Fadia Tala

Aspects of the reproductive phenology of Lessonia trabeculata (Laminariales: Phaeophyceae) from three populations in northern Chile

Abstract Lessonia trabeculata is a brown seaweed inhabiting the rocky subtidal zone along the coast of central and northern Chile, where it is the dominant kelp, and an important species in community structure. Morphological and reproductive aspects of this alga are dependent on environmental conditions and geographic distribution, and the present study gives data on its reproductive periodicity. The reproductive phenology for three populations from northern Chile (29–30°S) was evaluated by means of seasonal examination of morphological and reproductive characteristics of both macroscopic sporophytes and microscopic gametophytes. Comparative laboratory cultures of spores were made to determine seasonal differences in their capacity to produce viable plants. This species is perennial, and demonstrates year‐round presence of reproductive tissues, although showing variation in reproductive phenology over time and among populations. The size of blades increases in spring and summer, whereas its reproductive potential (e.g., area and proportion of the reproductive tissue and the release of spores) increases in autumn. Culture experiments showed that spring and summer reproductive tissue released zoospores which had low germination rates compared to those of autumn and winter, and which produced female gametophytes of low fertility. The population differences depended on the character analysed and the season of the year. The development of both phases of the life cycle of L. trabeculata may be influenced by the local environmental conditions and their seasonal changes, and were expressed as morphological and/ or reproductive changes in the plants. A better understanding of the seasonal adaptations may be obtained if future comparisons are made between widely separated populations or between individuals from the extremes of geographic distribution of the species.

First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d−1) and erosion (0.01 g dw d−1) than L. nigrescens (production 0.01 g dw d−1 and loss 0.002 g dw d−1). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m−2) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m−2). Spring net productivities of 42 g dw m−2d−1 (254 g ww m−2d−1; 11.46 gC m−2d−1) for L. nigrescens and 11 g dw m−2 d−1 (64 g ww m−2 d−1; 2.46 gC m−2d−1) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.

Repopulation of intertidal areas with Lessonia nigrescens in northern Chile

Intertidal rocky areas in northern Chile were repopulated experimentally with the brown alga Lessonia nigrescens using spore seeding and placement of reproductive fronds. The results were successful, and it is suggested that methods developed in the field can be done by people without special training.

Early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae) show recovery capacity following exposure to UV radiation

F. Tala, K. Véliz, I. Gómez, and M. Edding. 2007. Early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae) show recovery capacity following exposure to UV radiation. Phycologia 46: 467–470. DOI: 10.2216/06-56.1 This study examined the recovery capacity of early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata after exposure to artificial ultraviolet radiation (UV-B280–315 nm, UV-A315–400 nm). Spores (3 h postrelease) were exposed to different UV doses applied as daily pulses (0.5, 1, 2, 3, 4 h) during 6 days. Afterwards cultures were kept under PAR condition and fertility of gametophytes and formation of sporophytes measured up to day 45 (for L. nigrescens) and 65 (for L. trabeculata). The irradiation with UV-B radiation for 6 days strongly impaired spore germination: at biologically effective UV doses (BEDCaldwell > 2 kJ m−2; pulses > 2 h per day), complete mortality of the spores was observed. In contrast, spores irradiated with UV-A retained a germination capacity close to 80 and 70% under high doses (75 kJ m−2; 4 h per day). The surviving spores from both treatments exhibited a recovery during their further development as the fertility of gametophytes and formation of sporophytes increased with age of culture. In the intertidal L. nigrescens, fertility of gametophytes from spores irradiated with UV-B during 0.5 and 1 h per day was between 70 and 100% after 45 days. Treatments with UV-A did not affect markedly the fertility and production of sporophytes, as values were always between 80 and 100% after 45 days. In the subtidal L. trabeculata, recovery of cultures irradiated with UV-B and UV-A were lower, in particular the formation of sporophytes, as compared to L. nigrescens. Two major findings are outlined: (1) exposure of spores to UV-B radiation affects the further development of the life cycle, and (2) the surviving spores retained their viability and were able to complete the life history.

