Seasonal Differences In Abundance Research Articles

Seasonal Abundance and Types of Microplastics in Surface Waters of River Sabaki Estuary, Kenya

Increased demand for plastics has resulted in the generation of plastic waste, which poses a threat to the environment in general, and ultimately the marine environment. Estuaries and deltas are the main filters of marine ecosystem pollutants from inland sources. There have been limited studies on temporal variations in microplastic (MP) pollutants in tropical estuaries of Africa. In 2022, a twelve-month sampling survey study was conducted at Sabaki river estuary, in Kenya. A bucket was used to collect water samples, that were sieved through a 225μm sieve. A stereo microscope was used to identify microplastics and their polymer confirmed using FTIR spectroscopy. Data analysis on seasonal difference in abundance of microplastics in surface waters was performed using Minitab software at α ≤ 0.05. The results indicated that the April-June (A-J) long rains season had significantly (P ≤ 0.05) higher levels of MPs due to rainfall runoff, compared to other seasons, namely January –March (J-M), July-October (J-O) and November –December (N-D). The (J-M), (J-O) and (N-D) seasons had similar levels of MPs, which were lower compared to those observed during (A-J) long rains season by 44.3%, 54% and 25% respectively, compared to the highest concentration of 264 MPs m-3 observed during the A-J season. Fragments type of MPs were higher during the wet season, while fiber type of MPs dominated during the dry season. Film and form type of MPs were least abundant. Seasons significantly (P ≤ 0.05) influenced distribution of the different sizes of MPs. Small and medium sized category of MPs occurred and dominated during the dry season, while larger particles dominated during the wet season. Seven (7) differently colored MPs were observed during the study. White colored MPs were most prevalent (33%), followed by blue (23%), black (17%), brown (12%), yellow (5%), red (5%), and green (4%). Five types of plastic polymers were found in surface waters of river Sabaki estuary, namely polyethylene (PE), polypropylene (PP), polystyrene (PS), Polyethylene terephthalate (PET), and Acrylonitrile-butadiene-styrene (ABS).

Ichthyoplankton Assemblages from the Coasts of Hamsilos Nature Park, Sinop, Southern Black Sea: Biodiversity, Abundance, and Relationships with Environmental Variables

This study was conducted using monthly data collected between July 2015 and June 2016 in the marine area of Hamsilos Nature Park, located in Sinop, Southern Black Sea. The primary objectives were to determine the diversity of ichthyoplankton assemblages, examine seasonal variations, assess spatial differences between the inner and outer parts of Hamsilos Bay, and highlight the ecological relationships of the predominant species with environmental factors. The comprehensive collection during the study resulted in a mean abundance of 2217 eggs.10 m2 and 2743 larvae.10 m2, with 28 species belonging to 21 families identified. Specifically, Engraulis encrasicolus is the most abundant in spring and summer, Gaidropsarus mediterraneus is the most abundant in autumn, and Sprattus sprattus is the most abundant in winter. A temporal analysis revealed the highest abundances in August, September, and July, with the lowest in April, May, and February. Significant seasonal differences in abundance and diversity were detected. No spatial differences were found between the inner and outer areas of Hamsilos Bay. Small pelagic species dominated the ichthyoplankton community, while demersal species, though diverse, were less abundant. According to the results of the DistLM analysis, the structure of the ichthyoplankton community is influenced by temperature and salinity. During the study, the water temperature ranged from 8.35 °C in February to 25.50 °C in August, and the salinity varied from 17.67 psu in September to 19.04 psu in May.

Environmental and Seasonal Effects on Gerridae Assemblages (Heteroptera: Gerromorpha) from a Stream in Brazilian Savannah.

