A reef-associated zooplankton community was monitored at weekly intervals for 53 weeks. Samples were collected from quadrats of dense coral cover using emergence net traps. The numerical and biomass fluctuations of 15 taxonomic groups, 7 size classes and 5 feeding groups of the community were determined both temporally and spatially. The community was composed of abundant and diverse taxa (81) with cyclopoid copepods being the most important taxon. Larger-sized fauna (e.g. amphipods, decapods, mysids, etc.) were the second most important abundance and biomass contributors. Size class analysis illustrated a bimodal size distribution spectrum. The well developed second mode of the spectrum was attributed to substratum characteristics which permitted an enhanced macrofaunal/detritivore presence. Although week to week fluctuations of the abundance/biomass data were marked, diversity indices indicated a persistent and resilient community. The nocturnal vertical migrations of the fauna did not show a persistent pattern with the varying phases of 12 sequentially monitored lunar cycles. Substratum heterogeneity was primarily responsible for the spatial distribution pattern of the fauna. Although the data variance suggested stochasticity, time-series procedures determined that cross-correlations between the numerical abundances of taxa, size classes and feeding groups occurred without a lead or lag. Similar analyses identified chlorophyll a as the important environmental variable and also as a leading indicator of particular taxonomic, size and feeding group abundances. It was concluded that reef-associated zooplankton communities are abundant, diverse assemblages structured by periodicities which in combination act to form important links between tropical, inshore benthic and pelagic ecosystems.

The St. Lucia Estuary, Africa’s largest estuarine lake, is currently experiencing an unprecedented crisis related to freshwater deprivation. This has resulted in a reversed salinity gradient and drastically reduced water levels. These harsh environmental conditions, combined with the limited connection with the open ocean have lead to a loss of biodiversity in the system. The dominant zooplankton taxa include the copepods Pseudodiaptomus stuhlmanni and Acartia natalensis and the mysid Mesopodopsis africana. In March 2007, the closed-mouth state was briefly interrupted by an open-mouth phase, induced by a unique combination of extreme climatic events. With the incoming seawater, previously excluded marine taxa re-entered the system, increasing its diversity significantly. Salinity and temperature have been referred to as driving forces in aquatic ecosystems. The tolerance limits of the key mysid species were, therefore, investigated. Results showed that M. africana has some of the highest recorded upper salinity and temperature tolerances for a mysid. Because of their high biomass, mysids have the potential to affect microalgal standing stocks. Their grazing dynamics (in relation to autotrophic food availability) were investigated in two contrasting environments within the estuary. Ingestion rates and subsequently population grazing impacts on the total microalgal standing stocks were higher at the Mouth than at Charters Creek. This was attributed to the harsh environmental conditions in the latter region. Despite the lower ingestion rates exhibited here, these mysids seem capable of meeting their energetic requirements from a microalgal diet alone. Stable isotope data, though, show that they also utilise a heterotrophic diet. Results of the mixed model SIAR v 4 revealed the contribution of the different carbon sources to the diet of M. africana. Most unique was this mysid’s ability to modify its diet on both short temporal and spatial scales. Resource utilization between the dominant taxa was also compared. All three taxa appear to be opportunistic feeders, capable of incorporating a number of food items in their diet. Between food partitioning, predator avoidance strategies, and their common ability to survive in highly dynamic environments, these species are capable of co-existing, and together contribute to the overall resilience so far shown by the system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

