The problem of introduced species in management and mitigation

Helgol~nder Meeresunters. 33, 662-673 (1980)

The problem of introduced species in management

and mitigation

J. W.

Hedgpeth

5660 M o n t e c i t o A v e n u e ; Santa Rosa, California 95404, USA

ABSTRACT: One hundred years ago the striped bass Morone saxatilis was introduced in the San Francisco Bay estuarine system from the east coast of the United States. It was part of our national policy at the time to transplant all potentially useful species everywhere else. The policy was facilitated by completion of the transcontinental railroad in 1869. As a result, the present ichthyo- fauna of the San Francisco Bay area is largely alien. Introduction of eastern oysters Crassostrea virginica resulted in the inadvertent introduction of many species of invertebrates. Identification of these introduced species was not realized as a problem until recently, and no one knows how many exotic species there are. In other parts of the world there are examples of similar introductions, e.g. Crepidula fornicata and Rhithropanopeus harrisi in Europe. Although it is now the policy to frown upon and prohibit introductions, they cannot be prevented and the process still continues, as

witnessed by the examples of Elminius modestus in Europe and Palaemon macrodactylus in

California. In the USA the recently developed idea of "mitigation," the artificial replacement of disturbed or destroyed areas by development of quasi-natural areas in compensation, has been accompanied, at the hands of inexperienced practitioners, by potentially dangerous introductions of exotic species. The assumption, for example, that cordgrass (Spartina) should be equally beneficial everywhere in the world has led to the disrupting introduction of potentially hybridizing species in New Zealand and aggressive immigrants in Oregon marshes. This situation calls for more sophisti- cated understanding of the role of introduced species in natural aquatic ecosystems, and a higher degree of competence in systematic biology.

I N T R O D U C T I O N O F E X O T I C SPECIES

A h u n d r e d y e a r s ago, in J u l y of 1879, 132 s t r i p e d b a s s Nlorone saxatilis from N e w J e r s e y w e r e p l a n t e d in S a n F r a n c i s c o Bay. This p l a n t i n g o c c u r r e d d u r i n g t h e h e i g h t of h y d r a u l i c m i n i n g in t h e Sierra N e v a d a w i t h its r e s u l t i n g h e a v y silt l o a d s in the rivers a n d t h e bay, a n d a b o u t 15 y e a r s after t h e g r e a t e s t floods on r e c o r d h a d i n u n d a t e d m u c h of C a l i f o r n i a ' s C e n t r a l V a l l e y a n d t u r n e d t h e b a y t e m p o r a r i l y into a f r e s h w a t e r l a k e ; it t o o k h o l d a l m o s t i m m e d i a t e l y . S h a d (Alosa sapidissima) h a d b e e n p l a n t e d a f e w y e a r s before, a n d m a n y o t h e r s p e c i e s of fish from t h e e a s t e r n s e a b o a r d a n d t h e s t r e a m s of t h e m i d d l e p a r t of N o r t h A m e r i c a w e r e p l a n t e d in S a n F r a n c i s c o Bay. As a result, t h e fish fauna, w h i c h f o r m e r l y c o n s i s t e d m o s t l y of s a l m o n i d s , v i v i p a r o u s p e r c h ( E m b i o t o c i d a e ) a n d v a r i o u s c y p r i n i d s a n d s u c k e r s ( C a t a s t o m i d a e ) w a s c o m p l e t e l y altered. V a r i o u s f r e s h w a - ter basses, sunfish a n d others ( C e n t r a r c h i d a e ) , catfish a n d all sorts of s m a l l e r fry (some of t h e s e for m o s q u i t o control) n o w flourish in t h e w a t e r s of S a n F r a n c i s c o Bay. T h e s t r i p e d bass b e c a m e c o m m e r c i a l l y important, b u t in 1935 it w a s r e s t r i c t e d for sport f i s h i n g only as it b e c a m e a p p a r e n t that t h e stock c o u l d n o t s u p p o r t b o t h c o m m e r c i a l a n d r e c r e a t i o n a l

P r o b l e m of i n t r o d u c e d species 663 fishing. Today, however, it is s u f f e r i n g a s i g n i f i c a n t d e c l i n e , p r i m a r i l y b e c a u s e of the a l t e r a t i o n s i n C a l i f o r n i a ' s w a t e r system w h i c h i n v o l v e m a s s i v e d i v e r s i o n s of w a t e r from the b a y to irrigate the arid l a n d s of the s o u t h e r n part of t h e C e n t r a l V a l l e y a n d m a i n t a i n the m o n s t r o u s sewers of Los A n g e l e s . In a d d i t i o n to the diversions, there are great losses of e g g s a n d y o u n g fish t h r o u g h the p u m p s that s u p p l y the e n o r m o u s a q u e d u c t s (Chad- w i c k et al., 1977). At the s a m e t i m e this i n t r o d u c e d stock i n C a l i f o r n i a is d e c l i n i n g , the p a r e n t stock o n the east coast, e s p e c i a l l y i n C h e s a p e a k e Bay, is d e c r e a s i n g rapidly. I n l a r g e part this m a y b e d u e to t h e u n r e s t r i c t e d resort fishing, w i t h o u t b a g limits. So far, factors w h i c h m a y b e c o m m o n to both p o p u l a t i o n s , such as p e s t i c i d e pollution, i n d u s t r i a l diversions, etc., h a v e n o t b e e n i n v e s t i g a t e d to a s c e r t a i n if there are some c a u s e s i n c o m m o n for d i m i n i s h i n g stocks o n b o t h sides of the c o n t i n e n t .

Most of the i n t r o d u c t i o n s of fish a h u n d r e d years ago w e r e results of the policy of the U n i t e d States Fish C o m m i s s i o n to p o p u l a t e the w a t e r s of the U n i t e d States w i t h as m a n y u s e f u l or v a l u a b l e food s p e c i e s as possible. T h e effort w a s m a d e to t r a n s p l a n t fishes from the Pacific coast to the e a s t e r n s e a b o a r d , e s p e c i a l l y t h e salmons, i n c l u d i n g v a r i o u s m e m b e r s of the g e n u s Oncorhynchus to streams of the east coast, a n d e v e n to the l o w l a n d streams of Texas. R a i n b o w trout (Salmo gairdneri) a n d c h i n o o k s a l m o n (Onco- rhynchus tschawytscha] w e r e successfully p l a n t e d i n N e w Z e a l a n d streams, b u t d i d n o t s u c c e e d i n Chile.

