i n t h e l a g o o n i s n o t o r d i n a r i l y l i m i t e d by s e a l e v e l . Moreover, a v a i l a b l e d a t a (Smith - - e t a l . , 1971; Smith and J o k i e l , 1975) s u g g e s t t h a t s e d i m e n t l o s s from t h e l a g o o n t o t h e open ocean i s s m a l l ; w e assume t h i s l o s s t o b e 5% of t h e t o t a l l a g o o n i n p u t . Thus, a b o u t
1 6 X
l o 8
moles C/yr remain i n t h e l a g o o n and about 1 X 10' m o l e s / y r a r e l o s t t o t h e ocean.Export of CaC03 t o t h e open ocean i s o b t a i n e d by summing terms.
For t h e budget a s a whole t o b a l a n c e , t h e sum of t h e numbers i n t h e v a r i o u s compartments must e q u a l 0.
What a r e t h e i n o r g a n i c b u d g e t a r y c h a r a c t e r i s t i c s of o u r h y p o t h e t i - c a l a t o l l ? The l a g o o n i s o b v i o u s l y t h e major r e p o s i t o r y f o r CaC03, a c c o u n t i n g f o r a b o u t 65% of t h e t o t a l i n o r g a n i c c a r b o n f i x e d . The l o s s from t h e a t o l l i s t h e n e x t p r o c e s s i n q u a n t i t a t i v e i m p o r t a n c e , a t 25%, and t h e f o r e - r e e f and r e e f - f l a t a r e a s are small s i n k s f o r i n o r g a n i c c a r b o n , a c c o u n t i n g f o r o n l y a b o u t 10% of t h e t o t a l p r o d u c t i o n .
I t i s p o s s i b l e t o i n v e s t i g a t e t h e consequences o f changing t h e compartment s i z e s - - t h a t i s a l t e r i n g t h e s i z e of t h e a t o l l . A t o l l r e e f f l a t s and s l o p e s a r e f a i r l y c o n s t a n t i n w i d t h (Wiens, 1 9 6 2 ) , s o a l t e r - i n g t h e a t o l l s i z e p r i m a r i l y i n v o l v e s m a n i p u l a t i o n of lagoon d i a m e t e r s . For t h e f o l l o w i n g a n a l y s i s , t h e l a g o o n a r e a h a s been v a r i e d by powers of 1 0 , and t h e r e e f - f l a t and f o r e - r e e f a r e a s have b e e n a d j u s t e d t o m a i n t a i n c o n s t a n t w i d t h . A l l p r o d u c t i o n r a t e s p e r u n i t a r e a and depo- s i t i o n a l r a t e s on t h e f o r e - r e e f and r e e f f l a t a r e h e l d c o n s t a n t ; p r o p o r t i o n a l p a r t i t i o n i n g of f l u x from one compartment t o a n o t h e r i s m a i n t a i n e d . A s t h e a t o l l s i z e d e c r e a s e s , t h e l a g o o n d e p o s i t i o n r a t e i n c r e a s e s , and t h e c a r b o n l o s s i n c r e a s e s towards 50% ( F i g u r e 2 ) . A s t h e lagoon f i l l s i n ( o r d i m i n i s h e s i n h o r i z o n t a l dimensions t o O), t h e d e p o s i t i o n r a t e w i l l t h e n n e c e s s a r i l y v a n i s h ; t h e r e w i l l b e no f u r t h e r l a g o o n p r o d u c t i o n ; a l l e x c e s s s e d i m e n t s w i l l t h e n b e e x p o r t e d from t h e a t o l l .
The change of s e a l e v e l a l s o h a s d r a m a t i c e f f e c t s on t h e e x p e c t e d d e p o s i t i o n a l c h a r a c t e r i s t i c s of an a t o l l . To c o n s t r u c t t h e budget s o f a r , w e have assumed t h a t t h e r e e f - f l a t d e p o s i t i o n r a t e i s p r o p o r t i o n a l t o t h e r a t e of s e a - l e v e l change. Fore-reef d e p o s i t i o n i s 1 mm/yr b u t i n o u r budget i s n o t c o n t r o l l e d by changing s e a l e v e l . Lagoons a c c e p t most of t h e s e d i m e n t s d e l i v e r e d t o them. Modifying t h e budget t o a c c o u n t f o r s e a l e v e l change t h u s merely i n v o l v e s a l t e r i n g r e t e n t i o n on t h e r e e f f l a t .
