Seasonal Variability In Abundance Research Articles

Waterbird community changes in the Wilderness Lakes, South Africa (Part 3 of 3): Diving piscivores and scavengers

Estuarine waterbodies typically support diverse and abundant waterbird communities. However, global environmental degradation as a result of anthropogenic activities is leading to species level changes in biodiversity, with top predators such as piscivorous waterbirds being particularly vulnerable to ecosystem changes. The study aimed to document long-term spatial and temporal patterns of abundance of piscivorous and scavenging waterbirds in the Wilderness Lakes Complex (WLC) in the Garden Route National Park, South Africa, and where possible identify potential causes for observed trends. The abundance of waterbirds on these wetlands was determined biannually from 1992 to 2019, with counts conducted from a boat following a standardised route. Historical waterbird abundance data from the 1980s were also used to describe long-term abundance changes. Eight of the species exhibited seasonal variability in abundance with most, excluding Common Tern Sterna hirundo, being more abundant in winter. Substantial changes occurred in the abundance of several species over the four-decade study period, notably increases in Cape Cormorant Phalacrocorax capensis and Great Crested Grebe Podiceps cristatus, and decreases in Common Tern and Black-necked Grebe Podiceps nigricollis. Long-term abundance trends indicate a combination of declining, increasing, and stable populations. Although some species have undergone contrasting abundance changes on different waterbodies in the WLC the dominant pattern was a similar direction of change on most or all waterbodies and in different seasons. Local reasons for changes probably include loss of sandbanks, changing prey availability, and the absence of recreational disturbance on some waterbodies.Conservation implications: Drivers of changes in the abundances of piscivores are likely to be multifaceted, functioning on multiple spatial and temporal scales, and affecting different species in different ways. Recommended local corrective actions include managing emergent macrophyte encroachment on sandbanks, reducing recreational disturbance, managing processes affecting indigenous fish stocks, and protecting nesting sites.

Joint spatiotemporal models to predict seabird densities at sea

IntroductionSeabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type.MethodsUsing a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions. ResultsThe best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters).DiscussionOur results indicated that pelagic shearwaters (Ardenna spp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy.

Comparison of the seasonal variability in abundance of the copepod Pseudocalanus newmani in Lagoon Notoro-ko and a coastal area of the southwestern Okhotsk Sea

Replacement of the warm water of the Soya Warm Current (SWC) and the cold water of the East Sakhalin Current (ESC) occurs seasonally along the coast of the southwestern Okhotsk Sea, and sea ice covers the surface during winter. Pseudocalanus newmani is one of the dominant copepods in coastal waters of the northern hemisphere. To better understand the population dynamics of the copepod P. newmani in coastal areas of the southwestern Okhotsk Sea, this study compared the seasonal variation in P. newmani abundance in Lagoon Notoro-ko and a coastal area of the Okhotsk Sea with regard to developmental stage. We sampled P. newmani in the lagoon, including during the ice cover season, and the coastal waters. Pseudocalanus newmani was abundant at both sites in spring. During summer–fall, adults disappeared from the populations at both sites, whereas the early developmental stages were abundant and dominated the population. Total length of adult females decreased toward summer at both sites. Pseudocalanus newmani abundance in the lagoon increased in early winter, and larger females were found in the populations at both sites. These phenomena at both sites corresponded with seasonal variation in water temperature caused by seasonal water-mass replacement and sea ice.

Spatial and Temporal Structures of the Macrozoobenthos from the Intertidal Zone of the Kneiss Islands (Central Mediterranean Sea)

The present study analyses the spatio-temporal variability of the macrozoobenthos from the intertidal zone of the Kneiss Islands (Gulf of Gabes, Tunisia). Samples were collected once from 34 stations, while seasonal variations were studied by sampling four times at 12 stations over the period 2013-2014. A total of 159 macrobenthos taxa associated with intertidal Zostera noltei beds are identified from the 34 stations, with a taxonomic dominance of crustaceans (32%), molluscs (29%) and annelids (27%). Abundance varies from 9244 to 36,844 ind·m-2 with a mean value of 14,346 ind·m-2. Analysis of the trophic structure shows that the majority of stations are strongly represented by carnivores (41%), followed by the non-selective deposit feeders (16%). Cluster analysis and multidimensional scaling allow identification of three main benthic assemblages based on species abundance, corresponding to different sediment types and organic matter contents. The seasonal variability in abundance, diversity and community structure is mainly due to spring and summer recruitment. The biotic indices (i.e. AMBI, BO2A and BENTIX) show that the intertidal area of Kneiss Islands exhibits a good ecological status.

