In situ feeding rhythms of herbivorous copepods,and the effect of starvation

In situ diel variations in gut pigment contents of neritic (Acartia omorii andPseudocalanus minutus) and oceanic copepods (Calanus plumchrus andC. cristatus) were analyzed.A. omorii andP. minutus were sampled in Onagawa Bay on the east coast of Japan in May and August 1987, andC. plumchrus andC. cristatus were sampled in the Bering Sea in June 1986. Gut pigments were generally high at night, and bimodal feeding rhythms were observed in all species. The first peak of gut pigments occurred between sunset and midnight and was followed by a midnight decrease in gut pigment levels, resulting in eventual evacuation of the gut. The second peak was observed a few hours after sunrise. Incubation experiments indicated that ingestion rates of starved copepods were higher than those of acclimated copepods. This phenomenon was most notable at high food concentrations. Gut pigments of starved copepods rapidly increased after exposure to high concentrations of culturedThalassiosira decipiens. These findings suggest that in situ feeding behavior of herbivorous copepods includes periods of cessation or reduction in feeding during the night, and consequently, feeding activity is periodically enhanced with starvation. Starvation enhanced feeding behavior is most obvious in the large oceanic species,C. plumchrus andC. cristatus and is not distinct in small coastal species such asA. omorii.     

Gut pigment accumulation and destruction by arctic copepods in vitro and in situ

The results presented here were obtained at six locations during three cruises in 1985 (off the coast of Labrador), 1986 (at the eastern end of Viscount Melbourne Sound) and 1988 (off the coast of Labrador). In situ chlorophyll maximum concentrations were >7 gl^-1 at depths of between 0 and 30 m in all sampling areas. In feeding experiments copepods attained higher gut pigment concentrations the longer they had been previously starved and higher concentrations when fed in the dark than when fed in the light. Community ingestion rates calculated from changes in particulate chlorophyll were higher than estimates derived from gut pigment data except when copepods had been starved for 24 h. Differences between estimates by the two methods suggested pigment destruction. In feeding experiments pigment: biogenic silica ratios in food and faecal pellets suggested that the length of starvation period affected the degree of pigment destruction differently at different stations and that feeding in the light greatly increased pigment destruction. A comparison of pigment: silica ratios in the water column, and in faecal pellets collected from copepods which had fed there, suggested that pigment destruction may occur in situ sometimes and that the degree to which it occurs may be affected by feeding history, light, diel feeding behaviour and species composition.     

Under-ice feeding and diel migration by the planktonic copepodsCalanus glacialis andPseudocalanus minutus in relation to the ice algal production cycle in southeastern Hudson Bay,Canada

The marine planktonic copepodsCalanus glacialis Jaschnov andPseudocalanus minutus (Kroyer) typically dominate the copepod biomass in spring under the ice in southeastern Hudson Bay, Canada. Females of both species exhibited significant diel feeding cycles, as measured by gut pigment content, throughout a bloom of ice algae at the ice-water interface in 1986. Periods of grazing correlated well with a nighttime vertical migration by females to within 0.2 m of the ice-water interface, suggesting that feeding took place at or just below the thermohaline boundary between seawater and the interfacial layer containing the ice algae. Seasonal melting of the ice bottom in mid-May resulted in freshening of the surface layer and release of the ice algae into the water column. FemaleC. glacialis andP. minutus responded by ceasing migration to the interface. Gut pigment content, and by reasonable assumption, feeding activity in the water column, increased substantially immediately after this event. In mid-May, the water column phytoplankton consisted of flagellates, sedimenting ice algal cells, and diatoms (Navicula pelagica andChaetoceros sp.) previously found at the interface and then growing in the water column. We conclude that algae growing at the ice-water interface, and sedimenting or actively growing algae derived from this interfacial layer, are a regular and principal source of nutrition for these pelagic copepods during and immediately after the ice algal bloom.     

