AN EVALUATION OF CORAL REEF SURVEY METHODS BY COMPUTER SIMULATION R. A. Kinzie I11 INTRODUCTION A computer program package has been developed t o gene ra t e s imulated c o r a l d i s t r i b u t i o n s on a " reef . " These " reefs" can b e designed t o in- corpora te v a r i a t i o n s i n s p e c i e s number, s i z e of c o r a l heads of each spec i e s , and t h e p o s i t i o n of each spec i e s i n an "hierarchy of aggression" (Lang, 1973). The output from the reef -genera t ing program gives the l o c a t i o n and s i z e of each head a s we l l a s in format ion f o r each spec ies . The spec i e s information inc ludes cover , average head s i z e , and va r i ab i - l i t y of head s i z e . These " reefs" w i th known parameters a r e then "sampled" us ing s imula t ions of a number of techniques p re sen t ly used by r ee f workers. The methods s imulated a r e t he chain l i n k method (Por t e r , 1972, 1974; Loya, 1972); a l ine-poin t method wi th two sampling i n t e n s i - t i e s : 40 p o i n t s p e r 10 m and 20 p o i n t s pe r 10 m (Roy and Smith 1971); 2 a point-quadrat method us ing 25 uniformly placed po in t s i n a l m quadrat t h a t is placed a t t h ree p o s i t i o n s a long t h e 10 m t r a n s e c t l i n e ; and a count method t h a t simply counts t he heads of each spec i e s t h a t f a l l w i th in t h e t h r e e quadra ts . A l l of t h e s e methods except t h e quadrat-count technique g ive cover e s t ima te s f o r each spec i e s . From f i e l d s t u d i e s , w e ranked the cover e s t i m a t i n g methods according t o e f f o r t . The concept of e f f o r t i nc ludes t h e time spent under water count ing and t h e work involved i n p l ac ing the gear on t h e r e e f . From most d i f f i c u l t t o e a s i e s t they a r e : cha in l i n k , point-quadrat , 40 p o i n t s , and 20 po in t s . The f i r s t ques t ion we asked was whether t h e r e was enough improvement i n accuracy i n t h e use of t h e more d i f f i c u l t methods t o j u s t i f y t h e added e f f o r t (and hence reduced number of t r a n s e c t s t h a t could be run i n a given amount of t ime) . The second ques t ion we asked was whether t h e r e was a s i g n i f i c a n t quadra t - s ize e f f e c t and, i f s o , whether d i f f e r e n c e s i n t h e d e n s i t i e s of c o r a l s i n quadra ts of d i f f e r i n g s i z e s can be used i n determining the d i s p e r s i o n p a t t e r n s of t h e c o r a l s (Mor is i ta , 1959; Grieg-Smith, 1964). Another measure of d i spe r s ion p a t t e r n s was s imulated us ing a number of nearest-neighbor techniques (Clark and Evans, 1954; P i e lou , 1960). Department of Zoology, Univers i ty of Hawaii, Honolulu, Hawaii, USA METHODS We generated t h r e e s e r i e s of " reefs" i n o rde r t o s tudy the e s t ima te s of c o r a l cover and c o r a l abundance. The reef parameters we va r i ed were cover, head s i z e , and abundance. Keeping any one of t hese cons tan t and l e t t i n g t h e o t h e r two vary, we developed t h r e e s e r i e s : (A) cover of each spec i e s cons tan t ; (B) head s i z e of each spec i e s cons tan t (each of t he fou r spec i e s had a mean r a d i u s two times t h a t of the next smal le r s p e c i e s ) ; and ( C ) r e l a t i v e head s i z e and abundance were cons tan t whi le t h e cover was reduced by a f a c t o r of two i n each of t h e "reefs" i n t he s e r i e s . The reason f o r t hese s e r i e s was t o s e e i f t h e methods were d i f f e r e n t i a l l y s e n s i t i v e t o spec i e s which might have equal cover b u t which d i f f e r e d i n head s i z e and abundance. I n order t o e v a l u a t e t he d i spe r s ion e s t ima te s , we generated another s e r i e s of " reefs" t h a t ranged from uniform through random t o clumped. This was accomplished by varying head s i z e , o rde r of placement on the r e e f , and t h e degree of "aggressiveness" and hence the spacing of t h e heads. Three s e t s of t en t r a n s e c t s us ing each of t h e t r a n