Our aim here was to assess the seasonal (dry, ebb, and rainy seasons), spatial (upstream, intermediate, and downstream), and environmental effects on the dynamics of Gerridae assemblages (Heteroptera: Gerromorpha) in a Cerrado stream, in central-western Brazil. We sampled the insects on the water line between May 2011 and April 2014 with an 18 cm diameter sieve. We used the scanning method in 100 m of stream in each sampled locality. We sampled 3690 individuals of 19 species. There was a seasonal difference in abundance, which was a result of a lower abundance in the rainy season, but this did not differ between different environments. The estimated species richness was lower upstream and in the rainy season. Species composition was different between the upstream and downstream portions. It was also different among all seasons, with the greatest difference occurring between the rainy and dry seasons. The abiotic factors were responsible for structuring the assemblages in different seasons. The observed differences among seasons in abundance, richness, and species composition have implications for conservation since changes in the structure of the vegetation in the stream edges change the hydrological cycle of streams, and consequently the diversity of the Gerridae assemblages. There was variation in richness and composition between such small distances (upstream and downstream). This shows how sensitive this system can be, and how important elements of the stream's trophic, with the Gerromorpha, can be easily altered.

Partitioning resources through the seasons: abundance and phenology of carrion beetles (Silphidae) in southeastern Ontario, Canada

The coexistence of ecologically similar species is thought to require resource partitioning to minimize competition. Phenological, seasonal differences in activity may provide an important axis for resource partitioning. Here, we test for evidence of seasonal differences in activity within a diverse guild of carrion beetles (Silphidae) in a habitat preserve on the Frontenac Arch, southeastern Ontario, Canada, using a large-scale survey during their active seasons (April to October). We then used generalized additive models to test for differences in seasonal abundance among eight co-occurring carrion beetle species, including five species of burying beetles (Nicrophorinae: Nicrophorus Fabricius, 1775) and three species from the Silphinae subfamily. Consistent with previous work, all species showed seasonal variation in abundance, with peak abundance of most species occurring between June and August. All but one species (Nicrophorus sayi Laporte, 1840) showed positive relationships between abundance and temperature. We find evidence consistent with seasonal partitioning of resources among Nicrophorus habitat generalists that could potentially reduce competition for limited carrion resources. In contrast, we find little evidence for seasonal differences in abundance among Nicrophorus habitat specialists, which instead may partition resources spatially. Overall, our results provide evidence consistent with an important role for seasonal resource partitioning among carrion beetle species that show higher levels of spatial (habitat) overlap within a temperate beetle guild.

Size spectra analysis of a decade of Laurentian Great Lakes data

Size spectra analysis (SSA) is used to detect changes in food webs by simplifying complex community structures through abundance-versus-biomass considerations. We applied SSA to 10 years (2006–2015) of data on Great Lakes organisms ranging in size from picoplankton to macrozooplankton. Summer pelagic size spectra slopes were near the theoretical value of −1.0, but spring slopes were steeper, reflecting seasonal differences in abundance of small and large individuals. Pelagic size spectra slopes were relatively stable over the time period we examined. Height (the predicted number of organisms at the spectra midpoint) varied among lakes and was slightly higher in summer than spring in more productive basins. Including benthic data led to shallower slopes when combined with pelagic data, suggesting benthic organisms may increase food web efficiency; height was less affected by benthic data. Benthic data are not routinely included in SSA, but our results suggest they affect slopes and therefore SSA-based predictions of fish abundance. The ability of SSA to track changes in trophic energy transfer makes it a valuable ecosystem monitoring tool.

Population structure of Gobiidae in a tropical urban estuary

As spatiotemporal variations in estuaries affect the population structure of species, the study aimed to analyze the distribution of species of the family Gobiidae in the Capibaribe River's estuary city of Recife (northeastern Brazil). Sampling was performed bi-monthly from February 2009 to December 2012 at two sampling stations. The weight-length relationship of the species was determined using potential regression analysis. Density and biomass values were determined for each species per sampling station and season. The Mann-Whitney test was used to compare spatial and seasonal differences in abundance. A non-metric multidimensional scaling ordination was used to assess changes in species composition. Seven hundred eighty-eight individuals were caught. The most representative species of Gobiidae was Ctenogobius boleosoma, followed by Evorthodus lyricus and Gobionellus oceanicus. The relationship between total weight (TW) and standard length (SL) was potential and significant for both C. boleosoma (TW = 0.04SL2.1815) and E. lyricus (TW = 0.0272SL2.795), and both exhibited negative allometric growth. The analysis of the main species' spatial variation demonstrated a significant difference in the number of individuals for C. boleosoma (U = 528; p = 0.000005) and E. lyricus (U = 312; p = 0.000000). No significant difference in abundance was found between the dry and rainy season for either C. boleosoma (U = 1052.2; p = 0.4659) or E. lyricus (U = 1054; p = 0.4726). The two most abundant species have similar habits and customarily inhabit stressful environments. Ctenogobius boleosoma and E. lyricus are residents of the Capibaribe River's estuary, and both move to regions near the outfall of the river in the rainy season.

