Abundance, growth and recruitment of Mytilus galloprovincialis on the west coast of South Africa in relation to upwelling

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 607:113-127 (2018) - DOI: https://doi.org/10.3354/meps12794 Comparisons of life-history traits of the alien invasive Semimytilus algosus and three other mytilid mussels on the West Coast of South Africa Zannè Zeeman*, George M Branch, Deena Pillay Department of Biological Sciences and Marine Research Institute, University of Cape Town, Rondebosch 7700, South Africa *Corresponding author: zannezeeman@gmail.com ABSTRACT: The invasive mytilid mussel Semimytilus algosus was first recorded on South African shores in 2009 and rapidly spread to occupy 500 km of the West Coast, where it dominates lower portions of the rocky shore. To identify mechanisms underlying the invasive success of S. algosus, the life-history parameters survivorship, reproductive output, recruitment, growth rate and shell and byssus strength were compared among S. algosus and another alien, Mytilus galloprovincialis, and the indigenous mussels Aulacomya atra and Choromytilus meridionalis. To standardise the effects of wave exposure and shore height on life history patterns, all observations and sampling were limited to the low shore at the research site, Bloubergstrand. The 4 mussel species employed very different means of maximising survival and/or space occupancy. S. algosus proved to be a typical r-selected species, with low survival due to its weak shell and byssal strength. Unexpectedly, it grew relatively slowly but had a high reproductive output and exceptionally high recruitment rate that largely account for its invasive success. This study therefore demonstrates how life-history traits influence the invasive success of alien species and allows predictions about their relative impacts on intertidal rocky shores. KEY WORDS: Invasive species · Competition · Rocky shores · Recruitment · Growth · Reproduction Full text in pdf format Supplementary material PreviousNextCite this article as: Zeeman Z, Branch GM, Pillay D (2018) Comparisons of life-history traits of the alien invasive Semimytilus algosus and three other mytilid mussels on the West Coast of South Africa. Mar Ecol Prog Ser 607:113-127. https://doi.org/10.3354/meps12794 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 607. Online publication date: December 06, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Understanding how thermal tolerance varies in intertidal species is essential for predicting their responses to climate change, including future distribution patterns. This study investigates the upper thermal limits of the patellogastropod, Scutellastra granularis and pulmonate gastropod Siphonaria capensis, two sympatric limpet species from the west and southern coasts of South Africa. Cardiac performance (heart rate) was measured to determine sublethal (Arrhenius Breakpoint Temperature, ABT) and lethal (Flatline Temperature, FLT) thresholds under controlled temperature ramping. Results showed that Siphonaria exhibited higher sublethal (ABT: 40.23±1.96°C) and lethal (FLT: 45.15±2.13°C) thermal limits than Scutellastra (ABT: 35.78±1.58°C, FLT: 40.71±2.08°C), highlighting Siphonaria's greater thermal tolerance. Thermal Safety Margins (TSMs) also varied, with Scutellastra demonstrating site-dependent sensitivity, particularly lower at West Coast National Park (TSM: 3.19±1.41°C). The differences observed are attributed to phylogenetic and habitat adaptations: with Siphonaria's dual respiration system (lungs and gills) supporting a higher thermal tolerance, while Scutellastra's reliance on anaerobic pathways during low tides possibly results in limited thermal tolerance. These findings highlight the greater resilience of Scutellastra to warming, suggesting a greater ability to withstand future climatic conditions, unlike Siphonaria, which faces increasing vulnerability. The study provides a better understanding of the adaptive capacity of intertidal limpets and provides insight into species-specific risks under climate change.

Can we predict the effects of alien species? A case-history of the invasion of South Africa by Mytilus galloprovincialis (Lamarck)

The dependence of intertidal consumers on kelp-derived organic matter on the west coast of South Africa

Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.

Two invasive mussel species are known from South Africa, Mytilus galloprovincialis and Semimytilus algosus. Most of the existing research on these invaders has focused on the intertidal zone, with little attention paid to subtidal habitats. This study addresses this knowledge gap by quantifying the relative abundance and size of native and alien mussels from the high-shore down to the subtidal zone, while accounting for the effects of wave exposure. This was achieved through extensive surveys along the west coast of South Africa and the Cape Peninsula. At all shore zones, mussel abundance varied among species and wave exposures. In intertidal habitats, invasive species were recorded in greatest abundances at wave-exposed sites. Specifically, M. galloprovincialis was dominant in the high-shore, but this pattern changed down the shore. In the mid-shore, the invaders were equally dominant over native mussels, while in the low-shore S. algosus became the most abundant. Notably, the native Choromytilus meridionalis was absent intertidally. In the subtidal zone M. galloprovincialis was rarely present, whereas S. algosus maintained a strong presence. The maximum size of native Aulacomya atra and invasive S. algosus in the subtidal zone was roughly double that recorded in the intertidal zone. Importantly, these results highlight that observations made from intertidal studies of mussel invasions cannot be used to infer subtidal patterns.

