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EFFECTS OF IRRADIANCE AND GRAZING ON LOTIC ALGAL ASSEMBLAGES 1
Author(s) -
Steinman Alan D.,
McIntire C. David,
Gregory Stanley V.,
Lamberti Gary A.
Publication year - 1989
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.1989.tb00253.x
Subject(s) - biology , periphyton , streams , biomass (ecology) , zoology , algae , grazing , light intensity , irradiance , chlorophyll a , ecology , diatom , botany , computer network , physics , quantum mechanics , computer science , optics
A laboratory experiment was conducted for 75 days to examine how irradiance levels and grazing influence algal biomass and community structure. Twelve laboratory streams were used for experimental analyses, with four channels exposed to one of three irradiance levels (15, 100, or 400 μE·m −2 ·s −1 ). Three of the four stream at each light level were stocked with the snail Juga silicula (250·m −2 ), leaving one stream at each light level without snails. Grazed stream exposed to low light levels developed low amounts of algal biomass (<2 g AFDW·m −2 ) and were dominated by adnately attached diatoms. Mean algal biomass increased over time in the grazed streams exposed to intermediate light; by day 75, these streams were characterized by moderate algal biomasses (30‐40 g AFDW·m −2 ) and filamentous chlorophytes. Algal assemblages in high light, grazed channels had high levels of biomass at day 43 (70 g AFDW·m −2 ) that declined to 30 g AFDW·m −2 at day 75 and were dominated by chlorophytes. Among ungrazed streams, algal biomass at day 75 was relatively low in the low light streams (<7g AFDW·m −2 ) and was dominated by adnately attached diatoms. Ungrazed streams exposed to intermediate and high light levels had moderate biomasses (23 and 19 g AFDW·m −2 , respectively) and were dominated by chlorophytes and large diatoms. Grazing appeared both to delay and alter successional trajectories of algal assemblages, with alterations most noticeable during early seral stages at intermediate and high light levels. Grazing had the least effect on successional trajectories at low light.