Corresponding author: Renzo Perissinotto (
Academic editor: Ton de Winter
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,
Perissinotto R, Miranda NAF, Raw JL, Peer N (2014) Biodiversity census of Lake St Lucia, iSimangaliso Wetland Park (South Africa): Gastropod molluscs. ZooKeys 440: 1–43. doi:
Lake St Lucia is a large, complex estuarine lake situated on the South African east coast. It has been extensively investigated since the late 1940s, as it is the largest such system in Africa, the oldest protected estuary in the world and a Ramsar Wetland of International Importance since 1986 (
The rich biodiversity of the St Lucia estuarine lake is one of the main drivers of its special conservation status. Species are the building-blocks of any ecosystem, yet in the St Lucia case there are many misidentifications and several groups of invertebrates remain poorly investigated or completely ignored. A few detailed taxonomic studies of selected invertebrate groups have already been undertaken, starting from 2010, using a combination of traditional morphological analyses and molecular DNA barcoding. These have consistently revealed the occurrence of species that were either previously confused with others or completely unknown to science (e.g.
The class
The purpose of this study is thus to provide a comprehensive review of the diversity of gastropod molluscs in the St Lucia estuarine lake. This includes identifying species that are currently present in the system and comparing them with what was collected in past surveys. Changes in diversity over time are related to shifts in environmental and climatic conditions that have occurred during the past century. The compilation of an annotated and illustrated checklist of all gastropod species recorded so far within the system is designed to aid managers, researchers and visitors in the iSimangaliso Wetland Park with the identification of these important molluscs.
The St Lucia estuarine lake is located on the north coast of KwaZulu-Natal, between 27°52' to 28°24'S and 32°21' to 32°34'E. The system has a surface area of approximately 350 km2 (
Map of the St Lucia estuarine lake, with position of main collection sites used in the study. Adapted from
The first gastropod records from the St Lucia system date back to 1924, with specimens reposited in the KwaZulu-Natal Museum (NMSA), in Pietermaritzburg, ever since. Further collections were later undertaken during the two surveys of the University of Cape Town, in 1948–1949 and 1964–1965. Specimens collected during these surveys are currently reposited at the Iziko South African Museum (ISAM), in Cape Town. In 1982-1983, a dedicated collecting survey was undertaken throughout the lake system by the provincial conservation authority, the Natal Parks Board (NPB). The same authority, renamed Ezemvelo KwaZulu-Natal Wildlife (EKZNW), completed another similar survey during 2005, at the peak of the most recent drought. A number of publications containing gastropod records have also been published since 1954, mainly by researchers operating at the universities of KwaZulu-Natal, Zululand, Rhodes and Cape Town (e.g.
Specimens and data of gastropods collected at St Lucia in past surveys were obtained from the KwaZulu-Natal Museum in Pietermaritzburg and the Iziko South African Museum in Cape Town. Particularly rich collections from St Lucia were undertaken by the NMSA in 1987. Reference to specimens from either museum are here complemented with their accession numbers. Literature involving past macrobenthic surveys undertaken in the St Lucia Estuary (e.g.
Both NPB 1982–1983 and EKZNW 2005 collecting surveys were conducted at the onset of extreme drought conditions, when organisms within the estuarine lake were experiencing mass kills in response to hypersaline conditions and lake fragmentation/desiccation. Dead gastropods were mainly found washed up along the shorelines of St Lucia. The Natal Parks Board surveyed the banks of the whole lake from December 1982 to April 1983, collecting freshly dead specimens. These were later identified to species level by the late R.N. Kilburn. Ezemvelo KZN Wildlife surveyed the St Lucia banks in 2005, taking samples at fixed points along a number of transects in both South and North lakes (Figure
Two surveys were conducted in March and July 2012. The survey in March was conducted at Fani’s Island, St Lucia Mouth, Hell’s Gate, Makakatana, Lister’s Point, the Bridge over the Narrows and along a transect from Catalina Bay to Charter’s Creek. The Back Channel, Shark Basin and Mpate Mouth were also visited (Figure
List of localities mentioned in the study with their coordinates and key biophysical characteristics.
