Cyanobacteria are responsible for the largest number of harmful algal blooms (HABs) worldwide. HABs caused by the genus Microcystis are health threats because they often occur within close proximity to humans and produce phycotoxins such as microcystins that can contaminate drinking water and recreational areas. Molecular techniques enable accurate and rapid (~ 1 h) HAB detection that facilitates monitoring, “early warnings” of blooms, and corresponding management responses. Sandwich hybridization assay (SHA), the technique considered here, directly (no amplification) identifies and quantifies plankton species using ribosomal RNA (rRNA)‐targeted oligonucleotides. This project focused on the development of a new SHA method for the detection of Microcystis (16S rRNA) using laboratory cultures. Assay calibration curve and limits of detection were determined using Microcystis aeruginosa, though signal intensity differed significantly (p < 0.05) between three species (M. aeruginosa, Microcystis botrys, Microcystis wesenbergii). SHA results for M. aeruginosa raised under three light intensities (40, 60, and 100 μmol photons m−2 s−1) and two temperatures (25°C and 32°C) were greatest at the highest irradiance for both temperatures, but otherwise variable, yielding an overall significant (p < 0.05) interaction between light and temperature. The 32°C treatment also resulted in significantly lower (p < 0.05) Photosystem II quantum efficiency (Fv/Fm) and microcystins concentrations per light intensity. Spiked field experiments showed that SHA signal was not significantly affected (p > 0.05) by a mixed phytoplankton assemblage. The assay speed, wide detection range, and specificity indicate that this method has promise for additional field studies and HAB monitoring.

In 2014, the Atlantic mud fiddler crab Uca pugnax was found 80 km north of its previously known northern range limit. Two years before this shift was noted, we collected a total of 781 male and female specimens from 6 populations along a latitudinal transect extending from Wareham, Massachusetts (41.7615°N), to Tybee Island, Georgia (32.0139°N), USA. By assessing latitudinal and seasonal patterns in the hepatosomatic index (HSI; a measure of stored energy) and the reproductive status of females, we sought to determine whether adult physiological and reproductive limits might slow the northern expansion of U. pugnax. We did not find a latitudinal cline for HSI, suggesting that U. pugnax is a thermal generalist; however, both males and females in the southern part of the range showed greater seasonal fluctuations in HSI compared to northern conspecifics. Across the range, ovigerous females had a significantly reduced HSI, revealing the cost of reproduction. Ovigerous females were found in the May 2013 collection in Massachusetts be fore ocean conditions were permissible for larval development and earlier than previously reported for this species. U. pugnax is expected to closely track warming conditions in the Northwest Atlantic because adults in northern populations are able to maintain energy stores comparable to that of their southern conspecifics, and they release planktonic larvae in early spring, maximizing their dispersal potential.

No abstract

Nitrogen (N) inputs to developed coastlines are linked with multiple ecosystem and socio-economic impacts worldwide such as algal blooms, habitat/resource deterioration, and hypoxia. This study investigated the microbial and biogeochemical processes associated with recurrent, seasonal bottom-water hypoxia in an urban estuary, western Long Island Sound (WLIS), that receives high N inputs. A 2-year (2020–2021) field study spanned two hypoxia events and entailed surface and bottom depth water sampling for dissolved nutrients as inorganic N (DIN; ammonia-N and nitrite + nitrate (N + N)), organic N, orthophosphate, organic carbon (DOC), as well as chlorophyll a and bacterial abundances. Physical water quality data were obtained from concurrent conductivity, temperature, and depth casts. Results showed that dissolved organic matter was highest at the most-hypoxic locations, DOC was negatively and significantly correlated with bottom-water dissolved oxygen (Pearson’s r = −0.53, p = 0.05), and ammonia-N was the dominant DIN form pre-hypoxia before declining throughout hypoxia. N + N concentrations showed the reverse, being minimal pre-hypoxia then increasing during and following hypoxia, indicating that ammonia oxidation likely contributed to the switch in dominant DIN forms and is a key pathway in WLIS water column nitrification. Similarly, at the most hypoxic sampling site, bottom depth bacteria concentrations ranged ~ 1.8 × 10 4 –1.1 × 10 5 cells ml −1 pre-hypoxia, declined throughout hypoxia, and were positively and significantly correlated (Pearson’s r = 0.57; p = 0.03) with ammonia-N, confirming that hypoxia influences N-cycling within LIS. These findings provide novel insight to feedbacks between major biogeochemical (N and C) cycles and hypoxia in urban estuaries. Supplementary Information The online version contains supplementary material available at 10.1007/s10533-023-01021-2.