MEPS 241:215-220 (2002)  -  doi:10.3354/meps241215

Ontogeny of phototaxis and geotaxis during larval development of the sabellariid polychaete Phragmatopoma lapidosa

Daniel A. McCarthy1,*, Richard B. Forward Jr.2, Craig M. Young1

1Department of Larval Ecology, Harbor Branch Oceanographic Institution, 5600 US Hwy 1 N, Ft. Pierce, Florida 34946, USA
2Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, North Carolina 28516, USA

ABSTRACT: Thorson generalized that the larvae of intertidal animals should remain photopositive throughout larval life to facilitate encounters with shallow surfaces at settlement. We tested this idea for the sabellariid polychaete Phragmatopoma lapidosa by investigating ontogenetic changes in phototaxis and geotaxis of well-fed, laboratory-reared larvae. Larvae at each of 5 age groups were exposed to (1) 8 different light intensities from a directional light source in a horizontal trough and (2) complete darkness in a vertical chamber. Phototaxis changed with age. Half-day old larvae were not responsive to light, 1 d old larvae were positively phototactic, and all older larvae to 28 d age were negatively phototactic. Larvae from 0.5 to 28 d age were positively geotactic with the exception of 5 d old larvae, which lacked a defined response. Consequently, larvae of the predominantly intertidal P. lapidosa did not conform to Thorson¹s suggestion of continuous positive phototaxis in intertidal species.


KEY WORDS: Phototaxis · Geotaxis · Polychaete · Larvae · Phragmatopoma lapidosa


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