Trophic interactions in an austral temperate ephemeral pond inferred using stable isotope analysis

Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period

Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature

Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007)

Fish recruitment into a South African temporarily open/closed temperate estuary during three different hydrological mouth phases

Quantitative recruitment of ichthyofauna into a South African temporarily open/closed estuary (TOCE) was investigated during three distinct hydrological phases: closed overwash, open outflow and tidal mouth conditions. Maximum recruitment densities occurred during outflow conditions and declined when the system became tidally inundated. Recruitment densities were lowest during overwash events. Selective diel variation was evident, with higher night-time densities for each phase. This study highlights the importance of seasonal timing and duration of open conditions and overwash events for structuring ichthyofaunal community composition of southern African TOCEs.Keywords: breach, ichthyofauna, ICOLL, Mpekweni Estuary, outflow, overwash, species composition, tidal condition

Presence of microplastics in the tube structure of the reef-building polychaete Gunnarea gaimardi (Quatrefages 1848)

The prevalence of microplastics in the marine environment has resulted in a need to understand their association with various fauna. The aim of this study was to assess whether microplastic particles are present in the tube structure of the indigenous reef-building polychaete Gunnarea gaimardi, which occurs along the coast of South Africa. Sampling was conducted at nine stations along the west and southeast coastlines of South Africa, in July 2016 and April/May 2017. Microplastic particles were recorded in all tube structures of G. gaimardi, with the density ranging between 0.056 and 1.113 microplastic particles g–1 dry weight (dwt). There were no significant differences between sites (p > 0.05), resulting in an overall average of 0.275 (SD 0.215) microplastic particles g–1 (dwt). To the authors’ knowledge, this is the first study to show that synthetic polymers are found in the tubes of reef-building polychaetes along the coast of South Africa.Keywords: biogenic habitat, intertidal ecosystem, invertebrates, marine pollution, plastic particles, sabellariid, South Afric

Macrofaunal community structure in the littoral zone of a freshwater-deprived, permanently open Eastern Cape estuary

Spatial patterns in the macrofauna community structure within four distinct zones of the permanently open, freshwater-deprived Kariega Estuary on the southeastern coastline of southern Africa were investigated in March–May 2010. The zones within the littoral zone comprised a band of Zostera capensis (Setchell) exposed at spring low tide and comprising Zone I; a band of mud or sand, lacking vegetation, corresponded to Zone II; stands of Spartina maritima (Curtis) formed Zone III and a belt of Sarcocornia perennis (Miller) constituted Zone IV. Total macrofauna abundance and biomass during the study ranged from 16–816 ind/m2 and from 0.032–390.76 mg wwt/m2 and demonstrated no significant horizontal or vertical patterns (P > 0.05 in both cases). Multidimensional scaling (MDS) indicated that there were no significant spatial patterns in the macrofaunal community structure within the four zones which could be related to the predominance of euryhaline species, including Marphysa sanguinea (estuarine wonder worm), Arcuatula capensis (estuarine mussel), Macoma litoralis (littoral tellin) and Nassarius kraussianus (tick shell)  throughout the estuary. The absence of any distinct spatial patterns in the community structure of the macrofauna appears to be related to the virtual absence of any horizontal patterns in selected physico-chemical variables and availability of submerged macrophytes along the length of the estuary.  Comparisons with  historical data indicate that while there have been no significant changes in the estimates of the total macrofauna abundance and biomass within the estuary over the past three decades,  abundances of selected species have declined by as much as 80%. The decline in the abundances of these species appears to reflect the predominance of hypersaline conditions within the upper reaches of the estuary and intense fishing activities in the lower reaches of the system.Key words: long-term changes, macrobenthos, permanently open estuary, southern Africa, Upogebia africana

Common dolphin Delphinus delphis occurrence off the Wild Coast of South Africa

Despite their typical large group sizes, limited research exists on the occurrence of common dolphins Delphinus delphis because of the pelagic, offshore nature of this species and the lack of barriers to their movement in this environment. The main purpose of our study was to investigate the occurrence of common dolphins off the Wild Coast of South Africa (western Indian Ocean) and whether spatiotemporal and environmental conditions affected their encounter rate, relative abundance and mean group size. The annual sardine run in this region, during austral winter (May to July), is considered a main driver of dolphin occurrence; however, our boat-based surveys over the period 2014–2016 indicated that common dolphins occur and feed in this area outside of this time-frame. In terms of environmental factors, the largest group (~1 250 animals) was found in the deepest waters. Additionally, at Hluleka, dolphins were observed primarily feeding, which could suggest that this coastal area is highly  productive. As common dolphin distribution is thought to be correlated with prey distribution, our findings suggest that sufficient prey exists along the Wild Coast both during and outside the annual sardine run to sustain large groups of the dolphins and that their presence in the area is not solely a function of the sardine run. Keywords: boat-based survey, encounter rate, feeding behaviour, group size, relative abundance, sardine ru

The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m2 and 0 and 9.65 mg/dwt/m2 in the West Kleinemonde Estuary and between 0 and 108 ind/m2 and 0 and 0.318 mg/dwt/m2 in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m2 and 0 and 5.105 mg/dwt/m2. Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P < 0.05). Sex ratios were skewed in favour of females in all three estuaries. Females were encountered carrying young from an overall length of 2.5 mm throughout the year.Key words: Crustacea, Isopoda, temporarily open/closed systems, submerged vegetation, mouth breaching