Predation by the rock lobster Jasus lalandii is influential in regulating the composition of shallow-reef communities on the west coast of South Africa. Two previous and independent studies addressing this topic, but conducted 600 km apart (one in Cape Town and the other in Port Nolloth on the west coast of South Africa) and using different experimental protocols, revealed contradictory results regarding the feeding behaviour of J. lalandii. The Port Nolloth study showed that juvenile abalone Haliotis midae hiding under sea urchins Parechinus angulosus were safe from predation by rock lobsters, which seemed to prefer the sea urchins as food. However, the Cape Town study showed that rock lobsters preferentially selected juvenile abalone over sea urchins. Because of the importance of these results to abalone ranching and the South African abalone fishery, the experiments were repeated at the two study sites, using a standardized experimental protocol. Rock lobsters from both sites showed a strong preference for juvenile abalone over sea urchins, even in the presence of kelp Ecklonia maxima. There was no significant difference (F 3.92 = 0.09, p > 0.1) in abalone consumption by rock lobsters between the two sites. Therefore, at least in the absence of preferred prey such as mussels, sea urchins appear to provide only limited protection to juvenile abalone from rock lobsters.

Knowledge of cetacean occurrence and behaviour in southern African waters is limited, and passive acoustic monitoring has the potential to address this gap efficiently. Seasonal acoustic occurrence and diel-vocalizing patterns of sperm whales in relation to environmental conditions are described here using passive acoustic monitoring data collected off the west coast of South Africa. Four autonomous acoustic recorders (AARs) were deployed on 3 oceanographic moorings from July 2014 to January 2017. Sperm whale clicks were detected year round in most recording sites, with peaks in acoustic occurrence in summer and late winter through spring. Diel-vocalizing patterns were detected in winter, spring and summer. Higher percentages of sperm whale clicks were recorded by AARs deployed at 1100 m water depth compared to those concurrently deployed at 850 and 4500 m, likely inferring that the whales exhibited some preference to water depths around 1100 m. Acoustic propagation modelling suggested a maximum detection range of 83 km in winter for sperm whale clicks produced at 1100 m. Random forest models classified daylight regime, sea surface height anomaly and month of the year as the most important predictors of sperm whale acoustic occurrence. The continuous acoustic occurrence of sperm whales suggests that the study area supports large biomasses of prey to sustain this species’ food requirements year round. This is the first study to describe the seasonal acoustic occurrence and diel-vocalizing patterns of sperm whales off the west coast of South Africa, extending knowledge of the species previously available only through whaling records.

A total of 14 sightings of 25 humpback whales was recorded from temperate waters of the west coast of South Africa in summer (December–February). In addition, a 6,45 m individual (estimated age 6½ months) stranded at St Helena Bay in February 1982, and a 6,15 m individual (estimated age 4½ months) was found ensnared in the buoy line of a lobster trap off Saldanha Bay in December 1990. These records suggest that certain individuals, particularly juveniles, may not undertake the summer feeding migration. Although the 6,45 m individual was emaciated when stranded, the 6,15 m individual had been feeding on stomatopods, indicating that some individuals feed opportunistically during the summer off the west coast of South Africa.

The mid-Holocene (ca. 8200–4200 cal BP) brought about important climatic changes and environmental shifts to land and coastal systems, globally. Many of the human groups existing at that time were affected in various degrees by such important modifications to their foraging areas, including shorelines. Higher sea-levels (+1–3 m) were a prominent factor reshaping coastal landscapes and thus affecting coastal foraging in one or more ways. Hot and dry weather and relatively higher sea levels along the central west coast of South Africa impacted substantially on local coastal hunter-gatherer groups. These challenges were thought once to have been unsurmountable because of an apparent absence of sites dated to this period. Recently dated mid-Holocene assemblages allow us to gain insight into coastal resource procurement and overall subsistence, and also to derive more detailed coastal paleoecological data. The results show a predominantly terrestrial diet, while shellfish collection persisted amid prevailing environmental factors affecting mussel growth by supplementing their reduced mollusk takes with additional prey. Sizeable crustaceans were also procured in relatively large numbers in some localities, but not in all. This is the most-up-to date mid-Holocene subsistence record for the central west coast of South Africa which, apart from reconstructing changes in procurement strategies, reveals a trajectory of persistence in the face of climate change.