Impacts of physicochemical and heavy metal parameters on infestation level of the monogeneans, Quadriacanthus spp. infesting Nile catfish, Clarias gariepinus of different water localities in Nile Delta, Egypt.

Fish parasites can be used as bio-indicators to evaluate pollution degree in aquatic ecosystems. Limited research has, however, investigated the potentiality of these parasitic worms to tolerate various environmental factors. This study, therefore, investigated whether the gill, Quadriacanthus monogenean parasites of Bagrus bajad Forskål, 1775 are potential bio-indicators of aquatic ecosystem health. The seasonal differences in prevalence, mean intensity and abundance of Quadriacanthus species of Clarias gariepinus varied between each other and between the three localities. Most Quadriacanthus species exhibited their highest prevalence, mean intensity and abundance in Spring and/or Summer and their lowest values in Autumn and/or Winter. The seasonal differences in prevalence were significant for Q. kearni and Q. clariadis while a significant difference in the mean intensity between different seasons was recorded only for Q. aegypticus. Also, seasonal differences in the abundance were highly significant for Q. aegypticus and significant for Q. kearni. The total dissolved solids, Chlorides, Sulphate, Sodium, Cadmium and Lead were higher at Manzala Lake than standard permissible limits. The pH has significant correlations with the infestation levels of all Quadriacanthus spp. Dissolved oxygen showed a highly significant positive correlation with the mean intensity of Q. clariadis and a significant positive correlation with the abundance of Q. clariadis. Iron was the only heavy metal to record a significant positive relationship with the mean intensity of Q. kearni. It is noteworthy that Quadriacanthus species were found to have a noticeable ability to resist the effect of hazardous concentrations of many physicochemical and heavy metals parameters. Therefore, it is highly recommended that these monogeneans could be regarded as bio-indicators for water quality.

Temporal patterns of three sympatric pheasant species in the Nanling Mountains: N-mixture modeling applied to detect abundance

BackgroundThe reliability of long-term population estimates is crucial for conservation and management purposes. Most previous studies assume that count indices are proportionally related to abundance; however, this assumption may not hold when detection varies spatially and temporally. We examined seasonal variations in abundance of three bird species (Cabot’s Tragopan Tragopan caboti, Silver Pheasant Lophura nycthemera, and White-necklaced Partridge Arborophila gingica) along an elevational gradient, using N-mixture models that take into account imperfect detection in our bird data.MethodsCamera-trapping was used to monitor temporal activity patterns of these species at Guangdong Nanling National Nature Reserve from December 2013 to November 2017 (4 seasons per year). For abundance analysis (N-mixture modeling), we divided a year into 4 seasons, i.e. 3 months per season, and performed the analysis by season. Elevation was incorporated into the N-mixture model as a covariate that may affect abundance. We compared the N-mixture model with a null model (no covariate model) and selected the better model based on AIC values to make an inference.ResultsFrom 24 sampling sites, we obtained 6786 photographs of 8482 individuals of 44 bird species and 26 mammal species. Silver Pheasant was photographed much more frequently and showed higher temporal activity frequency than White-necklaced Partridge or Cabot’s Tragopan. Silver Pheasant was camera-captured most frequently in summer, and other two species in winters. All three species had two daytime activity peaks: between 6:00 a.m. and 10:00 a.m., and between 5:00 p.m. and 7:00 p.m., respectively. Our estimated abundance and detection probability from the N-mixture model were variable by season. In particular, all three species showed greater abundance in summer than in winter, and estimated abundance patterns of all three species were more similar with observed camera-trapping counts in summers. Moreover, in winter, elevation had a positive impact on abundance of Silver Pheasant and Cabot’s Tragopan, but not on White-necklaced Partridge.ConclusionsOur results demonstrate that the N-mixture model performed well in the estimation of temporal population abundance at local fixed permanent plots in mountain habitat in southern China, based on the modeling of repeated camera-trapping counts. The seasonal differences in abundance of the three endemic bird species and the strong effect of elevation on abundance of two species in winter were only indicative of variations in spatio-temporal distribution within species and between species. In identifying suitable habitat for endemic pheasants, the positive elevational effect also suggests that more attention should be paid to conservation of areas with higher elevation in the Nanling Mountains.

