Copepods In Summer Research Articles

Increasing picocyanobacteria success in shelf waters contributes to long-term food web degradation.

Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota-large diatoms, dinoflagellates and copepods-that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico- and nanophytoplankton biomass in coastal areas. Among the pico-fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico- and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light-harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega-3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition-related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters.

Bio-Ecology of the Oldest Lessepsian Fish Atherinomorus forskalii (Pisces: Atherinidae)

Although Atherinomorus forskalii is the oldest lessepsian fish species with a widespread distribution range, there have not been any study about its biological and ecological features. Therefore, we aim to understand its effects on coastal ecosystems by determining its feeding ecology and life span. Four hundred sixty-two specimens were obtained with Sabiki rigs from the Turkish coast of the Levantine Sea. The minimum, maximum and mean length values of the samples were determined as 4.5 cm, 12 cm and 8.2 cm ±0.07 respectively. In winter and spring, the species main food item was represented by pelagic gastropods, while copepods in summer and insects in autumn were the main food items. Although A. forskalii prefers small-sized invertebrates, it is observed that they consume juvenile fish larger than one third of their size. Its wide diet preference shows that it is an opportunistic feeder. These findings represent that A. forskalii feeds on native species and also is in food competition since its dietary overlaps. Ages were calculated between I and III, and the second age group was dominant with a ratio of 52.8%. The highest spawning activity took place between April and early July. The hepatosomatic index (HSI) and gonadosomatic index (GSI) values were calculated monthly, and they reached the highest points in May and June, respectively. The results showed that this small fish, which has been deprived of scientific interest until now, has been determined to have a bio-ecological superiority according to its syntopic species. Thus, it is revealed that it has a more negative impact on the coastal ecosystem than expected.

Carbon biomass, production rates and export flux of copepods fecal pellets in the Changjiang (Yangtze) River estuary

Copepod fecal pellets are ubiquitous throughout the oceans. Their production and export can represent a highly efficient pathway of carbon export. However, the role these fecal pellets play in carbon export in the Changjiang (Yangtze) River estuary is not well known. Two cruises were carried out in the Changjiang estuary in the spring and summer of 2013, during which time carbon biomass, production, and export of copepod fecal pellets were studied. Spring and summer fecal pellet carbon biomass ranged 0.30–1.01 mg C/m3 (mean=0.56±0.20 mg C/m3 ) and 0.31–1.18 mg C/m3 (mean=0.64±0.24 mg C/m3), respectively, significantly lower than phytoplankton. At most stations, fecal pellet carbon biomass was higher in surface or subsurface layers than deeper layers. Production rates ranged 0.65–1.49 pellets/(ind.∙h) (mean=1.02±0.27 pellets/(ind.∙h)) in spring and 0.62–1.34 pellets/(ind.∙h) (mean=0.98±0.22 pellets/(ind.∙h)) in summer, within the range reported in previous studies. Higher production rates of fecal pellets occurred at stations with higher chlorophyll a concentrations, and production rates of copepods of size 500–1 000 μm greater than copepods >1 000 μm during both cruises. The potential export flux of fecal pellets was slightly higher in summer (mean=68.95±14.37 mg C/(m2 ∙d)) than spring (mean=52.08±11.33 mg C/(m2 ∙d)) owing to higher summer copepod abundances. To our knowledge, this study is the first of its kind in the Changjiang estuary, and it confirms the significant role of copepod fecal pellets in local carbon export.

