Holdfast

Abstract: We present estimates of local population abundance, distribution and habitat prefer- ence for 2 European seahorse species, Hippocampus guttulatus and H. hippocampus. We predicted that these sympatric species would partition their habitat into 2 broadly defined habitat types: com- plex vegetated habitats and sparsely vegetated sand flats. We sampled populations using underwa- ter visual census techniques over landscape (100s to 1000s m) and microhabitat scales (<1 m). Over landscape scales, we estimated abundance and quantified habitat associations using generalized linear models. Over microhabitat scales, we tested for holdfast (attachment site) preferences using selection indices. Both species were patchy in distribution, but H. guttulatus mean density (0.073 ind. m -2 ) was one order of magnitude greater than that of H. hippocampus (0.007 ind. m -2 ). At a landscape scale, H. guttulatus abundance was positively correlated with an index of habitat com- plexity, the percentage of substrate covered by flora and sessile fauna. Conversely, H. hippocampus used more open and less speciose habitats that were subjected to greater oceanic influences. At microhabitat scales, both species significantly preferred grasping holdfasts over barren surfaces, but the species differed in holdfast preferences: H. guttulatus grasped all prospective holdfast types with equal probability while H. hippocampus significantly avoided both fauna and flora that formed large colonies or tracts of dense vegetation. Patterns in habitat use were consistent with differences in morphology and foraging strategy. Despite similar life histories, these sympatric species may respond differently to disturbances that modify habitat structure and complexity over landscape or micro- habitat scales.

Abstract: Four areas containing different cell morphologies were mapped on Porphyra blades and five different cell types (i.e. tapered with long extensions, large and vacuolated, vegetative and dividing, and reproductive: males and females) were identified in them. Tissues from these areas were dissociated, and protoplasts and single cells were isolated from the dissociated tissue of each distinct region. Regeneration rates of the isolated cells and protoplasts (isolates) varied depending on their morphological type. Regeneration rates were lowest in cultured isolates from the area just above the holdfast (ca. 1 %) and increased gradually to over 80% in isolates from areas of vegetative and reproductive regions away from the holdfast. Four distinct morphological patterns were observed among the regenerating plants. Cells isolated from vegetative areas developed into leafy plants while in liquid culture, and into calli when grown on solid medium. Isolates from reproductive areas developed into either a long thin or short thick filamentous plant. Those from ripe patches of carposporangia developed into thin conchocelis filaments, while isolates from non-differentiated cells bordering the ripe reproductive patches developed into thick filaments resembling the morphology of conchosporangial branches. The blade of Porphyra appears simple as it consists of a single cell layer; however, it is complex both morphologically and physiologically.