F i g u r e 3 shows t h e r e s u l t s of s u c h a l t e r a t i o n s . Up t o a s e a - l e v e l r i s e o f a b o u t 5 mm/yr, d e p o s i t i o n o n t h e r e e f f l a t would keep pace w i t h t h a t r i s i n g sea l e v e l . On a f a s t e r r i s e , r e e f f l a t d e p o s i t i o n r a t e would s t a b i l i z e , i f t h e environment r e t a i n e d a l l o f i t s p r o d u c t s . The
LAGOON AREA ( m 2 )
DEPOSITIONAL FACTORS as a FUNCTION
of ATOLL S I Z E
1 I I 1 - I I I I
LOSS of CaC03 DEPOSITION - from ATOLL SYSTEM -
r/) W
X
20-
F i g u r e - 2 . CaC03-C f l u x as a f u n c t i o n o f a t o l l s i z e .
A
H
1 -
10
I I I I ,
- -
B
1 I I I
lo5 lo6 lo7 lo8 lo9 0. lo5 lo6 lo7 lo8 10'
A Sea Level
rnm /yr
F i g u r e 3. CaC03-C f l u x a s a f u n c t i o n of s e a l e v e l r i s e .
f o r e - r e e f grows upward a t 1 mm/yr, r e g a r d l e s s of t h e r a t e o f s e a l e v e l change. The l a g o o n d e p o s i t i o n r a t e would i n c r e a s e on a f a l l i n g s e a b u t would a d j u s t t o a d e p o s i t i o n r a t e s i m i l a r t o t h a t of t h e f o r e - r e e f
d u r i n g a p e r i o d of r a p i d l y r i s i n g s e a l e v e l . T h i s s i m p l e d e p o s i t i o n a l model would b r e a k down a s t h e a t o l l physiography i s a l t e r e d away from i t s s t a r t i n g geometry due t o t h e change of s e a l e v e l and d e p o s i t i o n a l regime.
ORGANIC CARBON BUDGET
L e t u s now t u r n o u r a t t e n t i o n t o t h e o t h e r major a s p e c t of an a t o l l c a r b o n budget: t h e p r o d u c t i o n and consumption of o r g a n i c c a r b o n com- pounds. W e w i l l u s e our same h y p o t h e t i c a l a t o l l f o r t h e s e c a l c u l a t i o n s , a s w e l l a s t h e same f i v e compartment box model t o r e p r e s e n t t h a t a t o l l .
D e s p i t e t h e i r v e r y h i g h g r o s s p r o d u c t i o n r a t e s , c o r a l r e e f s have a g r o s s p r o d u c t i o n t o r e s p i r a t i o n r a t i o remarkably n e a r 1 . 0 . I t i s l i k e l y t h a t r e e f s somewhat t o e i t h e r s i d e of t h i s u n i t y P / R r a t i o can b e found.
Our own e x p e r i e n c e h a s been p r i m a r i l y w i t h a t o l l which seem t o b e v e r y s l i g h t n e t p r o d u c e r s of c a r b o n , s o w e g i v e o u r h y p o t h e t i c a l a t o l l a n e t community p r o d u c t i o n r a t e of a b o u t 4 m o l e s m-2day-1, o r a b o u t 1 . 5 moles m'2yr-1. T h i s c o r r e s p o n d s t o a P/R r a t i o of 1.007 i f t h e g r o s s produc-
t i o n r a t e of t h e community i s 6 g C m-2day-1. T h i s v a l u e i s v e r y c l o s e t o t h e n e t p r o d u c t i o n r a t e r e p o r t e d by Smith and J o k i e l (1975) f o r t h e l a g o o n a t Canton A t o l l . Lagoons a r e p a r t i c u l a r l y u s e f u l f o r e s t a b l i s h - i n g t h e n e t p r o d u c t i o n of a r e e f system, b e c a u s e t h e y i n t e g r a t e r e e f community metabolism o v e r a l o n g t i m e and a l a r g e a r e a .
