VERTICAL DISTRIBUTION AND PHOTOSENSITIVE VESICLES OF PELAGIC 



CEPHALOPODS FROM HAWAIIAN WATERS 



Richard Edward Young * 



ABSTRACT 



Vertical distribution data were obtained for 47 species ofpelagiccephalopods off Oahu, Hawaii. Peaks 

 in species richness occurred at 500-800 m during the day and in the upper 300 m at night. Over SO^f of 

 the individuals occurred in the upper 250 m at night. Approximately 60% of the species underwent diel 

 vertical migration, and most of these migrated into the upper 250 m. In five of nine groups of closely 

 related species, clear differences in habitat were found. 



Deepwater spawning appeared to occur in a variety of cephalopods. Two of the bathypelagic octopods 

 brooded their young at or above the upper limit of the remaining adult population. In doing so, the 

 extent of the upward migration of newly hatched individuals was reduced. 



Photosensitive vesicles occurred in all species. These organs probably detect downwelling daylight 

 for regulating vertical migration and counterillumination. The vesicles also appeared to form an 

 elaborate system for monitoring bioluminescent light from the animal's own photophores, from within 

 the mantle cavity, and from other animals located outside the visual field. 



Cephalopods must occupy a wide variety of ecolog- 

 ical roles in the pelagic realm of the open ocean: 

 the highest diversification of families and genera 

 is found in this environment. In order to under- 

 stand these roles, the vertical distribution of these 

 animals must be determined. A number of papers 

 have treated various aspects of the vertical dis- 

 tribution of oceanic cephalopods (e.g., Pearcy 

 1965; Clarke 1969; Roper 1969; Gibbs and Roper 

 1971; Clarke and Lu 1974, 1975; Lu and Clarke 

 1975a, b; Roper and Young 1975). Their vertical 

 habitats, however, remain poorly known. 



Data on the vertical distribution of cephalopods 

 is difficult to obtain: many species are uncommon, 

 and some avoid small trawls. In this study an 

 opening-closing net (modified Tucker trawl) pro- 

 vided unambiguous depth data, and a slightly 

 larger open net (3-m Isaacs-Kidd midwater trawl) 

 added considerable additional data; nevertheless, 

 fast-swimming species were poorly sampled. 



Extraocular photoreceptive organs, the photo- 

 sensitive vesicles, were examined in each species 

 for clues that would indicate the role of light in 

 regulating vertical distribution patterns. The or- 

 gans in squid, known as the parolfactory photo- 

 sensitive vesicles, lie near the brain within the 

 confines of the cephalic cartilage. In octopods the 

 organs, known as epistellar photosensitive vesi- 

 cles, lie within the mantle cavity adjacent to the 



'Department of Oceanography, University of Hawaii, Hono- 

 lulu, HI 96822. 



stellate ganglia. The photosensitive vesicles are 

 paired organs. Each organ, as the name implies, is 

 generally composed of a large number of small 

 vesicles. The individual vesicles contain photo- 

 sensitive cells similar to those of the retina, and 

 their photoreceptive nature has been well estab- 

 lished ( Nishioka et al. 1966; Mauro and Baumann 

 1968; Mauro 1977). The specific functions of the 

 photosensitive vesicles are unknown in both neri- 

 tic and oceanic cephalopods although many 

 suggestions have been made (see Packard 1972). 

 Several papers discussing the relationship of 

 vertical distribution to eye structure, biolumines- 

 cence and/or development of photosensitive vesi- 

 cles in selected species have already appeared 

 (Young 1972a, 1973, 1975a, c, d, 1977). Some data 

 on distribution taken during the initial phases of 

 this program have been published by Roper and 

 Young (1975). This paper examines the vertical 

 distribution of all pelagic cephalopods taken off 

 Hawaii and the morphology and orientation of 

 their photosensitive vesicles. 



MATERIALS AND METHODS 



Specimens were collected off the island of Oahu 

 in the Hawaiian archipelago at long. 158°20'W, 

 lat. 21 = 20 'N over depths between 1,500 and 4,000 

 m. Collections were made from September 1969 to 

 November 1974 primarily from the RV Teritu. 

 Over 3,300 specimens were taken in horizontal 

 tows during about 1,000 h of trawling time. 



Manuscript accepted January 1978. 

 FISHERY BULLETIN; VOL" 76. NO. 3, 1978. 



583''^ 



