Research Articles (Biodiversity and Conservation Biology)

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Trophic ecology of carnivorous zooplankton in the Benguela
(NISC and Taylor & Francis, 1992) Gibbons, Mark J.; Stuart, V.; Verheye, H.M.
Carnivorous zooplankton in the Benguela system have tended to be ignored by all but early taxonomists and a handful of recent researchers. An attempt is made here to address the importance of carnivores in this system but, because the database is poor, it was necessary to apply material from outside the region. The taxa covered include ctenophores, cnidarians (Scyphozoa and Hydrozoa, including Siphonophora), chaetognaths and hyperiid amphipods as well as such minor groups as pelagic gastropods and decapods. Most groups of carnivores within the Benguela are represented by only one or two "common" species. These tend to be epiplanktonic and generally concentrated inshore of the shelf-break, where their distributions are influenced by changes in local hydrography. Their densities frequently exceed those of herbivores. The dominant carnivores share a number of attributes: wide-ranging diets, high assimilation and growth efficiencies and mostly a Type I functional response to food concentration. They fall into two categories. The first is the gelatinous species, which have short lifespans and exhibit rapid growth and often massive reproductive response to high concentrations of food. They are patchily distributed and some appear to have behavioural traits that enable them to stay within localized patches of prey on which they may be dependent because of high metabolic costs. In the second category are crustacean predators and chaetognaths which have slower response times to the food environment but may have longer lifespans, lower daily maintenance needs and an ability to store lipids. They are less dependent on high densities of food organisms and can survive throughout winter, when gelatinous predators are rare. The effect of predation on abundance of copepods is estimated on the basis of both published and unpublished data. Should swarms of predators coincide with a critical gateway of zooplankton or larvae, then there may be total depletion. This applies especially to the nearshore zone of the West Coast and to semi-enclosed bays. The role of carnivorous zooplankton in the diets of commercially important fish species is stressed, but their importance in the regeneration of nutrients may be insignificant.
Ecological significance of deep-layer sloughing in the eulittoral zone coralline alga, Spongites yendoi (Foslie) Chamberlain (Corallinaceae, Rhodophyta) in South Africa.
(Elsevier, 1994) Keats, Derek; Wilton, P.; Maneveldt, Gavin
The crustose coralline alga Spongites yendoi (Foslie) Chamberlain (Corallinaceae, Rhodophyta) dominates the lower eulittoral zone along the South Coast of South Africa, together with the limpet Patella cochlear Born. This coralline alga was previously shown to undergo a deep-layer sloughing twice a year, as well as continuous epithallial sloughing. The hypothesis that deep-layer sloughing could perform an antifouling function was tested by determining the percentage cover of fleshy algae developing in a limpet exclusion experiment on live and killed coralline. Substantial fleshy algal cover developed in both limpet removal treatments, negating any possible antifouling function of deep-layer sloughing. A measurable decrease in the mean thickness of the coralline population was noted during periods of sloughing. A thicker crustose coralline, Leptophytum ferox (Foslie) Chamberlain & Keats, grew more slowly and was much more heavily burrowed and more weakly attached than S. yendoi. These results are consistent with a hypothesis that deep-layer sloughing contributes to the alga's relatively thin thallus, thereby conferring the advantages of faster growth and stronger attachment. However, further studies are still needed to evaluate these hypotheses further.
Feeding and vertical migration of the chaetognath Sagitta friderici (Ritter Zahony, 1911) in the southern Benguela during spring 1987, with notes on seasonal variability of feeding ecology
(NISC and Taylor & Francis, 1994) Gibbons, Mark J.; Stuart, V.
The feeding biology and the vertical migration of Sagitta friderici were examined over 24 h at two stations in the southern Benguela during spring (October) 1987. Together with studies conducted during summer (February 1991) and winter (May 1984), they serve to allow valuable generalizations of the biology and ecology of this abundant chaetognath. Populations migrate vertically and feed nocturnally, although the timing and the extent of migration vary between studies. S.friderici exhibits ontogenetic layering and the cross-shelf distribution of maturity stages differs, suggesting that it is able to take advantage of cross-shelf water movement in order to maintain populations in the nearshore waters of the West Coast. S.friderici prey almost exclusively on copepodg (cannibalism is rare), and there is a positive relationship between the lengths of predator and prey that is influenced by the size structure of the prey environment. This casts doubt on the validity of a chaetognath species-specific relationship between predator and prey size. S. friderici selects its prey on the basis of size, and not species. Daily ration is related linearly to prey density, so reflecting the low density of prey and providing support for theoretical predictions regarding ingestion rates under oceanic conditions. The impact of S. friderici predation on the copepod assemblage is generally less than 3% of the standing stock, although it could be much higher under conditions of low copepod biomass and poor secondary production.
