https://vital.seals.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://vital.seals.ac.za/vital/access/manager/Repository/vital:5665 Wed 21 Jul 2021 13:46:25 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26641 Wed 03 May 2023 13:21:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28390 Tue 27 Jul 2021 16:09:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5809 Tue 24 Aug 2021 16:43:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21330 Tue 15 Aug 2023 11:29:32 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30710 Tue 15 Aug 2023 11:20:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5607 Tue 15 Aug 2023 10:51:57 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27814 Tue 12 Oct 2021 15:49:22 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5690 Thu 13 May 2021 14:46:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5829 Thu 13 May 2021 13:43:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5765 50% of total chlorophyll-a at all these stations. Xl Within the IFZ (2 stations), nanophytoplankton dominated total integrated Chl-a biomass (range between 5.6 and 8.8 mg Chi-a. m-2) comprising, on average, 36% of the total. Picophytoplankton comprised an average of 12% of the total Chl-a biomass (range between 3.1 and 5.9 mg Chi-a. m-2) in the MIZ, 36% in the IFZ (range between 6.4 and 7.8 mg Chl-a . m-2) and 20% in the vicinity of the APF (range between 6.8 and 10.6 mg Chi-a. m-2). Total integrated primary production ranged between 316 and 729 mg C . m-2. d-1 at stations occupied in the vicinity of the MIZ, and between 292 and 317 mg C . m·2• d-l within the IFZ. At stations occupied in the region of the APF, total integrated production ranged between 708 and 926 mg C . m-2• dol. The contribution of various size fractions to total productivity generally displayed the same pattern as integrated Chl-a biomass. Microphytoplankton formed the most important contributor to total production at stations occupied in the MIZ and at the APF. Within the IFZ, nanophytoplankton dominated total daily production. Nutrient data suggest that concentrations of macro nutrients within the upper water column were above the threshold where growth would be limited. Preliminary results showed that concentrations of iron (Fe) were highest in the southern region of the MIZ and in the vicinity of the APF. During the second cruise, conducted in the vicinity of the Sub-Antarctic Front (SAF) and in the upstream, inter-island and downstream regions of the Prince Edward Islands, there was evidence of fresh water run-off from the islands, (i.e. decreased salinities and increased concentrations of ammonia and nitrate). Oceanographic data collected at the various production stations indicated that the upper water column was well mixed throughout the survey. Total integrated biomass during the study ranged between 8.5 and 20.1 mg Chi-a. m-2• No distinct patterns in total Chl-a biomass were evident. Picophytoplankton dominated total biomass comprising> 45 % of total pigment at all stations. Nanophytoplankton were the second most important contributor to total integrated biomass. Generally xu microphytoplankton contributed < 10 % of total ChI-a. Total daily integrated production was highest (442.6 mg Chi-a. m-2) at the single station occupied in the vicinity of the SAF. Outside this region, total areal production was lower, ranging from 94.5 to 353.0 mg C . m-2. d-1. With the exception of the station occupied in the vicinity of the SAF, total productivity was dominated by nanophytoplankton, which comprised between 48 and 66% of the total. Concentrations of macronutrients did not appear to be limiting to phytoplankton growth. The absence of a phytoplankton bloom in the vicinity of the islands appears to have been related to water column stability, which was influenced by the prevailing oceanographic regime during the survey. Previous studies have shown that when the SAF lies in close proximity to the islands, advecting forces prevail, resulting in the islands functioning as a flow-through system. During this study, the SAF lay immediately north of the islands. As a consequence no water was trapped in the leeward side of the islands. The results of the two cruises suggest that phytoplankton production in the four systems investigated: the Marginal Ice Zone (MIZ), Antarctic Polar Front (APF), Inter Frontal Zone (IFZ) and Prince Edward Islands (PEl), was largely controlled by water column stability. It is probable that the availability of iron, particularly in the region of the MIZ and APF, may have further contributed to the elevated production recorded in these two regions.]]