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Biodiversity census of Lake St Lucia, iSimangaliso Wetland Park (South Africa): Gastropod molluscs.

Perissinotto R, Miranda NA, Raw JL, Peer N - Zookeys (2014)

Bottom Line: As a result, only 10 indigenous and two alien aquatic gastropod species are currently found living in the St Lucia estuarine lake.The tick shell, Nassarius kraussianus, which was consistently found in large abundance prior to the recent dry phase, appears to have temporarily disappeared from the system, probably as a result of the extinction of Zostera marine grasses inside the lake.These include the invasive thiarid Tarebia granifera, which can be found in concentrations exceeding 5000 ind.m(-2), the lymnaeid Pseudosuccinea columella and the physid Aplexa marmorata.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST/NRF Research Chair in Shallow Water Ecosystems, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 South Africa ; School of Life Sciences, University of KwaZulu-Natal, P Bag X54001, Durban 4001 South Africa.

ABSTRACT
The recent dry phase experienced by the St Lucia estuarine system has led to unprecedented desiccation and hypersaline conditions through most of its surface area. This has changed only recently, at the end of 2011, with the onset of a new wet phase that has already caused a major shift to oligo- and mesohaline conditions. The estuary mouth, however, remains closed to the ocean, making the weak connection recently established between the St Lucia and the Mfolozi estuaries the only conveyance for marine recruitment. As a result, only 10 indigenous and two alien aquatic gastropod species are currently found living in the St Lucia estuarine lake. This is out of a total of 37 species recorded within the system since the earliest survey undertaken in 1924, half of which have not been reported in the literature before. The tick shell, Nassarius kraussianus, which was consistently found in large abundance prior to the recent dry phase, appears to have temporarily disappeared from the system, probably as a result of the extinction of Zostera marine grasses inside the lake. Population explosions of the bubble shell Haminoea natalensis, with its distinct egg masses, were recorded seasonally until 2009, but the species has subsequently not been observed again. A molecular DNA analysis of the various populations previously reported as belonging to the same assimineid species, variably referred to as Assiminea capensis, A. ovata, or A. bifasciata, has revealed that the St Lucia assemblage actually comprises two very distinct taxa, A. cf. capensis and a species provisionally referred to here as "A." aff. capensis or simply Assimineidae sp. In the mangroves, the climbing whelk Cerithidea decollata is still found in numbers, while ellobiids such as Cassidula labrella, Melampus semiaratus and M. parvulus are present in low abundances and all previously recorded littorinids have disappeared. A number of alien freshwater species have colonized areas of the system that have remained under low salinity. These include the invasive thiarid Tarebia granifera, which can be found in concentrations exceeding 5000 ind.m(-2), the lymnaeid Pseudosuccinea columella and the physid Aplexa marmorata.

No MeSH data available.


Haminoea natalensis: Aggregation of egg masses spawned during September 2006 in the shallows of Catalina Bay, on the Eastern Shores of South Lake (Photo: Lynette Clennell).
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Figure 4: Haminoea natalensis: Aggregation of egg masses spawned during September 2006 in the shallows of Catalina Bay, on the Eastern Shores of South Lake (Photo: Lynette Clennell).

Mentions: Species that were not found alive during the 2012–2013 survey, but have been previously documented as dominant within the system include Nassarius kraussianus and Haminoea natalensis. Both were only recorded as dead shells during 2012-2013, but in very large numbers and throughout the lake basins, particularly at Charter’s Creek, Catalina Bay and Fani’s Island (South Lake) (Figure 1, Table 1). While the last live record of Nassarius kraussianus during the recent closed mouth phase of the estuary dates back to the spring of 2006 (MacKay et al. 2010), Haminoea natalensis was found alive in large abundance at least until 2011. In the South Lake, at Charter’s Creek and Catalina Bay dense aggregations of freshly-spawned egg masses were observed in the spring of 2006 (Figure 4).


