Abstract

As the extent of hypoxia in coastal waters increases, the survivorship of jellyfish polyps relative to that of competing sessile organisms often increases, enabling them to reproduce more prolifically, leading to a medusa bloom in the following year. Quantifying the population of polyps can be used to predict when these blooms will occur. We used a time-delayed logistic equation to quantify the response to variable dissolved oxygen (DO) concentrations and temperatures in a population of moon jellyfish (Aurelia coerulea) polyps on substrates that carried competing sessile organisms. The availability of substrate depends on the DO threshold for each competitor, and substrates only become available to the polyps during hypoxic periods. We used the median sublethal concentration (SLC50) thresholds of hypoxia for different groups of benthic organisms to calculate the DO-dependent survivorship of A. coerulea polyps competing on the substrate. Since the median lethal time (LT50) for cnidarians is close to 240 h, we chose a 10-day delay in the time-delayed logistic equation. The carrying capacity is determined every 10 days depending on DO concentrations and temperature. The polyps reproduce by budding at a temperature-dependent rate after settling on the substrate during the hypoxic period, and thus, the annual polyp reproduction rate is determined by multiplying the temperature-dependent budding rate by the DO-dependent survivorship. The duration of hypoxia is a key factor determining the polyp population, which can increase more as the duration of hypoxia increases. Modeling simulations were compared to observed data. In this model, the DO and temperature distribution data make it possible to quantify variations in the population of the A. coerulea polyps, which can be used to predict the abundance and appearance of medusa the following year.

Highlights

  • Hypoxia in coastal waters is expected to increase because of eutrophication, climate change, stratification pattern change, and oxygen solubility [1,2]

  • We suggest a model that describes the polyp population dynamics on a substrate in competition with other sessile organisms depending on the dissolved oxygen (DO) concentration and temperature

  • Variations in polyp populations have been quantified as a function of DO concentration and temperature

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Summary

Introduction

Hypoxia in coastal waters is expected to increase because of eutrophication, climate change, stratification pattern change, and oxygen solubility [1,2]. Both the intensity and duration of hypoxia are increasing [3,4], while the number of coastal sites where hypoxia has been reported has increased exponentially at 5.54% per year [5]. Hypoxia profoundly affects the abundance and distribution of marine species in coastal waters [6,7,8]. Vertical and horizontal distributions of organisms follow oxygen gradients and discontinuities, and migratory behavior is constrained in response to oxygen availability [8]. Organisms such as cnidarians that have a high tolerance for low dissolved oxygen (DO)

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