Region | Site name | Latitude, Longitude | Comments |
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False Bay | Lister’s Point |
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Muddy and fossiliferous coquina substrate; sparse macrophyte cover. |
Mpophomeni Stream |
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Brackish forest stream with muddy sand substrate. | |
North Lake | Hell’s Gate |
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Muddy and fossiliferous coquina substrate; sparse macrophyte cover. |
South Lake | Catalina Bay |
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Limestone flat, muddy sand substrate; freshwater seepage from dune aquifers; exhibiting sedges such as |
Charter’s Creek |
|
Muddy sand substrate; submerged macrophytes such as |
|
Fani’s Island |
|
Muddy sand substrate; historic presence of |
|
Makakatana |
|
Sandy substrate, brackish conditions and relatively low turbidity; submerged macrophytes such as |
|
Narrows | Mpate River Mouth |
|
Muddy substrate, fringed by intertidal reeds |
St Lucia Bridge |
|
Muddy substrate, fringed by mangroves |
|
St Lucia Mouth | Honeymoon Bend |
|
Tidal influence; muddy substrate, fringed by |
Mfolozi Back Channel |
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Mfolozi Link Canal |
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Mfolozi-St Lucia Beach Spillway |
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Sandy substrate; recent shallow link between St Lucia Mouth and Mfolozi River; influenced by tide. | |
Shark Basin |
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Sandy mud substrate; fringed by reeds and sedges as well as mangroves; influenced by tides and freshwater draining from adjacent areas to the north. |
The survey also included the manual collection of dead gastropod shells along the shoreline of the lake, within close proximity of the sampling stations. Further collections on an opportunistic basis were undertaken throughout 2013. In the laboratory, each sample was emptied into a sorting tray and gastropods were separated and identified with the aid of specialized literature and, where necessary, external taxonomy experts. Suitable specimens and shells were photographed in a standardized way, so as to show morphological characteristics that aid in their identification in an illustrated checklist.
A total of 20 families and 37 species of gastropods have been found in the St Lucia estuarine system since 1924, with half of the species not previously recorded in the literature. These include
Gastropod species originally recorded from the St Lucia estuarine lake. Reference codes: B:
Species (original record) | Current valid name | Record year(s) | Reference(s) |
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Idem* | 1987, Jul–Nov 2012 | NMSA (E2145), PMRP 2014 | |
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Idem* | 1988 | NPB 1988 | |
Idem* | 1924, 1987 | NMSA (B7378, D5947) | |
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Idem | Jul 2012–Nov 2013 | RMP 2013 | |
Idem | 2006, Apr–Jul 2007, Feb 2007–Mar 2011, 2010 | PP 2008, MPA 2010, MPA 2011, NMSA (W8287) | |
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Idem* | Nov 2013 | PMRP 2014 | |
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Idem* | 1967, 1987 | NMSA (8083, E2164) | |
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Idem | Jul 1948–Jul 1951, Jul 1964 & Jan 1965, 2011–2013 | NMSA (A6384), ISAM (STL60), DMB 1954, MB 1970, PMRP 2014 | |
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Idem* | 1971 | NMSA (A1635) | |
1971 | NMSA (A1636) | ||
Idem* | 1971, 1987, Mar 2012 | NMSA (A1634, D9983, E460), PMRP 2014 | |
Idem* | 1987 | NMSA (D9980) | |
Idem* | Not reported ( |
NMSA (7128) | |
Idem | Jul 1948–Jul 1951, Jul 1964 & Jan 1965, Jan–Jul 1972 & Jan 1973 | ISAM (STL50B), DMB 1954, MB 1970, B 1975 | |
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Idem* | Aug 2013 | PMRP 2014 | |
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Probably comprising both |
Jul 1948–Jul 1951, Aug 1981–Jul 1982, Oct 2005 | DMB 1954, BKJC 1983, PP 2008 | |
Jul 1964 & Jan 1965, Jan–Jul 1972 & Jan 1973 | ISAM (STL104G), MB 1970, B 1975 | ||
|
Jan & May 1992 | W 1993 | |
2007–2009 | MPA2 2011 | ||
Idem | Jan 1927, 1987, 2011-2013 | NMSA (1987), RMP 2013, WPPC 2014 | |
