Pelagic Populations Research Articles

Pelagic flagellate populations in the southern North Sea, 1988–89. I. Qualitative observations

Pelagic flagellate populations in the southern North Sea, 1988–89. I. Qualitative observations

Variable Success in Breeding of the Roseate TernSterna dougalliion the Northern Great Barrier Reef

Breeding of Roseate Terns Sterna dougallii on the northern Great Barrier Reef (11°-15°S) was monitored between 1976 and 1994, and they were recorded breeding on the inshore rocky islands in most years, usually starting April-May. Between 50-5000 pairs were recorded breeding each year and indicate that the northern Great Barrier Reef is an important breeding area for Roseate Terns during peak years when large colonies of 1000-5000 pairs formed on low sand cays in the far northern Great Barrier Reef (11°s). On at least three occasions, breeding success was poor in these large colonies, with high mortality of the almost-fledged chicks. Growth in weight and wing length of Roseate Tern chicks was measured at Eagle Island (14°42′S) between 1983 and 1986 in order to assess the influence of food on growth rates and survival. Chicks took up to 35 days to fledge, significantly longer than the ecologically similar, more numerous Black-naped Tern Sterna sumatrana at the same site at the same time and also almost 10 days longer than Roseate Tern chicks from temperate North American colonies. These data suggest that conditions in northern Australia are rarely favourable for the rapid growth and breeding success of Roseate Terns. Pelagic fish populations around inshore islands in tropical Australia may only be able to support limited numbers of Roseate Terns during the breeding season. This makes northeastern Australian populations of this globally threatened species extremely vulnerable to changes in the availability of their prey during the breeding season.

Selection for fast growth during the larval life of Atlantic cod Gadus morhua on the Scotian Shelf

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 137:25-37 (1996) - doi:10.3354/meps137025 Selection for fast growth during the larval life of Atlantic cod Gadus morhua on the Scotian Shelf Meekan MG, Fortier L We tested the hypothesis that fast growing Atlantic cod Gadus morhua survived better than their population of origin in the winters of 1991-1992 and 1992-1993 on the Scotian Shelf (northwest Atlantic). Survivors were defined as fish &GT90 d of age at capture which comprised epibenthic juveniles &GT20 mm sampled mainly near the bottom. The majority of larvae and juveniles aged &LT=90 d at capture were sampled with a midwater trawl and were assumed to be representative of the pelagic population (survivors + non-survivors) from which epibenthic survivors originated. Standard length corrected for shrinkage was linearly correlated to lapillar radius (r2 = 0.97). Individual growth histories were reconstructed from the width of lapillar increments. Selection for fast growth was weak in the winter of 1991-1992 and back-calculated growth and length at age of survivors were not significantly larger than that of the population (repeated-measures MANOVA). In winter 1992-1993, a strong selection for fast growth was evident in late larvae 41 to 80 d old. The divergence in length at age between survivors and the population reached 4 mm at an age of 70 d, corresponding to a 13 d reduction in the duration of the larval phase. Survivors in the winter of 1992-1993 had larger hatch marks than the population, suggesting that the potential for fast growth may be reflected in traits present at hatching. Our results support the hypothesis that fast growth increases the survivorship of Atlantic cod during larval life in the plankton and indicate that the intensity of size-selective mortality may vary considerably from year to year. Growth selection . Fish larvae . Atlantic cod Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 137. Publication date: June 27, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Temporal variations of fossil Cladocera in the sediments of Lake Orta (N. Italy) over the last 400 years

We use Cladocera remains in the sediments to reconstruct the longterm history of Lake Orta, a lake which experienced severe pollution from copper and ammonium sulphate, and started to recover during the last 15 years. Both human and natural impacts were detected over almost 400 years. Pollution was manifested by a dramatic decrease in the number of remains, in the planktonic/littoral (P/L) ratio, and in chydorid species diversity. Most species, even those most tolerant to stress, disappeared. The recolonization of biota was initially sustained by one species of chydorid,Chydorus sphaericus, which had a three-fold increase at the beginning of the 1980s, when studies on plankton recorded the development of a pelagic population. This fact, and the appearance in the sediments ofAlona quadrangularis, attest to the development of filamentous algae which was reported in studies on the plankton. The colonization of the lake by pelagic species came only in the last twelve years and was manifested also as a stabilization of the P/L ratio. Two other periods of disturbance were detected in the sediments: the first, at the end of the 19th century, was related to the introduction of exotic fish species; the second occurred during the second half of the 17th century. This event probably cannot be ascribed to human impact, but may be related to a decrease in temperature in that period (the Maunder Minimum).

