THE FEEDING AND ECOLOGY OF TWO NORTH PACIFIC ABARENICOLA SPECIES (ARENICOLIDAE, POLYCHAETA) 1 -2 KATHARINE D. HOBSON 3 Department of Oceanography, University of JVashinf/ton, Seattle, U 7 ashinc/ton 98105 Lugworms (Arcnicola and Abarenicola spp.) often occur in dense populations on sandy or muddy beaches throughout the world. The two genera are separated on the basis of differences in the prostomium, mechanism of proboscis movement, number of oesophageal caeca, and length of the neuropodia (Wells, 1959). When Wells (1963) summarized the worldwide distribution of lugworms, he noted that, despite certain morphological differences, the mode of life seems to be basically the same for all lugworms. When two species live in the same geographical location, they occur in different habitats. Thus, the sympatric species are ecologically separated. Most behavioral studies on lugworms have been concerned only with Arcnicola marina Linne. Wells (1945) described the burrow of A. marina as consisting of a vertical tail shaft, a horizontal gallery, and a vertical head shaft. The head shaft is a column of sand loosened by an irrigation current set up by peristaltic waves of the lugworm's body. The sand is consumed at the base of the head shaft and deposited later as fecal castings on the sediment surface near the tail shaft. Wells (1949) recorded the irrigation of the burrow and found it to be cyclical, spon-taneous, and predominantly headward. Kriiger (1958) observed that A. marina could ingest particles suspended in the irrigation current by straining them off in the sediment of the head shaft. The purpose of my research was to compare the ecology of the two genera of lugworms and of two sympatric species by studying the environment and feeding of two species of Abarenicola in False Bay, San Juan Island, Washington. These two species and Arcnicola marina belong geographically to the same lugworm zone (see Wells, 1963). The study area (Fig. 1) was centered around the Friday Harbor Laboratories, San Juan Island. Most field work was conducted in False Bay, a roughly circular tide flat (diameter at widest point is 1.2 km.), which consists at low tide of a series of bars and troughs extending from the head to the mouth of the bay. The populations of Abarenicola pacified Healy and Wells and A. claparcdi i'a</a-bunda Healy and Wells are patchy and are separated from each other by a lugworm-1 Contribution No. 404 from the Department of Oceanography, University of Washington, Seattle, Washington. 2 From a thesis submitted in partial fulfillment of the requirements for the M.S. degree, University of Washington, 1966. 3 Present address : Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts. 343
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