> Thu 13 May 2021 10:40:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5725 Thu 13 May 2021 08:49:43 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5701 Thu 13 May 2021 08:45:56 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5923 Thu 13 May 2021 08:22:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5945 Thu 13 May 2021 08:18:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5815 Thu 13 May 2021 08:14:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5653 2 cm; chaetognaths, medusae, ctenophores and mysids), with particular emphasis on the chaetognaths Eukrohnia hamata and Sagitta gazellae, were investigated during three surveys conducted in late austral summer (April/May) of 2001, 2004 and 2005 in the Polar Frontal Zone in the vicinity of the Prince Edward Islands (46º45’S, 37º50’E), Southern Ocean. The 2001 survey formed part of the Marion Offshore Variability Ecosystem Study (MOVES II), while the 2004 and 2005 surveys formed part of the Dynamics of Eddy Impacts on Marion’s Ecosystem study (DEIMEC III and IV respectively). Macrozooplankton samples were collected using WP-2, RMT-8 and Bongo nets. Results of the hydrographic survey indicated that the region of investigation, the Polar Frontal Zone (PFZ), is an area of high mesoscale variability. During the 2004 survey the Antarctic Polar Front (APF) and the Subantarctic Front (SAF) merged to form an intense frontal feature with subsurface temperature and salinity ranging from 8.5-7.5ºC and 34.15-33.88, respectively. A cyclonic cold core eddy, believed to have been spawned from the APF, was observed during the 2005 survey. Macrozooplankton abundance and biomass ranged from 0 to 43.731 ind. m⁻³, and from 0 to 41.55 mg wwt m⁻³ respectively, during the three surveys. Among the carnivorous macrozooplankton, chaetognaths (Eukrohnia hamata and Sagitta gazellae) were most prominent, contributing up to 85% of the total biomass during all three surveys. Elevated biomass values were found near and within the frontal feature during the 2004 survey, and also along the eddy edge during the 2005 survey. However, hierarchical cluster analysis did not reveal the presence of distinct zooplankton groupings associated with the various water masses encountered during the surveys and this is probably due to the high mesoscale variability in oceanographic conditions that are characteristic of the PFZ. The total average predation impact of the selected carnivorous macrozooplankton during the 2001, 2004 and 2005 surveys accounted for 4.93 ± 6.76%, 0.55 ± 0.51% and 4.88 ± 4.45 of the mesozooplankton standing stock, respectively. S. gazellae had the highest consumption rate in all three surveys, consuming up to 800 g Dwt 1000m⁻³d⁻¹ during the study. Of the two chaetognaths, E. hamata dominated the chaetognath standing stock. The combined abundance and biomass values of E. hamata and S. gazellae ranged from 0 to 43.73 ind. m⁻³ and from 0 to 41.551 mg wwt m⁻³ respectively, during the three surveys. Inter-annual variability in the chaetognath densities was apparent. Highest abundances and biomasses tended to be associated with specific water masses, confirming the existence of a relationship between zooplankton community structure and hydrographic conditions. Generally, about 90% of the chaetognaths contained no food in their guts. S. gazellae consumed a wider variety of prey. Oil droplets occurred in the guts of ≈ 51% of E. hamata. Cannibalism was low in both species, but greater in S. gazellae than E. hamata. During the three surveys, the feeding rate values of E. hamata and S. gazellae went up to 0.48 and 2.099 prey d⁻¹ respectively. S. gazellae also had a greater predation impact on the mesozooplankton standing stock than E. hamata. The mean predation impact of the chaetognaths combined was 0.31 ± 0.291%, 0.52 ± 0.28% and 0.53 ± 0.56% of the mesozooplankton standing stock during the 2001, 2004 and 2005 surveys, respectively. During all three surveys, the majority of individuals (≈ 76%) of the chaetognaths were at stage I maturity, suggesting that during the time of study the chaetognaths were not reproducing. In both species a significant difference (log-linear analysis, p < 0.05) in maturities between the years investigated was observed. In general, there were no differences in lengths and maturities between the different water masses encountered during the surveys. The lengths of E. hamata and S. gazellae ranged from 5 to 24 mm and from 9.4 to 63.6 mm, respectively.]]> Thu 13 May 2021 08:13:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5773 Thu 13 May 2021 08:13:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5787 Thu 13 May 2021 08:05:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5832 Thu 13 May 2021 07:35:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5781 Thu 13 May 2021 07:26:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5729 Thu 13 May 2021 07:19:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5693 Thu 13 May 2021 07:16:52 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5812 Thu 13 May 2021 07:15:27 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5910 Thu 13 May 2021 07:15:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28392 Thu 13 May 2021 07:14:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5767 Thu 13 May 2021 07:13:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5874 Thu 13 May 