In a d d i t i o n to this effort to i n c r e a s e the s u p p l y of food fish, a t t e m p t s w e r e m a d e to e s t a b l i s h the e a s t e r n oyster Crassostrea virginica i n S a n Francisco Bay as soon as it w a s f e a s i b l e to t r a n s p o r t t h e m across t h e c o n t i n e n t after c o m p l e t i o n of the t r a n s c o n t i n e n t a l r a i l r o a d i n 1869. W i t h this effort t h e r e also b e g a n , a p p a r e n t l y , the s t e a d y i n f l u x of exotic i n v e r t e b r a t e s h i t c h h i k i n g , so to speak, a m o n g the oysters. M a n y of the species i n v o l v e d w e r e n o t r e c o g n i z e d at first as i n t r o d u c e d species, a n d some of t h e m m a y still n o t be. Lobsters w e r e i n t r o d u c e d i n the 1870's, b u t t h e y w e r e n e v e r h e a r d of a g a i n after b e i n g r e l e a s e d into the Pacific O c e a n at the G o l d e n Gate. T h e r e is still i n t e r e s t i n e s t a b l i s h i n g Homarus i n Pacific waters, b u t the c o n d i t i o n s do n o t s e e m right for it, a n d such a n i n t r o d u c t i o n is b e i n g d i s c o u r a g e d i n the w a r m e r s o u t h e r n w a t e r s b e c a u s e of p o s s i b l e c o m p e t i t i o n w i t h the n a t i v e species of Panulirus. C a r l t o n (1975), w h o h a s b e e n s t u d y i n g the records of i n t r o d u c e d species a l o n g t h e Pacific coast, e s t i m a t e s that t h e r e m a y b e as m a n y as 150 or 200 species of i n t r o d u c e d i n v e r t e b r a t e s . I n t r o d u c t i o n s c o n t i n u e d e s p i t e the fact that d e l i b e r a t e i n t r o d u c t i o n of exotic species is n o w d i s c o u r a g e d since some of t h e m m a y b e pests of c o m m e r c i a l l y v a l u a b l e species, such as oyster drills. T h e little e a s t e r n m u d crab Rhithropanopeus harrisi w a s first n o t i c e d i n S a n Francisco Bay i n the late 1930's (Jones, 1940) a n d a n o r i e n t a l s h r i m p Palaemon macrodactylus came to l i g h t s o m e t i m e after 1950 ( N e w m a n , 1963). A f r e s h w a t e r c l a m from the P h i l l i p i n e s w a s b r o u g h t in, p r o b a b l y as b a i t at some time or another, a n d is n o w a pest i n the a q u e d u c t s , w h e r e it a c c u m u l a t e s s e d i m e n t a n d r e d u c e s flow i n t h e canals. T h e latest a d d i t i o n to the f a u n a of S a n Francisco Bay a p p e a r s to b e a J a p a n e s e goby, Acanthogobius flavimanus.

a m p h i - a t l a n t i c s p e c i e s t h a t w a s d e s c r i b e d first from N o r t h A m e r i c a n s p e c i m e n s . H o w - ever, its r e c e n t e x p a n s i o n t•:the B l a c k S e a a n d the Baltic S e a {Pautsch & L a w i n s k i , 1966) w o u l d s u g g e s t t h a t it m a y b e a n i m m i g r a n t s p e c i e s f i n a l l y t a k i n g hold. It h a s e v e n r e a c h e d t h e C a s p i a n Sea. R. harrlsl is, as far as w e c a n t e l l at this time, a n i n o f f e n s i v e i n t r o d u c t i o n , u n l i k e t h e C h i n e s e m i t t e n crab, Eriocheir sinensis, w h o s e h a b i t of b u r r o w - i n g i n d i k e s a n d c a n a l s h a s c a u s e d m a i n t e n a n c e p r o b l e m s . E. sinensis is b e l i e v e d to h a v e m a d e its w a y from C h i n a i n t h e w a t e r t a n k s of s h i p s ( H o e s t l a n d t , 1948); it is a s p e c i e s t h a t l i v e s i n fresh w a t e r b u t r e p r o d u c e s in t h e sea. It w a s first n o t i c e d a b o u t 1912 in t h e r e g i o n of t h e l o w e r E l b e a n d W e s e r {Germany} a n d h a s s p r e a d south into F r a n c e a n d n o r t h into t h e G u l f of F i n l a n d .

O n e of the m o s t i m p o r t a n t i n t r o d u c t i o n s into E u r o p e a n w a t e r s is t h a t of t h e A m e r i - c a n A t l a n t i c b l u e crab, Callinectes sapidus. This is a m a j o r c o m m e r c i a l s p e c i e s of t h e A t l a n t i c c o a s t a l b a y s on t h e U n i t e d States. It w a s first n o t i c e d in E u r o p e a b o u t 1901 (Williams, 1974), b u t t h e r e is no r e c o r d or i n d i c a t i o n of t h e m e t h o d of h o w t h e species, a n d o t h e r d e c a p o d s w i t h s e v e r a l p l a n k t o n i c l a r v a l stages, m a d e t h e i r w a y across the ocean. Ca111nectes sapldus h a s b e e n r e p o r t e d at v a r i o u s l o c a l i t i e s from D e n m a r k to the B a y of Biscay, t h e M e d i t e r r a n e a n , A d r i a t i c a n d A e g a e a n S e a s (Holthuis, 1969). S o m e of t h e s e r e c o r d s a r e p r o b a b l y of i s o l a t e d o c c u r r e n c e r a t h e r t h a n e s t a b l i s h e d p o p u l a t i o n s , b u t t h e i m m i g r a n t p o p u l a t i o n s of t h e b l u e c r a b i n t h e e a s t e r n M e d i t e r r a n e a n , e s p e c i a l l y a l o n g the coast of Israel, h a v e b e c o m e of e c o n o m i c s i g n i f i c a n c e in t h e f i s h e r y (Holthuis & G o t t l i e b , 1955, 1958}. T h e r e is, i n c i d e n t a l l y , no r e c o r d as far as I k n o w of a n y a t t e m p t to i n t r o d u c e CalIinectes sapidus into S a n F r a n c i s c o Bay. If t h e a t t e m p t w a s m a d e , its f a i l u r e w o u l d i n d i c a t e t h a t w a t e r t e m p e r a t u r e s a r e too l o w for this s p e c i e s d u r i n g its r e p r o d u c - t i v e p e r i o d ; C. sapidusrequires t e m p e r a t u r e s of 20 ~ a n d a b o v e for r e p r o d u c t i o n {Norse, 1977).

