Influence of sedimentation in the absence of macrograzers on recruitment of an annual population of Macrocystis pyrifera in Metri Bay,Chile

The effects of sedimentation and substrate orientation on algal and sessile invertebrate assemblages were tested on an annual population of Macrocystis pyrifera in Metri Bay, southern Chile. In the laboratory, M. pyrifera zoospores were seeded on Crepipatella fecunda shells, the primary substrate for M. pyrifera in this system. The seeded shells were deployed at Metri Bay inside cages and were orientated vertically and horizontally under two sedimentation regimes (bottom and suspended). Due to differences in grazer accessibility and the species present between the sedimentation treatments, grazers (>1 cm) were excluded. We followed sporophyte development of M. pyrifera and the natural recruitment of other algal and invertebrate species. Sedimentation rates were significantly higher in the cages attached to the bottom compared to suspended cages (P < 0.001). In total M. pyrifera and three additional algal genera were detected and all algal recruits showed significantly greater recruitment on the horizontally orientated substrate compared to the vertical substrate. Macrocystis pyrifera sporophytes were present only on the horizontal, suspended (less sedimentation) treatment. In contrast, Ulva and Ectocarpus spp. also occurred in the horizontal, high sediment treatment. Invertebrate recruitment (amphipods, barnacles and spirorbids) dominated the vertically oriented shells regardless of sedimentation. Results indicate that high sedimentation negatively affected the development of M. pyrifera sporophytes while other opportunistic species were able to recruit under these conditions.     

Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana,Phaeophyceae)

Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10–22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10–14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16–18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.     

EFFECT OF HIGH IRRADIANCE ON RECRUITMENT OF THE GIANT KELP MACROCYSTIS (PHAEOPHYTA) IN SHALLOW WATER1

Laboratory and field experiments were done hi Still-water Cove, Carmel Bay, California, and Monterey Harbor, California, to determine the effect of photosynthetically active radiation (PAR) on the shallow (upper) limit of giant kelp, Macrocystis pyrifera (L.) C. Agardh. At shallow depths, M. pyrifera did not recruit or grow to macroscopic size from gametophytes or embryonic sporophytes transplanted to vertical buoy lines; sharp decreases in PAR with depth coincided with observed recruitment and sporophyte distributions. Shade manipulations indicated that settlement of M. pyrifera zoospores was decreased, but not prohibited, by high PAR. Postsettlement stages (gametophytes and embryonic sporophytes), however, survived only under shade. These results suggest that high PAR can inhibit the recruitment of M. pyrifera to shallow water by killing its postsettlement stages; whether or not ultraviolet (UV) radiation also inhibits recruitment was not tested. In either case, however, it appears that high irradiance (PAR and/or UV) regulates the shallow limit of M. pyrifera prior to temperature and desiccation stresses inherent to intertidal regions. In an additional experiment, recruitment or growth of transplanted gametophytes or embryonic sporophytes of Macrocystis integrifolia Bory also did not occur at shallow depths, suggesting that this shallow water species accesses high irradiance regions via a method other than sexual reproduction.     

A MULTISPECIES LABORATORY ASSESSMENT OF RAPID SPOROPHYTE RECRUITMENT FROM DELAYED KELP GAMETOPHYTES1

Recent work suggests that the ability to delay reproduction as resistant haploid gametophytes may be important for seaweeds that experience unpredictable disturbances or seasonal periods of poor conditions that result in adult sporophyte absence. Further, delayed gametophytes of some kelp species (order Laminariales) may produce sporophytes more rapidly than if they had never experienced a delay, conferring a competitive advantage when conditions improve or after disturbance events. Here, it was determined that the gametophytes of the canopy‐forming kelp Macrocystis pyrifera (L.) C. Agardh could delay reproduction in a one‐ to two‐cell state (<50 μm) for at least 7 months when grown under nutrient‐limiting conditions. These stages retained reproductive viability and produced sporophytes within 5 d once nutrients were increased. This finding suggests that gametophytes could potentially promote recovery of M. pyrifera populations after extended periods of sporophyte absence. In addition, the time required for sporophyte production between gametophytes of the four most conspicuous kelp species in Southern California that had delayed reproduction and gametophytes that had not was compared. For these four kelp species, a delay of at least 30 d conferred a 40%–76% reduction in the time required for sporophyte production once nutrients were received. Fecundity did not decrease with delay duration, suggesting there is no apparent cost of delayed development for kelps as has been observed in other organisms. Thus, delayed development may be a viable strategy for surviving and initially dominating in environments with variable quality.     

