Latitudinal gradients and poleward expansion of mangrove ecosystems in
South Africa: 50 years after Macnae’s first assessment
N Peer1* , A Rajkaran2 , NAF Miranda1 , RH Taylor3, B Newman4, F Porri5,6 , JL Raw7 , SP Mbense7 ,
JB Adams7 and R Perissinotto1
ABSTRACT
Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on
blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.
Keywords: brachyurans, community structure, distribution and diversity, gastropods, global change, mangrove ecology, range limits, survey
Review of progress with integrated coastal management in South Africa
since the advent of democracy
M Sowman1* and N Malan2
ABSTRACT
Worldwide, coastal environments are recognised as complex systems of immense biophysical, socioeconomic and cultural value. In South Africa, the promulgation of the Coastal White Paper in 2000, and the Integrated Coastal Management (ICM) Act of 2008, signalled a significant paradigm shift in coastal management and governance. This article reports on progress with ICM in South Africa from 1994 to the present time, and draws on information gathered from a comprehensive review of the published ICM literature, as well as various technical reports, an online survey, and information gleaned from participation in various meetings and workshops. Here, we review
the enabling legal and institutional framework for ICM in South Africa, examine the various programmes, plans, strategies and guidelines developed to support implementation of the ICM Act, discuss institutional developments, and reflect on preconditions for effective and sustained ICM implementation. Despite significant progress, key challenges to implementing this progressive ICM agenda include lack of political support, inadequate institutional capacity, lack of human and financial resources, uncertainty regarding ICM functions across different spheres of government, conflicting policy frameworks, lack of clarity regarding the application of ICM provisions on private and communal land, limited civil-society involvement in decision-making, and persistence of state-centric
approaches. Issues requiring urgent action are the establishment of a National Coastal Committee with broad representation, revitalisation of public interest in the coast, declaration of coastal public property and coastal access land, improved cooperation across relevant government agencies, allocation of funds for ICM, and greater commitment to a more deliberative and collaborative style of governance.
Keywords: coastal governance, coastlines, coastal public property, estuaries, government policy
Impacts of alien ‘ecosystem engineers’ overwhelm interannual and
seasonal shifts in rocky-shore community composition on Marcus Island,
South Africa
S Sadchatheeswaran1 , GM Branch1, CL Moloney1 and TB Robinson2*
ABSTRACT
The South African coastline has been invaded by numerous alien species. Rare pre-invasion (1980) and post-invasion datasets (2001 and 2012) exist for Marcus Island, a small land-tied island in Saldanha Bay, South Africa. These snapshot datasets of the island’s intertidal invertebrate community were complemented with monitoring across seasons, from 2014 to 2016. Invertebrate communities were compared among the summers of 1980, 2001, 2012, 2014, 2015 and 2016 to assess interannual differences, while invertebrates and algae were monitored quarter-annually to assess seasonal changes. In addition, the population dynamics of the alien mussel Mytilus galloprovincialis were monitored. Differences in invertebrate communities between consecutive summers were significant but much smaller than changes induced by the arrival of alien species. Invertebrate and seaweed communities differed among years and shore zones but not among seasons, whereas species diversity differed among years, seasons and shore zones, with zones having the strongest influence. The invasion by M. galloprovincialis, and ensuing spatial and temporal variability in its recruitment, emerged as the most important factor influencing community composition, overshadowing interannual and seasonal changes. This work highlights that the impacts of alien species can be distinguished from natural variability by combining long-term monitoring with surveys at finer temporal scales. This is an important step in extending our understanding of the impacts of marine alien species.
Keywords: Balanus glandula, biomonitoring, historical data, invasive species, Mytilus galloprovincialis, Saldanha Bay, Semimytilus algosus
Genetic diversity and population connectivity of the sea urchin Tripneustes
gratilla along the South African coast
M Brink1 , R Dale Kuys1, C Rhode1 , BM Macey2, KW Christison2 and R Roodt-Wilding1*
ABSTRACT
The collector sea urchin Tripneustes gratilla has been identified as a species with potential for aquaculture production in South Africa. The species’ roe is considered a culinary delicacy in Asia and Europe. However, T. gratilla remains genetically uncharacterised in South Africa. Therefore, the purpose of this study was to provide baseline genetic information consisting of estimates of genetic diversity and population stratification, which may aid in future sustainable use of this urchin resource. A total of 22 species-specific microsatellite markers were used for the genetic characterisation of T. gratilla samples from along the South African coast, at Haga Haga, Coffee Bay, Hibberdene, Ballito Bay and Sodwana Bay. A moderate level of genetic diversity was observed, with an average number of alleles of 7.89 and an average effective number of alleles of 6.57, as well as an average observed heterozygosity of 0.55. Population differentiation tests suggest that the geographically representative samples form part of a single, large interbreeding population, with a global Fst estimate of 0.02 (p > 0.05). This finding is likely explained by high levels of gene flow between these locations caused by extensive larval dispersal during the planktonic larval stage. The panmixia observed within these natural populations of T. gratilla indicate that they could be managed as a single genetic stock.