Jul 1948–Jul 1951, Jul 2012-May 2013 | ISAM (STL18A), DMB 1954, RMP 2013, MET 2014 | ||
Jul 1948, Jul 1964 & Jan 1965 | ISAM (STL64A), MB 1970 | ||
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Idem* | Not reported ( |
NMSA (B4786) | |
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Jul 1964 & Jan 1965 | MB 1970 | ||
Idem | Jul 1948–Jul 1951, Feb 1971, Dec 1972, Jan–Jul 1972 & Jan 1973, Dec 1981, Aut 2005 & Spr 2006 | NMSA (B5533, W1752, 9144), ISAM (STL6C), DMB 1954, B 1975, MCR 2010 | |
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Idem* | 1987 | NMSA (D5772) | |
Idem* | Jul-Nov 2012 | PMRP 2014 | |
Idem* | Jul 2013 | PMRP 2014 | |
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Jul 1972 & Jan 1973 | B 1975 | ||
Jul 1964 & Jan 1965 | MB 1970 | ||
Idem | Jul 1948–Jul 1951, Dec 1962, Apr 1963, Apr 1965, Jun 1987, 2006, 2007 | NMSA (A2362, A2228, D9971, E478), ISAM (STL6B), DMB 1954, PP 2008, MPA2 2011 | |
Aug 1981–Jul 1982 | BKJC 1983 | ||
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Jul 1948-Jul 1951 | DMB 1954 | ||
Jul 1964 & Jan 1965 | MB 1970 | ||
Idem | May 2007 | MPA2 2011 | |
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Idem | Jul 1948–Jul 1951, Jul 1964 & Jan 1965 | ISAM (STL43A), DMB 1954, MB 1970 | |
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Idem* | Nov 2012 | PMRP 2014 | |
Idem | Jul 1948, Jul 1964 & Jan 1965, May 2002–Apr 2003 | ISAM (STL104G), DMB 1954, MB 1970, PM 2013; VMT May 2002-Apr 2003 | |
Idem | May 2002-Apr 2003 | V 2004 | |
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Idem | Aug 2009, 2009–2010 | MPA1 2010, MPA2 2011 | |
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Idem* | 1982–1983 | NPB 1982-1983 | |
Idem | Aug 2009 | MPA1 2010 | |
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Idem | May 2002–Apr 2003 | V 2004 | |
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Idem | Jul 1964 & Jan 1965 | ISAM (STL237M), MB 1970, PMRP 2014 | |
Jul 1964 & Jan 1965 | ISAM (STL237Y), MB 1970 | ||
Idem* | 2012–2013 | PMRP 2014 | |
Idem | Jul 1964 & Jan 1965, Mar 2012 | ISAM (STL237N), MB 1970 |
The earliest records of gastropod specimens collected in the St Lucia system are from the KwaZulu-Natal Museum (NMSA) and date back as far as 1924. Seventeen species originating from St Lucia are currently reposited in its collections, mostly obtained during dedicated surveys conducted in 1987 (
Only 12 species were found alive within the system during the recent 2012–2013 survey. These include
Records of gastropod species collected at Lake St Lucia in relation to changes in salinity, water levels and mouth state during the period 1960-present. Dark gray bar indicates closed mouth, light gray bar indicates intermittent connection with the ocean. No continuous physico-chemical measurements are available for the period prior to 1960. Species codes: Aaf:
Of the typical estuarine species recorded in all surveys undertaken in the past in Lake St Lucia, only
Species that were not found alive during the 2012–2013 survey, but have been previously documented as dominant within the system include
Among the mangrove dwellers that were present in the past but have recently disappeared entirely from the system are all the
Typical estuarine and/or coastal marine species that are also among the new records may have entered the system only on sporadic occasions and/or for short periods of time under open mouth conditions. They include
Major climatic events and hydrodynamic processes control the gastropod species richness and abundance in the St Lucia estuarine lake (Figure
During the last decade, St Lucia has undergone some of the most dramatic shifts ever recorded in the region. These have caused an unprecedented crisis and triggered a burst of fresh research activity on the system. It is thus not surprising that of the total 37 species of gastropod recorded within the estuarine lake, 19 are new records arising from the recent escalation in analyses and collecting efforts. During the latest dedicated gastropod survey, undertaken between Jan 2012 and Nov 2013, a total of 15 species were recorded, with only 12 found still alive and four in reasonable abundance, even if intermittently. Among the latter group, two are actually alien invasive species, i.e.
