Bt. Hentschel et Pa. Jumars, IN-SITU CHEMICAL INHIBITION OF BENTHIC DIATOM GROWTH AFFECTS RECRUITMENT OF COMPETING, PERMANENT AND TEMPORARY MEIOFAUNA, Limnology and oceanography, 39(4), 1994, pp. 816-838
To reduce the supply of a potentially limiting food for meiobenthos, w
e developed a new method to inhibit benthic diatom growth by perfusing
pore waters with herbicide diffusing from a buried gel. Placing the g
el in a bottom-sealed chamber constrained the chemical gradient to the
vertical dimension so that concentrations in overlying pore waters co
uld be predicted from a one-dimensional diffusion model. Our goal was
to determine whether the meiofaunal oligochaete Amphichaeta leydigii a
nd juveniles of the polychaete Hobsonia florida, whose adults deposit
feed, share benthic diatoms as a limiting resource during recruitment.
We verified that gels containing the herbicide DCMU inhibited microal
gal growth in the laboratory. The field DCMU manipulation also signifi
cantly reduced diatom abundance relative to control gels. The recruiti
ng H. florida population was divided at median size into two classes.
Development of feeding tentacles begins at that size-suggesting that s
ize classes differ in feeding mode. Smaller juveniles showed no signif
icant response to the treatment, while larger juveniles and oligochaet
es both had significantly reduced abundances in DCMU patches. No other
dominant meiofauna showed significant responses to the treatment. Cal
culated concentrations of DCMU in surficial sediments were approximate
ly 0.01-0.1 x those that cause lethal or sublethal effects on animals,
and nontarget invertebrates showed no significant effects-implying th
at A. leydigii and H. florida abundances varied because of the effect
of DCMU on diatoms rather than as a direct response to the chemical it
self This evidence of a shared resource suggests food limitation as a
competitive bottleneck between the meiofaunal oligochaete and recruiti
ng H. florida juveniles and a critical stage in the life history of th
e deposit-feeding polychaete.