Morphology and Phylogenetics of Benthic Prorocentrum Species (Dinophyceae) from Tropical Northwestern Australia

Abstract

Approximately 70 species of Prorocentrum are known, of which around 30 species are associated with benthic habitats. Some produce okadaic acid (OA), dinophysistoxin (DTX) and their derivatives, which are involved in diarrhetic shellfish poisoning. In this study, we isolated and characterized Prorocentrum concavum and P. malayense from Broome in north Western Australia using light and scanning electron microscopy as well as molecular sequences of large subunit regions of ribosomal DNA, marking the first record of these species from Australian waters. The morphology of the motile cells of P. malayense was similar to P. concavum in the light microscopy, but differed by the smooth thecal surface, the pore pattern and the production of mucous stalk-like structures and a hyaline sheath around the non-motile cells. P. malayense could also be differentiated from other closely related species, P. leve and P. foraminosum, despite the similarity in thecal surface and pore pattern, by its platelet formula and morphologies. We tested the production of OA and DTXs from both species, but found that they did not produce detectable levels of these toxins in the given culturing conditions. This study aids in establishing more effective monitoring of potential harmful algal taxa in Australian waters for aquaculture and recreational purposes.

Keywords: Prorocentrum; benthic dinoflagellates; phylogeny; taxonomy.

Figure 1

Map of the north Western coastline of Australia, showing the sampling location.

Figure 2

Light micrographs of Prorocentrum concavum BRM1. (a) Right lateral view showing the central pyrenoid (arrow) with a starch sheath (ring-like structure) and the posterior nucleus (n). (b) Mid cell focus: note the pusule (p) and nucleus (n). Scale bars = 10 µM.

Figure 3

Scanning electron micrographs of Prorocentrum concavum BRM1. (a–c) Right lateral views. (d–f) Left lateral views: note the apical collar (arrow). (g) Apical to right lateral view showing the periflagellar area and the lateral flattening. (h) Ventral to left lateral view showing the intercalary band and the cell flattening. (i) Platelets in the periflagellar area. (j,k) Detail of thecal surface: note the large (arrowheads) and small (arrows) pores. Scale bars represent 10 μM in (a–h), 5 μM in (i), and 2 μM in (j,k).

Figure 4

Light micrographs of Prorocentrum malayense BRM2. (a) Right lateral view showing the central pyrenoid (arrow) with a starch sheath (ring-like structure) and the posterior nucleus (n). Note the irregular mucous stalk-like structures at the apical cell end (arrowhead); (b–d) the same cell in different focal planes. Note the periflagellar area (arrow), the skin-like sheath (double arrowhead) and the posterior nucleus (n); (e) irregular mucous stalk-like structures at the apical cell end; (f) cell division inside a hyaline mucus cover; (g) cell leaving its skin-like sheath; (h) disembodied remains of the sheaths. Scale bars = 10 μM.

Figure 5

Scanning electron micrographs of Prorocentrum malayense BRM2. (a,b) Right lateral views. (c) Left lateral view. (d,e) Details of thecal surface: note the large (arrowheads) and small (arrows) pores. (f–h) Platelets in the periflagellar area. (f) Outside view. (g) View of the sagittal suture plane of the right thecal plate. (h) Inside view. Scale bars represent 10 μM in (a–d) and 5 μM in (e–h).

Figure 6

Scanning electron micrographs of Prorocentrum malayense BRM2 showing sheaths around the cells. (a) Several cells sticking together in mucus. (b) Note the empty sheaths. (c) Two cells with sheaths sticking together on top of an empty sheath. (d) Note the irregular mucous stalk-like structures at the apical cell end (arrow). (e) Cell leaving its skin-like sheath. Scale bars = 10 μM.

Figure 7

Maximum likelihood (ML) phylogenetic trees of Prorocentrum species/strains based on the D1–D3 region of LSU rDNA. Numbers at nodes represent posterior probabilities from Bayesian inference (BI) and bootstrap support values from maximum likelihood analysis based on 1000 pseudo-replicates. * represents 1 and 100 support values for BI and ML, respectively. Sequences obtained in this study are highlighted in bold.