The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California's largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey & Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T. belli Hrabe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the amphipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted estimates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus, Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.     

Community structure and spatial variability of marine nematodes in tropical Australian pioneer seagrass meadows

The spatial variability in the community structure of infaunal free-living marine nematodes of pioneer seagrass (Halophilaand Halodule) meadows within a deltaic mangrove estuarine system and a bay mangrove system in tropical north-eastern Australia were examined. Nematode mean densities were intermediate ranging from 609 to 2744 inds./10 cm². A total of 152 putative species from 94 genera and 22 families were found across the four sites. The communities exhibited a high degree of dominance by Terschellingia longicaudata, Catanema sp 1, Terschellingia sp 2 and Metalinhomoeus insularis.Non-metric multi-dimensional scaling (nMDS) revealed that intra-site variability was low. This was reinforced by 1-way MANOVA, showing no significant inter-station differences between the six most dominant species at each site. The main system difference was reflected by a greater percentage of the Desmodoridae combined with a reduction of the Linhomoeidae in the bay system. At a species level system differences were manifested by a stenohaline, brackish water nematode assemblage in the deltaic system (M. insularis, Terschellingoidessp 1, Pseudolellasp 1) and, by a stenohaline, marine nematode assemblage in the bay system (Catanema sp 1, Spirinia parasitifera, Actinonemasp 1). These communities represent `hotspots' of diversity within a wider, mangrove-influenced depauperate fauna. The high degree of dominance found in each community was countered by moderate diversity and this, combined with the high number and speciation of deposit-feeding species, suggests that nematodes were more abundant in the meadows due to the abundance of microbial food. Notwithstanding the different salinity/CaCO₃ regimes, these communities exhibit both intra- and inter-site homogeneity with dominance by a conservative, deep-dwelling guild. The fact that this homogeneity exists suggests that these small-bladed seagrass species may play a greater role (sediment stability, fine particle settlement, organic detritus) in influencing the infaunal nematode community than was previously thought.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Aquatic nematodes from Ethiopia VII

Three species of Rhabdolaimus de Man, 1880 and two (of which one is new to science) of Udonchus Cobb, 1913 are described from sediment samples of two lakes, two rivers and a hot spring, Ethiopia. Udonchus merhatibebi n.sp. is characterized by a distinctly truncate lip region and small cardia surrounded by gland cells that he on the anterior intestine at 45 °. The presence of twelve rugae in the cheilostome in the genus Udonchus is reported here for the first time. As a result, the family Rhabdolaimidae has been moved from suborder Leptolaimina to the superfamily Microlaimoidea in the suborder Chromadorina. The family Rhabdolaimidae is also subdivided into the subfamilies Rhabdolaiminae Chitwood, 1951 and Undonchinae n. subfam.. Scanning electronmicroscopic pictures of the five species viz. R. aquaticus de Man, 1880, R. cf. minor Cobb, 1914, R. terrestris de Man, 1880, U. merhatibebi n.sp. and U. tenuicaudatus Cobb, 1913 are also given.Abbreviations ABE = anterior body end - ABW = anal body width - Amph = amphid - Amph W = amphidial fovea width - CBW = corresponding body width - GL = gonad length - G1L = anterior gonad length - G2L = posterior gonad length - L = length - LM = light microscope - LRW = lip region width - MBW = maximum body width - n = number of specimens - NR = nerve ring from the anterior end - Ph L = pharyngeal length (neck length) - RL = rectal length - SEM = scanning electron microscope - V-A = distance from vulva to anus - W = width     