2021 07:05:06 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5735 Thu 13 May 2021 07:03:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20500 Thu 13 May 2021 07:01:36 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5592 Thu 13 May 2021 06:59:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5696 0.05 in all cases). A key feature of the two investigations was the virtual absence of juveniles (total length < 15 mm) among the amphipod population, supporting the suggestion that they exhibit strong seasonal patterns in reproduction. Gut content analysis during both years indicated that for both the male and female amphipods’, copepods were the most prevalent prey species found in stomachs, followed by chaetognaths and pteropods. Results of electivity studies indicate that T. gaudichaudii is an opportunistic predator, generally feeding on the most abundant mesozooplankton prey. Results of in vitro incubations indicated that the total daily feeding rate of T. gaudichaudii during 2004 ranged from 11.45 to 20.90 ind. m⁻³ d⁻¹, which corresponds to between 0.12 and 1.64% of the total mesozooplankton standing stock. In 2005, the feeding rate ranged between 0.1 and 1.73% of the total mesozooplankton standing stock. The low predation impact of T. gaudichaudii during this study can be related to their low abundances and high interannual variability throughout the region of investigation.]]> Thu 13 May 2021 06:57:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5793 Thu 13 May 2021 06:54:20 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5732 Thu 13 May 2021 06:54:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5679 Thu 13 May 2021 06:52:07 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5638 Thu 13 May 2021 06:51:07 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5733 Thu 13 May 2021 06:47:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5633 Thu 13 May 2021 06:44:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5700 Thu 13 May 2021 06:42:32 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28393 70%. The results in this thesis have shown that the concentration of ethanol does not make any significant difference to the proportional change of length and width of the empty pupal casings and the third instar larvae. The recommendation is that when selecting the preservation technique, the integrity of the specimen for examination of other evidence (i.e. DNA or toxicological extraction) should take precedence. Although this thesis has not completely standardised the protocol for forensic entomotoxicology, it has indicated the areas that need to be focused on in order for standardisation to occur. Future studies should focus on standardisation, as this makes studies more comparable and ultimately makes entomotoxicological evidence admissible in the court of law.]]> Thu 13 May 2021 06:41:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5926 Thu 13 May 2021 06:33:46 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5872 Thu 13 May 2021 06:33:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5677 Thu 13 May 2021 06:30:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5807 Thu 13 May 2021 06:28:23 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5754 Thu 13 May 2021 06:27:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5920 Thu 13 May 2021 06:26:01 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5667 Thu 13 May 2021 06:25:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5794 Thu 13 May 2021 06:20:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29788 Thu 13 May 2021 06:19:43 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5723 Thu 13 May 2021 06:19:17 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5753 0.05) within species. I conclude therefore that in these three species spermatogenesis is aseasonal. No conclusions about seasonality of spermatogenesis could be made for S. coeruleoalba owing to the small sample size. Large Graafian follicles occurred in the ovaries of all four species in most months of the year. However, the presence of Graafian follicles can not be taken as an indication of timing of reproduction since they may be remnants of follicles that have not yet degenerated. In D. delphis, T. aduncus and S. coeruleoalba luteal bodies (corpora albicans or corpora lutea) occurred in most months of the year. Active corpora lutea will be present in all months, in some members of the population, since gestation is approximately 12 months. The sperm structure of D. delphis was examined by scanning electron microscopy. The sperm of D. delphis is essentially similar to that described for two other species of Cetacea (Physeter catodon and Tursiops aduncus), having an ellipsoidally shaped head and a short mid-piece with nine mitochondria. The sperm dimensions for D. delphis were head length, 4.4pm; head width, 2.0pm and mid-piece length, 2.4pm. An analysis of foetal age in D. delphis showed that the majority of the foetuses were conceived in January with birth occurring the following summer (December), suggesting that reproduction is seasonal. Neonates of T. aduncus were found throughout the year suggesting aseasonal reproduction. Foetal material was not available for S. coeruleoalba and S. chinensis. Seasonality of reproduction in the four species of dolphins studied has been discussed in relation to feeding, migration and worldwide distribution of the species.]]