Ebling Et Al. 1985 Storms and Kelp Community Structure

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Mar ine Biology 84 , 287-294 (1985) Mar ine. . . . . . . . . . . . Biology

9 Spr inger-Ver lag 1985

S e v e r e s t o r m d i s t u r b a n c e s a n d r e v e r sa l o f c o m m u n i t y st r u c t u r e

i n a s o u t h e r n C a l i fo r n i a k e l p f o r e s t

A . W . E b e l i n g , D . R . L a u r a n d R . J . R o w l e y

D e p a r t m e n t o f B i o l o g i c a l S c i e n c e s a n d M a r i n e S c i e n c e I n s t i tu t e , U n i v e r s it y o f C a l if o rn ia a t S a n t a B a r ba r a;

Santa B ar bar a , Cal i for n i a 93106 , USA

A b s t r a c t

Regula r o bse rva t i ons mad e ove r a pe r iod o f 5 y r i n fou r

pe rmanen t t r ansec t s p rov ided da t a on p l an t , sea u rch in ,

and f i sh dens i ti e s wh ich i nd i ca t e t ha t two u nus ua l ly seve re

win t e r s t o rms in t 980 ( " S t o r m I " ) a n d 1 9 8 3 ( " S t o r m I t " )

had d i f f e ren t e f f ec t s on a sou the rn Ca l i fo rn i a ke lp - fo re s t

com mun i ty . S to rm I r emove d a l l c anop ie s o f t he g i an t ke lp

Macrocyst is pyri fera , b u t s p a r e d m o s t u n d e r s t o r y k e l p s ,

m a i n l y Pterygophora cal i fornica . Hence , t he p rev ious ly

l a rge accumu la t i on o f de t ache d d r i f t ke lp , mos t ly

M . pyri fera , d i sappea red . Den ied t he i r p re fe r red d i e t o f

dr i f t ke lp , the sea urchins S t rongy loc e n t ro tu s f ranc i sc anus

a n d S . p u r p u r a t u s t hen emerged f rom she l t e r s t o f i nda l t e rna ti ve food . W i thou t e f fect i ve p reda to r s , t h ey con-

sumed mos t l i v ing p l an t s , i nc lud ing t he su rv iv ing unde r -

s to ry ke lps . Th i s weaken ed the im por t an t de t r i t u s -based

food cha in , a s ind i ca t ed i nd i rec t l y by dec l i n ing abunda nces

of a lga l t u r f and f i sh (Emb io toc idae ) t ha t e a t sm a l l

an ima l s l i v ing i n t u r f. In 1983 , S to rm I I r eve r sed t he

process by e l im ina t i ng exposed u rch ins , wh i l e c l ea r ing

rock su r faces fo r widespread ke lp se t t l emen t and g rowth .

B y s u m m e r 1 9 8 4 , t h e k e l p g r e w t o m a t u r i t y to f o r m

ex tens ive canop ie s de sp i t e e l eva t ed wa te r t empera tu re s

dur ing summer and fa l l o f 1983 . Thus , seve re s t o rms may

have vas t l y d i f f e ren t e f f ec t s on communi ty s t ruc tu re ,

d e p e n d i n g o n t h e s t a te o f t h e c o m m u n i t y b ef o r e t h e

d i s tu rbance .

I n t r o d u c t i o n

The f r equency , mag n i tude , a nd sca le o f ma jo r s t o rm

d i s tu r b a n c e s m a y d e t e r m i n e t h e s t r u c t u r e o f m a n y k i n d s

of na tu ra l comm uni t i e s , i nc lud ing t hose o f mar ine r ee fs

(Goreau , 1959 ; Conn e l i , I978 ; Pa ine , I979) . For exampIe ,

W o o d l e y e taL (1981) de sc r ibed hur r i cane - induced pe r -

t u r b at io n s o f a J a m a i c a n c o r a l - re e f c o m m u n i t y : l a r g e

amo unt s o f p r im ary subs t r a t e we re c lea red and se t t l ed bynew growths o f sessi le o rgan i sms , and change i n co mm uni ty

s t ruc tu re va r i ed w i th degree o f exposure t o t he fu l l fo rce o f

the w aves . Such changes wi l l pe r s i s t on ly i f the d i s tu rbance

ra t e exceeds r ecove ry t ime . H ence , geo graph ic d i f f e rences

in s t o rm f requency may accoun t fo r obse rved d i f f e rences

in t he com mu ni ty s truc tu re (Goreau , 1959) . How eve r , in

p l aces whe re seve re s t o rms a re r a re , such a s Jama ica

(Woodley e ta l . , 1 9 8 1 ) a n d s o u t h e r n C a l i fo r n i a ( D a y t o n

a n d T e g n e r, 1 9 8 4 ) , t h e c o m m u n i t y m a y e i t h er u n d e r g o

cycl es o f a l t e ra t i on and recove ry (Conn e l l and Sousa ,

1983) or persis t in the a l te red sta te i f recov ery t ime is long

(Suther land, 1981) .

Recove ry t ime o f sub t ida l ke lp fo re st s i n t em pera t ewa te r s ma y be d e l ayed by g raz ing sea u rch ins i f the

urch ins have ne i t he r adequa t e de t r i t a l food nor e f fec t i ve

preda to r con t ro l . In a ma tu re fo res t , mos t o f the ann ua l

p roduc t ion o f ke lps fo rms a l i t te r o f de t ached d r i f t (Ge ra rd ,

1976). Urch ins read i ly ea t such d r i f t (Vadas, 1977 ) an d

usua l ly spa re l i v ing p l an t s w he reve r su f f i ci en t supp l i e s a re

ava i l ab le ( e .g . Low ry and Pea r se , 1 973 ; Rosen tha l e ta l . ,

1974). I f the forest is dest roy ed by severe storms or o ther

agenc ie s , the u rch ins ma y have n o d r i f t t o ea t ( see Ha r ro ld

and Reed , 1984). I f uncon t ro l l ed by p reda to r s , d i sea se , o r

wa te r mot ion , t he u rch ins wi l l t hen m ove ou t ove r t he r ee f

t o g ra z e b a ck n e w g r o w t h a n d f o r m a " b a r r e n s " c o v e r ed

wi th l i tt le more t han c rus tose a lgae and pa t ches o f l ow tu r f

(Lawrence , 1975) . Urch ins a re ab l e t o r ema in i n a b a r rens

because t hey can subs i s t on l i t t le food (Ebe r t , 1967 ; Lang

and Mann , 1976). Th i s p reven t s r ecove ry o f t he imp or t an t

de t r i tu s -based food cha in ( see M ann , 1982), wh ich gene r -

a t e s much o f the sm a l l inve r t eb ra t e p rey t ha t f i sh ea t

(Mann , 1977 ; S imens t ad e ta l . , 1 9 7 8 ; L a u r a n d E b e l in g ,

1983) . Freq uenc y-dep ende n t fo rag ing by sea o t t e rs

(Enhydra lu tris) e f fec ti ve ly con t ro ls num bers o f exposed ,

g raz ing u rch ins i n den se ke lp fo re st s o f f t he Aleu t i an

Islands (e.g. Estes eta[., 1978) , Ala ska (Dugg ins , 1980),

and cen t ra l Ca l i fo rn i a (Lowry and Pea r se , 1973 ; Reed and

Fos t e r, 1984) . Ye t ke lp g rows abu nda n t ly o f f sou the rn



288

C a l i f o r n i a w h e r e o t t e r s a r e a b s e n t a n d W h e r e e x p o s e d

u r c h i n s o c c u r a b u n d a n t l y i n b a r r e n s p a t c h e s ( e .g . L e i g h t o n

e t a l . , 1966; Pearse e t a l . , 1970; North , 1971; Tegner , 1980).

