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In situ diet of the copepod Calanus sinicus in coastal waters of the South Yellow Sea and the Bohai Sea
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Xiaoyan YI1, 2, Yousong HUANG1, 2, Yunyun ZHUANG1, 2, Hongju CHEN1, 2, Feifei YANG2, Weimin WANG2, Donghui XU2, Guangxing LIU1, 2, *, Huan ZHANG1, 3
Acta Oceanologica Sinica | 2017, 36(6) : 68 - 79
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Acta Oceanologica Sinica | 2017, 36(6): 68-79
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In situ diet of the copepod Calanus sinicus in coastal waters of the South Yellow Sea and the Bohai Sea
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Xiaoyan YI1, 2, Yousong HUANG1, 2, Yunyun ZHUANG1, 2, Hongju CHEN1, 2, Feifei YANG2, Weimin WANG2, Donghui XU2, Guangxing LIU1, 2, *, Huan ZHANG1, 3
Affiliations
  • 1 Key Laboratory of Marine Environment and Ecology (Ocean University of China), Ministry of Education, Qingdao 266100, China
  • 2 College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
  • 3 Department of Marine Sciences, University of Connecticut, Groton 06340, USA
Published: 2017-06-01 doi: 10.1007/s13131-017-0974-6
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Copepods are a key trophic link between primary producers and predatory animals at higher trophic levels in the marine ecosystem. Knowledge of the in situ composition of the copepod diet is critical for the accurate evaluation of trophic relationships and energy transfer in marine food webs. In this study, we applied a PCR-based cloning technique developed previously to investigate the in situ diet of Calanus sinicus, an ecologically important large-sized calanoid copepod that dominates in the shelf waters around China, Japan and Korea. Analyses of the 18S rDNA sequences obtained from the copepod diet revealed the diverse food composition of C. sinicus from two stations (Y19 in the South Yellow Sea and B49 in the Bohai Sea). A total of 43 operational taxonomic units (OTUs) were detected, which belonged to 13 diverse lineages: Bacillariophyta, Dinoflagellata, Dictyochophyceae, Chrysophyta, Katablepharidophyta, Pelagophyceae, Apusozoa, Hydrozoa, Ctenophora, Echinodermata, Tunicata, Chaetognatha and marine fungi. The results indicate that during an algae bloom, C. sinicus can graze on the bloom causative species. When the abundance of phytoplankton in ambient water is relatively low, C. sinicus can choose eggs, larvae, or organic particles/detritus of various metazoans, especially hydrozoans and ctenophores, as alternative food sources. Our result suggests that C. sinicus is an omnivorous species, and its prey choice may depend on the food availability in the ambient waters.

copepod  /  in situ diet  /  molecular analysis  /  18S rDNA  /  ciliate blocking primer
Xiaoyan YI, Yousong HUANG, Yunyun ZHUANG, Hongju CHEN, Feifei YANG, Weimin WANG, Donghui XU, Guangxing LIU, Huan ZHANG. In situ diet of the copepod Calanus sinicus in coastal waters of the South Yellow Sea and the Bohai Sea[J]. Acta Oceanologica Sinica, 2017 , 36 (6) : 68 -79 . DOI: 10.1007/s13131-017-0974-6
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1 Introduction
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Copepods, especially the planktonic copepods such as those in the order Calanoida, are considered as the key trophic linkage between phytoplankton and higher trophic levels. The trophic relationship between copepods and other organisms has had a great impact on biogeochemical cycling and energy transfer in marine food webs (Ban et al., 1997; Calbet, 2008; Zöllner et al., 2009). To better understand the complexity of the copepod-based food chains, an accurate estimation of the diet composition is very important, because it provides information on how copepods obtain their required nutrients as well as on the nutrient recycling and energy flow of marine food webs (Turner, 2004). Information on copepod diets has largely stemmed from methods for analyzing gut pigments (Irigoien et al., 2004), dissection of grazers’ guts followed by microscopic analyses of the gut content (Buffan-Dubau et al., 1996) and use of stable isotope tracers (Verschoor et al., 2005). However, pigment-based methods are very sensitive to differential pigment breakdown, and pigments are not often specific to particular species (Irigoien et al., 2004). Besides, pigment-based methods do not yield data for heterotrophic prey (Nejstgaard et al., 2008). In the case of gut dissection, food content may not be easily identified, especially when they are partially digested and morphologically altered (Sautour et al., 2000). The usage of stable isotope tracers also could not exactly reflect the in situ prey composition of the copepod in the natural environment (Schmidt et al., 2003). Therefore, the lack of in situ diet information largely due to unavailability of a proper methodology, has hindered our understanding of the trophic relationships of plankton in the pelagic ecosystem.
