title for learn-about lugworms & relatives
  Predators & defenses
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Research study 1
 

graph showing difference in % worms Abarenicola pacifica defecating with and without their tail ends

Loss of parts of the body to predators is not uncommon in burrowing forms such as Abarenicola pacifica (F. Arenicolidae) and Axiothella rubrocincta (F. Maldanidae) that feed head-down and expose their tails while defecating, or in deposit-feeding forms such as Pygospio elegans (F. Spionidae) that feed on the sediment surface with head and tentacles exposed.  Fortunately, the parts are readily regenerated. But what effect is there be on burrowing and/or defecating. Research at Friday Harbor Laboratories, Washington on effects of experimental excision of tails in the first 2 species, or of tentacles in the last species show that losses of about 10% of the worms’ lengths do not affect burrowing, but do temporarily affect defecating.  When replaced in the field after being dug up and handled, control lugworms Abarenicola pacifica are mostly defecating normally after about 5d.  In comparison, only 50% of TAIL-EXCISED worms are defecating normally after 5d, and full recovery for most worms takes several days longer. Note, however, that a small fraction of worms have not fully regenerated (that is, enough for defecation to occur) even after 3wk. Woodin 1984 Biol Bull 166: 558.

NOTE  effects on defecation of tentacle loss in the spionid Pygospio are apparently not measurable because of its small size, but the author reports no significant change in mass of tubes after excision

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Research study 2
 

photograph of English sole Parophrys vetulusA study by researchers from the School of Fisheries, University of Washington on diets of 3 species of flatfishes (English sole Parophrys vetulus, Dover sole Microstomus pacificus, and rex sole  Glyptocephalus zachirus) in soft-bottom habitats in Puget Sound, Washington reveals a selective predation on Capitella spp.  The fishes eat more worms at night than in the day, suggesting that in this area the flatfishes, normally daytime feeders, have altered their behaviour to include nighttime feeding.  Becker & Chew 1987 Fish Bull 85: 471.

NOTE  all species categorised as being “small-mouthed” pleuronectids, specialised to feed on small infaunal and epifaunal benthic invertebrates

NOTE  thus, proportions of Capitella of all prey items in the stomachs significantly exceed their proportions in the natural habitat

 

English sole Parophrys vetulus showing mouth 1.3X

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Research study 3
 

histogram comparing numbers of predators of Capitella sp. at 2 siteshistogram comparing predation on Capitella sp. at 2 sitesResearchers at the Bamfield Marine Sciences Centre, British Columbia use a marking technique to follow and compare predation on Capitella sp. at 2 mudflat sites, Grappler and Bamfield.  Rectangular core samples are taken from mid-intertidal heights at each site and placed in trays in the laboratory.  To these trays and to equal numbers of predator-free (sieved-mud) control trays are added 100 sibling juveniles marked with neutral red.  The trays are set out in the field for 9d then returned to the laboratory and sieved to remove all worms, including surviving Capitella and any predatory worms present.  In addition to recording numbers of juveniles eaten, the authors also measure growth rates of the juveniles in situ (data not included here).  Results disclose a significant difference in numbers of predators at each site (see histogram on Left) and this is thought to explain the significant difference in mortality rates at the 2 sites (see histogram on Right). The authors note that juvenile mortality by predation thus appears to be a major factor affecting the recruitment and population dynamics of Capitella sp. at the 2 study sites. Qian & Chia 1994 Mar Ecol Progr Ser 111: 53.

NOTE  a 2-min immersion in a seawater solution of the vital die neutral red  is used to mark the worms

NOTE  predators in the Grappler site are mainly the polychaetes Nereis virense and Glycera americana, while those at the Bamfield site appear to be mainly spionid polychaetes.  The 2 sites are otherwise similar in physical and chemical features

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