Observations on the pelagic decapod Pasiphaea semispinosa in the Benguela upwelling ecosystem
(NISC and Taylor & Francis, 1994) Barange, M.; Macpherson, E.; Gibbons, Mark J.
Information on vertical and horizontal distribution patterns, abundance and morphology of the decapod Pasiphaea semispinosa in the Benguela upwelling system is presented. P. semispinosa is the dominant pelagic decapod in the system, occurring between 19 and 32°S along the mid and inner shelf in concentrations of 10-100•m-2• Although it is more abundant during abated than during active upwelling in the northern Benguela, it would appear to be equally abundant during both upwelling scenarios in the southern Benguela. In the southern Benguela, reproductive females are present during winter and juveniles dominate during active upwelling, but juveniles appear to be more common during abated upwelling in the northern Benguela. The estimates of abundance of P. semispinosa presented in this study are subject to sampling biases attributable to their vertical migratory behaviour and net avoidance capabilities.
Leptophytum foveatum Chamberlain & Keats (Rhodophyta, Corallinales) retaliates against overgrowth by other encrusting algae
(Elsevier, 1994) Keats, Derek; Maneveldt, Gavin
The encrusting coralline alga, Leptophytum foveatum, is the most abundant crustose alga in the lower eulittoral zone at Yzerfontein and other exposed sites on the West Coast of South Africa. The surface of this species is usually imbricate (appears scaly) as a result of the aparently spontaneous regeneration of margins at the surface of the thallus. The thicker, fleshy, brown crustose alga, Ralfsia verrucosa, usually overgrows the margins of the thinner L. foveatum; however, L. foveatum counteracts this overgrowth by regenerating margins at the thallus surface, and these are able to grow up and over the encroaching margin of R. verrucosa. Experiments in which these regenerated margins were removed showed that the regenerated margins are able to slow or stop the encroachment of R. verrucosa. It is suggested that the regeneration of thallus margins at the surface, away from the primary thallus margin, allows L. foveatum to maintain the advantages of being thin (e.g. more rapid lateral growth), but also gain some of the advantages of being thick (e.g. improved competitive ability).
Observations on euphausiid communities of the south coast of South Africa
(NISC (Pty) Ltd and Taylor& Francis, 1995) Gibbons, Mark J.
A total of 24 species of euphausiid was collected during a survey along the South African south coast during January 1992. Communities over the Agulhas Bank were of low diversity and abundance and were dominated by Nycliphanes capensis. Those at the shelf-edge were of high diversity and abundance and were dominated by Euphausia recurI'll and Thysalloessa gregaria. Such high diversity may be maintained by vertical scgregation at night. Few species displayed obvious diel vertical migration, although N. capen sis may be able to maintain itself on the shelf by means of this behaviour. E. recurl'Cl appeared to feed on phytoplankton throughout the water column at night, reflecting the distribution of food.
Clathromorphum tubiforme sp. nov. (Rhodophyta, Corallinaceae) in South Africa with Comments on Generic Characters
(Walter de Gruyter, 1995) Chamberlain, Yvonne; Norris, R.E.; Keats, Derek; Maneveldt, Gavin
A nongeniculate, crustose coralline alga (Rhodophyta, Corallinaceae) from South Africa, is found growing epiphytically on fronds of species of the geniculate genus Ampiroa. Analysis of the vegetative and reproductive morphology and anatomy of the alga shows that it belongs to the subfamily Melobesioideae and genus Clathromorphum. It is the only known representative of the genus in South Africa. It has tetrasporangial conceptacles that are significantly smaller than those of any other described species of the genus and it is described as the new species Clathromorphum tubiforme. The diagnostic features of Clathromorphum and other genera of the Melobesioideae are discussed and it is considered that, among melobesioid genera, Clathromorphum is probably most closely related to Melobesia.
