https://commons.ru.ac.za/vital/access/manager/Index en-us 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:4602 Wed 12 May 2021 23:23:51 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5492 Wed 12 May 2021 23:08:31 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3772 Wed 12 May 2021 23:00:32 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4618 Wed 12 May 2021 22:41:17 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5685 l5mm) were calculated as real densities from randomly placed quads i.e. not from areas of 100% cover. Density decreased up the shore; low, mid and high shore zones were significantly different from each other (ANOVA , p<0.0001; followed by multiple range tests). There was no significant difference between the densities of mussels at exposed and sheltered sites within each zone (ANOVA, p=0.7155). Recruit ( Wed 12 May 2021 19:52:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3982 Wed 12 May 2021 19:21:42 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4971 Wed 12 May 2021 18:50:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5741 15 mm) were positively correlated with recruit densities (1-5 mm) for both shore types (p15 mm) was significantly lower on exposed (mean of 3 348.m⁻²) than on sheltered shores (mean of 4 796.m⁻²) (pO.05). The effect of exposure on growth rate formed the focal point of this study and was determined using three different approaches. The first technique, mark-recapture, involved filing notches on the growing edges of mussels in the field. After 111 days, mussels were removed and the growth measured. The second approach used internal growth bands to measure growth rates, once the periodicity with which these bands were laid down was established. Thirdly, using Shepherd's length composition analysis (SLCA), growth rates were determined from length frequency distributions in 11 samples taken over 15 months. The general conclusion from all three approaches was that growth rate was twice as fast on the exposed shores as on the sheltered shores (p Wed 12 May 2021 18:40:51 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5033 Wed 12 May 2021 18:37:21 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1135 Wed 12 May 2021 18:31:20 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5248 Wed 12 May 2021 17:37:02 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3901 Wed 12 May 2021 17:35:49 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4651 Wed 12 May 2021 16:19:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3988 Wed 12 May 2021 15:56:54 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4000 Wed 12 May 2021 15:46:37 SAST ]]> https://commons.ru.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://commons.ru.ac.za/vital/access/manager/Repository/vital:4069 Thu 13 May 2021 07:10:21 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4605 Thu 13 May 2021 06:30:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4832 Thu 13 May 2021 06:26:21 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3998 Thu 13 May 2021 06:13:01 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3904 Thu 13 May 2021 05:05:44 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3994 Thu 13 May 2021 04:50:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5322 Thu 13 May 2021 04:37:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4619 Thu 13 May 2021 01:45:34 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4311 Thu 13 May 2021 00:40:08 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3003 Thu 13 May 2021 00:09:23 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2969 Thu 13 May 2021 00:06:32 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5270 Sun 16 Jun 2024 07:30:41 SAST ]]>