> Thu 13 May 2021 06:13:37 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30765 Thu 13 May 2021 06:11:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5713 Thu 13 May 2021 06:04:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5821 Thu 13 May 2021 06:04:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5632 Thu 13 May 2021 06:04:07 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5718 Thu 13 May 2021 05:56:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20726 Thu 13 May 2021 05:55:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5759 Thu 13 May 2021 05:42:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5768 500 μm) was investigated in the warm temperate, permanently open Kariega Estuary situated along the south-eastern coastline of South Africa. Spatial and seasonal patterns in the hyperbenthic community structure were assessed monthly at six stations along the length of the estuary over a period of twelve months. Data were collected using a modified hyperbenthic sledge, comprising two super-imposed nets. Physico-chemical data indicate the presence of a constant reverse salinity gradient, with highest salinities measured in the upper reaches and lowest at the mouth of the estuary. Strong seasonal patterns in temperature, dissolved oxygen and total chlorophyll-a (chl-a) concentrations were evident. Total average hyperbenthic densities ranged between 0.04 and 166 ind.m-3 in the lower net and between 0.12 and 225 ind.m-3 in the upper net. Hyperbenthic biomass values ranged between 0.02 and 11.9 mg.dry weight.m-3 in the lower net and between 0.02 and 17.4 mg.dry weight.m-3 in the upper net. A spatial and temporal pattern in total densities was detected with an increase in abundance over the period of September to October 2008 particularly in the middle reaches (Stations 3 and 4). Both the lower and upper nets were numerically dominated by decapods (mainly brachyuran crab zoeae) with the exception of June and July 2008 when mysids (mainly Mesopodopsis wooldridgei) dominated, making up 72.4 ± 58.14% of the total abundance in the lower net. A redundancy analysis (RDA) indicated that 99.2% of the variance in the hyperbenthic community structure could be explained by the first two canonical axes. Axis one, which accounted for 96.8% of the total variation detected in the ordination plot was highly correlated with sedimentary organic content and to a lesser extent the chl-a concentration within the Kariega Estuary. The correlations with the second canonical axis (2.4%) were less obvious, however, salinity and seston concentration were weakly correlated with this axis. Diel variability in the hyperbenthic community structure was assessed during March 2009. Samples were collected during the day and night (n = 6 for each period) using sampling gear described above. Total average hyperbenthic densities during the day (497.9 ± 254.1 ind.m-3) were significantly higher than night-time estimates (129.9 ± 38.5 ind.m-3; p<0.05). There were no significant differences in the average dayand night-time estimates of hyperbenthic biomass (p>0.05). A hierarchical cluster analysis identified two significantly distinct groupings, designated the day and night samples. Results from the SIMPER procedure indicated that the high densities of crab zoeae recorded during the day-time accounted for the majority of the dissimilarity between the day and night groupings (44.7%). In addition, it is apparent that several benthic species, especially from the cumacean and isopod orders, were absent from the hyperbenthos during the day-time and emerged into the water column at night.]]> Thu 13 May 2021 05:37:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5937 Thu 13 May 2021 05:33:32 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5727 Thu 13 May 2021 05:33:27 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38747 Thu 13 May 2021 05:31:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20803 Thu 13 May 2021 05:25:23 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27812 Thu 13 May 2021 05:20:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5664 Thu 13 May 2021 05:14:17 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5849 Thu 13 May 2021 04:53:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5922 Thu 13 May 2021 04:52:14 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5814 Thu 13 May 2021 04:51:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5916 2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.]]