Variability in the gut contents of individual A cartia tonsa from waters off Southern California

The gut contents of 169 individual Acartia tonsa from Los Angeles Harbor, California, USA, were measured during a 24 h period (16–17 June 1986) by gut pigment (fluorescence) and microscopic analyses. Individual gut-pigment levels varied 10-fold or more within sampling intervals. Some copepods with moderate (0.2 to 0.5 ng) to high (>0.5 ng) gut-pigment levels were present in samples from both day and night collections. While the percentage of copepods containing>0.5 ng pigment was about the same during the day (8%) as at night (10%), the percentage of copepods with 0.2 to 0.5 ng pigment rose from 17% during the day to 55% at night. Significant differences between pigment levels in copepods collected before and after evening twilight were suggestive of a nocturnal feeding habit regardless of intense individual variability in gut-pigment content. Food in the gut was distributed in parcels, indicative of intermittent feeding that potentially contributes to individual variability. Feeding was not synchronized during most of the day and night, but synchrony increased at evening and morning twilights. Although synchrony declined after evening twilight, individual gut-pigment contents were relatively elevated in most of the nighttime samples. Thus, active feeding seems neither to require nor to imply synchrony.     

Short-term changes in feeding and digestion by the copepodCalanus pacificus

The planktonic marine copepodCalanus pacificus exhibits an enhanced feeding rate, or hunger response, when exposed to food following short periods of starvation. In a scries of laboratory experiments with copepods collected from the main basin of Puget Sound, Washington, during 1982 and 1984, we measured maximum ingestion rate, assimilation efficiency, and digestive enzyme activity to determine the time scales over which the feeding behavior ofC. pacificus responds to increases in food. These laboratory results were then compared to field studies of diel fluctuations in digestive enzymes and gut fluorescence ofC. pacificus in Dabod Bay, a fjord of Puget Sound, during September, 1980, and the closely relatedC. marshallae off the Washington coast, in August, 1981. Laboratory experiments demonstrated that the hunger response ofC. pacificus lasts approximately 6 h before ingestion rate returns to a steady state level of about one-half maximum. On the order of 12h of starvation were required to induce the maximum ingestion rate of the hunger response. Digestive enzyme activities did not change over these time scales. Assimilation efficiency peaked within a few hours of the onset of feeding, with low initial rates possibly related to the period of starvation prior to feeding. These results were consistent with diel patterns observed in the field. The hunger response ofC. pacificus appears to be controlled by processes within the gut, and our results are discussed in relation to recent studies of the digestive processes of calanoid copepods.Contribution No. 1772 from the School of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Feeding and respiration rates of a planktonic copepod (<Emphasis Type="Italic">Calanus sinicus</Emphasis>) oversummering in Yellow Sea Cold Bottom Waters

The distribution, feeding and oxygen consumption of Calanus sinicus were studied in August 2001 on a transect across Yellow Sea Cold Bottom Waters (YSCBW) and two additional transects nearby. The distribution of C. sinicus adults and copepodites stage CV appeared to be well correlated with water temperature. They tended to concentrate in the YSCBW (>10,000 ind. m^–2) to avoid high surface temperature. Gut pigment contents varied from 0.44 to 2.53 ng chlorophyll a equivalents (chl a equiv.) ind.^–1 for adults, and from 0.24 to 2.24 ng chl a equiv. ind.^–1 for CV copepodites. We found no relationship between gut pigment contents and the ambient chl a concentrations. Although the gut evacuation rate constants are consistent with those measured for other copepods, their low gut pigment contents meant an estimated daily herbivorous ingestion of <3% of body carbon in the YSCBW and <10% outside the YSCBW. However, based on estimates of clearance rates, C. sinicus feeds actively whether in the YSCBW or not, so the low ingestion rates probably reflect shortage of food. Oxygen consumption rates of C. sinicus ranged from 0.21 to 0.84 l O₂ ind.^–1 h^–1, with high rates often associated with high temperature. From the oxygen consumption rates, daily loss of body carbon was estimated to be 4.0–13.7%, which exceeds our estimates of their carbon ingestion rates. C. sinicus was probably not in diapause, either within or outside the YSCBW, but this cold-water layer provides C. sinicus with a refuge to live through the hot, low-food summer.Communicated by T. Ikeda, Hakodate     

Diel changes in gut-cell morphology and digestive activity of the marine copepod Acartia tonsa