Decadal changes in zooplankton abundance and phenology of Long Island Sound reflect interacting changes in temperature and community composition

Between 1939 and 1982, several surveys indicated that zooplankton in Long Island Sound, NY (LIS) appeared to follow an annual cycle typical of the Mid-Atlantic coast of North America. Abundance peaked in both early spring and late summer and the peaks were similar in magnitude. In recent decades, this cycle appeared to have shifted. Only one large peak tended to occur, and summer copepod abundance was consistently reduced by ∼60% from 1939 to 1982 levels. In other Mid-Atlantic coastal systems such a dramatic shift has been attributed to the earlier appearance of ctenophores, particularly Mnemiopsis leidyi, during warmer spring months. However, over a decade of surveys in LIS have consistently found near-zero values in M. leidyi biomass during spring months. Our multiple linear regression model indicates that summer M. leidyi biomass during this decade explains <25% of the variation in summer copepod abundance. During these recent, warmer years, summer copepod community shifts appear to explain the loss of copepod abundance. Although Acartia tonsa in 2010–2011 appeared to be present all year long, it was no longer the dominant summer zooplankton species. Warmer summers have been associated with an increase in cyanobacteria and flagellates, which are not consumed efficiently by A. tonsa. This suggests that in warming coastal systems multiple environmental and biological factors interact and likely underlie dramatic alterations to copepod phenology, not single causes.

Evidence for ontogenetic feeding strategies in four calanoid copepods in the East Sea (Japan Sea) in summer, revealed by stable isotope analysis

Deciphering the ontogenetic feeding ecology of copepods is essential to understanding their role in the energy transfer of marine ecosystems. We used stable isotope analysis to examine the ontogenetic feeding strategies of the four coexisting calanoid copepods, Mesocalanus tenuicornis, Metridia pacifica, Calanus sinicus, and Neocalanus plumchrus, in the East Sea (Japan Sea) in summer. Moreover, we used the stable carbon and nitrogen isotope composition of small-sized plankton in three cell size fractions, pico- (< 2 μm), nano- (2–20 μm) and microplankton (20–200 μm), to identify the dietary preference at each developmental stage. The relative carbon masses of pico-, nano- and microplankton were 18, 38, and 44%, respectively, and their δ13C and δ15N values gradually increased with increasing size classes. The ontogenetic trophic position of four copepods were relatively low and ranged from 2.1 to 2.6, indicating that herbivores feed on small-sized phytoplankton, pico- and nanoplankton. Among copepodid stages, the δ13C and δ15N values of M. tenuicornis and C. sinicus differed significantly, while those of M. pacifica and N. plumchrus were not significantly different. In M. tenuicornis, the smallest species among the four copepods examined, the diet preference of CIV for picoplankton changed to nanoplankton in the adult stage. When M. pacifica developed from CIV to adult, the diet preference changed from pico- to microplankton. The proportion of microplankton in the diet of C. sinicus and N. plumchrus increased from CIV to female adult and from CIII to CV, respectively. During the developmental progress in copepodid stages, the smaller copepods significantly changed their dietary preference from pico- to microplankton, while the larger copepods consistently fed on microplankton. We suggest that smaller copepods have an advantage in survival at early copepodid stages compared with larger copepods in summer when microplankton biomass is relatively low.

Community structure and abundance of copepods in summer on a fringing coral reef off Ishigaki Island, Ryukyu Islands, Japan

Community structure and abundance of copepods in summer on a fringing coral reef off Ishigaki Island, Ryukyu Islands, Japan

Trophic role and top-down control of a subarctic protozooplankton community

Plankton succession was investigated in the subarctic Godthabsfjord, Western Greenland, from March to August 2010. The trophic role of protozooplankton (ciliates and hetero- trophic dinoflagellates) was evaluated with emphasis on their seasonal succession and as prey for the copepod community. The integrated protozooplankton biomass ranged between 0.1 and 4.0 g C m �2 , and was dominated by ciliates. Over the 6 mo study period, maximum potential ingestion rates of the protozooplankton ranged from 0.02 to 1.2 g C m �2 d �1 , corresponding to 30 to 194% of primary production d �1 or 0.5 to 37% of phytoplankton biomass d �1 . The highest copepod biomass (24 g C m �2 ) occurred in spring, with Metridia longa alone contributing up to 92% of the biomass. A grazing experiment with M. longa feeding on a natural plankton assemblage confirmed that this species cleared cells in the size range 10 to 60 µm with an average clearance rate of 2.4 ml µg C �1 d �1 . The copepod community, dominated by the genera Calanus, Metridia, Pseudocalanus, Oithona, Microsetella and Triconia/Oncaea, accounted for 72 to 93% of the copepod biomass in the spring. After the large calanoid copepod species left the surface layer, the protozooplankton increased numerically and were the most important grazers for some weeks until a late summer copepod community, dominated by cyclopoids Oithona spp., controlled the protist community. Our study indicated that protozooplankton succession is regulated by copepod grazing during most of the season, and that these protists provide an essential source of nutrition for the copepod populations.

