Bearded Goby Sufflogobius Bibarbatus Research Articles

Genetic structure ofSufflogobius bibarbatusin the Benguela upwelling ecosystem using microsatellite markers

The bearded goby Sufflogobius bibarbatus is an abundant endemic small fish species on the continental shelf of the northern Benguela. The goby habitat is characterised by generally low bottom oxygen concentrations that vary spatially and seasonally. In the present study of population structure, 13 samples of S. bibarbatus from inner and outer shelf areas between 19°S and 32°S were screened using ten microsatellite loci. The genetic data were analysed in relation to isolation by distance and depth. Furthermore, for the first time, this study examined genetic data in relation to bottom oxygen concentration at the sampling locations. The data show low but significant genetic heterogeneity (G-test; FST = 0.007, p < .05). There was weak but significant genetic differentiation along a latitudinal gradient across all sampling sites from 19.50°S to 32.37°S (Mantel test; r = .464, p = .001), but this disappeared when the southernmost sample was removed. On the other hand, a positive correlation of bottom oxygen concentration with pairwise FST (r = .336; p = .017) was observed among the sampling sites from the Northern Benguela shelf area. Overall, the data are complex but suggest that isolation by distance and bottom oxygen concentration may play a role in the genetic structuring of S. bibarbatus. The findings are discussed in relation to the species’ life history features and oceanographic characteristics of the Benguela upwelling ecosystem.

Winning Ways With Hydrogen Sulphide on the Namibian Shelf

The shelf sediments off Namibia are some of the most unusual and extreme marine habitats because of their extremely high hydrogen sulphide concentrations. High surface productivity of the northern Benguela upwelling system provides benthic life with so much carbon that biotic processes must rely on innovative mechanisms to cope with perennial anoxia and toxic hydrogen sulphide. Bottom dwelling communities are forced to adapt lifestyles to deal physically, physiologically and behaviourally with these stressful conditions. The upside of hydrogen sulphide is that it fuels extensive mats of large sulphide-oxidizing bacteria on the seabed, which create detoxified habitat niches and food for the animals living there. The threat of hypoxic stress exacerbated by hydrogen sulphide is largely overcome in the water column by microbes that detoxify sulphide, allowing animals in the upper water layers to thrive in this productive upwelling area. The bearded goby Sufflogobius bibarbatus is a cornerstone species that successfully couples the inhospitable benthic environment with the pelagic. Benthic studies have as yet not characterized the sulphidic shelf communities, which have the potential to uncover biotic adaptations to toxic sulphide. This ancient shelf upwelling system has long operated under hypoxic pressure, balancing always the abundance of particulate food against oxygen limitation and hydrogen sulphide toxicity. Challenges faced by this unique system could include environmental changes related to climate change, or man-made physical disturbances of the anoxic, sulphide-rich seabed sediments.

Adaptation to hypoxic environments; bearded gobies Sufflogobius bibarbatus in the Benguela upwelling ecosystem

The oceans of the world are slowly losing oxygen, in part because of climate change and in part because of anthropogenic eutrophication. This deoxygenation affects marine organisms in species-specific ways. This paper reviews what is known on how hypoxia tolerant species respond to low dissolved oxygen, using the bearded goby Sufflogobius bibarbatus as a model system. This species is endemic to the Benguela upwelling ecosystem, where, off Namibia, 9000 km2 of the shelf is hypoxic. Here, the species is now considered central to ecosystem functioning and in recent decades it has sustained commercial fisheries. Unlike their predators, S. bibarbatus has strong anti-predator responses as they can remain alert and escape threats in anoxic and severely hypoxic waters and can cope with sulphide shocks. Populations display diel vertical migration and shuttle between suboxic seabed refugia during the day to more oxygenated waters higher up in the water column at night and whilst they may share the water column with predators they may reduce their predation risk by associating with jellyfish (Aequorea forskalea and Chrysaora fulgida). The spatial distribution of S. bibarbatus varies with changes in available oxygen and populations expand and contract with climate-induced changes in the distribution of hypoxic waters. This species has an unusual diet and plays an important role in ecosystem functioning. It is a batch-spawner, with a protracted spawning season. Remarkably, males display alternative reproductive tactics and reproduction can take place at oxygen levels <0·5ml l-1 dissolved oxygen on the shelf break. Gaps in knowledge are identified and future works are proposed.

First records of reproductive behaviour and early development of the bearded goby Sufflogobius bibarbatus

Data on developmental characteristics from fertilization to 2 days post-hatching during captivity of the anoxia tolerant bearded goby Sufflogobius bibarbatus, one of the keystone prey species for many of the commercial fish populations, sea mammals and birds in south-west Africa, are presented.

Characterization of polymorphic microsatellite markers for the bearded goby Sufflogobius bibarbatus

Fourteen polymorphic microsatellite markers with tetranucleotide repeats were developed for the bearded goby (Sufflogobius bibarbatus) from partial genomic DNA libraries using a repeat enrichment protocol, and characterized using two putative populations from the northern Benguela. The average number of alleles per locus ranged from 4 to 34, and the observed heterozygosities across loci were between 0.237 and 0.983. We also tested the utility of these markers in two other marine gobies; sand goby Pomatoschistus minutus and two-spotted goby Gobiusculus flavescens. These polymorphic markers can be employed to investigate population structure and related questions of the bearded goby.