Aquatic nematodes from Ethiopia V

Three species of chromadorids two of which are new to science are described from bottom samples of Lake Tana, L. Ziway and River Abbay, Ethiopia. Achromadora inflata n. sp. and Ethmolaimus zullinii n. sp. are characterized by a uniquely inflated and offset anterior end. The latter is an exception in its genus also by its possession of a well developed dorsal tooth and inconspicuous ventrosublateral denticles. Prodesmodora nurta Zullini, 1988 is reported here for the first time out of its type locality and is described in detail. SEM pictures of Ethmolaimus zullinii n. sp. and Prodesmodora nurta, and complete setae maps of the three species are also presented.Abbreviations used ABE = anterior body end - ABW = anal body width - Amph = amphid - Amph W = amphidial fovea width - CBW = corresponding body width - CSL = cephalic setae length - Ddent = dorsal denticle - GL = gonad length - L = length - LM = light microscope - LRW = lip region width - MBW = maximum body width - n = number of specimens - NR = nerve ring from the anterior end - PBE = posterior body end - Ph L = pharyngeal length (neck length) - PrL = prerectal length - RL = rectal length - SEM = scanning electron microscope - V-A = distance from vulva to anus - Vdent = ventral denticle - W = width     

Aquatic nematodes from Ethiopia II

Eight species of the genus Monhystrella, six of which are new to science, are described from bottom samples collected from three lakes, two rivers and a hot spring in Ethiopia. Monhystrella hoogewijsi n. sp. is identified by a distinctive bulge on the lip region, position of the amphids, offset and well developed single pharyngeal terminal bulb, tail shorter than vulva-anus distance, tail elongate-conoid for two-thirds of its length, and by the shape and size of the spinneret outlet; M. jacobsi n. sp. by its slender body, distinctively offset and distended lip region, indistinct and weakly expanding single terminal pharyngeal bulb, and shape and size of the tail and spinneret outlet; M. arsiensis n. sp. by its single terminal pharyngeal bulb, position of amphids, shape and length of tail and spinneret outlet; M. woitorum n. sp. by its hemispherical lip region, double terminal pharyngeal bulb, shape and length of the spinneret outlet, and shape and length of tail; M. ethiopica n. sp. by its bipartite stoma, size of amphid in relation to corresponding body width, filiform tail and shape and length of spinneret outlet. M. atteae n. sp. differs from all known Monhystrella species in having an inflated cap-like lip region and fine crystalloid bodies. M. macrura (de Man, 1880) Andrássy, 1981 and M. lepidura altherri (Juget, 1969) Jacobs, 1987 are reported from Ethiopia for the first time. Crystalloid bodies in the genus Monhystrella is reported here for the first time. Also the presence of a hyaline coelomocyte next to the germinal zone of the reproductive system is reported for the first time in the genus here in all eight species. The structures used in the taxonomy of the genus are reviewed.     

Possible importance of algal toxins in the Salton Sea, California

In response to wildlife mortality including unexplained eared grebe (Podiceps nigricollis) die-off events in 1992 and 1994 and other mortality events including large fish kills, a survey was conducted for the presence of algal toxins in the Salton Sea. Goals of this survey were to determine if and when algal toxins are present in the Salton Sea and to describe the phytoplankton composition during those times. A total of 29 samples was collected for toxicity analysis from both nearshore and midlake sites visited biweekly from January to December 1999. Dinoflagellates and diatoms dominated most samples, but some were dominated by a prymnesiophyte (Pleurochrysis pseudoroscoffensis) or a raphidophyte (Chattonella marina). Several types of blooms were observed and sampled. The dinoflagellate Gyrodinium uncatenum formed an extensive, dense (up to 310000 cells ml^–1) and long-lasting bloom during the winter in 1999. A coccolithophorid, Pleurochrysis pseudoroscoffensis, occurred at high densities in surface films and nearshore areas during the spring and summer of 1999. These surface films also contained high densities of one or two other species (an unidentified scrippsielloid, Heterocapsa niei, Chattonella marina). Localized blooms were also observed in the Salton Sea. An unknown small dinoflagellate reached high densities (110000 cells ml^–1) inside Varner Harbor, and an unidentified species of Gymnodinium formed a dense (270000 cells ml^–1) band along part of the southern shoreline during the summer. Three species known to produce toxins in other systems were found. Protoceratium reticulatum (=Gonyaulax grindleyi) and Chattonella marina were found in several samples taken during summer months, and Prorocentrum minimum was found in low densities in several samples. Extracts of most samples, including those containing known toxic species, showed a low level (<10% mortality across all concentrations) of activity in the brine shrimp lethality assay and were not considered toxic. All sample extracts tested in the mouse bioassay showed no activity. One sample extract taken from the bloom of the small dinoflagellate was highly active (100% mortality across all concentrations) in the brine shrimp lethality assay, but the active material could not be isolated. While dense algal blooms are common at the Salton Sea, no evidence gathered in this study suggests that algal toxins are present within phytoplankton cells; however, toxins actively excreted by cells may have been missed. Blooms of phytoplankton likely contribute to wildlife mortality at the Salton Sea. Possible mechanisms including intoxication due to ingestion of feathers in grebes and waterlogging caused by changes in surface tension are discussed.     