Population Size and Factors Affecting At-Sea Distributions of Four Endangered Procellariids in the Tropical Pacific

We used at-sea censuses to quantify pelagic behavior, relationships between density and habitat variables, and to estimate population size of four taxa of procellariids in the eastern tropical Pacific: subspecies of Puffinus auricularis (Townsend's Shearwater, P. a. auricularis, and Newell's Shearwater, P. a. newelli) and subspecies of Pterodroma phaeopygia (Galapagos Dark-rumped Petrel, Pt. p. phaeopygia, and Hawaiian Dark-rumped Petrel, Pt. p. sandwichensis). All are considered threatened or endangered with extinction. Birds commuting from colonies ranged 650 km (P. a. auricularis) to 1,300 km (P. a. newelli and Pt. p. sandwichensis). P. a. auricularis foraged at upwelling fronts in the Costa Rica Current over the continental slope of Mexico, while P. a. newelli preferred ocean fronts in the Equatorial Counter Current. Unlike the shearwaters, petrel densities correlated most strongly with distance to the colony and wind speed, although the two petrels each foraged in distinctly different current systems. Foraging behavior of the shearwaters was energy demanding, but they frequented highly productive feeding areas and rested often. The petrels appeared to forage more opportunistically and conserved energy by flying more efficiently. Foraging behavior was consistent with wing morphology of each group. Pelagic population estimates (adults and subadults grouped) were 46,000 P. a. auricularis, confidence interval (CI) = 18,000 to 89,000; 84,000 P. a. newelli, CI = 57,000 to 115,000; 19,000 Pt. p. sandwichensis, CI = 11,000 to 34,000; and 88,000 Pt. p. phaeopygia, CI = 54,000 to 130,000. On the basis of breeder to non-breeder ratios in these and closely related species, we estimated breeding populations of 10,600, 18,000-19,000, 3,750-4,500, and 20,000 pairs, respectively. Calculation of minimal and maximum estimates indicated breeding populations larger than previously thought for P. a. auricularis, P. a. newelli, and Pt. p. sandwichensis, but similar for Pt. p. phaeopygia.

Microbial activity and phosphorus dynamics in eutrophic lake sediments enriched with Microcystis colonies

SUMMARY1. Sediments from hypereutrophic Lake Vallentunasjön were enriched with Microcystis colonies from the lake water, thereby simulating the conditions after the autumn sedimentation. Release of phosphorus to the overlying lake water was followed during 2–3 weeks in the laboratory. X‐ray microanalysis of individual Microcystis and bacterial cells, and chemical phosphorus fractionation, were used to assess the phosphorus pool size in different fractions of the sediment.2. Benthic Microcystis colonies, most of these having survived within the sediment for 1 year or more, were less susceptible to decomposition, and the specific growth rate of bacteria in their mucilage was lower than for other sediment bacteria.3. Pelagic Microcystis colonies from late August were resistant to decomposition, when placed on the sediments. When Microcystis colonies from a declining pelagic population in October were added to the sediments, however, a substantial fraction of these colonies was decomposed. The specific growth rate of mucilage bacteria was five times higher than for other sediment bacteria.4. Release of molybdate‐reactive phosphorus to the overlying lake water was larger from sediment cores enriched with Microcystis colonies than from control cores. Chemical phosphorus fractionation showed a decrease in organic‐bound phosphorus (residual P).5. X‐ray microanalysis showed that the phosphorus bound in Microcystis cells decreased by ‐0.300 mg g−1 DW in the October experiment, due both to a decrease in biomass (i.e. mineralization) and to a decrease in phosphorus content in the remaining cells. Heterotrophic bacteria increased their cellular concentration of phosphorus. The net release of phosphorus from the Microcystis and bacterial pools corresponded to 74% of the decrease of organic‐bound phosphorus in the chemical phosphorus fractionation, and to 65% of the decrease of total phosphorus in the upper 0–1 cm of the sediment.6. Benthic bacteria and cyanobacteria may thus contribute significantly to changes in phosphorus content and turnover of the sediment by changes in their biomass, turnover rate and cellular phosphorus content.