First report of the melobesioid alga (Corallinales, Rhodophyta) Mesophyllum incisum (Foslie) Adey in South Africa
(Elsevier, 1997) Keats, Derek W.; Maneveldt, Gavin W.
Mesophyllum incisum is reported and studied for the first time in South Africa. It has a th all us surface (SEM) with Leptophyturn-type epithallial cells. TetraJbisporangial conceptacles are mound-like and lack a peripheral rim but have a flattened pore plate. The rosette cells surrounding the tetrasporan gial po res are distinct from su rrounding roof cells (SEM, surface view) in be ing narrower, and sunken below the level of the surrounding pore plate. The cells of filaments bordering the tetrasporangial conceptacle pore canal differ from the othe r roof cells within the pore plate in being more elongate, narrower, and often more densely staining. Pore canal filaments also generally contain fewer cells than the surrounding filaments of the pore plate and th e pore can al is more-Dr-less parallel sided. Our material agrees closely with the species as reported in Australia.
Two new melobesioid algae (Corallinales, Rhodophyta), Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., in South Africa and Namibia
(International Phycological Society, 1997) Keats, Derek; Maneveldt, Gavin
Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., the fourth and fifth species in this apparently southern hemisphere genus, are described from southern Africa. Synarhrophyton robbenense occurs on rock and shells in the subtidal zone. Its thalli are minutely warty, with the surface covered by short, narrow protuberances that are fused into elongate, scrolled structures. The surface [scanning electron microscopy (SEM)] is of the Leptophytum type. Mature tetraibisporangial conceptacles have raised rims and sunken pore plates. The pore plates are composed of filaments made up of two or three cells plus an enlarged epithallial cell. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are narrower and more elongate than cells of the pore plate and surrounding vegetative filaments. Tetralbisporangial pores are surrounded by five to eight rosette cells that tilt somewhat toward the pore in surface SEM view. Tetraibisporangial conceptacles do not become buried in the thallus, but are shed on senescence, often leaving shallow craters on the surface. Synarthrophylon munimenlum occurs on rocks and shells in low-shore tide pools, and on rock, shells, and kelp holdfasts in the subtidal zone. Thalli are usually smooth, occasionally warty, but never show protuberances that are fused into scrol l-like structures. The thallus surface (SEM) is made up of Leptophytum-type epithallial cells. Tetral bisporangial conceptacle roofs are volcano-shaped with a raised peripheral rim and sunken pore plate. The pore plates are composed of filaments made up of five to seven cells plus an epithallial cell. The rosette cells that surround the tetral bisporangial pore are distinct from surrounding roof cells (SEM, surface view) in being narrower and sunken below the level of the surrounding pore plate. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are more or less similar in size and shape to cells of the pore plate and surrounding vegetative filaments.
Of dead man's fingers, cord weed and hanging wrack: common brown seaweeds of the Cape Peninsula
(Botanical Society of South Africa, 2000) Maneveldt, Gavin; Frans, Rene
In this, the second in the series on common intertidal seaweeds of the Cape Peninsula, we look at the brown seaweeds common to our rocky shores, with the exception of kelp, which will be covered in the next issue of Veld & Flora. Unlike the green seaweeds mentioned in the previous issue, these brown seaweeds are generally slower growing and are less tolerant of salinity and temperature extremes and thus more prone to desiccation stress. They therefore tend to occur lower down on the shore than the green seaweeds.
Video observations on the habitat association of demersal nekton in the mid-shelf benthic environment off the Orange River mouth
(NISC and Taylor & Francis, 2000) Sulaiman, A.; Hissman, K.; Schauer, J.; Wickens, P.A.; McMillan, I.; Gibbons, Mark J.