Unde r s uch c i rcums tances , ke lp fo re s t s may be l e s s re s i l i en t

a n d o c c u r m o r e s p o r a d i c a l l y ( N o r t h , 1 9 71 ),

T h u s , m a t u r e k e l p f o r e s t s a n d t h e i r p r o d u c t i v e d e t r i t a l

f o o d c h a i n s m a y p e r s i s t o f f s o u t h e r n C a l i f o r n i a o n l y

b e c a u s e s t o r m s p o w e r f u l e n o u g h t o d e s t r o y t h e m a n d

e l i m i n a t e d r i ft k e l p a r e r a r e h e r e ( s e e D a y t o n a n d T e g n e r ,

1984) . Once de s t royed , howeve r , fo re s t s w i thou t a re s ource

o f d r i f t m a y b e s l o w t o r e c o v e r u n l e s s s e a u r c h i n s a r e

con t ro l l ed (Nor th , 1971 ; Wi l s on e t a l . , 1980). Yet a s torm

s t r o n g e n o u g h t o r e m o v e k e l p m a y a l s o r e m o v e u r c h i n s o r

a l t e r t h e i r b e h a v i o r , e s p e c i a l l y e x p o s e d i n d i v i d u a l s i n

b a r r e n a r e a s ( C o w e n e t a l . , 1982 ; Ha r ro ld and R eed , 1984) .

T h u s , t h e p r o c e s s m a y b e r e v e r s i b l e .

I n o u r s t u d y , w e s h o w t h a t t w o u n u s u a l l y s e v e r e

s to rms , wh ich s u rp r i s ing ly s t ruck coas ta l s ou the rn Ca l i -

fo rn ia on ly th ree yea rs apa r t , s t a r t ed reve rs ib le p roces s e s .

T h e f ir s t s t o r m i n i t i a t e d a p r o c e s s l e a d i n g t o d e f o r e s t a t i o no f o u r s t u d y r e e f : d r i f t k e l p w a s e l i m i n a t e d , h u n g r y

u r c h i n s l e f t s h e l t e r , r e g r o w t h w a s g r a z e d b a c k , s e c o n d a r y

p r o d u c t i o n p r o b a b l y f e l l , a n d f i s h a b u n d a n c e d e c l i n e d .

T h e s e c o n d s t o r m , o f s i m i l a r f o r c e , i n i t i a t e d t h e p r o c e s s o f

r e f o r e s t a t i o n : e x p o s e d u r c h i n s w e r e d e c i m a t e d , k e l p

r e g r e w , d r i f t a g a i n a c c u m u l a t e d o n t h e b o t t o m , a n d t h e

d e t r it u s f o o d c h a i n w a s r e s t o r e d . W e a t t r i b u t e m u c h o f th i s

r e v e r s a l i n c o m m u n i t y f o r m t o m a r k e d c h a n g e s i n t h e

b e h a v i o r , d i s tr i b u t io n , a n d a b u n d a n c e o f g r a z i n g se a

u rch ins .

W e d o c u m e n t e d t h i s b y m o n i t o r i n g f o u r i m p o r t a n t

c o m p o n e n t s o f th e d e t r it a l f o o d c h a i n a c c o u n t i n g f o r m u c h

o f t h e o b v i o u s c o m m u n i t y s t r u c t u r e a t o u r s t u d y s i te : ( 1 )

k e l p s , b o t h g i a n t k e l p M a c r o c y s t i s p y r i fe r a w h i c h f o r m s a

s u r f a c e c a n o p y , a n d t h e u n d e r s t o r y k e l p s P t e r y g o p h o r a

c a l i f o r n i c a a n d L a r n i n a r i a f a r f o w i i which r i s e l e s s than 1 m

o f f t h e b o t t o m ; ( 2 ) a lg a l t u r f w h i c h h o u s e s m a n y o f t h e

s e c o n d a r y p r o d u c e r s s u c h a s s m a l l c r u s t a c e a n s , m o l l u s k s ,

and worms ; (3 ) g raz ing s ea u rch ins S t r o n g y l o c e n t r o t u s

f r a n c i s c a n u s a n d S . y u r p u r a t u s ; a n d ( 4 ) e p i b e n t h i c f i s h e s i n

t h e s u r f p e r c h f a m i l y E m b i o t o c i d a e w h i c h a r e t h e p r i n c i p a l

e x p l o it e r s o f s m a l l i n v e r t e b r a t e p r e y l i vi n g i n t h e t u r f

( L a u r a n d E b e l i n g , 1 98 3) . R e su l t s o f th i s m o n i t o r i n g a n d

o t h e r w o r k p r o v i d e a u n i q u e v i e w o f a r e e f c o m m u n i t y a s

f o r es t , as b a r r e n s, a n d i n t r a n s i ti o n b e t w e e n t h e t w o c o n d i -t ions .

M a t e r i a ls a n d m e t h o d s

W e m o n i t o r e d d e n s i t ie s o f t h e se f o u r g r o u p s o f o r g a n i s m s

a t N a p l e s R e e f , a n i s o l a t ed o u t c r o p o f s h a le l o c a t e d 1 .6 k m

o f f s h o r e a b o u t 2 3 k m w e s t o f S a n t a B a r b a r a , s o u t h e r n

C a l i f o r n ia ( 3 4 ~ 1 1 9 ~ T h e r e e f c o v e r s 2 .2 h a ,

ranges in dep th f rom 5 to 15 m, a nd cons i s ts o f a s e ri e s _~

r i l l s and r idges runn ing pa ra l l e l t o the coas t (E be l ing e t a l . ,

1 98 0) . R e g u l a r o b s e r v a t i o n s w e r e m a d e d u r i n g a 5 y r s p a n

i n f o u r p e r m a n e n t t r a n s e c t s i te s m a r k e d N E , S E , M , a n d

A. W. Ebeling et al .: Storm disturbances o f a kelp forest

N M i n F i g . 1 D . T h i s i n c l u d e d i n t e r v a l s b e f o r e a n d a f t e r

t h e l a r g e s to r m s o f 1 9 8 0 ( " S t o r m I " ) a n d 1 9 8 3 ( " S t o r m I I " ) .

T wo t rans ec t s i t e s (NE , SE ) we re in an ex tens ive s t and o f

u n d e r s t o r y k e l p o v e r t h e r e e f b a s e. S u b s t r a t e a t t h e N E

s i t e was o r ig ina l ly a mos a ic o f s and , cobb le , and p a r t ly

e n c r u s t e d r o ck , b u t w a s s c o u r e d b y S t o r m I . T h r o u g h o u t

m o s t o f t h e s t u d y t h e m o r e p r o t e c t e d S E s i te r e m a i n e d

c o v e r e d w i t h s a n d m e r g i n g w i t h c o b b l e . T h e t w o o t h e r

t r a n s e c t s it e s (M , N M ) w e r e n e a r t h e r e e f t o p a t 7 t o 8 m

dep th , among c re s t s and r i l l s w i th h igh u rch in -dens i t i e s ,

r i ch a lga l tu r f , and in t ens e fo rag ing b y s u r fpe rch . S i t e M

was in a r i l l ; S i t e NM was loca ted a long the no r th s lope o f

t h e r e e f . P e r m a n e n t 6 0 m t r a n s ec t s o f p o l y p r o p y l e n e r o p e

h a d b e e n a n c h o r e d a n d m a i n t a i n e d a t S i te s N E a n d N M

f o r fi sh c e n s u si n g a n d o t h e r s t u d i e s ( s ee E b e l i n g a n d L a u r ,

1984). A s imi la r t r an s ec t was cons t r uc ted a t S i t e SE fo r

m o n i t o r i n g a p e r s i s t en t s t a n d o f u n d e r s t o r y k e I p. A t