W h i l e o n e m i g h t s p e c u l a t e t h a t t h e e m i g r a t i o n into E u r o p e from A m e r i c a b y

Callinectes sapidus m i g h t p o s s i b l y h a v e b e e n a c h i e v e d b y the s t r a y i n g of g r a v i d f e m a l e s from A m e r i c a (which d o e s not, h o w e v e r , e x p l a i n t h e c o l o n i z a t i o n of t h e M e d i t e r r a n e a n ) , t h e s p e c t a c u l a r a p p e a r a n c e of a N e w Z e a l a n d b a r n a c l e , Elminius modestus, i n E u r o p e i n 1943 m u s t h a v e b e e n m a n a g e d b y u n w i t t i n g h u m a n i n t e r v e n t i o n . V o y a g e t i m e s from N e w Z e a l a n d h a d not c h a n g e d s i g n i f i c a n t l y for a h u n d r e d y e a r s , a n d it a p p e a r s t h a t t h e s u d d e n a p p e a r a n c e of this b a r n a c l e o n British s h o r e s m a y h a v e b e e n r e l a t e d to t h e i n c r e a s e d v o l u m e of s h i p p i n g d u r i n g W o r l d W a r II, a n d c o n s e q u e n t l y i n c r e a s e d n u m b e r s of b a r n a c l e s , thus p r o v i d i n g a " c r i t i c a l m a s s " t h a t e n a b l e d e s t a b l i s h m e n t of t h e s p e c i e s so far from h o m e ( H e d g p e t h , 1957a). Six s p e c i e s of b a r n a c l e s not p r e v i o u s l y r e c o r d e d in N e w Z e a l a n d w e r e i d e n t i f i e d a m o n g the f o u l i n g o r g a n i s m s o n a n oil p l a t f o r m con- s t r n c t e d in O s a k a J a p a n a n d f l o a t e d to N e w Z e a l a n d (Foster & W i l l a n , 1979).

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Fig, 1. Southeast coast of England (Essex and Kent) s h o w i n g areas w h e r e oysters Crassostrea

virginica from the USA have b e e n reset and the localities and dates of initial appearance of other

s i g n i f i c a n t n u m b e r s , a n d s i n c e it h a s s i m i l a r f e e d i n g h a b i t s , m a y c o n s t i t u t e a c t i v e com- p e t i t i o n for food w i t h the oysters. T h e o y s t e r drill Urosalpinx cinerea l i k e t h e J a p a n e s e o y s t e r drill on t h e Pacific coast, p r e y s u p o n y o u n g o y s t e r s a n d m a y b e a s e r i o u s pest.

A n e x o t i c e e l grass, Zostera nolti, h a s e s t a b l i s h e d itself i n W i l l a p a Bay, W a s h i n g t o n . This s p e c i e s , w h i c h m a y h a v e c o m e from J a p a n as s e e d o n oysters, is f i n d i n g its p l a c e on t h e b a r e i n t e r t i d a l surface b e t w e e n the n a t i v e Z. marina a n d Salicornia. It m a y b e c o m e t r o u b l e s o m e in time, p r e - e m p t i n g s p a c e w h e r e t h e p r i n c i p a l a g e n t of p r i m a r y p r o d u c t i - v i t y h a s b e e n s e s s i l e d i a t o m s w i t h a rich s e c o n d a r y p r o d u c t i o n of v a r i o u s w o r m s , d e t r i t u s - f e e d i n g s n a i l s a n d s m a l l c r u s t a c e a n s .

It is to b e n o t e d t h a t our c o n c e r n in t h e s e v a r i o u s i n t r o d u c t i o n s h a s not b e e n for the n a t u r a l c o m m u n i t y into w h i c h w e h a v e i n t r o d u c e d them, b u t for t h e p r o d u c t i o n of the o y s t e r s t r a n s f e r r e d from p l a c e to p l a c e . T h e s i g n i f i c a n c e of i n t r o d u c t i o n of e x o t i c s p e c i e s is still not c o m p l e t e l y u n d e r s t o o d , b u t often the s i d e effects or c o i n c i d e n t i n t r o d u c t i o n s of o t h e r s p e c i e s of p o t e n t i a l h a r m to t h e e n v i r o n m e n t into w h i c h t h e y a r e i n t r o d u c e d h a v e b e e n i g n o r e d . H o w e v e r , t h e r e a c t i o n a n d c o n c e r n for i n t r o d u c t i o n of s e a w e e d s d i s c u s s e d b e l o w i n d i c a t e s t h a t w e a r e b e g i n n i n g to r e a l i z e t h a t i n t r o d u c t i o n s of e x o t i c s p e c i e s are not a n u n m i x e d b l e s s i n g .

S e a w e e d s a r e i m p o r t a n t s o u r c e s of i o d i n e a n d a l g i n a t e , a n i m p o r t a n t p l a n t a d d i t i v e a n d i n e r t c o m p o n e n t of drugs. T h e C h i n e s e h a v e d e p e n d e d on Laminaria for i o d i n e for 1500 y e a r s (Neushul, 1978), a l t h o u g h it d o e s not occur n a t u r a l l y on t h e C h i n e s e coasts. In the last 20 y e a r s or so t h e C h i n e s e h a v e u n d e r t a k e n c u l t u r e of Laminaria ( u s i n g s t e r i l e stock) i n t h e i r o w n w a t e r s w i t h s u c h s u c c e s s t h a t t h e y i e l d c o m p a r e s w i t h t h a t of t h e