> Thu 13 May 2021 04:32:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5925 Thu 13 May 2021 04:23:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5751 Thu 13 May 2021 04:22:58 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5913 0.05). The multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, (2) and restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. E. triacantha was found to have the highest daily ingestion rate ranging from 1 226.1 to 6 029.1 ng pigm ind⁻¹d⁻¹, while the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4 to 943.0 ng pigm ind⁻¹ d⁻¹). The total grazing impact of the selected euphausiids ranged from < 0.1 to 20.1 μg pigm m⁻²d⁻¹, corresponding to < 0.15 % of the areal chl-a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggested that phytoplankton represented a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements. A cyclonic cold-core eddy spawned from the region of the APF located in the southwest Indian sector of the PFZ was the dominant feature during the 2005 survey. The total areal chl-a biomass throughout the region was low, ranging between 5.6 and 11.4 mg chl-a m⁻², and was significantly higher within the core of the eddy compared to the surrounding waters (p < 0.05). RMT-8 and WP-2 total euphausiid abundance and biomass estimates were high, and ranged from 0.004 to 0.36 ind m⁻³ and 0.065 to 1.21 mg dwt m⁻³, and from 0.01 to 18.2 ind m⁻³ and 0.01 to 15.7 mg dwt m⁻³, respectively. A distinct spatial pattern in the euphausiid community was evident with the Antarctic species, Euphausia frigida, E. triacantha and E. superba predominating within the core of the eddy, while the PFZ waters were characterized by the sub-Antarctic species, E. longirostris, Stylocheiron maximum, Nematoscelis megalops and Thysanoessa gregaria. The eddy edge acted as a transition zone where species from both regions co-occurred. Within the survey area the combined ingestion rate of the six numerically dominant euphausiid species ranged between 0.02 and 5.31 μg pigm m⁻²d¹, which corresponded to a loss of between < 0.001 and 0.11 % of the available chl-a biomass. E. triacantha and juvenile T. macura were identified as the dominant grazers. There was no apparent spatial pattern in the grazing activity of the euphausiids within the region of investigation. The average daily rations of the euphausiids examined were < 2 % of their body carbon. The low daily ration of the euphausiids could be ascribed to the predominance of small picophytoplankton in the region of investigation, which are too small to be grazed efficiently by larger zooplankton. The marked spatial patterns in species composition and the elevated abundance and biomass of euphausiids, suggest that the mesoscale eddies contribute to the spatial and temporal heterogeneity of the planktonic community of the PFZ and may represent important foraging regions for many of the apex predators within the region.]]> Thu 13 May 2021 04:21:56 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5875 Thu 13 May 2021 04:15:57 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5756 Thu 13 May 2021 04:13:04 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5643 Thu 13 May 2021 04:12:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5862 Thu 13 May 2021 04:10:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5595 Thu 13 May 2021 04:07:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5811 Thu 13 May 2021 04:06:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28391 Thu 13 May 2021 03:53:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5636 Thu 13 May 2021 03:50:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30613 Thu 13 May 2021 03:47:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5795 Thu 13 May 2021 03:42:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5583 0.05 in all cases). Numerical analyses failed to identify any effect of the sandprawn density on the macrofaunal community structure. The rate of bioturbation was, however, strongly correlated to the sand prawn density. Similarly, the microphytobenthic alga concentrations were significantly negatively correlated to the sand prawn densities ((P < 0.05). The absence of any distinct impact of the sandprawn on the macrobenthic community structure appeared to be related to their low densities in the lower reach of the estuary during the study. To better understand the role of the sandprawn as an ecosystem engineer, a caging experiment was conducted using inclusion and exclusion treatments (n= 5 for each treatment). Densities of the sandprawn in the inclusion treatments (80 ind m⁻²) were in the range of the natural densities within the estuary. The experiment was conducted over a period of 18 weeks in the lower reach of the estuary during summer. The presence of the sandprawn, C kraussi, contributed to a significant decrease in the microphytobenthic algal concentrations and the abundance and biomass of the macrofauna (P < 0.05 in all cases). The decrease in the microphytobenthic algal concentrations in the presence of the sandprawn appeared to be related to the res-suspension of the sediments (bioturbation) generated by the burrowing and feeding activities of the sandprawn. The observed decrease in macrofaunal abundances and biomass in the inclusion treatments appeared to be mediated by both the decreased food availability (mainly the microphytobenthic algae) and the burial of organisms within the sediments. Numerical analysis indicated that the sandprawn did, however, not contribute to a change in the species composition of the macrofauna. Results of the current study indicate that C.kraussi plays an important role in structuring the invertebrate community and energy flow within temporarily/open closed Kasouga Estuary.]]