M id ree f S i te M , s t ee l p ins m arke d ends o f a 13 m t rans ec t

f o r m e a s u r i n g m a c r o i n v e r t e b r a t e d e n s i ti e s a l o n g t h e g e n t l y

s lop ing s ide o f a r i l l.S i n c e t h e s t u d y w a s o p p o r t u n i s t i c , w e c o u l d n o t p r e -

d e s i g n a l l s a m p l i n g , a n d h a d t o e x t e n d n e w o b s e r v a t i o n s

f r o m p r e v i o u s o n e s m a d e f o r o t h e r s t u d i e s . H e n c e , n o t a l l

m o n i t o r i n g w a s q u a n t i t a t i v e a n d n o t a l l m e a s u r e m e n t s

were m ade a t e ach t rans ec t s it e. T he s t a t e o f the ke lp fo re s t

b e f o r e a n d a f t e r S t o r m s I a n d I I w a s m a p p e d f r o m f i e l d

n o t e s a n d m e a s u r e m e n t s m a d e d u r i n g r e e f w i d e s u r v e y s

th ro ugh ou t the 5 y r in t e rv a l (F ig . 1 ). W e fee l t ha t t h i s is

a d e q u a t e b e c a u s e m a n y c h a n g e s w e r e w i d e s p r e a d a n d

d r a m a t i c : f o r e x a m p l e , f r o m a t h i c k , c o n t i n u o u s k e l p f o r e s t

t o a n e x p o s e d " b a r r e n s " . A t l e a s t o n c e a s e a s o n , w e

s u r v e y e d t h e r e e f a n d r e d e f i n e d l i m i t s o f k e l p s t a n d s a n d

s u b s t r a t e t y p e . W e c o u n t e d k e l p - s p o r o p h y t e r e c r u i t s i n0 .25 m 2 quad ra t s nea r o u r t r an s ec t s i t e s du r ing t imes o f

m a x i m u m s e t t l e m e n t . W a t e r t e m p e r a t u r e w a s m e a s u r e d

s e m i -w e e k l y a t th e s u r fa c e a n d t 3 m d e p t h d u r i n g

1 9 7 9 - 1 9 8 1 , b u t n o t d u r i n g 1 9 8 2 , a n d i r r e g u l a r l y d u r i n g

1983.

R eg u La r o b s e r v a t i o n s o f p l a n t c o v e r a n d o f s ea u r c h i n

a n d f i s h d e n s i t i e s w e r e a v e r a g e d p e r b i m o n t h l y i n t e r v a l .

P e r c e n t u n d e r s t o r y k e l p c o v e r w a s e s ti m a t e d o n c e e v e r y

t w o m o n t h s i n t h i r t y 0 .7 5 m 2 q u a d r a t s p l a c e d r a n d o m l y

a l o n g t h e N E t r a n s e c t b o t h b e f o r e a n d a f t e r S t o r m I, a n d

a long the SE t rans ec t s a f t e r S to rm I on ly . S imi la r ly , we

e s t i m a t e d a l g a l t u r f c o v e r i n 1 5 q u a d r a t s a l o n g t h e N Mtrans ec t be fo re a nd a f t e r S to rm I . Sea u rch in dens i t i e s

w e r e m e a s u r e d 1 t o 7 ti m e s w i t h i n b i m o n t h l y i n t e r v a l s

b e f o r e a n d a f t e r S t o r m I a t T r a n s e c t S i te M a n d o c c a s i o n a l l y

a f t e r S t o r m I a t S i t e N E . S i n c e a b u n d a n c e s o f t h e t w o

urch in s pec ie s we re s t rong ly co r re l a t ed ( r = 0 .85 , n = 69 ,

P < 0 . 0 0 1 ) , w e p o o l e d d e n s i ti e s f o r c o u n t s o f t o ta l a d u l t s

i n a 1 3 X 1 m b a n d d e l i m i t e d b y a m e t e r b a r p u s h e d a l o n g

t h e s i d e o f a n y l o n l i n e s t r e t c h e d b e t w e e n t w o p i n s .

S u r f p e r c h d e n s it i e s w e r e o f t o t a l a d u l t a n d s u b a d u l t

i n d i v i d u a ls o f th e 5 p r i n c i p a l s p e c i e s i n h a b i t i n g t h e r e e f

( s ee L aur and E be l ing , 1983 ; E be l ing and L aur , 1984) :

E r n b i o t o c a j a c k s o n i , E . l a te r a li s , H y y s u r u s c a r y i, R h a c o c h i l u s

t o x o t e s , a n d D a m a l i c h t h y s v a c c a . We coun ted f i s h 4 to 10



A. W. Ebeling et al.: Storm disturbances of a kelp forest 289

A / / / / / / / / / / / / / A / . 7 . ' / . ' / . ' / ' / ' J : / r D

S U M M E R , 1 9 79

P R E S T O R M |

} 3 0 M I l

S P R I N G , 1 9 8 1 ' B A R R E N S '

. : : ~ " : " ~ . . : : : : ~ : : : : ~ : : : : : : ~ : : : g : : : ; : : ~ : : : : : : : : : : :: : : :: : : :: 5 : : :

S E

S P R , N , 1 9 8 0 ]P O S T S T O R M I . . . . 9 S P R IN G , 1 9 8 3

9 " P O S T S T O R M I I

C

F A L L , 1 9 8 0 " 9 9 9 S U M M E R , 1 9 84

Fig. 1. Naples Reef, southern California, showing distributions of matu re giant kelp, Ma crocystis pyrifera (coarse hatching), matureunderstory kelp - mostly Pterygophora californica (large dots), newly recruited plants (fine hatching o r small dots), majo r sea-urchin fronts(asterisks), and continuous rocky substrate (stippled) befor e and a fter Storms I and II . (D) gives scale (30 m), de pth contours (7, 11, 15 m)and transect si tes (bars m arked NE , SE, M, NM)

t i m e s w i t h i n b i m o n t h l y i n t e r v a l s ( a b o u t w e e k l y ) a l o n g a

t r an sec t l i n e a t S i t e NM , t a l l y in g a l l i n d iv id u a l s seen

w i t h i n ~ s p a c e e s t i m a t e d t o b e 3 m w i d e o v e r t he b o t t o m

an d ex t en d in g 1 .5 m u p wa rd .

T h e l i tt e r o f d r if t a l g a e ( " d r i f t" ) w a s s a m p l e d a t N a p l e s

a n d c o m p a r a b l e r e e fs in s h o r e a b o u t 6 k m a w a y . U n l i k e

N a p l e s , t h e i n s h o r e r e e f s w e r e f o r e s t e d d u r i n g t h e e n t i r e

5 y r s t u d y p e r i o d . C o l l e c t e d u n d e r d e n s e s t a n d s o f g i a n t

k e l p , t h e i n s h o r e s a m p l e s i n c l u d e d d r i f t f r o m a c c u m u l a -

t i o n s l i k e t h o s e w e s a w ( b u t d i d n o t s a m p l e ) a t N a p l e s

b e f o r e S t o r m I . S a m p l e s w e r e t a k e n b y S C U B A d i v e r s

s tu f f i n g as mu ch a lg ae as t h ey co u ld i n to n e t b ag s d u r in g

5 m i n s w i m s o u t f r o m m i d r e e f in r a n d o m c o m p a s s d i re c -

t i o n s . B a g s w e r e w e i g h e d f u l l a n d e m p t y ( t o s u b t r a c t t h e

w e i g h t o f t h e b a g ) w h e n r e t u r n e d t o t h e d i v i n g s k if f.

Resu l t s

K e l p f o r e s t a n d r e e f

S to rms I an d I I i n i ti a t ed p e r i o d s o f k e lp l o s s an d r ese t t l e -

m e n t a t N a p l e s R e e f (F i g . 1 ). I n s u m m e r 1 9 7 9 b e f o r e

S t o r m I, a l a r g e s u r f a c e c a n o p y o f g ia n t k e l p , M acrocys t i s

pyrifera, co v er ed t h e r ee f (F ig . 1 A) . I t ex t e n d ed i n sh o re ,

s u p p o r t e d b y h o l d fa s t s a n c h o r e d t o s m a l l e r r e e f s o r e v e n



290 A.W. Ebeling et al .: Storm disturbances o f a kelp forest

s a n d b o t t o m ( s e e N o r t h , t 9 7 1 ). L a r g e f i e ld s o f u n d e r s t o r y

k e l p , m a i n l y P t e r y g o p h o r a c a I i f o r n i c a w i t h w i d e l y s c a t t e r e d

i n d i v i d u a l s o f L a r n i n a r i a f a r l o w i i, c o v e r e d m u c h o f th e

e a s t w a r d r e e f b a s e. S m a l l e r st a n d s e x t e n d e d s o u t h -

w e s t w a r d o r f o r m e d p a t c h e s o n t o p o f th e r e e f . T h e n , f o r

t w o w e e k s i n F e b r u a r y 1 98 0, S t o r m I g e n e r a t e d w a v e s t h a t

r e a c h e d t h e e x t r a o r d i n a r y h e i g h t o f 6 m i n t h e S a n t a

B a r b a r a C h a n n e l ( w a v e h e i g h t d a t a e s t i m a t e d f r o n t A R C O

O i l P l a t f o r m " H o l l y " a n d p r o v i d e d b y C . F u s a r o ) . T h i s

w a s m o r e t h a n t w i ce t h e m a x i m u m w a v e h e i g h t r e co r d e d

d u r i n g t h e p r e v i o u s 7 y r ( H a r g e r , 1 9 7 9 ) . T h e p o w e r f u l

s u r g e s w e p t a w a y s a n d , s c o u r e d o f f cr u s ts o f c o r a ll i n e

a l ga e , a n d b r o k e o f f sl a b s o f sh a l e t o c r e a t e l a r g e a r e a s o f

b a r e r o c k ( " n e w s u r f a c e s " ) . W a t e r m o t i o n r e m o v e d a l l

c a n o p i e s o f g i a n t k e l p f r o m N a p l e s R e e f a n d e n v i r o n s .

