The likelihood of sampling American eelgrass and starry stonewort in Cayuga Lake varied by date, depth, and location

• Published in: Journal of Aquatic Plant Management 2024, Vol.62 (1), p.30
• Format: Report
• Language: English
• ISSN: 0146-6623
• DOI: 10.57257/JAPM-D-23-00015

Understanding the phenology of aquatic, invasive species is important from theoretical and management perspectives, particularly if phenology differs among or within waterbodies in the invaded range. Variability in the likelihood of sampling invasive starry stonewort [Nitellopsis obtusa (Desv.) J. Groves] and American eelgrass (Vallisneria americana Michx.) in Cayuga Lake, New York, was evaluated with respect to date, geographical location, and water depth. Following point-intercept methodology, 25,741 samples were collected at 22 sites among 3 locations (northern, middle, southern) from 2020 through 2022. Based on logistic regression, the likelihood of sampling both species followed quadratic relationships with increasing date and water depth. Relationships differed among locations and between species, but variability was notably greater for starry stone-wort. American eelgrass was most likely to be sampled at 2.5 m of water compared to 3.5 m for starry stonewort. The likelihood of sampling American eelgrass increased from June through August, peaked in September, and declined through November and was similar among locations. Overall, the likelihood of sampling starry stonewort increased from June to peak near the end of July and was very low by November. Among locations, the date of peak likelihood of sampling starry stonewort differed by 42 d. If sampling likelihoods are positively correlated with biomass phenology, large variability in the likelihood of sampling starry stone-wort due to water depth and date among locations reflects an inability to generalize the phenology of this species in Cayuga Lake. Reported regional differences in phenology further highlight challenges in generalizing this aspect of starry stonewort life history. Key words: aquatic plant management, invasive species, macroalgae, Nitellopsis obtusa, Vallisneria americana.