Morphometric measurements of the gut cells of the marine calanoid copepod Acartia tonsa were made over a 24 h diel cycle to test the hypothesis that feeding rhythms in this copepod are limited by the cycles of blishter-like cells (B-cells) in the gut. Copepods were collected from Long Island Sound, New York, USA, in June 1991. Experimental treatments included low (1 g chlorophyll al^-1) and high (10 g chlorophyll al^-1) food concentrations. Copepods were fixed and embedded in Epon at six time intervals over the 24 h period, and semi-thin sections through the length of Midgut Zone II were analyzed for gut-cell area and vacuole area, with area measurements integrated to yield estimates of gut-cell volume and vacuole volume. Concurrent measurements of gut fluorescence, a measure of gut fullness, and digestive enzyme activities also were made. A diel cycle in gut fluorescence was observed, most notably in the low-food treatment, which exhibited a 3-fold increase in gut pigments. There was little consistent change in digestive enzyme activities over this time span. Gaps in the gut wall indicative of spent B-cells were observed in 17 of 39 copepods, with no trend over time or food treatment. Generally, only a single gap was seen in any one copepod. B-cells were vacuolated throughout the 24 h period. Morphometric analyses revealed a correlation between gut fluorescence and both maximum vacuole area and vacuole volume, as well as percent vacuolated cell volume, in the low-food treatment. The high-food treatment, which had a relatively smaller increase in gut fluorescence (1.5-fold) during the night cycle, showed no significant increase in vacuole size. B-cells appear to have a life-cycle greater than the diel feeding period, and while B-cell vacuoles respond to the ingested food during the diel cycle, production of B-cells does not appear to be a limiting factor in A. tonsa's feeding cycle.     

Vertical distribution and nocturnal migration of zooplankton in relation to the development of the seasonal thermocline in Patraikos Gulf

Vertical distribution and nocturnal migration of zooplankton species in relation to the development of the seasonal thermocline in the shallow waters (90 m) of Patraikos Gulf (Ionian Sea, Greece) were investigated using a WP-2 closing net. Juvenile and adult copepods accounted for a mean of 91% of the total collected in three sampling periods, i.e. May, July and September 1985.Ctenocalananus vanus, Paracalanus parvus andOithona plumifera were the dominant copepods. The majority of the zooplankton tend to aggregate at the thermocline layer. Among copepods the two congeneric speciesClausocalanus pergens andC. furcatus exhibited different migratory responses to the development of the thermocline.C. pergens occurred in the lower part of the thermocline andC. furcatus in the upper region or above. The diel vertical migration of all species could be divided into four types: (1) no vertical migration; (2) upward migration at night; (3) occasional migration; and (4) reverse migration (down at night). In July when the strongest thermocline developed, most zooplankters rose close to the surface at night. For most species, temperature discontinuity did not limit their diel migration.Please address all correspondence and requests for reprints to Dr J.J. Lykakis     

Food and feeding dynamics of the larval Antarctic fishNototheniops larseni

The feeding dynamics of larvae of the Antarctic fishNototheniops larseni were analyzed from data collected over three years in Bransfield Strait and adjacent waters (Antarctica). Seasonal feeding was examined from 1977/1978 (November–March). The diel feeding cycle was investigated during a 96 h station established in February 1976, while food selection was analyzed using larvae and zooplankton samples collected in February 1982. Hatching occurs in early spring, and larvae fed on eggs of calanoid copepods and on cyclopoid copepods. Copepod eggs were the principal food near the pack ice, and cyclopoids in open waters. Cyclopoids were the staple food in summer. Eggs of the Antarctic krillEuphausia superba were ingested selectively and formed major portions of the larval summer diet in neritic (Joinville Island) and oceanic (Elephant Island) spawning areas ofE. superba. In the fall, copepods predominated in the diets. Most abundant and most frequently ingested prey in summer and fall wereOncaea spp. Feeding commenced at dawn and continued at least until dusk. Krill eggs were taken chiefly during morning hours and egg incidence declined during the day, suggesting that eggs were ingested soon after spawning. Prey size at the onset of feeding was estimated as 0.130 to 0.330 mm. Size-selective feeding was evident in small larvae, while in larger larvae median prey length remained constant. High feeding incidence among yolk-sac larvae in spring, high overall feeding incidence in summer, and size-selective foraging of small larvae suggested favorable feeding conditions in the 1977/1978 season. Yolk-absorption times in Antarctic fish larvae vary on a scale of weeks and may be further retarded due to early feeding. Hence, year-to-year variability of yolk incidence inN. larseni indicated variable biotic environments of early feeding larvae rather than temporal shifts of hatching periods. As hatching periods are constant between years in contrast to the variable retreat of the pack ice and subsequent onset of the production cycle in space and time, maternal yolk reserves are probably utilized to compensate for such variations.     