Ecophysiological plasticity of annual populations of giant kelp (Macrocystis pyrifera) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile

Annual populations of Macrocystis pyrifera in Southern Chile have been the main focus of studies intending to understand how these populations can couple consecutive sporophytic generations. Research has included studying the population dynamics and gametophytic responses to environmental conditions and the role of recruitment, grazing, and the use of benthic filter feeders as secondary substrate. Adult sporophytes undergo senescence due to changes in abiotic factors during summer and autumn producing 100 % mortality. This study provides evidence about the environmental factors driving the decline in sporophyte populations occurring in summer and fall by monitoring two independent kelp populations and also by running experiments using 400 L tubular photobioreactors with semicontrolled environmental factors for testing the capacity for new recruits to recover population levels under winter conditions. The study of natural populations of giant kelp indicates that high temperatures (>15–17 °C) explain the high mortality of adult plants in summer. On the other hand, the sporophytes established in late winter/early spring are able, under high nitrogen availability, to increase their chlorophyll content significantly, allowing the individuals to reduce their light saturation point and thus allow a higher productivity under the low light conditions that exist in late winter and early spring. These results, in addition to the recruitment facilitation produced by filter feeders, help to explain how giant kelp can deal with, and couple sporophytic generations, in variable environments. These results also emphasize the highly plastic physiology of giant kelp that enables this species to colonize diverse habitats across its large distributional range.     

ARRESTED DEVELOPMENT OF GIANT KELP (MACROCYSTIS PYRIFERA,PHAEOPHYCEAE) EMBRYONIC SPOROPHYTES: A MECHANISM FOR DELAYED RECRUITMENT IN PERENNIAL KELPS?1

Delayed recruitment of microscopic stages in response to cyclical cues is critical to the population dynamics of many annual and seasonally reproducing perennial seaweeds. Microscopic stages may play a similar role in continuously reproducing perennials in which adult sporophytes are subject to episodic mortality, if they can respond directly to the unpredictable onset and relaxation of unfavorable conditions. We experimentally evaluated the potential for temporary reduction in limiting resources (light, nutrients) to directly delay recruitment of giant kelp (Macrocystis pyrifera (L.) C.A. Agardh) gametophytes and embryonic sporophytes. Laboratory cultures were subjected to limiting conditions of light and nutrients for 1 month and then exposed to nonlimiting conditions for 10 days. Gametophytes in all treatments failed to recruit to sporophytes after 2 weeks, suggesting they are not a source of delayed recruitment in giant kelp. Sporophytes in light‐limited treatments, however, survived and grew significantly slower than non–light‐limited controls. When stimulated with light, light‐limited sporophytes grew from 2 to>10 times faster than unstimulated controls depending on nutrient availability. These results suggest that limiting resources can delay recruitment of embryonic giant kelp sporophytes for at least 1 month. Flexible timing of recruitment from embryonic sporophytes may enhance persistence of continuously reproducing perennial species when mac‐ roscopic adults are subject to episodic large‐scale removals.     

Compensatory growth of the kelp Macrocystis integrifolia (Phaeophyceae, Laminariales) against grazing of Peramphithoe femorata (Amphipoda, Ampithoidae) in northern-central Chile

