Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsPeter KornmannDeceased.Formerly at the Biologische Ansfalt Helgoland, Meeresstaation, D-2192, Helgoland, Germany

This investigation complements two previous publications by Kornmann & Sahling [1977, 1983]. The paper summarizes floristic changes that have taken place in the marine macroalgal flora of Helgoland, North Sea, over the past 100 years. Moreover, taxonomical and, partly, life history data are given on 5 genera of green algae, e.g.Ulva, including the description of a new species,Ulva tenera; 5 genera of brown algae, e.g.Fucus ceranoides, Sargassum muticum, both species being new records for Helgoland; and 6 genera of red algae, e.g.Porphyra; Mastocarpus stellatus, which is also a new record for Helgoland.)

Acrochaete wittrockii (Wille) Nielsen is a heteromorphic diplohaplont. The haplophase consists of isomorphic, dioecious filamentous epiphytes on brown algae. Several generations follow each other by triflagellate zoospores from spring to early summer. By late summer and throughout autumn, quadriflagellate zoopores are produced by the epiphytic thalli; they give rise to male and female gametophytes of a globular, pseudoparenchymatic appearance in culture. The gametophytes produce anisogamic biflagellate gametes which, after gametic union, develop into diploid unicellular sporophytes. After 6–7 days, the sporophyte produces triflagellate zoospores, repeating the life history when germinating on brown algal hosts. Alternatively, triflagellate zoospores which settle on the bottom of petri dishes, develop into unicellular, autonomous sporangial plants. Their triflagellate spores repeat the epiphytic stage on brown algal hosts, or the sporangial plant cycle on non-living substrate, respectively.

This revision of sevenPorphyra species of Helgoland was based on a study of the structure of their fertile thalli and the behaviour of their spores. Regarding the reproductive organization the species may be arranged in two groups.P. leucosticta andP. purpureo-violacea are obligate monoecious species. Asexual thalli have never been observed in the field. The other five species are generally dioecious. Isomorphic sexual thalli and asexually propagating ones are mixed in uniform populations. Carpospores originating from sexual fusion develop into the diploid Conchocelis phase. Sporangia of asexual plants, though homologous in formation, produce spores of different kinds: aplanospores that give rise to the vegetative thallus directly (inP. umbilicalis, P. insolita n. sp. andP. ochotensis) and spores that develop into haploid Conchocelis (inP. laciniata and inP. linearis). P. laciniata — formerly considered synonymous withP. purpurea — is an independent species.

Article Pilayella macrocarpa Foslie (Ectocarpales, Phaeophyceae) in Helgoland and the Rejection of Pilayella varia Kjellman was published on January 1, 1990 in the journal Botanica Marina (volume 33, issue 3).

In June 1988,L. pusillus was collected for the first time in the Helgoland area. On the basis of observations in cultures, Pedersen's hypothesis that the microthalli ofL. pusillus are identical with those of threePilocladus species is discussed. The general morphology as well as the shape and dimensions of the unilocular sporangia are clearly different inPilocladus andLitosiphon microthalli. Therefore, Pedersen's opinion cannot be accepted.

Because of significant differences in their morphologies and growth patterns Erythrocladia irregularis and E. subintegra cannot be considered congeneric. The frond of E. irregularis consists of branched filaments with free ends, whereas the thallus of E. subintegra represents an orbicular disc with marginal growth. Therefore a new genus, Sahlingia, is created to include E. subintegra.

Sorocarpus Pringsh. is a later synonym forBotrytella Bory. Four species of the genus are known from northern European coasts. Three of them are found at Helgoland (North Sea), type locality of bothBotrytella uvaeformis (Pringsh.) andB. reinboldii (Reinke). A third species, most frequently seen, still remains unnamed. Plants of similar habit, however, have been described from Japan. The type species for the genus,Botrytella micromora Bory, was originally published asEctocarpus siliculosus β.uvaeformis by Lyngbye. A sample from Danish waters proved to be identical with it. In a previous paper (Kornmann & Sahling, 1984), the life history of two species was studied and the investigation is now extended to include the other two, demonstrating the conformity of the four species with the genus characters as to morphological and developmental features.

Studies on the sexuality and the heteromorphous life cycle ofErythrotrichia ciliaris provided decisive criteria for the establishment of the genusErythrotrichopeltis (Kornmann, 1984). This genus was transferred by Wynne (1986) toPorphyrostromium Trevisan 1848. In the present studyErythrotrichia obscura, the original species of Berthold's (1882) classical observations on the sexuality of this genus, is incorporated toPorphyrostromium. Previously regarded as synonyms,Porphyrostromium ciliare (Carm. ex Harv.) Wynne andP. obscurum (Berth.) nov. comb. proved to be distinct species, differing both in the filamentous and in the peltoid phases of their life cycle. The relationship betweenP. ciliare andP. boryanum (Montagne) Trevisan, type species of the genus, may only be elucidated by future investigations on the basis of field collected material.

APorphyropsis-like epiphytic specimen found in the harbour of Helgoland was grown in culture and proved to be identical with the JapanesePorphyra yezoensis. Life history studies on this economically important alga resulted in some interesting and hitherto unknown details. The variability of the adult frond is fundamentally determined by the pattern of spore germination. Settled onChaetomorpha filaments, monospores elongate within 20 minutes; the epiphytic germlings are attached to the substrate by a typical basal cell and give rise exclusively to elongated fronds provided with a cuneate base. Unattached spores, however, germinate into buds with rhizoids; they develop into elongated elliptical to oval fronds provided with round or cordate bases. Only plants with male areas were observed in the cultures, butConchocelis was abundantly produced from cells of aged thalli. Grown in mussel-shells, the filamentous phase liberated conchospores for a long time.