M o s t h o l d fa s t s fr o m w h i c h s t ip e s h a d b e e n t o r n e v e n t u a l l y

d i e d . T h e n e a r e s t s u r v i v i n g k e l p f o r e s t W a s m o r e t h a n 6 k m

away . Ye t the s tu rd ie r s t ipe s o f P . c a l i f o r n i c a e n d u r e d

a b o u t t h e r e e f b a s e t o g r o w n e w b l a d e s d u r i n g s p r i n g

1 9 8 0 . T h i s p r o d u c e d a n e w u n d e r s t o r y c a n o p y u n s h a d e db y s u r f a c e k e l p . K e l p s p o r o p h y t e s r e c r u i t e d m o s t l y t o n e w

s u r fa c e s i n d e n s i t ie s o f a b o u t 5 0 m - ~ ( n = 2 2 ) . H o w e v e r ,

adu l t s ea u rch ins s oo n l e f t r e fuges in c racks and c rev ice s to

g r a z e b a ck t h e n e w g r o w t h .

C o n t i n u e d g r a z i n g b y s e a u r c h i n s e l i m i n a t e d m o s t o f

t h e r e m a i n i n g s t a n d s o f m a c r o a l g a e . T h i s p r o c e ss w a s w e l l

u n d e r w a y b y f a ll 1 9 8 0 (F i g . 1 C ) . B y t h e n u r c h i n s h a d

s t ri p p ed t h e r e e f o f n e w k e l p s p o r o p h y t e s a n d m o s t

v e g e t a t iv e r e g r o w t h , p r i m a r i l y o f u n d e r s t o r y k e l p s a n c h o r e d

t o c o n t i n u o u s r o c k s u r f a c e s . T h e o n l y s u r v i v i n g f i e l d o f

u n d e r s t o r y k e l p w a s a t S i t e S E . H e r e , t h e s a n d y s u b s t r a t e

s e e m e d t o d e t e r a l o n g f r o n t o f l a r g e r e d s e a u r c h i n s

( S t r o n g y l o c e n t r o t u s f r a n c i s c a n u s ) a d v a n c i n g f r o m t h en o r t h . H o w e v e r , e v e n t h e S E k e l p s t a n d w a s e l i m i n a t e d i n

s p r i n g 1 9 8 1 ( F i g . 1 D ) . A g a t h e r i n g f r o n t o f r e d u r c h i n s

s u d d e n l y i n v a d e d t h e p r e v i o u s l y in v i o l a t e a r e a o f s a n d y

s u b s t ra t e t o d e s t r o y t h e w h o l e s t a n d ( a b o u t 1 h a ) w i t h i n a

m o n t h ( 2 4 M a r c h - 2 5 A p r il ). T h e c o m m u n i t y r e m a i n e d i n

th i s ba r ren co nd i t io n un t i l s p r ing 1983 .

F o l l o w i n g b e n i g n s e a so n s o f 1 9 8 1 a n d 1 98 2, t h e w i n t e r

s t o r m s e r i e s o f 1 9 8 3 ( S t om a I I ) w a s a l s o u n p r e c e d e n t e d i n

m a g n i t u d e ( s e e D a y t o n a n d T e g n e r , 1 9 8 4 ) . W a v e s a g a i n

r e a c h e d 6 m o r m o r e i n h e ig h t . T h e p o w e r f u l s u r g e c r e a t e d

ex tens ive new s u r face s on Nap le s Ree f , t he f i r s t s ince

1 9 8 0. ( M e a s u r e d d u r i n g a 5 0 m i n d i v e , 31 s c a rs f r o m

de ta che d s ha le s l abs ave rage d 1 .3 m_+ 1.0 (SD) in b re ad th ,

a b o u t t h e s a m e a s s c ar s p r o d u c e d b y S t o r m I . S a n d a n d

r o c k s c o u r e d e v e n l a r g e r a r e a s . ) P o p u l a t i o n s o f e x p o s e d

u r c h i n s o n t h e e l e v a t e d p a r t s o f t h e r e e f w e r e d e c i m a t e d .

O n l y t h o s e i n d i v i d u a l s s h e l t e r i n g i n d e e p e r w a t e r a b o u t

t h e r e e f b a s e w e r e s p a r e d i n s u b s t a n t ia l n u m b e r s . K e l p

s p o r o p h y t e s r e c r u i t e d t o m o s t r e e f a r e a s ( F i g . 1 E ) , b u t i n

d e n s it i es m o r e t h a n 1 0 t i m e s g r e a t e r o n n e w s u r f a ce s t h a n

o n o l d ( H a r r i s e t a l . , 1984) . Sporo phy te s ave raged 558 m -2

on new s u r face s a t T ran s ec t S i t e M (Har r i s e t a L , 1984) and

518- -+600 (SD) on s imi la r s u r face s a t S i t e NM (n=28 ,

0 .2 5 m 2 q u a d r a t s p l a c e d h a p h a z a r d l y o n n e w s u r fa c e s i n

J une 1983) . T hus , i n s p r ing 1983, mos t o f the ree f and

s u r r o u n d i n g b a s e s u p p o r te d a d e n s e c a n o p y o f n e w k e l p

s poro phy te s s o me 5 to 40 cm ta l l (F ig . 1 E ) . Ind iv id ua l s o f

P t e r y g o p h o r a c a l i f o r n i c a o u t n u m b e r e d t h o s e o f M a c r o c y s ti s

p y r i f e r a b y a b o u t 1 0 : 1 . E n o u g h p l a n t s s u r v i v e d t h e f o l -

l o w in g c a l m s u m m e r a n d w i n t e r to p r o d u c e w e l l - d ev e l -

o p e d s u r f a c e a n d u n d e r s t o r y c a n o p i e s i n s p r i n g - s u m m e r

1983, the f i rs t in the are a s ince 1979 (Fig . 1 F) . K elp s tand s

w e r e d e s t r o y e d o n l y in t h e f e w p l a c e s w h e r e a d u l t r e d

u r c h i n s w e r e s t i l l a b u n d a n t a n d c o u l d a s s e m b l e a s f r o n t s

nea r new s u r face s, A t S i t e N M (F ig . 1 E , F ) , fo r exam ple ,

u r c h i n s h a d c o n s u m e d a l l s p o r o p h y t e s b y m i d - A u g u s t

1983 . Su rv iv ing the s to rm in deep re fuges , t he s e u rch ins

s o o n f o r m e d f r o n t s a n d m o v e d u p s l o p e t o g r a z e b a c k a l l

s t an d s o f y o u n g k e l p a n d m o s t a l g al t u r f b e f o r e fa ll .

W a t e r t e m p e r a t u r e v a r i e d y e a r l y a s w e l l a s s e a s o n a l l y

(F ig . 2 ). R e la t ive to typ ica l s ea s ona l va lue s m eas u red

d u r i n g 1 9 7 9 - 1 9 8 1 , b o t h s u r f a c e a n d 1 3 m t e m p e r a t u r e s

d e c r e a s e d a s u s u a l d u r i n g t h e s p r i n g u p w e l l i n g p e r i o d o f

1 9 8 3 , b u t t h e n r e a c h e d u n u s u a l h i g h s d u r i n g s u m m e r a n d

fall 1983.