The PCR-based molecular technique has an obvious advantage over the traditional methods of studying in situ copepod diets in its sensitivity, specificity and efficiency (Nejstgaard et al., 2003; Motwani and Gorokhova, 2013; Hu et al., 2014; Huang et al., 2014). Numerous studies aiming to explore the trophic relationships of marine organisms have been carried out (King et al., 2008; Pompanon et al., 2012 and refs therein). Eukaryotic small subunit ribosomal RNA gene (SSU rDNA, or 18S rDNA) is the most extensively used DNA marker for taxonomic classification of organisms due to its high copy number in the genome and overall good phylogenetic resolution (López-García et al., 2001; Moon-van der Staay et al., 2001; Bråte et al., 2010). In the previous study, we developed several non-copepod 18S rDNA primer sets to successfully depress the 18S rDNA amplification of the copepods, especially for the calanoida (Guo et al., 2012). The non-copepod18SF2 & R2 primer set proved to be useful in amplifying this gene from most of eukaryotic lineages while excluding that of the copepod in the in situ diet study of the copepod (Hu et al., 2014; Huang et al., 2014). However, the presence of symbiotic apostome ciliate DNA compromises the efficacy of this method to detect the genuine diet species (Guo et al., 2012). To overcome this shortcoming, we, as well as the other researchers, have developed blocking primers which bind to the regions unique to the 18S rDNA of the apostome ciliates, and the results show that the co-amplification of the 18s rDNA of the apostome ciliates could be minimized largely by the addition of the block primers (Hu et al., 2014; Yi et al., 2014).
Calanus sinicus is an ecologically important large-sized calanoid copepod which is distributed widely in the shelf waters of China, Japan and Korea, and dominates the mesozooplankton in the coastal waters including the South Yellow Sea and the Bohai Sea (Chen, 1964; Hulsemann, 1994; Uye, 2000). Many studies have been carried out on diet composition of C. sinicus. Initially, herbivorous diatom, e.g., species in Genera Coscinodiscus, Melosira and Cyclotella, were considered as the main food source of this copepod (Li, 1964; Yang, 1997). More recent studies indicated that C. sinicus could ingest ciliates, bacteria, and even copepods besides phytoplankton (Huo et al., 2008; Chen et al., 2010; Liu et al., 2011). However, methodological limitations of previous studies (as mentioned above) could not accurately estimate the prey organisms of C. sinicus in natural waters, and the relative importance of different food sources within the natural diet of C. sinicus remains uncertain.
In this study, we explored the diet composition and the feeding strategies of the C. sinicus population in the coastal waters of the South Yellow Sea and the Bohai Sea of China using a PCR-based protocol developed previously. Our data suggests that C. sinicus feeds on a variety of prey including those previously known, as well as those that were unsuspected. C. sinicus in the South Yellow Sea are likely to prey on the eggs, larvae or organic particles/detritus of metazoans, especially hydrozoans and ctenophores, as supplementary food sources when phytoplankton abundance is low, while C. sinicus in the Bohai Sea can graze on the brown tide alga Aureococcus anophagefferens when the bloom occurs.
2 Materials and methods
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2.1 Ambient water sample collection and microscopic analyses
To explore the plankton composition that might be potential food of C. sinicus, ambient water samples were collected in the South Yellow Sea and the Bohai Sea on June 15 and 25, 2011 at Stas Y19 and B49, respectively (Fig. 1 and Table 1). Water samples of three depths (3 m, 10 m and 20 m; 750 mL each) were collected simultaneously using Niskin Water Sampler assembled on a CTD profiler (Seabird 911 plus, USA). Water samples were fixed on site immediately as mentioned above. Plankton samples were concentrated through settling down by gravity for three days in the dark for further microscopic analyses as reported (Lin et al., 2009).