Artificial induction of sporulation in Lessonia (Phaeophyta, Laminariales)

The effects of three physical variables on sporulation, germination and gametophyte survival were evaluated on two species of Laminariales at Coquimbo, Chile (30° S). Parameters were evaluated using reproductive fronds of Lessonia nigrescens Bory and Lessonia trabeculata Villouta and Santelices with treatment variables including type of pre-rinse, dehydration, and temperature. Although the response was slightly different in the two species, it was found that pre-rinsing the blades with tap water produced marked sporulation without affecting germination and survival. Minor effects were observed with other variables, including positive effects of lower temperature and negative effects of longer dehydration periods. The high commercial value of these two species has promoted much interest in their artificial propagation in Chile.

The variable routes of rafting: stranding dynamics of floating bull kelp Durvillaea antarctica (Fucales, Phaeophyceae) on beaches in the SE Pacific

Dispersal on floating seaweeds depends on availability, viability, and trajectories of the rafts. In the southern hemisphere, the bull kelp Durvillaea antarctica is one of the most common floating seaweeds, but phylogeographic studies had shown low connectivity between populations from continental Chile, which could be due to limitations in local supply and dispersal of floating kelps. To test this hypothesis, the spatiotemporal dynamics of kelp strandings were examined in four biogeographic districts along the Chilean coast (28°–42°S). We determined the biomass and demography of stranded individuals on 33 beaches for three subsequent years (2013, 2014, 2015) to examine whether rafting is restricted to certain districts and seasons (winter or summer). Stranded kelps were found on all beaches. Most kelps had only one stipe (one individual), although we also frequently found coalesced holdfasts with mature males and females, which would facilitate successful rafting dispersal, gamete release, and reproduction upon arrival. High biomasses of stranded kelps occurred in the northern‐central (30°S–33°S) and southernmost districts (37°S–42°S), and lower biomasses in the northernmost (28°S–30°S) and southern‐central districts (33°S–37°S). The highest percentages and sizes of epibionts (Lepas spp.), indicative of prolonged floating periods, were found on stranded kelps in the northernmost and southernmost districts. Based on these results, we conclude that rafting dispersal can vary regionally, being more common in the northernmost and southernmost districts, depending on intrinsic (seaweed biology) and extrinsic factors (shore morphology and oceanography) that affect local supply of kelps and regional hydrodynamics.

Float and Raft: Role of Buoyant Seaweeds in the Phylogeography and Genetic Structure of Non-buoyant Associated Flora

Many seaweed species (primary rafters) float at the sea surface and travel with marine currents after detachment from benthic habitats. Various studies have confirmed that dispersal via floating sporophytes and/or gametophytes influences the phylogeography and genetic population structure of these buoyant seaweeds. In addition, non-buoyant seaweeds (secondary rafters) that grow attached to or intermingled with these primary floaters may also become dispersed by rafting on their floating hosts. Here, we examine reports of non-buoyant seaweed species associated with buoyant seaweeds and discuss potential consequences for their phylogeography and/or genetic population structure. We found that mostly red and brown algae have been reported with floating seaweed rafts, most of them growing as epiphytes and some as obligate parasites (e.g. endophytes) that travel with their hosts. Molecular evidence suggests dispersal associated with primary floaters in 16 non-buoyant seaweeds, although colonization of distant sites could also have occurred via other floating substrata such as wood, buoys, and other man-made materials. Transoceanic dispersal has been inferred for non-buoyant seaweeds (for example, Gracilaria chilensis and Capreolia implexa) based on low levels of genetic structure and shared haplotypes among populations separated over vast distances of open ocean (e.g. New Zealand–Chile). Some non-buoyant species suspected or shown to be dispersed by rafting are from intertidal habitats, and these algae can resist physiologically stressful conditions during long trips at the sea surface. However, subtidal and low intertidal non-buoyant species have higher potential to be transported because they cohabit with common raft-forming kelps, often growing on them as epiphytes. We conclude that buoyant seaweeds play an important role in driving the phylogeography, evolution, connectivity and distribution of non-buoyant associated seaweeds. Dispersal of non-buoyant seaweeds via these floating seaweeds may have been underestimated in the past.