Alga l d r i f t

L o s s o f g ia n t k e l p e l i m i n a t e d t h e m a i n s o u r c e o f a l g al d r i f t

( T a b l e 1 ). B e f o r e S t o r m I , b e n t h i c a c c u m u l a t i o n s o n

Table 1. Mean w eights (+ SEM ) of detached drift algae at NaplesRe ef and similar rocky inshore reefs. Mea ns with different letters(in parentheses) are significantly different by analysis of varianceof data values (x) transformed to log (x + 1) and Dunc an's mul-tiple-range test (P < 0.05). Storm I occurred in Febru ary 1980,

Storm II in Fe bruary 1983

Locality and Date Depth n Mean wet wtdate (m) (g)

Ins ho reRee f l J u ly -Aug . 1980 8 -12 12 3 192+432(A)

Inshore Reef2 July-A ug. 1980 3-10 12 3 227_+606 (A)

Naples ReefJul y-A ug . 1980 7-15 14 90_+ 27 (C)Sep .-O ct. 1983 7 15 12 482 _+ 11 (B)Ju ly - Aug . 1984 7 15 13 1 969-+ 184 (A)

Inshore Ree f 1 July -A ug . 198 4 8-12 12 2 300-+ 159 (A)

2 2

2 O?v 1 8

1 6

XE 1 4

1 2

1 0

x S u r f a c e [ 1 9 8 3•

o 1 3 m- - x~. -' \ • x

9 o ", " , . - - ~ - . S u r f a c e/ . o x / o x o \ \ o " ~ m e a n s ,

c '< L - " " ( t ~ ' - . . ~ it'/'~ / ~ x l l ~ m_--- ~ ~ • / ~ ; m e a n s ,

~ 1 9 7 9 8 1

I j I F I M I - A I M I j I j I A I S I O I N I D - I

Fig. 2. 1983 temperature readings from N aples R eef plotted o nenvelopes delimiting the ranges o f monthly means based on semi-

weekly observations taken during 1979-1981



A. W. Ebeling et aL. Storm disturbances o f a kelp forest 291

: . . 6 0

~ f9

" ~ 4 0

c- 6

20

0

- 2 .

S torm I 2 1 . } _ . _ 4 S t o rm ] [

6 / a X " i " 4 2 [ A ~ k . . . . Sea urchins at si te M ~. /{ . J l_ _ ; _ I . ' ~ . "~:" / X T ~ ~ Kelp cover at NE(n=30) \ /

. ~ - " ~ " \ ~ - - ~ Kelpcover at SE \

I 't~ _ L % 3 "

300

-oo3

200 ~ =

= SO~ : : 3 "

1 0 0 ~-~

0

20

~ 8 1 o _g_ -

0

. •- -o Surfperch ] - NM -n209 ~10 e_ o Alga l tu rf cov er (n = 15) i a, / ~

3 , 0

{~ 0J I M I M I J I S I N I J I M I M I J I s I N ] j IM I M I J I S I N ] I M I j I s I N ] j I M I M I J i S IF A J A O O I V A J A 0 D I F A a A O D I J A O D I E A J A O

1979 1980 1981 1982 1983

Fig. 3. Strongylocentrotus franciscanus plus S. purpuratus, Pterygophora cali fornica, Embiotocidae, and algal turf. Bimonthly means(+_ SEM ) of pooled sea urchin counts (S. franciseanus+ S. purpuratus), percent cover of understory kelp (mostly P. californica), embiotocid

surfperch densities, and percent cover o f algal tu rf at monitored transect s ites on Naples R eef (see Fig. 1 D) before and after Storms I andII. Numbers next to urchin an d fish means a re sample sizes

N a p l e s R e e f r e s e m b l e d t h o s e u n d e r i n s h o r e f o r es t s.

D e t a c h e d M acrocys t i s pyr i f e ra m a d e u p t h e g r e a t e s t

p o r t i o n b y f a r , f o l l o w e d b y u n d e r s t o r y k e l p s a n d o t h e r

b r o w n a l g a e , a n d s m a l l a m o u n t s o f f o l io s e r e d a l g a e . A f t e r

S to rm I , a lga l d r i f t d rop ped to l es s than 100 g pe r s am ple

a n d c o n t a i n e d l i t t l e o r n o k e l p , a s c o m p a r e d t o m o r e t h a n

3 k g o f m o s t l y M . pyr i f e ra c o l l e c t e d u n d e r a p e r s i s t e n t

f o r e st a t a n i n s h o r e r e e f a b o u t 6 k m a w a y . D r i f t a l g a l

a b u n d a n c e a t N a p l e s r e m a i n e d l o w t h r o u g h o u t t h e

ba r rens pe r iod ( J u ly 1980 to M arch 1983) , As no teda b o v e , k e l p r e c r u i t m e n t w a s h i g h a t N a p l e s f o l l o w i n g

S t o r m I I , a n d t h e y o u n g f o r e s t b e g a n p r o d u c i n g s u b s t a n t ia l

am oun t s o f d r i f t by fa lI t 983 . R e f l ec t ing fo re s t s t ruc tu re ,

t h is n e w s u p p l y i n c l u d e d n o t i c e a b l e a m o u n t s o f a n e a r l y -

a r r iv i n g , f a s t- g r o w i n g s p e c ie s o f n o n - i a m i n a r i a n b r o w n

alga , Desmares t i a s pp . , a s we l l a s abundan t ke lp . In and

abou t re fuges , s ea u rch ins he ld va r ious b i t s and p iece s

o f a l g a e ( 8 0 % o f I 0 0 p i e c e s e x a m i n e d w e r e h e l d b y o n e

o r m o r e u r c h i n s ) . B y A u g u s t 1 98 4, d r i ft a g a i n r e a c h e d

a m o u n t s t y p i c al o f s u m m e r a c c u m u l a t i o n s u n d e r a m a -

tu re ke lp fo re s t (T ab le I ) .

S e a u r c h i n d e n s it y a n d u n d e r s t o r y k e l p c o v e r

S e a u r c h i n d e n s i ti e s v a r i e d w i t h c o n d i t i o n s i m p o s e d b y t h e

two s to rms (F ig . 3 : t op g raph) . B e fo re S to rm I , dens i t i e s o f

e x p o s e d ( c o u n t a b l e ) u r c h i n s o f b o t h s p e c ie s a t T r a n s e c t

S i t e M ave rag ed 7 .9 to 14 . 2m -2 , w i th p u rp le u rch ins

(S t rongy l ocen t ro t us purpura t us ) o u t n u m b e r i n g r e d u r c h i n s

(S . f rane i scanus ) b y 3 : 1 . T h e t r a n s e c t w a s o n t h e s l o p i n g

s ide o f a r il l, howeve r , an d w e cou ld s ee (bu t d id no t

coun t ) c lu s t e r s o f ind iv idua l s s he l t e r ing in c rev ice s and

u n d e r b o u l d e r s a b o v e a n d b e l o w t h e s l o p e . A f t e r S t o r m I ,

d e n s it i es o f e x p o s e d u r c h i n s d o u b l e d f r o m M a r c h 1 9 8 0 a t

tke s t a r t o f the b a r ren s pe r iod to ov e r 23 rn -~ in I98 t , a s

the ra t io o f s pec ie s dens i t i e s rem a ine d 3 :1 . S ince tho r oug h

s ea rches revea led fa r f ewer s he l t e r ing u rch ins , t he inc rea s e

p r o b a b l y r e f l e c t e d a n e m e r g e n c e o f i n d i v i d u a l s t h a t h a d

b e e n h i d i n g b e f o r e ( s e e R u s s o , 1 9 7 9 ; H a r r o l d a n d R e e d ,

1984) . T hen a f t e r a s e r i e s o f s ma l l e r s to rms du r in g fa l l-

w in te r 1982-1983 , dens i t i e s fe l l t o n i l w i th S to rm l I i n

1 9 8 3 . D u r i n g 1 9 8 3 - 1 9 8 4 t h e f e w a d u l t i m m i g r a n t s s o u g h t

s h e lt e r u n d e r b o u l d e r s a t t h e r i l l b o t t o m .

