Mesozooplankton Dynamics Research Articles

Evaluation of estuarine mesozooplankton dynamics at a fine temporal scale: the role of seasonal, lunar and diel cycles

In order to study the influence of physical forcing at different temporal scales, zooplankton was sampled at a fixed station located at the mouth of Mondego estuary (southern Europe). Samples were collected during diel cycles, over neap and spring tides. Zooplankton abundance and diversity were estimated for each sampling period Holoplankton were dominated by three taxa: Copepoda, with 48% of total zooplankton abundance, Cladocera (16%) and Medusae (12%). Meroplankton occurred mainly as barnacle and decapod larvae. Copepoda were the most diverse group, represented by 26 species follomed by Decapoda larvae (21) and Medusae (16). In order to assess significant dfferences between seasons, a univariate analysis was carried out. Higher abundance and diversity were found in warm months, particularly at neap tides, when water temperature and salinity were higher. Multivariate analysis revealed significant seasonal differences in species composition. The estuarine community was strongly dependent on allochthonous events, such as tidal exchange and river inflow. The results of our study show that the period of higher river flow, coincident with winter, resulted in changes in the zooplankton community. Short-term temporal variations in the species composition and abundance were also attributed to tidal and diel cycles. Zooplankton reached significantly higher densities at night (P < 0.05), suggesting the occurrence of vertical migrations. By emphasizing the importance of dijferent timescale changes in the zooplankton community of the Mondego estuary, this study will be useful fir the design of more efficient sampling programs, aiming at documenting changes in the zooplankton at a broad but also at a fine temporal scale.

Vertical distribution and seasonal dynamics of mesozooplankton in the Iceland Basin

The abundance and seasonal vertical distribution of dominant zooplankters in the Iceland Basin was studied from data collected on four cruises between November 1996 and June 1997. Copepods were by far the most abundant group, making up ∼70% or more of the mesozooplankton. Two species constituted >90% of the copepod biomass: Calanus finmarchicus and Pareuchaeta norvegica. A seasonal migration pattern was evident in C. finmarchicus, P. norvegica, Oithona spp., and Metridia lucens: from December to February they inhabited the deeper layers, whereas from April to June they were most abundant in the upper layers. The vertical distribution of Pleuromamma robusta was rather similar year round. Oncaea spp. stayed deep during winter, but only a limited part of the population rose to upper waters during the summer. The reproduction of C. finmarchicus took place in May in the surface layers and it was linked to the phytoplankton spring bloom. In contrast, the reproduction of P. norvegica occurred at depth in February and was uncoupled to the spring bloom. Calanus hyperboreus is an expatriate in the Iceland Basin that does not reproduce there. The data on Oithona spp. and Oncaea spp. indicate that the former group reproduces between April and June in the upper layers, whereas the latter appears to reproduce year round at depth. As judged by the incidence of adults of both sexes the reproduction of M. lucens took place in spring and summer. The breeding of P. robusta was probably not confined to a particular season of the year.

Zooplankton of Lake Kivu, East Africa, half a century after the Tanganyika sardine introduction

The introduction into Lake Kivu of the planktivorous fish Limnothrissa miodon at the end of the 1950s raised major concern about the fate of mesozooplankton, but few data were available to assess the impact of predation. In this study, we followed zooplankton variations in Lake Kivu for 3.5 years. Present Lake Kivu mesozooplankton is dominated by cyclopoid copepods (Thermocyclops consimilis, Mesocyclops aequatorialis and Tropocyclops confinis), but cladocerans and rotifers are also present. Each year, total crustacean abundance in the plankton increased to a distinct seasonal maximum following a rise of phytoplankton production associated with a deep epilimnetic mixing in the dry season (August–September). This dependence on phytoplankton resource suggests that mesozooplankton dynamics in Lake Kivu is mainly bottom-up controlled, contrary to expectations from the food web structure. However, measurements of body size indicate that sardine predation affects the cladoceran Diaphanosoma excisum, whereas the larger copepods may efficiently escape predation by migration in the deep mixolimnion at daytime. Total biomass of mesozooplankton in Lake Kivu is lower than in lakes Tanganyika and Malawi. This may be related to the disappearance of a large grazer that existed before the sardine introduction, whereas the large lakes of the same region have a more complex pelagic food web, with piscivorous fish, and with calanoid copepods, which can more efficiently exploit phytoplankton production.

