PARASITES OF BENTHIC AMPHIPODS: DINOFLAGELLATES 

 (DUBOSCQUODINIDA: SYNDINIDAE) 



Phyllis T. Johnson 1 



ABSTRACT 



During a 2V2-yr survey, 13 species of benthic amphipods collected from the continental shelf of the north- 

 eastern United States were found infected by dinoflagellates. Prevalences ranged from <1% to 67%, 

 depending on amphipod species, time, and place of collection. The parasites are assigned to the order 

 Duboscquodinida, family Syndinidae, based on similar life histories and a similar kind of mitosis ("mitose 

 syndinienne"). Two types of organisms were involved, both apparently more closely related to 

 Hematodinium Chatton and Poisson than to other described syndinids. Morphology and development 

 of the parasites and host-parasite interactions are discussed. A cytochemical method used to determine 

 presence or absence of basic nuclear proteins was strongly positive for basic proteins in spores and 

 prespores but negative in most other stages. A few spores in four infections possessed a distinct flagellum, 

 but in the absence of living material, shape of spores and whether they were biflagellate could not be 

 determined. With three possible exceptions in the group of 303 infections studied, the syndinids were 

 not recognized as foreign by their hosts, and in joint infections of syndinids and fungi, only the fungi 

 were being attacked by host hemocytes. High prevalences in certain of the amphipod species suggest 

 that the syndinids might be population regulators in these species. 



This paper is one of three that describe and discuss 

 the more common parasites found in populations of 

 benthic amphipods of the continental shelf of the 

 northeastern United States. The other papers con- 

 cern microsporidans and ciliates (Johnson 1985, 

 1986). 



Because my observations on the parasites dis- 

 cussed in this paper were based on examination of 

 histological sections, I could not determine whether 

 spores were typical "dinospores". However, agree- 

 ment with other developmental stages of well- 

 studied species of syndinids from copepods and an 

 amphipod, and the nuclear type, indicates that the 

 parasites of benthic amphipods are related to species 

 currently placed in the Syndinidae, order Dubosc- 

 quodinida (sensu Chatton 1952 and Cachon 1964). 

 Previously described syndinids occur intracellular- 

 ly in radiolarians and in copepod and shrimp eggs 

 (Chatton 1952; Stickney 1978) and extracellu- 

 larly in the hemocoel of copepods, an amphipod, 

 and portunid and cancrid crabs (Chatton and Pois- 

 son 1931; Chatton 1952; Manier et al. 1971; 

 Newman and Johnson 1975; MacLean and Ruddell 

 1978). 



The relationship of the Duboscquodinida to free- 

 living dinoflagellates is in doubt (Cachon 1964; Ris 

 and Kubai 1974; Siebert and West 1974; Hollande 

 1975; Loeblich 1976; Herzog et al. 1984). Lacking 



a definitive consensus, the parasitic protists dis- 

 cussed here are provisionally referred to the Dino- 

 flagellata. 



The data presented and discussed in this paper 

 show that species of syndinids are probably ubiqui- 

 tous hemocoelic parasites of benthic and epibenthic 

 amphipods, and may be population regulators in 

 some species. 



METHODS 



The data are based on material collected during 

 monitoring surveys carried out over a 2V2-yr period 

 by the Northeast Fisheries Center, National Marine 

 Fisheries Service. The 35 stations where benthic am- 

 phipods were collected during the surveys are shown 

 in Figure 1. Amphipods were sampled during 11 

 cruises, but not all stations were visited on each 

 cruise, so that stations were sampled from 1 to 10 

 times each during the survey. A Smith-Mclntyre 2 

 grab and occasionally an epibenthic sled or scallop 

 dredge were used to obtain the samples. The 11 sta- 

 tions indicated by solid circles on Figure 1 had the 

 most consistent and numerous populations of am- 

 phipods, and were sampled at least five times each. 

 They yielded the majority of data presented here. 



Amphipods were preserved in 10% seawater 

 Formalin. Up to 30 individuals of each species pres- 



'Northeast Fisheries Center, National Marine Fisheries Service, 

 NOAA, Oxford, MD 21654. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Manuscript accepted October 1985. 

 FISHERY BULLETIN: VOL. 84, NO. 3, 1986. 



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