Seasonal variability in the abundance of Arctic charr (Salvelinus alpinus (L.)) recorded using hydroacoustics in Windermere, UK and its implications for survey design

Abstract – Hydroacoustic surveys are an important tool for assessing the abundance of Arctic charr (Salvelinus alpinus (L.)) in lakes, the requirement for which is increasing because of new environmental legislation. Consequently, survey demand is now such that assessments must be undertaken with the minimum of effort compatible with scientific validity. One major complication is seasonal variability in abundance, with which surveyors have attempted to deal by defining somewhat arbitrary seasonal sampling windows. The definition of more objective windows was pursued by analysing variations in the seasonal abundance of Arctic charr in Windermere, UK, recorded using day and night hydroacoustic surveys at monthly intervals from 1991 to 2001. Two alternative sampling windows for night surveys free of significant internal seasonal effects were revealed, i.e., December to September and September to December. It was also found that day surveys gave a useful, although lower, estimate of abundance as compared with night surveys.

Seasonal variability in abundance, respiration and lipid composition of Arctic under-ice amphipods

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 292:251-262 (2005) - doi:10.3354/meps292251 Seasonal variability in abundance, respiration and lipid composition of Arctic under-ice amphipods Iris Werner1,*, Holger Auel2 1Institute for Polar Ecology, Wischhofstraße 1–3, Gebäude 12, 24148 Kiel, Germany2Marine Zoology (FB2) University of Bremen, PO Box 330440, 28334 Bremen, Germany *Email: iwerner@ipoe.uni-kiel.de ABSTRACT: The Arctic under-ice amphipods Apherusa glacialis, Onisimus glacialis, O. nanseni and Gammarus wilkitzkii are autochthonous below the pack ice, i.e. they occur in this habitat during all seasons. In this study, seasonal dynamics in abundance were only evident in A. glacialis. Respiration rates did not differ significantly between summer and winter in any species, indicating that the under-ice habitat is a comparatively stable environment in terms of seasonal variations. The assessment of total lipids and fatty acid biomarkers revealed differences in feeding behaviour and overwintering strategy among the amphipod species. A. glacialis is strictly herbivorous, feeding on ice-algae at the underside of the ice during the productive season. The species overwinters in an active state, fuelled at least partly by internal lipid reserves stored during summer. O. glacialis switches from a predominantly herbivorous diet in summer to metazoan prey, including planktonic copepods, in winter, so that lipid catabolism is less important to winter survival. The congener O. nanseni relies on an opportunistic omnivorous diet throughout the year, with a higher proportion of metazoan prey during summer compared to O. glacialis. G. wilkitzkii is able to exploit a wide spectrum of food sources, from predominantly ice algae in summer to more ice fauna and planktonic copepods in winter. This species partly meets its energy requirements by using internal lipid reserves during winter. KEY WORDS: Seasonal dynamics · Overwintering strategies · Cryo-pelagic coupling · Arctic foodweb · Apherusa glacialis · Onisimus glacialis · Onisimus nanseni · Gammarus wilkitzkii Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 292. Online publication date: May 12, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Energy density and variability in abundance of pigeon guillemot prey: support for the quality–variability trade‐off hypothesis

