Species Description: Cells of Prorocentrum lima are approximately oval, with the anterior narrower than the posterior, thus often egg-shaped (Figures 1-5). The cell is laterally compressed and composed of two valves with a small cluster of eight periflagellar platelets. The right valve has an indentation where the periflagellar area is found (Figures 2-4). The valves have numerous pores, except in the central area (Figures 3-5), where a large pyrenoid is present beneath the valves (Figure 2). There is a row of marginal pores at the valve periphery (Figures 4 & 5). The valves are smooth, except for the pores, which are reported as mucocysts rather than trichocysts (Zhou & Fritz 1993). A thorough morphological examination of specimens from many locations was carried out by Nagahama et al. (2011), who emended the description and illustrated the variability in cell outline. The nucleus is located in the posterior of the cell (Figure 1), and the species is photosynthetic, with a number of small brown chloroplasts (Figures 1 & 2). Because of widespread interest related to its toxicity, P. lima has been the subject of many genetic investigations, and GenBank http://www.ncbi.nlm.nih.gov lists nearly 200 nucleotide sequences for this species.
Habitat and Regional Occurrence: Prorocentrum lima is a benthic species that is most often associated with epiphytism on seaweeds, but is also free-living on sandy or muddy substrata as well as solid surfaces such as pilings, submerged lines, etc. It is most common in tropical and subtropical locations throughout the world, but frequently occurs in cold temperate locations such as Canada and the northern U.S. East coast (Maranda et al. 2007), and the coast of Norway (Throndsen et al. 2007). Its presence in the plankton must be considered as adventitious.
IRL Distribution: P. lima can occur throughout most of the year in the IRL, but since there is no consistent sampling for dinoflagellates in IRL benthic habitats, records of its presence depend on its adventitious occurrence in the plankton (e.g. Badylak & Phlips 2004).
Size: This species varies considerably in size as well as shape: 31-57µm in length; 20-46 µm wide.
Abundance & Growth: As Maranda et al. (2007) point out, quantitative evaluation of P. lima is difficult due to habitat complexity of this primarily benthic species. These authors found 103-104 cells per gram dry weight of substratum (brown algae, oyster cages, lines, buoys, etc.) from the coast of New England. Okolodkov et al. (2007) reported nearly 30,000 cells per gram of wet weight substratum from the Gulf of Mexico. Its growth rate is relatively slow. Faust (1993a) found 0.2-0.3 divisions per day, and Morton & Norris (1990) reported 0.6 divisions per day.
Reproduction: Normal population growth in P. lima is through asexual reproduction. However, a peculiar form of division has been documented by Faust (1993a), in which multiple divisions occur within a hyaline envelope, resulting in as many as 32 cells. These cells were non-motile and considered to be “division cysts”, a process that contrasts with normal cell division in which each daughter cell sheds the parental valves and forms a new theca. These observations are based on laboratory studies, and apparently have not been observed in natural populations, though Faust (1993a) suggests that their formation may be a means of surviving adverse environmental conditions. Isogamous sexual reproduction in P. lima was also described by Faust in a subsequent report (Faust 1993b) based on both natural and laboratory populations. After gametic fusion, a spherical, pale yellow hypnozygote cyst was formed, which had a smooth three-layered cell wall. Average cyst size was 70-75 µm, larger than most vegetative cells. In contrast with most other dinoflagellates, the cysts could germinate in a week or less, with meiosis of the germinating cell following excystment.
Toxicity: Prorocentrum lima is a toxic species. The primary toxins are okadaic acid (OA) and dinophysistoxin (DTX) and their derivatives. These toxins are responsible for diarrhetic shellfish poisoning (DSP) in humans. The amount and relative abundance of toxins varies among strains of P. lima (Morton & Tindall 1995; Bravo et al. 2001). According to Murray (2010), every culture of P. lima tested has been found to produce okadaic acid and its analogs in varying quantities. The abundance and associated toxicity of P. lima in the IRL, spatially and temporally, is uncertain.
Badylak, S & EJ Phlips. 2004. Spatial and temporal patterns of phytoplankton composition in a subtropical coastal lagoon, the Indian River Lagoon, Florida, USA. J. Plankton Res. 26: 1229-1247.
Bravo, I, Fernandez, ML & RA Martinez. 2001. Toxin composition of the toxic dinoflagellate Prorocentrum lima isolated from different locations along the Galician coast (NW Spain). Toxicon 39: 1537-1545.
Faust, M. 1993a. Alternate asexual reproduction of Prorocentrum lima in culture. 115-120. In: Smayda, TJ & Y Shimizu (Eds.). Toxic Phytoplankton Blooms in the Sea. Elsevier Science Publishers, Amsterdam.
Faust, M. 1993b. Sexuality in a toxic dinoflagellate, Prorocentrum lima. 121-126. In: Smayda, TJ & Y Shimizu (Eds.). Toxic Phytoplankton Blooms in the Sea. Elsevier Science Publishers, Amsterdam.
Maranda, L, Corwin, S & PE Hargraves. 2007. Prorocentum lima (Dinophyceae) in northeastern SA coastal waters. I. Abundance and distribution. Harmful Algae 6: 623-631.
Morton, SL & DR Tindall. 1995. Morphological and biochemical variability of the toxic dinoflagellate Prorocentrum lima isolated from three locations at Heron Island, Australia. J. Phycol. 31: 914-921.
Morton, SL & J Norris. 1990. Role of temperature, salinity, and light on the seasonality of Prorocentrum lima (Ehrenberg) Dodge. 201-205. In: Graneli, E et al. (Eds.). Toxic Marine Phytoplankton. Elsevier Publishing, New York.
Murray, S. 2010. Benthic Dinoflagellates. 213-259. In: Hallegraeff, G. et al. (Eds.). Algae of Australia: Phytoplankton of Temperate Coastal Waters. ABRS, Canberra and CSIRO. Melbourne, Australia.
Nagahama, Y, Murray, S, Tomaru, A & Y Fukuyo. 2011. Species boundaries in the toxic dinoflagellate Prorocentrum lima (Dinophyceae, Prorocentrales), based on morphological and phylogenetic characters. J. Phycol. 47: 178-189.
Okolodkov, YB, Campos-Bautista, G, Garate-Lizarraga, I, Gonzalez-Gonzalez, J, Hoppenrath, M & V Arenas. 2007. Seasonal changes of benthic and epiphytic dinoflagellates in the Veracruz reef zone, Gulf of Mexico. Aquat. Microb. Ecol. 47: 223-237.
Throndesn, J, Hasle, GR & K Tangen. 2007. Phytoplankton of Norwegian Coastal Waters. Almater Forlag, Oslo. 343pp. Zhou, J & L Fritz. 1993. Ultrastructure of two toxic marine dinoflagellates, Prorocentrum lima and Prorocentrum maculosum. Phycologia 32: 444-450.