Field and culture studies on the Tilopteridales (Phaeophyceae) in Newfoundland

Kuhlenkamp, Ralph (1990) Field and culture studies on the Tilopteridales (Phaeophyceae) in Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The family Tilopteridaceae (Tilopteridales, Phaeophyceae) consists of three monospecific genera of which two species, Tilopteris mertenaii and Haplospora globosa, occur throughout the North Atlantic and Arctic Ocean. The third species, Phaeosiphoniella cryophila} is restricted to four localities in Newfoundland and, aside from its initial description, is little known. Both Phaeosiphoniella and Haplospora develop prostrate systems when their rhizoids come in contact with the substrate. These prostrate discs are functionally, and to some degree also morphologically, equivalent to crusts of species of the Sphacelariales or Scytosiphonales and serve as perennating structures during the summer. Upright filaments are produced from the prostrate systems only under winter conditions. Combined culture and field studies showed that uprights of Phaeosiphoniella are restricted to water temperatures of less than 10°C and light intensities of less than 8 μmol m⁻² s⁻¹ while prostrate discs withstand up to 20°C. -- Phaeosiphoniella reproduces exclusively through fragmentation and abscission of branch systems. The sporadically occurring antheridia or sporangia are functionless and the reproductive system is more reduced than in the other two species. -- Quantitative DNA fluorometry confirmed that Tilopteris and Phaeosiphoniella exhibit only one level of ploidy, whereas the two generations in Haplospora show different ploidy levels, although the number of chromosomes does not change. -- The reduced life cycles shown in Tilopteris and Phaeosiphoniella might indicate that both species are derived forms and have formerly possessed a sexual life cycle with an alternation of generations such as seen in Haplospora. This study suggests that Phaeosiphoniella represents a relic species which exists only at the extremes of its former area of distribution. Members of the Tilopteridaceae, especially Phaeosiphoniella, might be regarded as species with weak competitive capabilities, but with the ability to live in areas of high physical disturbance where competition with other algae is low.

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