Avian disease at the Salton Sea

A review of existing records and the scientific literature was conducted for occurrences of avian diseases affecting free-ranging avifauna within the Salton Sea ecosystem. The period for evaluation was 1907 through 1999. Records of the U.S. Department of Agriculture, Bureau of Biological Survey and the scientific literature were the data sources for the period of 1907–1939. The narrative reports of the U.S. Fish and Wildlife Service's Sonny Bono National Wildlife Refuge Complex and the epizootic database of the U.S. Geological Survey's National Wildlife Health Center were the primary data sources for the remainder of the evaluation. The pattern of avian disease at the Salton Sea has changed greatly over time. Relative to past decades, there was a greater frequency of major outbreaks of avian disease at the Salton Sea during the 1990s than in previous decades, a greater variety of disease agents causing epizootics, and apparent chronic increases in the attrition of birds from disease. Avian mortality was high for about a decade beginning during the mid-1920s, diminished substantially by the 1940s and was at low to moderate levels until the 1990s when it reached the highest levels reported. Avian botulism (Clostridium botulinum type C) was the only major cause of avian disease until 1979 when the first major epizootic of avian cholera (Pasteurella multocidia) was documented. Waterfowl and shorebirds were the primary species affected by avian botulism. A broader spectrum of species have been killed by avian cholera but waterfowl have suffered the greatest losses. Avian cholera reappeared in 1983 and has joined avian botulism as a recurring cause of avian mortality. In 1989, avian salmonellosis (Salmonella typhimurium) was first diagnosed as a major cause of avian disease within the Salton Sea ecosystem and has since reappeared several times, primarily among cattle egrets (Bubulcus ibis). The largest loss from a single epizootic occurred in 1992, when an estimated 155000 birds, primarily eared grebes (Podiceps nigricollis), died from an undiagnosed cause. Reoccurrences of that unknown malady have continued to kill substantial numbers of eared grebes throughout the 1990s. The first major epizootic of type C avian botulism in fish-eating birds occurred in 1996 and killed large numbers of pelicans (Pelecanus occidentalis & P. erythrorhynchos). Avian botulism has remained as a major annual cause of disease in pelicans. In contrast, the chronic on-Sea occurrence of avian botulism in waterfowl and shorebirds of previous decades was seldom seen during the 1990s. Newcastle disease became the first viral disease to cause major bird losses at the Salton Sea when it appeared in the Mullet Island cormorant (Phalacrocorax auritus) breeding colony during 1997 and again during 1998.     

