AN INVESTIGATION OF THE VERTICAL DISTRIBUTION OF SELECTED BENTHIC MARINE ALGAE WITH A TIDE–SIMULATING APPARATUS1

The growth yields of 8 species of red and 4 species of green algae, collected from various vertical levels on the western Atlantic (New Jersey) shore, were investigated in a range of emersion-submersion regimes in the laboratory. The sinusoidal tide-simulating apparatus consisted of a plexiglass frame connected by a nylon thread to a rotating wheel, powered by an electric motor geared to make one revolution every 12 h. Inocula of settled spores on glass cover-glasses were placed at 6 levels on the frame and alternately raised out of, and lowered into, a seawater tank every 6 h with consequent subjection to 0, 18, 37, 58, 79, and 100% submergence regimes per tidal cycle. There was little correlation between the vertical position of a species on the shore in nature and its ability to grow as the percentage submergence per tidal cycle increased. All species tested grew best when continuously submerged, even those that are usually restricted to elevated positions on the shore in nature. The majority grew well in all regimes in which there was some submergence per tidal cycle, except for one sublittoral species (Callithamnion byssoides) whose growth decreased sharply as the percentage exposure to the air was increased.     

AN IN SITU STUDY OF RECRUITMENT,GROWTH AND SURVIVAL OF SUBTIDAL MARINE ALGAE: TECHNIQUES AND PRELIMINARY RESULTS12

Fouling plates (Plexiglas squares and concrete blocks) were bolted in a horizontal position to racks on the ocean floor at a depth of 12 m. Some of these were periodically taken from the sea, subjected to nondestructive microscopic survey in the laboratory, and then replaced. Others were: a) left undisturbed as controls; b) variously caged to exclude larger predatory animals; or, c) had sediment removed from them at intervals. Populations developing on the periodically surveyed plates were similar to those on undisturbed plates. Populations on undisturbed plates were significantly different from those on partially caged plates. The exclusion of large predators by complete caging resulted in highly significantly different communities from those on partially caged plates. Completely caged Communities were composed mainly of worms, barnacles and bryozoans. Summer-installed plates supported significantly different populations at the end of the experimental period (12 mo) from winter-installed plates. Plant growth rates were slow, not exceeding 2 cm/mo, and the mortality rates were often high. A few species had high rates of recruitment and survival each month. Most had high recruitment only in the most favorable growth periods and high loss rates. Physical conditions on the sea floor were measured. The methods developed during this study make it possible to quantitatively describe the growth and reproduction of populations of benthic marine algae in the sea.     

DESICCATION PROTECTION AND DISRUPTION: A TRADE‐OFF FOR AN INTERTIDAL MARINE ALGA1

For marine algae, the benefits of drying out are often overshadowed by the stresses involved. Here we used laboratory and field experiments to examine both the costs and benefits of desiccation in the intertidal turf alga Endocladia muricata (Endlichter) J. Agardh. Laboratory experiments showed that when Endocladia is dry, photosynthesis stops, but thermotolerance increases to the point that the alga is protected from heat‐induced mortality. Drying rates measured in a wind tunnel, combined with tidal data and measured wave splash, indicate that a substantial fraction of the year is spent “drying out” (～30% of the total time available for photosynthesis). During these periods, the rate of drying determines how much time is spent hydrated and potentially engaged in photosynthesis, but also vulnerable to high temperatures. Turf algae such as Endocladia dry from the edge of a clump inward. Consequently, the clump center remains hydrated longer than the clump edge. The resulting regionalization of a clump results in notable patterns of frond mortality (“fairy rings,” and zoned patterns of frond bleaching) within the Endocladia zone.     

PROPOSAL OF ECTOCARPUS SILICULOSUS (ECTOCARPALES,PHAEOPHYCEAE) AS A MODEL ORGANISM FOR BROWN ALGAL GENETICS AND GENOMICS1,2

The emergence of model organisms that permit the application of a powerful combination of genomic and genetic approaches has been a major factor underlying the advances that have been made in the past decade in dissecting the molecular basis of a wide range of biological processes. However, the phylogenetic distance separating marine macroalgae from these model organisms, which are mostly from the animal, fungi, and higher plant lineages, limits the latters' applicability to problems specific to macroalgal biology. There is therefore a pressing need to develop similar models for the macroalgae. Here we describe a survey of potential model brown algae in which particular attention was paid to characteristics associated with a strong potential for genomic and genetic analysis, such as a small nuclear genome size, sexuality, and a short life cycle. Flow cytometry of nuclei isolated from zoids showed that species from the Ectocarpales possess smaller haploid genomes (127–290 Mbp) than current models among the Laminariales (580–720 Mbp) and Fucales (1095–1271 Mbp). Species of the Ectocarpales may complete their life histories in as little as 6 weeks in laboratory culture and are amenable to genetic analyses. Based on this study, we propose Ectocarpus siliculosus (Dillwyn) Lyngbye as an optimal choice for a general model organism for the molecular genetics of the brown algae.