On the seasonal migration of the cyanobacterium Gloeotrichia echinulata in Lake Erken, Sweden, and its influence on the pelagic population

The quantity and distribution of colonies of Gloeotrichia echinulata migrating from the sediments into the water column were studied in Lake Erken by the use of inverted traps. The epilimnetic population and the phosphorus status of the epilimnetic colonies were quantified. The numbers of colonies in the traps were greatest in the shallower areas. As the stratification became weaker and the epilimnetic population declined, the amount of colonies in all the traps increased markedly. Most of the colonies in the traps were due to redistribution within the water column. On the assumption that no epilimnetic uptake of phosphorus occurred in G. echinulata, the internal loading of phosphorus due to migrating colonies was calculated to be between 0.4 and 0.6 mg P m-2 day-1 during July and August. The proportion of newly migrated colonies in the epilimnetic G. echinulata population was calculated to be around 50% for the period before the epilimnetic population maximum. The increasing phosphorus content of the epilimnetic colonies after the population maximum indicates that the migration continued even after this.

Predation by an introduced clam as the likely cause of substantial declines in zooplankton of San Francisco Bay

The clam Potamocorbula amurensis was introduced into the San Francisco Bay estuary (California, USA) in 1986 and became abundant in late 1987. Within a year, chlorophyll concentration and the abundance of adults of 3 common estuarine copepod species had declined by 53 to 91 %, providing an opportunity to examine mechanisms by which benthic grazing might control the abundance of pelagic populations. Declines in chlorophyll and abundance of the 3 species of copepod coincided approximately with the geographic range of the clam population. The decline in abundance of the copepod Eurytemora affinis was accompanied by a decrease in the ratio of nauplii to adults, but not in the ratio of eggs to females. Therefore, the decline in abundance may be due to elevated mortality of nauplii rather than food limitation of reproductive rate. We argue that direct predation by P. amurensis is the cause of the reduced sunrival of nauplii, and therefore of the depressed abundance of adults. Experimentally determined clearance rates of P. amurensis on E. affins nauplii averaged 0.11 1 clam-' d-'. If that clearance rate applied in the field, the clams could remove 8.2% of the nauplii d-I. This removal rate is sufficient to explain the observed rate of population decline. P. amurensis appears to have become well established, and copepod populations of the bay so far have failed to rebound. Thus this invasion may have permanent effects. In a broader sense, predation on zooplankton by soft-bottom benthos may be an important, and heretofore overlooked, source of mortality in shallow waters. Selectivity occurring through differences in escape response and vertical position could make bivalve predation an important influence on biomass and species composition of inshore zooplankton.

Long-Term Variability of Pelagic Fish Populations and Their Environment: Proceedings of the International Symposium, Sendai, Japan, 14-18 November 1989

Long-Term Variability of Pelagic Fish Populations and Their Environment: Proceedings of the International Symposium, Sendai, Japan, 14-18 November 1989

The probable effects of climate change on invertebrate growth and reproduction with particular reference to Ireland

Summary The variability of the mild Irish climate is described. The effect of a slight rise in temperature is discussed as far as aquatic organisms are concerned. The effect is likely to be most marked on pelagic populations of marine organisms such as squid and also on intertidal animals. A rise in mean sea level is an indirect result of global warming, and this is likely to have an effect on estuarine organisms and mud flat dwellers. It is suggested that those organisms which are close to the southern limits of their distribution in Ireland may disappear from our fauna. Examples are given from earlier periods and from the present-day fauna. There is likely to be an expansion of the distribution of southern forms which at the moment are near the northern limit of their range. As far as terrestrial animals are concerned, the problem of whether the rainfall pattern will also change is discussed. The likely effects of this on parasite and free-living populations (including the fauna of temporary water bodie...

Long-term variability of pelagic fish populations and their environment

Long-term variability of pelagic fish populations and their environment

Long-term variability of pelagic fish populations and their environment

Long-term variability of pelagic fish populations and their environment

Mechanisms governing fluctuations in pelagic fish populations

A comprehensive and systematic review of 10 years' study on global fluctuations of clupeoid populations is presented and earlier ideas further developed. Historically, sardine and herring have undergone fluctuations of very large amplitude over long periods in a cyclic manner. Such a fluctuation, called Subtype IB, could not have evolved in any other than a marine environment. Sardine and herring have shown concomitant cycles of variation in biomass, but the two cycles are completely out of phase with each other. Sardine dominate the temperate pelagic fish community and changes in its abundance are responsible for structural changes of the community.