This thesis investigates the relationships between mercury (Hg) and stable isotope of carbon (δ13C) in marine pelagic zooplankton (Calanus spp., Themisto spp. and Euchaeta spp.) with water mass characteristics in the North Water Polynya (NOW) and in the Mackenzie shelf – Amundsen Gulf area. Two ship based sampling field expeditions were carried out in late summer of 2005 and 2006 in both regions on board the CCGS Amundsen. In the North Water (NOW) polynya, higher levels of water Hg, depleted δ18O, lower salinity and lower nitrate levels were measured at sampling locations near the Prince of Wales glacier (POW) on the eastern coast of Ellesmere Island in the Smith Sound area. These results suggest that the glacier may be a source of Hg to this region which, in turn, is responsible for the correspondingly high concentrations of THg and MMHg measured in Calanus spp. and Euchaeta spp. at the same locations. The Mackenzie shelf – Amundsen Gulf region was characterized by fresher surface water properties (low salinity and depleted δ18O) in the western part and was strongly linked to the influence of the Mackenzie River. Higher THg concentrations in zooplankton were associated with larger fractions of both meteoric water and sea-ice melt. These findings suggest that in the western Arctic, inorganic Hg uptake in zooplankton via-absorption near surface water was highly driven by freshwater inputs into the system. Based on the analysis of three main genus Calanus spp. (mostly adult females Calanus hyperboreus), Euchaeta spp. and Themisto spp. (mostly adult Themisto libellula), THg and MMHg concentrations were the highest in the carnivorous copepod Euchaeta spp. in the North Water polynya followed by the omnivorous hyperiid amphipod Themisto spp. The herbivorous copepod Calanus spp. had both the lowest THg and MMHg concentrations in the Eastern and the Western Arctic. In addition, the Western Arctic is the area in which each zooplankton genus had the most depleted carbon and the most enriched nitrogen. The highest concentrations of THg in Calanus spp., Euchaeta spp. and Themisto spp. were measured in the Western Arctic as well as the highest MMHg in Calanus spp. and Themisto spp. The highest %MMHg was calculated in the Archipelago for Themisto spp., in the Eastern Arctic for Euchaeta spp. and in the Western Arctic for Calanus spp. The relationships observed between THg, MMHg, %MMHg and δ13C in all three major zooplankton taxa and water mass properties were in agreement with what have been previously described in the literature. Our findings suggested that both Hg and δ13C can be used as tracers to help understand zooplankton vertical distribution, feeding ecology and ultimately to predict climate changes impact at lower trophic level in the pelagic food web. The implications for marine mammals foraging in these regions are also discussed.

Mercury (Hg) is one of the primary contaminants of concern in the Arctic marine ecosystem. Methyl Hg (MeHg) is known to biomagnify in food webs. During the International Polar Year - Circumpolar Flaw Lead study, sea ice, seawater, bottom ice algae, phytoplankton and the herbivorous copepods were collected from the Amundsen Gulf to test whether ice algae and phytoplankton assimilate Hg from their habitat, and whether Hg bioaccumulates from the seawater to the primary consumers. Sea ice algae were found to accumulate Hg primarily from the bulk bottom ice, and the sea ice algae bloom depleted Hg stored within the bottom section of the ice. Furthermore, biodilution of Hg was observed to occur in sea ice algae. Higher concentrations of Hg were also found in phytoplankton and in grazing copepods. A positive correlation between MeHg and trophic level suggests the occurrence of MeHg biomagnification even at these low trophic positions.

