Alan Whittick

The effect of an artificial diet on the biochemical composition of the gonads of the sea urchin (Strongylocentrotus droebachiensis)

Green sea urchins (Strongylocentrotus droebachiensis), taken from the wild were fed on a grain-based artificial diet over a 9-week period. At intervals, the animals were harvested and the gonads analysed for proximate composition, lipid class distribution, fatty acid and carotenoid pigment compositions. During the feeding period the lipid content decreased and the moisture content increased. Meanwhile, the protein content was highest after 9 weeks of feeding on the artificial diet. Major non-polar lipid classes were triacylglycerol (TAG), free fatty acids (FFA) and sterols (ST) while dominant polar lipid classes were phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The content of PC was much higher than that of PE on week 0. However, PE became dominant on week 9 after feeding on the artificial diet. The fatty acids 14:0 and 16:0 were the major saturated fatty acids (SFA), consistently present in the total, non-polar and polar lipids of sea urchin gonads. Polyunsaturated fatty acid (PUFA) 20:5n-3 (eicosapentaenoic acid, EPA) was the highest on week 0 while 18:2 n-6 became dominant with increased feeding period with a concurrent decrease in the content of 20:5n-3. Further, 20:1n-15 was the major monounsaturated fatty acid (MUFA) at week 0, but its content decreased significantly (P<0.05) after introducing the artificial diet. The total carotenoid content decreased by 50% at the end of the feeding period. Major carotenoids present in sea urchin gonads were echininone and β-carotene. The relative content of echininone was lowest at week 0, but increased when the urchins were fed on the artificial diet with a simultaneous reduction in β-carotene levels. The study demonstrates the importance of feed supply in lipid composition of sea urchin gonads.

Spatial and temporal distributions of dominant epiphytes on the stipes of Laminaria hyperborea (Gunn.) Fosl. (Phaeophyta: Laminariales) in S.E. Scotland

Abstract The epiphytic flora of the stipes of Laminaria hyperborea (Gunn.) Fosl. at St. Abbs Head, Berwickshire, Scotland has been examined. Four species Palmaria palmata (L.) O. Kuntze, Ptilota plumosa, (C. Ag.) Huds., Membranoptera alata (Huds.) Stackh., and Phycodrys rubens (L.) Batt. make up > 95% of the epiphyte biomass. The species show two distinct patterns of zonation, one with depth the other with respect to position on the host stipe. Palmaria is found on the upper parts of the stipes at 1 and 2 m depth, with the three other species found lower on the stipe. At 6 m depth Ptilota occupies the position on the stipe where Palmaria had occurred in the shallower water. In the deepest samples (12m) Ptilota was absent and its position on the stipe was occupied by Phycodrys and Membranoptera. This zonation is reflected in the biomass of the epiphyte species, Palmaria is restricted to the shallow waters, Ptilota reaches its greatest biomass at intermediate depths while Membranoptera and Phycodrys are most abundant at 6 m and below. Palmaria, Membranoptera, and Phycodrys show similar patterns of seasonal changes in epiphyte biomass with a peak in September and a decline in winter. Ptilota, which in the British Isles is considered to be a species of northern distribution, shows an earlier peak biomass and a correspondingly earlier decline in abundance.

Effect of season and artificial diet on amino acids and nucleic acids in gonads of green sea urchin Strongylocentrotus droebachiensis

The content of total and free amino acids (FAA) in green sea urchin (Strongylocentrotus droebachiensis) gonads varied with the season and feeding on an artificial diet. Glycine was the dominant amino acid in each season contributing 12.9-16.6% to the total amino acid (TAA) content, peaking in the spring. In the FAA profile, glycine accounted for 30.3-61.4% in different seasons. A grain-based artificial diet had noticeable effects on the total and FAA compositions of S. droebachiensis. Although, glycine was the dominant amino acid in the TAA profile during early harvesting, tyrosine in gonads became more dominant on week 9 of feeding. Furthermore, glycine was the dominant amino acid in the FAA pool after feeding the artificial diet. The total FAA content in the gonads increased significantly (P<0.05) from 20.6 on week 0 to 180.6 mg/g dry mass tissue on week 3. There were no significant (P<0.05) changes between week 6 and week 9. Deoxyribonucleic acid (DNA) content exceeded that of ribonucleic acid (RNA) in each season, while in cultured urchins, RNA content exceeded that of DNA only on week 6. The RNA/DNA ratio was significantly increased in the summer, whereas this ratio was increased up to week 6 followed by a decrease on week 9 in cultured counterparts.