Seasonal variations in the abundance and body size distribution of the ocean sunfish Mola mola in coastal waters off southern Portugal

AbstractThe present work expands the existing knowledge on M. mola ecology by assessing, for the first time, its abundance (and body size distribution) in the southern waters of Portugal and relating the associated temporal variations with environmental variables. There were significant seasonal differences in abundance, with peaks in spring and autumn and lower values throughout the summer. Ocean sunfish abundance was positively correlated with sea surface temperature and chlorophyll a, indicating that a combination of both temperature and productivity dictates spatial use. Complementarily, the absence of a relationship between abundance and water transparency may reveal a strategy in spatial use favouring a medium-term steady food supply over short-term improved feeding opportunities. Specimens ranged between 31.8 and 230.0 cm (total length), with 98% of all individuals measuring between 31.8 and 59.9 cm. As the vast majority of specimens analysed were immature, seasonal differences in abundance should not be related to spawning.

Do vegetated rooftops attract more mosquitoes? Monitoring disease vector abundance on urban green roofs

Green roof, an increasingly common constituent of urban green infrastructure, can provide multiple ecosystem services and mitigate climate-change and urban-heat-island challenges. Its adoption has been beset by a longstanding preconception of attracting urban pests like mosquitoes. As more cities may become vulnerable to emerging and re-emerging mosquito-borne infectious diseases, the knowledge gap needs to be filled. This study gauges the habitat preference of vector mosquitoes for extensive green roofs vis-à-vis positive and negative control sites in an urban setting. Seven sites in a university campus were selected to represent three experimental treatments: green roofs (GR), ground-level blue-green spaces as positive controls (PC), and bare roofs as negative controls (NC). Mosquito-trapping devices were deployed for a year from March 2015 to 2016. Human-biting mosquito species known to transmit infectious diseases in the region were identified and recorded as target species. Generalized linear models evaluated the effects of site type, season, and weather on vector-mosquito abundance. Our model revealed site type as a significant predictor of vector mosquito abundance, with considerably more vector mosquitoes captured in PC than in GR and NC. Vector abundance was higher in NC than in GR, attributed to the occasional presence of water pools in depressions of roofing membrane after rainfall. Our data also demonstrated seasonal differences in abundance. Weather variables were evaluated to assess human-vector contact risks under different weather conditions. Culex quinquefasciatus, a competent vector of diseases including lymphatic filariasis and West Nile fever, could be the most adaptable species. Our analysis demonstrates that green roofs are not particularly preferred by local vector mosquitoes compared to bare roofs and other urban spaces in a humid subtropical setting. The findings call for a better understanding of vector ecology in diverse urban landscapes to improve disease control efficacy amidst surging urbanization and changing climate.

Different thermal responses in two coexisting aphids may account for differences in their seasonal abundance in cotton fields

ABSTRACTThe coexistence of species competing for resources can be facilitated by differential effects of temperature on fitness components. The coexisting cotton aphids Aphis gossypii Glover and Acyrthosiphon gossypii Mordvilko show seasonal differences in abundance in North-Western China, the former reaching higher field abundances and declining later in the season than the latter. We hypothesized that differences in responses to temperature might be the proximate mechanism driving this difference in population dynamics between the two species. Aphids from laboratory-reared colonies and directly collected from the field in early summer were used to study their development, survival and reproduction under a range of constant temperatures. Life-table parameters suggest that A. gossypii performed better than Ac. gossypii under all temperature treatments tested, and the difference tended to be strongest under high temperatures. These observations are consistent with the higher numbers and the later decline of A. gossypii in the field compared with Ac. gossypii. Our findings help in understanding the seasonal population dynamics of both species, as well as in forecasting pest trends under global warming scenarios.