Salinity and fish effects on Salton Sea microecosystems: benthos

The Salton Sea, the largest lake in California, has a surface elevation 69 m below sea level which is maintained predominantly by the balance of agricultural runoff and evaporation. The lack of outflowing streams is resulting in a gradual buildup of salts in the lake, increasing the salinity. A 15 month microcosm experiment was conducted to determine the effects of salinity and tilapia ( Oreochromis mossambicus) on an assemblage of benthic and planktonic Salton Sea algae and invertebrates. This article reports the responses of the benthic invertebrates. Microcosms (312 l fiberglass tanks) were set up without tilapia at 30, 39, 48, 57, and 65 g · l-1. Additional microcosms were set up with tilapia at 39 and 57 g · l-1. In the absence of fish Gammarus mucronatus dominated the benthos at the lower salinities, and Trichocorixa reticulata and the larvae of Ephydra riparia were most abundant above 48 g · l-1. The most abundant meiofaunal species included the harpacticoid copepod. Cletocamptus deitersi, three nematodes, the rotifer Brachionus plicatilis, ciliates, including Condylosoma sp. and Fabrea salina, two foraminiferans including Quinqueloculina sp., and a large flagellate. Most meiofaunal species responding to salinity were most abundant at 65 g · l-1, especialy after 6 months when Gammarus dominated the lower salinities. The tilapia reduced the abundance of macrofaunal species, especially at 39 g · l-1, and generally increased the abundance of meiofaunal species and ciliates. The microcosm benthic macro- and meiofaunal communities were most likely structured by Gammarus, salinity and tilapia. Gammarus reduced the other species by predation and changing the detritus from an algal base to a fecal pellet base. Gammarus was itself reduced by tilapia and by reduced reproductive success above 39 g · l-1. More species were therefore able to compete at higher salinities and in the presence of tilapia. Tilapia also affected the benthos by depositing loosely packaged fecal material which may support more meiofaunal species than either the robust Gammarus fecal pellets that were abundant at 39 g · l-1 or the algae-fecal pellet mix at 57 g · l-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Barnacle growth rate on artificial substrate in the Salton Sea,California

The Salton Sea is one of the few saline, inland lakes in the world with a population of barnacles, Balanus amphitrite. It is also one of California’s most impaired water bodies due to excessive nutrient loading which leads to phytoplankton blooms and low dissolved oxygen. Currently, B. amphitrite growth is limited due to lack of hard substrate in and around the Sea. We have hypothesized that artificial substrate could support the growth of B. amphitrite and their filter-feeding would lead to improved water quality. Periodic harvesting of the barnacles would result in the permanent removal of nitrogen and phosphorus from the Sea. A 44-day in-situ experiment was carried out in the Salton Sea to assess the rate of barnacle growth and phosphorus and nitrogen sequestration on burlap sheets suspended vertically from a floating line. Burlap panels were collected weekly and the barnacles analyzed for Ca, total-P, inorganic-P, total-N, total-C, CaCO₃, and organic matter content. After 44 days of growth, the barnacle mats weighed 7.4 kg m⁻² on a dry weight basis, with 80% of the mass as shell material. The nutrient sequestration was 9.4 g P m⁻² and 100 g N m⁻². Approximately half of the P was inorganic and appears to be coprecipitated with the calcium carbonate shell material. Results indicate that harvesting barnacles grown on artificial substrate in the Salton Sea would not be an effective method for removing N or P from the lake because of the relative proportions of shell material and organic material. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Chemical and physical characteristics of the Salton Sea, California

A 1-year sampling program was conducted to assess current chemical and physical conditions in the Salton Sea. Analyses included general physical conditions and a suite of water quality parameters, including nutrients, trophic state variables, major cations and anions, trace metals and organic compounds. Samples were collected from three locations in the main body of the lake and from the three major tributaries. Nutrient concentrations in the Salton Sea are high and lead to frequent algal blooms, which in turn contribute to low dissolved oxygen concentrations. The tributaries consist primarily of agricultural return flows with high nutrient levels. Concentrations of trace metals and organic compounds do not appear to be of major concern. Two geochemical models, PHRQPITZ and PHREEQC, were used to evaluate potential chemical reactions limiting the solubility of selected water quality variables. Modeling indicated that the Salton Sea is supersaturated with respect to calcite, gypsum, and other minerals. Precipitation of these minerals may serve as a sink for phosphorus and limit the rate of salt accumulation in the Salton Sea.     

