Michael Neushul

The microclimate inhabited by macroalgal propagules

Propagules exist in a world dominated by viscous physical forces because of their very small size and relatively slow swimming speeds. The planktonic and benthic environments are heterogeneous physically, chemically, and biologically when viewed on the spatial scale of a macroalgal propagule. Macroalgal propagules coexist in the plankton with a wide diversity of other microscopic organisms but we are limited largely to speculation in matters concerning the importance of various biological interactions in the planktonic microenvironments. The layer of water near the bottom where propagules attach is called the boundary layer and is physically, chemically, and biologically distinct from the water above it. Many physical and chemical properties of the boundary layer environment are consequences of the metabolic or secretory activities of the organisms which inhabit the microbial film, but many properties are also influenced by abiogenic factors. Nutrient concentrations in some patches are likely to be much h...

ROLE OF SETTLEMENT DENSITY ON GAMETOPHYTE GROWTH AND REPRODUCTION IN THE KELPS PTERYGOPHORA CALIFORNICA AND MACROCYSTIS PYRIFERA (PHAEOPHYCEAE)1

Laboratory studies were used to examine how variation in the density of spore settlement influences gametophyte growth, reproduction, and subsequent sporophyte production in the kelps Pterygophora californica Ruprecht and Macrocystis pyrifera (L.) C. Ag. In still (non‐aerated) cultures, egg maturation in both species was delayed when spores were seeded at densities 300 · mm−2. Although the density at which this inhibition was first observed was similar for both species, the age at which their eggs matured was not. P. californica females reached sexual maturity an average of 4 days (or ∼ 30%) sooner than did M, pyrifera. As observed previously in field experiments, per capita sporophyte production was negatively density dependent for both species when seeded at spore densities of 10 · mm−2. Total sporophyte production (i.e. number · cm−2) for both species, however, was greatest at intermediate densities of spore settlement (∼ 50 spores · mm−2). In contrast, total sporophyte production by P. californica steadily increased with increasing spore density in aerated cultures; highest sporophyte density was observed on slides seeded at a density of 1000 spores · mm−2. Preliminary experiments with P. californica involving manipulation of aeration and nutrients indicate that inhibition of gametophyte growth and reproduction at higher densities of spore settlement in non‐aerated cultures was probably caused by nutrient limitation.

PHOTOSYNTHETIC PHYSIOLOGY AND CHEMICAL COMPOSITION OF SPORES OF THE KELPS MACROCYSTIS PYRIFERA, NEREOCYSTIS LUETKEANA, LAMINARIA FARLOWII, AND PTERYGOPHORA CALIFORNICA (PHAEOPHYCEAE)1

Recently released spores of the kelps Macrocystis pyrifera (L.) C. Ag., Nereocystis luetkeana (Mert.) Post. and Rupr., Laminaria farlowii Setch., and Pterygophora californica Rupr. had different levels of net photosynthesis. Spore‐specific photosynthesis–irradiance relationships were similar in many respects for M. pyrifera, N. luetkeana, and L. farlowii spores. All three species had low rates of net light‐saturated photosynthesis. In contrast, spores of P. californica had higher photosynthetic potential and overall net photosynthesis than the other three species. On a cell carbon basis, however, photosynthetic rates in N. luetkeana spores were similar to those of P. californica spores and higher than those of M. pyrifera spores. Chlorophyll a content of spores varied 10‐fold among species. The rank order of significant differences in chlorophyll a content was P. californica > L. farlowii > N. luetkeana > M. pyrifera. As a result, chlorophyll‐specific measurements suggest M. pyrifera and N. luetkeana spores had much higher quantum efficiency and photosynthetic potential than either P. californica or L. farlowii spores. Maternal carbon and nitrogen investment significantly differed in spores of M. pyrifera, N. luetkeana, and P. californica with P. californica > M. pyrifera > N. luetkeana. Carbon content in spores of each of these three species increased by about 30% during 12 h of saturating irradiance. We suggest that the photosynthetic capabilities of and maternal investment in spores may be related to the spore as a unit of dispersal, to the reproductive ecology of the parental sporophytic stages, and to the growth and physiology of the germling gametophyte stages.

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.

HAPLOID PARTHENOGENETIC SPOROPHYTES OF LAMINARIA JAPONICA (PHAEOPHYCEAE)1

Parthenogenetic sporophytes were obtained from three strains of Laminaria japonica Areschoug. These sporophytes grew to maturity in the sea, producine spores that all grew into female gametophytes. These female gametophytes gave rise to another generation of parthenogenetic sporophytes during the next year, so that by the year 1990 parthenogenetic sporophytes had been cultivated for 12, 9, and 7 generations, respectively, for the three strains. When female gametophytes from parthenogenetic sporophytes were combined with normal male gametophytes, normal sporophytes that reproduced and gave rise to both female and male gametophytes were obtained. The parthenogenetic sporophytes were shorter and narrower than the normal sporophytes of the same strain.