Influence of oceanographic features on the spatial and seasonal patterns of mesozooplankton in the southern Patagonian shelf (Argentina, SW Atlantic)

Surveys conducted during spring, summer and late winter in 2005–2006 over the southern Patagonian shelf have allowed the seasonal distribution of mesozooplankton communities in relation to water masses and circulation to be investigated. In this system, most of the shelf is dominated by a distinct low salinity plume that is related to the runoff from the Magellan Strait (MSW), while the outer shelf is highly influenced by the cold and salty Subantarctic water (SAW) of the boundary Malvinas Current. Separating these two, the Subantarctic Shelf water mass (SASW) extends over the middle shelf. Correspondingly, the structure of the MSW and SAW mesozooplankton communities was found to be clearly different, while the former and the SASW assemblages were barely separable. This relatively fresh water mass is actually a variant of Subantarctic water that enters into the region from the south and the shelf-break, and hence its mesozooplankton community was not significantly different from that of the SAW water mass. Dissimilar species abundance, in turn associated with different life histories and population development, was more important than species composition in defining the assemblages. Total mesozooplankton abundance increased about 2.5-fold from the beginning of spring to late summer, and then decreased at least two orders of magnitude in winter. Across all seasons copepods represented >70–80% of total mesozooplankton over most of the shelf. Copepod species best represented through all seasons, in terms of both relative abundance and occurrence, were Drepanopus forcipatus and Oithona helgolandica. Although seasonal differences in abundance were striking, the spatial distribution of mesozooplankton was largely similar across seasons, with relatively higher concentrations occurring mainly in Grande Bay and surroundings. The well defined spatial patterns of mesozooplankton that appear from our results in conjunction with the southward wide extension of the shelf and the predicted current path and speed suggest that plankton production is locally enhanced in the Grande Bay area and has the potential to be exported downstream.

Avian Communities of a Mixed Mopane-Acacia Savanna in the Cuvelai Drainage System, North-Central Namibia, During the Dry and Wet Season

Abstract Studies were conducted by means of the Line Transect Method in late rainy season (March), in the middle of dry season (July) and at beginning of rainy season (November).Th e total length of all transects was c. 11 km. In total, 70 resident and 13 nonresidentspecies were recorded. Th e number of species in dry season was significantly lower than in rainy season (x2-test: 14.1; p < 0.01). Th e highly significant seasonal differences in abundance were recorded for the following species: Streptopelia senegalensis, Streptopelia capicola, Uraeginthus angolensis, Cisticola juncidis, Upupa africana, Cynniris mariquensis, and Numida meleagris. In overall, five species have been classified as dominants: Streptopelia senegalensis, Streptopelia capicola, Uraeginthus angolensis, Plocepasser mahali and Cypsiurus parvus. They comprised together 43.9 %. Significant variations in the dominance structure between the wet and dry season have been evidenced. Granivores were much more numerous in the dry than in the wet season, while for the insectivores the reverse was true. Although Sorensen Coefficient was much the same between all three seasons, the Shannon’s Diversity Index was lower in July than in March and November.

Examination of an Estuarine Fish Assemblage Over an Inshore Artificial Reef

The perceived value of oyster reefs as fish habitat has led to many restoration projects in areas of historically high oyster populations. This study evaluated fish usage of a limestone cobble mimic oyster reef in Barataria Bay, Louisiana, as compared to a mud-bottom reference site. Emphasis was given to species of economic and ecological importance, including spotted seatrout (Cynoscion nebulosus), Atlantic croaker (Micropogonias undulatus), and bay anchovy (Anchoa mitchilli). There were no observed differences in community structure or catch per unit effort (CPUE) between habitats, likely due to high variability in the data, though seasonal differences were observed. CPUE of spotted seatrout, Atlantic croaker, and bay anchovy did not differ between habitats. Seasonal differences in abundance were detected, with significantly higher CPUE of spotted seatrout in summer, of Atlantic croaker in spring and summer, and of bay anchovy in winter. Spotted seatrout and Atlantic croaker were both significantly larger over the artificial reef, while bay anchovy were significantly larger over the mud bottom. Spotted seatrout, a prized recreational fishing species in Louisiana, appeared to be the only species that showed higher biomass, determined by numbers and size, at the the artificial reef. This is important in the context of managing habitat enhancement projects. While the reef did not increase numbers or species richness of the overall fish community, it did have an effect on one recreationally important species. Therefore, the success of such projects is based as much on the intended purpose, as its affect on the overall community.