D i s r u p t i o n s i n n o r m a l s e a s o n a l c y c le s o f u n d e r s t o r y

k e l p c o v e r w e r e r e l a t e d t o i n c r e a s e d d e n s i ti e s o f e x p o s e d

s e a u r c h i n s (F i g . 3 : t o p g r a p h ) . A l t h o u g h u n d e r s t o r y c o v e r

w a s m e a s u r e d a t a d i f f e r e n t tr a n s e c t s it e ( N E ) t h a n u r c h i n

d e n s i t i e s ( M ) , t h e r e l a t i o n w a s g e n e r a l l y r o b u s t a n d h e l d

r e e fw i d e . B e f o r e S t o r m I a t S i te N E , t h e u n d e r s t o r y

c a n o p y h a d u n d e r g o n e i t s u s u a l s e a s o n a l c y c l e o f t h i n n i n g

f r o m m o r e t h a n 5 0 % c o v e r i n s u m m e r t o a b o u t 1 5% c o v e r

in w in te r (F ig . 3 : t op g raph) . We s aw few u rch ins a t S i t e

N E t h e n , a n d n o p l a n t s h a d b e e n g r a z e d . T h e a b r u p t

d e c l i n e i n c o v e r i n s p r in g a n d s u m m e r 1 98 0 o c c u r r e d a s

l a r g e r e d u r c h i n s a p p e a r e d , f o r m e d f r o n t s , a n d c o n s u m e d

the p lan t s . S to rm I I r educ ed u rc h in den s i t i e s a t S it e NEf r o m 3 . 2 + 0 . 5 ( S E M ) m -2 ( n = 5 h a p h a z a r d l y p l a c e d

t rans ec t s ) t o 0 .3_+0. 1 (n =4 ) , a f t e r wh ich ke Ip rec ru i t ed

a b u n d a n t l y t o t h e a r e a ( F i g. 1 E ) . B y c o m p a r i s o n , l a r g e r e d

u r c h i n s c o u n t e d s e p a r a t e l y a t S i te M w e r e r e d u c e d f r o m

5 . 6 - + 0 . 5 m -2 ( n = 2 0 c o u n t s f r o m S e p t e m b e r 1 98 0 to

Sto rm II) to 0.4 _+ 0.1 (n = 23).

C o n t i n u e d u n d e r s t o r y c o v e r a t T r a n s e c t S i t e S E i n -

d i c a t e d t h a t , w i t h o u t u r c h i n g r a z i n g , c o n d i t i o n s f a v o r e d

ke lp g row th a f t e r S to rm I (F ig . 3 : t op g raph) . Un graz ed

d u r i n g 1 9 8 0 , u n d e r s t o r y k e l p a t S i te S E u n d e r w e n t a f u l l

s e a s o n a l c y c l e o f t h i n n i n g a n d r e g r o w t h o f b l a d e s a f t e r

S t o r m I . U r c h i n s e v e n t u a l l y i n v a d e d t h e s a n d y s i te a n d

e l i m i n a t e d p l a n t s i n s p r i n g 1 9 8 1 . T h e r e w a s n o s u b s e q u e n t



292 A.W . Ebeling et aI.: Storm disturbances of a kelp forest

k e l p r e c r u i t m e n t t o t h is a r e a , w h i c h r e t a i n e d i t s s a n d c o v e r

t h r o u g h o u t t h e s t u d y .

S u r f p e r c h d e n s i ty a n d t u r f c o v e r

E m b i o t o c i d s u r f p e r c h d e n s i t i e s c o r r e l a t e d s t r o n g l y w i t h

t u r f c o v e r a t T r a n s e c t S i t e N M ( F i g. 3 : b o t t o m g r a p h ;

r = 0 . 8 0 , P < 0 . 0 0 1 , n = 2 1 ) . B e f o r e S t o r m I , b o t h v a r i e d

s e a so n a l ly , i n c r e as i n g d u r i n g t h e s p r in g a n d s u m m e r . B o t h

f e ll d u r in g t h e b a r r e n s p e r i o d b e t w e e n S t o r m s I a n d I I ,

t h e n i n c r e a s e d a f t e r S t o r m I I , t h o u g h n o t t o p r e v i o u s

m a x i m a . T h e s i t e n o l o n g e r a t t r a c t e d t h e a b u n d a n c e o f

s u r f p e r c h r e c o r d e d b e f o r e S t o r m I . T h e a b r u p t d e c l i n e i n

t u r f c o v e r a f te r J u n e 1 9 8 3 o c c u r r e d a s f r o n t s o f u r c h i n s

g razed the i r way up the s lope a t t h i s s i t e (F ig . 1 E , F ) .

B e f o r e th i s, h o w e v e r , c o v e r o f t u r f a n d o f u n d e r s t o r y k e l p

a p p e a r e d c o n t r o l l e d b y t h e s a m e r e e f w i d e p r o c e s se s .

D i s c u s s i o n a n d c o n c l u s i o n s

T h e t w o la r g e s to r m s m a r k e d p e r i o d s o f d i s a p p e a r a n c e

a n d r e a p p e a r a n c e o f a k e l p f o r es t . H o w e v e r , t hi s r e v e r sa l

o f c o m m u n i t y f o r m w a s r e l a t e d l e s s t o t h e f r e q u e n c y o f

s t o r m d i s t u r b a n c e t h a n t o t h e m a g n i t u d e a n d s c a l e o f

i n it i al e f f ec t s c o u p l e d w i t h t h e f r e q u e n c y o f b i o l o g i c a l

d i s t u r b a n c e b y g r a z i n g s e a u r c h i n s . T h e s t o r m s a f f e c t e d

o n e p a r t o f th e c o m m u n i t y d i r ec t l y a n d a n o t h e r p a r t

i n d i r e c t l y ( s e e C o w e n e ta l . , 1982; Fos ter , 1982). The

r e v e r s a l o c c u r r e d b e c a u s e d i r e c t e f f e ct s o f S t o r m I w e r e

i n d i r e c t e f f ec t s o f S t o r m I I a n d vice versa: Sto rm I (1980)

d e s t r o y e d k e l p , w h i c h a l t e r e d t h e f e e d i n g b e h a v i o r o fu r c h in s ; S t o r m I I ( 1 9 8 3) d e c i m a t e d u r c h i n s , w h i c h a l l o w e d

s u c ce s sf u l r e c r u i t m e n t o f k e l p .

A f t e r S t o r m I ( F e b r u a r y 1 98 0) , n e w k e l p p l a n t s a p -

p e a r e d d u r i n g s p r in g a n d e a r l y s u m m e r w h e n n u t r i e n t a n d

l i g h t l e v e l s f a v o r p l a n t r e c r u i t m e n t a n d g r o w t h ( e . g .

H a r g e r , 1 9 7 9; D e a n a n d D e y s h e r , 1 98 3) . H o w e v e r , n e a r l y

a l l w e r e e a t e n b y s e a u r c h i n s , w h i c h h a d p r e s u m a b l y

e m e r g e d f r o m r o c k y h i d i n g p l a c e s o n c e l o c a t e d n e a r a c -

c u m u l a ti o n s o f d r i ft k e lp a n d s m a l l e r a m o u n t s o f o t h e r

a l g a e . U r c h i n s a r e k n o w n t o a l t e r t h e i r f e e d i n g b e h a v i o r

f r o m q u i e t l y s h e l t e ri n g a n d h o l d i n g d r i f t, t o m o v i n g a b o u t

a n d g r a z i n g l i v e p l a n t s w h e n d r i f t f o o d i s u n a v a i l a b l e( D e a n e ta l . , 1 9 8 4 a n d r e f e r e n c e s t h e r e i n ; H a r r o l d a n d

R e e d , 1 9 8 4 ) . A t N a p l e s t h e c h a n g e w a s m a n i f e s t a s a n

a p p a r e n t d o u b l i n g o f u r c h i n d e n s i t ie s a t o u r r e g u l a r l y

m o n i t o r e d m i d r e e f si te ( F i g. 3 : t o p g r a p h ) , a s w e w e r e a l s o

a b l e t o s ee a n d c o u n t t h e p r e v i o u s l y h i d d e n i n d i v i d u a ls .