F i g u r e 4 summarizes t h e o r g a n i c c a r b o n b u d g e t . Reef s e d i m e n t s commonly a v e r a g e a b o u t 0.5% by weight o r g a n i c c a r b o n (Smith and J o k i e l , 1 9 7 5 ) . T h i s amounts t o a b o u t 5% o f t h e t o t a l c a r b o n i n t h e s e d i m e n t s , s o o r g a n i c c a r b o n r e t a i n e d by each of t h e a t o l l compartments i s f i x e d a t t h i s p e r c e n t a g e of t h e i n o r g a n i c c a r b o n r e t e n t i o n , w h i c h h a s a l r e a d y been e s t a b l i s h e d . There i s no p a r t i c u l a r b a s i s t o a r g u e f o r a n y t h i n g o t h e r t h a n a n even d i v i s i o n of carbon t r a n s p o r t from e a c h a t o l l compart- ment t o i t s v a r i o u s p o s s i b l e s i n k s . The b u d g e t t u r n s o u t n o t t o b e p a r t i c u l a r l y s e n s i t i v e t o t h i s p o i n t .
While t h e magnitude of t h e s e v a r i o u s numbers might b e a l t e r e d some- what, t h e budget c l e a r l y p r e d i c t s a s u b s t a n t i a l e x p o r t of even t h e mini-
s c u l e n e t e x c e s s o r g a n i c c a r b o n produced by t h e a t o l l . Moreover, t h e p r o p o r t i o n a l o r g a n i c c a r b o n e x p o r t from t h e t h r e e r e e f s u b u n i t s i s c o n s i d e r a b l y h i g h e r t h a n t h e i n o r g a n i c c a r b o n e x p o r t . I t i s t e m p t i n g t o a s c r i b e t h i s d i f f e r e n t i a l t r a n s p o r t t o a n a r t i f a c t of t h e b u d g e t ; t h a t d o e s n o t s e e m t o b e t h e c a s e . Broecker and T a k a h a s h i (1966) ob- s e r v e d s u c h a b u d g e t a r y d i s c r e p a n c y f o r t h e Bahama Banks; t h e y s u g g e s t e d t h a t t h e y had f a i l e d t o o b t a i n a mass b a l a n c e among t h e terms. Smith and J o k i e l (1974) a s c r i b e d a s i m i l a r d i s c r e p a n c y a t Canton A t o l l t o d i f - f e r e n t i a l t r a n s p o r t of o r g a n i c m a t e r i a l , and e v i d e n c e f o r d i f f e r e n t i a l t r a n s p o r t c a n b e r e c o n s t r u c t e d f o r t h e Enewetak windward r e e f f l a t
(Smith, 1973; Johannes and G e r b e r , 1974; M a r s h a l l , 1 9 6 5 ) . What a r e t h e mechanisms ?
Organic C I 1.000 Lagoon = P I 0 8 m 2
moles x 1 0 - ~ / ~ r Reef Flat ~2x10 7 m 2
7 2 Fore-Reef = P l O m
CARBON DIOXIDE
Figure 4. Compartment diagram of organic C flux in a coral atoll.
