J. McLachlan

BONNEMAISONIA HAMIFERA HARIOT IN NATURE AND IN CULTURE23

In culture tetraspores of the sporophyte (Trailliella intricata) of Sonnemaisonia hamifera gave rise to male gametophytes only. In the Gulf of St. Lawrence tetrasporangia occur annually during the autumn, but mature gametophytes have not been recorded. However, gametophytes with antheridia were found during the winter on the Atlantic coast of Nova Scotia. Both phases are capable of vegetative propagation, and this is probably the usual method of reproduction in nature.

ENDOPHYTIC ALGAE OF CHONDRUS CRISPUS (RHODOPHYTA). III. HOST SPECIFICITY1

Susceptibility of rhodophycean macroalgae to infection by the green endophytes, Acrochaete operculata Correa & Nielsen and A. heteroclada Correct & Nielsen was studied. Cross‐infection experiments showed that A. operculata is host specific and developed only in sporophytic fronds of Chondrus crispus Stackh. and Iridaea cordata (Turn.) Bory. Although A. operculata penetrated equally the multilamellar outer cell wall of sporophytic and gametophytic fronds of C. crispus, subsequent development was arrested in the gametophytic fronds. Susceptibility of the sporophytic phase of C. crispus was detected early in the development of the host, at a discoid stage that is structurally distinct from the adult fronds. The evidence strongly suggests that host specificity in A. operculata is determined by cell‐wall composition of the hosts, likely the carrageenan fraction. In contrast, A. heteroclada was not host specific, infecting all offered hosts, including carrageenophytes and agarophytes. Germination occurred on the surface of the hosts and led to the development of an epiphytic stage. Subsequent penetration in many cases involved total displacement of cortical tissue in the infected frond.

ANTIALGAL ACTIVITY OF SOME SIMPLE PHENOLS1

The antialgal activity of a number of simple phenols was examined for their effect on the growth of 7 species of unicellular marine algae. The 3 knoiun algal phenols, 5‐bromo‐3,4‐dihydroxybenzaldehyde; 2,3‐dibromo‐4,5‐dihydroxybenzylalcohol, and 3,4‐dihy‐droxyphenylethylamine, were highly toxic as were other ortho dihydroxy compounds. Monohydroxy compounds were notably less toxic. Skeletonema costatum and Olisthodiscus sp. were the most sensitive organisms examined and Dunaliella tertiolecta was the most resistant. Possible ecological implications of these results are discussed.

Gracilaria (Gigartinales, Rhodophyta) and productivity☆

Gracilaria is a genus with a large number of species, many of which have been utilized for a variety of purposes. The chaotic state of the intraspecific taxonomy is a major deterrent in relating information and studying this genus. The majority of species occur in warm-water and tropical habitats, although the greatest standing stocks, usually as free-living populations, are known from temperate areas. High levels of production have been reported for experimental systems, but only over relatively short periods of time. Under field conditions, estimates have indicated at best modest rates of production. Production can be limited by a number of factors, but temperature and nutrients, especially nitrogen, are likely the most commonly limiting elements; light is probably of secondary importance. It is suggested that there is considerable potential within the genus for attaining high rates of growth and increasing production. To achieve these, however, it will be necessary to manage species of Gracilaria under natural conditions.

Occurrence of Prorocentrum lima, a DSP toxin-producing species from the Atlantic coast of Canada

A species of Prorocentrum (Dinophyta, Prorocentrales), isolated from a phytoplankton net sample from the Atlantic coast of Nova Scotia, has been brought into unialgal culture. The sample was collected at an aquaculture site immediately following an incident of diarrhetic shellfish poisoning (DSP) due to the consumption of contaminated mussels. This clonal isolate has been identified as P. lima, based on its morphological characteristics. Analysis of the culture extract, using high performance liquid chromatography (HPLC) with fluorescence detection, indicated the presence of the DSP toxins, okadaic acid (OA) and dinophysistoxin-1 (DTX-1).

Endophytic algae of Chondrus crispus (Rhodophyta). V. Fine structure of the infection by Acrochaete operculata (Chlorophyta)

The sequence of events taking place during infection of the algal host Chondrus crispus by the algal endophyte Acrochaete operculata was characterised at the ultrastructural level. Infection required settlement of quadriflagellate zoospores on the outer cell wall of the host. The host outer cell wall did not represent a barrier against penetration by the endophyte, which digested its way through. The extent of further spread of A. operculata in C. crispus was determined by the life-history phase of the host. In sporophytic fronds, colonisation of inner tissues occurred by digestion of the intercellular matrix, and infection spread throughout the frond. In gametophytic thalli, infection remained localised, forming a characteristic papule. In spite of these differences, degenerative changes at the cellular level were similar in the two phases of the host. Damage was caused by compression and by penetration of host cells. Final breakdown of the host resulted from the combined effects of A. operculata and bac...

