New study helps explain recent scarcity of bay nettles southside daily university of kansas shop

Compiling and analyzing population data for five different jelly species in the years between 1984 and 2012, it is the most comprehensive study of bay jelly populations ever undertaken. Then-doctoral student josh stone tests the buoyancy of a bay nettle in the zooplankton ecology laboratory at VIMS. (southside daily/courtesy D. Malmquist/VIMS)

The two most common species in the study, the bay nettle chrysaora chesapeakei and the comb jelly mnemiopsis leidyi, are both transparent, jellylike predators that drift with the currents, but differences in their size, anatomy, feeding behavior, and life cycles translate into stark differences in their population dynamics and impacts on the chesapeake ecosystem. Kansas state vs university of kansas the bay nettle chrysaora chesapeakei. (southside daily/courtesy J. Lefcheck/VIMS)

For chrysaora, a stinging jelly painfully familiar to many bay enthusiasts, the team confirmed and further quantified a preference for warm, relatively salty waters — recording peak abundances between july and september in waters above 70 degrees, and at salinities of 16 parts per thousand (bay waters range from near 0 ppt where tributaries enter to around 32 ppt — as salty as the ocean — near the bay mouth).

The bay nettle’s preference for saltier water helps explain widespread reports of its scarcity this summer in many of the chesapeake bay tributaries it typically inhabits, as freshwater runoff from record rains drastically lowered their salinity.

It was particularly wet in may — the rainiest in richmond since record-taking began there in 1872 — just when the nettles’ bottom-dwelling life stage begins to bud off its tiny, sensitive, free-floating medusae. University of kansas medical school the comb jelly mnemiopsis leidyi. Southside daily/courtesy S. University of kansas careers wilson/VIMS)

“we found that mnemiopsis populations were primarily controlled by bay nettle predation,” stone said. “they were most abundant in june, during a brief window between waters warming above 65 degrees and the bloom of their bay-nettle predators in july.”

By comparing year-to-year fluctuations in jelly populations and environmental conditions in the bay over a span of more than two decades, the researchers discovered a downward trend in the overall abundance of bay jellies that runs counter to reports of increasing jelly abundance in other areas of the world.

Facing less predation due to the scarcity of bay nettles, populations of their comb jelly prey then increase, but not enough to offset the loss of biomass occasioned by decreased abundance of the much larger nettles. The copepod arcatia tonsa, a common resident of the chesapeake bay. (southside daily/courtesy S. Wilson/VIMS)

Wetter, warmer springs would also increase the prevalence of low-oxygen bottom waters in the bay, which the researchers found to be another contributor to lower reproductive rates among bay nettles. The bay anchovy anchoa mitchilli. (southside daily/courtesy VIMS juvenile trawl survey)

“predicted future increases in spring streamflow and spring hypoxia due to global climate change would further decrease bay-nettle abundance,” stone said,”possibly allowing for future increase in comb jelly populations and concurrent decreases in the number of copepods. That’s troubling, because copepods are a major pathway for transferring food energy from phytoplankton to commercial finfish, especially through the bay anchovy.”

“our native comb jelly was introduced to the caspian and black seas, where it didn’t have predators, became invasive, and contributed to the crash of several fisheries,” stone said. “it has a natural predator here, the bay nettle, but fewer bay nettles leads to more comb jellies. Bay nettle populations are already at a lower level due to increases in hypoxia and other factors, and we can’t afford to find out how detrimental further declines in their populations would be to bay fisheries.”

“in chesapeake bay, increases in the area affected by hypoxia may help keep comb jellies away from their prey, because copepods and larval fish avoid these zones, while the comb jellies do not,” stone said. “even so, continued decreases in bay nettle populations due to climate change may have wide-ranging impacts throughout the chesapeake bay’s food web. Number of students at university of kansas even though we don’t like getting stung by jellyfish, they are an important and natural part of the bay ecosystem.”

Stone, J.P., steinberg, D.K. & fabrizio, M.C., 2018. Long-term changes in gelatinous zooplankton in chesapeake bay, USA: environmental controls and interspecific interactions. Estuaries and coasts, p. 1-15. Https://doi.Org/10.1007/s12237-018-0459-7