VERTICAL DISTRIBUTION OF SEAWEED SPORES IN A WATER COLUMN OFFSHORE OF NORTH CAROLINA¹

Abstract

Differences in the vertical distribution of seaweed spores in a 20 m water column 30 km off the coast of North Carolina were documented. Spores were collected on plastic, and glass slides that were subsequently transferred to incubator cultures where germlings were grown and counted. Spores of green algae and bangiophycidean red algae were collected throughout the water column, whereas spores of brown algae and florideophycidean red algae occurred almost exclusively near the bottom. The occurrence of some kinds of spores in the upper water levels suggests relatively large dispersal shadows for those species. The taxa recovered in the upper levels were typically opportunistic organisms, many of them epiphytes. The collection of many Enteromorpha individuals in the upper and mid levels was of particular interest since locally this genus only occurs in abundance in shallow water habitats 35 km or more from the study site.

The settlement, attachment and establishment of marine algal spores

“…Similarly, Schonbeck & Norton (1979) referred to the oogonial sheaths around Pelvetia zygotes providing more buoyancy. Supporting evidence for differential settlement rates of algal spores and their influence on dispersal capability was provided by Amsler & Searles (1980) who found differences in the vertical distribution of seaweed spores in coastal waters; they suggested these differences indicated differences in evolutionary tactics of spore dispersal. Certainly the relatively large and dense embryospores of Sargassum, for example, sink rapidly (> 0.5mm s 1; Deysher & Norton, 1982) compared to the spores of many red algae, thereby increasing their chances of an early and more successful settlement.…”

A bank of microscopic forms on disturbed boulders and stones in tide pools

“…They maintain a persistent pool of propagules that quickly recruit on new substrate and would replenish the bank whenever they are destroyed by boulder overturning or grazing. Most of these species are ephemerals, with large dispersal shadows (Amsler & Searles 1980, Sousa 1984, Hoffmann & Ugarte 1985, Reed et al 1988. Enteromorpha clathrata and Blidingia minima -not found in the macroscopic vegetation, but whose propagules often appeared in the water -can also be ascribed to thls group.…”

Seaweed biogeography of the mid-Atlantic coast of the United States

“…Codium fragile subsp, tomentosoides (van Goor) Silva has moved south from Long Island Sound to the North Carolina coast in tess than 25 years (Seafles et al, 1984), demonstrating that the lack of substrate is not a serious problem to dispersal in that species. Studies of colonization in offshore habitats (Amsler & Searles, 1980;Peckol & Searles, 1983) indicate a limited ability of the dominant species in that habitat to colonize by spores. The whole question of dispersal and colonization by spores vs. vegetative fragmentation is unresolved and this could be an appropriate region in which to study it because of the patchy distribution of substrates and, therefore, the discontinuous populations of seaweeds.…”