Keywords: clustering, gene flow, microsatellite DNA, multiplex assays, population genetics
Sharks caught in the KwaZulu-Natal bather protection programme, South
Africa. 14. The smooth hammerhead shark Sphyrna zygaena (Linnaeus)
ML Dicken1,2*, H Winker3,4, MJ Smale5,6 and G Cliff1,7
ABSTRACT
The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p <0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats.
Keywords: CPUE, drumlines, generalised additive mixed model, length frequency, sex ratio, shark nets, stomach contents
A multimetric-index approach using fisheries data to assess fish
assemblage structure in relation to salinity gradient in a tropical West
African estuary
J Kantoussan1*, JM Ecoutin2, R Laë2 , OT Thiaw3 and L Tito de Morais2
ABSTRACT
This study examines the effects of increasing salinity on fish assemblage structure in the Casamance Estuary, Senegal, using a series of indices. The study data were derived from commercial fishery surveys conducted between April and July 2005. Analysis of within-trophic-group diversity in the Casamance Estuary shows a significant drop in the diversity of apex predators in the upper, more saline reaches of the estuary. By contrast, primary consumers adapted well to salinity changes and exhibited higher taxonomic diversity in the upper reaches of the estuary than in the lower reaches. The findings also indicate decreases in average sizes of the landed species
and the trophic levels among fish catches in the direction of the upper reaches. However, the catch per unit effort (CPUE) was globally higher in the upstream area of the estuary as compared with the downstream area. This increasing CPUE trend from the lower towards the upper reaches is attributed to (i) the high primary productivity in the upper Casamance Estuary; (ii) the increasing abundance of euryhaline fish species in an upstream direction; and (iii) ‘telescoping’ of the food chain through the presence of mostly herbivorous fishes in the upper reaches. Such a situation likely facilitated high fish production in the upstream area of the estuary, though multimetric indices indicated unfavourable living conditions for many fish taxa in this area.
Keywords: biological indicators, Casamance Estuary, ecosystem monitoring, fishery statistics, inverse hypersaline estuary, Senegal,
taxonomic diversity
The age and growth of hottentot seabream Pachymetopon blochii before
and after the South African linefish state of emergency in 2000
MW Farthing1*, AC Winkler1, K Anderson1, S Kerwath2, C Wilke2 and WM Potts1
ABSTRACT
The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa’s Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa’s linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as Lt = 418.063 (1 – e−0.104(t – [−4.709])) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management.
Keywords: age structure, gonochoristic fish, growth model, intraspecific competition, linefishery, Sparidae, Western Cape, whole otoliths
Population abundance and seasonal migration patterns indicated by
commercial catch-per-unit-effort of hakes (Merluccius capensis and
M. paradoxus) in the northern Benguela Current Large Marine Ecosystem
JN Kathena1,2*, D Yemane3,4 , N Bahamon5 and T Jansen2,6
ABSTRACT
We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance indices for assessment purposes and to infer ecological and behavioural information on northern Benguela hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration patterns were described for the first time and were found to correspond to the known spawning areas and seasons for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for
total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons.
Keywords: catchability, CPUE time-series, hake fishery, geostatistical modelling, Namibia, seasonal distribution, ship identifiers, stock assessment
Genetic variability of the Lessepsian migrant mussel Brachidontes
pharaonis (Bivalvia: Mytilidae) in Tunisia
M Antit1,2, N Amor3*, J Urra4, AN Alagaili3 and S Farjallah5
ABSTRCAT
The present study used two mitochondrial markers (16S rRNA and COI) to assess the genetic diversity of a newly founded Lessepsian migrant mussel, Brachidontes pharaonis, in Tunisian waters. The species appears to be restricted to only one population in Rades Harbour, in the northern part of the country. Phylogenetic analyses revealed the monophyly of B. pharaonis in Tunisia. Both molecular markers revealed high genetic variability of the B. pharaonis population. Haplotype networks and demographic analyses confirmed the recent expansion events within this population. Multiple human-mediated introduction events involving several founder populations and
intensive population growth rates are probably the main causes of the high polymorphism observed within this invasive mollusc.
Keywords: founder effect, invasive species, Mediterranean Sea, mitochondrial genes, phylogenetic trees, population genetics
Unique ‘spring-loaded’ gnathopod in the recently re-discovered and highly
range-restricted estuarine amphipod Quadrivisio aviceps
C Griffiths* and J Landschoff
ABSTRACT
The amphipod Quadrivisio aviceps (KH Barnard 1940), previously known from just three records collected at two small estuaries in the Western Cape, South Africa, was re-discovered at one of the original collection sites (the Palmiet River lagoon). The population at the second site (the Klein River estuary) appears to have died out, and surveys of other nearby estuaries failed to detect any additional populations. The species thus now appears to be restricted to a few hundred metres within a single small estuary, making it perhaps South Africa’s most range-restricted marine crustacean. The gnathopod 2 of males has an extremely unusual shortened and elbowed
dactyl, as well as a newly discovered and unique horseshoe-shaped ‘spring’ of elastic resilin tissue inserted within the muscles of the propodus. The function of the structure could not be confirmed, but it is thought to be a previously unknown vibration or sound-generating mechanism.
Keywords: click mechanism, endemicity, Maeridae, nano-CT scan, range restriction, South Africa, taxonomy