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.     

Analysis of phytoplankton pigments by HPLC before,during and after mass occurrence of the microflagellate Corymbellus aureus during the spring bloom in the open northern North Sea in 1983

Daily observations in April and May 1983 near a subsurface drifter launched in the Fladen Grounds area of the North Sea revealed that a large crop of the microflagellate Corymbellus aureus Green, producing up to 3 g C m^-2 d^-1, succeeded the diatoms dominating during the earlier phase of the spring bloom. The concentration of fucoxanthin was highest during the first half of May, while pigment fingerprints of high-performance liquid chromatograms of suspended matter sampled during the second half of May were dominated by 19-hexanoyloxyfucoxanthin, the main carotenoid of C. aureus (0.8x10^-9 mg cell^-1). This colonial Prymnesiophycean was described for the first time less than 10 years ago and has nerver been reported to be present in the North Sea. After 16 May the C. aureus population rapidly lost its growth potential, but the peak of the bloom in terms of cell number was found several days later (up to 9x10⁶ cells per dm³ on 19 May). The population then started to decline; senescence was associated with decreasing pigment contents of cells. The low growth rate of copepods registered during the second half of May was probably related to the poor quality of C. aureus as copepod food: the concentration of a phaeophorbide a typically found in copepod fecal pellets was highest during the diatom phase of the spring bloom preceding the C. aureus bloom.     

Accumulation of paralytic shellfish poisoning toxins in planktonic copepods during a bloom of the toxic dinoflagellate<Emphasis Type="Italic"> Alexandrium tamarense</Emphasis> in Hiroshima Bay,western Japan

Concentrations of paralytic shellfish poisoning (PSP) toxins in toxic dinoflagellate cells and in marine planktonic copepods were monitored during the bloom of Alexandrium tamarense in Hiroshima Bay, western Japan. Concentration of the toxins retained by copepods was a function of the ambient toxin concentration, i.e. the product of A. tamarense cell density and cellular toxicity. The toxin concentration in copepods increased with the increase of toxicants in the seawater then leveled off, but decreased significantly at higher concentrations. In the field, the maximum toxin concentration was 1.2 pmol ind^-1, whereas in the laboratory, the copepod Acartia omorii accumulated a much higher concentration of PSP toxins (24 pmol ind^-1). Feeding avoidance against Alexandrium tamarense and a shift to alternative food sources such as diatoms in the field might keep their toxin levels lower than their potentially maximum level. The copepod toxin levels in the field were not so high as to cause an instantaneous lethal effect on their predator fishes but may reach possibly lethal levels after a few days' continuous feeding. Overall toxin retention by copepods after 12 h feeding and 2 h starvation was only 2.5% of total ingested toxins, which suggested that a significant amount of toxins was released into the seawater. Measurements of toxin reduction and gut evacuation suggested that the toxins were removed through both fecal evacuation and metabolism (e.g. excretion, decomposition and transformation). The results, as a whole, imply that copepods can be a link for PSP toxin flux in both pelagic and benthic food webs and can also be a sink for toxins by metabolizing and removing them from the environment.Communicated by T. Ikeda, Hakodate     

In situ grazing rate of the copepod population in the western subarctic North Pacific during spring

