CRUSTACEA DECAPODA (BRACHYURA AND ANOMURA) 



237 



Knudsen (1967) showed that the coral-inhabiting xanthid 

 crabs, Trapezia and Tetraha, ate coral polyps after first 

 macerating them and, hence, were true parasites rather 

 than commensals. The coral burrowing crabs, family 

 Hapalocarcinidae (Fize and Serene, 1957), were used by 

 Knudsen in unpublished studies. The portunid crab, 

 Thalamita Integra, was used by Pomeroy and Kuenzler 

 (1967) in studies of phosphorus turnover by coral reef 

 animals. Highsmith (1981) involved the xanthid crabs, 

 Tetraha and Maldiuia, in studies of coral erosion by inver- 

 tebrates and fishes. Intertidal crabs of the family Xanthidae 

 were utilized by Havens (1974) in studies of competitive 

 exclusion (the partitioning of food resources). Wenner 

 (1977) and Wenner and Fusaro (1979) conducted studies 

 of population structure and dynamics using the Pacific 

 mole crab, Hippa pacifica. The xanthid 



crabs — Dacryopi/umnus eremita, Eriphia sebana, Phx^mo- 

 dius ung:jlatus, Pilumnus hngicornis, and Trapezia 

 speciosa — were shown by Danforth (1967, 1970) to host 

 epicarid isopod parasites of hitherto undescribed species. 

 The hermit crabs Dardanus were shown by Humes (1971) 

 to be hosts of harpacticoid copepods. The hermit crabs 

 Calcinus and Diogenes were used by Orians and King 

 (1964) in studies on shell selection and invasion rates. 



Systematic studies have been published on the genus 

 Petrolisthes, family Porcellanidae, by Haig (1981); on 

 coral-inhabiting crabs by Garth (1964); and on swimming 

 crabs, family Portunidae, by Stephenson and Rees (1967), 

 with additional studies by Garth, Haig, and Knudsen in 

 progress. 



POISONOUS CRABS 



During the 1970s Garth and Alcala (1977) showed 

 beyond a reasonable doubt that numerous reef-inhabiting 

 crabs of the Indo-West Pacific are harmful when eaten 

 because they are poisonous. Included among these are 

 several common Enewetak species: Daldorfia horrida (Lin- 

 naeus), Atergatis floridus (Linnaeus), Eriphia sebana (Shaw 

 and Nodder), and Zozvmus aeneus (Linnaeus). The first is 

 an elbow crab, family Parthenopidae; the remaining three 

 are members of the family Xanthidae, as are most of the 

 crabs found to be toxic to man and to domestic animals. 

 The poison, a saxitoxin, is chemically indistinguishable 

 from that produced by certain mollusks. It causes vomiting, 

 followed by locomotory and neurological symptoms which, 

 if not treated, result in paralysis and death. 



Crab-caused fatalities have been documented, and the 

 crabs were identified by competent taxonomists in the 

 Ryukyu Islands, the Philippines, and Palau. Native popula- 

 tions of many South Sea island groups have traditions of 

 killer crabs and vernacular names for the poisonous 

 species. Although no poisonings from crabs are known to 

 have occurred at Enewetak Atoll, crabs known to be poi- 

 sonous elsewhere are common on the reef at Enewetak. 

 Caution is urged in the handling of these crabs (a person 

 who has handled such a crab might experience numbness 



after touching his tongue to his hand). Abstinence from 

 their culinary use is also advised. 



FOSSIL CRUSTACEANS 



Fossil anomuran and brachyuran decapod species 

 obtained by U. S. Geological Survey drillings at Enewetak 

 and reported by Roberts (1964) include Callichirus armatus 

 (A. Milne Edwards), Ca//ichirus articulatus (Rathbun), 

 Actaeodes hirsutissimus (Riippell), and Etisus laevimanus 

 (Randall). Although known from elsewhere in the 

 Indo-West Pacific, these four species have not been found 

 living at Enewetak. This could mean cither that subtle 

 changes have occurred in the reef environment that render 

 Enewetak no longer a suitable habitat or, as seems more 

 likely, that the suite of species inhabiting Enewetak is 

 changing constantly as new species are introduced, become 

 established, are eliminated by competitors, and become 

 locally extinct until reintroduced in another cycle. It is also 

 possible that further and more diligent searching may yet 

 uncover these four species at Enewetak in the living state. 



COLLECTING DECAPOD 

 CRUSTACEANS' 



Enewetak Atoll ascends abruptly to the surface where 

 the North Equatorial Current, the prevailing trade winds, 

 and the oceanic waves strike the atoll. Waves refract all 

 the way around the atoll reef and penetrate the lagoon 

 through channels or over the algal ridge. Therefore, we 

 felt that every compass point, from windward to leeward, 

 would have unique physical factors that influenced distribu- 

 tion of both coral species (plus morphotypes of coral 

 species) and decapod crustaceans. This proved useful. 

 Since several other experts were to receive crustacean 

 specimens beyond our interest, much time was spent hunt- 

 ing new corals, crinoids, algae, and sediments that har- 

 bored decapods. 



The intertidal zone is shallow (based on Kwajalein 

 information), yet while zones are compressed, a centimeter 

 elevation on the reef flat would usually yield some different 

 brachyuran. We also believed zones directly below and 

 above the tidal range were relatively shallow but became 

 thicker (or deeper) down into the lagoon depth, or to the 

 height of land and its vegetation on islands. 



This, in theory, kept us close to the intertidal zone 

 where we thought the greatest species density of decapods 

 was to be, and apparently is, found. We collected on all 

 but three of the 34 named islands. The northwest chain 

 from Bogallua Island to Bogon Island was considered too 

 dangerous for camping trips as opposed to Tday M-boat 

 runs. Our radio carried less than 5 miles and the Equa- 

 torial Current flowed westward. Later, the Garth-Knudsen 

 teams found the restricted access limited the work on the 

 northwest chain as compared to that done on the more 

 accessible islands. 



"This section was provided by Jens Knudsen. 