This thesis investigates the relationships between mercury (Hg) and stable isotope of carbon (δ13C) in marine pelagic zooplankton (Calanus spp., Themisto spp. and Euchaeta spp.) with water mass characteristics in the North Water Polynya (NOW) and in the Mackenzie shelf – Amundsen Gulf area. Two ship based sampling field expeditions were carried out in late summer of 2005 and 2006 in both regions on board the CCGS Amundsen. In the North Water (NOW) polynya, higher levels of water Hg, depleted δ18O, lower salinity and lower nitrate levels were measured at sampling locations near the Prince of Wales glacier (POW) on the eastern coast of Ellesmere Island in the Smith Sound area. These results suggest that the glacier may be a source of Hg to this region which, in turn, is responsible for the correspondingly high concentrations of THg and MMHg measured in Calanus spp. and Euchaeta spp. at the same locations. The Mackenzie shelf – Amundsen Gulf region was characterized by fresher surface water properties (low salinity and depleted δ18O) in the western part and was strongly linked to the influence of the Mackenzie River. Higher THg concentrations in zooplankton were associated with larger fractions of both meteoric water and sea-ice melt. These findings suggest that in the western Arctic, inorganic Hg uptake in zooplankton via-absorption near surface water was highly driven by freshwater inputs into the system. Based on the analysis of three main genus Calanus spp. (mostly adult females Calanus hyperboreus), Euchaeta spp. and Themisto spp. (mostly adult Themisto libellula), THg and MMHg concentrations were the highest in the carnivorous copepod Euchaeta spp. in the North Water polynya followed by the omnivorous hyperiid amphipod Themisto spp. The herbivorous copepod Calanus spp. had both the lowest THg and MMHg concentrations in the Eastern and the Western Arctic. In addition, the Western Arctic is the area in which each zooplankton genus had the most depleted carbon and the most enriched nitrogen. The highest concentrations of THg in Calanus spp., Euchaeta spp. and Themisto spp. were measured in the Western Arctic as well as the highest MMHg in Calanus spp. and Themisto spp. The highest %MMHg was calculated in the Archipelago for Themisto spp., in the Eastern Arctic for Euchaeta spp. and in the Western Arctic for Calanus spp. The relationships observed between THg, MMHg, %MMHg and δ13C in all three major zooplankton taxa and water mass properties were in agreement with what have been previously described in the literature. Our findings suggested that both Hg and δ13C can be used as tracers to help understand zooplankton vertical distribution, feeding ecology and ultimately to predict climate changes impact at lower trophic level in the pelagic food web. The implications for marine mammals foraging in these regions are also discussed.

Mercury (Hg) is one of the primary contaminants of concern in the Arctic marine ecosystem. Methyl Hg (MeHg) is known to biomagnify in food webs. During the International Polar Year - Circumpolar Flaw Lead study, sea ice, seawater, bottom ice algae, phytoplankton and the herbivorous copepods were collected from the Amundsen Gulf to test whether ice algae and phytoplankton assimilate Hg from their habitat, and whether Hg bioaccumulates from the seawater to the primary consumers. Sea ice algae were found to accumulate Hg primarily from the bulk bottom ice, and the sea ice algae bloom depleted Hg stored within the bottom section of the ice. Furthermore, biodilution of Hg was observed to occur in sea ice algae. Higher concentrations of Hg were also found in phytoplankton and in grazing copepods. A positive correlation between MeHg and trophic level suggests the occurrence of MeHg biomagnification even at these low trophic positions.

No description available.

Several lines of evidence suggest small alpine lakes and ponds are sensitive to nitrogen deposition. Paleolimnological studies, nutrient bioassays, and mesocosm experiments show the positive effects of nitrogen on aquatic alpine primary producers. In particular, alpine pond ecosystems have been inferred to be nitrogen-limited based on low availability of dissolved inorganic nitrogen relative to total phosphorus. However, nitrogen-limitation of alpine ponds has never been tested at the whole-ecosystem level. I performed a replicated in situ whole-pond experiment, consisting of two crossed treatments (2 nitrogen x 2 phosphorus levels) applied across 16 natural alpine ponds (n = 4) immediately following ice-out in 2008. Surprisingly, neither nutrient amendment stimulated phytoplankton or zooplankton abundance although subtle shifts in community composition were detected over a two-month period. Intensive grazing pressure exerted by high densities (> 100 individuals/ m2) of herbivorous Branchinecta paludosa (fairy shrimp) may have suppressed planktonic responses to nutrient additions. Another ecological explanation for the lack of a positive effect of nutrients on phytoplankton abundance was competition from periphyton, which are comparatively more abundant in most shallow ponds on an areal basis. Therefore, density-dependent ecological interactions (competition and predation) may mediate the responses of phytoplankton to nitrogen deposition over ponds situated in extreme environments. / Ecology

Thesis (Ph. D.)--Woods Hole Oceanographic Institution, 1977. / "October 1978." "Technical report." WHOI-78-59. "AD-A060 220." Includes bibliographical references (p. 201-220).

Diss. (sammanfattning) Uppsala : Univ., 2007. / Härtill 5 uppsatser. Med svensk sammanfattning.