Phycoperiphyton Development on an Artificial Substrate in the River Wye System, Wales, U. K. Part 1: Biomass Variation

Abstract

N i c t u wny:The phycoperiphyton on Perspes slides is inrestigated after an exposure for four weeks at six stat,icns in the upper course of the River IVye Syst,em from June 1979 to June 1981. The pigment contents were between 0.1 and 48 m g h n~ chloiophyll-a as well as 0.01 and 18 nipin12 phaeophytin with a unimodal or bimodal annual variation (minima in winter, maxima in Xpril and July). The biomass was between 55 and 11,000 cells/cm2 and is closely.rorrelated with c.lilorophyll in the annual variation. The algal community colonizing the artificial substrate shows only a very slight similarity to that on t,he nat,ural stones cf the water. The S0RENSEN index lies bet\veen 0.1 a.nd 0.7, the bioniass 011 the artificial sitbstrat)e nmount,s to only 0.7 ... 0.01 ooo, the rhlorophyI1 quantity only 0.5 ... 0.007of the values on t,he natural stones. Therefore, the periphyton on artificial substrates represents only B more or less restricted selection of t,he real natural phycoperiphyton. At four of the six stations, bioniass and chlorophyll are positively correlated with each other and with t,emperature and phosphorus concentration and negatively correlated wit'h flow, current velocity, oxygen concentration. linrdness and nitrate concent,ration. the phaeopliytin quant.ity only 1 ... 0.003 IiitroduetioiiThe qnantitative iiieasureinetits of the phycoperiphyton are often made difficiilt by the heterogeneous distribution of the popiilations, the variety of colonised substrata and the technical problems in rneasiiring the surface area of these substrates (CAT-TANEO, GHITTORI and VENDEGNA). Some other obstacles involve size variation of organisms and the difficulties in actual removal of the attached algae in flowing water without any loss or in a state cansing snbsequent difficnlties for the ineasrirenient of populations or photosynthetic pignients. To overconie some of these difficrilties, several authors have adapted the use of standardised artificial substrata for algal colonisation.A4ccording to TUCHMAE and BLINN and TITCIIMAN and STEVENSOX, artificial substrata can be used for comparing their algal coiiiniunities with those coloiiising the natural substrata. However, HELLAWELL reported t h a t the use of artificial substrata in quantitative studies is of doubtful value, particularly when the high numbers of colonising algae appear to be very unstable (BVTCHER; TIPPETT). The colonisation of such substrata by herbivorous invertebrates inay lead to anonialous results (LVND and TALLING). TIPPETT severely criticised the use of artificial substrata, and pointed out that the method, a t its best, can only he coiiiparative and shows relative changes in the flora.

The Epipelic Algal Flora of the River Wye System, Wales, U. K. 2. Algal Phyla and Species Population Dynamics

“…The other taxa ( Table 2 ) showed very inconsistent, insignificant to highly insignificant or even a lack of correlation between any of them, on both substrata at all sites. A similar finding was also reported for algal taxa colonising both the perspex (artificial substratum) and stone surfaces (ANTOINE & BENSON- EVANS, 1986). Therefore, the distribution of the algal taxa in the epilithic and epipelic algal communities of the River Wye System was not comparable during most of the study period.…”