A semi-quantitative assessment is made of the animals observed in archived videotapes taken from the research submersible Jago, during diamond mining and exploratory surveys off the mouth of the Orange River on the west coast of southern Africa (28° IS'S, 29°11 'S) in November 1996. The seabed environment is described and nekton associations with substratum features are identified. The area is characterized by heterogeneity to its physical and biological struture. The variety of observed nekton is low, and communities are dominated by goby Sufflogobius bibarbatus, juvenile hake Merluccius spp. and cuttlefish Sepia spp. (on soft substrata), as well as false jacopever Sebastes capen sis and kingklip Genypterus capensis (on rocky substrata)
Of sea lettuces and green sea intestines: common intertidal green seaweeds of the Cape Peninsula
(Botanical Society of South Africa, 2000) Maneveldt, Gavin; Frans, Rene
Most of us know seaweed as that slippery stuff growing on the rocks or lying strewn along the beach at low tide making the beach smell. But do we really know much about them? Although not entirely true, seaweeds (or marine algae) are generally considered to be plants because they use solar energy to produce carbohydrate food from carbon dioxide and water (photosynthesis). They are simpler than land plants as they have no roots or shoots. Seaweeds absorb nutrients directly from the seawater; and therefore have no need for roots or complex conductive tissue. Some large seaweeds do however have root-like structures called holdfasts and leaf-like fronds that act like shoots. The photosynthetic pigments they possess reflect certain colours of light, producing what appear to be green, brown and red seaweeds, and thus they are divided into three main groups: green brown and red. In this article we examine some of the green seaweeds that occur in the Cape Peninsula.
Of purple laver, tongue weed and hedgehog seaweed: common red seaweeds of the Cape Peninsula
(Botanical Society of South Africa, 2001) Maneveldt, Gavin; Frans, Rene
The fourth part of our series on the common intertidal seaweeds of the Cape Peninsula looks at the red seaweeds, which form by far the largest group of seaweeds on the Peninsula and dominate the mid to lower intertidal area to a large extent. Like the brown seaweeds many of the reds are fleshy and bulky and generally occur lower down the shore because they are less tolerant of salinity and temperature extremes than some of the common green seaweeds.
Genetic and morphological variation of the lanternfish lampanyctodes hectoris (myctophiformes: myctophidae) off Southern Africa
(Taylor and Francis Group, 2001) Florence, W. K.; Hulley, P. A.; Stewart, B. A.
Genetic and morphological variation within the southern African population of Lampanyctodes hectoris was analysed. A total of 15 enzymes, encoding 22 isozyme loci, was examined (n = 327); seven were polymorphic. The percentage of polymorphic loci ranged from 13.6 to 27.3%. The mean heterozygosity was generally low and ranged from 0.003 to 0.005. Genetic divergences between specimens from four areas along the west coast of southern Africa were negligible, genetic distance values (D) ranging from 0 to 0.00011. The results showed the population of L. hectoris to be genetically invariant. Principal Component Analysis was performed separately on ratios of 13 morphometric and 6 meristic variables (n = 446), and there was evidence of extensive overlap between fish from all areas. However, discriminant analysis suggested some morphological variability within this population. Although genetically the population of L. hectoris seems to be homogenous, morphologically it appears to be variable. A combination of these results suggests that there is no clear genetic basis for the slight morphological differentiation within the population.
Of dinner plate, cochlear and pacman corallines: seven common intertidal encrusting red seaweeds of the Cape Peninsula
(Botanical Society of South Africa, 2001) Maneveldt, Gavin; Frans, Rene
In the fifth and final part of this series of articles on common intertidal seaweeds of the Cape Peninsula, we look at encrusting coralline algae. These encrusting coralline and red seaweeds are widespread in shallow waters in all the world’s oceans, where they often cover close to 100% of rocky substrates. Nowhere are they more important than in the ecology of coral reefs. Not only do encrusting coralline algae help cement the reef together, but they make up a considerable portion of the mass of the reef itself and are important primary products and food for certain herbivores.
Of sea bamboo, split fan kelp and bladder kelp: three common kelp species of the Cape Peninsula and West Coast
(Botanical Society of South Africa, 2001) Maneveldt, Gavin; Frans, Rene
The third part in our series on the common intertidal seaweeds of the Cape Peninsula looks at the kelps, the giant brown seaweeds that occur in the subtidal and intertidal gullies of the Cape Peninsula and the west coast. Like trees an ancient forest, kelp dominate the canopy of the subtidal zone in the cool, nutrient-rich waters of the South African west coast. Kelp is the largest and fastest growing of the seaweeds, growing as much as 13 mm in a day. Some of these seaweeds as the giant kelp (Macrocystis pyrifera) of central and southern California are known to grow to over 30 m in length.