Compensation of tissue loss has been considered an alternative strategy for seaweeds that have no or only minor chemical or structural defense against herbivory. Compensatory responses are facilitated by resource transfer among different tissues and have been suggested for large kelps. Macrocystis integrifolia (Bory) is a common kelp species from northern-central Chile, which is characterized by high growth rates and the absence of lipophilic chemical defenses against herbivore grazing. Herein, we used the giant kelp M. integrifolia to test for compensatory growth in response to grazing by the nest-dwelling amphipod Peramphithoe femorata (Krøyer). Amphipods were allowed to graze inside nests on subapical blades of M. integrifolia sporophytes for 14 days. We measured growth and chemical composition (C, N, laminaran and mannitol) of apical and subapical blades of grazed and ungrazed (control) sporophytes. Our results revealed the capability of M. integrifolia to maintain elongation rates in grazed subapical blades, which were similar to those of subapical blades from ungrazed sporophytes. Apical blades grew slower in grazed than in ungrazed sporophytes indicating a trade-off between apical and subapical blades when herbivores were present. Thus, compensation occurs in blades directly attacked by grazers and is probably mediated by vertical resource allocation within sporophytes to subapical blades, a suggestion supported by the fact that stipe internodes in these regions grew more on grazed sporophytes. In general, our study indicates that M. integrifolia exhibits compensatory growth against the herbivore amphipod P. femorata, and we suggest that this could be an important strategy of large kelp species to tolerate moderate grazing intensities.     

REPRODUCTIVE LONGEVITY OF DRIFTING KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE) IN MONTEREY BAY,USA1

Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long‐distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach‐cast drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow drifter trajectories and to measure drifting speed. Experimental drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio‐tagged drifters was 7.12 km·day^?1, suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890 km (±363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter‐hemispheric gene flow.     

Urchin grazing of kelp gametophytes in warming oceans

Sea urchins can cause extensive damage to kelp forests, and their overgrazing can create extensive barren areas, leading to a loss of biodiversity. Barrens may persist when the recruitment of kelp, which occurs through the microscopic haploid gametophyte stage, is suppressed. However, the ecology of kelp gametophytes is poorly understood, and here we investigate if grazing by juvenile urchins on kelp gametophytes can suppress kelp recruitment and if this is exacerbated by climate change. We compared grazing of Ecklonia radiata gametophytes by two species of juvenile urchins, the tropical Tripneustes gratilla and the temperate Centrostephanus rodgersii, at winter (19°C), summer (23°C), and ocean warming (26°C) temperatures for the low-latitude range edge of E. radiata, which is vulnerable to ocean warming. We examined the rate of recovery of gametophytes following grazing and determined whether they survived and formed sporophytes after ingestion by sea urchins. Both T. gratilla and C. rodgersii grazed E. radiata gametophytes, reducing their abundance compared to no grazing controls. Surprisingly, temperature did not influence grazing rates, but gametophytes did not recover from grazing in the ocean warming (26°C) treatment. Gametophytes survived ingestion by both species of sea urchin and formed sporophytes after ingestion by T. gratilla, but not C. rodgersii. These results suggest complex grazer–gametophyte interactions, in which both negative (reduced abundance and poor recovery with warming) and positive (facilitated recruitment) effects are possible. Small grazers may play a more important role in kelp ecosystem function than previously thought and should be considered in our understanding of alternate stable states.     

High acclimation potential in floating Macrocystis pyrifera to abiotic conditions even under grazing pressure – a field study

The persistence of floating seaweeds, which depends on abiotic conditions but also herbivory, had previously been mostly tested in outdoor mesocosm experiments. In order to investigate if the obtained mesocosm results of high seaweed persistence under natural environmental conditions and under grazing pressure can be extrapolated to field situations, we conducted in situ experiments. During two summers (2007 and 2008), Macrocystis pyrifera was tethered (for 14 d) to lines in the presence and absence of the amphipod Peramphithoe femorata at three sites (Iquique, Coquimbo, Calfuco). We hypothesized that grazing damage and seaweed persistence vary among sites due to different abiotic factors. By incubating the sporophytes in mesh bags, we were either able to isolate (grazing) or exclude (control) amphipods. To test for a mesh bag artifact, a set of sporophytes was incubated without mesh bags (natural). Mesh bags used to exclude herbivores influenced sporophyte growth and physiological performance. The chlorophyll a (Chl a) content depended largely on grazers and grazed sporophytes grew less than natural and control sporophytes within the two summers. A decrease in Chl a content was found for the sites with the highest prevailing irradiances and temperatures, suggesting an efficient acclimation to these sea surface conditions. Our field‐based results of sporophyte acclimation ability even under grazing pressure widely align with previous mesocosm results. We conclude that M. pyrifera and other temperate floating seaweeds can function as long‐distance dispersal vectors even with hitchhiking mesoherbivores.     

Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site

Kelp forests are highly productive and species‐rich benthic ecosystems in temperate regions that provide biogenic habitat for numerous associated species. Diverse epifaunal communities inhabit kelp sporophytes and are subject to variations in the physical environment and to changes experienced by the kelp habitat itself. We assessed seasonal variations in epifaunal invertebrate communities inhabiting giant kelps, Macrocystis pyrifera, and their effects on this seaweed. Six seasonal samplings were conducted over a year at an upwelling‐dominated site in northern‐central Chile where physical conditions are known to fluctuate temporally. More than 30 taxa were identified, among which peracarid crustaceans stood out in both diversity and abundance. Species richness and abundance differed among sporophyte sections (holdfast and fronds) and throughout the year. The frond community was dominated by two grazers (the amphipod Peramphithoe femorata and the isopod Amphoroidea typa), while suspension feeders, grazers, and omnivores (the amphipod Aora typica, the isopod Limnoria quadripunctata, and polychaetes) dominated the holdfasts. Abundances of the dominant species fluctuated throughout the year but patterns of variation differed among species. The most abundant grazer (P. femorata) had highest densities in summer, while the less abundant grazer (A. typa) reached its peak densities in winter. Interestingly, the area of kelp damaged by grazers was highest in autumn and early winter, suggesting that grazing impacts accumulate during periods of low kelp growth, which can thus be considered as ‘vestiges of herbivory past.’ Among the factors determining the observed seasonal patterns, strong variability of environmental conditions, reproductive cycles of associated fauna, and predation by fishes vary in importance. Our results suggest that during spring and early summer, bottom‐up processes shape the community structure of organisms inhabiting large perennial seaweeds, whereas during late summer and autumn, top‐down processes are more important.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

EXCHANGES OF INFORMATION,ENERGY & MATERIALS IN SYMBIOSES

We investigated patterns of spore dispersal in the giant kelp Macrocystis pyrifera by collecting 80 independent measurements of spore dispersal from isolated individuals and isolated groups of individuals over a two‐year period. Our results indicate that giant kelp spores routinely disperse both short (i.e. a couple meters) and long (i.e. hundreds to thousands of meters) distances depending on the oceanographic conditions. One consequence of spore dispersal over short distances is self‐fertilization (i.e., fertilization between male and female gametophytes derived from the same sporophyte). Field experiments designed to test the effects of self‐fertilization on lifetime fitness in Macrocystis revealed significant inbreeding depression. Birth rates in self‐fertilized populations were ca. 50% of those produced from outcrossing, which lead to significant differences in cohort size that persisted up through the adult stage. In contrast to outcrossed populations, very few individuals produced from selfing became reproductively mature, and those that did were significantly less fecund than outcrossed individuals. By contrast, long‐range dispersal of spores leads to increased rates of outcrossing. However, long‐range dispersal is typically accompanied by massive dilution of spores, leading to low densities of spore settlement. Sparse spore settlement decreases the overall chance of fertilization in the microscopic gametophyte generation thereby reducing the potential for colonization of the macroscopic sporophyte stage. Large population size of adult sporophytes coupled with the synchronous release of spores in response to environmental cues can help offset the effects of spore dilution and extend the distances over which giant kelp is able to colonize.     

