Carol A. Simon

Spionid polychaetes infesting cultured abalone Haliotis midae in South Africa

A study was conducted to identify and quantify the spionid polychaetes that infest cultured abalone Haliotis midae at aquaculture facilities on the west (Farm A), south (Farms B and C) and east (Farm D) coasts of South Africa. The relationship between total intensity of infestation by the polydorids and the condition of their hosts at Farms A, B and D were also measured. The abalone were infested by Dipolydora capensis, Polydora hoplura and a Boccardia sp. However, the intensity of infestation differed among sites, suggesting that both geographical and farm-specific conditions may influence species composition. Total intensity of infestation has a negative impact on the condition of abalone at the three farms tested, but at Farms A and B, this effect was reduced in larger abalone.

The genus Boccardia (Polychaeta: Spionidae) associated with mollusc shells on the south coast of South Africa

Three species of Boccardia ( B. polybranchia, B. pseudonatrix and B. proboscidea ) were associated with mollusc shells on the south and south-east coasts of South Africa. Boccardia polybranchia was widely distributed along the coast and falls within the known distribution range of this species. Comparisons with material from other, international, locations showed that some specimens have been misidentified. No characters could be found to characterize distinct species for different regions within the range of B. polybranchia , as currently recognized. Boccardia pseudonatrix was found only at the most eastern site, increasing its known distribution range. Boccardia proboscidea , a non-indigenous species, was found only on abalone farms and was most abundant in the west.

Population structure and growth of polydorid polychaetes that infest cultured abalone Haliotis midae

Polydorid polychaetes can infest cultured abalone thereby reducing productivity. In order to effectively control these pests, their reproductive biology must be understood. The population dynamics and reproduction of polydorids infesting abalone Haliotis midae from two farms in South Africa is described using a length-based, age-structured model. Shells were infested mainly by introduced Boccardia proboscidea. Polydora hoplura and Dipolydora capensis were also present but in numbers too few to identify factors influencing infestation. At both farms, B. proboscidea lived for a minimum of 12 months. Growth rate, size at maturity, maximum size, infestation intensity, recruitment, percentage of the population brooding and mortality appear to be affected by abalone feeding regime and water temperature, and these factors need to be considered in controlling infestation. Brooders and recruits were present throughout the year, but increased significantly during mid- to late winter/early spring when water temperature and day length increased. Treatment measures should therefore be implemented throughout the year but with increased effort when water temperature increases.

Infestation of the abalone, Haliotis midae, by the sabellid, Terebrasabella heterouncinata, under intensive culture conditions, and the influence of infestation on abalone growth

Abstract Heavy infestation by the shell-infesting sabellid, Terebrasabella heterouncinata, has been shown to cause a reduction in the growth rate and marketability of cultured abalone. This worm is endemic to South Africa and the locally cultured abalone, Haliotis midae, are under constant threat of infestation. An understanding of factors that influence abalone growth and sabellid infestation levels under intensive culture conditions is therefore imperative to controlling infestation levels. Abalone were held on an abalone farm at stocking densities of 18%, 23% and 28% of the surface area available to the abalone. They were fed kelp or a pelleted diet, Abfeed™. Their growth and infestation levels were monitored for 14 months. Within the range of abalone sizes used for this study kelp-fed abalone grew significantly better than Abfeed™-fed abalone (F1,197=7.99; P≤0.005), while stocking density had no effect (F2,196=1.41; P≤0.246) on growth. Abalone that became infested grew at the same rate as those that did not (0.09≤P≤1). No growth-limiting effect of infestation was detected. There was no effect on total intensity (i.e., the total number of worms per sample of 60 abalone; 0.41≤P≤1 and 0.17≤P≤1), or prevalence (i.e., the percentage of infected abalone within a sample; 0.50≤P≤1 and 0.19≤P≤1) of infestation by diet and stocking density, respectively. There was a significant positive coefficient of correlation of 86.2% between the level at which an increase in total intensity starts, and the average increase in total intensity per day (F1,10=62.2; P≤0.0001). A regression model is presented to estimate total intensity based on prevalence. The greatest increase in total intensity levels coincided with the onset of spring, and a possible seasonal component to the reproduction of this sabellid is discussed.

