I still have not counted the rest of the November samples, but here is the spreadsheet with native cladoceran and copepod data (the two major zooplankton groups) for each date.
The issue of invasive species has been gaining importance as invasions have become more common throughout ecosystems. Since the success of an invasion can be affected by the suitability of abiotic factors, Kristen A. Work and Moshe Gophen conducted a study at the University of Oklahoma that was featured in Freshwater Biology to determine whether variations in food availability, turbidity, temperature, and conductivity affected the survival, reproductive, and molting rates of Daphnia lumholtzi.
D. lumholtzi was chosen as the test subject because it is a cladoceran zooplankton with an increased ability to colonize North America due to the similarity between the water temperature of its native habitat and the new habitat, and due to its long head and tail spines which make it undesirable to many predators. The results of the experiment showed that reproductive rates increased with food concentration and temperature, was not affected by conductivity, and was best at no turbidity. Molting rates increased with temperature, was strongly affected by turbidity, and was not significantly affected by food supply or conductivity. Survival rates were best at moderate conductivity, declined with temperature, and was not significantly affected by food supply. However, it is important to note that D. lumholtzi was able to survive and reproduce in all of the conditions tested. Overall, this study emphasized that the sustainability of abiotic factors can be used to predict whether cladoceran zooplankton species are likely to invade a habitat or not.
After first showing up in the southern United States in the early 1990′s, the Daphnia lumholtzi, an invasive aquatic species, has now spread north into Lake St. Clair says Claudiu Tudorancea, whose research was funded by the Aquatic Invasive Species program of Fisheries and Oceans Canada. A total of 41 Daphnia lumholtzi were recovered from Lake St. Clair. Of the 41 specimen caught, 39 were females and two were males. Of the 39 females, three were carrying eggs. This is important because it demonstrates that the Daphnia lumholtzi are reproducing successfully in Lake St. Clair. Very little information is known about the Daphnia lumholtzi, but more importantly, very little is know about the ecological effects caused by the Daphnia lumholtzi. Scientists do speculate that Daphnia lumholtzi could harm larval and juvenile fish by lower the zooplankton available for these fish. However, more research needs to be conducted to support this claim.
Journal of Great Lakes Research. Volume 35, 2: 313-316 (2009)
Discrete and Continuous Dynamical Systems Series B 12: 2 p. 481-493 (2009)
Since its invasion to North America in 1991, Daphnia lumholtzi has continuously competed with the native Daphnia species. The long spines characteristic of D. lumholtzi prevent the water flea from being a suitable food source for young fish. As a result, they outcompete other Daphnia species. This could cause larger scale problems through the disruptions of food chains. Hao Wang out of the Georgia Institute of Technology monitored the competition between D. lumholtzi and the native D. pulex. Four tanks were set up: tank with only D. pulex, one with only D. lumholtzi, one without Daphnia as the control and one with both species. They were subjected to two different light sources, one of high intensity and one of low intensity. The results showed that D. lumholtzi was more competitive at higher light intensity while D. pulex was more competitive at lower light intensity. The researchers conclude that this study could lead to predictive assumptions of future invasion.
Journal of Great Lakes Research Volume 35: 313-316, 2009.
D. lumholtzi has recently been found in Lake St. Clair of the Laurentian Great Lakes. According to Cladiu Tudorancea of the Great Lakes Laboratory for Fisheries and Aquatic Sciences, this alien species native to Australia, Africa, and Southeast Asia is rarely found in areas like the Great Lakes. Although this area is different than its native region, the warm, turbid region of the lake is sufficient to support D. lumholtzi. Common features of the species in both the Australia and the United States are a well-developed head spine, fornices, and carapace spine. However, the D. lumholtzi cannot have been transported to the United States via ballast water due to genetic differences between species found in Texas and Missouri and those from Australia. Finally, according to current trends, they can spread to areas of Lake Ontario, Lake Huron, and Lake Michigan, especially as climate changes occur. This challenge of native cladocerans may signify less suitable zooplankton for larval and juvenile fish.
Journal of Plankton Research. Volume 23: 425-433, 2001.
The success of an invader relies on the ability of that species to adapt to its new surroundings. One key factor that has a large effect on an aquatic species ability to populate new waters is temperature. In areas such as the northeastern United States, higher water temperatures during the late summer months cause a decline in some species of zooplankton. In 2001, a study investigated the effect water temperature has on Daphnia lumholtzi.
The test took place in a Kansas reservoir. Daphnia lumholtzi from the reservoir were collected for the test, and the temperature of the water was taken from the top .25 m during the collection. Daphnia lumholtzi was only found in the water between the months of July and September, when the water temperature was between 25 and 30 degrees Celsius. From this data, researchers were able to conclude that when water temperature was over 25 degrees Celsius, Daphnia lumholtzi were able to outcompete other plankton species, but did not thrive under lower temperatures. This data can be applied broadly because the it doesn’t allow the invasive species to populate regions with colder waters or dominate certain areas year round.