Macrocystis h a r v e s t on t h e C a l i f o r n i a coast, a n d t h e y e x p o r t it to J a p a n (Cheng, 1969; T s e n g , 1975). A few y e a r s a g o t h e p o s s i b i l i t y of t r a n s p l a n t i n g t h e g i a n t k e l p Macrocystis pyrifera into E u r o p e a n w a t e r s on t h e Brittany coast w a s c o n s i d e r e d (Perez, 1972). A l t h o u g h Dr. W. North, w h o h a s h a d c o n s i d e r a b l e e x p e r i e n c e w i t h e x p e r i m e n t a l p l a n t - i n g of this s p e c i e s in its h o m e w a t e r s , w a s of t h e o p i n i o n t h a t it c o u l d not b e n a t u r a l i z e d in E u r o p e , o p p o s i t i o n to t h e i d e a w a s v e h e m e n t ; Russell (1978), for e x a m p l e , u r g e d t h a t i n t r o d u c t i o n of Macrocystis " s h o u l d b e r e s i s t e d . " E v i d e n t l y this o p p o s i t i o n w a s i n s p i r e d in p a r t b y t h e e x a m p l e of the J a p a n e s e Sargassum muticum, w h i c h h a s b e c o m e n a t u r a l i z e d in British C o l u m b i a a n d the C h a n n e l I s l a n d s off the C a l i f o r n i a m a i n l a n d , a n d h a s r e c e n t l y a p p e a r e d a r o u n d t h e Isle of W i g h t a n d is soon e x p e c t e d on t h e British m a i n l a n d .

D o m e s t i c a t i o n of s e a w e e d , e s p e c i a l l y t h e l a r g e k e l p s , in t h e s e n s e of c u l t i v a t i n g crops of k n o w n g e n e t i c c o m p o s i t i o n , a p p e a r s to b e on t h e w a y (Neushul, 1978; S a n b o n - s u g a & N e u s h u l , 1978). T h e s e w o r k e r s h a v e d e v e l o p e d s t e r i l e h y b r i d s of Macrocystis a n d

Pelagophycus; s u c h h y b r i d s if c o m m e r c i a l l y successful w o u l d - or s h o u l d - c a l m s o m e of t h e o p p o s i t i o n to d o m e s t i c a t i o n of s e a w e e d s in e x t r a t e r r i t o r i a l w a t e r s . As M. N e u s h u l r e m a r k s (in lit.) t h e u s e of s t e r i l e h y b r i d s " w o u l d b e a v e r y safe w a y to e n h a n c e m a c r o - a l g a l m a r i c u l t u r e . " H o w e v e r , a c c o r d i n g to Dr. W. N o r t h (in lit.) the F r e n c h h a d p l a n n e d to u s e s t e r i l e p l a n t s (not hybrids), b u t this d i d n o t r e a s s u r e critics of t h e s c h e m e .

U N P L A N N E D I M P A C T S

P r o b l e m of i n t r o d u c e d species 667 C a n a l . T h e first c a n a l b e t w e e n t h e M e d i t e r r a n e a n a n d Red Seas w a s c o n s t r u c t e d i n a n c i e n t t i m e s from the d e l t a of t h e Nile to the G u l f of Suez; after v a r i o u s p e r i o d s of d i s u s e it w a s f i n a l l y a b a n d o n e d i n the 8th c e n t u r y A.D. This c a n a l w a s m a i n t a i n e d b y fresh w a t e r from the Nile, a n d c o n s e q u e n t l y there m a y h a v e b e e n little i n t e r c h a n g e of m a r i n e f a u n a b e t w e e n the two seas. T h e m o d e r n canal, c o m p l e t e d i n 1869, is a h u n d r e d m i l e s long. U n t i l r e c e n t l y the h y p e r s a l i n e Bitter Lakes a n d the fresh w a t e r s of the Nile w e r e effective filters a g a i n s t f a u n a l i n t e r c h a n g e (Hedgpeth, 1957b); recently, however, the salt deposits of t h e Bitter Lakes h a v e b e e n r e d u c e d a n d the i n f l o w of fresh w a t e r into the d e l t a of t h e Nile h a s b e e n r e d u c e d b y c o n s t r u c t i o n of the A s w a n Dam, a n d m i g r a t i o n s from the Red S e a h a v e i n c r e a s e d (Thorson, 1971a, b).

A m o n g the m o r e s p e c t a c u l a r m i g r a t i o n s i n the last two d e c a d e s h a s b e e n that of the l i z a r d fish Saurida undosquamis w h i c h first a p p e a r e d i n the M e d i t e r r a n e a n i n 1952. T h e p o p u l a t i o n i n c r e a s e d r a p i d l y a n d b y 1955/56 it h a d b e c o m e o n e of t h e i m p o r t a n t c o m m e r c i a l fishes, a c c o u n t i n g for 1 1 % of t h e total fish l a n d i n g s . T h e fishery for lizard fish i n c r e a s e d u n t i l 1959, w h i l e at the s a m e t i m e that for h a k e Merluccius merluccius d e c l i n e d . B e n - Y a m i & G l a s e r (1974) h a v e a s s o c i a t e d this p o p u l a t i o n s u r g e w i t h a c o m p l e x i n t e r p l a y of p h y s i c a l a n d e c o l o g i c a l factors, t h o u g h t h e y do not c o n s i d e r the c h a n g e s i n flow a n d silt l o a d of the Nile since c o n s t r u c t i o n of the A s w a n Dam. U n d o u b t - e d l y a s i m i l a r i n t e r p l a y of factors a c c o m p a n i e d t h e i n t r o d u c t i o n of striped b a s s i n S a n Francisco Bay i n 1879, b u t w e l a c k the n e c e s s a r y information, e s p e c i a l l y o n i n t e r a c t i n g species.

