Cody Dawson is a Master's student in the Phycology Lab under the expert tutelage of Mike Graham. He received his BS in Biology from Humboldt State University where he was mainly working with invertebrates and predator-prey dynamics. Upon joining MLML in 2014, he discovered a love for seaweed which led him to a project surrounding their physiology that would become his life for the next 3 years. With the completion of his MS, he will be moving onto to study the trophic ecology of nearshore ecosystems in the Alaskan Beaufort Sea at the University of Texas at Austin as a part of his PhD.
Nearshore rocky ecosystems along exposed shorelines experience frequent disturbances due to turbulent swells and wave action. These disturbances directly affect subtidal algal communities that provide biogenic habitat along the coast. This habitat shapes faunal communities by providing refuge through structural complexity. In central California, kelps are the most notable providers of biogenic habitat, but, seasonally, a prolific fucoid, Stephanocystis osmundacea, adds a considerable amount of habitat into the environment. While diminutive and bushy during the winter, this alga produces canopy-forming reproductive fronds during the spring and summer months that add to the biogenic refuge. The purpose behind this study was to understand how the frequency and timing of disturbances affect the physiology of Stephanocystis. This was accomplished by performing manipulations on the reproductive and vegetative tissues of the alga, including: full reproductive removal (-R), haphazard vegetative blade damage (-V), no removal (C), and damage of both reproductive and vegetative structures (-All). Using measurements of changes in total length (cm) as a proxy for biomass allowed for an in situ assessment of the response by the alga. This external response measurement was coupled with stable isotope analysis of internal response using carbon and nitrogen as a bioindication of fitness. Removal of reproductive fronds during spring elicited a dormancy response, while damage to the vegetative tissue reduced growth, possibly by limiting overall photosynthetic capacity. These results suggest that spring frond growth is important to reproductive fitness and removal can stimulate a life history trade-off between reproduction and survival. Winter manipulations elicited no response due to the dormancy period of this species. Enrichment values for ∂C and ∂N were consistent with reported values for other brown algal species but, because of the timing of extraction, the internal chemistry of the individuals rebounded and the ability to detect a response was lost. Both the natural and manipulated populations had similar ∂C and ∂N when separated by tissue and time of year, which indicates that while the alga may be impacted from an external perspective, it will recover internally and stay as a viable part of the reproductive population. Understanding how these seaweeds respond to biomass loss provides a better perspective of disturbance effects on this species and the ecosystem it helps support.
Chemical competition between microscopic stages of Macrocystis pyrifera and five native kelp species: does giant kelp always lose?
A Thesis Defense by Suzanne Christensen
Monday, March 19th, 2018 at 12pm
MLML Seminar Room
Suzanne Christensen came to the United States from Sweden in 2004 where she began her educational journey at Foothill College in CA. She transferred to San Jose State University where she was able to attend a few classes at MLML as an undergrad before graduating with a B.S in marine biology in 2010. A year later she joined the MLML community as a graduate student in the Phycology lab. During her time at MLML, Suzanne worked as graduate student assistant for the marine ecology class for one semester and she also worked for the MLML Front Desk for almost all of her time at the laboratories. In addition she also worked for Tenera Environmental for a few months as a research assistant in 2015 before finding out she was about to be a mom. After welcoming the new addition to her family, Suzanne worked part-time at the end of 2016 helping coordinate the Friends of Moss Landing Marine Labs program. She began fulltime employment in 2017 in Santa Cruz, CA, culturing algae and purifying algal pigments that are used to conjugate antibodies.
The giant kelp Macrocystis pyrifera is often considered competitively dominant to other kelp species due to its high productivity. However, on the microscopic level, previous studies found that Macrocystis can be inferior to other kelp species through microscopic interspecies chemical competition. Recruitment failure can be caused by neighboring kelps because there is no species’ specificity in the stereochemistry of the signaling chemical used during reproduction to initiate spermatozoid release; therefore, Macrocystis spermatozoid release is pre-empted by that of its competitors. To date, this interaction has been tested between Macrocystis and only one other kelp taxon, Pterygophora. To test whether Macrocystis is always chemically outcompeted microscopically, I investigated the competitive outcome, by tracking sporophyte production, between Macrocystis and five native kelps using laboratory studies. Tests with Pterygophora californica and Ecklonia arborea showed asymmetric results indicating that Macrocystis was the inferior kelp. Studies using Alaria marginata and Egregia menziesii found symmetric results where both competing species did poorly in the presence of Macrocystis. Lastly, when Macrocystis was settled with Postelsia palmaeformis, there was no significant difference in sporophyte production between polycultures and monocultures for either species. These results indicate that the competitively superior species will vary depending on the specific species interaction . Studying how Macrocystis competes with species microscopically is essential to understanding its recruitment and subsequent population structure which provides the biogenic habitat in the dynamic kelp forest.
MLML John H. Martin Scholarship, COAST graduate award, Myers Trust grant, SJSU Graduate Equity Fellowship, H. T. Harvey Memorial Fellowship, and David and Lucille Packard Foundation.
Physiological effects of nitrate, light, and intertidal position on the red seaweeds Mazzaella flaccida and Mazzaella splendens
A Thesis Defense by Stephan A. Bitterwolf
Friday, November 3rd at 12pm
MLML Seminar Room
California’s intertidal seaweeds Mazzaella flaccida and Mazzaella splendens reside in different intertidal zones. The yellow-green M. flaccida is found in the high- and mid-intertidal, while the brown-purple M. splendens is found in the mid- and low-intertidal. These differences in intertidal position and blade color, in addition to minute differences in morphology, are typically used to differentiate these species in the field. However, a reciprocal transplant study by Foster (1982) found that, not only can M. flaccida and M. splendens reside in each other’s zone, but the color of M. splendens can change to the yellow-green of M. flaccida. Thus, Foster (1982) suggested that these two species may be conspecifics. Presently, genetic evidence supports the separation of both species, however, little progress has been made towards determining the cause, mechanism, and impact of this chromatic plasticity on thallus physiology. The present study serves to further our understanding of this chromatic plasticity in Mazzaella through a series of field and laboratory experiments. In the field experiment, 360 individuals (180 of each species, 90 controls and 90 experimental) were reciprocally transplanted within the intertidal zones of 3 central California sites. Thereafter, transplants were monitored monthly from June – October for blade size and presence. In October, all transplants were removed for pigment analysis. In the laboratory experiments pigment concentrations of both species were quantified from seaweeds cultured in reduced or replete irradiances and nitrate concentrations. Differences in blade size, pigment composition, and survival between site, intertidal zone, species, and culture treatment were investigated with 2-way ANOVAs and non-parametric tests. In these experiments: (1) greening was documented only for seaweeds in the culture experiments, (2) survival was greatest in the low intertidal zone, (3) high intertidal seaweeds contained greater photoprotective pigment content, (4) M. flaccida exhibited increased capacity to regulate photoprotective pigments, and 5) M. splendens exhibited increased capacity of phycobilin pigments. The results of this study illustrate how these intertidal seaweeds can survive adverse conditions such as nutrient limitation or increased light stress/desiccation by cannibalizing phycobiliproteins and increasing photoprotective pigments. The differing extent of each species to regulate photoprotective and phycobilin pigments supports their current classification as separate species.
Acknowledgements from Stephan: This work would not have been possible without the support I received from mentors, labmates, students, family, and friends. Thanks all :D!
Funding: NSF GRFP, Myers Trust, and MLML Wave.
CDFW Permit: #13419