Photoautotrophic Euendoliths and their complex ecological effects in marine bioengineered ecosystems

Photoautotrophic euendolithic microorganisms are ubiquitous where there are calcium carbonate substrates to bore into and sufficient light to sustain photosynthesis. The most diverse and abundant modern euendolithic communities can be found in the marine environment. Euendoliths, as microorganisms infesting inanimate substrates, were first thought to be ecologically irrelevant. Over the past three decades, numerous studies have subsequently shown that euendoliths can colonize living marine calcifying organisms, such as coral skeletons and bivalve shells, causing both sub-lethal and lethal damage. Moreover, under suitable environmental conditions, their presence can have surprising benefits for the host. Thus, infestation by photoautotrophic euendoliths has significant consequences for calcifying organisms that are of particular importance in the case of ecosystems underpinned by calcifying ecosystem engineers. In this review, we address the nature and diversity of marine euendoliths, as revealed recently through genetic techniques, their bioerosive mechanisms, how environmental conditions influence their incidence in marine ecosystems and their potential as bioindicators, how they affect live calcifiers, and the potential future of euendolithic infestation in the context of global climate change and ocean acidificationinfo:eu-repo/semantics/publishedVersio

Euendolithic infestation of Mussel Shells indirectly improves the thermal buffering offered by Mussel Beds to associated Molluscs, but one size does not fit all

Mussel beds form important intertidal matrices that provide thermal buffering to associated invertebrate communities, especially under stressful environmental conditions. Mussel shells are often colonized by photoautotrophic euendoliths, which have indirect conditional beneficial thermoregulatory effects on both solitary and aggregated mussels by increasing the albedo of the shell. We investigated whether euendolithic infestation of artificial mussel beds (Perna perna) influences the body temperatures of four associated mollusc species during simulated periods of emersion, using shell temperature obtained via non-invasive infrared thermography as a proxy. Shell temperatures of the limpet Scutellastra granularis and the chiton Acanthochitona garnoti were higher in non-infested than infested mussel beds during simulated low tides under high solar irradiance and low wind speeds. However, this was not the case for the limpet Helcion pectunculus or the top shell Oxystele antoni. Morphological differences in mollusc shape and colour could, in part, explain this contrast between species. Our results indicated that endolith-induced improvements in humidity and temperature in mussel beds could benefit associated molluscs. The beneficial thermal buffering offered by euendolithic infestation of the mussel beds was effective only if the organism was under heat stress. With global climate change, the indirect beneficial effect of euendolithic infestation for invertebrate communities associated with mussel beds may mitigate intertidal local extinction events triggered by marine heatwaves.National Research Foundation - South Africa 64801; French National Research Agency (ANR) SAN22202;info:eu-repo/semantics/publishedVersio

Monitoring the oceanic flow between Africa and Antarctica: report of the first Good Hope cruise

The Southern Ocean plays a major role in the global oceanic circulation, as a component of the Meridional Overturning Circulation, and it is postulated that it has a great influence on present-day climate. However, our understanding of its complex three-dimensional dynamics and of the impact of its variability on the climate system is rudimentary. The newly constituted, international GoodHope research venture aims to address this knowledge gap by establishing a programme of regular observations across the Southern Ocean between the African and Antarctic continents. The objectives of this programme are fivefold: (1) to improve understanding of Indo-Atlantic inter-ocean exchanges and their impact on the global thermohaline circulation and thus on global climate change; (2) to understand in more detail the influence these exchanges have on the climate variability of the southern African subcontinent; (3) to monitor the variability of the main Southern Ocean frontal systems associated with the Antarctic Circumpolar Current; (4) to study air-sea exchanges and their role on the global heat budget, with particular emphasis on the intense exchanges occurring within the Agulhas Retroflection region south of South Africa, and (5) to examine the role of major frontal systems as areas of elevated biological activity and as biogeographical barriers to the distribution of plankton. We present here preliminary results on the physical and biological structure of the frontal systems using the first GoodHope transect that was completed during February-March 2004

Conserving pattern and process in the Southern Ocean: designing a Marine Protected Area for the Prince Edward Islands