T h e P a n a m a C a n a l is n o t a n o p e n c h a n n e l like the p r e s e n t Suez C a n a l , b u t a n e l a b o r a t e system of locks that are o p e r a t e d b y fresh w a t e r from G a t u n Lake (85 feet a b o v e sea level). This a r r a n g e m e n t p r e v e n t s the p a s s a g e of all b u t a few h a r d y species, m o s t l y a s s o c i a t e d w i t h f o u l i n g g r o w t h o n vessels. T h e c a n a l is n o w obsolete for the v o l u m e of traffic a n d t h e e n o r m o u s size of m o d e r n oil tankers, n o t only b e c a u s e of the w i d t h of the locks, b u t b e c a u s e the fresh w a t e r s u p p l y from G a t u n Lake is i n a d e q u a t e , b e c a u s e of the s m a l l c a t c h m e n t area, to operate the locks f r e q u e n t l y e n o u g h . For some years t h e r e h a s b e e n d i s c u s s i o n of a n e w c a n a l at sea level, p e r h a p s to the south of the p r e s e n t canal. T h e m e a n t i d a l r a n g e o n the A t l a n t i c side of the I s t h m u s is a b o u t a foot w h e r e a s o n the Pacific side it is 12.6 feet, a n d the m e a n sea l e v e l is 30 cm h i g h e r o n the Pacific side. T h e s e differences will r e q u i r e locks, since t h e y w o u l d set u p c u r r e n t s of at least 2 k n o t s i n a n o p e n c a n a l ; large ships c a n n o t b e m a n a g e d i n such c u r r e n t s i n a n a r r o w canal.

T h e prospect of a s e a - l e v e l c a n a l of some sort across the I s t h m u s of P a n a m a has s t i m u l a t e d d i s c u s s i o n a b o u t p o s s i b l e m i g r a t i o n of o r g a n i s m s from one o c e a n to the other. Briggs (1968, 1969) v i e w s this prospect w i t h c o n s i d e r a b l e alarm, p r e d i c t i n g a mass m i g r a t i o n of Pacific species, i n c l u d i n g Acanthaster planci a n d p o i s o n o u s sea s n a k e s (Pelamis platurus) into t h e A t l a n t i c w i t h r e s u l t a n t c o m p e t i t i o n w h i c h w o u l d " r e s u l t i n t h e i r r e v o c a b l e loss of n o t o n e or two b u t h u n d r e d s or e v e n t h o u s a n d s of species" (Briggs, 1974). T h e l o n g g e o l o g i c a l history of i n t e r c h a n g e b e t w e e n the o c e a n s d u r i n g p e r i o d s w h e n t h e c o n t i n e n t s w e r e n o t j o i n e d b y the isthmus, w i t h the r e s u l t i n g d e v e l o p m e n t of m a n y g e m i n a t e pairs of species, suggests that Briggs' p r e d i c t i o n s are o n the drastic side.

t h a t t h e p r o b l e m of o p e r a t i o n of t h e l o c k s m i g h t b e s o l v e d b y c o n v e r t i n g G a t u n L a k e to a saIt l a k e b y p u m p i n g s e a w a t e r b a c k to o p e r a t e t h e locks. T h i s w o u l d of c o u r s e e l i m i n a t e t h e f r e s h w a t e r b a r r i e r to m i g r a t i o n , w h i c h so far h a s p r e v e n t e d a l l b u t a f e w e u r y h a l i n e s p e c i e s from p a s s i n g from o n e o c e a n to t h e o t h e r ( M c C o s k e r a n d D a w s o n , 1975). U n d e r t h e p r e s e n t system, w i t h G a t u n L a k e c o n s i t u t i n g a f r e s h w a t e r b a r r i e r , s o m e h i g h l y e u r y h a l i n e f o u l i n g s p e c i e s h a v e p a s s e d t h r o u g h often ( M e n z i e s , 1968}. T h e p r o p o s a l to c o n v e r t t h e e n t i r e c a n a l s y s t e m to s e a w a t e r w i t h o u t a n y c o n s i d e r a t i o n of p o s s i b l e a d m i x t u r e s of Pacific a n d A t l a n t i c b i o t a , is, as N e w m a n (1972) states: " t h e i d e a ot c o n n e c t i n g t h e t r o p i c a l A m e r i c a n m a r i n e b i o t a s b y a s e a w a y w i t h o u t a n effective a n t i b i o t i c b a r r i e r is p r e s e n t l y i n d e f e n s i b l e . " T h e c o n c e r n o v e r t h e p r o p o s a l to a l t e r t h e p r e s e n t r e g i m e of t h e P a n a m a C a n a l i n one w a y or a n o t h e r h a s g e n e r a t e d a m o d e s t v o l u m e of i n f o r m e d scientific o p i n i o n , m o s t of it u n f a v o r a b l e (Rubinoff, 1968, 1970; SheIIey, 1968; S p r i n g e r , I973). T h e most r e c e n t d e v e l o p m e n t in t h e l o w - l e v e I c a n a l s c h e m e (March, 1980) is d i s c u s s i o n s b e t w e e n J a p a n e s e f i n a n c i a l a n d d e v e l o p m e n t i n t e r e s t s a n d P a n a m a n i a n officials a b o u t c o n s t r u c t i n g s u c h a canal, w i t h o u t locks, w e s t of t h e e x i s t i n g canal. N o c o n s i d e r a t i o n of e n v i r o n m e n t a l i m p a c t is a p p a r e n t in t h e r e p o r t s of t h e s e d i s c u s s i o n s .

For s o m e s p e c i e s a c a n a l w i t h its s a l i n i t y d i f f e r e n c e s a n d f l u c t u a t i n g c u r r e n t p a t t e r n s acts as a " s e l e c t i v e b a r r i e r " as in t h e c a s e of t h e S u e z C a n a l for c a l a n o i d c o p e p o d s a n d l a r v a l d e c a p o d s (Kimor, 1971). T h e B o s p h o r u s acts i n a s i m i l a r m a n n e r as a n a t u r a l filter r e s t r i c t i n g the p e n e t r a t i o n of M e d i t e r r a n e a n forms to t h e B l a c k Sea, a l t h o u g h in this c a s e the d i f f e r e n c e s in s a l i n i t y a n d t h e a z o i c b e l o w a b o u t 200 m a r e s i g n i f i c a n t factors in the process. S o m e e l e m e n t s of t h e B l a c k S e a f a u n a a r e c o n s i d e r e d to b e r e l i c t s of a " p r e - B o s p h o r o u s " p e r i o d (Caspers, 1968).

T h e a c t i o n of d i s p e r s a l or m i g r a t i o n t h r o u g h a c a n a l or n a r r o w p a s s a g e i n v o l v e s , i n a d d i t i o n to t h e p r i m a r y b a r r i e r of t h e n a r r o w p a s s a g e , t h e n a t u r e of t h e s e d i m e n t s , h y d r o l o g i c a l g r a d i e n t s a n d b i o l o g i c a l factors.