Distribution and community characteristics of planktonic copepods in the northwest coastal waters off Hainan Island

We analyzed the structure, distribution, and seasonal changes of planktonic copepod communities, as well as their relationships with environmental factors using data collected from 21 stations in the northwest coastal waters off Hainan Island between November 2008 and July 2009. A total of 44 species of planktonic copepods was identified, with 25, 23, 22, and 23 species found in autumn (November), winter (January), spring (April) and summer (July), respectively. The dominant species were mainly warm water species, such as Canthocalanus pauper, Subeucalanus subcrassus, Temora turbinate, Acartia spinicauda, Calanopia elliptica and Euchaeta concinna, etc. There were significant changes in copepod abundance among seasons; total copepod abundance was highest in winter with 409 ind./m, followed by autumn with 144 ind./m, spring with 55 ind./m and summer with 17 ind./m, respectively. Distributional data showed that an area of high copepod density appeared in the southern portion of the study area in winter, while there was an area of high copepod density in the center of the survey area in autumn. Copepod abundance was higher in deeper waters, and lower in the coastal areas in spring and summer. Species diversity index was highest in summer and followed by spring, autumn and winter in turn. The evenness index of spring and summer copepod communities was higher than those of autumn and winter. The structure of these planktonic copepod communities reflects tropical and subtropical floristic characteristics. Species composition varied significantly with season, and copepod abundance was noticeably affected by water temperature and diatom cell abundance. We 第 3 期 孙柔鑫等: 海南岛西北沿岸海域浮游桡足类的分布及群落特征 321 detected no obvious correlationship between copepod abundance and salinity.

Effect of light and food on the metabolism of the Arctic copepod Calanus glacialis

Reduction in sea-ice thickness and cover is expected to lead to earlier underwater light penetration and thus earlier onset of the spring bloom and a longer open water production in the Arctic. The goal of this study was to understand how these climate-induced changes in light and food regimes may impact the key zooplankton grazer Calanus glacialis CV. We studied this copepod’s metabolic response to starvation (filtered sea water; FSW) and algal food (Food) under two different light regimes (light vs. dark) when it was in dormancy (diapause) in winter (November) and active in summer (July). Respiration was measured as indicator of metabolism and was measured for 9 days for copepods exposed to: Dark+FSW, Dark+Food, Light+FSW and Light+Food. The in situ respiration in winter was three times lower than in summer. In winter, light was the main factor to increase the copepod’s metabolism to a level comparable with that of active copepods in summer, but respiration only remained high if food was present. In summer, it was the combined effect of light and Food that increased the respiration, although Food seemed more important than light with time. Copepods reduced their metabolism with time when food was absent, regardless of the light regime, probably preparing for diapause. These results suggest that C. glacialis can quickly adapt to a changing light and food regime in the Arctic, being able to wake up from diapause if light and thus food appear and postpone its diapause if the food availability is still favorable.

Summer copepod production in subtropical waters adjacent to Australia's North West Cape

Growth and secondary production of pelagic copepods near Australia's North West Cape (21° 49′ S, 114° 14′ E) were measured during the austral summers of 1997/1998 and 1998/1999. Plankton communities were diverse, and dominated by copepods. To estimate copepod growth rates, we incubated artificial cohorts allocated to four morphotypes, comprising naupliar and copepodite stages of small calanoid and oithonid copepods. Growth rates ranging between 0.11 and 0.83 day−1 were low, considering the high ambient temperatures (23–28°C). Calanoid nauplii had a mean growth rate of 0.43±0.17 day-1 (SD) and calanoid copepodites of 0.38±0.13 day-1. Growth rates of oithonid nauplii and copepodites were marginally less (0.38±0.19 day−1 and 0.28±0.11 day−1 respectively). The observed growth rates were suggestive of severe food limitation. Although nauplii vastly outnumbered copepodite and adult copepods, copepodites comprised the most biomass. Copepodites also contributed most to secondary production, although adult egg production was sporadically important. The highest copepod production was recorded on the shelf break (60 mg C m-2 day-1). Mean secondary production over both shelf and shelf break stations was 12.6 mg C m-2 day-1. Annual copepod secondary production, assuming little seasonality, was estimated as ~ 3.4 g C m-2 year-1 (182 kJ m-2 year-1).

An impact of seasonal squid migrations and fishing on the feeding spectra of subantarctic notothenioids Patagonotothen ramsayi and Cottoperca gobio around the Falkland Islands

Seasonal changes in the diet of two abundant notothenioid fishes, rock cod Patagonotothen ramsayi (Nototheniidae) and frogmouth Cottoperca gobio (Bovichthidae) were studied on the Falkland Island shelf. The rock cod is a near-bottom browser, feeding mostly on gelatinous and crustacean plankton. The diet of juveniles [10–16 cm total length (TL)] includes mostly copepods in summer and comb jellies Mnemiopsis leydyi in winter. Adult rock cod (17–34 cm TL) in summer consumed mainly plankton, with comb jellies and salps being of primary importance. In winter they mainly took benthos, primarily ophiuroids and lobster krill (Munida spp.), and the comb jelly. During the fishing season, rock cod also scavenge on fishing discards. The frogmouth is a benthic ambush predator; both small (11–30 cm) and large (31–80 cm) representatives feed on the rock cod throughout the year. During the seasonal offshore migration of the squid Loligo gahi (June–August), this prey predominated in the large frogmouth diet, with crab, Peltarion spinosulum, of secondary importance. The region is seasonally exploited by the squid trawl fishery. As the fishing season commences (August–September), discarded rock cod also becomes an important food item for the frogmouth. Seasonal offshore migrations of L.gahi into the common depth range of both notothenioids have a significant direct (change in the C. gobio diet) and indirect (scavenging on fishing discards and targeting bottom scavengers by P. ramsayi and C. gobio during the squid fishing) impact on their diets over the Falkland shelf. The niche breadth of rock cod varied from 2.63 to 3.21 and that of frogmouth varied from 2 to 6.29, depending on fish size and season.

Variations in Stable Carbon Isotope Ratio of the Copepod Acartia tonsa during the Onset of the Texas Brown Tide

The Laguna Madre of South Texas is a shallow coastal lagoon whose dominant primary producers shifted from seagrasses to phytoplankton with the onset of the Texas brown tide, which persisted from 1990 through 1997. Acartia tonsa is the dominant component of the mesozooplankton and forms an important link in both the phytoplankton and detritus-based pelagic food webs. Stable carbon isotope ratios of A. tonsa, as well as the two major primary producers: phytoplankton (as particulate organic carbon) and seagrasses, were measured from March 1989 to October 1991. Zooplankton samples were collected at four locations in the Laguna Madre: two in shallow water (c. 1 m) over seagrass beds and two in slightly deeper water (c. 2–3 m) over a muddy bottom in a secondary bay without seagrasses. We found seasonal trends in the isotopic composition of A. tonsa collected within both habitats as well as distinct differences between the average {ie995-1} values of individuals collected in the two regions. Isotopic ratios of animals collected during the summer months were generally 4–8‰ enriched in 13C compared with those collected in the winter, at all stations. A. tonsa collected over seagrass beds were 2–5‰ more enriched in 13C than those collected over muddy bottoms. These observations suggest carbon derived from seagrasses can be an important source of nutrition for these copepods in summer, especially for copepods living over seagrass beds. The effects of the persistent brown tide decreased the contribution of seagrasses as a carbon source for A. tonsa during the summer of 1991. The pathway by which seagrass carbon enters the diet of A. tonsa is unclear, but the two pathways considered most likely are through copepods feeding on microzooplankton that have fed on bacteria nourished on seagrass carbon, or by copepods feeding directly on particles of seagrass detritus.

