Abstract. The morphology of dinoflagellate cysts (dinocysts) is related not only to the
genetics of the motile dinoflagellate from which it derives, but is also
dependent on a range of environmental factors including salinity, temperature
and nutrient status. Although this knowledge improves our understanding of
the drivers behind dinocyst morphological variations, it makes the taxonomy
governing their description somewhat complex. In basins such as the Black
Sea, where environmental change can be extreme and occurs on relatively short
(millennial) timescales, taxonomy becomes particularly challenging.
Morphological continua can be observed between described forms, displaying a
large range of intermediate phenotypes that do not necessarily correspond to
any genetic difference. As these morphological nuances may preserve
information about palaeoenvironments, it is important to find a systematic
method of characterising morphotypes. Here, we show a dinocyst matrix within
which dinocysts are described according to their similarity to (or difference
from) described forms based on key descriptive parameters. In the example set
out here, cyst shape and degree of process and/or ectophragm
development are taken as two key parameters in Pyxidinopsis psilata and Spiniferites cruciformis, and can allow the description of
intermediate forms even though the definitions do not overlap. We review some frequently occurring morphotypes and propose that using
matrices to show the gradual variation between endmember forms is the most
pragmatic approach until cyst–theca studies and genetic sequencing can be
used to demonstrate relationships between genotypes and morphotypes. As prior
studies propose salinity to be a primary driver of intraspecific variability,
the endmembers presented may represent salinity extremes within an overall
brackish environment. Although we cannot assign each morphotype to a value or
a range of an environmental parameter (e.g. salinity) as the different
morphotypes can occur in the same sample, using this matrix allows
preservation of information about morphological variability without creating
taxonomic categories that are likely to require alteration if genetic
evidence becomes available.
Algal blooms are natural phenomena that may cause human health problems, millions of dollars in losses and ecological disasters worldwide. Anthropogenic pressures like eutrophication may increase the frequency and intensity of these phenomena. The Black Sea is characterized by rapid changes in salinity and temperature in surface waters. In addition, it has suffered increasing environmental pressure from human activities. This work presents the first cultures of Gymnodinium aureolum to be isolated from the Black Sea. Morphological and phylogenetic analyses confirmed our strain as G. aureolum. The effects of temperature and salinity on growth were tested in experiments combining two temperatures and five salinities in 10 experimental treatments. This provides baseline data on the physiological adaption and acclimatization potential of the species to bloom under present and future climatic scenarios in the Black Sea. Gymnodinium aureolum grew exponentially in all experimental treatments, except for cultures at salinity 5. Growth rate increased significantly with increasing temperature reaching the maximum at 20 °C and salinity 15 (0.38 ± 0.02 d−1). This suggests an adaptation to the salinity and temperature of Black Sea waters and, together with previous records of G. aureolum in both water and sediments, supports the idea that this may be a bloom-forming population of G. aureolum.
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