2.2 Copepod sampling and DNA isolation
Copepods were collected at the same sites. Net tow was performed from the bottom to the surface of the sea at a speed of 0.5 m/s using a plankton net (mouth diameter 31.6 cm, 160-μm mesh size) with a filtering cod end. To minimize stimulation of the copepods which might cause defecation, the net contents for genomic DNA isolation were gathered without washing the net. Samples were fixed on site immediately using 2% Utermöhl’s solution (Utermöhl, 1958) and stored at 4°C for a short period of time until copepod sorting and DNA extraction (within 1 month), a storage condition without detectable DNA degradation in the samples (Zhang and Lin, 2002).
C. sinicus adults were sorted under a stereomicroscope (Leica S8APO, Leica Corporation) in the laboratory. The appendages of the copepods were carefully removed and the remaining body parts were washed five times individually in 0.45 µm-filtered and autoclaved seawater (salinity 31 to eliminate the detritus and/or associated phytoplankton cells loosely attached to the body. The surface of each copepod was examined under stereomicroscope to confirm no visible microorganisms, especially the apostome ciliates, attached (Guo et al., 2012). To study the population as a whole, we pooled 30 copepods obtained into a single sample for each of the station because the diet profiles differed greatly among the copepod individuals (Guo et al., 2012; Huang et al., 2014). Then, 30 copepod individuals from the same station were homogenized with a pestle in a 1.5 mL micro-tube with 0.5 mL DNA buffer (1% SDS, 0.1 mol/L EDTA, 200 µg/mL proteinase K), and incubated at 55°C for 2 d and the genomic DNAs were extracted following a CTAB protocol (Zhang and Lin, 2005). DNA concentration and quality were measured using a NanoDrop 2000C spectrophotometer (Thermo Scientific, USA).
2.3 PCR amplification, cloning and sequencing for copepod samples
Since in C. sinicus DNA samples isolated from both Stas B49 and Y19, apostome ciliates was detected, we combined apostome ciliate blocking primer (Ciliate18Sblk1, Table 2) with non-copepod18S primers (10:1) and the PCR was performed with 1 cycle of initial denaturing for 3 min at 94°C, 5 cycles of denaturing 10 s at 95°C, 60 s at 68°C, followed by 30 cycles of 95°C for 10 s, 54.2°C for 30 s, 72°C for 40 s, and finally 10 min at 72°C (Yi et al., 2014). The PCR products were purified and cloned into T-vector, and 60 random clones of each sample were sequenced after plasmid isolation.
The 18S rDNAs of the copepod samples of the two stations were also PCR- amplified with the universal primer set 18ScomF1 and 18ScomR1 (Table 2) using the genomic DNAs isolated from the in situ fixed copepods as templates. PCR was performed with 1 cycle of initial denaturing for 3 min at 94°C, 35 cycles of 95°C for 30 s, 56°C for 30 s, 72°C for 40 s, and finally 10 min at 72°C, and the amplicons were purified and directly sequenced as reported (Zhang et al., 2005) to confirm the identity of the copepods.
2.4 Sequence and phylogenetic analyses
All original sequences were manually inspected to remove the vector and primer sequences and to correct reading errors. The sequences were searched against the NCBI nt database using the Basic Local Alignment Search Tool (BLAST) (Altschul et al., 1997). Homologous sequence information was determined based on top hits from BLAST. The best hits were aligned with our cloned sequences using Clustal X v2.1 (Larkin et al., 2007). Maximum Likelihood (ML) tree was inferred with 1000 resampling bootstrap analyses using MEGA 5.0 (Tamura et al., 2011). Rarefaction analyses and diversity indices were estimated by Mothur (Schloss et al., 2009).
