Ecological roles of noctiluca scintillans in marine food web : as a predator, "prey" and nutrient regenerator

Abstract

Noctiluca scintillans is a cosmopolitan red tide forming heterotrophic dinoflagellate, which plays a crucial role in marine food web. My thesis study is to qualify and quantify the ecological significance of N. scintillans as a predator, nutrient regenerator and atypical “prey” (of which a newly described marine ciliate Strombidium hongkongense, within its prey size range, becomes the predator) in marine food web. To achieve these goals, both field studies and laboratory observation and experiments were conducted. A case study in Port Shelter, Hong Kong showed that the population dynamics of N. scintillans in this semi-enclosed bay was mainly governed by hydrographical (temperature and water stability), meterological (favorable wind) and biological factors (phytoplankton food supply). N. scintillans actively interacted with other trophic compartments in the existing ecosystem, but its population growth was more directly and largely related to the abundance and composition of phytoplankton assemblages, especially diatoms. Laboratory experiments further showed that growth and grazing of N. scintillans were mainly constrained by prey quantity, quality and composition. Its feeding strategy, i.e. preferential feeding and better growth on organisms containing sufficient phosphorous (P), eicosapentaneoic acid (EPA) and/or α- linolenic acid (ALA), and physiological characteristics, i.e. almost homeostasis but susceptible to P-limitation, and multiple releasing pathways of metabolic products, are of great importance in determining the energy transfer and nutrient flux in its existing environment, and shaping the food web structure. Our laboratory results are applicable to the real field situation and able to explain at least part of the biological processes that lead to the formation and decline of N. scintillans blooms.

Date of Award	2016
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology