Feeding of marine planktonic copepods on mixed phytoplankton

The feeding of juveniles and adults of the copepods Eucalanus pileatus, Temora stylifera and T. turbinata fed a mixture of the phytoplankton Skeletonema costatum, Leptocylindrus danicus and Rhizosolenia alata f. indica was studied at 20°C. E. pileatus nauplii, copepodids and adult females ingest similar percentages of the 3 algae in terms of carbon. Temora juveniles younger than CII ingest mainly S. costatum; at more advanced developmental stages, the ingestion rate on S. costatum remains constant whereas feeding on L. danicus and R. alata f. indica increases with increasing body weight. Feeding on high concentrations of large particles reduces the grazing pressure on small particles, thus favoring zooplankton which require small-sized food.     

A recirculating seawater aquarium system for inland laboratories

We have designed and installed a 7,500 l recirculating aquarium system for the purpose of maintaining marine gastropods in an inland laboratory. It is completely nonmetallic and can be adapted for any number of isolated living compartments. Vonvenient and efficient filtration is achieved by the use of disposable cartridge filters. The water temperature is regulated by a direct expansion cooling coil and a hot water heating coil without the intervention of secondary heat transfer fluids. Most of the water is stored in an underground reservoir which contributes to thermal stability, and the water temperature varies <±0.1°C per week. The pH and specific gravity remain at 8.0±0.1 and 1.023+0.002-0.001, respectively, for as long as 4 months. We have no evidence that any animal (Aplysia, Hermissenda, Tritonia) has died due to poor water quality. The system is constructed from readily available components, is moderate in cost, and has performed reliably for over 2 years.     

Effects of anoxia on the viability of subitaneous eggs of planktonic copepods

The effect of anoxia on the viability (as evidenced by hatching) of newly spawned and fully developed subitaneous eggs of three species of copepods, Acartia tonsa (Dana), Centropages hamatus (Lilljeborg), and Labidocera aestiva (Wheeler) was determined for eggs produced in the laboratory by adults collected from inshore waters of the northeastern Gulf of Mexico between January and August 1992. Hatching success decreased to 50% or less when eggs were exposed to oxygen concentrations <0.06 mll^-1 for more than 12 d, except for newly spawned eggs of L. aestiva, which still showed 50% survival after 32 d of exposure to anoxia. For all three species, newly spawned eggs survived exposure to anoxia longer than fully developed eggs. The results indicate that the increasing occurrence of anoxia in estuarine and coastal waters could have a major impact on the population growth of these important food web organisms.     

Towards a global model of in situ weight-specific growth in marine planktonic copepods

The dependency of in situ weight-specific fecundity of adult females (as egg production) and growth of juveniles (as somatic production) upon individual body weight in marine planktonic copepods was examined. A compilation was made of results where wild-caught individuals were incubated in natural seawater (often pre-screened to remove large organisms), at near in situ temperatures, over short periods of the order of 24 h. The results demonstrate that for the adult broadcast-spawning group weight-specific fecundity rates are dependent upon body weight, but independent of temperature. We postulate this may be the result of global patterns in available phytoplankton. Weight-specific growth rates are dependent upon individual temperature and body weight in juvenile broadcast-spawners, with rates declining as body weight increases. Sac-spawners have growth/fecundity rates that are independent of body weight in adults, juveniles, and both combined, but which are temperature-dependent. Globally applicable equations are derived which may be used to predict growth and production of marine copepods using easily quantifiable parameters, namely size-distributed biomass and temperature. Some of the variability in growth which remained unaccounted for is the result of variations in food quantity and quality in the natural environment. Comparisons of the rates compiled here over the temperature range 10 to 20 °C with previously compiled food-saturated rates over the same temperature interval, revealed that in situ rates are typically sub-optimal. Adults appear to be more food-limited than juveniles, adult rates in situ being 32 and 40% of those under food saturation in broadcasters and sac-spawners, respectively, while juvenile in situ rates are on average ∼70% of those at food saturation in both broadcasters and sac-spawners. Received: 18 September 1997 / Accepted: 13 May 1998     

Seasonal study of planktonic copepods and their benthic resting eggs in northern California coastal waters

Few investigations have examined the occurrence of zooplankton resting eggs in the sea bed of waters deeper than 20 m. In this study the distribution and abundance of planktonic copepods and their benthic resting eggs in coastal waters off northern California, U.S.A., were determined and related to environmental parameters (temperature, salinity, depth, and sediment grain size). Sediment cores, net tows, and CTD profiles were obtained in April and October 1989, and February, April, and October 1990. Water depths in the study area ranged from approximately 60 to 120 m. The mean abundance of eggs was as high as 1.2×10⁵ m^-2 for Acartia clausi Giesbrecht and 1.9×10⁵ m^-2 for Tortanus discaudatus Thompson and Scott. These egg concentrations are comparable to those reported previously for shallower more protected regions. The abundance of eggs in the sediments decreased with increasing depth of the water column. For the region as a whole, eggs were least abundant in muddy sediments. The mean abundance of eggs in the sea bed also varied seasonally and annully. Benthic resting eggs of A. clausi were more abundant in April 1989 than in April 1990, and adults of the species were never found in the plankton samples. The lack of adults is not unusual since results of previous studies indicate that A. clausi is a cold-water species, and in this region water temperatures are colder in summer, than in winter, due to upwelling. Temperature and salinity data indicated that the upwelling season had commenced by the time of the April 1990, but not the April 1989 sampling. Thus, the reduced abundance of benthic eggs in April 1990 may have been due to egg-hatching in response to reduced temperatures. The results suggest that the presence of A. clausi in coastal waters off northern California is linked to recruitment from benthic resting eggs.     

Spatio-temporal changes in diversity and community structure of planktonic copepods in Sagami Bay, Japan

Seasonal changes in diversity and community structure of planktonic copepods at a shelf site in Sagami Bay, Japan was studied in relation to cross-shelf interaction of species components. Seasonal mesozooplankton samples were collected from the shelf station (St. M) of the north-west part of Sagami Bay from 1995 to 1997. Vertical multi-layered samples were collected near the center of Sagami Bay (St. P) in June 1996. A total 185 copepod species were identified from the two stations. We observed a clear seasonal succession in calanoid diversity and community structure at St. M from a simple shelf water community (>11 species) during spring blooming periods to highly diverse and mixed communities (ca 20–30 species) of shelf water species coupled with various Kuroshio Current species during late summer to autumn. Cluster and non-metric multidimensional scaling ordination analyses showed two distinct calanoid community groups. One group, which included samples of St. M and the surface layer of St. P, consisted of shelf water species, such as Calanus sinicus, Ctenocalanus vanus, Paracalanus spp., and Kuroshio species, such as, Canthocalanus pauper, Scolecithrix danae, etc. The other cluster was restricted to the samples collected from mid and deep layers at St. P, which consisted of meso- and bathypelagic species and Oyashio species (cold-current species, such as Neocalanus cristatus, Pseudocalanus spp., Eucalanus bungii and Metridia pacifica). In the mid and deep layers at St. P, the population of dormant copepodid stage V (CV) of Eucalanus californicus and C. sinicus were dominant. The deep CV population of C. sinicus might be ecologically discriminated from the surface and shelf water population due to their larger body length and dormant life cycle. E. californicus was also collected at the shelf site during each spring bloom period, whereas the population might descend into the mid- and deep-layers of the central bay before summer. Our results suggest that the seasonal fluctuation of community structure in the shelf water was controlled by both physical (Kuroshio Current) and biological factors, i.e., spring bloom and ontogenetic vertical migration of E. californicus. In particular, transport and diffusion processes of Kuroshio Current in Sagami Bay played a key role in controlling the shelf water calanoid community.     

Reproductive periodicity of meiobenthic copepods: Seasonal of continuous?

Much of the literature on meiofauna reproductive periodicity suggests continuous reproduction throughout the year. Field data collected over a two-year period in the North Inlet area, South Carolina (USA) indicate that the dominant meiobenthic copepods at each station sampled are in a reproductive state all year whereas less abundant species have distinct seasonal reproductive periods. Reproduction throughout the year is not restricted to, nor does it encompass all of, the interstitial copepods with a low number of eggs. In those species where seasonality is evident, there is a temporal separation of the most closely allied copepods, and when one species is present the other is absent. Alternation of reproductive cycles in these species reduces competition and allows for maximum resource utilization.     

Phytoplankton pigments in the gut concents of planktonic copepods from coastal waters off southern California

Phytoplankton xanthophylls in the gut contents of the copepods Calanus pacificus, Corycaeus anglicus, and Paracalanus parvus, collected from 5 stations off San Onofre, California, in June 1982, were measured by reverse phase, high-performance liquid chromatography (HPLC). The dinoflagellate pigment, peridinin, was usually the most abundant xanthophyll in the guts of all three species of copepods. Evidently, feeding was principally on dinoflagellates (which dominated the phytoplankton biomass). The level of feeding activity, rather than the class of phytoplankton ingested, seemed to differentiate the behaviors of the copepods. Xanthophyll content per unit copepod wet weight was higher in Corycaeus anglicus and Paracalanus parvus than in Calanus pacificus. Chlorophyll a fluorescence of the copepod gut contents was measured in conjunction with the analysis of gut xanthophylls. The xanthophyll content of the gut varied directly with the concentration of chlorophyll a in the gut. Xanthophyll content was not related to the concentration of pheopigments in the gut. Apparently, the xanthophylls that were detected were due to the presence of recently ingested phytoplankton biomass.     

Comparative life histories of three species of planktonic calanoid copepods in Dabob Bay,Washington

The life history patterns of Calanus marshallae Frost, C. pacificus Brodsky, and Metridia lucens Boeck were determined in Dabob Bay, Washington, USA, during 1973 and October 1981–September 1982. C. marshallae emerged from diapause and moulted to adults in January–February. One major generation was observed, having been produced mainly during early to mid-March. Most surviving individuals spawned in March, arrested development at the C5 stage, and were in diapause by late May. However, some individuals developed to adults by late April and produced a very minor second generation. C. pacificus emerged from diapause and moulted to adults in February–March. The first generation produced during the spring lagged slightly behind the C. marshallae generation. C. pacificus produced two additional generations, one in late spring and one in the fall. The production of the three generations coincided with or closely followed phytoplankton blooms. Some C. pacificus arrested development at the C5 stage and entered diapause during the summer, but the majority of the population did not do so until fall. M. lucens did not appear to enter a diapause state. The fall and winter population was chiefly adult females which mostly remained at depth and were reproductively immature. Nevertheless, naupliar M. lucens were found on all sampling dates, indicating that reproduction never ceased as it did for the two Calanus species. M. lucens produced generations in late winter/early spring, late spring, and late summer/early fall. Interspecific comparisons between the life histories observed in Dabob Bay and intraspecific comparisons between the life histories in Dabob Bay and other locations are made. The advantages or disadvantages conferred to the copepods by their differing life histories are also discussed.     

Seasonal and long-term variations in the body size of planktonic copepods in the northern Baltic Sea

Seasonal and long-term variations in the body size of planktonic copepods were studied in the northern Baltic Sea. The influence of temperature, salinity and phytoplankton concentration to the body size of Eurytemora affinis, Acartia bifilosa and Limnocalanus macrurus (Calanoida) was examined at three sea areas, differing in their hydrographical and trophic conditions (an archipelago area and an enclosed bay on the SW coast of Finland in 1992 and at an open sea station in the Gulf of Bothnia in 1991). There was an inverse relationship between copepod body length and temperature, while there was a direct effect of phytoplankton concentration. According to multiple regression analysis, the relative importance of these factors varied according to species, developmental stage and study area. In the archipelago area, copepod body size was mainly determined by temperature, while in the open Gulf of Bothnia, phytoplankton concentration was usually more important. Interannual variation in the summer body length of E. affinis and A. bifilosa was examined using samples collected over 18 years (1967 to 1984) in the archipelago area. In this analysis, the inverse relationship between water temperature and copepod body size disappeared; in E. affinis the average female length correlated positively with summer temperature. We suggest that the length and timing of the study period greatly influence the investigator's view of the factors regulating copepod body size.     

Subitaneous, diapause, and delayed-hatching eggs of planktonic copepods from the northern Gulf of Mexico: morphology and hatching success

Experiments were conducted to examine the morphology and hatching success of eggs, either spawned by freshly caught planktonic copepods or recovered from bottom sediments in the northern Gulf of Mexico. Collections were made between August 1992 and September 1995. Eggs of nine species were described and these differed in their diameter, color and surface attributes. Three types of eggs were distinguished: subitaneous, diapause, and delayed-hatching. Three species, Labidocera aestiva Wheeler, Acartia tonsa Dana, and Centropages velificatus (Oliveira) produced only subitaneous eggs. Hatching success varied greatly among these species. Two species, Labidocera mirabilis Fleminger and Centropages hamatus (Lilljeborg) produced diapause eggs and subitaneous eggs. The length of the refractory phase of the diapause eggs differed greatly both within and between these two species. A third type of dormant egg, delayed-hatching, was recognized in Labidocera scotti Giesbrecht and Pontella meadi Wheeler. The existence of delayed-hatching eggs may be an adaptive response of subtropical species to less seasonal fluctuation. Based upon morphological characteristics of the eggs and rearing of nauplii to an identifiable stage, benthic dormant eggs of eight species of calanoid copepods were also identified. Received: 9 September 1996 / Accepted: 1 October 1996     

Detritus as food for estuarine copepods

A variety of detrital foods derived from marsh plants were fed to the copepods Eurycemora affinis and Scottolana canadensis. The copepods did not survive well or produce eggs when feeding on detritus with smaller amounts of microbiota, but did well when a rich and abundant microbiota was present. Ciliated protozoans appear to be particularly important in the transfer of detrital energy to copepods.Contribution No. 703, Center for Environmental and Estuarine Studies, University of Maryland.     

Bacteria as food for marine harpacticoid copepods

Feeding experiments were carried out on the harpacticoid copepods Tisbe holothuriae and Paramphiascella vararensis, using various species of marine and brackish water bacteria as food. Short-term experiments with ³H-labelled bacteria are described, as well as experiments covering longer periods of time using non-labelled, dried bacteria. Results show that for both T. holothuriae and P. vararensis, the amount of dry bacteria consumed ranged from 2.06 to 7.07 g copepod^-1 day^-1, indicating a carbon requirement of 1 to 3.5 g copepod^-1 day^-1. The food value of the bacteria strains tested is given in terms of the generation time of the copepods raised on these bacteria.     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. I. Centropages abdominalis

Population dynamics and production of the calanoid copepod Centropages abdominalis were studied from November 1986 to November 1987 in Fukuyama Harbor, in the central part of the Inland Sea of Japan. This species was present in the plankton during a cold-water period from November to June (temperature range: 8.9 to 21.1 °C), with a peak abundance (23 600 ind m^–3) in February. During this period, six generations could be detected, and each generation time agreed well with that predicted from food-satiated laboratory experiments, indicating that the natural population was not food-limited. The population suffered extremely high mortality during the period from egg to naupliar stage (N) II: only 0.02 to 4% of the eggs survived to NII. However, the mortality in stages older than NII was almost negligible. The growth rate of C. abdominalis increased exponentially with increasing temperature. Its biomass and production rate showed marked seasonal variations largely in parallel with numerical abundance. The estimated production between 7 November 1986 and 29 May 1987 was 355 mg C m^–3 or 2.66 g C m^–2, 95% of which occurred during February and March. The daily production rate to biomass ratio increased exponentially with temperature from 0.18 at 8.9°C to 0.37 at 19°C.     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. II. Acartia omorii

Population dynamics and production of the calanoid copepod Acartia omorii Bradford were studied from November 1986 to November 1987 in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was present in the plankton from October to July (temperature range: 8.9 to 24.3°C), with peaks in February-March and June. During this period, nine generations could be detected, for which the mean population egg production rate and midstage abundance of each life stage older than naupliar Stage (N) II were determined to trace survival. The population suffered extremely high mortality during the early life stages: on average only 2.5% of the eggs produced recruited into NII. This large loss is probably concentrated within the egg stage, due to predation, including cannibalism, by omnivorous copepods, in addition to sinking loss of eggs in the water column. However, the mortality from NII to copepodite Stage (C) V was negligible, indicating low predation pressure by large carnivores. The biomass of A. omorii showed marked seasonal variations in parallel with numerical abundance. The instantaneous growth rate of each stage increased exponentially with increasing temperature. The integrated production rate of A. omorii from 7 November 1986 to 21 July 1987 was 749 mg Cm^-3 or 5.62 g Cm^-2     

Suspension-feeding by herbivorous calanoid copepods: A cinematographic study

Many planktonic calanoid copepods are commonly described as filter-feeders. Direct observations using high-speed micro-cinematography indicate that these animals are suspension-feeders. They capture and handle the food particles not passively according to size and shape but, in most cases, actively using sensory inputs for detection, motivation to capture, and ingestion.     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. III.Paracalanus sp.

Population dynamics and production of the calanoid copepodParacalanus sp. were studied from November 1986 to November 1987 in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was perennial, with a large abundance peak in June/July and small peaks in September/October and November/December. During a year of investigation, 15 generations Gould be detected. For each generation, the mean population egg production rate and the mean daily midstage abundance front NIII to CV were determined to obtain a survival curve from egg to CV. The mortality was extremely high during the early life stages: on average only 7.1% of the eggs produced might survive into NIII. This high mortality might be caused by predation by sympatric omnivorous copepods, in addition to sinking loss of eggs from the waten column. The biomass ofParacalanus sp. showed marked seasonal variations largely in parallel with numerical abundance. The instantaneous growth rate of each developmental stage increased exponentially with temperature up to 20 °C, above which the rate was constant. The annual integrated production rate was 734 mg C m^–3 yr^–1 or 5.5 g C m^–2 yr^–1.     

Strain-related physiological and behavioral effects of <Emphasis Type="Italic">Skeletonema marinoi</Emphasis> on three common planktonic copepods

Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA) and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects. Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology, which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds and their potential implications on different copepod species.     

Hastigerina pelagica: Foraminiferal habitat for planktonic dinoflagellates

Hand-collection of specimens by SCUBA diving in the Florida Current revealed that the planktonic foraminiferan Hastigerina pelagica harbors on its surfaces 3 species of planktonic dinoflagellates: Pyrocystis fusiformis, P. noctiluca and, predominanty, Dissodinium elegans. Undamaged H. pelagica is unique in possessing a gelatinous, bubble-like capsule completely surrounding the test. While attached to the surface of this capsule, the dinoflagellates frequently reproduced asexually, and appeared healthy in all respects. They were not assimilated by the foraminifera. The number of D. elegans per foraminiferan increased with increased surface area of the gelatinous capsule, averaging approximately 6 dinoflagellates/foraminiferan, with a maximum of 79. Surface-space utilization per D. elegans remained constant with increased foraminiferan size. The use of the foraminifera in a facultative commensal or symbiotic association and the value of surfaces in that association is postulated.     

海水循环养殖系统水处理工艺综述

论述了海水循环养殖系统(RAS)需要控制的水质参数及相关单元水处理工艺.RAS需要对盐度、pH、温度、溶解氧等水质参数进行监测控制,并常采用物理、生物、化学处理的组合工艺,使固体物质、氨氮、亚硝酸盐、硝酸盐、有机物以及致病微生物等的浓度维持在安全范围内.固体物质根据粒径和可沉降性的不同,可采用沉降、过滤、泡沫分离或生物过滤法去除;氨氮、亚硝酸盐以及硝酸盐主要通过生物的硝化和反硝化作用去除;有机物主要通过生物降解去除;化学药剂消毒以及紫外辐照是RAS常用的消毒方法,消毒剂残余及消毒副产物对水质和动物健康的影响是选择合适消毒方法需要考虑的两个关键因素.最后,列举了几种海水RAS常用的组合处理工艺,并提出了针对性的改进建议.