Importance of the macrofauna for the feeding of young fish species from infralittoral of Arrozal - Cananeia lagoon estuarine region (25º02'S-47º56'W): Brazil

The aim of this study was to establish the importance of the macrofauna as food for young fish species that inhabit the infralittoral adjacent to the lower marsh. The sampling site is located at Arrozal, Cananeia lagoon estuarine region (25o02'S and 47o56'W) and the collectings were realized monthly, during a year. The results suggest that the studied area could be considered as a nursery ground for young fish species. The local macrofauna is composed mainly by several groups of crustaceans and has a marked temporal variation. Mysids were dominant in Spring, copepods in Summer, mysids and bivalves were co-dominants in the Autumn and amphipods in Winter. Mysids, copepods, ostracods, tan aids and other epifaunal crustaceans were more consumed than other items. According to the trophic habits, the twelve fish species could be divided into three groups: the first and the third as mysids and copepods eaters respectively, and the second group with a balanced diet reflecting more than the other groups the seasonal variation of the macrofauna collected by the dredge. Benthonic and benthopelagic organisms were considered the major food source, being consumed by 75% of the analysed fish species, in Cananeia infralittoral.

Importance of the macrofauna for the feeding of young fish species from infralittoral of Arrozal: Cananeia lagoon estuarine region (25º02'S-47º56'W) - Brazil

The aim of this study was to establish the importance of the macrofauna as food for young fish species that inhabit the infralittoral adjacent to the lower marsh. The sampling site is located at Arrozal, Cananéia lagoon estuarine region (25º02'S and 47º56'W) and the collectings were realized monthly, during a year. The results suggest that the studied area could be considered as a nursery ground for young fish species. The local macrofauna is composed mainly by several groups of crustaceans and has a marked temporal variation. Mysids were dominant in Spring, copepods in Summer, mysids and bivalves were co-dominants in the Autumn and amphipods in Winter. Mysids, copepods, ostracods, tan aids and other epifaunal crustaceans were more consumed than other items. According to the trophic habits, the twelve fish species could be divided into three groups: the first and the third as mysids and copepods eaters respectively, and the second group with a balanced diet reflecting more than the other groups the seasonal variation of the macrofauna collected by the dredge. Benthonic and benthopelagic organisms were considered the major food source, being consumed by 75% of the analysed fish species, in Cananéia infralittoral.

Studies on the meiofauna of Sagar Island

Mean number of total meiofauna individuals in the intertidal estuarine sediments around the island ranged from 1/10 cm2 to 517/10 cm2. Nematodes and copepods were the dominant taxa comprising over 80% of the total fauna. Higher meiofaunal densities occurred over the lower shore. The fauna was concentrated mostly in top 4 cm of sediment, showing little submergence towards higher tidal levels. No diurnal and seasonal vertical migrations of meiofauna were observed. Two small seasonal peaks of meiofaunal abundance were noted. Total population values were highest in summer and lowest during monsoon. Nematodes reached their maximum in winter and copepods in summer. Variations in salinity appeared to be responsible for the seasonal pattern. The present meiofaunal densities are considerably lower than those recorded in other areas. The highly fluctuating hydrographical conditions and the fine sediment with silt-clay fraction, poor drainage, low oxygen content, etc., are considered responsible for the paucity of meiofauna in this area.