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 276 (1663): 1865-1873 MAY 22 2009
The water flea known as Daphnia lumholtzi, is an invasive species that was found its way from the tropic regions of Africa, Asia, and Australia to the United States. Found first in areas of Texas and Missouri, its population rapidly expanded through out southeastern and mid-western states and was recently found in the Laurentian Great Lakes. This tiny invader has been successful in its growth believed to be due to a high thermal tolerance, which allows for climates to change and it still remain established. Daphnia lumholtzi competes with native Daphnia for food and can affect plankton populations (Engel 2009).
Inducible Defenses as Key Adaption’s for the Successful Invasion of Daphnia lumholtzi in North America, is a study by Katherine Engel on how the Daphnia lumholtzi is able adapt so well in its environment (2009). Tested in this experiment was the lumholtzi versus other native Daphnia. The two were put into a controlled laboratory experiment where in the absence of predators, the native species was dominant. When predators such as the Heckel fish and Sunbleak fish were introduced, the Daphnia lumholtzi showed why it has become an invasive threat. Due to the chemicals given off by the predator fish, the water flea mutated what seemed to be an almost armor like helmet and tail. This “armor” allowed the Daphnia lumholtzi in the presence of predators to be significantly more dominant then the native species (2009).
More information on D. lumholtzi is still needed to assess the potential risk that it could cause. With its adaptive and mutant like abilities, this invasive species could be more prone to expanding its population and furthering its invasion.
Journal of Great Lakes Research. Vol. 35: 313-316, 2009.
Originally from Australia, South East Asia, and Africa, Daphnia lumholtzi arrived in southern United States in 1991. Since then, the population has begun to spread North and more recently have reached the Laurentian Great Lakes through ballast water discharge. The spread of this tropical species in the temperate great lakes has aroused the scientific community and led to nationwide studies.
Claudiu Tudorancea, Aquatic Bioservices, Kelly Bowen and Jocelyn Gerlofsma, Great Lakes Laboratory for Fisheries and Aquatic Sciences, worked together to research the spread of D. lumholtzi in the Great Lakes. They established 10 sampling stations and found D. lumholtzi in a warm, turbid, nutrient rich area near a sea wall. Other studies had similar results, and concluded that D. lumholtzi are prominent in areas with high temperatures during warmer seasons. From their data and trends of other studies, the team concluded that warm, shallow embayments are suitable for D. lumholtzi and that if climate change predictions are correct then D. lumholtzi spread will continue.
Oecologia 116, 556-564 (1998)
Although many animals possess permanent structures to deter predation (e.g., porcupines, sea urchins, and sticklebacks), others develop defensive mechanisms only in response to predator-related cues. Daphnia Lumholtzi, a species of zooplankter that exhibits extreme “cyclomorphosis” (or changes in body shape) with a large helmet and long tail spine, is a particularly successful case in point. Spines make prey difficult to handle by increasing the effective cross-sectional diameter of prey, thereby restricting gape-limited predators such as planktivores. In addition to its spines, D. lumholtzi also has lateral fornicles and is virtually transparent. Given its relative size, these numerous antipredatory defenses seem extreme, but are likely related to high predation pressure in its native ecosystems. Yet given its role as an invader, the pertinent question is whether or not that same pressure exists in ecosystems that play host to its invasion.
Kolar and Wahl (1998) examined selectivity for D. lumholtzi (relative to a control, D. pulex) by juvenile bluegill in the laboratory and field. It was found that bluegill consumed more D. pulex on average than D. lumholtzi when the species were presented alone. That is, when the daphnids were offered together in equal numbers, bluegill selected against D. lumholtzi. Bluegill foraging behavior helps to explain the observed nonrandom feeding. Essentially, bluegill capture efficiency foraging on D. pulex was high (85-100%) and handling times were low (usually too short to detect); predation was an effectively linear sequence consisting of orientation, attack, capture, and ingestion. Conversely, efficiencies were lower (40-96%) and handling times were longer (1-3 s) when foraging on D. lumholtzi. Because spending such large portions of time attempting to swallow prey that could be spent foraging incurs negative energetic consequences for fish, bluegill showed avoidance behavior in their selection; that is, after successive unprofitable attempts, the bluegill would begin orienting toward and then rejecting D. lumholtzi more often than striking. Thus, the tactic of frustrating planktivores with such defenses demonstrates the ability of zooplankton morphology to deter fish predators.
In 1990, Daphnia Lumholtzi was introduced to the United States and rapidly established itself as an aquatic invader by out competing native zooplankton for resources. As a result, native fish populations suffer because D. Lumholtzi is inedible for many species due to its spiny structure.
Kao Wang of the Georgia Institute of Technology and Katherine Dunning (among others) of Arizona State University conducted a study to see how light levels affected D. Lumholtzi populations. The team tested the invasive D. Lumholtzi and the native D. Pulex in two different light treatments and found that D. Lumholtzi consistently out competed the native species in the high light treatment, and vice versa in the low light treatment. From these results, the team created models exhibiting the “chaotic coexistence” of the Daphnia species. Using this, Wang et al. (2009) say that it may be possible to develop strategies which may control the spread of D. Lumholtzi.