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

Tubes of the ampharetid polychaete Sabellides sibirica are a prominent yet spatially variable habitat feature in shallow-water flatfish nurseries around Kodiak, Alaska, USA. Juvenile flatfish associate with the edges of worm tube regions but seldom use the dense 'turf-like' worm beds that sometimes form on the bottom in the late summer. The present study used a fine-scale analysis (2 to 3 m) to examine how juvenile flatfish distribution changed with worm tube heterogeneity, i.e. density and patchiness. Using a video sled, 8 transect lines (similar to 250 m each) were repeatedly surveyed from late summer to mid-winter in a worm tube region of Pillar Creek Cove, half of which were experimentally disturbed using simulated trawl gear. Results indicated that juvenile flatfish (mainly northern rock sole Lepidopsetta polyxystra) increasingly use patches of bare substrate as worm tube densities increase. However, the simulated trawl disturbance resulted in a unique 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 disturbance, whereas natural patches persisted throughout the entire study. Flatfish abundance increased in trawl-disturbed worm tube beds for only a short period (2 d), possibly due to episodic foraging opportunities rather than physical changes in habitat. These results indicate that worm tube habitat is provisionally resilient to disturbance, and its heterogeneity (density, patchiness, and patch type) is an important component of habitat quality for juvenile flatfish in Alaska.