Polydora and Dipolydora (Polychaeta: Spionidae) Associated with Molluscs on the South Coast of South Africa, with Descriptions of Two New Species

ABSTRACT Wild molluscs from five sites and farmed oysters and abalone from one site each along the south coast of South Africa were examined for shell-boring Polydora and Dipolydora. One new species each of Dipolydora and Polydora are described. D. keulderae sp. n. belongs to the D. barbilla / D. bidentata group and was present at all the sites sampled. P. dinthwanyana sp. n. belongs to the P. ciliata / P. websteri group and was recorded only at Haga Haga, the most easterly site sampled. In total, five Dipolydora species (D. cf. armata, D. capensis, D. cf. giardi, D. keulderae and D. normalis) and three Polydora species (P. cf. ciliata, P. dinthwanyana and P. cf. hoplura) were recorded. All but D. normalis bored into mollusc shells and while the rest of the worms showed no host preference, the larger, subtidal Haliotis spp. and Turbo sarmaticus usually hosted the largest number of species at each site. D. normalis and P. dinthwanyana were recorded only at Haga Haga, P. cf. ciliata only at Port Elizabeth and the rest at all the sites. This study extends the known distributions of D. normalis, D. cf. armata and P. cf. ciliata in South Africa.

Lost in translation? Standardising the terminology used in marine invasion biology and updating South African alien species lists

Confusion between terms and ambiguities among definitions have long plagued the field of invasion biology. One result is disruption in flow of information from researchers to policy-makers and managers who rely on science to inform regulatory frameworks and management actions. We reviewed the South African marine biology literature to quantify the current usage of terminology describing marine invasions and found a variety of terms in use, few of which are defined when used. In response, we propose standard terminology that aligns with international practice. We then interpreted the Blackburn unified framework for biological invasions within the marine context and used this as a transparent way to apply the standardised terms to an updated list of marine alien species for the country. This resulted in the recognition of 36 alien and 53 invasive species within South Africa. Most notably, follow-up research is required to confirm the status of at least 11 listed species, the majority of which have been recorded only once, or not in the past 25 years. It is hoped that by standardising terminology, marine science in South Africa will better support authorities charged with managing the threat posed by marine alien species.

Observations on the composition and larval developmental modes of polydorid pests of farmed oysters (Crassostrea gigas) and abalone (Haliotis midae) in South Africa

This study provides preliminary insights into how the culture method of molluscs and the larval developmental mode of pest polydorids may determine which species become pests. A total of 10 species were identified on oysters and abalone in offshore and oysters in onshore culture on the west coast of South Africa. One-factor PERMANOVA showed that abalone and oysters cultured offshore housed similar communities of worms, but that they differed significantly from the communities housed by oysters cultured onshore. Oysters from onshore were infested mainly by Polydora hoplura, but also by Polydora cf. websteri and Boccardia pseudonatrix. All these species produce adelphophagic larvae or a mixture of these and planktotrophic larvae. Adelphophagic larvae usually only emerge soon before they settle, which would probably enhance their ability to recruit locally and establish local populations. By contrast, worms from molluscs grown offshore were infested by high abundances of P. hoplura and lower abundances of up to five more species per individual host. All hatched broods observed with these female P. hoplura contained planktotrophic larvae which have a long planktonic phase before settling. This would presumably enhance their ability to reach hosts in the offshore.

