Sedimentation and composition of wall communities in Alaskan fjords

The effects of suspended sediments on the composition of wall communities i n Alaskan fjords were investigated by quantitative assessment of underwater photo-quadrats. In fjords with actively retreating tidewater glaciers, sus pended sediment levels were extremely high at the heads and were exponentia lly lower at the mouths. Fjords without glaciers had low suspended sediment levels throughout. The per cent cover and number of species were lowest wh ere sedimentation was highest, at the heads of glacial fjords. Here the wal l communities were dominated by a sparse cover of small serpulid worms. Ric her communities comprising mostly algae, sponges, hydroids, bryozoans, tuni cates and brachiopods were found in fjords without glaciers, and at the mou ths of glacial fjords. There was a positive correlation between water clari ty and community composition along a gradient from heads to the mouths of f jords with high suspended sediment levels.