Population growth of microcrustaceans in water from habitats with differing salinities

Abstract

Inland salt marshes are a rare habitat in North America. Little is known about the invertebrates in these habitats and their ability to cope with the brackish conditions of the marsh. We studied the population growth of ostracods found in an inland salt marsh (Maple River salt marsh) and of copepods found in the wetland habitat immediately adjacent to the freshwater Kalamazoo River. By studying these species in water from both habitats, we aimed to find out if they performed differently in the two habitats. We also tested Daphnia pulex in water from the two habitats due to the history of Daphnia spp. as model organisms. We found that copepods performed better in water taken from the Maple River salt marsh, and the ostracods and D. pulex performed equally well in either water. This was unexpected, since ostracods are found in the salt marsh and copepods in the freshwater area. As a second experiment, we tested the invertebrates in pairwise interactions. In water from the Kalamazoo River, ostracods outperformed the other two species, but there was no difference between D. pulex and copepods. No species outperformed the other in salt marsh water. Our results show no local adaptation to salinity, suggesting that ostracods and copepods may be limited in their respective distributions by dispersal limitation or habitat suitability.

Invertebrates from naturally brackish areas are less impacted by road salt and alternative deicers

“…The results are consistent with previous studies, which show that individuals in the genus Daphnia are able to tolerate some salt but not at high levels (Breen & Cahill, 2021; Coldsnow et al, 2017; Liu & Steiner, 2017). Our experiment (particularly the population‐level IPD measure) was not designed to calculate a precise LC50 for road salt alternatives.…”

“…Delaune et al (2021) found that ostracods were affected by road salt application, but only over a long (~70 day) experiment, and the ostracods in that study were collected in freshwater. Breen and Cahill (2021) found that individuals of Heterocypris sp. from the MRSM were able to survive in the lab for 2 weeks in 2.5 psu water from the marsh.…”

“…Each replicate was fed daily. Ostracods and individuals of D. pulex were fed a suspension of brewer's yeast and water (as in Breen & Cahill, 2021), midge larvae were fed TetraMin Tropical Flakes Fish Food, and E. fetida received dry Magic Worm Food (Magic Products, Amherst Junction, Wisconsin). The experiment ran for 3 weeks.…”

“…Based on the method of Searle et al (2016), and following Breen and Cahill (2021), we calculated the integrated population density through time for the population trajectories in the treatment replicates of D. pulex , ostracods, and E. fetida . This method uses the trapezoid rule to calculate the area under the population growth trajectory (with each time step measured as a trapezoid), creating a variable called Integrated Population Density (IPD).…”

“…The salinity at the seep site in the marsh ranges 1.166–3.597 psu (Cahill et al, 2021), high enough that the community at the seep is distinct from that in the adjacent freshwater area. Work by Breen and Cahill (2021) showed that ostracods from the marsh are able to tolerate 2.5 psu in the lab and can also cope with freshwater conditions (0.3 psu). The organisms in this marsh are clearly adapted to deal with NaCl in higher concentrations than most freshwater organisms, and in fact, the salt extracted in the Great Lakes region and used on the roads is from the same geologic origin as the salt feeding the Maple River Salt Marsh (Michigan Department of Environmental Quality, n.d.).…”