3 Results
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3.1 Phytoplankton community and A. anophagefferens bloom
Water samples from different depth were analyzed microscopically. Results revealed 26 different species for each station respectively, which belonged to diatoms, dinoflagellates, cryptophytes and pelagophytes (Tables A1–A4). For the phytoplankton community in Sta. Y19, the total cell abundance was 3.8×104 cells/L. Diatoms dominated the species number (50%) and accounted for 37% of the phytoplankton abundance, followed by cryptophytes, dinoflagellates, and pelagophytes in cell abundance, accounting for 33%, 22% and 8%, respectively. For Sta. B49 in the Bohai Sea, a brown tide bloom of A. anophagefferens was breaking out during sampling period with cell concentration reaching 1.4×107 cells/L. This species accounted for >99% cell abundance of the whole phytoplankton community. Besides A. anophagefferens, 15 species of diatoms, 9 species of dinoflagellates and 1 species of pelagophyte were also detected (Table A2).
Microscopic analyses clearly showed that the phytoplankton abundance at Sta. B49 (1.4×107 cells/L) was significantly higher than that at Sta. Y19 (3.8×104 cells/L), even when the bloom causative species A. anophagefferens was excluded, cell abundance at Y19 in the South Yellow Sea was still lower, about one half of that at B49 in the Bohai Sea. The cell abundance of phytoplankton matched the biomass measured by chlorophyll a concentration of two stations. Chlorophyll a of the algal bloom at Sta. B49 was 14.8 μg/L, 5 times higher than that of Sta. Y19 (Table 1).
3.2 Molecular confirmation of C. sinicus and identification of apostome ciliates
The sequence of 1.75-kb 18S rDNA amplified from the copepod samples showed 99% identity to the reported C. sinicus sequence in GenBank (GU969174). This result molecularly confirmed the identity of C. sinicus collected in the two stations in addition to morphological identification.
The PCR using the apostome ciliate-specific 18S rDNA primer set (Vampe18SF and Vampe18SR) gave positive results for the copepod samples from both Y19 and B49, indicating C. sinicus from both stations hosted the parasitic ciliates.
3.3 Analyses of in situ diet of C. sinicus
18S rDNA libraries were constructed for in situ diet analyses of C. sinicus, and 60 clones were randomly picked and sequenced for each sample respectively. The partial 18S rDNA sequences obtained in this study had been deposited in the GenBank under accession numbers KT825583-KT825682. Fifty-one (Sta. Y19) and 49 (Sta. B49) high quality sequences of ~0.75 kb were obtained, which were clustered into 26 and 23 unique OTUs using 99.5% cut-off, respectively (Tables 3 and 4). The OTUs corresponded to species from 13 diverse lineages including Bacillariophyta (diatoms), Dinoflagellata (dinoflagellates), Dictyochophyceae (dictyochales), Chrysophyta (chrysophytes), Katablepharidophyta (katablepharidophytes), Pelagophyceae (pelagophytes), Apusozoa, Hydrozoa (hydrozoans), Ctenophora (ctenophores), Echinodermata (echinoderms), Tunicata (tunicates), Chaetognatha (arrow worms) and marine fungi (Fig. 2). No apostome ciliates were detected. The rarefaction curve (Fig. 3) showed that the current sequencing depth has not exhausted the diet diversity. Chao and the ACE parameter estimator indicated that the maximal number of OTUs to be 61 and 109.5 respectively (Table 5). The Shannon and Simpson index indicated that the species distribution of Sta. Y19 was more uniform.
Sequence analyses revealed a wide range of organisms including phytoplankton, metazoans and marine fungi. The number of phytoplankton (marine algae) sequences accounted for 18% and 73% respectively in Stas Y19 and B49, while the proportion of metazoans were 59% and 17%, and the marine fungi accounted for 23% and 10%, respectively (Fig. 4).