M I T I G A T I O N

M i t i g a t i o n , t h e i d e a t h a t u n a v o i d a b l e or i r r e p a r a b l e d a m a g e to a n e n v i r o n m e n t m a y b e c o m p e n s a t e d for b y u n d e r t a k i n g s o m e e c o l o g i c a l a m e l i o r a t i o n s o m e w h e r e e l s e as r e p l a c e m e n t for t h e d a m a g e , is a r e c e n t c o n c e p t in e n v i r o n m e n t a l m a n a g e m e n t . It s e e m s to o w e its i n s p i r a t i o n , i n p a r t at least, to t h e p r a c t i c e of s t a b i l i z i n g s p o i l b a n k s a c c u m u l a t - i n g from h a r b o r a n d c h a n n e l d r e d g i n g s w i t h m a r s h p l a n t s a n d u l t i m a t e l y e s t a b l i s h i n g m a r s h e s on t h e s e sites. This p r o c e d u r e w a s d e v e l o p e d b y t h e U n i t e d S t a t e s A r m y C o r p s of E n g i n e e r s , c h a r g e d w i t h d e v e l o p i n g h a r b o r s a n d m a i n t a i n i n g c h a n n e l s a n d w a t e r - ways. This necessi'ty h a s b e e n m a d e into a v i r t u e a n d t h e e m p h a s i s n o w s e e m s to b e on " h a b i t a t d e v e l o p m e n t " r a t h e r t h a n s t a b i l i z a t i o n of f r e s h l y d r e d g e d m a t e r i a l . T h e p r o c e - d u r e is d e s c r i b e d in s o m e d e t a i l in t h e C o r p s of E n g i n e e r s T e c h n i c a l R e p o r t DS-78-16 (United States, 1978).

P r o b l e m of i n t r o d u c e d s p e c i e s 669

b e f o r e a n d n o w s u p p o r t i n g a g o o d s e c o n d growth, or s o m e p r o p e r t y i n a c c e s s i b l e to its e q u i p m e n t as " m i t i g a t i o n " for t h e d a m a g e to a n e n v i r o n m e n t of e c o l o g i c a l or e s t h e t i c s i g n i f i c a n c e . In p r a c t i c e this a p p r o a c h c a n l e a d to i n c o n g r u o u s c o m p r o m i s e s t h a t satisfy no one, a n e x e r c i s e not in a p p l i e d e c o l o g y b u t in m i s a p p l i e d e c o l o g y . A p a r t i c u l a r l y g r i e v o u s e x a m p l e of this sort of " m i t i g a t i o n " is t h e o p e n i n g u p of a n o l d c o w p a s t u r e to t h e t i d a l w a t e r s of H u m b o l d t Bay, C a l i f o r n i a , i n c o m p e n s a t i o n for t h e d e s t r u c t i o n of W o o d l e y Island, a n a t t r a c t i v e f e a t u r e of t h e d o w n t o w n w a t e r f r o n t a r e a of E u r e k a (the city on H u m b o l d t Bay) b e c a u s e of its g r o w t h of t r e e s a n d a g g r e g a t i o n s of birds, e s p e c i a l l y e g r e t s , for a m a r i n a for f i s h i n g boats, w i t h p a r k i n g lots, g a u d y hot d o g stands, w a r e h o u - ses a n d t h e l i k e . A l l of this to confront ~a city b e a u t i f i c a t i o n s c h e m e i n v o l v i n g r e d e s i g n of streets, a n d r e h a b i l i t a t i o n of V i c t o r i a n a r c h i t e c t u r e i n t e n d e d to i n s p i r e b o t h c i t i z e n s a n d tourists w i t h p l e a s i n g vistas. M a n h a s s i n c e t i m e i m m e m o r i a l i m p r o v e d u p o n n a t u r e to his o w n taste, a n d p e r h a p s h a s as o f t e n b e e n g u i l t y of such j a r r i n g i n c o n s i s t e n c i e s , b u t t h e c o n c e p t of m i t i g a t i o n g i v e s s a n c t i o n to s u c h m i s d e e d s in t h e n a m e of e n v i r o n m e n t a l q u a l i t y . It is a n o t i o n t h a t s h o u l d not b e k i n d l y r e c e i v e d , a n d is p a r t i c u l a r l y d a n g e r o u s b e c a u s e it m a y e n c o u r a g e i n t r o d u c t i o n s of a g g r e s s i v e p l a n t s .

W i t h r e s p e c t to m a n a g e m e n t of c o a s t a l r e g i o n s , t h e m o s t d a n g e r o u s p l a n t s i n v o l v e d i n s u c h m i t i g a t i o n s c h e m e s a r e t h e s p e c i e s of c o r d g r a s s Spartina. H e r e w e a r e d e a l i n g not o n l y w i t h d e l i b e r a t e or a c c i d e n t a l i n t r o d u c t i o n s , b u t w i t h w h a t a p p e a r s to b e a s p o n t a n e o u s h y b r i d . C o r d g r a s s is m o s t c h a r a c t e r i s t i c a l l y f o u n d on s a l t m a r s h l a n d s of the e a s t e r n U n i t e d S t a t e s a n d G u l f coasts. It d o e s not o c c u r n a t u r a l l y in N e w Z e a l a n d , w h e r e it h a s b e e n i n t r o d u c e d , or a l o n g t h e n o r t h w e s t coast of t h e U n i t e d S t a t e s a n d C a n a d a , a l t h o u g h it h a s b e e n r e c e n t l y i n t r o d u c e d in at l e a s t o n e p l a c e in O r e g o n . It is not a m a j o r m a r s h l a n d p l a n t in m o s t l o c a t i o n s of C a l i f o r n i a e x c e p t t h e b a y s s o u t h of Los A n g e l e s .

