Physical and Biological Zonation of Subarctic Tidal Flats at Frobisher Bay, Southeast Baffin Island

Abstract

<p> The interaction of biological and physical processes has resulted in distinct morphological and biological zonation across the Subarctic macrotidal tidal flats at the head of Frobisher Bay. The tidal flats have been divided into six morphological zones which are closely related to the three biological communities found there. </p> <p> Faunal species of the Upper Flat inhabit the beach and fines flat morphological zones where ice action during breakup and freezeup has the greatest influence. Species inhabiting these zones are hardy, and freshwater tolerant. Many are highly motile and recolonize the area after ice breakup. </p> <p> The Middle Flat extends from 5.0 m ALLT to 2.2 m ALLT. It is inhabited by motile polychaetes at its upper end (bouldery flat >4.5 m ALLT). with more sedentary species appearing towards its lower end (very bouldery flat). Below 2.2 m ALLT, on the Lower graded flat, sedentary infauna such as Cyrtodaria kurriana, Mya truncata and sabellid polychaetes, dominate the substrate. </p> <p> The three major processes acting on the tidal flats are, in order of importance, tidal, ice and wave action. Exposure indices, generated from tidal data, reveal 2 critical tidal heights at around 4 m and 7.5 m ALLT, in Frobisher Bay. The boundary between motile and less motile fauna, and bouldery and very bouldery morphological zones, occurs around 4.0 m ALLT. Of the flora and fauna only Fucus evanescens is found beyond the 7.5 m ALLT limit. </p>