Investigations into the diet and feeding ecology of the bearded goby Sufflogobius bibarbatus off Namibia

The bearded goby Sufflogobius bibarbatus has come to replace sardine Sardinops sagax in the diets of many top predators within the marine environment off Namibia, and it is playing a key role within the region's foodweb. Previously published information on the diet of the bearded goby has been derived from small samples and has been contradictory. We investigated the gut contents of over 3 500 specimens of S. bibarbatus from two separate studies. The results indicate that the species has a fairly generalised diet, feeding mostly on benthic and pelagic animals (phytoplankton was rare), in a way that reflects ontogeny, habitat and likely prey availability. Smaller, more pelagic individuals included a substantial number of pelagic organisms in their diet and the proportion of benthic organisms increased with the size of the goby. Given the importance of this species in recycling benthic carbon through the foodweb of the northern Benguela ecosystem, there is a need to describe and quantify the benthic food environment.

Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures

The bearded goby Sufflogobius bibarbatus has become a key component of the pelagic food web off Namibia following the crash in pelagic fish populations during the 1970s, and its bio- mass is increasing despite significant predation pressure and apparent life-history constraints. The integrated feeding of the bearded goby was studied from samples collected during April 2008, using stable isotope ratios (δ 13 C, δ 15 N, δ 34 S) and fatty acids, to resolve conflict amongst previous dietary studies based on gut-content analysis and to understand how diet could influence its success within the region. Isotopes of carbon and nitrogen suggest that the now abundant jellyfish could contribute up to 74% of the diet, and δ 34 S signatures indicate that the diatom- and bacteria-rich sulphidic sedi- ments on the central shelf may contribute around 15% to the diet. Fatty acid analyses provided sup- port for sulphur bacterial and jellyfish-feeding amongst gobies, and further suggest that small gobies fed more on zooplankton while large gobies fed more on sedimented diatoms. Both data sets suggest that ontogenetic changes in diet were linked to changes in habitat: pelagic when small, more demersal when large. The study highlights the value of using multiple tracers in trophic studies and indicates that the dietary flexibility of the bearded goby, in conjunction with its behaviour and physiology, likely contributes to its success within the northern Benguela ecosystem.

Cross-shelf observations of diet and diel feeding behaviour of the bearded goby Sufflogobius bibarbatus off Namibia

The diet of the bearded goby Sufflogobius bibarbatus was studied at two 48 h stations off the Namibian coast. The inner station (120 m) was characterised by a deep layer of low-oxygen bottom water (<0.5 ml DO l−1 or <10% oxygen saturation) scarcely inhabited by metazoan animal life. Gobies at this station were ∼75 mm total length (TL) and displayed a strong vertical size gradient. The diet of all fish was dominated by sedimented diatoms, and digestion appeared to occur primarily in the oxygen-rich water column at night. By contrast, the environment at the offshore station was characterised by a thin layer of oxygen-poor bottom water, and a richer benthic and zooplankton food environment. Pelagic-caught gobies were significantly shorter (43.3 mm TL) than demersal-caught individuals (99.9 mm TL) throughout 24 h, and the difference in habitat was reflected by differences in diet: pelagic-caught fish ate mostly zooplankton whereas demersal-caught fish ate mostly benthic infauna. In contrast to the situation inshore, digestion appeared to take place throughout 24 h. The results presented here indicate a strong relationship between diet, feeding behaviour and environment, and strengthen conclusions about the dietary opportunism of this species.

Behavioural and physiological adaptations of the bearded goby, a key fish species of the extreme environment of the northern Benguela upwelling

Nutrient-rich, upwelling marine areas with high productivity often produce sediments dominated by organic-rich mud. Here, intense decay processes create hypoxic conditions with high concentrations of hydrogen sulphide and methane in the muddy surface layers. Such environments are inhospitable to most forms of life and those organisms that can survive in these areas tend to be specialists that cope with anoxic or hypoxic conditions, e.g. sulphide-oxidising bacteria and chemo- lithotrophic bacteria. Surprisingly, during recent acoustic and survey work in the northern Benguela region off the coast of Namibia, it was observed that the bearded goby Sufflogobius bibarbatus spends much of the day on the seabed interacting with the hypoxic and sulphidic mud, making a diel vertical migration (DVM) to spend the night in more oxygenated, but jellyfish-rich waters. We describe a series of experiments that demonstrate physiological and behavioural adaptations that enable the gobies to cope with hypoxia, anoxia and exposure to sulphide for prolonged periods of time. We also observed that the fish burrow directly into the muddy substrate when threatened and that, unlike another fish species common to this area, the horse mackerel Trachurus capensis, the gobies tolerate the presence of jellyfish.

Preliminary evidence for genetic heterogeneity of the goby (Sufflogobius bibarbatus) in the Benguela ecosystem

PCR-RFLP analysis of mitochondrial DNA (NADH-3/4 gene and the control region) of the Benguelan bearded goby Sufflogobius bibarbatus revealed weak, but significant genetic differentiation (overall FST = 0.137) that could not be predicted by hydrodynamics alone, thus warranting further investigations to understand the forces behind population divergence within an ecosystem having complex dynamics.

Production and consumption by planktivorous fish in the northern Benguela ecosystem in the 1980s

In the 1980s, abundance of four abundant planktivorous fish in the northern Benguela ecosystem (15–29°S, coast to 500 m contour) — pilchard Sardinops sagax, anchovy Engraulis capensis, bearded goby Sufflogobius bibarbatus and lanternfish, mainly Lampanyctodes hectoris — was estimated to be 1,8 million tons wet mass on average. These fish consumed 3,7 million tons dry mass of plankton, mostly zooplankton, and produced 0,1 million tons of carbon annually. There is considerable uncertainty regarding the estimates of abundance and diet; hence also of consumption and production.