Time series sampling with a multi-layer plankton sampler was carried out in the western subarctic North Pacific during spring 1991. Neocalanus cristatus, N. flemingeri and Eucalanus bungii dominated and accounted for 88.5% of the copepod population in volume. Neocalanus spp. were distributed in the upper mixed layer, while E. bungii was mainly distributed between 120 and 300 m throughout the day and night. In contrast, Metridia pacifica, Pleuromamma scutullata and Gaetanus simplex showed clear diel vertical migration. Grazing activities were estimated simultaneously by gut fluorescence. Nocturnal grazing was observed for diel migrating species. Neocalanus spp. did not have a diel feeding rhythm and had relatively low gut fluorescence. E. bungii was considered to be dormant during the observation period. The estimated grazing rate of the copepod population on phytoplankton was 1.4 to 2.0% of the primary production while the metabolic requirement was 8.3 to 12.4% of the primary production. These facts suggest that the copepod population was unimportant as primary consumers and that microzooplankton plays a much more important role in sustaining low standing stock of phytoplankton and a high nutrient concentration in the western subarctic Pacific Ocean.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Diel and seasonal changes in the distribution of fish on a southeast Brazil sandy beach

The effect of diel and seasonal changes in the distribution of fishes on a subtropical sandy beach on the southeastern coast of Brazil were studied. Seine netting was carried out on both seasonal and diel scales between July 1998 and June 1999. A total of 46 fish species was recorded, six being numerically dominant: Anchoa tricolor, Gerres aprion, Harengula clupeola, Atherinella brasiliensis, Mugil liza and Diapterus rhombeus. Seasonal changes in abundance of dominant species were detected. Species dominant in winter were Anchoa tricolor, H. clupeola and Atherinella brasiliensis; in spring, Anchoa tricolor and G. aprion; in summer G. aprion and D. rhombeus; and in autumn M. liza and H. clupeola. Overall, diel patterns did not reveal any significant trends; however, if we consider each season separately, an increase in A. tricolor abundance was recorded during the day in winter/spring, being replaced at night by H. clupeola in winter, and by G. aprion in spring. Increases in number of individuals and biomass at sunset, and decreases during the night were recorded. The winter/spring inshore/offshore movements at diel scale performed by the three most abundant species demonstrate that diel fluctuation acts more at a species-specific level than at a structural one; in summer there was no evidence of diel movements due to a heavy influx of G. aprion and D. rhombeus, which use the area throughout day and night, increasing overall abundance. Seasonal movements seems to be related to ontogenetic change in species, while diel movements in the fish assemblage seem to be more related to physiological requirements, such feeding activity of each particular species, than to physico-chemical conditions.Communicated by O. Kinne, Oldendorf/Luhe     

Diel vertical migration and feeding patterns of Mysis mixta (Crustacea,Mysidacea) in the Baltic Sea

The extent of the nocturnal vertical migration of Mysis mixta Lilljeborg varied between early July and late October (of 1985 and 1986) in a coastal area of the Baltic Sea. Migration was more restricted in early July and late October. Seasonal changes in surface light levels and transparency were sufficient to explain the observed differences. Mysids avoided light levels above 10^-4 lux throughout the study period. Smaller juveniles migrated higher up than larger juveniles and adults. A two-layered distribution with part of the population close to the bottom was observed at night. Zooplankton were more abundant in water layers above the main concentration of mysids. M. mixta fed on phytoplankton, detritus, copepods, cladocerans, rotifers and tintinnids. Diel changes in gut fluorescence indicated a higher intake of phytoplankton at night, but levels were low compared to primarily herbivorous zooplankton. Comparisons of stomach contents of mysids caught at the bottom in the evening and in the water column at night showed a higher ingestion of zooplankton at night and of detritus during the day. Mysids caught at the bottom at night had an intermediate diet. Copepods and cladocerans constituted between 90 and 100% of ingested material by weight in all mysid groups.     