T h i s h i g h d e n s i t y o f e x p o s e d s e a u r c h i n s p r o b a b l y

e x c e e d s t h a t a t w h i c h l i v i n g p l a n t s c a n s u r v i v e i n t h e

a b s e n c e o f d r if t . R e d u r c h i n s ( S t r o n g y l o c e n t r o t u s f r a n -

c iscanus ) a r e l a r g e r a n d m o r e a c t i v e t h a n p u r p l e u r c h i n s

(S . ] )urpura tus ) . L e i g h t o n et al. ( 1 9 66 ) c o n c l u d e d t h a t a l g a e

c a n r e c o l o n i z e s u c c es s f u ll y a m o n g u r c h i n s w h o s e d e n s i ti e s

a r e n o t m u c h m o r e t h a n 1 r e d u r c h i n o r 1 0 p u r p l e u r c h i n s

m - 2, m u c h l es s t h a n w e o b s e r v e d a t m i d r e e f . P r e s u m a b l y ,

e i t h e r s p e c i e s c o u l d h a v e p r e v e n t e d p l a n t r e c o l o n i z a t i o n

h e r e b e c au s e p u r p l e u r c h in s o u t n u m b e r e d r e d u r c h in s b y

3 :1 . E v e n a t t h e d e e p e r a n d f l a t te r s it e a l o n g t h e r e e f b a s e

( F ig . 1 , Si te N E ) , u n d e r s t o r y k e l p c o v e r w a s c o m p l e t e l y

d e s t r o y e d w h e r e t h e r a t i o w a s o n l y 0 .5 : 1 a n d r e d u r c h i n s

w e r e f e w e r ( 2 = 3 . 2 m - 2 ) th a n a t t h e m i d r e e f (5 .6 ) b e f o r e

S t o r m I I . F u r t h e r m o r e , t h e g r a z i n g p o w e r o f r e d u r c h i n s

m a y b e u n d e r e s t i m a t e d i f i t is b a s e d o n l y o n d e n s i ti e s o f

d i s p e r s e d o r s t a t i o n a r y i n d i v i d u a l s . S u c h i n d i v i d u a l s m a y

b e c o m e m o r e d e s t r u c t i v e w h e n t h e y a g g r e g a t e a s d e n s e ,

m o v i n g f r o n t s ( D e a n e t aL , 1984).

A c o m p a r i s o n o f k e l p c o v e r t r e n d s i n d i c a te s t h a t

s e a s o n a l r e g r o w t h a f t e r S t o r m I w o u l d h a v e b e e n n o r m a l

b u t f o r u r c h i n g r a z i n g . H a v i n g d u r a b l e h o l d f a s t s a n d

s t ipes (Reed an d Fos te r , 1984) , und e rs to ry ke lp p lan t s

g r e w n e w b l a d e s a f t e r S t o r m I , b u t w e r e d e v o u r e d b y r e d

u r c h i n s a t S i te N E d u r i n g M a y - A u g u s t 1 9 8 0 . Y e t t h e

p r o c e s s w a s d e l a y e d f o r a l m o s t a y e a r i n a d j a c e n t S i t e S E

w h o s e s a n d y s u b s t r a t e m a y h a v e t e m p o r a r i l y d i s c o u r a g e d

u r c h i n m o v e m e n t s ( s e e B r e e n a n d M a n n , 1 9 7 6 ; T e g n e rand Day ton , 1977) .

D i s p e r s e d o v e r t h e w h o l e r e e f , m o v i n g a n d g r a z i n g

a d u l t s e a u r c h i n s m a y h a v e p r e v e n t e d a n y l a r g e - s c a l e

r e c r u i t m e n t o f k e lp a n d o t h e r a l g a e b e t w e e n s t o r m s .

U r c h i n s a t e m o s t l i v i n g p l a n t s b e c a u s e t h e a c c u m u l a t i o n

o f d r i ft k e lp a n d o t h e r a l g a e w a s n i l. T h e y s u r v i v e d i n t h e

o p e n b e c a u s e t h e y c o u l d s u b s i s t o n a l t e r n a t i v e f o o d s a n d

h a d f e w p r e d a t o r s ( s e e " I n t r o d u c t i o n " ) . I n t h e a b s e n c e o f

s ea o t t e r s, t he l a rge Ca l i fo rn ia s heep head f i sh S e m i c o s s y p h u s

p u l c h e r (Cow en , 1983) and s p in y lobs te r P a n u l i r u s in t e r -

r u p tu s ( T e g n e r a n d L e v i n , 1 9 8 3 ) m a y c o n t r o l u r c h i n n u m -

b e r s. Y e t s h e e p h e a d a b u n d a n c e a t N a p l e s R e e f w a s

p r o b a b l y f a r l e s s t h a n t h a t n e e d e d t o c o n t r o l e x p o s e durch ins (Cowen , 1983) , and lobs te r s we re ove r f i s hed and

r a r e ( o w n p e r s o n a l o b s e r v a t i o n s ) .

E v e n t h o u g h S t o r m I I c r e a t e d a s m u c h o r m o r e d i s -

tu rbance a s S to rm I , i t had the reve rs e b io log ica l e f fec t on

t h e r e e f c o m m u n i t y . D e n s e s t a n d s o f k e lp s p o r o p h y t e s

a p p e a r e d o n n e w r o c k s u r f a c e s b a r e d b y t h e s t o r m . P l a n t

s e t t l e m e n t w a s u n u s u a l l y h e a v y , d e s p i t e a n u n c e r t a i n

s o u r c e o f p r o p a g u l e s a n d t h e p r e s u m e d l i m i t e d d i s p e r s a l

d i s ta n c e o f k e l p s p o r e s (s e e A n d e r s o n a n d N o r t h , 1 96 6;

D a y t o n , 1 9 7 3 ) . W a v e a c t i o n d e c i m a t e d t h e p o p u l a t i o n o f

u r c h i n s b e c a u s e m o s t i n d i v i d u a l s w e r e f o r a g i n g i n t h e

o p e n a n d e x p o s e d t o t h e f u l l fo r c e o f t h e s u r g e . W i t h o u t

g r a z in g u r c h i n s, t h e y o u n g k e l p p l a n t s s u r v i v e d a n d g r e w .

Als o , an in i t i a l co ve r o f e a r ly -a r r iv ing , f a s t -g rowing f i l a -

m e n t o u s b r o w n a l ga e ( E c t o c a r p u s s pp . and Gif ford ia s pp . )

m a y h a v e p r o t e c t e d y o u n g k e l p p l a n t s f r o m g r a z i n g f i s h

(Har r i s e t a L , t 9 8 4 ) . T h e k e l p u n d e r s t o r y s o o n r e a c h e d

p r e - d i s t u r b a n c e ( 1 9 79 ) l e v e ls o f p e r c e n t c o v e r .

A l t h o u g h t h e d e n s i t y o f k e lp r e c r u i ts w a s m o r e t h a n 1 0

t i m e s g r e a t e r a f t e r S t o r m I I t h a n a f t e r S t o r m I , th e l a c k o f

k e l p r e g r o w t h a f t e r S t o r m I w a s m o r e l i k e l y d u e t o g r a z i n g

u r c h i n s t h a n t o r e c r u i t m e n t l i m i t a t i o n . W h e r e v e r t h e y

s u r v i v e d S t o r m I I , u r c h in s w e r e f u l l y c a p a b l e o f d e s t r o y i n g

e v e n t h e d e n s e s t s t an d s o f y o u n g k e l p . F o r e x a m p l e ,

u r c h i n s t h a t h a d s u r v i v e d u n d e r b o u l d e r s w i t h i n a s u r g e



A.W.Ebeling et al.: Storm disturbances of a kelp forest 293

s h a d o w b e l o w S i t e N M s o o n m o v e d u p s l o p e t o e l i m i n a t e

s p o r o p h y t e s t h a t h a d r e c r u i t e d h e a v i l y t o e x t e n s i v e n e w

su r faces t h e re .