Flagellate Cryptobia branchialis (Bodonida: Kinetoplastida), ectoparasite of tilapia from the Salton Sea

An infestation of young tilapia, Oreochromis mossambicus Peters, by the flagellate Cryptobia branchialiswas observed at the Salton Sea, California, in September, 1997. This is the first report of C. branchialis in a highly saline water-body (43 g l^–1). Ultrastructure of C. branchialis as well as its effect on the gills of tilapia were studied using the scanning and transmission electron microscopy. No direct effect of C. branchialis on the epithelial cells of fish gills was observed. However, alterations of gill general structure, such as deposition of copious mucus on the gill surface, swelling of filaments, reduction of respiratory lamellae and their transformation into short club-shaped structures were found in infected fish. This suggests mortality of young tilapia may arise from decreased gill function in response to Cryptobia infestation.     

Aquatic nematodes from Ethiopia III

Six species of the genus Eumonhystera, one of which is new to science, are described from bottom samples of Lake Tana and two associated rivers, River Abbay and R. Gelda, Ethiopia. E. geraerti n.sp. can be identified by being the only species in the genus that combines very posteriorly positioned vulva [V% = 68.2 ± 0.7 (67.3–69.3)] with very anteriorly positioned amphids (Amph-ABE/LRW = 0.8). The other five species encountered, E. dispar (Bastian, 1865) Andrássy, 1981, E. filiformis (Bastian, 1865) Andrássy, 1981, E. pseudobulbosa (von Daday, 1896) Andrássy, 1981, E. mwerazii (Meyl, 1957) Andrássy, 1981, and E. vulgaris (de Man, 1880), Andrássy, 1981, are described in detail. The identities of some of the already described populations of E. dispar, E. filiformis and E. vulgaris are questioned and clearer and better ways of defining each of these three species are suggested. A peritrophic-like membrane on the outer side of the brush-border of the intestine of E. mwerazii, a species reported here for the first time out of its type locality, is reported. Also, scanning electronmicrographs of sectioned and entire specimens of E. mwerazii are presented. All species are reported from Ethiopia for the first time.     

Biology and migration of Eared Grebes at the Salton Sea

The Eared Grebe (Podiceps nigricollis Brehm) is the North American bird species most closely associated with highly saline habitats, and in winter and early spring it is the most abundant waterbird at the Salton Sea. During the fall, the great majority of the North American population stages at hypersaline lakes in the Great Basin, departing in early winter for wintering areas in southern California and Mexico, principally in the central Gulf of California. On the northward return flight, nearly all the population passes through the Salton Sea, where concentrations of >1 million have been reported in February–March. After staging for several weeks, grebes leave in March–April and migrate toward breeding grounds in the northern United States and southern Canada. The Sea's development as the species' major spring staging area may be as recent as the 1960s, and presumably awaited the establishment of appropriate prey populations of marine worms. In the past decades, two major dieoffs at the Sea each resulted in the undiagnosed death of tens of thousands of birds. Whether the cause(s) are endemic to the Sea or involve the grebes' migration routes and stopover locations is unknown. Because of problems in estimating numbers, the significance of these mortality events is hard to evaluate. Population trends are better studied at fall staging areas, especially Mono Lake, where population turnover is inconsequential, grebes are virtually the only species present, and numbers can be ascertained by aerial photography.     

Thalassomonhystera traesti n.sp., Eumonhystera andrassyi and three Monhystrella species (Monhysteridae: Nematoda) from Li River, China

A new Thalassomonhystera species, i.e. T. traesti n.sp., and a new subspecies, Monhystrella lepidura chinensis n. subsp., together with Eumonhystera andrassyi (Biró, 1969) Andrássy, 1981, Monhystrella macrura (de Man, 1880) Andrássy, 1981 and Monhystrella iranica Schiemer, 1965 are described from Li River at Guiling, China. Thalassomonhystera traesti n.sp. is characterised by a combination of the following characters: expanded lip region, large and anteriorly situated amphids, prominent inner labial sensilla, and slender spicules and tube-like gubernaculum in males. Monhystrella lepidura chinensis n. subsp. belongs to Monhystrella lepidura (Andrássy, 1963) Andrássy, 1968 but differs from the three hitherto described subspecies in its possession of a pharynx that posteriorly expands into a double bulb. Monhystrella macrura, M. iranica and Eumonhystera andrassyiare reported here for the first time from China.     