Summary 1. The quality‐variability trade-off hypothesis predicts that (i) energy density (kJ g − 1 ) and spatial‐temporal variability in abundance are positively correlated in nearshore marine fishes; and (ii) prey selection by a nearshore piscivore, the pigeon guillemot ( Cepphus columba Pallas), is negatively affected by variability in abundance. 2. We tested these predictions with data from a 4-year study that measured fish abundance with beach seines and pigeon guillemot prey utilization with visual identification of chick meals. 3. The first prediction was supported. Pearson’s correlation showed that fishes with higher energy density were more variable on seasonal ( r = 0·71) and annual ( r = 0·66) time scales. Higher energy density fishes were also more abundant overall ( r = 0·85) and more patchy at a scale of 10s of km ( r = 0·77). 4. Prey utilization by pigeon guillemots was strongly non-random. Relative preference, defined as the difference between log-ratio transformed proportions of individual prey taxa in chick diets and beach seine catches, was significantly different from zero for seven of the eight main prey categories. 5. The second prediction was also supported. We used principal component analysis (PCA) to summarize variability in correlated prey characteristics (energy density, availability and variability in abundance). Two PCA scores explained 32% of observed variability in pigeon guillemot prey utilization. Seasonal variability in abundance was negatively weighted by these PCA scores, providing evidence of risk-averse selection. Prey availability, energy density and km-scale variability in abundance were positively weighted. 6. Trophic interactions are known to create variability in resource distribution in other systems. We propose that links between resource quality and the strength of trophic interactions may produce resource quality‐variability trade-offs.

Seasonal and interannual variation in abundance of Calanus finmarchicus (Gunnerus) and Calanus helgolandicus (Claus) in inshore waters (west coast of the Isle of Man) in the central Irish Sea

The seasonal and interannual variability in abundance of Calanus finmarchicus and Calanus helgolandicus in the Irish Sea was examined on the west side of the Isle of Man (central Irish Sea) between 1995 and 2001. There was considerable interannual variability in abundance of both species that was greater than that seen in adjacent seas. In general, maximum abundance occurred between May and July each year with C. finmarchicus tending to occur earlier in the year than C. helgolandicus. There was a significant difference in interannual maximum abundances in the area (14-18 stations treated as replicates) with most years having a low abundance and one year a relatively high abundance. The maximum abundance of C. finmarchicus (1996) coincided with a low (negative) index value of the North Atlantic Oscillation (NAO), and with a high abundance of young gadoids (cod, haddock and whiting) in the water column and a large settlement of plaice. A high abundance of helgolandicus coincided with a relatively high (positive) index value of the NAO in 2000. The magnitude of interannual and seasonal variability in abundance was in close agreement with data from an inshore area (Port Erin Bay, Isle of Man) between 1907 and 1920. As with many Calanus populations, the adults in both species were predominantly female. As shown previously, Calanus is not one of the numerically dominant copepod species in the Irish Sea. However, the presence of young stages of Calanus within the central Irish Sea suggests that it must support a breeding population.

Macrozooplankton communities and environmental variables in the Barents Sea marginal ice zone in late winter and spring

The horizontal distribution of macrozooplankton (≥3 mm) was studied with respect to changes in environmental conditions along 3 transects across the marginal ice zone (MIZ) in the NW Barents Sea during late winter (March 2000) and spring (May 1999). The water masses, which were identified by their salinity and temperature characteristics, largely determined the macrozooplank- ton composition, but season (late winter vs spring), geographical area (latitude and longitude) and bottom depth were also important. Almost 80% of the total macrozooplankton variability could be explained by changes in these environmental variables. Ice cover and the algal bloom situation had no significant impact on the horizontal macrozooplankton distribution early in the season (March to May). We sampled 3 main water masses: cold and less saline Arctic water (ArW), warm and saline Atlantic water (AtW) and mixtures of these (MIX); 5 distinct macrozooplankton communities were found, 2 in ArW (ArW bank and ArW slope), 2 in MIX (warm, >1°C, and cold, <0°C, MIX) and 1 in AtW. These communities were characterised by differences in species abundance rather than differ- ences in taxonomic composition. Numerically important macrozooplankton were Calanus glacialis, C. hyperboreus, Thysanoessa inermis and Aglantha digitale. These were also important in terms of wet biomass together with Beroe cucumis, Clione limacina and Sagitta elegans. Good indicator species for ArW were C. glacialis, C. limacina, Mertensia ovum and Parathemisto libellulla, and for AtW Thysanoessa spp. (T. inermis, T. longicaudata and T. raschii). Characteristic for MIX, i.e. the Polar Front region, was low macrozooplankton abundance, biomass and species richness compared to AtW and ArW. Seasonal variability (late winter vs spring) accounted for 21% of the total macro- zooplankton variability. Particularly the herbivores showed large seasonal variability in abundance and biomass, most probably due to their seasonal migration patterns.

