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|Title:||The habitat value of aquatic macrophytes for macroinvertebrates|
|Authors:||Aquatic Plant Control Research Program (U.S.)|
Miller, Andrew C.
Beckett, David C.
Way, Carl M.
Bacon, Edmond J.
Eau Galle Reservoir
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: In Eau Galle Reservoir, mean densities of bottom-dwelling macroinvertebrates among Ceratophyllum (35,260 organisms/m²) and Potamogeton (18,387 organisms/m²) were much greater than in no-plant zones (2,730 organisms/m²). Immature tubificids (without capilliform chaetae), the most commonly collected oligochaete taxon, were seven times more abundant in sediments associated with Ceratophyllum and nine times more dense in Potamogeton beds than in the no-plant zones. Very little difference in percent organic matter or particulate organic matter was noted among sediments from Ceratophyllum, Potamogeton , and no-plant areas. In the no-plant zones, 90.4 percent of the invertebrates were within the top (0- to 5-cm) depth fraction. Six percent were in the 5- to 10-cm depth fraction, and only 3.6 percent were in the 10- to 15-cm fraction. As in the no-plant zones, over 90 percent of the invertebrates collected below the Ceratophyllum and Potamogeton were in the 0- to 5-cm depth fraction. Although relatively few animals were found deeper than the 0- to 5-cm depth fraction, the organisms that were present 5 to 15 cm below the water-sediment surface were numerically dominated by nematodes, tubificids, and the gastropod Amnicola limnosa. Potamogeton nodosus had means of approximately 155 and 127 organisms per plant in June and August 1987. Seventy-six species of invertebrates were collected on these plants. In June 1987, a single P. nodosus plant supported 555 invertebrates (which included 177 chironomid larvae and 143 naidid worms) representing 36 taxa. Changes in invertebrate species composition occurred from early in the growing season of P. nodosus (June) to the peak of plant development (August). The oligochaete Nais pardalis existed in large numbers (15.3 individuals/plant) and was numerically dominant in June 1987, whereas it was completely absent from P. nodosus in August 1987. Not only did large phenological changes in invertebrate composition occur over the growing season of P. nodosus, but these changes were predictable and repeatable year after year. Studies on zooplankton in Eau Galle Reservoir were conducted during the summer of 1986. In sparse vegetation, rotifers made up 46.9 percent of the zooplankton assemblage, with approximately equal numbers of copepods (26.1 percent) and cladocerans (25.5 percent). However, in dense vegetation, copepods comprised more than 50 percent of the sample, while rotifers (20.2 percent) and cladocerans (21.8 percent) were subdominant. In the sparse vegetation, rotifers were more numerous than copepods. Macroinvertebrate assemblages were compared on live and imitation (plastic) plants in a Louisiana borrow pit lake to investigate the effects of stem and leaf structure on colonization. These plastic plants were morphologically similar to live plants and were colonized by diatoms, filamentous algae, and macroinvertebrates. Live Ceratophyllum demersum contained greater species diversity, species richness, evenness, and from 3 to 10 times as many organisms (per stem length) as the plastic Ceratophyllum and plastic Vallisneria, respectively. Ephemeropterans were the most common organisms on the live C. demersum and plastic Ceratophyllum, whereas ephemeropterans and chironomids were approximately codominant on plastic Vallisneria. Gastropods comprised 22 percent of the total number of individuals on the live C. demersum, which was 3.6 and 6 times their percentage on the plastic Ceratophyllum and plastic Vallisneria, respectively. Plastic Vallisneria and Ceratophyllum had a more even distribution of taxa across feeding guilds with a greater percentage of collector/gatherers, piercers/herbivores, and predators than the assemblages on the live plants. Differences between macroinvertebrates associated with live and plastic plants could not be explained by variation in stem and leaf morphology but appeared to be related to the density of the epiphytic algal community (algae growing on plants) that provided additional habitat for macroinvertebrates.
|Appears in Collections:||Technical Report|