OFFSHORE DISTRIBUTION OF HYDRACTINIA ECHINATA 



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By Arthur S. Merrill, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 



Oxford, Maryland 21634 



ABSTRACT 



New distributional records for this hydroid are listed 

 from 81 offshore locations along the Middle Atlantic 

 region and from Georges Bank, off Massachusetts. The 

 species was commonly found living on the shells of ani- 

 mals having some degree of mobility — sea scallops (Placo- 

 pecten magellanicus ) , and gastropod shells inhabited by 



predominantly gravelly — a mixture of sand, pebble, and 

 shell. Depths at sampling stations ranged from 16 to 80 

 fathoms; depths where the hydroid occurred ranged from 

 16 to 62 fathoms. Deeper stations had soft substrates con- 

 taining silt and clay, unsuitable for semimotile animals 

 and lacking the hard substrate necessary for hydroid 



pagurid crabs. The bottom substrate for these aninoals is colonization. 



Hydractinia echinata (Fleming:) is circum- 

 polar in its principal distribution (Fraser, 

 1946). Fraser (1944) documented the distribu- 

 tion of this hydroid in the western Atlantic, 

 mostly in shoal waters from Salmon Bay, 

 Labrador, to Charleston Harbor, S.C. He re- 

 corded numerous locations around the New 

 England coast but none from Georges Bank, 

 although he did include a locality from Georges 

 Basin, near Georges Bank. Only a few scattered 

 and inshore localities were listed for the great 

 Middle Atlantic region. Deevey (1950) ex- 

 tended the range to the Gulf of Mexico. 



The purpose of this paper is to describe the 

 bathymetric distribution of Hydractinia echi- 

 nata. Eighty-one new locations on Georges 

 Bank, off Massachusetts, and on the continental 

 shelf of the middle Atlantic bight from depths 

 3f 16 to 62 fathoms (fig. 1), complement 

 Fraser's (1944) records from Cape Cod north- 

 ward. I acquired these data while on research 

 cruises relating to the sea scallop, Placopecten 

 rnagellanicus (Gmelin) (Merrill, 1962; Merrill 

 and Posgay, 1964). This paper is part of a 

 general study to evaluate the significance of 

 an adverse effect of this hydroid epizoon on 

 the commercially important sea scallop (Mer- 

 rill, 1967). 



The hydroid was found colonizing the shells 

 of live sea scallops and the shells of gastropods 



FISHERY BULLETIN: VOLUME 66, NO. 2 



occupied by pagurid crabs. The scallops and 

 crabs are mobile and inhabit hard rather than 

 soft bottom. Generally, the substrates of sta- 

 tions shallower than 60 fathoms were pre- 

 dominantly sand, pebble, and shell, whereas 

 those deeper than 60 fathoms contained much 

 silt and clay. Depths of the sampling stations 

 ranged from 16 to 80 fathoms. The deepest 

 record for the hydroid was 62 fathoms, which 

 coincided with the greatest depth at which 

 scallops and crabs were taken. 



Data on the bathymetric range of Hydrac- 

 tinia echinata are S'pa.rse. Verrill (1885) stated 

 it was common from low water to 60 fathoms. 

 Smith and Harger's (1874) greatest depth was 

 65 fathoms. Fraser (1944, 1946) reported the 

 following deepwater locations: 42''02'15" N., 

 70°15' N. [sic]. Cape Cod Bay, 362 fathoms; 

 42°03' N., 70°37' W., 30 miles off Cape Cod light, 

 106 fathoms ; 52°01' N., 68°00'30" W., off Cape 

 Cod, 86 fathoms. The first two positions are 

 shoal waters, under 25 fathoms. Furthermore, 

 Cape Cod has no water 362 fathoms deep, nor 

 has the w^hole Gulf of Maine. His third location 

 in 86 fathoms is possible. 



A few records from Georges Bank have been 

 noted in the literature. Smith and Harger 

 (1874) listed Hydractinia polyclina (= Hy- 

 dractinia echinata) from five stations on the 

 Bank near Cultivator Shoal, the Northern 



281 



Published July 1967 



