Modeling loss and recovery of Zostera marina beds in the Chesapeake Bay: The role of seedlings and seed-bank viability

Abstract

Loss and recovery processes following a documented large scale decline in Zostera marina beds in the York River, Virginia in 2005 were modeled by coupling production and sexual reproduction models. The reproduction model included formulations for reproductive shoot production, seed production, seed-bank density, seed viability, and seed germination. After the model was calibrated and validated using in situ water quality and plant performance measurements from two different sites, model scenarios were run for three years (1 year pre-decline, 2 years post-decline) to quantify the effects of (1) the presence or absence of sexual reproduction, (2) increases in water temperatures from ambient to ambient +5°C in 1°C increments, and (3) the potential interactive effects of light and temperature conditions on bed maintenance and re-establishment. Model projections of Z. marina production following the decline corresponded to in situ measurements of recovery only when sexual reproduction was added. However, a 1°C increase in temperature resulted in a complete loss of biomass after two consecutive years of temperature stress following the depletion of the viable sediment seed bank. Interactions between light and temperature stress resulted in overall lower production and resilience to declines under lower light conditions due to corresponding decreases in photosynthetic rates and increases in respiration. Model results highlight (1) the need to incorporate sexual reproduction into Z. marina ecosystem models, (2) the projected sensitivity of established beds to consecutive years of stress, and (3) the negative effects of multiple stressors on Z. marina resilience and recovery.