Sequences of diatoms, dinoflagellates, chrysophytes and katablepharidophytes were represented in both diet clone libraries, while sequences of pelagophytes (A. anophagefferens, 99% identity) and dictyochales (Florenciellales sp., 95% identity) were unique in Sta. B49. In Sta. Y19 diet library, dinoflagellates were relatively abundant (12%). The library of Sta. B49 samples was dominated by A. anophagefferens, accounting for 41% of the all sequences obtained. In the two clone libraries, chrysophytes were represented by the three species, Isochrysis sp., Emiliania huxleyi and Chrysochromulina campanulifera. Diatoms included Phaeodactylum tricornutum and Stephanopyxis turris, while katablepharidophytes only included Katablepharis sp.. Metazoans were the substantial components of the diet. Sequences of gelatinous jellyfish, including hydrozoans and ctenophores, and arrow worms, were detected in both station samples, while sea urchin (Archaeopneustes) and tunicate (Oikopleura sp.) were only detected at Sta. Y19. Jellyfish sequences were the most abundant in the diet library of Sta. Y19 sample, and Clytia gracilis (100% identity) accounted for the majority of all the jellyfish sequences. The detected jellyfish species including Clytia gracilis, Hydrichthys boycei, Ectopleura crocea, Eudendrium glomeratum, Euplokamis sp., and the species of Chaetognatha were Aidanosagitta sp. and Sagitta sp.. Also notable in both diet libraries were the marine fungi. Asterotremella music (99% identity), Cadophora-like marine fungi (99% identity) and Malassezia restricta (99% identity) were detected in both stations. Aspergillus sp. (100% identity), Cladosporium sp. (99% identity) and Valsa ambiens (100% identity) were only found in Sta. Y19, while Dioszegia zsoltii (99% identity) and Rhodotorula lamellibrachiae (99% identity) were unique to Sta. B49.
4 Discussion
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It is evident that PCR-based molecular technique has advantages over the traditional morphology-based methods on unveiling the in situ diet information of copepods and other zooplankton in the natural environment (Nejstgaard et al., 2003; Boling et al., 2012; Maloy et al., 2013; Hu et al., 2014; Huang et al., 2014; Yi et al., 2014; Hu et al., 2015), largely because oftentimes the prey organisms in the gut of the predators are already partly digested and morphologically indistinguishable, yet they can still be detected as long as the DNA of the targeted gene (18S rDNA for example) is intact.
Our results expanded the knowledge of the copepod in situ diet composition using PCR-based molecular technique in this study. C. sinicus likely feeds on various organisms which were unknown previously, ranging from phytoplankton to metazoans. Various marine microalgae including diatoms, dinoflagellates, chrysophytes, pelagophyceae, dictyochales, and katablepharidophytes were detected in the C. sinicus diet. Ctenophores and hydrozoans make up a substantial part of the C. sinicus diet in the South Yellow Sea, as well as echinoderms, an important metazoan in the study area. It has been found that jellyfish (ctenophores and hydrozoans) sequences dominated the 18S rDNA diet libraries of C. sinicus in the Huanghe (Yellow River) Estuary, along with various algae and mollusks (Huang et al., 2014). Tunicates, cladocerans, ophiuroids (brittle stars) and various algae have been detected in the diet of the calanoid copepod Canthocalanus pauper from the South China Sea (Hu et al., 2015). It is worthwhile to note that we also observed the diet compostion of C. sinicus during a brown tide bloom.
4.1 Prey diversity
The dietary analyses of C. sinicus in this study generated 43 unique OTUs, among which 26 and 23 were found at Stas Y19 and B49, respectively. Dinoflagellates and diatoms were present in both ambient water samples and copepod diet samples. However, although sequences of chrysophytes, katablepharidophytes, and dictyochales were detected in the diet samples, they were not found in the ambient water, likely due to the lower resolution power of the morphology-based methods. The sequences of the brown tide species A. anophagefferens dominated B49 diet samples. A. anophagefferens was also the dominant species found in the B49 ambient water sample through microscopic analyses (Table A2), so it was not surprising to find many A. anophagefferens sequences in the library. Diatoms have been considered the main prey of C. sinicus (Li, 1964; Yang, 1997). Our data showed that in both stations, compared to diatoms represented by P. tricornutum and Skeletonema sp., dinoflagellates were more abundant in the copepod diet (Fig. 4). In a study on the diet of copepod Acartia tonsa, it was found that diatoms were of lower nutritional value than dinoflagellates (Jones and Flynn, 2005), also the development of the copepod C. helgolandicus was found to be arrested when feeding exclusively on the diatom Skeletonema costatum (Ianora et al., 2004). Whether or not C. sinicus selectively feed on dinoflagellates requires in deep sequencing of the diet organisms using technique such as Illumina high throughput sequencing.