Spartina foliolosa, t h e s p e c i e s o c c u r r i n g in S a n F r a n c i s c o Bay a n d n o r t h w a r d s , m a y b e a s o u v e n i r of S p a n i s h c o l o n i a l times, w h e n t h e p r i n c i p a l f o r a g e p l a n t s of t h e C a l i f o r n i a l o w l a n d s a n d h i l l s i d e s , t h e w i l d oat Arena fatua, t h e b u r c l o v e r Medicago hispida and

t h e f i l a r e e l~rodium moschatum a n d E. circutatium a l o n g w i t h t h e y e l l o w m u s t a r d

Brassica campestris (and s e v e r a l o t h e r s p e c i e s of m u s t a r d ) w e r e i n t r o d u c e d from S p a i n .

Spartina foliolosa in S a n F r a n c i s c o Bay d o e s not s e e m to b e as a g g r e s s i v e a s p e c i e s as t h o s e of e a s t e r n m a r s h l a n d s ; c e r t a i n l y t h e e v i d e n c e s u g g e s t s it is m o r e s u b j e c t to control b y h y d r o g r a p h i c c o n d i t i o n s t h a n b y e c o l o g i c a l i n t e r a c t i o n w i t h o t h e r s p e c i e s . It also s e e m s to b e less p r o d u c t i v e t h a n Spartina s p e c i e s of t h e s o u t h e a s t A t l a n t i c m a r s h e s , p e r h a p s m o r e s i m i l a r in t h i s r e s p e c t to t h e Spartina of E n g l i s h m a r s h e s ( M a h a l l & Park, 1976). N e t p r o d u c t i o n of Spartina alterniflora m a y b e as m u c h as 17.8 tons p e r a c r e u n d e r c e r t a i n c o n d i t i o n s as c o m p a r e d w i t h 14.7 tons p e r a c r e for H a w a i i a n s u g a r c a n e a n d 5.7 for a n A m e r i c a n corn f i e l d (Odum, 1974). S u g g e s t i o n s t h a t this p r o d u c t i o n m a y in t u r n b e a s i g n i f i c a n t p a r t of t h e n u t r i e n t b u d g e t s of c o a s t a l w a t e r s (as d i s t i n g u i s h e d from t h a t r e c y c l e d in t h e m a r s h itself) a r e e v i d e n t l y s o m e w h a t o p t i m i s t i c (Haines, 1975).

s i g n i f i c a n t r e g i o n s for s e c o n d a r y p r o d u c t i v i t y as d e m o n s t r a t e d b y t h e w o r k of Wolff (1977) a n d N i c h o l s (1977) a n d it s e e m s o b v i o u s t h a t i n j u d i c i o u s p l a n t i n g of Spartina,

e s p e c i a l l y of i n t r o d u c e d species, s h o u l d b e a v o i d e d as a p o t e n t i a l d a n g e r to e c o s y s t e m s of t h e t i d a l flats.

T h e British s p e c i e s is Spartina maritima. A c c o r d i n g to t h e s u m m a r y b y H u b b a r d (1965), t h e A m e r i c a n S. alterniflora w a s first c o l l e c t e d in E n g l i s h m a r s h e s in 1829, b u t it w a s p r o b a b l y p r e s e n t s e v e r a l y e a r s b e f o r e t h a t time. As e a r l y as 1870 a h y b r i d b e t w e e n t h e s e s p e c i e s (not t h e n r e c o g n i z e d as such) w a s d i s c o v e r e d a n d n a m e d S. townsendi. T h e o c c u r r e n c e a n d s p r e a d of this h y b r i d h a s b e e n d o c u m e n t e d for Poole H a r b o u r w h e r e it w a s c o l l e c t e d i n 1899, b u t it w a s a p p a r e n t l y p r e s e n t at l e a s t as e a r l y as 1887. In a n y event, t h e p l a n t s p r e a d t h r o u g h o u t Poole H a r b o u r a n d its o b v i o u s s u c c e s s as a c o l o n i z e r of t i d a l flats a n d p r o t e c t i o n a g a i n s t e r o s i o n a n d a n a g e n t for l a n d r e c l a m a t i o n l e d to its i n t r o d u c t i o n in m a n y o t h e r p a r t s of t h e w o r l d ( G o o d m a n et al., 1959). D u r i n g t h e l a t e 1920's S. townsendi w a s i n t r o d u c e d i n G e r m a n y , D e n m a r k a n d r e m o t e r l o c a l i t i e s , i n c l u d i n g A u s t r a l i a a n d N e w Z e a l a n d , w h e r e it w a s w e l c o m e d at first as a u s e f u l p l a n t (Harbord, 1949). H o w e v e r , its r a p i d s p r e a d in the A v o n - H e a t h c o t e e s t u a r y n e a r Christ- c h u r c h h a s e n d a n g e r e d a r e a s u t i l i z e d b y b i r d s a n d t h r e a t e n s to r e d u c e t h e w a t e r surface a r e a of t h e b a y , a n d it h a s b e e n d e c l a r e d a " n o x i o u s w e e d " in N e w Z e a l a n d (G. A. Knox, in lit.).

In a n u m b e r of p l a c e s in E n g l a n d its a g g r e s s i v e g r o w t h h a s r e q u i r e d r e m e d i a l action. In o t h e r r e g i o n s , after a p p a r e n t success, it h a s s t a r t e d to " d i e b a c k " w h i c h s u g g e s t s t h a t d e l i b e r a t e r e c l a m a t i o n p r o j e c t s u t i l i z i n g this p l a n t m a y h a v e a d u b i o u s future ( G o o d m a n et al., 1959).

T h e h y b r i d Spartina is o b v i o u s l y not a n u n m i x e d b l e s s i n g , a n d m a y at b e s t b e a n u n r e l i a b l e p l a n t for r e c l a m a t i o n p u r p o s e s in t h e l o n g r u n w h e n it is not a d a n g e r o u s l y a g g r e s s i v e i m m i g r a n t . A n o t h e r e a s t e r n s p e c i e s , Spartina patens, w a s i n t r o d u c e d at t h e m o u t h of the S i u s l a w I s l a n d in O r e g o n , w h e r e it is a p p a r e n t l y r e p l a c i n g the n a t i v e Carex lyngbyia (Dr. P. P. Rudy, p e r s o n a l c o m m u n i c a t i o n ) . This is not a h y b r i d s p e c i e s , a n d m a y i n the l o n g r u n t u r n out to b e a m o r e s e r i o u s i n t r o d u c t i o n , for e v e n if it s h o u l d d i e b a c k , d i s r u p t i o n of t h e n a t i v e flora a n d its a s s o c i a t e d f a u n a l c o m p l e x h a v e a l r e a d y o c c u r r e d . In S a n F r a n c i s c o B a y one not too w e l l - i n f o r m e d c o n s u l t a n t p l a n t e d b o t h Spartina maritima