Reproduction strategies of Macrocystis pyrifera (Phaeophyta) in Southern Chile: The importance of population dynamics

Macrocystis pyrifera is an ecologically dominant species along the temperate Northern and Southern Pacific Coast of America, showing some similarities and differences at population and community level. In general, this kelp is reported to be reproductive all year round. Annual populations present in wave-protected areas of southern Chile suggest that the reproductive strategies of this population can be different. In this study we explore the reproductive strategies of annual M. pyrifera present in wave-protected areas and perennial populations encountered in exposed areas of southern Chile (41^∘S). Our results show that M. pyrifera present in wave-exposed locations has a reproductive strategy that is similar to populations in the northern hemisphere. These populations reproduce all year round and their strategy is to produce high numbers of sporophylls and ensure that most of them (over 90%) become sporogenous. On the other hand, the protected populations with an annual life cycle, produce more spores per area of sorus. In a few months, they are able to produce sufficient propagules to recolonize areas before the adult plants disappear in autumn.     

A COMPARISON OF DRAGON KELP,EUALARIA FISTULOSA, (PHAEOPHYCEAE) FECUNDITY IN URCHIN BARRENS AND NEARBY KELP BEDS THROUGHOUT THE ALEUTIAN ARCHIPELAGO1

The Aleutian Archipelago coastal ecosystem has undergone a dramatic change in community composition during the past two decades. Following the removal of ～99% of the sea otters, Enhydra lutris, from the ecosystem, changes to the benthic communities resulted in widespread losses to most of the region’s kelp beds and corresponding increases in the prevalence of urchin barrens. Within the urchin barrens, the few kelps that have remained are exposed to elevated light, nutrients and currents, all of which may enhance their physiological condition and thus result in greater fecundity. To explore this further, we examined patterns of sporophyte fecundity in the dominant canopy‐forming kelp, Eualaria fistulosa, in both urchin barrens and in nearby kelp beds at seven Aleutian Islands spanning a range of 800 km. We found that the average weight of E. fistulosa sporophyll bundles was significantly greater on sporophytes occurring in the urchin barrens than in the nearby kelp beds. Furthermore, the average number of zoospores released per cm² of sporophyll area was also significantly greater in individuals from the urchin barrens than the nearby kelp beds. When these two metrics were combined, our results suggest that individual E. fistulosa sporophytes occurring in the urchin barrens may produce as many as three times more zoospores than individual E. fistulosa sporophytes occurring in the nearby kelp beds, and thus they may contribute disproportionately to the following year’s sporophyte recruitment in both urchin barrens and the adjacent kelp beds.     

SPORE SUPPLY AND HABITAT AVAILABILITY AS SOURCES OF RECRUITMENT LIMITATION IN THE GIANT KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE)1

The causes of spatial variation in the recruitment of benthic marine algae are frequently misunderstood because of difficulties in distinguishing among the many factors that influence the supply and establishment of microscopic propagules. We used the recently constructed San Clemente Artificial Reef (SCAR) experiment to examine the roles of dispersal distance, size of spore source, and habitat availability as sources of variation in the recruitment of the giant kelp Macrocystis pyrifera (L.) C. Ag., a species whose recruitment has often been considered to be dispersal limited. Sparse colonization on SCAR by adult Macrocystis occurred within 6 months after reef construction via drifters (i.e. individuals from neighboring kelp beds that became dislodged and set adrift). The abundance of drifters on SCAR declined exponentially with distance from the nearest source population (San Mateo), suggesting that San Mateo was the likely source of drifters. Dense recruitment of small Macrocystis sporophytes was observed within 8 months of reef construction. The density of recruits on SCAR showed an initial increase with distance from San Mateo before declining exponentially. Nonetheless, substantial recruitment was observed at the most distant locations on SCAR located 3.5 km from San Mateo. In contrast to drifters, the density of recruits was positively correlated to the bottom cover of artificial reef substrate. Importantly, no correlation was found between the local density or fecundity of drifters and the local density of kelp recruits suggesting that recruitment on SCAR resulted from widespread spore dispersal rather than from the local dispersal of spores from drifters.     

Farming of the Giant Kelp Macrocystis Pyrifera in Southern Chile for Development of Novel Food Products

This study explores the potential cultivation of the giant kelp Macrocystis pyrifera (L.) C.A. Agardh in southern Chile, for the development of novel food products. The study demonstrates the importance of considering the collection site of the parent sporophytes for successful cultivation. This study also shows that the ropes must be seeded with 10,000 to 40,000 spores ml⁻¹, depending on the culture method used. We also demonstrated that under environmental conditions in southern Chile, the seeded ropes must be put at sea at the latest during autumn (April) in order to reach the harvesting season in December. However, several other management aspects must be considered to improve the quality of the product. Our final estimation indicates that over 14.4 kg m⁻¹of rope (fresh weight) can be produced and from this total production, over 70% can reach the quality to produce different food products that are already being introduced in oriental countries. The remaining 30% can be used for abalone feeding and is also available for the organic fertilizer industry located in Chile.     