Resting eggs of lake‐ Daphnia I. Distribution, abundance and hatching of eggs collected from various depths in lake sediments

SUMMARY. 1. Resting eggs (ephippia) of Daphnia galeata, D. hyalina, D. cucullata and D. galeata X D. hyalina hybrids were collected from the upper 8 cm of sediments at various water depths from two glacial lakes in the Northern Federal Republic of Germany.2. The horizontal distribution of ‘intact’ ephippia (i.e. those containing two apparently healthy eggs) was extremely patchy, with mean densities in the upper 8 cm ranging from 1325 to 113,907 m−2 (coefficient of variation, C=65.5%; Schöhsee, Holstein) and 25,343–159,143 m−2 (C=58.5%; Kel‐lersee. Holstein). Ephippial densities were greatest in sediments from deep waters. The highest densities of intact ephippia were in the upper 4 cm of sediment, with progressively fewer with increasing depth.3. A proportion of eggs obtained from sediments during autumn (September‐November 1985) and spring (March‐May 1986) were exposed to continuous light (approximately 18 W m−2) at three temperatures (6, 12, 20°C), and the incidence of hatches recorded.4. Hatching success was consistently low (maximum 14.4%), with most hatching occurring at 12°C. There was no significant difference between the hatching success of ephippia collected during autumn and spring. Decapsulation of ephippial eggs inhibited hatching. Hatching was highly synchronous within each treatment, and the pattern did not differ significantly with sediment depth, though hatching success was lower in deep sediments. A huge reservoir of ephippia is present in lake sediments, of which a proportion may remain viable for many years. Periodic recruitment of hatchlings to the pelagic population may provide an important mechanism for the maintenance of genetic diversity in Daphnia populations, as well as affecting rates of evolutionary change.

On the pelagic occurrence and dispersal of the benthic amphipod Corophium volutator

Field data on the pelagic occurrence of Corophium volutator were obtained in 1981–82 in the Dollard (Ems estuary). The pelagic population density averaged over a tidal half cycle was in the range 0–15 m-3. The pelagic population represents about 0.06% of the benthic population. On most sampling days pelagic occurrence resulted in a net flood surplus transport.

Pressions sélectives et nouveautés évolutives : une hypothèse pour comprendre certains aspects des fluctuations à long terme des poissons pélagiques côtiers

The extinction during periods much longer than the duration of a species life cycle followed by a quick resurgence to high abundance levels is sometimes observed in marine coastal pelagic stocks. Japanese sardine (Sardinops melanosticta), Pacific sardine (Sardinops sagax), and Peruvian and Chilian anchovy (Engraulis ringens) are presented as examples. Interpretations of these stocks' fluctuations are reviewed. Climatic events and the influence of commercial harvesting do not always appear sufficient to explain such recoveries. Approaches derived from marine and terrestrial ecology as well as from evolutionary biology may lead to a better understanding of the biological reasons for the maintenance and recovery of depleted biomasses. The importance of interspecific competition during periods of low biomass levels is discussed. The possible consequences of strong selective pressures on population dynamics and the adaptive potential of pelagic species are emphasized. Lastly, evolutionary novelties that appear when a species is becoming depleted are considered. From these considerations, we hypothesize that the long attractive periods of low abundance can result from strong selective pressures and from the reduced influence of climatic events. The recovery of depleted biomasses would be the result of an adaptive process (microevolution). Natural selection could therefore act as another regulation mechanism for marine pelagic populations. A model using catastrophe theory is proposed to ilustrate the long-term regulation of these pelagic systems.

Studies on the seasonal biochemistry of the Northern krillMeganyctiphanes norvegica in the Kattegat

A well defined pelagic population of the Northern krill,Meganyctiphanes norvegica was sampled annually at a specific location in the Skandinavian Kattegat, and the major biochemical components were measured. Protein and lipid were the main constituents and underwent the most pronounced seasonal changes, clearly correlated to the prevailing supply of food organisms. The amount of lipid increased to a maximum of 48% of the dry weight towards winter, out of phase with gonad maturation, and therefore interpretable as deposition of overwintering reserves. Utilisation of stored reserves proceeds over winter, with loss of lipid, and decrease in weight but not in length. Comparison with literature data showed similarities with other krill populations from different geographical locations. The biochemical components ofEuphausia superba, the key organism of the marine Antarctic ecosystem, resembled those ofM. norvegica. Special polar adaptations are not obviously expressed in the proximate biochemical composition.

