FISHERY BULLETIN: VOL. 83, NO. 4 



Table 1.— Sampling cruises for benthic amphipods, July 1980- 

 December 1982. 



consistent, and usually numerous, amphipod popula- 

 tions and were sampled five or more times. They 

 yielded the majority of data presented in this pa- 

 per. 



Collections of bottom sediments and accompany- 

 ing biota were made with a 0.1 m^ Smith-Mclntyre^ 

 grab. Generally a single grab was taken at each sta- 

 tion sampled. If the first grab contained few amphi- 

 pods but was from a station where they usually were 

 abundant, a second and sometimes a third grab was 

 taken. Sediment contained in the grab was washed 

 through a 1.0 mm sieve, and amphipods were either 

 collected with forceps or gently scraped from the 

 sieve and placed in a jar of 10% seawater Formalin. 

 On cruises A, B, and E (see Tkble 1), supplemental 

 specimens were collected at some stations by use of 

 an epibenthic sled or scallop dredge 



Storage of samples was in Formalin except that 

 amphipods were transferred temporarily into 30 ppt 

 artificial seawater for identification and enumera- 

 tion, inspection for various gross lesions, and for 

 determination of life-history stages and microspori- 

 dan infections of the muscle in the case ofAmpelisca 

 agassizi (Judd). A stereomicroscope was used for 

 these procedures. Up to 30 and occasionally more 

 individuals of each species in the sample, depending 

 on numbers present, were processed for histologi- 

 cal examination by standard means. Finished tissue 

 sections were stained with hematoxylin and eosin. 

 Depending on size and number to be embedded, 1 

 to 12 amphipods of a single species from a single 

 station were embedded on their sides in each paraf- 

 fin block. Several serial sagittal sections were taken, 

 first laterally and then near the midline of the amphi- 

 pods. Because of unavoidable variations in size and 

 depth of the amphipods in the block, not all were sec- 

 tioned at the same levels. Parts of the hemocoel, 



^Reference to trade names does not imply endorsement by tiie 

 National Marine Fisheries Service, NOAA. 



skeletal muscle, and appendages of all amphipods 

 were present in sections. Usually, parts of the gills, 

 hepatopancreas and other parts of the gut, heart, 

 brain, and gonads were also present. Other tissues 

 and organs, particularly the antennal gland, hemo- 

 poietic tissues, eyes, and ventral nerve cord, often 

 were not included. 



Measurements of microsporidan spores were 

 based on fixed material, either whole or embedded, 

 sectioned, and stained. 



RESULTS 



The amphipod population sampled at any one time 

 at a particular station was a mixture of up to 14 dif- 

 ferent species. Commonly five to eight species were 

 collected in a single grab except at station 23, which 

 was strongly dominated by Ampelisca agassizi. Of 

 eight samples from station 23, three contained only 

 A. agassizi, and A. agassizi made up 94 to 99% of 

 the remaining samples. Ibtals of the eight samples 

 from station 23 were 2,788 individuals of A. 

 agassizi and 23 individuals of other species (99% A. 

 agassizi). 



Ampelisca agassizi was the most numerous and 

 broadly distributed of the species investigated, and 

 occurred at 17 stations including the 11 major ones. 

 Certain information on the life history of this species 

 is pertinent. It is an annual, tube-building species 

 that produces a single brood of young (Bousfield 

 1973). Overwintering is in the juvenile stage Gonads 

 of both sexes develop during the subadult stage 

 Breeding begins in the spring, and newly ovigerous 

 females are found from spring through autumn. 

 Postovigerous females tend to remain in the popula- 

 tion for an unknown period after the young are re- 

 leased from the brood pouch. Adult males are pelagic 

 or epibenthic, probably short-lived, and usually were 

 missing from samples collected with the Smith- 

 Mclntyre grab. Only the adult male has strongly 

 developed transverse pleosomal muscles (muscles of 

 the first three abdominal segments) (Fig. 2). 

 Presumably, these muscles aid in swimming. The 

 transverse muscles lie lateral to the longitudinal 

 muscles and are developed during the subadult stage 

 They can be seen in various stages of development 

 through the translucent cuticle of subadult 

 males. 



Females of the gammaridean, tube-dwelling 

 amphipods so far studied leave their tubes to molt 

 to the adult stage Mating and egg extrusion take 

 place in the water column (Mills 1967). Population 

 dispersal is presumed to occur either by ovigerous 

 females settling away from their original location 



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