LAGCXDN PLANKTON 



213 



researchers used rather coarse mesh nets which did not 

 adequately sample this group consisting mostly of smaller 

 forms; this perhaps accounts for the few species recorded. 

 About 27 species were recorded at Enewetak Lagoon by 

 Barnett (1967) and included those species identified there 

 previously; Gerber (1981) identified 28 species which 

 included most of Barnett's species and several additional 

 species. Only one cyclopoid copepod, Corycaeus curtus, 

 recorded at Rongelap has not been found at Enewetak 

 Lagoon. In the surrounding waters of Bikini Atoll, 29 

 species were found by Chiba et al. (1955), but only 13 of 

 these occur within the lagoon at Enewetak. Four cyclopoid 

 genera were recorded at Majuro Atoll Lagoon from the 

 stomach contents of plankton feeding fishes (Hobson and 

 Chess, 1973), all of which have been recorded from 

 Enewetak and include Oncaea sp., Conjcaeus sp., 

 Sapphirina sp., and Saphirella sp. For identification and 

 taxonomy of cyclopoid copepods at Enewetak, the follow- 

 ing works should be consulted: Dahl (1912), Dakin and 

 Colefax (1940), Farran (1911), Giesbrecht (1889), Mori 

 (1937), Motoda (1963), Scott (1909), and Wilson (1942). 



Few harpacticoid copepods are strictly holoplanktonic, 

 and of these, five species have been found in the 

 Enewetak Lagoon. They include members of the first three 

 families presented in the checklist under this order. Gilmar- 

 tin (1958) identified one of these species, Barnett (1967) 

 identified three species, and Gerber (1981) found four of 

 these species. At a shallow station (2 m depth) behind a 

 windward reef area of the lagoon, Gerber (1981) collected 

 in net tows 16 species of harpacticoids that are believed to 

 be epibenthic types. These were restricted to the shallow 

 station and may have been inadvertently washed from 

 adjacent coral reefs. Harpacticoid copepods were also in 

 the lagoon plankton and in the gut contents of various 

 fishes (e.g., Gerber and Marshall, 1974; Hobson and 

 Chess, 1978), but these were not identified. A thorough 

 study of the epibenthic harpacticoid copepods has not 

 been made at any location in the Marshall Islands. The five 

 pelagic species noted above were not identified from net 

 tow samples in the neighboring waters of Bikini Atoll 

 (Chiba et al., 1955). This suggests that they are probably 

 neritic types, surviving best in shallower protected areas 

 such as atoll lagoons. 



Both Barnett (1967) and Gerber (1981) identified 

 members of a single genus belonging to the other Monstril- 

 loida. Whether the same species were represented in both 

 studies is not known, because no identifications were made 

 to the species level. Monstrilloid copepods occurred only 

 rarely in net collections in both studies, and no reference 

 indicates that they occur outside of atoll lagoons in the 

 Marshall Islands. Information on the identification and tax- 

 onomy of harpacticoid and monstrilloid copepods from 

 Enewetak are scarce, but the following works are helpful: 

 Dakin and Colefax (1940), Lang (1948), Scott (1909), and 

 Vervoort (1964). 



Mysidacea 



A detailed investigation of the mysids at Enewetak 

 Atoll has not been carried out. A planktonic mysid was 



collected in net tows by Gilmartin (1958) at Enewetak 

 Lagoon, but the specimen was not identified. Swarms of 

 mysids belonging to two genera (Sirie//a and Mysinae) were 

 observed and collected over lagoon patch reefs at 

 Enewetak by Hobson and Chess (1978); Gerber (1981) 

 identified eight species of mysids from net tows at a 

 nearby shallow station; and Murano (1983) identified seven 

 species from net tows and emergence traps at depths 

 between 2 and 10 m. Further samplings, especially at 

 night, would no doubt reveal additional specimens. Uniden- 

 tified mysids were recorded in the plankton and in the gut 

 contents of plankton feeding fishes at nearby Majuro Atoll 

 Lagoon by Hobson and Chess (1973). Plankton tows in the 

 oceanic waters near Bikini Atoll by Chiba et al. (1955) 

 revealed two species of mysids, Sihella thompsoni and 

 Siriella sp., and Tattcrsall (1951) described two additional 

 species of Siriella from the Marshall Islands (S. vulgaris ros- 

 trata. S ar^omala) and Anchialina t\;pica and A. penicillata. 

 As noted earlier, the genus Siriella was first recorded 

 inside the lagoon at Enewetak by Hobson and Chess 

 (1978), and later two other lagoon Siriella were identified 

 to species by Murano (1983). Several excellent works by 

 Hansen (1910) and Tattersall (1957) have proved useful in 

 identifying the mysids from Enewetak. 



Isopoda 



The isopods which have been collected in plankton net 

 hauls from Enewetak Lagoon have not been identified to 

 genera (e.g., Gilmartin, 1958; Hobson and Chess, 1978; 

 and Gerber, 1981). This group is generally scarce in such 

 samplings indicating that they arc most likely of epibenthic 

 origin rather than planktonic. Planktonic isopods from 

 other atoll lagoons or in the oceanic waters in the Marshall 

 Islands have not been collected. 



Amphipoda 



At least three and possibly four species of holoplank- 

 tonic amphipods that belong to the suborder Hyperiidea 

 have been reported from the Enewetak Lagoon (Gerber, 

 1981). Earlier plankton collections by Gilmartin (1958) 

 revealed one unidentified species, and Hobson and Chess 

 (1978) recorded but did not identify several species of 

 hyperiids. Many more nonplanktonic species occur within 

 the lagoon (Barnard, 1965), and these arc mostly gam- 

 marids which occur in the epibenthic shallow water habitat 

 discussed elsewhere in this book. Barnard (1965) reported 

 one gammarid species, Si/nopia variabilis, which was col- 

 lected from Enewetak and Ifaluk Lagoons by both plankton 

 haul and dip-netting with a night light; it is included in the 

 checklist. Hyperiid amphipods have been recorded at 

 Majuro Atoll (Hobson and Chess, 1973) where one 

 species, Lestrigonus benga/ensis, was identified from net 

 tows and made up an important dietary component of 

 antherinid fish. In the oceanic waters around the Marshall 

 Islands, Chiba et al. (1955) collected nine species of 

 planktonic amphipods, none of which appear to occur in 

 Enewetak Lagoon. These are Ox\jcephalus porcellus, 

 Phronima pacifica. Phronima sp., Leptocotis tenuirostris, 