Zooplankton biomass and indices of grazing and metabolism during a late winter bloom in subtropical waters

The development of the so-called late winter bloom in subtropical water was studied in an oceanic area north of the Canary Islands from January to May 2000. Zooplankton was sampled at short-term intervals (1–4 days) during the bloom (January–March), and biomass, indices of grazing (gut fluorescence) and metabolism (electron transfer system activity, ETS) were measured in four different size fractions (100–200, 200–500, 500–1000 and >1000 µm). During the bloom, ETS activity and gut fluorescence increased before the development of zooplankton biomass. At the end of February, the presence of an impressive cloud of dust formed in the Sahara desert was related to an increase in chlorophyll and small zooplankton a week later. The increments in biomass were the consequence of consumption by zooplankton as inferred from the indices of grazing and metabolism. Estimated grazing from gut fluorescence and gut evacuation rates during the period of study accounted for 55% of the assessed total ingestion from respiration and normal values of assimilation, showing the importance of the non-pigmented food in the diet of zooplankton in these waters. In contrast, the sharp decreases in zooplankton biomass observed during the bloom appeared during the dark period of the moon, the days in which the diel vertical migrants reach the shallower layers, in agreement with previous works in the area. Thus, the development of the late winter bloom in this region is suggested to be driven by the interplay between resource and consumer controls.Communicated by S.A. Poulet, Roscoff     

Mass occurrence of Salpa fusiformis in the spring of 1984 off Ireland: implications for sedimentation processes

Zooplankton species composition and biomass were investigated during the spring of 1984 in three areas west of Ireland. In general, biomass of the gelatinous zooplankters [Salpa fusiformis (Cuvier) forma gregata and solitaria, Cymbulia sp., Euclio sp.; max. 360 mg Cm^-3] exceeded that of other zooplankton namely copepods (max. 70 mg C m^-3). Feeding by salps in the upper layers of all areas during the observed diatom spring bloom resulted in sedimentation of diatom-rich salp fecal pellets. This process ended the diatom spring bloom prior to nutrient depletion in surface waters and, thus, prior to mass sedimentation of algal cells.Publication No. 17 of the SFB 313 at Kiel University     

Further studies of short-term variation in the pigment composition of a spring phytoplankton bloom

Phytoplankton sampled at the chlorophyll maximum during the spring bloom at Loch Ewe, Scotland during 1986, were analysed using high-performance liquid chromatography for chloropigments and carotenoids. The day-to-day proportions of the pigments remained relatively stable throughout the bloom, with good preservation of chlorophyll a even at the sediment surface. Chlorophyllide a and phaeophorbide a appeared towards the end of the bloom. The major carotenoids remained stable throughout the bloom, but became rapidly degraded on sedimentation under the oxic conditions. The pigment data is related to the nutrient status of the bloom, when slow steady growth occurred without nutrient limitation. These data contrast sharply with data from the 1983 spring bloom at Loch Ewe when acute nutrient limitation took place.     

Age structure,growth rates,movement patterns and feeding in an estuarine population of the cardinalfish Apogon rueppellii

The biology of a population of the cardinalfish Apogon rueppellii has been studied over several years (1977–1983) in the Swan Estuary in south-western Australia, using ramples collected monthly from the shallows by beach seine and from various depths by otter trawl. While the life cycle of this species typically lasts for one year, at the end of which time the mean length is 50 to 60 mm, some individuals survive for a further year and attain lengths up to 104 mm. A. rueppellii shows a marked tendency to move offshore into deeper water during the winter months. This tendency is more pronounced in the 1+ than in the 0+ year class and in larger than smaller 0+ individuals. An inshore movement of A. rueppellii in the spring is followed by spawning and by oral brooding by the males, which leads to the recruitment of large numbers of a new 0+ year class on to the banks during the summer. The offshore movement is correlated with changes in salinity and temperature. The larger catches taken by otter trawl during the day than at night indicate that A. rueppellii exhibits a diel pattern of activity. Mean fecundity ranged from 70 in the 45 to 49 mm size class to 345 in the 90 to 94 mm size class. Measurements of fecundity and the number of oral-brooded eggs demonstrated that the majority of the eggs released by the female are collected and incubated by the males. Copepods are ingested in relatively greater amounts by small than by large A. rueppellii, whereas the reverse situation occurs with larger crustaceans, polychaetes and small fish. The presence of greater amounts of copepods in the diet during the day and of amphipods at night probably reflects the diel activity patterns of the prey.