Distribution, hatch-date, growth, and mortality of larval Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea

2014 ◽  
Vol 95 (1) ◽  
pp. 161-174 ◽  
Author(s):  
Chiyuki Sassa ◽  
Motomitsu Takahashi ◽  
Youichi Tsukamoto
Keyword(s):  
Growth Rate ◽  
East China Sea ◽  
East China ◽  
The East China Sea ◽  
Hatch Date ◽  
China Sea ◽  
Key Species ◽  
New Moon ◽  
Adult Habitat ◽  
Shelf Region

We examined the distribution, hatch-date, growth, and mortality of larval Benthosema pterotum, a dominant pseudoceanic myctophid in the shelf region of the East China Sea, during early autumn when the main spawning has been predicted. This species is a key species in the food web of this area. Larvae were abundant in the area south of Cheju Island (60–80 m depth), corresponding with the adult habitat. Occurrence of the larvae was restricted to the onshore side of the shelf-break salinity front, indicating that this front acted as a barrier restricting the offshore dispersion of the larvae. In the area where the larvae occurred, a cyclonic eddy is formed, which is considered to limit the dispersal of the larvae, enabling them to recruit into the area of adult habitat. Modes of hatch-date appeared from late August to early September and from mid to late September, suggesting that large-scale spawning events occurred at least twice during the spawning season. Since the modes coincided with the new moon period, B. pterotum is suggested to spawn periodically once a month around the new moon, resulting in efficient mating and fertilization. Mean absolute growth rate (0.26 mm d−1) and weight-specific growth rate (18.8% of dry body weight d−1) were higher than previously reported values of other subtropical–tropical myctophids, which would be related to the high food availability in the study area. Daily instantaneous mortality coefficient during the first two weeks after hatching was estimated to be 0.28 d−1 (equivalent to 24.7% mortality d−1).

Reproductive biology of Benthosema pterotum (Teleostei: Myctophidae) in the shelf region of the East China Sea

2013 ◽  
Vol 94 (2) ◽  
pp. 423-433 ◽  
Author(s):  
Chiyuki Sassa ◽  
Seiji Ohshimo ◽  
Hiroshige Tanaka ◽  
Youichi Tsukamoto
Keyword(s):  
Reproductive Biology ◽  
East China Sea ◽  
Trophic Levels ◽  
East China ◽  
Hepatosomatic Index ◽  
The East China Sea ◽  
Spawning Period ◽  
China Sea ◽  
Key Species ◽  
Shelf Region

Benthosema pterotum is a dominant myctophid in the shelf region of the East China Sea (ECS). They are a key species linking secondary producers and upper trophic levels. We examined the reproductive biology of B. pterotum in the ECS, based on 3065 specimens (10.7–54.8 mm standard length (SL)) sampled during cruises in 1999 and 2004–2009 to enable data over a 12 month cycle to be assessed. Between 14 and 30 mm SL, the ratio of females to males was ~1:1; it increased with SL, and all individuals ≥46 mm SL were females. The gonadosomatic index (GSI) at 50% sexual maturity of females and males was 3.91 and 0.24, respectively. Based on this criterion, females and males can mature at sizes larger than 28 mm and 24 mm SL, respectively. Although mature females having GSI ≥3.91 occurred over nine months (May–January), mean GSI of females peaked sharply during August–September, i.e. the primary spawning period. The hepatosomatic index peaked during April–July, and declined during August–September, indicating storage of materials and energy for reproduction. Based on data from seasonal bottom trawl surveys, small individuals of B. pterotum began to occur abundantly in autumn, and modal body lengths increased progressively during spring–summer, corresponding to the above reproductive seasonality. Oocytes at various sizes were found in mature ovaries, indicating that they are multiple spawners. Egg size at hydration ranged from 0.5 to 0.85 mm. Batch fecundity was positively correlated with SL, and ranged from 253 to 1942 eggs in fish from 30.1–54.8 mm SL.

scholarly journals Seasonal and spatial patterns of picophytoplankton growth, grazing and distribution in the East China Sea

2014 ◽  
Vol 11 (7) ◽  
pp. 1847-1862 ◽  
Author(s):  
C. Guo ◽  
H. Liu ◽  
L. Zheng ◽  
S. Song ◽  
B. Chen ◽  
...  
Keyword(s):  
Growth Rate ◽  
East China Sea ◽  
Mortality Rates ◽  
East China ◽  
Ecological Niches ◽  
The East China Sea ◽  
Average Growth ◽  
China Sea ◽  
Chlorophyll Maximum ◽  
Grazing Mortality

