Phytoplankton depletion in the benthic boundary layer caused by suspension-feeding Nereis diversicolor (Polychaeta):grazing impact and effect of temperature

A Vedel
1998 Marine Ecology Progress Series  
Mesocosm and field studies were conducted to examine phytoplankton depletion in b e n t h~c boundary layers caused by suspension-feeding N e r e~s d~vers~color populations at different temperatures It was demonstrated that the a b~h t y of the worms to deplete the bottom water of phytoplankton was highly correlated with temperature dependent f~ltration and water pumplng capac~ty At the optimum temperature of 17 8"C, the worm population (57 g m-2 dry wt) was able to deplete the water column of
more » ... e water column of phytoplankton to a maximum h e~g h t of 26 cm, In unstirred water The height of the algal depleted layer was controlled by a combination of the clearance capacity of the worms and the strength of vertical water m m n g generated by the water jets elected from the worm tubes The algal concentration in the boundary layer was reduced from the lnitial7000 to l0000 Rhodomonas cells m1 ' to a nunlmum of 1500 to 3000 cells ml ' within 2 to 4 h In the f~e l d the maximum height of the phytoplankton depleted zone was only 4 to 8 cm but considerable (25 to 40"(,) phytoplankton depletion occurred In the bottom layer, even at moderate to hlgh wind speeds (6 to 8 m s l ) Wlnd speeds were less than 8 nl S-' for approximately 70% of the season (March to August 1995) and thus algal depletion above dense populations of suspens~on-feeding N d~verslcolor may occur frequently In the shallow Odense Fjord, Denmark Due to the presence of an algal depleted boundary layer, N dlverslcolor was not able to control phytoplankton b~omass at the f~e l d s~t e in Odense Fiord, in spite of a considerable increment In f~ltration capacity from 1 7 to 6 9 m3 m-' d-' ( 3 to 14 t~m e s the water column a day) from March to August 1995 KEY WORDS: Phytoplankton depletion . Benthc boundary layer . Temperature effect . Grazing impact . Phytoplankton control O Inter-Research 1998 Resale of full a r t~c l e not pernl~tted
doi:10.3354/meps171125 fatcat:e5w2eocotbglzdawlo3keiuaze