LAGOON
0.800 0.125 R E E F FLAT
0.100 0.0 5 0 FORE-REEF
0.05 0
P e r h a p s t h e most c o n s p i c u o u s mechanism i s t h e r e l a t i v e e a s e w i t h which t h e biomass i s d i s l o d g e d by m e c h a n i c a l o r b i o l o g i c a l e r o s i o n . I n d e e d , t h i s dislodgement and s u b s e q u e n t t r a n s p o r t of o r g a n i c m a t e r i a l s a r e a p p a r e n t l y of c o n s i d e r a b l e i m p o r t a n c e t o t h e f e e d i n g p a t t e r n s of r e e f organisms (Smith and Marsh, 1 9 7 3 ) . Even though e r o s i o n of CaC03 a l s o o c c u r s , t h i s h e a v i e r m a t e r i a l i s l i k e l y t o s e t t l e more r a p i d l y . The second mechanism t o b e c o n s i d e r e d may b e a s i m p o r t a n t , o r p e r h a p s more so--the f l u x of d i s s o l v e d o r g a n i c m a t e r i a l . Lacking any tendency
t o s e t t l e ( s h o r t of a d s o r p t i o n t o o t h e r m a t e r i a l s ) , t h e d i s s o l v e d o r g a n i c compounds a r e r e a d i l y t r a n s p o r t e d from t h e system. Thus,
d e s p i t e i n i t i a l concerns a b o u t a model s u g g e s t i n g s i g n i f i c a n t l y g r e a t e r f l u x of o r g a n i c t h a n of i n o r g a n i c r e e f p r o d u c t s , we conclude t h a t
r e s u l t s t o t h e c o n t r a r y would b e a l l t h e more s u r p r i s i n g .
OTHER BUDGETS
The d i s c u s s i o n s o f a r h a s i n v o l v e d c a r b o n ; b u t t h e c a r b o n b u d g e t s , by i m p l i c a t i o n , t e l l u s a g r e a t d e a l a b o u t o t h e r m a t e r i a l s . For example, some c a t i o n s s u c h a s Mg o r S r have b u d g e t s which a r e v e r y s i m i l a r t o t h a t of CaC03. I n p o l l u t e d s y s t e m s , one might p r e d i c t pathways of t h e p o l l u t a n t ( e . g . , t r a c e m e t a l s ) from a knowledge of t h e i r co-occurrence w i t h carbon compounds. A l t e r n a t i v e l y , p o l l u t a n t d i s t r i b u t i o n i n t h e ecosystem might c a r r y s i g n i f i c a n t c l u e s a b o u t chemical b e h a v i o r of t h e m a t e r i a l s i n q u e s t i o n .
N e t n u t r i e n t b u d g e t s must l o o k somewhat l i k e t h e o r g a n i c c a r b o n b u d g e t , a l t h o u g h t h e r e may b e d i f f e r e n c e s i n t h e d e t a i l s of g r o s s s o u r c e s , s i n k s , and i n t r a s y s t e m p a r t i t i o n i n g . L e t u s b r i e f l y c o n s i d e r two r e c e n t n u t r i e n t b u d g e t s t u d i e s which have p r o v i d e d e x c i t i n g i n s i g h t s i n t o c o r a l r e e f s . Webb e t a l . , (1975) r e p o r t e d on t h e f l u x of n i t r o g e n t h r o u g h t h e windward r e e f f l a t community of Enewetak A t o l l . The r e e f a p p a r e n t l y e x p o r t s a l l forms of f i x e d n i t r o g e n , y e t t h a t community main- t a i n s i t s g r o s s o r g a n i c carbon p r o d u c t i o n t o r e s p i r a t i o n r a t i o n e a r 1 . 0 . The most obvious c o n c l u s i o n from t h e o b s e r v a t i o n i s t h a t t h e community must o f f s e t t h e n i t r o g e n e x p o r t w i t h an e q u i v a l e n t r a t e of n i t r o g e n f i x a t i o n . Subsequent s t u d i e s (Wiebe e t a l . , 1975) n o t o n l y v e r i f i e d t h i s h y p o t h e s i s b u t a l s o i s o l a t e d s e v e r a l of t h e i m p o r t a n t n i t r o g e n - f i x i n g organisms i n t h e community. The h i g h n i t r o g e n - f i x i n g c a p a c i t y of t h a t community h a s c o u n t e r e d i t s l o c a t i o n i n t h e n i t r o g e n - p o o r ocean w a t e r s of t h e M a r s h a l l I s l a n d s by e x p l o i t i n g an a l t e r n a t i v e , and l a r g e , n i t r o g e n r e s e r v o i r ( a i r ) .