Reefw id e , k e lp s su rv iv ed d esp i t e a n E1 Ni f i o i n t ru s io n

o f w a r m , n u t r i e n t - p o o r w a t e r t h a t h a s p e r s i st e d s i n ce

w i n t e r 1 9 8 2 - 19 8 3 o f f c o a s t a l s o u t h e r n C a l i f o r n i a ( F i e d le r ,

1 98 4) . A s a l so o b s e r v e d o f f S a n D i e g o s o m e 3 0 0 k m t o t h e

s o u t h ( D a y t o n a n d T e g n e r , 1 9 8 4 ) , h o w e v e r , w a t e r c o o l e d

to u su a l l ev e l s i n sp r i n g 1 9 8 3 i n d i ca t i n g a s t ro n g p u l se o f

u p w e l l i n g a n d n u t r i e n t e n r i c h m e n t . T h i s a n d i n t e r m i t t e n t

s h oa l in g o f t h e t h e r m o c l i n e d u r i ng t h e s u m m e r m a y h a v e

s u p p l ie d p l a n t s w i t h t h e n u t r i e n ts r e q u i r e d f o r c a n o p y

reg ro wth i n sp r i n g 1 9 8 4 ( see Harg er , 1 9 7 9 ; No r th et a l . ,

1 98 2) . U n d e r s t o r y k e l p s a n d l o w e r f r o n d s o f g i a n t k e l p

m a y h a v e b e e n n o u r i sh e d f r o m t i m e t o t i m e b y n u t r ie n t -

r i c h w a t e r b e l o w t h e t h e r m o c l i n e . T h e y g r e w n e w b l a d e s

o r f r o n d s d u r i n g t h e s p r i n g u p w e l l i n g p e r i o d , a n d f o r m e d

w e l l - d e v e l o p e d s u r f a c e a n d u n d e r s t o r y c a n o p i e s b y s u m -

m e r . C o n s e q u e n t l y b a b y s u r f pe r c h , w h i c h r e q u i r e a c o v e r

o f u n d e r s t o r y k e l p f o r p r o t e c t i o n f r o m p i s c iv o r e s , re a p ~p e a r e d f o r t h e f i r st t im e s i nc e d e f o r e s t a t i o n a f t e r S t o r m I

(Eb e l i n g an d Lau r , 1 9 8 4 ) . Dr i f t k e lp b eg an t o accu mu la t e .

H e n c e , t h e r e m a i n i n g u r c h i n s w e r e a b l e t o e x p l o i t a

r e n e w e d d e t r i ta l s u p p l y a n d r e a s s u m e t h e i r s h e lt e r i n g

m o d e .

S u r f p e r c h a b u n d a n c e a p p a r e n t l y d e p e n d e d o n o u t p u t s

o f t h e d e t r i t u s -b a s e d f o o d c h a i n . T h e s t r o n g c o r r e l a t i o n o f

a d u l t n u m b e r s w i t h a l g a l - t u r f c o v e r i n d ic a t e s t h a t t h e f is h

w e r e t r a c k i n g t h e ir f o o d s u p p l y o f s m a l l p r e y t h a t l iv e i n

tu r f (Lau r an d Eb e l i n g , 1 9 83 ; S to u d er , 1 98 3 ). M a n y o f

t h e s e p r e y , s u c h a s a m p h i p o d s a n d c r a b s , a r e f a c u l t a t i v e

d e t r i t i v o res , i n g es t i n g p l an t l i t t e r an d o th e r r e fu se co a t ed

wi th b ac t e r i a l s l ime (M an n , 1 9 8 2 ) . Befo re u rch in s h adi n v a d e d o u r s i te , b o t h t u r f c o v e r a n d s u r f p e r c h d e n s i t y

v a r i e d s e a s o n a l l y , i n c r e a s i n g d u r i n g t h e s p r i n g - s u m m e r

p r o d u c t i v i ty p u l s e ( F ig . 3 : b o t t o m g r a p h ) . T h e n b o t h

r e m a i n e d a t l o w l e v e l s d u r i n g t h e e x t e n d e d b a r r e n p e r i o d

b e f o r e S t o r m I I . O v e r l a p i n m i c r o h a b i t a t u s e b e t w e e n s u r f -

p e r c h s p e c i e s i n c r e a s e d a s f i s h c o n g r e g a t e d a b o u t t h e r e e f

c r e st a n d a d j a c e n t s l o p e w h e r e u r c h i n s w e r e f e w e r a n d t u r f

p e r s i s t ed (S to u d er , 1 9 8 3 ) . Ho wev er , t h e p red i c t ab l e i n -

c r e a s e i n t u r f a n d f is h a f t e r S t o r m I I w a s n o t f u l l y r e a li z e d ,

b ecau se o u r s i t e (F ig . 1 , S i t e NM ) was ev en tu a l l y o v er ru n

b y su rv iv in g u rch in s ( see ab o v e) .

T h a t s e v e r e s t o r m s m a y c a t a l y z e r e g e n e r a t i v e a s w e l l a s

d e g e n e r a t i v e p r o c e s s e s m a y h e l p e x p l a i n w h a t N o r t h

( 1 9 7 1 ) d e s c r i b e d a s " i r r e g u l a r c h a n g e s " i n s o u t h e r n C a l i -

fo rn i a k e lp fo res t s . I n o u r ex am p le , S to rm I se t f o r t h

p ro cesses d i s ru p t i n g t h e d e t r i t u s -b ased fo o d ch a in t o t h e

e x t e n t th a t t h e r e e f c o m m u n i t y w a s u n a b l e t o r e s u m e i ts

p r e v i o u s f o r m . T h is h a p p e n e d d e s p i t e th e f a c t s th a t ( 1 )

w i n t e r - s t o r m d i s t u r b a n c e s g e n e r a l l y p r e c e d e t h e s e a s o n o f

m a x i m u m l i g h t a n d p r o d u c t i v i t y ( H a r g e r , 1 9 79 ; N o r t h

et al . , 1 98 2 ), an d (2 ) l o s s o f t h e su r f ace c an o p y o f g i an t

k e l p a l l o w s l i g h t f o r u n d e r s t o r y g r o w t h t h a t w o u l d o t h e r -

w i s e b e s u p p r e s s e d b y s h a d i n g ( F o s t e r , 1 9 82 ; D a y t o n a n d

Teg n er , 1 9 8 4 ; Day to n et a l . , 1984; Reed and Foster , 1984) .

S t o r m I I r e v e r s e d t h e d e g e n e r a t i v e p r o c e s s b y r e m o v i n g

s e a u r c h in s a n d a i d i n g k e l p r e c r u i t m e n t . T h u s , o u r f i n d in g s

su g g es t t h a t i f p r ed a to r s o r o th e r ag en c i es co n t ro l u r ch in

n u m b e r s ( s e e " I n t r o d u c t i o n " ) , s t o r m e f f e c ts s h o u l d b e

r e g e n e r a t i v e ( C o w e n e t a l . , 1982; Foster, 1982). But in

m a t u r e f o r e s ts w h e r e u r c h i n p o p u l a t i o n s a r e p o o r l y

r e g u l a t e d , s e v e r e s t o r m s m a y h a v e d e g e n e r a t i v e e f f e c t s

b e c a u s e t h e y e l i m i n a t e t h e d e t r i tu s b a s e .

A c k n o w l e d g e m e n t s . W e t h a n k M . F o s t e r , R . L a r s o n , a n d D .

Ree d fo r r ev i ewin g t h e man u scr ip t . A . Du Bo i s , C . Eb e l i n g ,

J . J en k in s , T , M i l l e r , an d T . P ear so n s h e lp ed wi th f i e l d

w o r k . S . A n d e r s o n p r o v i d e d t e c h n i c a l a s s i s t a n c e w i t h

e q u i p m e n t a n d b o a t i n g op e r a ti o n s. D . M c L a r e n a n d R .

P an za d ra f t ed i l l u s t r a t i o n s . Th e M ar in e S c i en ce In s t i t u t e

s u p p l i e d a d m i n i s t r a t i v e se r v ic e s . T h e w o r k w a s s u p p o r t e d

b y N S F G r a n t s O C E 7 9 - 2 5 0 08 a n d O C E 8 2 - 0 81 8 3 .

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