Effects of Chaetomorpha valida bloom development on the structure and succession of the phytoplankton community in Apostichopus japonicus culture ponds

Abstract

Phytoplankton is an important producer in aquaculture ecosystems and is the basis of both the structure and function of culture ecology. The structure and succession of phytoplankton communities are very sensitive to ambient conditions and are regulated by a combination of physical, chemical and biological factors acting as important indicators and evaluation indexes of the aquaculture ecosystem (Buesseler, 1998;Segura et al.., 2013).Normally, the phytoplankton community is a dynamic system with both species (mostly Bacillariophyta, Chlorophyta and Pyrrophyta) and their populations changing over time, showing Abstract Phytoplankton is very important to aquaculture ecosystem and is vulnerable to ambient conditions. In recent years, Chaetomorpha valida, an invasive filamentous green alga, has been blooming in Apostichopus japonicus culture ponds. Here, we conducted a 5-month investigation, examining whether that bloom affects the structure and succession of the pond phytoplankton community. Differences in dissolved oxygen, light and nutrient concentrations in both bloom and normal (non-bloom) areas varied monthly. The species and populations of phytoplankton communities in both the bloom and normal areas showed no significant differences when C. valida biomass was low, but through time, differences became increasingly significant. Species in normal areas remained relatively stable as the numbers and species of the dominant species changed little and the diversity and evenness indexes increased monthly. In bloom areas, species abundance decreased gradually with most of the decrease affecting Bacillariophyta. Here, the number of dominant species remained stable from May to July but decreased significantly in August and September. Diversity and evenness indexes also decreased significantly, and the differences between the 2 areas increased rapidly. Results showed that C. valida bloom in A. japonicus culture ponds influenced both the structure and succession of the phytoplankton community, contributing to comprehensive assessment of the effects of C. valida bloom on aquaculture ecology. K E Y W O R D Saquaculture ponds, filamentous green algae, green tide, phytoplankton community, species competition

Evaluation of the potential of the green tide macroalgae Chaetomorpha valida as a food source for Apostichopus japonicus

“…Chaetomorpha valida is an invasive filamentous green macroalgae blooming in lagoons and the Apostichopus japonicus culture areas over the past decade in Northern China, especially along the Shandong Peninsula (Chen et al, 2020; Chi et al, 2009; Silva et al, 2008). During the algal outbreak, the thalli formed algal mats 2–30 cm thick, reaching the average biomass of 2.0–3.1 kg WW/m 2 (Chen et al, 2020). At present, the massive thalli are mainly discarded and rotten after manual salvage, resulting in a waste and secondary pollution.…”