There i s no s u c h a l t e r n a t e phosphorus p o o l , and t h e phosphorus c o n t e n t of ocean w a t e r s impinging upon Enewetak A t o l l i s a l s o low.
P i l s o n and B e t z e r (1973) determined t h a t t h e Enewetak r e e f - f l a t com- munity r e t a i n s phosphorus w i t h g r e a t t e n a c i t y . These a u t h o r s quoted
S a r g e n t and A u s t i n (1949) a s a n t i c i p a t i n g d i u r n a l o s c i l l a t i o n s of phosphorus u p t a k e and r e l e a s e i n synchrony w i t h oxygen p r o d u c t i o n and
consumption. T h a t s y n c h r o n y d o e s n o t e x i s t , and P i l s o n and B e t z e r p o i n t o u t t h a t i f i t d i d , t h e r e e f community would h a v e a r e q u i r e m e n t o f up t o 150% o f t h e a v a i l a b l e phosphorus on a midday low t i d e i n o r d e r
t o match t h e r a t e of o r g a n i c c a r b o n p r o d u c t i o n .
S u b s e q u e n t s t u d i e s (Pomeroy -- e t - a l . , 1 9 7 4 ) s u g g e s t t h a t t h e s t r o n g r e t e n t i o n and i n t e r n a l c y c l i n g o f p h o s p h o r u s r e p r e s e n t s a complex p a t t e r n o f l e a k a g e by some members o f t h e r e e f community a n d e f f e c t i v e p h o s p h o r u s c a p t u r e by o t h e r s . T h i s p a t t e r n s p e a k s t o t h e c o m p l e x i t y of t h e p h o s p h o r u s c y c l e on a c o r a l r e e f .
SUMMARY
To summarize b r i e f l y , we hope t h a t we h a v e a c c o m p l i s h e d s e v e r a l o b j e c t i v e s w i t h t h e s e b u d g e t a r y a n a l y s e s . We h a v e d e r i v e d a CaC03 p r o d u c t i o n , t r a n s p o r t a t i o n , and d e p o s i t i o n model which a p p e a r s c o n s i s - t e n t w i t h a v a i l a b l e d a t a and w i t h t h e c h a r a c t e r i s t i c s o f c o r a l a t o l l s . A s i m i l a r b u d g e t f o r o r g a n i c c a r b o n s u g g e s t s t h a t w h i l e a t o l l s show a v e r y low n e t p r o d u c t i o n r a t e , t h e y e x p o r t most o f t h e o r g a n i c material t h e y do p r o d u c e . N u t r i e n t b u d g e t s h a v e p r o v e n u s e f u l i n s u g g e s t i n g t h e e x i s t e n c e o f v a r i o u s s t r a t e g i e s o f n u t r i e n t f l u x and c y c l i n g i n t h e a t o l l e c o s y s t e m .
Such b u d g e t a r y a n a l y s e s are by no means e n d s i n t h e m s e l v e s , b u t t h e y do p r o v i d e a u s e f u l b a s e on which t o b u i l d f u r t h e r s t u d i e s of c o r a l r e e f p r o c e s s e s and w i t h which t o e v a l u a t e t h e q u a n t i t a t i v e s i g n i f i c a n c e o f t h o s e p r o c e s s e s .
REFERENCES
B r o e c k e r , W. S . , a n d T a k a h a s h i , T. 1 9 6 6 . Calcium c a r b o n a t e p r e c i p i t a t i o n on t h e Bahama Banks. J . Geophys. Res. 17:1575-1602.
J o h a n n e s , R . E . , a n d G e r b e r , R . 1974. Import a n d e x p o r t o f n e t p l a n k t o n by a n Eniwetok c o r a l r e e f community. p p . 97-104, i n : P r o c e e d i n g s o f t h e Second I n t e r n a t i o n a l C o r a l Reef Symposium, Vol. 2. G r e a t B a r r i e r Reef Committee, B r i s b a n e .