Regional scale climate forcing of mesozooplankton dynamics in Chesapeake Bay

A 16-yr (1985–2000) time series of calanoid copepod (Acartia tonsa andEurytemora affinis) abundance in the upper Chesapeake Bay was examined for links to winter weather variability. A synthesis of sea level pressure data revealed ten dominant, winter weather patterns. Weather patterns differed in frequency of occurrence as well as associated precipitation and temperature. The two dominant copepod species responded differently to winter weather variability.A. tonsa abundance showed little response to winter weather and did not vary in abundance during wet or dry springs.E affinis responded strongly to winter weather patterns that produced springs with high freshwater discharge and low salinities. During wet springs,E. affinis abundance increased overall and its area of dominance extended further down estuary. The different response of the two species is likely related to several factors including residence time, development time, salinity tolerance, food limitation, and life history strategy. Important fish species that rely on zo oplankton as food resources were also related to winter weather variability and spring zooplankton abundance.Morone saxatilis (striped bass) andAnchoa mitchilli (bay anchovy) juvenile indices were positively and negatively correlated toE. affinis abundance, respectively. *** DIRECT SUPPORT *** A02BY003 00004

Seasonal Dynamics of Mesozooplankton in Brazilian Coastal Waters

The composition, numerical abundance and seasonal distribution of mesozooplankton, in addition to copepod biomass, were studied in the Sao Sebastiao Channel (SSC) during different seasonal periods and hydrographic regimes. Two stations were sampled every 3 months from January 1996 to July 1997 and also in July 1998 and January 1999. Temporal differences in oceanographic conditions in the SSC were observed; there was clear seasonal variation in the thermohaline structure. Phytoplankton composition, standing-stock and biomass also showed consistent seasonal variation, peaking during summer due to advection of cold and nutrient-rich South Atlantic Central Water (SACW). Sixty-nine mesozooplankton taxa were identified and counted. Mesozooplankton density also increased during summer, ranging from 93 to 12,774 ind m−3. In contrast, a unimodal peak of copepod biomass was recorded during winter and under the influence of the oligotrophic Coastal Water (CW), suggesting that copepod biomass at SSC is driven by resource control. There was no significant evidence of seasonal pattern in overall community composition or evidence of changes due to water mass advection. The mesozooplankton community was continuously dominated by coastal and warm-water species, particularly the copepods Acartia lilljeborgi, Paracalanus aculeatus, P. quasimodo, Parvocalanus crassirostris, Corycaeus giesbrechti and Oithona oswaldocruzi, the cladocerans Penilia avirostris and Evadne tergestina, in addition to the appendicularians Oikopleura longicauda and O. dioica, all of which are perennial species in the SSC. This taxonomic composition may represent an efficient biotic structure for rapid recycling of primary production during periods of SACW influence.

Spatial and temporal variability in factors affecting mesozooplankton dynamics in Chesapeake Bay: Evidence from biomass size spectra

Zooplankton biomass in Chesapeake Bay was estimated with an optical plankton counter mounted on a towed body (Scanfish). Normalized zooplankton biomass size spectra were calculated for three Bay regions three times a year across 4 yr. Zooplankton biomass was maximum during April, and the zooplankton size at peak biomass was large compared with July and October. The variability of the normalized zooplankton biomass size spectrum in April was related to freshwater input, a proxy for nutrient loading, lower temperatures, and salinities. The normalized zooplankton biomass size spectrum showed little interannual variability in July, and the curvature of the biomass size spectrum was reduced. The lack of variability in July normalized zooplankton biomass size spectra was related to gelatinous zooplankton and fish predators. Normalized zooplankton biomass size spectra in October were similar to April and had the lowest total zooplankton biomass. October normalized zooplankton biomass size spectra were affected by gelatinous predators in the upper Chesapeake Bay and by fish predators in the middle to lower Chesapeake Bay. Food limitation did not appear to affect normalized zooplankton biomass size spectra because measured particulate carbon concentrations were always in excess of estimated maintenance food concentrations. The ratio of phytoplankton biomass to zooplankton biomass was higher than in other aquatic systems and was consistent across the year. The zooplankton biomass-to-fish biomass ratio varied seasonally, with April samples having the highest ratios and October the lowest. The normalized zooplankton biomass size spectra in Chesapeake Bay have more negative, and a wider range of, linear regression slopes than other aquatic systems. Normalized zooplankton biomass size spectra in Chesapeake Bay were influenced by climatologically driven variation in the densities of predators and prey. The variability of the normalized zooplankton biomass size spectrum was indicative of a highly eutrophic ecosystem.

Inter-annual variations of planktonic food webs in the northern Adriatic Sea

The temporal dynamics of microphytoplankton, microzooplankton and mesozooplankton were monitored over 37 months in the Adriatic Sea in order to identify alterations in the plankton structures, which can lead to, or enhance the production of macro-aggregates, that affected the entire northern basin in summers 2000 and 2002, and to assess any negative effects of mucilage on plankton temporal patterns. Samples were collected monthly, from June 1999 to July 2002, on three transects at 9 stations across the northern and central Adriatic Sea. Besides the high year-to-year variations in abundances and taxonomical composition, plankton communities only showed a clear seasonal succession during 2001, when since April a grazing food web developed and was able to control large sized phytoplankton increase. In spring–summer 2000 and 2002 consumer abundances remained quite low and the dominant mesozooplankton summer species ( Penilia avirostris) did not reach its usual summer maximum. The lack of an efficient top control was more evident on the northernmost transect, where generally grazing food web prevails over the microbial one. A large part of the microphytoplankton blooms, although not particularly intense, was exported to the bottom in the particulate phase, where it was processed by bacteria, enhancing the production of refractory dissolved material.