Seasonal acoustic occurrences and diel singing patterns of humpback whale (Megaptera novaeangliae) songs and Antarctic minke (Balaenoptera bonaerensis) whale are described using acoustic recordings from the west coast of South Africa and Maud Rise, Antarctica. Acoustic data were recorded from early 2014 to early 2017. Acoustic occurrences (i.e., presence) of humpback and minke whale sounds were identified through visual scrutiny of spectrograms of recorded data. Environmental conditions associated with humpback whale song occurrences were ranked according to their model-predicted relative importance. In South Africa, humpback whale songs were detected from June to December but peaked in September. In Antarctica, humpback whale songs were detected from March to May (singing peaked in April). Minke whale sounds were only recorded in 2014, between June and September in Antarctica and between September and November in South Africa. Humpback whales were more vocally active at night in all recording sites whereas minke whales were more vocally active during the day. This is the first study to describe the seasonal acoustic occurrences of humpback and minke whales off the west coast of South Africa. Such knowledge could be essential for the conservation and management of these species in both South Africa and Antarctica.

The west coast of South Africa is well known for its Cenozoic unconsolidated marine and aeolian placer deposits. The gem-quality diamond deposits have been effectively depleted; however, the significant heavy mineral concentrations are actively exploited at Namakwa Sands. This world-class mineral sand has an inferred resource of some 900 million tons at a grade of ~10% total heavy minerals (THMs) from which high-grade concentrates of zircon, rutile and leucoxene are extracted and titanium slag and pig iron are produced. Gangue minerals consist of garnet, pyroxene, kyanite, amphibole, apatite and monazite. Several other resources including satellite deposits proximal and distal to the mine area, extensive diamond mine dumps and present-day beach placers demonstrate the vast heavy mineral potential along the west coast. The increased global demand for the rare-earth elements (REEs) uranium and thorium has initiated interest in the economic potential of gangue minerals from these placer deposits. The present quantitative mineral distribution and mineral chemistry study has shown that monazite, impure zircon, leucoxene and garnet are common constituents that host significant concentrations of the REEs uranium and thorium. The total estimated resources in the Namakwa Sands deposit amount to 250 kt REEs, 4.7 kt uranium and 10.5 kt thorium. Monazite is the most significant contributor to the total thorium and light REE resource, whereas zircon is a heavy REE and U-enriched. Garnet and leucoxene show low concentrations of these elements and make a minor contribution to the total resources. Results from the Namakwa Sands deposit suggest that the west coast of South Africa as a whole presents a vast untapped resource for these elements. Considering the anticipated increasing demand for rare earths and possibly thorium, these resources could be produced as a low-cost by-product from existing and future ilmenite–zircon–rutile producers, thereby increasing the in situ value of the placers and ultimate revenue.

Detrital zircon geochemistry and U–Pb geochronology as an indicator of provenance of the Namakwa Sands heavy mineral deposit, west coast of South Africa

A field experiment demonstrating the influence of seabird guano on intertidal primary production

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 118:1-12 (1995) - doi:10.3354/meps118001 A suspended migration of humpback whales Megaptera novaeangliae on the west coast of South Africa Best, P. B., Sekiguchi, K., Findlay, K. P. Between 5 October and 19 November 1993, 62 sightings of 155 humpback whales were made from the lighthouse at Cape Columbine, South Africa, in 3 episodes about 9 d apart. For 59 groups tracked by theodolite, the average distance offshore peaked at 2 to 2.5 km. Independent information on offshore distribution was obtained from 1112 km searched by a ski-boat in the vicinity of Cape Columbine, from which the proportions of humpback whale groups in 2 strata (0 to 5 and >5 km) from the shore as seen from the lighthouse did not differ from those expected from the boat data. Net directions of movement for 51 groups were distributed equally to all 4 quadrants of the compass, and those groups showing a concerted directionality of movement were headed equally to the north and to the south. Of the same 51 groups, 70% travelled at net speeds of less than 1.5 km h-1. Migratory indices for individual groups (average speed/net speed) ranged as high as 82, and those with the lowest indices (corresponding to those most likely to be migrating) were distributed equally between northerly and southerly directions. Individual identification photographs taken of 27 humpback whales over 20 d revealed only 10 individuals, 5 of which were resighted on more than 1 occasion and up to 20 d apart. Apparent feeding behaviour by humpback whales was seen on 10 occasions over 38 d, and the production of reddish particulate faeces indicative of recent feeding was seen on 7 occasions, at a defecation rate of 0.22 whale-1 h-1. Faecal samples collected contained euphausiid remains (possibly Euphausia lucens) on 2 occasions and amphipods on another. Overall the data indicated that the southward migration of humpback whales expected at this time of year on the west coast of South Africa had been suspended, probably in response to locally abundant prey. Humpback whale . Migration . Feeding . South Africa Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 118. Publication date: March 09, 1995 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 1995 Inter-Research.