Acoustic observations of jellyfish in the Namibian Benguela
(Inter-Research, 2001) Brierley, Andrew S.; Axelson, Bjorn Erik; Buecher, Emmanuelle; Sparks, Conrad A.J.; Boyer, Helen; Gibbons, Mark J.
Multi-frequency acoustic data (18, 38 and 120 kHz) were collected in conjunction with pelagic trawl sampling for gelatinous macrozooplankton during a cruise to the Namibian Benguela in September 1999. Sampling focused specifically on the scyphozoan Chrysaora hysoscella and the hydrozoan Aequorea aequorea, both of which occur in large numbers, are probably of major ecological importance, and physically hamper pelagic fishing and diamond extraction activities. C. hysoscella was detected predominantly at an inshore station and A. aequorea was found in greatest abundance further offshore in deeper water. Echo-sounder observations were linked directly to net catches, and relationships between catch density (number of individuals m–3) and nautical area scattering coefficients (sA) at each frequency were determined for both species in order to estimate target strength (TS) using the comparison method. TS for C. hysoscella (mean umbrella diameter 26.8 cm) was –51.5 dB at 18 kHz, –46.6 dB at 38 kHz and –50.1 dB at 120 kHz; for A. aequorea (mean central umbrella diameter 7.4 cm) TS was –68.1 dB at 18 kHz, –66.3 dB at 38 kHz and –68.5 dB at 120 kHz. These TS values compared favourably with previously published estimates for related species. Jellyfish were caught at high numerical densities (maxima 3 C. hysoscella per 100 m3, 168 A. aequorea per 100 m3). These high densities, combined with the not unsubstantial TS at frequencies used for fisheries surveys, imply that jellyfish could potentially bias acoustic estimates of fish abundance. We suggest a simple multifrequency approach that could be used to discriminate between echoes from jellyfish and some commercially important pelagic fish in the northern Benguela ecosystem.
Hydromedusae off the Orange River Mouth, Southern Africa
(NISC (Pty) Ltd and Taylor& Francis, 2003) Sparks, Conrad A.J.; Gibbons, Mark J.
A total of 242 zooplankton samples from the upper 100 m of the water column was collected discontinuously from March 1997 to January 1999 off the Orange River mouth on the west coast of southern Africa. Six species of hydromedusae were recovered at generally low abundance, of which Euphysa aurata, Leuckartia octona and Proboscidactyla menoni were dominant. E. aurata and L. octona showed evidence of seasonality in abundance. The low diversity of the fauna was remarkable and it is hypothesized that this might be attributable in part to sedimentation from the Orange River, and in part to locally weak circulation and the wide extent of the continental shelf.
Observations on the ecology of Pleurobrachia pileus (Ctenophora) in the southern Benguela ecosystem
(NISC (Pty) Ltd and Taylor & Francis, 2003) Buecher, Emmanuelle; Thibault-Botha, D.; Gibbons, Mark J.
The vertical distribution, abundance and size composition of a population of Pleurobrachia pileus was studied during a six-day drogue study conducted off the west coast of South Africa in February 1995. The population was centred in deep water, possibly because of the presence of a potential predator, Beroe sp., at shallower depths. The population of P. pileus failed to display clear patterns of migration, although nocturnal recruitment from deeper water resulted in a deepening of the depth of occupation then. The population was dominated by individuals <4 mm polar diameter, and large animals were confined to the upper water layers. These results are discussed with reference to possible spawning activities. Using published equations relating size to clearance rates, it was estimated that the population could remove up to 27% of integrated mesozooplankton standing stocks, and in excess of 100% (293%) at some depths.
The chromista
(Wiley Online, 2003) Maneveldt, Gavin; Keats, Derek
As a group, the chromists show a diverse range of forms from tiny unicellular, flagellates to the large brown algae known as kelp. Molecular studies have confirmed the inclusion of certain organisms once considered Fungi, as well as some heterotrophic flagellates. Despite their diversity of form and feeding modes, a few unique characters group these organisms.

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