Biodiversity census of Lake St Lucia, iSimangaliso Wetland Park (South Africa): Gastropod molluscs.

Perissinotto R, Miranda NA, Raw JL, Peer N - Zookeys (2014)

Haminoea natalensis: Aggregation of egg masses spawned during September 2006 in the shallows of Catalina Bay, on the Eastern Shores of South Lake (Photo: Lynette Clennell).
© Copyright Policy - creative-commons-attribution
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196252&req=5

Figure 4: Haminoea natalensis: Aggregation of egg masses spawned during September 2006 in the shallows of Catalina Bay, on the Eastern Shores of South Lake (Photo: Lynette Clennell).
Mentions: Species that were not found alive during the 2012–2013 survey, but have been previously documented as dominant within the system include Nassarius kraussianus and Haminoea natalensis. Both were only recorded as dead shells during 2012-2013, but in very large numbers and throughout the lake basins, particularly at Charter’s Creek, Catalina Bay and Fani’s Island (South Lake) (Figure 1, Table 1). While the last live record of Nassarius kraussianus during the recent closed mouth phase of the estuary dates back to the spring of 2006 (MacKay et al. 2010), Haminoea natalensis was found alive in large abundance at least until 2011. In the South Lake, at Charter’s Creek and Catalina Bay dense aggregations of freshly-spawned egg masses were observed in the spring of 2006 (Figure 4).

Bottom Line: As a result, only 10 indigenous and two alien aquatic gastropod species are currently found living in the St Lucia estuarine lake.The tick shell, Nassarius kraussianus, which was consistently found in large abundance prior to the recent dry phase, appears to have temporarily disappeared from the system, probably as a result of the extinction of Zostera marine grasses inside the lake.These include the invasive thiarid Tarebia granifera, which can be found in concentrations exceeding 5000 ind.m(-2), the lymnaeid Pseudosuccinea columella and the physid Aplexa marmorata.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST/NRF Research Chair in Shallow Water Ecosystems, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 South Africa ; School of Life Sciences, University of KwaZulu-Natal, P Bag X54001, Durban 4001 South Africa.

ABSTRACT
The recent dry phase experienced by the St Lucia estuarine system has led to unprecedented desiccation and hypersaline conditions through most of its surface area. This has changed only recently, at the end of 2011, with the onset of a new wet phase that has already caused a major shift to oligo- and mesohaline conditions. The estuary mouth, however, remains closed to the ocean, making the weak connection recently established between the St Lucia and the Mfolozi estuaries the only conveyance for marine recruitment. As a result, only 10 indigenous and two alien aquatic gastropod species are currently found living in the St Lucia estuarine lake. This is out of a total of 37 species recorded within the system since the earliest survey undertaken in 1924, half of which have not been reported in the literature before. The tick shell, Nassarius kraussianus, which was consistently found in large abundance prior to the recent dry phase, appears to have temporarily disappeared from the system, probably as a result of the extinction of Zostera marine grasses inside the lake. Population explosions of the bubble shell Haminoea natalensis, with its distinct egg masses, were recorded seasonally until 2009, but the species has subsequently not been observed again. A molecular DNA analysis of the various populations previously reported as belonging to the same assimineid species, variably referred to as Assiminea capensis, A. ovata, or A. bifasciata, has revealed that the St Lucia assemblage actually comprises two very distinct taxa, A. cf. capensis and a species provisionally referred to here as "A." aff. capensis or simply Assimineidae sp. In the mangroves, the climbing whelk Cerithidea decollata is still found in numbers, while ellobiids such as Cassidula labrella, Melampus semiaratus and M. parvulus are present in low abundances and all previously recorded littorinids have disappeared. A number of alien freshwater species have colonized areas of the system that have remained under low salinity. These include the invasive thiarid Tarebia granifera, which can be found in concentrations exceeding 5000 ind.m(-2), the lymnaeid Pseudosuccinea columella and the physid Aplexa marmorata.

No MeSH data available.