In 2002, a sand berm closed off the St Lucia Estuary from the ocean, leading to a prolonged period of mouth closure, which still persists currently. The mouth was breached from the seaward side for a brief period of six months, between March and August 2007, by a combination of extreme events linked to Cyclone Gamede (
Since the end of 2011, the system has entered a wet phase, with above average rainfall leading to occasional flooding and the prevalence of oligo- to polyhaline conditions throughout the extent of the system. This was compounded by the excavation of a beach spillway in July 2012, which has since contributed substantial freshwater inflow from the Mfolozi River into the St Lucia system and also partial exchange of water with the open ocean (
Historical collections and surveys have, however, recorded numerous species of euryhaline marine and estuarine species, even in the uppermost reaches of the estuarine lake. For instance, the tick shell
Apart from causing the disappearance of marine grasses, prolonged mouth closure would also lead to the eventual death of barnacle and oyster beds (
Among the 20 species not previously recorded from the St Lucia estuarine lake are typical mangrove dwellers, such as
Population explosions of the bubble shell
The taxonomy of assimineids, or sentinel snails, is poorly understood and currently under revision in South Africa. In the St Lucia Estuary, there are inconsistencies in the literature in terms of what species of
Three of the five predominant alien invasive freshwater gastropods in South Africa have been recently recorded from St Lucia:
As the freshwater-dominated phase of St Lucia continues, the potential for alien invasive gastropods to enter and spread within the system increases. The consequences of these expansions vary depending on the species.
In addition to the threats from freshwater alien invasive species, estuaries are also threatened by the invasion of marine species from coastal sources (
Throughout its history, the St Lucia estuarine lake has experienced drastic shifts in hydrological states, from extreme dry conditions accompanied by hypersalinity and desiccation, to floods followed by freshwater dominance. The state of the mouth has also varied from an extended open bay joined to the Mfolozi River to extreme constriction and prolonged closure. The latest period of closure has been unprecedented and virtually uninterrupted since 2002. Although the monitoring of gastropod diversity within the system has been erratic until recently, there are clear indications that higher diversity has coincided with periods when the estuarine lake was under tidal influence, with a normal salinity gradient decreasing from the estuary basin to the northern lakes (e.g. 1964–1965). Drastic declines were observed when the system experienced hypersaline (e.g. 1948–1951) or flood conditions (e.g. 1987), with a closed mouth state compounding the problem by preventing any recruitment from the ocean. During the last decade, St Lucia has undergone some of the most dramatic shifts ever recorded in the region. Despite the intense, dedicated gastropod surveys undertaken in 2012-2013, only 12 species were found still alive, with four in reasonable abundance. Among these, unfortunately two are actually alien invasive species, i.e.