Unique qualities and special problems of the African Great Lakes

The African Great Lakes consist of large, deep rift valley lakes (e.g. Malawi & Tanganyika) and shallower lakes between the Eastern and Western Rifts (e.g. Victoria). They are a group comparable in size to the North American Great Lakes, but are old. Most are seasonally thermally stratified, and wind is the decisive factor that determines the annual cycle of cooling and mixing. Lakes Tanganyika, Malawi and Kivu are meromictic, with deep relict hypolimnia. Large magnitudes and time scales of periodic internal motion, where these have been measured, appear unique among lakes. These lakes harbour the world's richest lacustrine fish faunas, and the family Cichlidae provides the supreme example of geographically circumscribed vertebrate evolution. The lakes provide a unique comparative series of natural laboratories for evolutionary studies. Primary production is generally high, but in the deeper lakes standing stocks of plankton and of small fish species are low. These pelagic populations are characterised by very high P:B ratios. The fisheries are productive and of socio-economic importance. Large-scale mechanised fishing is not compatible with the survival of the diverse fish communities. Cichlids appear especially vulnerable to unselective fishing. Aquatic reserves might offer a means of survival for at least some communities. Various pollution threats exist. Because water retention times are long, extremely long for some deep lakes, and flushing rates are low, the lakes are vulnerable to pollution which would be long-lasting. Introductions of alien fishes have mostly had undesirable or disastrous results. While the faunas are one of the significant natural heritages of mankind, their conservation must realistically be linked to the legitimate development of the lakes for the well-being of the people who live there. Scientific value alone will not protect the lakes. Just as survival of African terrestrial wildlife in extensive reserves depends heavily upon tourism, so also might the cichlid flocks in underwater reserves. Greater interest from the international scientific community is needed to further rational development and conservation of these great lakes.

Further experiments on larval behaviour of the tubicolous polychaete Spirorbis inornatus L'Hardy & Quiévreux

Laboratory experiments indicate that there are many ecologically isolated populations of Spirorbis inornatus L'Hardy & Quiévreux, each tending to select the algal substratum which supported their parents. In some algae certain parts of the thallus are particularly favourable for settlement and, in some areas, this involves adaptation of the local population, e.g. to settle on fronds of Laminaria in sheltered localities. Other parts are unfavourable and these are generally the parts which are most illuminated in their natural orientation (e.g. the upper sides of Himanthalia buttons and the outer sides of Laminaria holdfast branches). These parts are active in producing antibiotics, which may thus have an antifouling role, deterring settlement of larvae whether or not those larvae come from populations adapted to settling upon other parts of the thallus. Most larvae from populations on the turf-alga Chondrus settle without any pelagic phase, whereas the majority from populations on Himanthalia and Laminaria holdfasts become pelagic. The proportions choosing holdfasts in laboratory experiments are high, however, suggesting that the need for skill in such choice, by these pelagic populations, more than balances any effect from outcrossing.

Meganyctiphanes norvegica in the Kattegat

From 1979 to 1983 a population ofMeganyctiphanes norvegica was regularly found in a confined location in the northern Kattegat. The development of this pelagic population was followed over one complete year-cycle, and is discussed in light of published data on landlocked and oceanic populations. In the Kattegat,M. norvegica mature at the age of 9 to 12 months. Copulation starts in january, but fully developed spermatophores are present in males for at least 9 months. Spawning starts in April and continues until October with a marked peak in July. As only 10 to 15% of the gravid females belong to the II-group, it is concluded that recruitment is due to the I-group. Linear growth is fastest in spring and early summer, rises to a second maximum in October and stagnates during winter. The weight development shows some discontinuties caused by spawning or the accumulation of reserves towards winter. Weight decreases during winter. Growth in length and in weight runs largely parallel in both sexes, and can be closely correlated with the prevailing food supply. Diurnal vertical migration could be demonstrated. The results indicate a continuous development, which suggests the existence of an autonomous palagic population, a well suited subject for long-term investigation.