Brostoff et al. Saline Systems 2010, 6:11 http://www.salinesystems.org/content/6/1/11 SALINE SYSTEMS RESEARCH Open Access Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers WN Brostoff1*†, JG Holmquist2†, J Schmidt-Gengenbach2, PV Zimba3 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 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. Background been the focus of researchers and environmental man- Branchiopods and algae/cyanobacteria are often the agers in recent years in part because several species are dominant organisms inhabiting the flat, internally listed as Threatened or Endangered Species in the Uni- drained, and generally low-elevation playas [1] of arid ted States [5]. The branchiopods of the playas and pans basins in the desert U.S. Southwest, particularly the of the arid southwest U.S. have received less attention, smaller playas referred to as pans [2-4]. This study perhaps because threatened or endangered species have investigated 1) branchiopod assemblage structure of not been reported [6]. flooded, low-salinity pans in the western Mojave Desert, Algae are often dominant and conspicuous as floating California, USA, and 2) possible grazing effects of these filamentous aggregations in inundated pans, on the moist shrimps on algae. The distribution and diversity of fairy, edges of the pans, and on both the dry pan surface and tadpole, and clam shrimps in ephemeral pools have 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 * Correspondence: [email protected] 2 † Contributed equally moist surfaces of the pans at 4 μmol C/m /sec, a rate 1Environmental Planning, U.S. Army Corps of Engineers, 1455 Market St., San that is the same order of magnitude as nearby upland Francisco, CA 94103, USA vegetation (no such data are available for algae during Full list of author information is available at the end of the article © 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. Brostoff et al. Saline Systems 2010, 6:11 Page 2 of 8 http://www.salinesystems.org/content/6/1/11 the inundated phase). The fate of such productivity is The soil composition was 20% clay, 40% sand, and 40% unclear, although fairy and clam shrimps ingest and silt. The pans were surrounded by dunes, ranging from digest planktonic and benthic algae, along with detritus 0.5 to 10 m in height; many dunes have a luxuriant bio- and suspended organics, via non-selective filter feeding tic crust cover, particularly adjacent to frequently inun- or scraping [8-13], and algal material can be the primary dated areas [7]. The vegetation around the pans is food resource of these shrimps [13-16]. Adult tadpole characteristically halophytic occurring in narrow belts of shrimps are opportunistic predators and scavengers, and strongly salt tolerant species. These communities are the tadpole shrimp Lepidurus lemmoni Holmes con- generally dominated by Atriplex spp., especially A. con- sumes the fairy shrimp Branchinecta mackini Dexter in fertifolia.(Torr.&Frem.)S.Wats.,Allenrolfea occiden- our Mojave assemblage [17]. One fairy shrimp species talis (S. Wats.) Kuntze, Suaeda moquinii (Torr.) Greene, present in the Mojave assemblage, (Branchinecta gigas Sarcobatus vermicularis (Hook.) Torr., Kochia califor- Lynch), is largely carnivorous, and B. mackini is a nica S. Wats., and Nitrophila occidentalis (Moq.) common prey item [18-20]. Branchinecta gigas may also S. Wats., as well as grasses such as Distichlis spicata (L.) consume filamentous algae [[20], but see [21]]. Fairy, E. Greene. When flooded, the Edwards waters range clam, and tadpole shrimps (the latter only as juveniles) from pH 8.8 to 9.2 [27], and salinity ranged from 0 to consume suspended detritus [17,22] though neither 10 g/L (refractometer measurements during study site carnivory nor detritivory were considered in the present reconnaissance). Turbidity appeared to be related to study. These ephemeral desert waters also support wind speed and was often > 3,000 NTU. The pans and insect (Hemiptera: Notonectidae; pers. obs.) and avian playas contain water for at least two weeks in 51% of predators [17]. the years, but may remain dry for several years at a time We characterize branchiopod species composition and [25], a typical “intermittent” flood regime [23]. When abundance from field collections and explore the rela- moist or inundated, filamentous and/or mat-forming tionship between the shrimps and planktonic and algae were often conspicuous on the substrate or in the benthic algae in intermittently flooded [sensu [23]] pans water column. When dry, the surfaces of many of the in the western Mojave Desert using laboratory micro- pans are covered with biotic crusts dominated by blue- cosm experiments. This study is an initial effort towards green algae; the main constituents are Microcoleus better understanding of the trophic relationships in this vaginatus (Vauch.) Gom. and Scytonema sp. Agardh [7]. ecosystem. Branchiopods were surveyed at EAFB by Simovich et al. (unpublished) and Sassaman [28] who reported three Methods species of fairy shrimps (Branchinecta gigas, B. lindahli Study site Packard and B. mackini), two tadpole shrimps (Lepidurus The study site was in the western Mojave Desert lemmoni and Triops newberryi Packard), and a clam between Rogers and Rosamond Playas ("Dry Lakes”), on shrimp (Eocyzicus digueti Richard). Although waterbirds Edwards Air Force Base (EAFB), about 90 km NE of Los were present when the pans were inundated, fish were Angeles, California, U.S.A. at 34° 50.68’, 117° 55.54’ [7]. absent (pers. obs.). The pan-dune complex includes 3000 pans ranging in size from 0.005 to 125 ha (mean size - 0.5 ha [24]). The Field collections pans are comprised of impermeable silt-clay. The 0.25 Shrimps were collected in April 2001 when many of the km2 site was established by resource managers and pans in and around the study site had been inundated researchers because the habitat is representative of the for several weeks. Two pans (Pans 1 and 2) had been larger dune pan environment at EAFB and has been previously surveyed for algae in a study of biotic crusts used for ecological research and hydrologic modeling in and numerically correspond to site locations in that support of resource management [3,7,25]. The area has study [7]. We also studied two additional pans: Pan 3, restricted access, is at least 200 m from the nearest sel- for which a pilot study indicated the presence of Bran- dom-used unimproved road, and shows few signs of chinecta gigas, and Pan 4 from a lightly disturbed area recent anthropogenic disturbance. The site, a complex about 2 km south of the study site. of pans (small playas [2,26]) and dunes between two Shrimps were sampled with a throw trap using proto- large playas, included three medium-sized (ca. 2 ha) colsderivedfromSogardetal.[29,30]andHolmquistet pans and many smaller pans ranging in size from 0.5 ha al. [31,32]. Throw traps have been shown to be highly to <1 m2 [7]. Sodium accumulation ratio (SAR) of sur- efficient, relative to other collecting devices, for quantita- face pan soil was 836, electrical conductivity was 12,620 tively sampling demersal organisms [33-35]. This method μS/cm, sodium concentration was 418 meq/l, and pH yields densities, because the trap encloses a known area was 9 (Soil Testing Laboratory Division of Agriculture and virtually all fauna are removed. The trap, constructed and Natural Resources, University of California, Davis). of sheet aluminum, was a 0.75 m × 0.75 m box without a Brostoff et al. Saline Systems 2010, 6:11 Page 3 of 8 http://www.salinesystems.org/content/6/1/11 top or bottom. The clearing device was a 0.5 m-wide successive net passes until two passes failed to collect framed and handled net (bar seine) with 0.5 mm square additional shrimps.