Metazoans, such as hydrozoans, ctenophores, arrow worms, echinoderms and tunicates, are rarely considered as prey for copepods. In this study, however, sequences of these metazoans were detected in relatively high frequency, especially in Sta. Y19 (Fig. 4 and Table 3). In the previous study, using PCR-based methods, we detected many sequences of ctenophores and hydrozoans (Huang et al., 2014). Other researchers have also found that tunicate Oikopleura sp., echinoderm Ophionereis reticulate, arrow worms and other metazoans could constitute the potential diet of the calanoid copepod C. pauper (Hu et al., 2014, 2015). Considering body size of adult C. sinicus collected in this study, 2.6–3.5 mm, and the diameter of its mouthpart, it is unlikely that C. sinicus could eat the adults of the metazoans such as hydrozoans, ctenophores, echinoderms, arrow worms and tunicates. Instead, C. sinicus could eat eggs, larvae, organic particles or detritus of these metazoans. A study using gut dissection and microscopic examination method also suggested that copepods could prey on hydrozoans and arrow worms (Schnetzer and Steinberg 2002). Using the gut pigments analyses method, Zhang et al. (2006) found that non-phytoplankton food accounted for 6%–60% of the diet composition of C. sinicus in June. Our result is consistent with these studies.
Microscopic analyses indicated that in June 2011, the abundance of phytoplankton was low in the South Yellow Sea, but zooplankton was abundant (average abundance 12 288 ind./m3). Among zooplankton, species proportion of planktonic larva, cnidarians, tunicates, chaetognath accounted for 28%, 13%, 3%, 3% respectively. Abundance of tunicate (Oikopleura dioica) were high especially in the western part of the South Yellow Sea including our sampling site (700 ind./m3), and the larvae of sea urchins (echinoderms) were also detected microscopically in this region. On the other hand, the metazoan excluding crustaceans were few (84 ind./m3) in the Bohai Sea. The larvae or eggs of these metazoans could be the dominant food supply for the C. sinicus population at Sta. Y19 when the phytoplankton abundance was low (Table 1 and Tables A1–A4).
The marine fungi sequences were found in both Stas Y19 and B49. As an important component of microorganisms in the marine ecosystem, most marine fungi are either parasitic or symbiotic to the marine organisms including copepods, or attach to nutrient-rich sediments. Only a minority are free-living (Richards et al., 2012). So far, there is little research on the relationship between marine fungi and copepods. It is possible that the fungi detected in our samples were either parasites or constituted the diet of C. sinicus. Marine fungi were also found in the diet of European eel larvae in the Sargasso Sea (Riemann et al., 2010) and in the diet of calanoid copepods C. pauper, Termora turbinate and Subeucalanus subcrassus in the Sanya Bay, China (Hu et al., 2015) through molecular approach. More studies combining the molecular approach with other methodologies are needed to confirm the trophic relationship between marine fungi and copepods such as C. sinicus.
Free-living ciliates are an important food group of calanoid copepods (Saiz and Calbet, 2011), but we did not detect any of their sequence in this study. Altough the blocking primer was desgined based on the apostome ciliate 18S rDNA sequence, it might also inhibit the amplification of free-living ciliates 18S rDNA. The addition of blocking primer is necessary in the cloning based Sanger sequncing method (Guo et al., 2012; Hu et al., 2014). In the furture study, to overcome this shortage, instead of using blocking primers to block the amplification of apostome ciliate 18S rDNA, development of new primers that are sutable for high throughput sequenicg method is needed.