A re‐examination of the morphology and reproduction of Nothocladus lindaueri (Batrachospermales, Rhodophyta)

The vegetative morphology and reproduction of the freshwater rhodophyte Nothocladus lindaueri Skuja [=Batrachospermum lindaueri (Skuja) Necchi et Entwisle] were examined by light and electron microscopy. It was confirmed that this alga has a typical batrachospermalean pit plug with two cap layers, the outer one of which is domed. During elongation of hair cells, the primary wall is broken, forming a basal collar. Hair cells have a single nucleus and abundant Golgi bodies, en‐doplasmic reticula (ER) and vesicles. Dividing apical cells of the fascicles have a nucleus with art adjacent zone of exclusion, the latter containing a single polar ring. Branched trichogynes and fertilized carpogonia are shown for the first time in this species. Carpogonial branch and involucral cells contain a prominent axial nucleus, proplastids, ER and vesicles. The pit plugs disintegrate among these cells leaving open pit connections. Carpogonia have plentiful mitochondria and vesicles. The wall at the trichogyne apex is thickened and densely stained. The carposporophyte centre consists of a mass of fusion cells with open pit connections, and indeterminate gonimoblast filaments arise from this mass. The combination of a symmetrical carpogonial base, a carposporophyte centre consisting of a mass of fusion cells, and exclusively indeterminate gonimoblast filaments appears to be unique among the members of the Batrachospermaceae. The specimen of N. lindaueri contains epiphytic filaments of Audouinella meiospora producing both spermatangia and monosporangia. Spermatium formation in N. lindaueri remains unknown.

The reproductive ecology of Plumaria elegans (Bonnem.) Schmitz (Ceramiaceae: rhodophyta) at its northern limits in the western Atlantic

Abstract The phenology of Plumaria elegans (Bonnem.) Schmitz was studied in insular Newfoundland, Canada, the northernmost known limit of its distribution in the western Atlantic. The population is composed of triploid parasporangial plants with an apomeiotic life cycle. Mitotic parasporangia are produced during summer and autumn, but may be found all year round. Culture experiments show that growth and reproduction are primarily controlled by water temperature.

Olpidiopsis antithamnionis n. sp. (Oomycetes, Olpidiopsidaceae), a parasite of Antithamnion floccosum (O. F. Müll.) Kleen from Newfoundland

SummaryOlpidiopsis antithamnionis n. sp. (Oomycetes, Olpidiopsidaceae) parasitic on Antithamnion floccosum (O. F. Müll.) Kleen (Rhodophyta, Ceramiaceae) is described from three sites in Newfoundland, Canada, and from culture.Axial cells of the main and determinate branches of the host are the primary sites of fungal attack, although tetrasporangia and rhizoidal cells are also susceptible. Successful re-infection of A. floccosum was achieved in the laboratory although A. boreale and the trailliella-phase of Bonnemaisonia hamifera, both occurring with A. floccosum in the field, were immune. Regeneration of the host cells was observed, a phenomenon not previously reported in the fungal parasitism of other filamentous benthic marine algae.

Aspects of the life history of Rhodophysema elegans (Rhodophyta, Peyssonneliaceae)

The life history of Rhodophysema elegans is described from laboratory culture and the field in Newfoundland, Canada. Sexual plants are lacking and tetraspores germinate to produce new tetrasporangial plants. Approximately 30–35 chromosomes were counted in vegetative cells of successive generations. There was no evidence of chromosome pairing in the early stages of division of tetrasporangial initials, indicating that the tetrasporangia are apomeiotic.