Causes of rarity and range restriction of an endangered, endemic limpet, Siphonaria compressa

Angel, Andrea; Branch, George M.; Wanless, Ross M.; Siebert, Timony

doi:10.1016/j.jembe.2005.12.031

Cited by 32 publications

(42 citation statements)

References 47 publications

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“…But bait collection is one potential impact that has received considerable attention (Wynberg and Branch, 1997;Hodgson et al, 2000;Napier et al, 2009), and it is thought to have a marked effect on the soft-sediment fauna of the other large saltmarsh and seagrass system in the Western Cape, Langebaan Lagoon, in which the polychaetes Aquilaspio sexoculata and Pseudopolydora antennata are attracted to sites disturbed by bait collection, while Scoloplos and Notomastus avoid them (Simon (2000), cited in Hanekom et al (2009); A. sexoculata under the generic name Prionospio and P. antennata under the generic name Polydora). Langebaan shows many close faunal similarities to Knysna and might be considered to function ecologically in a similar manner; they are the only known localities of the endangered and endemic false limpet Siphonaria compressa that lives on Nanozostera leaves (Allanson and Herbert, 2005;Angel et al, 2006), for example, and they are the only known sites where the starfish Parvulastra exigua occurs in abundance on a sandflat with eelgrass (Pillay et al, 2010b;and this study). At Knysna, Aquilaspio sexoculata was the fifth most widespread species, occurring in 57% of the core samples, and its abundance pattern was very strongly correlated with that of Pseudopolydora cf antennata (Spearman r s 5 0.37; Po0.0001), the two comprising almost 6% of the total individuals, while Scoloplos and Notomastus were rare, being found in only eight cores (o3.5%) and a single core, respectively.…”

Section: Discussionmentioning

confidence: 80%

Spatial variation in abundance and diversity of the smaller surface and near‐surface eelgrass‐associated intertidal macrobenthos within a warm‐temperate estuarine bay in the Garden Route National Park, RSA

Barnes

2010

Aquatic Conservation

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ABSTRACT1. Smaller members (o10 mm) of the sediment-surface macrobenthos of Nanozostera capensis meadows across 9 km 2 of the marine Outer Basin of the Knysna estuarine bay (Garden Route National Park, Western Cape, South Africa) were investigated at a series of 24 stations.2. Ordination (nMDS) disclosed the existence of five clusters of stations related to degree of exposure. Relatively sheltered stations were dominated by two endemic species of deposit-feeding microgastropod, and they supported significantly higher macrobenthic densities but lower species diversity and less evenness than relatively exposed stations. The latter were dominated by polychaetes and also possessed more suspension feeders, equivalent to more open seagrass beds in other latitudes. Species richness per station, however, was relatively constant across the whole basin.3. The smaller benthic macrofauna, totalling 82 species, was found to include several animals (o5 mm) hitherto unknown from the region, including one gastropod genus (Cornirostra) not previously known from Africa.4. Species were patchily distributed across all scales from 1 m to 41 km, but variance partitioning showed components of total variance to decrease with increasing spatial scale: sample (46.5%), station (30.0%), site (23.5%).5. These findings are discussed in relation to conservation site selection in rich but faunistically heterogeneous seagrass beds that are impacted by bait collection or other human disturbance.

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Section: Discussionmentioning

confidence: 80%

Spatial variation in abundance and diversity of the smaller surface and near‐surface eelgrass‐associated intertidal macrobenthos within a warm‐temperate estuarine bay in the Garden Route National Park, RSA

Barnes

2010

Aquatic Conservation

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“…Observations made in the tidal Langebaan Lagoon (Angel et al, 2006) and the Knysna estuary (this study) point to a resilience that allows recovery from infrequent, often severe, episodes of biological stress: floods, high Downloaded by [North West University] at 19:30 20 December 2014 water temperatures and habitat loss. High summer in the Knysna estuary, when water temperatures in the shallows at low water spring tide (LWST) reach 33-36°C, is often associated with 'browning' of eelgrass leaves (habitat loss) over wide shallow areas (Allanson, personal observation).…”

Section: Introductionmentioning

confidence: 69%

Reproduction and growth of the endangered siphonariid limpetSiphonaria compressa(Pulmonata: Basommatophora)