South Africa is currently proclaiming a Marine Protected Area (MPA) in the Exclusive Economic Zone (EEZ) of its sub-Antarctic Prince Edward Islands. The objectives of the MPA are to: 1) contribute to a national and global representative system of MPAs, 2) serve as a scientific reference point to inform future management, 3) contribute to the recovery of the Patagonian toothfish (Dissostichus eleginoides), and 4) reduce the bird bycatch of the toothfish fishery, particularly of albatrosses and petrels. This study employs systematic conservation planning methods to delineate a MPA within the EEZ that will conserve biodiversity patterns and processes within sensible management boundaries, while minimizing conflict with the legal toothfish fishery. After collating all available distributional data on species, benthic habitats and ecosystem processes, we used C-Plan software to delineate a MPA with three management zones: four IUCN Category Ia reserves (13% of EEZ); two Conservation Zones (21% of EEZ); and three Category IV reserves (remainder of EEZ). Compromises between conservation target achievement and the area required by the MPA are apparent in the final reserve design. The proposed MPA boundaries are expected to change over time as new data become available and as impacts of climate change become more evident

Physical and biological variability in the Antarctic Polar Frontal Zone: report on research cruise 103 of the MV SA Agulhas

A detailed hydrographic and biological survey was carried out in the region of the South-west Indian Ridge during April 2002. Hydrographic data revealed that the Andrew Bain Fracture Zone, centred at 30oE, 50oS, functions as an important choke point to the flow of the Antarctic Circumpolar Current, resulting in the convergence of the Antarctic Polar Front (APF) and the southern branch of the Sub-Antarctic Front (SSAF). Total chlorophyll-a concentration and zooplankton biomass were highest at stations occupied in the vicinity of two frontal features represented by the APF and SSAF. These data suggest that the region of the South-west Indian Ridge is an area of elevated biological activity and probably acts as an important offshore feeding area for the top predators on the Prince Edward Islands

Residency patterns and migration dynamics of adult bull sharks (Carcharhinus leucas) on the east coast of southern Africa:

Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean  = 533 km) with eight of these sharks returning to the study site

Comparative feeding ecology of bull sharks (Carcharhinus leucas) in the coastal waters of the southwest Indian Ocean inferred from stable isotope analysis.

As apex predators, sharks play an important role shaping their respective marine communities through predation and associated risk effects. Understanding the predatory dynamics of sharks within communities is, therefore, necessary to establish effective ecologically based conservation strategies. We employed non-lethal sampling methods to investigate the feeding ecology of bull sharks (Carcharhinus leucas) using stable isotope analysis within a subtropical marine community in the southwest Indian Ocean. The main objectives of this study were to investigate and compare the predatory role that sub-adult and adult bull sharks play within a top predatory teleost fish community. Bull sharks had significantly broader niche widths compared to top predatory teleost assemblages with a wide and relatively enriched range of δ(13)C values relative to the local marine community. This suggests that bull sharks forage from a more diverse range of δ(13)C sources over a wider geographical range than the predatory teleost community. Adult bull sharks appeared to exhibit a shift towards consistently higher trophic level prey from an expanded foraging range compared to sub-adults, possibly due to increased mobility linked with size. Although predatory teleost fish are also capable of substantial migrations, bull sharks may have the ability to exploit a more diverse range of habitats and appeared to prey on a wider diversity of larger prey. This suggests that bull sharks play an important predatory role within their respective marine communities and adult sharks in particular may shape and link ecological processes of a variety of marine communities over a broad range

Striping patterns may not influence social interactions and mating in zebra: Observations from melanic zebra in South Africa

Colouration serves many functions in animals including crypsis, aposematism, mimicry, intraspecific communication, communication between species and thermoregulation (Caro, Caswell Stoddard, & Stuard‐Fox, 2017). On occasions, abnormalities or discontinuous variations in colouration and/or patterning of an individual within a population can occur, leading to albinism (Osinga, ‘t Hart, & Vader, 2010), leucism (Reisinger, Mufanadzo, de Bruyn, & Bester, 2009) or melanism (Eizirik et al., 2003; Majerus, 1998). Melanism, a rare condition occurring when a group of pigments (pheomelanin or eumelanin) is overproduced, has been reported in a variety of mammal species

A dual isotope plot representing the sampled fish community and individual bull sharks.

<p>Fish groups represented by the mean δ¹³C and δ¹⁵N values (±SD). Adult individual bull sharks are represented by squares and sub-adults are represented by triangles. </p

A dual isotope plot representing the niche widths of bull sharks (black line), fish group 1 (red line) and fish group 2 (green line).

<p>Calculated niche width is represented by the small sample size corrected ellipses (solid lines) and displayed in a δ¹³C-δ¹⁵N niche space. </p