> Thu 13 May 2021 03:41:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5591 Thu 13 May 2021 03:41:27 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5615 Thu 13 May 2021 03:32:33 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5791 0.05). Total integrated mesozooplankton abundance and biomass during the study ranged between 3934.9 and 308521.4 ind.m-2 (mean = 47198.19; SD±62411.4 ind.m-2) and between 239.8 and 4614.3 mg Dwt.m-2 (mean = 1338.58; SD ±1060.5), respectively. Again, there were no significant spatial patterns in the total mesozooplankton abundance or biomass within the region of study (p>0.05). No significant correlations were found between biological (chlorophyll-a concentrations and zooplankton abundance) and physico-chemical variables (temperature and salinity) (p>0.05). The total mesozooplankton community was numerically dominated by copepods of the genera Pleuromamma, Calanus, Oncaea and Oithona. Other important representatives of the mesozooplankton community included the tunicate, Salpa thompsoni, and the pteropod, Limacina retroversa. At the 40% similarity level, numerical analysis identified five distinct mesozooplankton groupings within the survey area. Differences between the groupings were associated with changes in the relative contribution of numerically dominant species rather than the presence or absence of individual species. No groupings were associated with any specific feature of the front within the survey area. The feeding rates of the six most numerically abundant mesozooplankton species (Calanus simillimus, Limacina retroversa, Pleuromamma abdominalis, Clausocalanus breviceps, Oncaea conifera, Salpa thompsoni) accounting for on average 39% of the total mesozooplankton counts, were investigated using the gut fluorescence technique. For all species, the total gut pigment contents during the night time were significantly higher than the daytime values (p<0.05 for all species). The gut evacuation rates (k) for selected mesozooplankton ranged between 0.14 and 0.81 h-1. The ingestion rates ranged between 147.8 and 5495.4 ng(pigm)ind-1.day-1 which corresponded to a daily ration of between 2.4 and 10.9% body carbon. The combined grazing impact of the selected species on the daily phytoplankton standing stock was highly variable and ranged between 1.2 and 174.1% with an average of 27.3% (SD±38.78%) within the survey area. The highest grazing impact (>60%) was typically associated with those stations where the pteropod, L. retroversa, and the tunicate, S. thompsoni, contributed more than 5% of the total mesozooplankton counts. No significant differences were found in the grazing impact of any or all selected species situated either north, south or in the immediate vicinity of the front (p>0.05 in all cases). The lack of defined spatial patterns in the mesozooplankton abundance and community structure suggests that the STC did not act as a significant biogeographic barrier to the distribution of mesozooplankton during the study. It is presumed that the large scale mixing event caused by a storm prior to this study was responsible for the observed lack of elevated biological activity within the region of the STC.]]> Thu 13 May 2021 03:30:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5909 Thu 13 May 2021 03:27:52 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5692 Thu 13 May 2021 03:16:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5662 Thu 13 May 2021 03:15:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29207 Thu 13 May 2021 03:15:17 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5674 Thu 13 May 2021 03:14:48 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5908 Thu 13 May 2021 03:13:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5840 Thu 13 May 2021 03:06:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5724 Thu 13 May 2021 03:05:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5857 Thu 05 Aug 2021 14:16:22 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:39135 Sat 01 Jun 2024 16:48:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5745 Mon 30 Aug 2021 14:30:22 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28157 Mon 19 Jul 2021 10:53:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5656 Mon 12 Jun 2023 15:39:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28158 Fri 06 Aug 2021 10:26:50 SAST ]]>