Seasonal variability in abundance and diversity of soil gymnamoebae along a short transect in southeastern USA.

The abundance and diversity of gymnamoebae in three subsoils varying in compaction and water retention along a 1.2 m transect were documented as the local climatic conditions changed from late summer 1999 through mid-summer 2000. The mean density of gymnamoebae for the loose soil (1,655/g) was greater than either the most compact (1,468/g) or moderately compact soil (851/g). Minimum densities occurred in middle and late summer for all soils while significant (F = 38.803, < or = 0.0002) density peaks at 3.212/g occurred in early summer in the most compact soil, 2.928/g in the least compact, and 2,209/g in the moderately compact soil. Limax non-eruptive gymnamoebae (mt 2) correlated (r = 0.49, p < or = 0.016) with moisture while eruptive limax gymnamoebae ( 3) correlated with temperature (r = 0.07, p < or = 0.024), moisture (r = 0.58, p < or = 0.001) and precipitation (r = 0.46, p < or = 0.029). Flattened or discoid amoebae (mt 4) dominated throughout most of the survey, and the two limax groups showed inverse relationships. Chi-square analyses showed significant differences in the numbers of limax eruptive gymnamoebae compared to all other morphotypes on all but one sampling period.

Variability in abundance, vertical distribution and ontogenetic migrations of Thysanoessa longicaudata (Crustacea: Euphausiacea) in the north-eastern Atlantic Ocean

The vertical distribution, seasonal and ontogenetic migrations and seasonal variability in abundance of Thysanoessa longicaudata (Kroyer) were investigated using the Longhurst-Hardy Plankton Recorder for a 4 yr period (March, 1971 to May, 1975) at Ocean Weather Station “I” (59°00′N; 19°00′W) in the north-eastern Atlantic Ocean. Of 8 species of euphausiids identified at this position, the vast majority were T. longicaudata (for example, 99.5% of the total euphausiids in 1972 belonged to this species). From March to October the majority of calyptopes, furciliae and adults of T. longicaudata were found in the upper 100 m. The major spawning occurred in spring at a water temperature of 9° to 10°C and calyptopes and furciliae appeared in late April, reaching their maximum abundance in May. There was no evidence of large-scale diurnal migrations, although an extensive ontogenetic migration of young developmental stages was observed. The eggs were found from 100 m down to 800 m, the maximum depth of sampling, and the vertical distribution of the three naupliar stages showed a “developmental ascent” as they matured. During the main reproductive period in May, over 70% of all nauplii were below 500 m while more than 94% of Calyptopis Stage I were above 500 m with their maximum abundance in the euphotic zone (0 to 50 m). Calyptopis Stage I is the first feeding stage and it is this stage which shows the largest ontogenetic migration. Brief descriptions of the egg and nauplii are given.

Vertical distribution and seasonal abundance of Aglantha digitale (O.F. Müller) (Coelenterata: Trachymedusae) and other planktonic coelenterates in the northeast Atlantic Ocean

The vertical distribution and seasonal variability in abundance of the hydromedusa Aglantha digitale (O.F. Muller) and other coelenterates from the north-east Atlantic Ocean are described. The coelenterates were abundant from May to September and reached peak numbers in June, July and September when concentration of 40 individuals m −1 were recorded. A. digitale numerically dominated the codenterate population and accounted for over 80% of the dry weight biomass in hauls taken from 1971 to 1974. The data suggests a 2½ month development period for this medusa from egg to mature adult (8 mm) which supports previous published data. During the growth of the medusa there were considerable changes in the ratios of wet to dry weights. At a bell-height of 1 mm the mean dry weight was 22% of mean wet weight and at 8 mm the mean dry weight was 5% of mean wet weight; the percentage decreased further in the largest specimens to 2% at 25 mm. The majority of A. digitale occurred in the upper 100 m but in late July the larger specimens extended their distribution to the limit of sampling (500 m). The two most abundant siphonophores , Dimophyes arctica (Chun) and Nanomia cara A. Agassiz, were found deeper than the main population of A. digitale . It is suggested that coelenterates could be an important source of nitrogen for the development of the late bloom of phytoplankton in the north-east Atlantic Ocean.