Ontogenesis and reproduction of the Helgolandian taxa of the Erythropeltidaceae have been studied. In all species monospores are only produced from differentiated sporangia. FilamentousConchocelis-like stages have not been observed. Sexual reproduction was formerly demonstrated in the heteromorphous genusErythrotrichopeltis (Kornmann, 1984). Based on these features a revised classification for the family is presented.Porphyropsis imperfecta, a new species, is a widespread epiphyte in sublittoral habitats.

Ontogenesis and reproduction of the Helgolandian taxa of the Erythropeltidaceae have been studied. In all species monospores are only produced from differentiated sporangia. FilamentousConchocelis-like stages have not been observed. Sexual reproduction was formerly demonstrated in the heteromorphous genusErythrotrichopeltis (Kornmann, 1984). Based on these features a revised classification for the family is presented.Porphyropsis imperfecta, a new species, is a widespread epiphyte in sublittoral habitats.

In culture experimentsErythropeltis discigera (Berth.) Schmitz andErythrotrichia discigera Berth. proved to be heteromorphous stages in the life history of the same entity, incorporated into the new genusErythrotrichopeltis. There is no obligate alternation of generations, the peltoid and the trichoid phase both propagate asexually by monospores. In addition, the trichoid phase releases spermatia in abundance, while carpogonia cannot be distinguished from vegetative cells. Thus far, the present statements are in full accordance with Berthold's observations, made at Naples more than 100 years ago, which have, however, recently been challenged. Moreover, the cultivation experiments made supplement Berthold's results as to the post fertilization process. A few days after the appearance of spermatia, peltoid plants are met with among the filamentous ones: they obviously originate from carpospores. The transition of the peltoid to the trichoid phase, at first observed accidentally in 3-month old moribund cultures, was reconstructed on more than one occasion by designed experiments. This study was started with discoid plants isolated from crude cultures of sublitoral algae from Helgoland (North Sea). NeitherErythrotrichia discigera Berth. norErythropeltis discigera (Berth.) Schmitz were ever found in the field around Helgoland. Recognized by Batters to be identical withBangia ciliaris Carmichael, the name of the typical representative of the new genus isErythrotrichopeltis ciliaris (Carm. ex Harv. in Hook.) nov. comb.

Complementary to a previous publication (Kornmann & Sahling, 1977), this investigation deals mainly with microscopic algae occurring in the rocky littoral of Helgoland island (North Sea). Based on the results obtained from cultivation experiments, the heterogeneousUlvella-complex of Dangeard has been rearranged and partly included in a new genusStromatella, andPlanophila respectively. The life history ofChlorocystis cohnii proved to be heteromorphic, the zygotes developing into a Codiolum-sporophyte. Also inHalochlorococcum marinum, some of the biflagellate swarmers give rise to Codiolum-like cells.Chlorocystis andHalochlorococcum, up to now members of the Chlorococcales, are incorporated into the new Codiolophycean order, Chlorocystidales. Three newHalochlorococcum species are described, the epiphytic"Chlorochytrium" moorei also being combined with this genus. Supplementary observations on some crustose red algae from transparent substrates are included in this study, as well as findings of some species not previously reported for the Helgoland area.

The vesicular thallus ofHalicystis is generally embedded in crusts of coralline algae by a rhizoidal part. Only in former unsuccessful attempts to elucidate the development ofHalicystis has this fact been regarded as being important. Starting fromDerbesia zoospores, the gametophyteHalicystis was attained in free culture. These vesicles, however, are unlike those of the natural plants in morphological aspect: they develop as a local increase of a rhizoidal filament. To grow into vesicles of natural shape in culture, the zoospores ofDerbesia need a calcareous substratum, e. g. fragments of oyster-shell.

The vesicular thallus ofHalicystis is generally embedded in crusts of coralline algae by a rhizoidal part. Only in former unsuccessful attempts to elucidate the development ofHalicystis has this fact been regarded as being important. Starting fromDerbesia zoospores, the gametophyteHalicystis was attained in free culture. These vesicles, however, are unlike those of the natural plants in morphological aspect: they develop as a local increase of a rhizoidal filament. To grow into vesicles of natural shape in culture, the zoospores ofDerbesia need a calcareous substratum, e. g. fragments of oyster-shell.

Shell-boring microthalli in Helminthocladia and Scinaia (Nemaliales, Rhodophyta). Spores shed from pink mussel shells were shown to develop into branched monosiphonous thalli, their filaments penetrating into shell fragments. Isolates from four single germlings were cultivated. Two of these produced gametophytes ofHelminthocladia andScinaia; the others have so far only reproduced by tetraspores or monospores. Evidently the microthalli of some genera of the Nemaliales — which are, with the exception ofNemalion multifidum, known only from cultures — are shell-inhabiting and have therefore not been found in nature. The adult algae occur mainly on shells and CaCO3 substrates. Until the beginning of the century,Helminthocladia andScinaia frequently occurred at Helgoland, but they have not been found there for more than 50 years. Their microthalli, however, are still present as shell-boring algae. This study is intended to stimulate similar ones in other genera of the Nemaliales so as to obtain a broader basis for discussion of systematic and phylogenetic relationships.