a n d S. alterniflora as p a r t of a m u d flat s t a b i l i z a t i o n project, thus e s t a b l i s h i n g t h e p o t e n t i a l for fresh h y b r i d i z a t i o n to p r o d u c e S. townsendi (Dr. H. T. H a r v e y , in lit.). It is m y u n d e r s t a n d i n g t h a t s o m e effort h a s b e e n m a d e to u p r o o t t h e o f f e n d i n g i n t r o d u c t i o n s ; it is e a r n e s t l y to b e h o p e d t h a t S a n F r a n c i s c o Bay, w i t h all its p r e s e n t t r o u b l e s , w i l l not h a v e to e n d u r e a r e p e t i t i o n of the E n g l i s h a n d N e w Z e a l a n d e x p e r i e n c e s .

C O N C L U D I N G REMARKS

P r o b l e m of i n t r o d u c e d species 671 p l a n n e d . All a t t e m p t s to e s t a b l i s h A t l a n t i c lobsters i n t h e n o r t h e a s t e r n Pacific h a v e failed. T h e s p e c t a c u l a r success w i t h shad, s t r i p e d bass a n d m a n y other fishes into S a n Francisco Bay a n d its fresh w a t e r t r i b u t a r i e s m a y b e more a n i n d i c a t i o n of a d i s t u r b e d e s t u a r i n e e n v i r o n m e n t w i t h a v a i l a b l e n i c h e s for c o l o n i z a t i o n t h a n of i n t r o d u c t i o n into a n i n t e g r a t e d e c o s y s t e m i n a s t e a d y state condition. T h e s p o n t a n e o u s a c c l i m a t i o n of the b l u e crab Callinectes sapidus is a h a p p y e x a m p l e of a v a l u a b l e s p e c i e s that s u c c e e d e d w i t h o u t a p p a r e n t h u m a n i n t e r v e n t i o n . H e r e a g a i n , however, it m a y r e p r e s e n t coloniza- tion of a n u n o c c u p i e d n i c h e .

In most of t h e s e e x a m p l e s of i n t e n t i o n a l or a c c i d e n t a l i n t r o d u c t i o n s w e h a v e n o clear e v i d e n c e of t h e effects of the i n t r o d u c t i o n o n other species, for the most part b e c a u s e w e h a v e n o a d e q u a t e b a s e l i n e s of p r e - i n t r o d u c t i o n c o n d i t i o n s for e v a l u a t i n g the i m p a c t of the i n t r o d u c t i o n s . This is p a r t i c u l a r l y true for the case of S a n Francisco Bay. T h e effects of t h e i n t r o d u c t i o n of p l a n t s like Spartina a n d Zostera o n s e d i m e n t a t i o n a n d c o n s e q u e n t a l t e r a t i o n of h y d r o g r a p h i c r e g i m e s a r e a l m o s t i m m e d i a t e l y a p p a r e n t , b u t some i n t r o d u c - e d i n v e r t e b r a t e s m a y s u r v i v e for m a n y y e a r s after their i n t r o d u c t i o n before p r o d u c i n g o b v i o u s p o p u l a t i o n s . Eriocheir sinensis a n d Rhithropanopeus harrisi a p p e a r to b e e x a m p l e s of this i n E u r o p e a n waters.

I n Europe, w h e r e the flora a n d f a u n a are fairly w e l l k n o w n , the p r e s e n c e of i n t r o d u c e d s p e c i e s m a y b e n o t i c e d almost i m m e d i a t e l y , or at least p e r h a p s w i t h i n a d e c a d e of i n t r o d u c t i o n . In r e g i o n s w h e r e the b i o t a is not a d e q u a t e l y k n o w n , i n t r o d u c - tions m a y b e u n n o t i c e d for m a n y years. Of course it m a y b e said, i n v i e w of the n u m b e r of cosmopolitan, p a n t r o p i c a l , c i r c u m b o r e a l , etc., species a n d the catastrophes of s e a - l e v e l c h a n g e s , v o l c a n i c upsets, shifting rivers a n d the like, that m a n ' s activities are i n s i g n i f i - cant c o n t r i b u t i o n s to l o n g - t e r m n a t u r a l processes i n f l u e n c i n g distribution. P e r h a p s so, b u t at the s a m e t i m e p r e m a t u r e i n t r o d u c t i o n s w i t h o u t the a c c o m p a n i m e n t of such p h y s i c a l c h a n g e s m a y a c c e l e r a t e c h a n g e s i n ecosystems that will u l t i m a t e l y affect m a n ' s d e p e n d e n c e o n the p r o d u c t i v i t y of coastal waters. P r o v o k i n g M o t h e r N a t u r e is a risky b u s i n e s s .

D e t e c t i o n of n e w a d d i t i o n s to m a r i n e a n d e s t u a r i n e b i o t a a n d of the c h a n g e s t h e y m a y p r e c i p i t a t e i n the e n d e m i c b i o t a calls for a h i g h l e v e l of s u r v e i l l a n c e a n d c o m p e - t e n c e i n s y s t e m a t i c b i o l o g y a n d a n a d e q u a t e staff i n m u s e u m s a n d c o n s e r v a t i o n a g e n c i e s to r e v i e w collections a n d detect a l i e n species. A d e q u a t e a n d accurate species lists m a y w e l l b e the most i m p o r t a n t d a t a b a s e s for i m p l e m e n t a t i o n of all our e n v i r o n m e n t a l concerns, as S l o b o d k i n et al. (1980) suggest, for w i t h o u t a clear k n o w l e d g e of w h a t w e are d e a l i n g with, m o d e l s a n d e l a b o r a t e food w e b d i a g r a m s h a v e little m e a n i n g . A vigorous, a g g r e s s i v e m i g r a n t into the system m a y i n v a l i d a t e our concepts of t h e status q u o a n d r e q u i r e r e c o n s i d e r a t i o n s of m a n a g e m e n t a n d p r o t e c t i v e p r o c e d u r e s .

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