Effects of natural and anthropogenic disturbance on polychaete worm tubes and age-0 flatfish distribution

Abstract

ABSTRACT: Tubes of the ampharetid polychaete Sabellides sibirica are a prominent yet spatiallyvariable habitat feature in shallow-water flatfish nurseries around Kodiak, Alaska, USA. Juvenileflatfish associate with the edges of worm tube regions but seldom use the dense ‘turf-like’ wormbeds that sometimes form on the bottom in the late summer. The present study used a fine-scaleanalysis (2 to 3 m) to examine how juvenile flatfish distribution changed with worm tube hetero-geneity, i.e. density and patchiness. Using a video sled, 8 transect lines (~250 m each) were repeat-edly surveyed from late summer to mid-winter in a worm tube region of Pillar Creek Cove, half ofwhich were experimentally disturbed using simulated trawl gear. Results indicated that juvenileflatfish (mainly northern rock sole Lepidopsetta polyxystra) increasingly use patches of bare sub-strate as worm tube densities increase. However, the simulated trawl disturbance resulted in aunique kind of patchiness, typified by long, thin exposed regions of bare substrate referred to as‘combing’. Unlike natural patches, evidence of combing disappeared 2.5 mo after the initial distur-bance, whereas natural patches persisted throughout the entire study. Flatfish abundance in-creased in trawl-disturbed worm tube beds for only a short period (2 d), possibly due to episodicforaging opportunities rather than physical changes in habitat. These results indicate that wormtube habitat is provisionally resilient to disturbance, and its heterogeneity (density, patchiness, andpatch type) is an important component of habitat quality for juvenile flatfish in Alaska.KEY WORDS: Coastal habitats · Benthic recovery · Patchiness · Habitat heterogeneity · Northernrock sole