HYBRIDIZATION OF MACROCYSTIS (PHAEOPHYTA) WITH OTHER FLOAT‐BEARING KELPS1,2

Sporophytes were produced in 22 out of 23 attempts to cross Macrocystia angustifolia Bory with Pelagophycus porra (Lemon) Setchell. Representative samples of these plants were raised in a surge‐tank under greenhouse conditions to several meters in length. The plants resulting from this intergeneric cross were intermediate in morphology between the parental genera. The intermediate plants were similar to those found fry one of the authors (MN) in 1957, and by others since then, in California kelp beds where Macrocystis and Pelagophycus co‐occur, A cross between M. angustifolia and Nereocystis luetkeana (Mertens) P. & R., also produced normal sporophytes. The taxonomic, evolutionary, morphogenetic and genetic implications of these hybridizations are discussed.

Diel periodicity of spore release from the kelp Nereocystis luetkeana (Mertens) Postels et Ruprecht

Abstract Sorus abscission and associated spore release were monitored in the laboratory from Nereocystis luetkeana (Mertens) Postels et Ruprecht plants collected at three sites in central California, U.S.A. Nearly 80% of the sori were released in the interval between 2 h before sunrise and 4 h after sunrise. This dawn abscission pattern was observed on each day and from plants collected at all sites. Short-term observations in nature confirmed the pattern. Sori from individual plants were usually abscised at intervals of 2–4 days. Sori often began releasing spores before abscission and, in nature, probably continue to release spores as they are falling through the water column. > 50% of the spores released from abscised sori in the laboratory were released in the 1st h after abscission at a mean rate two to four orders of magnitude higher than previously reported for related macroalgae; nearly 95% had been released within 4 h. This sorus abscission-spore release mechanism is probably adaptive in maximizing the photosynthetic potential of the spores, maximizing the potential dispersal of some of the spores, and ensuring that a proportion of the spores will be retained near the parents.

SEDIMENTATION STUDIES OF RED ALGAL SPORES1

More than 1000 spores from 11 species of red algae were collected; their differences in size and sinking rates were measured using a new micro‐video technique. A relationship between size and sinking rate was shown with larger spores generally sinking faster than smaller ones. Variability in spore size, or lack thereof, is a species characteristic. Cryptopleura violacea (J. G. Ag.) Kylin and Neoagardhiella baileyi (Kutz.) Wynne and Taylor were found to produce a wide range of spore sizes. Such variability in size may be related to differences in spore formation. Centrifugation was used to separate the contents of spores to show differences in them. The ecological implications of these observations are considered.

INTERGENERIC HYBRIDIZATION AMONG FIVE GENERA OF THE FAMILY LESSONIACEAE (PHAEOPHYCEAE) AND EVIDENCE FOR POLYPLOIDY IN A FERTILE PELAGOPHYCUS×MACROCYSTIS HYBRID

Hybridization was attempted by combining gametophytes between intergeneric pairs among the following taxa in the Lessoniaceae: Macrocystis pyrifera (L.) C. Agardh, M. integrifolia Bory, M. angustifolia Bory, Pelagophycus porra (Leman) Setch., Nereocystis luetkeana (Mert.) Post & Rupr., Dictyoneurum californicum Rupr., and Dictyoneuropsis reticulata (Saud.) Smith. Hybrid sporophytes were produced in some combinations involving Macrocystis × Pelagophycus and Macrocystis × Dictyoneurum, and in all combinations of Dictyoneuropsis × Dictyoneurum. This is the first report of intergeneric hybrids involving Dictyoneurum. Gametophytes of P. porra had 16–24 chromosomes. Gametophytes from a fertile Macrocystis‐Pelagophycus hybrid were crossed with Macrocystis and Pelagophycus gametophytes. Hybrid male gametophytes and Pelagophycus female gametophytes produced sporophyte progeny, but hybrid males with Macrocystis females did not. A single hybrid female gametophyte did not produce gametophytes in combination with hybrid males, Pelagophycus males or Macrocystis males. The hybrid gametophytes had approximately 30 chromosomes. It is hypothesized that the hybrid is an alloploid, containing a complete set of Macrocystis and Pelagophycus chromosomes, which may have allowed meiosis and sporogenesis to proceed normally in the hybrid sporophyte found in the sea. Thus, reproductive isolating mechanisms appear to operate at both pre‐ and postzygotic stages, and both can be overcome in intergeneric hybrids.

STUDIES ON DEVELOPING AND RELEASED SPERMATIA IN THE RED ALGA, TIFFANIELLA SNYDERAE (RHODOPHYTA)1

Developing and released spermatia of the red alga, Tiffaniella snyderae (Farl.) Abb. were studied. Spermatia were observed under hydrodynamically defined conditions and found to be released from the exposed spermatangial heads in a spermatium‐plus‐strand unit that remained connected to the spermatangial head. Interactions of single‐spermatial strands resulted in the formation of multi‐spermatial strands as long as 600 μm with as many as 47 spermatia along their length; however, most were 100–200 μm with 8–21 spermatia. Strand length and number of spermatia were correlated. Spermatial strands contracted or extended and rotated as the water velocity past the plant was changed, and in still water the strands retracted into a clump on the spermatangial head surface. Each strand type exhibited a characteristic threshold water velocity at which it reached maximum length, and above which it broke and was carried away. Fluorescence microscopy showed that the strands did not contain nucleic acid (DNA) and could thus be differentiated from filamentous blue‐green algal and bacterial epiphytes. Histochemical staining indicated that the strands and spermatial vesicles contained an acidic, sulfated polysaccharide. Chelation of Ca2+ with EGTA resulted in strand breakdown suggesting that this divalent cation may be involved in strand integrity.