Allanson¹,

Msizi²

2010

Invertebrate Reproduction & Development

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The critically endangered pulmonate marine mollusc, Siphonaria compressa, is the smallest of the Siphonariidae (4-4.5 mm shell length) and lives only on eelgrass leaves near low water of spring tide in the Knysna estuary and Langebaan Lagoon, South Africa. The species exhibits indeterminate growth. Mating has been observed between adult individuals but exchange of spermatophores has to be confirmed. The limpet has a relatively short life cycle and releases completely metamorphosed juveniles from a protective spawn packet after 13 days at 25ºC and 18 days at 17ºC incubation. An attempt is made to assess generation time using growth in laboratory held individuals matched to the von Bertalanaffy growth function, and supported by sampling and analysis of natural populations during spring and summer. A measure of support has been found for the laboratory growth model. Early attempts are made to suggest reasons for, and the possible evolution of, the miniaturization shown by S. compressa.

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“…Between 1977 and 1980, however, densities of P. exigua rose almost 200-fold, and followed immediately after a period of dredging and blasting to establish a harbour in the adjacent Saldanha Bay in 1976. This increased siltation in the lagoon and was associated with a collapse in eelgrass beds (Angel et al 2006). With the decay of these beds, with which P. exigua is strongly associated (Fig.…”

Section: Discussionmentioning

confidence: 94%

Unexpected effects of starfish grazing on sandflat communities following an outbreak

Pillay

Branch²,

Steyn³

2010

Mar. Ecol. Prog. Ser.

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Starfish are significant determinants of community structure in marine ecosystems. The starfish Parvulastra (Patiriella) exigua is normally found on intertidal rocky shores. We examined a major outbreak of this species in Langebaan Lagoon, a marine embayment on the west coast of South Africa, and the only known soft-sediment ecosystem where P. exigua flourishes. We document this outbreak and describe subsequent field caging experiments testing the influence of this starfish on soft-sediment community structure. Grazing by P. exigua resulted in a reduction in microalgal biomass that was linearly related to starfish density, but it promoted bacterial density. Macrofaunal communities at intermediate densities of P. exigua were different and more diverse to those at high and low starfish densities, with Shannon-Wiener and Fischer's α indices peaking at intermediate density of P. exigua. It is possible that P. exigua at intermediate densities promotes co-existence of macrofauna by reducing the competitive edge held by dominant species. However, this effect may also be due to the balance between (1) negative effects of microalgal depletion and incidental grazing on invertebrate recruits at high densities of P. exigua, and (2) enhancement of bacteria by P. exigua leading to increased biofilm coverage on the sediment, which promotes macrofaunal recruit diversity in soft sediments. We suggest a need for caution when citing results from marine soft sediments as evidence for the intermediate disturbance hypothesis without knowledge of the promotive and inhibitory effects of the target organism.KEY WORDS: Population outbreak · Disturbance · Recruitment · Biofilms · Macrofauna · Promotive effects · Inhibitory effects Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 398: [173][174][175][176][177][178][179][180][181][182] 2010 Lagoon on the west coast of South Africa between 1975 and1983. We also present results from a manipulative field experiment testing the effects of this starfish on community structure at more natural densities following the outbreak. P. exigua is relatively small (5 cm in diameter) and is very common on intertidal rocky shores in South Africa and Australia (Branch & Branch 1980, Jackson et al. 2009). It rarely occurs in intertidal lagoonal sandflats or other soft-sediment ecosystems, although the population in Langebaan Lagoon has been established there for at least the last 50 yr (Day 1959).Starfish are important structuring agents of invertebrate communities in rocky and coral reef ecosystems. Paine (1974) identified the keystone role of the starfish Pisaster ochraceus in intertidal rocky communities, demonstrating that its predation on mussels reduces their competitive edge, leading to increased diversity of co-occurring rock-occupying species. The coraleating crown-of-thorns starfish Acanthaster planci is a major determinant of coral reef community structure in the Indo-Pacific notorious for its devastating effects, and is regarded as a gre...

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Causes of rarity and range restriction of an endangered, endemic limpet, Siphonaria compressa

Cited by 32 publications

References 47 publications

Spatial variation in abundance and diversity of the smaller surface and near‐surface eelgrass‐associated intertidal macrobenthos within a warm‐temperate estuarine bay in the Garden Route National Park, RSA

Spatial variation in abundance and diversity of the smaller surface and near‐surface eelgrass‐associated intertidal macrobenthos within a warm‐temperate estuarine bay in the Garden Route National Park, RSA

Reproduction and growth of the endangered siphonariid limpetSiphonaria compressa(Pulmonata: Basommatophora)

Unexpected effects of starfish grazing on sandflat communities following an outbreak

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