THE EFFECTS OF HIGH IRRADIANCE ON THE SETTLEMENT COMPETENCY AND VIABILITY OF KELP ZOOSPORES1

Elevated irradiance has a profound effect on the successful dispersal and establishment of kelp zoospores, affecting their physiology and viability. The research to date, however, has been on zoospores localized near the benthos, with little attention on the importance of vertical transportation and subsequent exposure to increased irradiance. Therefore, we wanted to investigate the effects of exposure to high irradiance on the reproductive planktonic life‐history stages of kelps Macrocystis pyrifera (L.) C. Agardh and Pterygophora californica Rupr. Zoospores of both species were exposed to different irradiances (75, 275, 575, 1,025 μmol photons · m^?2 · s^?1) over varying durations (1, 2, 4, 8, 12 h) and subsequently monitored for settlement competency, gametophyte development, and reproductive viability. Settlement success for M. pyrifera was uniform throughout all irradiance × time treatments, while settlement for P. californica decreased with increasing exposure time but not irradiance, although settlement was generally reduced at the highest irradiance level. Following zoospore settlement, germ tube development was visible in the gametophytes of both species within 1 week, although a significant decline of germ tube density in P. californica was observed with increasing irradiance. Similarly, a decrease in germ tube development with increasing exposure was observed across all irradiance levels for M. pyrifera, but irradiance itself was not significant. Further development into embryonic sporophytes was remarkably similar to gametophyte development, suggesting that the effect of exposure of kelp zoospores to high irradiance on subsequent sporophyte production is mediated through gametophyte development as well as zoospore survival.     

Culture studies on early development of Lessonia trabeculata (Phaeophyceae,Laminariales): Seasonality and acclimation to light and temperature

Lessonia trabeculata is an important economic and ecological algal resource of Chile. Due to intense use in abalone and alginate industries, severe problems of over‐harvesting are emerging. We compared sporophyte‐initiation and ‐growth in two populations from northern and southern Chile (Bahía Inglesa and Maicolpué) under laboratory conditions. Irradiance and temperature were the most important factors affecting gametophyte development. Meiospores harvested in spring exhibited maximum reproductive and growth potential, while spores released during autumn were moribund, and died within a few days. In both study sites, we found evidence for acclimation: Meiospores collected in summer required higher levels of irradiance and temperature for maximum development than winter spores. Juvenile sporophytes from both localities responded similarly to temperature and/or irradiance. The best conditions for recruitment of sporophytes from both localities were 15°C and white fluorescent light of 40–70 μmol m^?2 s^?1. Although due to its low growth potential L. trabeculata is not a good candidate for mariculture, our results provide the necessary knowledge for laboratory‐based seedling production, which is needed for restoration and repopulation projects in damaged areas.     

Sexual compatibility and hybrid formation between the giant kelp species <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> and <Emphasis Type="Italic">M. integrifolia</Emphasis> (Laminariales,Phaeophyceae) in Chile

Two species of giant kelp inhabit the coast of Chile: Macrocystis integrifolia and M. pyrifera, representing important economic resources. As part of our efforts to domesticate these kelps for mariculture, and to obtain superior cultivars, we studied their biological relationship. Hybridization experiments with clonal gametophyte cultures showed reciprocal cross-fertility and produced fertile hybrid sporophytes with intermediate morphological characters. This hybridization potential in the laboratory contrasts with the persistence of two morphologically well-defined sister taxa in natural habitats on the Pacific coast of South America. We conclude that M. integrifolia and M. pyrifera are conspecific and speculate that unknown mechanisms support the co-existence of two morphologically distinct taxa on the subspecific level.