s e c t methods were run on each of t he " reefs . " The measure of co r r ec tnes s was how many t i m e s o u t of t e n t h e cover e s t ima te w a s w i t h i n f 20% of the c o r r e c t cover. A mean and s tandard dev ia t ion of co r r ec tnes s were obtained. The v a r i a b l e s i z e d quadra t method used t h e e n t i r e " reef , " so i t was a c t u a l l y notaf1sampl ing" method. The sample s i z e of t he nearest-neighbor technique had t o be v a r i a b l e because of t h e d i f f e r e n t numbers of c o r a l heads of each spec ies . RESULTS The accuracy of a l l the methods was q u i t e poor. I n no case was t h e accuracy of a cover e s t ima te g r e a t e r than seven o u t of t e n and usua l ly i t was l e s s than f i v e ou t of t en ; t h a t is , e s t ima te s of cover were w i t h i n 2 20% of the t r u e va lue l e s s than f i v e o u t of t e n t imes. There is a tendency f o r t h e smaller, more abundant c o r a l s t o have t h e i r cover estima- t ed more c o r r e c t l y than l a r g e r , r a r e r c o r a l s even though both spec i e s have equal cover (A "reefs") . A t moderate l e v e l s of cover a l l t h e methods a r e about equal ly bad; hence t h e r e i s l i t t l e t o recommend those methods consuming more t i m e . I n add i t i on , u t i l i z a t i o n of more r a p i d techniques w i l l al low more t ran- s e c t s t o b e run. While t h e accuracy of any one of t h e s e w i l l be low, t he f a c t t h a t a l a r g e r a r e a of t h e r ee f under s tudy w i l l be sampled w i l l a t l e a s t g ive a more i n c l u s i v e p i c t u r e of t he r e e f . I f c o r a l s a r e r e l a t i v e l y r a r e (10 t o 15% cover ) , t h e more time consuming methods do show more s e n s i t i v i t y than t h e f a s t e r techniques. I f cover i s l e s s than 5%, none of t h e methods a r e a t a l l accura te . The r e s u l t s of t h e s t u d i e s on d i s p e r s i o n estimates a r e less c l e a r . We had no abso lu t e ranking of t h e d i s p e r s i o n p a t t e r n s of t h e c o r a l s ( s ee P ie lou , 1960) , s o t h e d i f f e r e n c e s de t ec t ed by t h e methods w e r e no t d i r e c t l y t e s t a b l e . However, bo th methods s imula ted d i d rank t h e spec i e s more o r less i n t h e way t h a t w e p r ed i c t ed , wi th e f f e c t s of "aggression" i n c r e a s i n g uni formi ty , and smal l s i z e combined wi th l a s t choice of p o s i t i o n on the r ee f caus ing aggrega t ions . I n a d d i t i o n , w e had no f i e l d in format ion comparable t o ou r s t u d i e s on cover e s t i m a t e s on t h e d i f f i - c u l t i e s of t h e u s e of t h e d i s p e r s i o n e s t i m a t e s under water . We a r e , however, s a t i s f i e d , t h a t ou r s imu la t i ons a r e reasonable approaches t o t h e a c t u a l f i e l d techniques. CONCLUSIONS When c o r a l spec i e s a r e r e l a t i v e l y abundant o r have high cover t h e r e is l i t t l e t o recommend t h e more l abo r ious and t i m e consuming sampling methods. I n f a c t , t h e f a s t e r methods a r e t o be p r e f e r r e d , because more t r a n s e c t s can be run i n t h e same amount of time--covering a wider a r e a of the r e e f , thus improving r e l i a b i l i t y i f no t accuracy. When s p e c i e s a r e moderately r a r e , t h e more t i m e consuming methods may be j u s t i f i e d , and when s p e c i e s a r e uncommon only very ex t ens ive work would b e expected t o g ive reasonably a c c u r a t e r e s u l t s anyway. We a r e prepar ing documenta- t i o n f o r t h i s program package and w i l l make i t a v a i l a b l e t o i n t e r e s t e d p a r t i e s . A more d e t a i l e d d i s c u s s i o n of t h e programs and an extended a n a l y s i s of t h e r e s u l t s i s presen ted elsewhere (Kinzie and Snider , i n p r e s s ) . ACKNOWLEDGEMENTS This r e sea rch was supported by NSF Grant No. GA35836. REFERENCES Clark , P. J . , and Evans, F. C. 1954. 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