K i n s e y , D . W. 1972. P r e l i m i n a r y o b s e r v a t i o n s o n community m e t a b o l i s m and p r i m a r y p r o d u c t i v i t y o f t h e p s e u d o - a t o l l r e e f a t One T r e e , i n : P r o c e e d i n g s of t h e G r e a t B a r r i e r Reef Symposium o n C o r a l s a n d C o r a l R e e f s . Mandapam Camp, I n d i a . Mar. B i o l . Assoc. I n d i a : 13-32.
Land, L. S. 1 9 7 4 . Growth o f a West I n d i a n ( J a m a i c a n ) c o r a l r e e f . pp. 409-412, i n : P r o c e e d i n g s of t h e Second I n t e r n a t i o n a l C o r a l Reef 'Symposium, Vol. 2. Great B a r r i e r Reef Committee, B r i s b a n e . M a r s h a l l , N. 1965. D e t r i t u s o v e r t h e r e e f a n d i t s c o n t r i b u t i o n t o
a d j a c e n t waters o f Eniwetok A t o l l . E c o l . 46: 343-344.
P i l s o n , M. E. Q.,and B e t z e r , S . B. 1973. Phosphorus f l u x a c r o s s a c o r a l r e e f . E c o l . 54:581-588.
Pomeroy, L. R . , P i l s o n , M . E. Q.,and Wiebe, W. J . 1974. T r a c e r s t u d i e s o f t h e exchange o f phosphorus between r e e f w a t e r and o r g a n i s m s on
t h e windward r e e f o f Eniwetok A t o l l . pp. 87-96, i n : P r o c e e d i n g s o f t h e Second I n t e r n a t i o n a l C o r a l Reef Symposium, Vol. 1. G r e a t Barrier Reef Committee, B r i s b a n e .
S a r g e n t , M . C.,and A u s t i n , T. S. 1949. O r g a n i c p r o d u c t i v i t y of a n a t o l l . T r a n s . Am. Geophys. Union 30:245-249.
Smith, S . V . 1973. Carbon d i o x i d e dynamics: a r e c o r d of o r g a n i c c a r b o n p r o d u c t i o n , r e s p i r a t i o n , and c a l c i f i c a t i o n i n t h e Eniwetok windward r e e f f l a t community. Limnol. Oceanogr. 18:106-120.
S m i t h , S. V.,and J o k i e l , P. L. 1 9 7 5 . Water c o m p o s i t i o n and biogeo- c h e m i c a l g r a d i e n t s i n t h e Canton A t o l l l a g o o n : 2. Budgets of phosphorous [ s i c ] , n i t r o g e n , c a r b o n d i o x i d e , and p a r t i c u l a t e m a t e r i a l s . Mar. S c i . Comrn. 1: 165-207.
S m i t h , S . V.,and Marsh, J . A . J r . 1973. O r g a n i c c a r b o n p r o d u c t i o n on t h e windward r e e f f l a t o f Eniwetok A t o l l . Limnol. Oceanogr.
18:953-961.
Smith, S. V.,and P e s r e t , F . 1974. P r o c e s s e s of c a r b o n d i o x i d e f l u x i n t h e Fanning I s l a n d l a g o o n . P a c . S c i . 28:225-245.
Smith, S. V . , Roy, K . J . , S c h i e s s e r , H. G . , S h e p h e r d , G . L . , a n d
Chave, K. E. 1971. F l u x of s u s p e n d e d c a l c i u m c a r b o n a t e (CaC03), Fanning I s l a n d Lagoon. P a c . S c i . 25:206-221.
Webb, K . L . , DuPaul, W . , Wiebe, W . , S o t t i l e , a n d J o h a n n e s , R . E. 1975.
Enewetak (Eniwetok) A t o l l : A s p e c t s of t h e n i t r o g e n c y c l e on a c o r a l r e e f . Limnol. Oceanogr. 20:198-210.
Wiebe, W. J . , J o h a n n e s , R. E.,and Webb, K. L. 1975. N i t r o g e n f i x a t i o n i n a c o r a l r e e f community. S c i . 1 8 8 ~ 2 5 7 - 2 5 9 .
Wiens, H. J . 1962. A t o l l Environment and Ecology.Yale U n i v e r s i t y P r e s s , New Haven and London. 532 pp.
