Abstract
Small marine copepods are key components of the pelagic food webs in Chinese coastal waters, but very few studies have addressed their trophodynamics, with even fewer studies addressing their diel feeding rhythms. In this study, the diel feeding rhythm and grazing selectivity of the copepod assemblage in Daya Bay during September 30 to October 2, 2014, were studied based on gut pigment analysis. Small copepods (body length < 1.5 mm) including Paracalanus parvus, Temora turbinata, Acrocalanus gibber, Temora stylifera, Euterpe acutifrons, and Acrocalanus gracilis, accounted for 73.9–100% of the total copepod abundance. The copepod assemblage generally exhibited a diurnal feeding pattern, characterized by a higher gut pigment content and ingestion rate during the daytime, consistent with variation in the ambient Chl α concentration. Fifty-five percent of the phytoplankton standing stock per day was consumed by the copepod assemblage, wherein diatoms, prymnesiophytes, and cyanobacteria were the main prey items with average contributions of 19.4–32.9% to the gut pigment contents. The copepod assemblage showed a strong feeding preference for prymnesiophytes, a weak feeding preference for diatoms, and avoidance of cyanobacteria. These results suggest a strong top-down control on phytoplankton community, especially on small groups from small copepods in the Daya Bay ecosystem.
Highlights
Copepods are the predominant mesozooplankton in marine pelagic system (Longhurst, 1985)
Small copepods usually selectively graze on picoand nano-phytoplankton and relatively may consume more of smaller sized phytoplankton relative to large copepods in many systems (Zervoudaki et al, 2007; Isari and Saiz, 2011), which means that energy and material may be transferred from pico- and nanophytoplankton through small copepods to higher trophic level more efficiently under the circumstance that a miniaturization trend has been occurring in phytoplankton community in many marine systems (Shen, 2001; Wei, 2003; Chen et al, 2010; Wu et al, 2017; Chiba, 2019)
The diel feeding rhythm is generally proposed to be dependent on the diel vertical migration of marine copepods (Champalbert et al, 2003), but non-migratory species show diel feeding rhythms (Hayward, 1980; Tang et al, 1994)
Summary
Copepods are the predominant mesozooplankton in marine pelagic system (Longhurst, 1985). Small copepods (∼1 mm in length) including adults and juveniles of calanoid genera such as Paracalanus, Clausocalanus, and Acartia and non-calanoid species and it has been increasingly recognized that they, accounting for up to 90% of copepod abundance, represent an extremely important constitute of copepod community in coastal and estuarine waters (Hopcroft et al, 1998; Turner, 2004; Liu et al, 2013; Han, 2015; Cheng, 2019). Their abundance and biomass, have historically been significantly underestimated in the copepod community in early studies, owing to the usage of coarse mesh nets (∼500 μm). It is expected that the diel feeding rhythm of a copepod assemblage will be more complicated with entangled aforementioned factors and the variable community composition
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