Polydorid polychaetes (Spionidae) on farmed and wild abalone (Haliotis midae) in South Africa: an epidemiological survey

Although there has been an increase in our understanding of the shell-boring polydorids that infest abalone Haliotis midae in South Africa, abalone from a limited number of farms, and wild populations from east of Cape Agulhas only, have been examined. To gain further knowledge and a more complete understanding of the local distribution of polydorids, we examined up to 30 abalone from each of 14 farms in the Northern, Western and Eastern Cape provinces, and five wild sites in the Western Cape, west of Cape Agulhas. Farm and wild communities were significantly different from each other (ANOSIM, r = 0.632, p < 0.002) and Bray–Curtis cluster analysis showed that most farms clustered separately from wild sites. Boccardia proboscidea was present on all but one of the infested farms, whereas some were also infested by Dipolydora capensis. By contrast, D. capensis was present at all wild sites sampled, whereas B. proboscidea was absent from these sites. Polydora hoplura, a common shell-boring pest, was present at only two farms and two wild sites. There appeared to be some exchange of polydorids among farms and between farms and wild abalone. The farm on the East Coast did not cluster with any other sites, indicating a unique composition of polydorids on that coast. No new, potentially problematic, species was encountered, although four species showed an increase in their known distribution.

The effect of diet and live host presence on the growth and reproduction of Terebrasabella heterouncinata (Polychaeta: Sabellidae)

Summary The effect of diet type and the presence or absence of a live host on the growth and production of eggs and larvae by Terebrasabella heterouncinata were quantified. Diet was shown not to have a significant effect on the time in which the worms on live hosts reached their maximum size. Diet did, however, influence the maximum size and consequently the growth rate of worms, which were larger and grew faster on kelp-fed abalone than on those fed a commercial pellet diet. Despite diet having no effect on fecundity and offspring size, kelp-fed worms matured earlier. The maximum size of kelp-fed worms was unaffected by the absence of a live host, suggesting that the worms do not rely on the host for food. The absence of a live host reduced the growth and sexual maturation rates of worms. There was no difference in the size of offspring in the two treatments, but fewer worms matured sexually and fewer broods were produced on “shells only” than on live hosts. The lower growth rate and reproductive output of worms on “shells only” may be due to the diversion of energy from growth and reproduction to burrow expansion.

Extracellular digestion in two co-occurring intertidal mussels (Perna perna (L.) and Choromytilus meridionalis (Kr)) and the role of enteric bacteria in their digestive ecology

The style enzymes and enteric bacteria of two intertidal mussels, Perna perna (L.) and Choromytilus meridionalis (Kr), were tested for activity on ten structural and storage carbohydrates. Both mussels digested the storage carboyhydrates amylose, glycogen and laminarin, and the structural carbohydrate carboxymethyl cellulose (CMC). C. meridionalis broke down the digested storage carbohydrates with equal efficiency, while P. perna digested laminarin and glycogen more efficiently than amylose. P. perna produced large volumes of enzymes with low dissociation rates, while the opposite was true for C. meridionalis. As a result, P. perna released significantly more glucose (ANOVA: P<0.05) from all substrates, even though it had significantly lower specific enzyme activities (P<0.05). Likewise, both mussels could digest bacteria isolated from their guts, but P. perna digested more bacterial strains, more efficiently, than C. meridionalis. In contrast, C. meridionalis housed larger populations of gut bacteria which digested carbohydrates more efficiently than those from P. perna. Mixed bacterial cultures from both mussels showed consistently high activity on storage carbohydrates. Activity was consistent, but low, on two structural carbohydrates (CMC and mannan) but sporadic on the other structural compounds (carrageenin, fucoidan and xylan). Electron microscopy showed that both mussels housed two distinct populations of bacteria: resident spirochaete bacteria (presumably Cristispira spp) in the style, and a mixture of rod, coccoid and filamentous bacteria associated with the gut contents. The sporadic presence of bacteria which digest most structural carbohydrates, and their association with the gut contents, indicate that these bacteria are transient. This means that the association between the mussels and their enteric bacteria is incidental rather than obligatory. The spirochaete bacteria in the style have an obligate relationship with the mussels and may increase the amount of carbohydrases produced, but not the range of enzymes available to the host.