WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



significant seasonal trend in the size-frequency 

 distributions of P. suspiriosum. 



DSB III did not take P. suspiriosum, so its diet 

 was not examined. 



DISCUSSION 



Color Pattern and 



Daytime Vertical Distribution: 



Role of Countershading 



Sergestids display two basic color patterns. One 

 group, including Sergestes and species of Sergia in 

 Yaldwyn's (1957) "S. challengeri" species group, is 

 "half-red!' that is, its members are semitrans- 

 parent except for the eyes and viscera, with red, 

 stellate, subcuticular chromatophores scattered 

 over the body and appendages, most concentrated 

 on the cephalothorax. All half-red sergestids have 

 well-developed photophores; Sergestes species 

 have internal photophores, the organs of Pesta, 

 and the half-red Sergia species have external 

 cuticular lensed photophores. The other group, 

 including the remaining species of Sergia and 

 Petal id i inn, is "all-redT that is, its members are 

 covered with a relatively uniform red cuticular 

 pigment. All-red sergestids have simple lensless 

 cuticular photophores or else lack photophores 

 altogether. 



Foxton (1970) showed that most mid-water 

 decapods in the Fuerteventura area (Canary Is- 

 lands) are either half-red or all-red. He found that 

 half-red shrimps generally live shallower than 700 

 m during the daytime, while all-red shrimps 

 generally live below 700 m. He concluded that the 

 half-red color pattern and complex photophores 

 are adaptations for concealment by countershad- 

 ing to match the light intensity of the surrounding 

 waters when viewed from any angle, the photo- 

 phores producing a ventrally directed beam of 

 light to fill in the shadow of the animal. He 

 suggested that the half-red pattern gives way to 

 the all-red pattern at the depth where biolumi- 

 nescent light becomes more important than pene- 

 trating surface light. Although many all-red 

 decapods have simple photophores, he concluded 

 that their function does not involve daytime 

 countershading. Donaldson (1975) did not discuss 

 this phenomenon, but an examination of his ver- 

 tical distribution data for the Bermuda area shows 

 the same daytime pattern of shallower half-red 

 sergestids and deeper all-red sergestids, the 

 dividing line again being approximately 700 m. 



Other mid-water animals show similar depth- 

 related changes in color patterns during the 

 daytime. Badcock (1970) noted that mesopelagic 

 fishes in the Fuerteventura area tend to be silvery 

 above 650-700 m and dark below that depth. 

 Amesbury (1975) found the same pattern in 

 Hawaiian mesopelagic fishes, several independent 

 analyses of community structure locating a major 

 faunal boundary at 675-700 m between mostly 

 silvery shallow mesopelagic fishes and mostly dark 

 deep mesopelagic fishes. 



Figure 33 shows how half-red and all-red ser- 

 gestids difi'er in depth during the daytime in 

 Hawaiian waters. The half-red species range from 

 425 to 725 m, with maximum abundance in the 600- 

 to 625-m interval. The all-red species range from 

 625 to 1,500 m, with maximum abundance at 

 700-725 m. 



Rather surprisingly, the depths of maximum 

 abundance for the two types are only 100 m apart, 

 and there is a large amount of overlap in their 

 ranges, particularly in the zone between 650 and 

 725 m. Nearly half of the half-red sergestids below 

 650 m are Sergestes erectus, a species often taken 

 in large numbers in tows that also take large 



NUMBER /lO^M^ 

 HALF-RED ALL-RED 



150 100 50 50 100 150 



-1 1 



300- 



1500-' 



Figure 33.-Daytime vertical distribution of half-red and all-red 

 Hawaiian sergestids. Half-red species are on the left (half-red 

 Sergia spp. crosshatched), all-red species on the right. Scale of 

 light intensity is from unpublished data of E. M. Kampa, at lat. 



28°N. 



825 



