Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers

Brostoff Wn, Holmquist Jg, Schmidt-Gengenbach J, Zimba, Zimba Pv

Description

Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous blue-green algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species. Results We found two species of fairy shrimps ( Branchinecta mackini and B. gigas ), one tadpole shrimp ( Lepidurus lemmoni ), and a clam shrimp ( Cyzicus setosa ) in our wet-season field survey. We collected Branchinecta lindahli in a pilot study, but not subsequently. The dominant taxa were C. setosa and B. mackini , but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition ( Microcoleus vaginatus dominated all treatments). Conclusions The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment.

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• Publié par: biomed
• Publié le: 01 janvier 2010
• Nombre de lectures: 9

Extrait

Brostoffet al.Saline Systems2010,6:11 http://www.salinesystems.org/content/6/1/11

SALINE SYSTEMS

R E S E A R C HOpen Access Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers 1*†2†2 3 WN Brostoff, JG Holmquist, J SchmidtGengenbach , PV Zimba

Abstract Background:Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous bluegreen algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species. Results:We found two species of fairy shrimps (Branchinecta mackiniandB. gigas), one tadpole shrimp (Lepidurus lemmoni), and a clam shrimp (Cyzicus setosa) in our wetseason field survey. We collectedBranchinecta lindahliin a pilot study, but not subsequently. The dominant taxa wereC. setosaandB. mackini, but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition (Microcoleus vaginatusdominated all treatments). Conclusions:The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment.

Background Branchiopods and algae/cyanobacteria are often the dominant organisms inhabiting the flat, internally drained, and generally lowelevation playas [1] of arid basins in the desert U.S. Southwest, particularly the smaller playas referred to as pans [24]. This study investigated 1) branchiopod assemblage structure of flooded, lowsalinity pans in the western Mojave Desert, California, USA, and 2) possible grazing effects of these shrimps on algae. The distribution and diversity of fairy, tadpole, and clam shrimps in ephemeral pools have

* Correspondence: [e-mail] †Contributed equally 1 Environmental Planning, U.S. Army Corps of Engineers, 1455 Market St., San Francisco, CA 94103, USA Full list of author information is available at the end of the article

been the focus of researchers and environmental man agers in recent years in part because several species are listed as Threatened or Endangered Species in the Uni ted States [5]. The branchiopods of the playas and pans of the arid southwest U.S. have received less attention, perhaps because threatened or endangered species have not been reported [6]. Algae are often dominant and conspicuous as floating filamentous aggregations in inundated pans, on the moist edges of the pans, and on both the dry pan surface and adjacent upland areas where the algae form characteristic biotic crusts [7]. Brostoff et al. [3] estimated the photo synthesis of the constituent algae in biotic crusts on 2 moist surfaces of the pans at 4μmol C/m /sec, a rate that is the same order of magnitude as nearby upland vegetation (no such data are available for algae during

© 2010 Brostoff et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.