A 12-year study of the seasonal and interannual dynamics of mesozooplankton in the Laptev Sea: Significance of salinity regime and life cycle patterns

Over a 12-year period (1989–2000) the spatial and temporal distribution of zooplankton in the Laptev Sea (Arctic Siberia) has been investigated. A total number of 111 taxa from 10 phyla were found. Sixteen species are reported from this region for the first time. The distribution and abundance of zooplankton on the Laptev Sea shelf is dependent on the main direction of river water spread, which varies between years. While the western and northeastern Laptev Sea shelf is dominated by a marine–neritic fauna, the central part is inhabited by a transitional brackish–marine assemblage. A brackish–neritic community characterizes the eastern and southeastern regions, where lowest salinities usually prevail. Closer to estuaries the summer zooplankton consists of both freshwater and brackish-water species, whereas in winter brackish-water species are dominant. Average zooplankton abundance varies seasonally and interannually, particularly in the southeastern Laptev Sea. The amplitude of these variations mainly depends on the state of the populations of the most common Copepoda species, the intensity of their reproduction, and their success in overwintering. Two seasonal abundance maxima were found, at the end of winter and at the end of summer. During the period of highest reproduction in summer the abundance may be 50 times greater than during overwintering. The average population abundance can vary by the factor of 2 in summer and in winter from year to year.

Mesozooplankton dynamics in nearshore waters of the Great Barrier Reef

Zooplankton dynamics (community composition, juvenile somatic growth rate, adult egg production, secondary production) were studied in coastal waters of the Great Barrier Reef. Two sectors were compared, one adjacent to a catchment of near-pristine land use patterns, the other to a more intensively farmed catchment. Sampling was conducted in the austral winter (August) and summer (January–March) of two succeeding years. Gradients in zooplankton community composition were weak, with only moderate effects of season and sector. Overall, 37% of zooplankton biomass was in the 73–150 μm size fraction, 26% in the 150–350 μm fraction, and 38% was >350 μm. There was no biomass difference and only small differences in community composition between samples taken during the day and at night; ostracods and large calanoid copepods were occasionally more common at night. Carbon-specific growth rates averaged 0.29 d −1 for cyclopoid copepods and 0.35 d −1 for calanoid copepods, with no difference between sectors. Calanoid copepod growth showed a significant relationship to chlorophyll concentration, but cyclopoid copepods did not. Copepod egg production was low (7.9 ± 5.9 eggs female −1 d −1) and apparently food-limited. Copepod secondary production was lower in August (mean = 2.6, range 1.4–4.0 mg C m −2 d −1) than in January–March (mean = 8.5, range 2.4–15.5 mg C m −2 d −1). Secondary production by mesozooplankton in the 73–100 μm size range averaged 0.9% of total phytoplankton production.

Epipelagic mesozooplankton dynamics around the Mascarene Plateau and Basin, Southwestern Indian Ocean

It has been suggested that the obstruction of the South Equatorial Current by the Mascarene Plateau might cause upwelling, nutrient enrichment and enhanced chlorophyll and secondary production levels downstream. A study conducted in April and May 2001 showed variability in biomass and community structure which appeared to support this hypothesis but, in the absence of supporting physical and biochemical measurements, we were unable to confirm it. In June and July 2002 the sampling was repeated with the supporting environmental measurements available from a large research vessel. In this paper we present the results from this sampling programme, compare them with the 2001 results, and examine both datasets in the light of physical and other environmental data gathered during the 2002 programme in order to evaluate the evidence for significant upwelling around the Mascarene Plateau. The evidence is inconclusive: the 2002 dataset shows only a little evidence of topographic upwelling. However, the mesozooplankton and other physical and biochemical data from the 2002 sampling programme indicate support for the theory of an open-ocean upwelling between 5 and 10 degrees S across the central and western Indian Ocean from 50 to 90 degrees E, due to Ekman divergence along the northern edge of the South Equatorial Current. It is possible that these two separate sources of upwelling may coexist and combine at times, producing the very high levels of biomass found during 2001.

Attraction Toward Feeding Conspecifics when Food Patches are Exhaustible

Animals that forage in groups commonly share patches of food discovered by one or a few individuals.

Mesozooplankton dynamics in the northern Baltic Sea: implications of variations in hydrography and climate

Mesozooplankton dynamics in the northern Baltic Sea: implications of variations in hydrography and climate

Mesozooplankton dynamics in the Benguela ecosystem, with emphasis on the herbivorous copepods

Recent research developments on the ecology, dynamics and trophic position of copepods in the Benguela ecosystem are synthesized. Attention is focused on herbivorous species of the southern Benguela and how they cope with the physical and biological variability characteristic of this upwelling region. Copepods constitute on average approximately half of the total zooplankton carbon and. are most abundant during the upwelling season. They are able to maintain large population densities within local coastal upwelling areas by combining ontogenetically based vertical migration behaviour with features of the current system. Some species have developed finely tuned strategies to overcome periods of starvation between upwelling bouts by storing lipid reserves or by entering temporary developmental arrest. In situ measurements of production rates of local species are among the highest recorded for copepods. Despite an apparent excess of food, copepods exert only limited impact on the phytoplankton, removing on a...