The parasite fauna of the Patagonian toothfish Dissostichus eleginoides off the Falkland Islands

The parasite fauna of juvenile Dissostichus eleginoides, while they inhabit the Falkland's shelf, was examined, giving new detailed information on spatial, ontogenic and seasonal variations. A total of 24,943 parasites from 15 different taxa were found in the stomach of 502 individual fish. Parasite species composition and abundance allowed separation of toothfish by area between the north-west and south-east of the Falklands. The digenean, Elytrophalloides oatesi, and the nematodes, Hysterothylacium spp. and Anisakis spp., were the most common, all with a prevalence >20%. For some seasons ontogenic changes in abundance were significant in these three parasite taxa, and this is discussed in terms of ontogenic and seasonal changes in diet. Elytrophalloides oatesi and Hysterothylacium spp. showed spatial and seasonal differences in abundance with greater numbers in the warmer waters of the north-west and during the summer months. Differences in abundance of E. oatesi between the Falklands and other regions indicate its potential for use as a biological tag to study toothfish movements and population structure; however, more seasonal data would be required before this technique could be used.

Comparing seasonal dynamics of the Lake Huron zooplankton community between 1983–1984 and 2007 and revisiting the impact of Bythotrephes planktivory

Zooplankton community composition can be influenced by lake productivity as well as planktivory by fish or invertebrates. Previous analyses based on long-term Lake Huron zooplankton data from August reported a shift in community composition between the 1980s and 2000s: proportional biomass of calanoid copepods increased while that of cyclopoid copepods and herbivorous cladocerans decreased. Herein, we used seasonally collected data from Lake Huron in 1983–1984 and 2007 and reported similar shifts in proportional biomass. We also used a series of generalized additive models to explore differences in seasonal abundance by species and found that all three cyclopoid copepod species (Diacyclops thomasi, Mesocylops edax, Tropocyclops prasinus mexicanus) exhibited higher abundance in 1983–1984 than in 2007. Surprisingly, only one (Epischura lacustris) of seven calanoid species exhibited higher abundance in 2007. The results for cladocerans were also mixed with Bosmina spp. exhibiting higher abundance in 1983–1984, while Daphnia galeata mendotae reached a higher level of abundance in 2007. We used a subset of the 2007 data to estimate not only the vertical distribution of Bythotrephes longimanus and their prey, but also the consumption by Bythotrephes in the top 20m of water. This epilimnetic layer was dominated by copepod copepodites and nauplii, and consumption either exceeded (Hammond Bay site) or equaled 65% (Detour site) of epilimnetic zooplankton production. The lack of spatial overlap between Bythotrephes and herbivorous cladocerans and cyclopoid copepod prey casts doubt on the hypothesis that Bythotrephes planktivory was the primary driver underlying the community composition changes in the 2000s.

Seasonal abundance and habitat use of Australian parrots in an urbanised landscape

Certain native species are able to tolerate the urban landscape to the point where they are sometimes found in higher abundance in cities than they are in the surrounding natural vegetation. To improve understanding of the resource requirements of Australian parrots, we investigated the seasonal abundance and habitat use of 13 species in different landscape units in the major urban centre of Sydney, Australia. The urban landscape was divided into four urban zones and 528 surveys were conducted over a period of two years throughout four habitats of remnant vegetation, golf courses, street scapes and recreational parks, as well as the surrounding natural landscape, during both breeding and non-breeding seasons. Significant seasonal differences in abundance existed for two granivorous and one nectarivorous species. Abundance was significantly higher in the outer urban zone than in the non-urban zone and species assemblage differed significantly between all urban zones and the non-urban zone during the breeding season but only between the city and non-urban zone during the non-breeding season. Remnant vegetation was also characterised by a significantly different community assemblage to other habitats during the breeding season. Understanding how fauna utilise the urban landscape, particularly high profile fauna such as parrots, has the potential to assist in both management and conservation of urban diversity.

