MANN: CONADAL DEVKLOl'MENT IN ARCTICA ISLANDICA 



lighter than cytoplasm and a distinct 



nucleolus. 

 Ripe: 

 Male: Follicles filled with spermatozoa in 



swirling patterns. 

 Female: Predominantly free oocytes with dis- 

 tinct nucleus and nucleolus. 

 Partially spent: 

 Male: Follicles disorganized and often 



empty. Some full follicles remaining. 

 Female: Follicles disorganized. Some mature 



ova remaining, some undergoing cy- 



tolysis. 

 Spent: 

 Male: Follicles disorganized and empty, 



few spermatozoa remaining. 

 Female: Follicles disorganized and empty, 



few ova remaining. 



The report of Loosanoff (1953) was used for 

 comparison throughout the procedure. The clas- 

 sification of gonadal development into stages is, 

 by definition, qualitative. A quantitative option 

 of describing female gonadal development as a 

 function of mean ova diameter was considered 

 inapplicable in the present study because ova 

 were often elongated or otherwise nonspherical 

 in shape, especially during development from 

 oogonia to oocytes. 



Hydrographic measurements were made at 

 each station on each collection date. A vertical 

 profile, from surface to bottom at 5 m intervals, 

 was made of temperature and conductivity using 

 either a model 6D or S8000 Hydrolab Water 

 Quality Analyser (Hydrolab Corporation, Austin, 

 Tex.) 3 and the conductivity measurements were 

 converted to salinity. On six occasions these data 

 were supplemented by vertical profiles of dis- 

 solved oxygen content and pH measured with the 

 same instrument. 



RESULTS 

 Hydrographic Observations 



Figure 1 depicts the seasonal temperature 

 structure of the water column at Stations A-D. 

 No marked differences were recorded between 

 the 2 yr of the study; hence data have been pooled. 

 An intense seasonal thermocline was initiated in 

 April-May and reached a maximum intensity at 



3 Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



between 20 and 30 m depths in August. Surface 

 waters cooled during the fall months of Septem- 

 ber and October. A uniform temperature struc- 

 ture throughout the water column was evident 

 from November through April. 



The intense nature of the thermocline and its 

 relationship to depth at sample stations (A-D) is 

 illustrated in Figure 2 for August 1979. Maxi- 

 mum bottom temperatures recorded at Stations 

 A-D, respectively, were 15.4°, 14.0°, 12.9°, and 

 12.6°C, and they occurred earliest at the two 

 shallower stations. 



Salinity values recorded during the study 

 agreed well with those reported previously by 

 Ketchum and Corwin (1964). Surface to bottom 

 salinities increased from 30.907.. to 32.087.. dur- 

 ing July at Station A and from 31.597..to 32.857.. 

 at Station D. Salinities were highest but rela- 

 tively stable throughout all depths and stations 

 during the winter months (all values ranged 

 from 32.307.. to 33.527.,). 



Dissolved oxygen data were in general agree- 

 ment with those summarized for the Middle 

 Atlantic region by Williams and Godshall (1977). 

 Surface waters to 20 m depth were at or within 

 10% of saturation throughout the year. A gradual 

 decline in percentage saturation was evident be- 

 low the seasonal thermocline from April to late 

 August (Fig. 3A). This was most obvious imme- 

 diately adjacent to the sediment-water interface 

 where a minimum dissolved oxygen level of 65% 

 saturation was recorded at Station D in August 

 1979. Concurrently pH also decreased reaching a 

 minimum of 7.9 (Fig. 3B) at the sediment-water 

 interface at all stations in August 1979. 



Gonadal Observations 



A rctica islandica is dioecious. Out of 669 speci- 

 mens, hermaphroditism was found in only 2 indi- 

 viduals which contained spatially separate de- 

 veloping male and female follicles (Fig. 4). Serial 

 sectioning indicated that gonadal maturation 

 occurred initially in tissues at the dorsal extrem- 

 ity of the gonadal mass and progressively later 

 moving toward the ventral extremity (Fig. 5). 

 Multiple spawnings in the same animal during 

 one annual cycle, originating from tissues in a 

 similar spatial sequence, were suggested by the 

 presence of spent follicles in dorsal sections, 

 while follicles in the ventral sections of the same 

 specimen were in late active or ripe condition. No 

 evidence was found of a second maturation of 

 spent, dorsal gonadal follicles following spawn- 



317 