4.2 Eggs, larvae or particles/detritus of ctenophores and hydrozoans as food of C. sinicus
Gelatinous jellyfish including hydrozoans and ctenophore are substantial component detected in diet composition, especially Clytia and Euplokamis. The abundance of both hydrozoan and ctenophore species are high in the South Yellow Sea and the Bohai Sea in summer, and a common ctenophore in both waters is Pleurobrachia globose (Du et al., 2013). Intriguingly, instead of P. globose, Euplokamis sp. was the only ctenophore species detected in the diet libraries of C. sinicus. Our previous study (Huang et al., 2014) also showed that the Euplokamis sequences dominated (40%) the diet library of C. sinicus in the adjacent waters of the Huanghe Estuary in the Bohai Sea. The hydrozoans Clytia gracilis, Eudendrium glomeratum and Hydrichthys boycei were found in Sta. Y19, and Ectopleura crocea was detected in B49 diet library (Tables 3 and 4), while Rathkea octopunctata and Eirene menoni were detected in C. sinicus near the Huanghe Estuary (Huang et al., 2014). All these hydrozoan species were not detected microscopically. These results suggest that C. sinicus may have a low digestion rate toward the ingested ctenophore and hydrozoan eggs or larvae, that these jellyfish have higher gene copy numbers of 18S rDNA in the genome, or that C. sinicus selectively prey on this rather less abundant jellyfish in the form of eggs or larvae to support their reproduction and development.
Besides in the form of eggs or larvae, jellyfish could also be ingested in the form of organic particles/detritus. Although plankton (both phyto- and zooplankton) are the dominant food composition of copepod like C. sinicus, there are some researches showed that other food sources such as marine snow could also be part of the diet (Chen et al., 2010). Marine snow is always combinations of fecal pellets from zooplankton, fish, and organic aggregates (such as discarded appendicularian houses) from some metazoans (Turner, 2015). Particles or detritus of jellyfish could be part of marine snow and be eaten by copepod like C. sinicus.
4.3 Potential control of C. sinicus to brown tide
During our sampling at Sta. B49, a brown tide bloom broke out. Both microscopic and molecular analyses confirmed the bloom species was A. anophagefferens. A. anophagefferens brown tides were first recorded in several bays on the northeastern coast of USA (Sieburth et al., 1988). China is the third country in the world where A. anophagefferens brown tide bloom has been reported (Zhang et al., 2012). The temperature, salinity and chlorophyll a concentration data obtained in our sampling (Table 1) were consistent with those reported in Zhang et al. (2012). It is clear that both studies detected the same brown tide bloom in the coastal waters of the Bohai Sea.
Our diet data of C. sinicus sampled in the A. anophagefferens bloom clearly showed that this brown tide causative species was the dominant food of the copepod. Zooplankton (such as copepods) grazing over phytoplankton cells is an important regulatory factor of algal blooms (Calbet et al., 2003; Barofsky et al., 2010). In our study when brown tide broke out, the phytoplankton in the ambient water was overwhelmingly dominated by A. anophagefferens (more than 99% of total cells counted), C. sinicus mainly grazed on this tide causative species. The grazing of C. sinicus on A. anophagefferens cells provided more evidences that this copepod may play an important ecological role in the marine ecosystem by regulating the dynamics of certain harmful algal blooms.
Acknowledgements
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The authors thank Fang Jing and Li Zishang and the crew of R/V Dongfanghong II for collecting the field samples. The authors also thank Zhang Yushan Minnie from University of Connecticut helped improve the English writing of the manuscript.
Funding
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  • The National Natural Science Foundation of China under contract Nos 31372509, 41076085 and 41328009.
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doi: 10.1007/s13131-017-0974-6
  • Receive Date：2016-03-21
  • Online Date：2026-04-14
  • Published：2017-06-01
Article Data
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History
  • Received：2016-03-21
  • Accepted：2016-08-02
Funding
The National Natural Science Foundation of China under contract Nos 31372509, 41076085 and 41328009.
Affiliations
    1 Key Laboratory of Marine Environment and Ecology (Ocean University of China), Ministry of Education, Qingdao 266100, China
    2 College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
    3 Department of Marine Sciences, University of Connecticut, Groton 06340, USA

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表12种不同金属材料的力学参数
科
Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
total species (%)		 属
Genus		 种数
Number of
species		 占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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