We thank the iSimangaliso Park Authority and Ezemvelo KZN Wildlife for providing permits and logistical support for this project. Special thanks go to Mthobisi S. Ngubane, Ricky H. Taylor and Lynette Clennell for contributing with field collections and laboratory analyses. Elizabeth Hoenson (ISAM, Cape Town), Dai Herbert (NMSA, Pietermaritzburg) and Winston Ponder (Australian Museum, Sydney) are thanked for assisting with specimen identifications and access to museum records. We are also grateful to Frank Wesselingh and an anonymous reviewer for their valuable comments on the draft manuscript. This work is based on the research supported by the South African Research Chairs Initiative of the Department of Science and Technology (DST) and National Research Foundation (NRF) of South Africa. Any opinion, finding and conclusion or recommendation expressed in this material is that of the author(s) and the NRF does not accept any liability in this regard.
Note: The number in square brackets at the end of a reference corresponds to the in-text citations used in the
Annotated and Illustrated Checklist of the Gastropod Molluscs of Lake St Lucia
17 mm, Inhaca Island, Jul 1970
RN Kilburn leg.
19 mm, Mhlanga Estuary, Feb 2013
NAF Miranda leg.
23 mm, St Lucia False Bay, Oct 1924
HWB Marley leg.
23 mm, St Lucia False Bay, Feb 2013
NAF Miranda leg.
14 mm, St Lucia Mouth, Feb 2013
NAF Miranda leg.
21 mm, St Lucia Catalina Bay, Feb 2010
NAF Miranda leg.
30.5 mm, St Lucia False Bay, Mar 2012
R Perissinotto leg.
9.3 mm, St Lucia Charter’s Creek,1967
R Kilburn leg.
36 mm, St Lucia Bridge, Nov 2012
NAF Miranda leg.
7.8 mm, Zululand, Sep 1971
R Kilburn leg.
14 mm, St Lucia Estuary, Nov 1971
R Kilburn leg.
13 mm, St Lucia River Estuary, Nov 1971
RN Kilburn leg.
15 mm, St Lucia Estuary, Aug 1987
RH Taylor leg.
18 mm, Lake St Lucia
Burnup Collection.
14 mm, Kosi Bay Estuary, July 1987
DG Herbert leg.
34 mm, Mfolozi Channel, Aug 2013
NK Carrasco leg.
0.8 mm, St Lucia False Bay, Jul 2012
NAF Miranda leg.
2 mm, St Lucia Catalina Bay, Nov 2012
NAF Miranda leg.
55 mm, St Lucia Bay, 1978
M Lavoipierre leg.
11 mm, St Lucia Charter’s Creek, Mar 2012
NAF Miranda leg.
25 mm, Mission Rocks, Apr 1987
R Kilburn leg.
71 mm, Durban, Aug 1968
BJ Young leg.
52 mm, St Lucia False Bay, Jul 2013
NAF Miranda leg.
18 mm, St Lucia Charter’s Creek, Apr 1963
AC van Bruggen leg.
11 mm, St Lucia Catalina Bay, May 2007
L Clennell leg.
175 mm, Salt Rock, Aug 2009
DG Herbert leg.
53 mm, St Lucia Estuary, Apr 2007
C Fox leg.
30 mm, Durban Bay, Sep 1972
BJ Young leg.
14 mm, St Lucia Catalina Bay, Nov 2012
JL Raw leg.
16 mm, Durban, Mar 2002
D Nadasan leg.
8.1 mm, Uvongo, Mar 1996
M Coke leg.
12 mm, St Lucia Catalina Bay, Feb 2010
NAF Miranda leg.
12 mm, St Lucia Catalina Bay, Nov 2012
NAF Miranda leg.
11 mm, St Lucia Catalina Bay, Jul 2009
NAF Miranda leg.
8.8 mm, Mhlanga Lagoon, Dec 1995
D Herbert & L Davis leg.
12 mm, St Lucia Mouth, Mar 2012
N Peer leg.
18 mm, St Lucia Mission Rocks, Apr 1988
D Brink leg.
10 mm, St Lucia Mouth, Mar 2013
SM Ngubane leg.
12 mm, St Lucia Mouth, Mar 2013
SM Ngubane leg.