Salinity and fish effects on Salton Sea microecosystems: zooplankton and nekton

The Salton Sea is the largest inland lake in California. Currently (1997) the salinity of the lake is about 44 g l-1 and is increasing gradually as a result of continued agricultural wastewater inflows, high evaporation rates, and lack of an outlet. A microcosm experiment was carried out to determine the effects of salinity (30, 39, 48, 57, and 65 g l-1) on Salton Sea algae and invertebrates in outdoor aquatic microcosms. The experiment was also designed to assess the effects of tilapia ( Oreochromis mossambicus) on this community at two of these salinities (39 and 57 g l-1). Fiberglass tanks containing Salton Sea water were adjusted to the appropriate salinity by the addition of salts, identically inoculated with organisms from the Salton Sea and other saline water bodies in the region, and monitored for 15 months. Planktonic and nektonic invertebrates were sampled monthly at night from the upper part of the water column. The dominant invertebrates present were Gammarus mucronatus, Artemia franciscana, Trichocorixa reticulata, and an assemblage of ciliate protozoans. Gammarus decreased and Trichocorixa increased with increasing salinity. Artemia was present only at the two highest salinities. Rotifers, harpacticoid and cyclopoid copepods, barnacle larvae, and protozoans all showed marked and varied responses. During the latter half of the experiment, the invertebrate assemblage was dominated by Gammarus at 30 and 39 g l-1, by protozoans at 48 g l-1, and by protozoans and Trichocorixa at 57 and 65 g l-1. The presence of tilapia caused a 99 percent reduction in Gammarus at 39 g l-1 and a 70–90 percent decrease in Trichocorixa at 57 g l-1. These were accompanied by substantial increases in rotifers, copepods, and certain protozoans, and decreases in other protozoans. As the salinity of the Salton Sea continues to increase, large changes in the invertebrate populations are expected. This study suggests that the principal change would be an increase in Trichocorixa densities, the loss of Gammarus, and the appearance of Artemia at about 60–70 g l-1, when both fish and invertebrate predators are likely to be scarce or absent. Protozooplankton abundance is likely to increase when tilapia declines and later decrease when and if large Artemia populations develop. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preliminary studies of cyanobacteria, picoplankton, and virioplankton in the Salton Sea with special attention to phylogenetic diversity among eight strains of filamentous cyanobacteria

Cyanobacterial diversity in the Salton Sea, a high-salinity, eutrophic lake in Southern California, was investigated using a combination of molecular and morphological approaches. Representatives of a total of 10 described genera (Oscillatoria, Spirulina, Arthrospira, Geitlerinema, Lyngbya, Leptolyngbya, Calothrix, Rivularia, Synechococcus, Synechocystis) were identified in the samples; additionally, the morphology of two cultured strains do not conform to any genus recognized at present by the bacteriological system. Genetic analysis, based on partial 16S rRNA sequences suggested considerable cryptic genetic variability among filamentous strains of similar or identical morphology and showed members of the form-genus Geitlerinema to be distributed among three major phylogenetic clades of cyanobacteria. Cyanobacterial mats, previously described from the Sea were, in fact, composed of both filamentous cyanobacteria and a roughly equivalent biomass of the sulfur-oxidizing bacterium Beggiatoa, indicating their formation in sulfide rich regions of the lake. Flow cytometric analysis of the water samples showed three striking differences between samples from the Salton Sea and representative marine waters: (1) phycoerythrin-containing unicells, while abundant, were much less abundant in the Salton Sea than they were in typical continental shelf waters, (2) Prochlorococcus appears to be completely absent, and (3) small (3–5 m) eukaryotic algae were more abundant in the Salton Sea than in typical neritic waters by one-to-two orders-of-magnitude. Based on flow cytometric analysis, heterotrophic bacteria were more than an order of magnitude more abundant in the Salton Sea than in seawater collected from continental shelf environments. Virus particles were more abundant in the Salton Sea than in typical neritic waters, but did not show increases proportionate with the increase in bacteria, picocyanobacteria, or eukaryotic algae.