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Constanza Chianale Cerda


Constanza Chianale collecting the red alga Palmaria palmata at Letete, New Brunswick. Constanza has become an expert at recognizing reproductive tetrasporophytes and male gametophytes (photo credit: Thierry Chopin).

PhD Candidate: 2011 - present

Doctoral Work: Progress in the understanding of the reproductive biology and cultivation steps of the red macroalga Palmaria palmata (dulse) for its use as a complementary inorganic extractive species in an Integrated Multi-Trophic Aquaculture (IMTA) system in the Bay of Fundy, Canada

Abstract from most recent presentation:Since 2001, two kelps, Saccharina latissima and Alaria esculenta, have been successfully cultivated as the inorganic extractive component of the Integrated Multi-Trophic Aquaculture (IMTA) system on the east coast of Canada. These two species of seaweeds are cultivated at the sites from fall until early summer when they are harvested before the erosion of the blades takes place and their fouling compromises the quality of the final products. The absence of year round crops at the sites, and the need to increase the biomitigative capacity of the IMTA system during summer, led to the investigation into the development of the cultivation of Palmaria palmata, a red macroalga commonly known as dulse and naturally abundant during this time of the year.

Palmaria palmata has been harvested for centuries for direct human consumption as a sea vegetable, as well as for therapeutic purposes. Due to its high protein content, it is also harvested as food source for aquatic animals.

It has a complex life history, alternating an asexual tetrasporophyte phase with a sexual gametophyte phase; moreover, female gametophytes are dwarf microscopic crusts, while male gametophytes are macroscopic and indistinguishable from the tetrasporophytes when they are not reproductive. It is also interesting to note that the tiny females become sexually mature very rapidly: they produce trichogynes within a few days of existence; however, the number of trichogynes declines and they become rare on females 4-5 months old, which by then have grown into small, mis-shapen and stunted organisms. In contrast, males produce spermatia only after they are 8-12 months old. Consequently, precociously fertile females are almost certainly unable to mate with males of the same gametangial generation and are most probably fertilized by older males from the preceding generations that have over-wintered.

The knowledge of the reproductive, ecological and basic biology of P. palmata is necessary to cultivate it appropriately and develop the key steps for its commercial production. Data have been collected since July 2010 to correctly document the identification and occurrence of the different generations of P. palmata in the Bay of Fundy on a year-long basis (most previous knowledge was limited to the summer when it is hand-harvested and sun-dried). The relationship between the different reproductive stages and the length of the individuals was also determined.

Red algae release into the environment non-motile tetraspores (no flagella), which are much larger than the motile spores from brown seaweeds such as kelps. These red algal spores are also characterized by the absence of a rigid cell wall; they are protected by a surrounding transparent mucilage that is responsible for the adhesion of the spores to the substrate. The lack of a rigid cell wall makes these tetraspores fragile and difficult to handle, especially during the first hours after their release, a period that is critical for their settlement and germination. Given these characteristics, the technique developed for the quantification of kelp spores cannot be used. Various techniques for the quantification of red algal spores were tried: counting in a 1ml solution, using a grid, using a Neubauer chamber, using dilutions, and, finally, using a Coulter counter not only counting but also sizing the tetraspores. This last method was retained as it is both rapid and reliable.

Experimental combinations of time of desiccation, darkness and seawater temperature have been tested to induce tetraspore releases. A methodology is now in place to obtain massive releases.

Throughout the year, the spores obtained were seeded over different substrates to determinate the best material for settlement and germination, and the optimal laboratory culture conditions for P. palmata before transfer to the IMTA sites.

We are progressing with the cultivation of this species with a complex life history. It may represent an effective mechanism for maintaining heterozygosity in a population, but it has made its commercial cultivation not easy to develop and, to our knowledge, no previous attempts have succeeded at a large scale.