Abstract. Dynamics of picophytoplankton population distribution in the East China Sea (ECS), a marginal sea in the western North Pacific Ocean, were studied during two cruises in August 2009 (summer) and January 2010 (winter). Dilution experiments were conducted during the two cruises to investigate the growth and grazing among picophytoplantkon populations. Comparisons of phytoplankton growth (μ0) and microzooplankton grazing rates (m) on seasonal (summer and winter), spatial (plume, transitional and Kuroshio regions) and vertical (surface and depth of chlorophyll maximum) scales were made. The three picophytoplankton populations occupied different ecological niches and showed different distribution patterns (especially in summer), which is, however, not coincident with their maximum growth rate. The distribution and population transition of picophytoplankton is therefore a result of the balance between growth and grazing mortality. Average growth rates (μ0) for Prochlorococcus (Pro), Synechococcus (Syn) and picoeukaryotes (Peuk) were 0.36, 0.81 and 0.90 d−1 in summer, and 0.46, 0.58 and 0.56 d−1 in winter, respectively. Average grazing mortality rates (m) were 0.46, 0.63 and 0.68 d−1 in summer, and 0.25, 0.22 and 0.23 d−1 in winter for Pro, Syn and Peuk, respectively. The spatial pattern of both growth and grazing mortality rates showed decreasing trends from the inshore to offshore region, indicating a strong influence of the nutrient gradient induced by Yangtze River input. In summer, Pro, Syn and Peuk were dominant in Kuroshio, transitional and plume regions, respectively, while in winter all the three populations tended to thrive in the offshore regions, particularly for Pro and Syn. Vertically, picophytoplankton exhibited the highest abundance at ~ 20 m in summer and at the surface in winter. Both growth rate and grazing mortality were higher at the surface than in the deep chlorophyll maximum (DCM) layer. On average, protist grazing consumed 84, 79 and 74% and 45, 47 and 57% of production for Pro, Syn and Peuk in summer and winter, respectively.

scholarly journals Bottom-up and top-down controls on picoplankton in the East China Sea

2013 ◽  
Vol 10 (5) ◽  
pp. 8203-8245 ◽  
Author(s):  
C. Guo ◽  
H. Liu ◽  
L. Zheng ◽  
S. Song ◽  
B. Chen ◽  
...  
Keyword(s):  
Growth Rate ◽  
East China Sea ◽  
Yangtze River ◽  
East China ◽  
The East China Sea ◽  
Top Down ◽  
Bottom Up ◽  
China Sea ◽  
Plume Region ◽  
Grazing Mortality

Abstract. Dynamics of picoplankton population distribution in the East China Sea (ECS), a marginal sea in the western North Pacific Ocean, were studied during two "CHOICE-C" cruises in August 2009 (summer) and January 2010 (winter). Dilution experiments were conducted during the two cruises to investigate the growth and grazing among picophytoplantkon populations. Picoplankton accounted for an average of ~29% (2% to 88%) of community carbon biomass in the ECS on average, with lower percentages in plume region than in shelf and kuroshio regions. Averaged growth rates (μ) for Prochlorococcus (Pro), Synechococcus (Syn) and picoeukaryotes (peuk) were 0.36, 0.89, 0.90 d−1, respectively, in summer, and 0.46, 0.58, 0.56 d−1, respectively, in winter. Seawater salinity and nutrient availability exerted significant controls on picoplankton growth rate. Averaged grazing mortality (m) were 0.46, 0.63, 0.68 d−1 in summer, and 0.22, 0.32, 0.22 d−1 in winter for Pro, Syn and peuk respectively. The three populations demonstrated very different distribution patterns regionally and seasonally affected by both bottom-up and top-down controls. In summer, Pro, Syn and peuk were dominant in Kuroshio, transitional and plume regions respectively. Protist grazing consumed 84%, 78%, 73% and 45%, 47%, 57% of production for Pro, Syn and peuk in summer and winter respectively, suggesting more significant top-down controls in summer. In winter, all three populations tended to distribute in offshore regions, although the area of coverage was different (peuk > Syn > Pro). Bottom-up factors can explain as much as 91.5%, 82% and 81.2% of Pro, Syn and peuk abundance variance in winter, while only 59.1% and 43.7% for Pro and peuk in summer. Regionally, Yangtze River discharge plays a significant role in affecting the intensity of top-down control, indicated by significant and negative association between salinity and grazing mortality of all three populations and higher grazing mortality to growth rate ratio (m / μ) in plume region than Kuroshio region in summer. The gradient of bottom-up factors caused by Yangtze River input and Kuroshio warm current intrusion also exerted important influence on picoplankton abundance evidenced by the significant correlations. Vertically, picoplankton exhibited highest abundance at subsurface layer around 20 m thick in summer, while at surface in winter. Both growth rate and grazing mortality were higher at surface than at the deep chlorophyll maximum (DCM) layer. Our study first systematically described the bottom-up and top-down regulations of different picoplankton populations between contrasting seasons, different depths, and among different regions in the ECS, which provide insights for better understanding the population dynamics of picoplankton and trophic transfer in microbial food web in highly dynamic shelf ecosystems and in general.

The East China Sea Seafloor Observatory and its upgraded project

2011 ◽  
Author(s):  
Huiping Xu ◽  
Changwei Xu ◽  
Rufu Qin ◽  
Yang Yu ◽  
Shangqin Luo ◽  
...  
Keyword(s):  
East China Sea ◽  
East China ◽  
The East China Sea ◽  
China Sea ◽  
Seafloor Observatory
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