Bacterial response to a weak 2006 El Niño condition in an upwelling area of the Humboldt Current System

Abundance and production of the pelagic heterotrophic bacteria community were studied at northern Chile during winter and summer periods of 2006–2007 in relation to seasonal changes in physical and chemical variables, including the influence of a weak El Niño event. Bacterial abundance was estimated by flow cytometry and secondary bacterial production by protein synthesis after bacterial uptake of14C-isoleucine. Bacterial biomass showed high values in the range of 2.84 at 96.6 µ g C l−1d−1with a bacterial growth efficiency (BGE) of 37.4% in the summer of 2007, and 2.7% in the winter of 2006. High amounts of C (~1.2 to 1.8 g C m−2d−1) were used for bacterial respiration in the upper 20 m. Environmental impact on bacterial abundance and BGE was reflected in a positive correlation with phytoplankton biomass (r2 > 0.40P < 0.05), and a lack of correlation with temperature (P > 0.05). Seasonal differences in abundance and BGE were mainly attributed to an ‘abnormally’ warm winter of 2006, which caused a greater stratification of the water column—a weaker and much deeper oxycline. The oxycline is normally shallower (<20 m) in the zone because of the ascent of the oxygen minimum zone (OMZ) upon upwelling. Winter 2006 conditions indicated presence of a weak El Niño event. Bacteria abundance increased during this warming event, but their metabolic activity was drastically reduced, resulting in a very low BGE. Our study suggests that changes from a prevailing sub-oxic to a highly oxygenated water column could have impacted the bacterial community, thus reducing its productive capacity. Therefore, variation in vertical distribution of the OMZ forced by upwelling variability and the El Niño impact might play an important role in the dynamics of the microbial component in this highly productive upwelling system.

Diel and seasonal variation in the use of a nearshore sandflat by a ray community in a near pristine system

Knowledge of movements and habitat use is necessary to assess a species’ ecological role and is especially important for mesopredators because they provide the link between upper and lower trophic levels. Using acoustic telemetry, we examined coarse-scale diel and seasonal movements of elasmobranch mesopredators on a shallow sandflat in Shark Bay, Western Australia. Giant shovelnose rays (Glaucostegus typus) and reticulate whiprays (Himantura uarnak) were most often detected in nearshore microhabitats and were regularly detected throughout the day and year, although reticulate whiprays tended to frequent the monitored array over longer periods. Pink whiprays (H. fai) and cowtail stingrays (Pastinachus atrus) were also detected throughout the day, but were far less frequently detected. Overall, there was no apparent spatial or temporal partitioning of the sandflats, but residency to the area varied between species. In addition, ray presence throughout the year suggests that previously observed differences in seasonal abundance are likely because of seasonal changes in habitat use rather than large-scale migrations. Continuous use of the sandflats and limited movements within this ray community suggests that rays have the potential to be a structuring force on this system and that focusing on nearshore habitats is important for managing subtropical ray populations.

Seasonal abundance of the Atlantic bobtail squid Sepiola atlantica in Galician waters (NE Atlantic)

The abundance of the bobtail squid Sepiola atlantica was assessed for Areamilla beach at Ría de Vigo. Sampling was carried out monthly and simultaneously by two scuba divers at two sandy submersed zones between December 2007 and November 2009. A total of 505 specimens of S. atlantica (204 juveniles, 149 males and 152 females) were collected. The mean annual abundance of the species was 0.01±0.01 ind./m2 from December 2007 to November 2008, and 0.02±0.01 ind./m2 from December 2008 to November 2009. Abundances were not significantly different between the two depth zones for each year, nor for seasons. However, total abundance was significantly different between seasons. Abundance showed a seasonal pattern with the lowest values in summer. For each season populations were formed by specimens of different size during the two sampling years, as well in both depth zones. Spawning occurs throughout the year. Two peaks of recruitment, one in summer and another in autumn, were observed. Whether seasonal differences in abundance are due to migration of the individuals from shallow to deeper zones related to changes in bottom temperature is discussed.