Author: Dr. Jessica F. Muhlin, Associate Professor of Marine Biology, The Corning School of Ocean Studies, Maine Maritime Academy
Thank you for giving me an opportunity to gush about my favorite organisms on the planet- THE ALGAE!
Algae are an amazingly diverse group of organisms that are central to life on Earth. The ancestral algal lineage, the cyanobacteria, through the evolution of photosynthesis is responsible for elevating levels of atmospheric oxygen and provided the breathing room for the diversity of eukaryotic organisms evolve in an aerobic environment. It is interesting, however, that while the algae are essential to every healthy ecosystem as well as beautiful and commercially important they are not taught in primary or secondary schools. Indeed, phycologists, or scientists who study algae, always have their work cut out for them to teach the general public to understand and appreciate the algae.
To accompany the Ocean Lovin segment on fucoid algae reproduction, here are a few clarifying pieces of information and helpful resources.
The word algae is plural. The singular word for an individual is alga. The word algaes doesn’t exist. Algae can be unicellular or multicellular. They span both the prokaryotic (lineages across the Tree of Life (more on this later).
1. Basic terminology.
The word algae is plural. The singular word for an individual is alga. The word algaes doesn’t exist. Algae can be unicellular or multicellular. They span both the prokaryotic (https://en.wikipedia.org/wiki/Prokaryote) and eukaryotic (https://en.wikipedia.org/wiki/Eukaryote) lineages across the Tree of Life (more on this later).
All seaweeds are algae, but not all algae are seaweeds. Seaweed is a term for big algae (=macroalgae) that lives in the marine environment. Algae, however, can be microscopic (=microalgae), as well as found in lakes, streams, ponds, in ice, in the desert, and within symbiotic relationships (think corals and lichens, among others).
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Image of Fucus vesiculosus which a seaweed (marine macroalga) on the left and an image of diatoms (marine microalgae) on the right (from Wikipedia).
All kelps are seaweed, but not all seaweeds are kelps. Kelps are an order within the brown algal lineage, the Laminariales. There are many other orders of brown algae.
2. Origins and relationships.
As mentioned before, the algae are an amazingly diverse group. Indeed, algal lineages span both prokaryotic (=cyanobacteria) and eukaryotic domains. Eukaryotic algal lineages, denoted by stars in the figure below are flung across the Tree of Life. One common mistake is to informally call seaweeds “plants”. This phylogenetically would work for red algae and green algae that are part of the Archaeplastids, but not for brown algae which are part of the Stramenopiles. All land plants derived from a green alga, but other algal lineages, such as brown algae, are genetically very distant from land plants. Just because they also photosynthesize, doesn’t mean that they are the same thing.
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Image modified from [1] Worden et al. (2015).
It is confusing how disparate the algae appear to be on a phylogenetic tree until you reckon the process of primary and secondary endosymbiosis. This fascinating process is wonderfully described by [2] Archibald (2015) and could be the focus of a future podcast.
3. Algal reproduction –> Fucoid reproduction.
The focus of the podcast has been on reproduction of ocean organisms. Reproduction among the algae is just as fascinating and diverse as the diversity of algae! Across algal lineages, many different reproductive strategies are employed.
Some algae can reproduce asexually and sexually, whereas others alternate between a haploid and diploid stage. Some algal species are oogamous, having male and female gametes (=sperm and egg), whereas other algal species have two different gamete types but they aren’t oogamous- they can been isogamous or anisogamous. The most complicated life histories are championed by some red algal species that have triphasic life histories (one haploid and two diploid states=another great podcast topic).
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Fucus vesiculosus sperm (left) and eggs (right).
Fucoid algae, relatively speaking, have a simple life history and are excellent models to understand external fertilization in the marine environment. There are decades worth of wonderful literature regarding fucoid reproduction and ecology. This includes work by Dieter Müller [3] characterizing pheromones, Betty Moss [4] describing A. nodosum zygote and germling attachment as well as epidermal shedding with scanning and transmission electron microscopy, Ester Serrão and Gareth Pearson [5] who worked with Susan Brawley at the University of Maine and now are at the University of Algarve in Portugal. The reproductive ecology of algae are less studied compared to marine invertebrates but can provide tremendous insight into achieving high fertilization success in an dynamic environment.
Within the fucoid species Fucus vesiculosus and Ascophyllum nodosum, there are separate male and female individuals. Males produce biflagellated sperm and females produce eggs. Other species in the genus Fucus, such as F. spiralis and F. distichus are hermaphroditic, producing both eggs and sperm.
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Immunofluorescence image of F. vesiculosus sperm swarming an egg (left), line drawing of a biflagellated sperm (Image from here).
The timing of reproduction for Fucus vesiculosus and Ascophyllum nodosum are different. F. vesiculosus is reproductive in the Gulf of Maine from early fall through January and if the winter is mild, it can be reproductive in the winter and spring. Reproduction occurs surrounding new and full moons (=spring tides). A. nodosum, however, has a very short reproductive season of only 3-7 weeks and is water temperature dependent with reproduction being documented in March, April and as late as May. Because of A. nodosum’s reproductive timing associated with water temperature, it is an indicator species in the University of Maine’s Cooperative Extension and Maine Sea Grant program Signs of the Seasons: A New England Phenology Program (https://extension.umaine.edu/signs-of-the-seasons/).
Works cited/research websites:
[1] Worden et al. (2015) Rethinking the marine carbon cycle: Factoring in the multifarious lifestyles of microbes. Science 347 (6223), 1257594-1-10.
[2] Archibald, J.M. (2015) Endosymbiosis and Eukaryotic Cell Evolution. Current Biology 25, R911–R921.
[3] Müller D.G. and G. Gassman (1978) Identification of the sex attractant in the marine brown alga Fucus vesiculosus. Nature 65, 389.
[4] Moss, B. (1975) Attachment of zygotes and germlings of Ascophyllum nodosum (L.) Le Jol. (Phaeophyceae, Fucales) Phycologia 14(2), 75-80.
[5] Ester Serrão and Gareth Pearson: Coordinators of the Biogeographical Ecology and Evolution group: https://www.ccmar.ualg.pt/en/group/biogeographical-ecology-and-evolution
Filed under: Data, History, Outreach, Teaching Image may be NSFW.
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