Ecophysiological characteristics of Porphyra spp. (Bangiophyceae, Rhodophyta): seasonal and latitudinal variations in northern-central Chile

The red macroalga Porphyra C. Agardh is one of the most ecologically successful genera that lives in the upper intertidal zone. Biochemical, physiological, and morphological acclimation strategies allow their growth and distribution as well as a quick recuperation between tidal regimens. Studies of Porphyra are poorly developed in Chile, and management and exploitation proposals need to be supported by biological and ecophysiological approaches. This study evaluated seasonal and latitudinal physiological performances of Porphyra spp. via maximum quantum yield (Fv / Fm), pigments, proteins, phenolic compounds, and antioxidant activity in order to describe how algae can acclimate to their environment and to provide insights to their management and use. Sampling was done at three costal sites in Chile between 25°S and 34°S between winters 2010 and 2011. A total of four different morphotypes were identified (one in the north, one in the center, and two in the south locations) and evaluated separately. Results showed seasonal and latitudinal patterns for all ecophysiological variables studied, with a general tendency of decrease in Fv / Fm, pigments, and soluble proteins during spring–summer seasons accompanied by an increase in the antioxidant capacity. Latitudinal differences were observed with a tendency of higher values for ecophysiological traits in central and southern morphotypes. Phenology patterns were different between an annual population in the north location and a perennial one for central-south populations. The taxonomic clarity should be evaluated in order to better understand if there exists intraspecific (dependent on morphology) or interspecific variation.

Daily and seasonal changes of photobiological responses in floating bull kelp Durvillaea antarctica (Chamisso) Hariot (Fucales: Phaeophyceae)

Abstract: Floating seaweeds are important dispersal vehicles, especially for organisms with limited movement capacities and for the seaweeds themselves. The persistence of floating seaweeds is determined by the balance between their acclimation potential and the environmental pressures at the sea surface. Solar radiation is the most important inducer of physiological stress, varying in intensity throughout the day and the year. Therefore photoinhibition and subsequent recovery can change depending on the daily radiation dose and season. The bull kelp Durvillaea antarctica is one of the most common floating seaweeds in the southern oceans, including New Zealand, Chile, and most subantarctic islands. Herein, daily cycles of maximum quantum yield (Fv/Fm), photoinhibition and recovery levels were examined in microcosm experiments with floating D. antarctica throughout the year, focusing on the blade side exposed to solar radiation (sunny vs shadow side). Also, the effect of simulated wave action (blade turnover) and ultraviolet radiation (UVR) on photoinhibition and recovery of Fv/Fm was evaluated. Significant differences in maximum quantum yield were observed between blade sides, with lowest values on the sun-exposed side, especially during noontime and spring/summer months. Phlorotannins and pigments were measured during seasons with the most intense solar radiation (late spring, early summer), when Fv/Fm values were lowest. Phlorotannin, but not pigment concentrations, differed between sunny (lower concentration) and shadow blade sides (higher concentration) and throughout the daily cycle. Both blade sides had similar photoinhibition and recovery levels when blades were constantly turned over. Absence of UVR favoured the recovery capacity of Fv/Fm in both blade sides, suggesting that the photorecovery potential of floating kelps depends on the environmental conditions that kelp rafts face at the sea surface (e.g. cloudy vs sunny days, intense seawater movement and splashing vs calm sea conditions). The results confirm that photobiological stress is more severe during summer and on continuously sun-exposed blade sides, thereby damaging the blades and suppressing the floating time of D. antarctica.

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.