Population structure of Chondrus crispus Stackhouse (Gigartinaceae, Rhodophyta) along the coast of Prince Edward Island, Canada: distribution of gametophytic and sporophytic fronds

Abstract Chondrus crispus Stackhouse populations in sublittoral Prince Edward Island are composed of both gametophytes and sporophytes. The overall ratio of phases is ≈ 1:1. Although there were considerable local variations in the distribution of these two generations, the 1:1 ratio is in contrast with previous reports of gametophytic : sporophytic ratios for C. crispus . It is proposed that because of the soft friable substratum disturbance affects the sublittoral biotic community and results in extensive removal of both fronds and plants of C. crispus . The evidence suggests that the gametophytic : sporophytic ratio of fronds in populations of C. crispus in Prince Edward Island results from stochastic events, with both generations having equal chances of becoming established.

Ecological studies of the alga, Acanthophora spicifera (Vahl) Børg. (Ceramiales: Rhodophyta): Vegetative fragmentation☆

Abstract The propagation of Acanthophora spicifera (Vahl) Borg. was studied on a fringing-reef platform at Galeta Point, Caribbean Panama. Manipulative experiments and detailed descriptive data indicated that fragmentation accounted for this algas standing crop and distribution. Fragments were broken off by turbulence in the fore reef, transported by currents across a seagrass meadow, snagged, and attached or entangled in the back reef. Accumulations of ≈66 g (dry wt.)·m −2 occurred. A. spicifera was a major contributor to drift biomass, and, depending on prevailing current velocities, fragments entering the back reef had a 49 to 93% chance of recruiting. Higher current velocities (≈0.24m·s −1 ) decreased the ability of free-floating fragments to snag by decreasing the frequency of fragment-substratum contacts. 25% of the snagged fragments remained > 3 days, and fragments required Laurencia papillosa (Forsk.) Grev. or to another frond of Acanthophora spicifera . Fragments were unable to recruit into plots of Thalassia testudinum Bank ex Konig and Sims. Tetrasporic plants were common, comprising as much as 96% of fore-reef and 80% of the back-reef populations. In October, 3% of the fore-reef population had cystocarps; otherwise, no other gametophytes were found. The percentage of spore-bearing tetrasporophytes was significantly greater in the Laurencia zone than in the fragment-derived Acanthophora zone. Vegetative fragmentation was demonstrated as an effective means of propagation, while the ecological significance of tetraspores was unclear.

Biology of Furcellaria lumbricalis (Hudson) Lamouroux (Rhodophyta: Gigartinales), a commercial carrageenophyte

Information on the commercially utilized marine red alga Furcellaria lumbricalis is summarized from published sources. Biological aspects under discussion include: nomenclature, taxonomy, morphology, development and life history, distribution, phenology, ecophysiology, growth and resource management. A brief history of the utilization of this species, and an account of its chemical constituents including the hydrocolloid furcellaran are also presented.

Benthic marine algal flora of the north shore of Prince Edward Island (Gulf of St. Lawrence), Canada☆

Abstract A seaweed community along 60 km of shoreline in the southern Gulf of St. Lawrence has been studied for 5 years. Because of severe ice action along the shores, the algal flora is largely restricted to subtidal levels, which are accessible only during the ice-free months, April to early December. A total of 52 Rhodophyta, 50 Phaeophyta, 19 Chlorophyta and 5 Cyanophyta was identified, mostly occurring between mean low water and 10 m depth. The normally intertidal dominants Focus vesiculosus L. and Chondrus crispus Stackh. flourish at depths of 0–2.5 m and 2.5–5 m, respectively. Chondrus and Furcellaria lumbricalis (Huds.) Lamour. co-dominate the algal benthos at 5–7.5 m, and F. lumbricalis becomes prevalent at 7.5–10 m. Phyllophora truncata (Pallas) A. Zin. and Phyllophora pseudoceranoides (Gmel.) Newr. & A. Tayl. are the main perennials at 10–15 m, and often at 15–20 m as well. Below 15 m, the flora diminishes markedly, and at 20–25 m consists chiefly of Agarum cribrosum (Mert.) Bory, crustose corallines and Polysiphonia urceolata (Lightf. ex Dillw.) Grev. Laminarians other than Chorda occur only as scattered plants or small patches and do not exceed 1 m length. The algal community is relatively undiversified and is especially deficient in green algae. Despite higher surface-water temperatures during summer, the flora is essentially a cold-water one as is indicated by both composition and low R/P and (R+C)/P ratios of 1.06 and 1.45, respectively.