WALTERS: ECOLOGY OF HAWAIIAN SERGESTID SHRIMPS 



Reproduction and Growth 



It is diffcult to determine when sergestids 

 spawn. Copulation occurs long before spawning; 

 female Sergia gardineri whose ovaries have not 

 started to mature often bear spermatophores. 

 Eggs are spawned directly into the water rather 

 than being carried on the appendages as in the 

 carideans. Some spawning probably occurs year 

 around, as sexually mature females can be cap- 

 tured at any time of the year. In Sergesfeff, the 

 anterior lobes of the ovary vary greatly in size, 

 filling much of the carapace at maximum develop- 

 ment. However, there is no correlation of ovary 

 development with carapace length in adult 

 females. One possible explanation is that a female 

 may spawn several batches of eggs over a period of 

 several months, the ovaries regressing in size 

 between batches. 



Recruitment to a catchable size can be deter- 

 mined from the quarterly size-frequency histo- 

 grams. Omori (1969) found that Sergia lucens 

 required about 2 mo from spawning to recruit- 

 ment; assuming the time is similar for Hawaiian 

 species, a maximum in recruitment implies a 

 maximum in spawning about one quarter earlier. 

 Most Hawaiian sergestids showed peak recruit- 

 ment in either the second (April-June) or third 

 (July-September) quarter. Species with maximum 

 recruitment in the second quarter included Ser- 

 gestes annatu^, S. sargassi, Sergia inequalis^, and 

 S. bisulcafa. Species with maximum recruitment 

 in the third quarter included Sergefites atlanticus, 

 S. consobrinus, S. pectinatui^, Sergia scintillans, 

 and S. gardineri. Some species showed no signif- 

 icant difference from one quarter to the next; 

 these included Sergestes orientalis, Sergia bigeni- 

 mea, and probably S. tenuiremifi and Petalidium 

 snspiriosiim. Sergestes vigilax had somewhat 

 higher recruitment in quarters two and three than 

 during the rest of the year. Sergestes erectus 

 showed no particular recruitment maximum, but 

 intermediate-sized shrimp were most abundant in 

 the fourth quarter. Sergia fulgens is a peculiar 

 case, to be discussed later. 



Size-frequency data indicate that most 

 Hawaiian sergestids appear to live about 1 yr, in 

 agreement with most other studies (Pearcy and 

 Forss 1969; Omori 1969; Donaldson 1973). The 

 size-frequency histograms of Sergia bisculcata 

 indicate that this species has a 2-yr life span, 

 though the conclusion is based on a small sample. 

 Donaldson concluded that S. robusta may also live 



2 yr. Genthe (1969) arrived at a 2-yr life span for 

 Sergestes similis off California, though Pearcy and 

 Forss found a 1-yr life span for the same species off 

 Oregon. Genthe asserted that juveniles less than 5 

 mm CL are 9 to 11 mo old, which seems too old. His 

 data support a 1-yr life span if a 2- to 3-mo larval 

 development time is assumed. Probably only a few 

 large all-red species live more than a single year. 



Sergia fulgens differed from all other Hawaiian 

 species by showing an extremely modal size- 

 frequency distribution and varying drastically in 

 abundance from one month to the next (Figure 

 18). This behavior can best be explained by as- 

 suming that S. fulgens is an expatriate species 

 occasionally moving into Hawaiian waters from 

 elsewhere. Adult females from the December 1970 

 cruise and the May 1973 cruise (Teuthis XXI) had 

 small ovaries with eggs about 150 jum in diameter. 

 Mature females of the closely related but smaller 

 species S. scintillans had proportionately larger 

 ovaries with eggs about 260 jum in diameter. Omari 

 (1969) reported an average diameter of 255 /xm for 

 another closely related species, S. lucens. It thus 

 appears that the large female S. fulgens are not 

 ripe. While it is possible that female S. fulgens 

 continue to grow to 18 or 20 mm CL before 

 spawning and that ripe females have never been 

 captured, it seems more likely that S. fulgens do 

 not reproduce in Hawaiian waters and that the 

 local population is carried in by currents from its 

 normal breeding range. Unfortunately, the geo- 

 graphic range of S. fulgens is almost totally 

 unknown; in addition, it is very similar or identical 

 to S. talismani in the Atlantic. Influxes of S. 

 fulgens did not coincide with captures of Sergestes 

 tantillus, an equatorial species occasionally found 

 in Hawaiian waters, but little more can be in- 

 ferred about the source of the local population of S. 

 fulgens. 



Interspecific Relationships 



The 20 species of Hawaiian sergestids exhibit a 

 variety of specializations in morphology and habit 

 that appear to minimize interspecific competition 

 and allow them to coexist as a stable assemblage. 

 Most obvious is the division into half-red and 

 all-red species, related to shallow and deep day- 

 time depth ranges and the different concealment 

 strategies required. The all-red sergestids are 

 subdivided by size and nighttime vertical dis- 

 tribution, as are the half-red sergestids, which are 

 also further subdivided by photophore type and 



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