Gracilaria: A dynamic habitat

Nick Partington, St. Olaf College

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The findings: In my previous post, I described the methods we would be taking this summer to explore how the biodiversity of fishes differ among dense and sparse patches of the invasive alga Gracilaria vermiculophylla. We followed these methods, and we produced some interesting results!

We finally sorted and identified all of the fishes we collected from our samples this summer, and were able to measure the biodiversity between dense and sparse habitats. In particular, we were interested in four measurements of biodiversity. The first, abundance, is simply the overall number of fishes collected from each habitat type. The second, species evenness, measures how evenly individual fishes

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Some of the fishes we collected this summer, separated by species and sample.

are distributed among the different species collected in each habitat type. Finally, diversity took into account species richness, which counts the total number of species collected, and the Simpson’s Diversity Index, which quantifies diversity based on the number of species and the relative abundance of each of those species.

These measurements provided us with some interesting results. In the end, we collected a greater abundance of individuals in sparse sites than in dense sites. We also saw both greater species evenness and greater species richness in dense sites. Additionally, the Simpson’s Diversity Index showed a greater diversity of fishes in dense sites.

As I mentioned, abundance of individuals and species richness were both calculated by simply counting the overall number of individuals and species, respectively, collected in each site. Species evenness, on the other hand, required a bit more analysis. Figure 1 shows rank abundance curves for both sparse and dense patches of G. vermiculophylla. These curves tell us how evenly individuals are distributed among the species collected from each site. For each habitat type, species are ranked from 1 to 10 in decreasing order of abundance. That rank is then compared with the abundance of each species. The slope of the resulting line is what we are interested in. Basically, the flatter the line, the greater the species evenness. In our analysis, the line representing dense sites had a flatter slope, signaling greater species evenness in dense sites than in sparse sites.

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Figure 1. Rank abundance curves for both dense and sparse habitats. The slope of the curve representing dense habitats is closer to 0, indicating greater species evenness in those sites.

As I mentioned, overall we found a greater abundance of individual fishes in sparse sites, while we had greater species evenness, species richness, and diversity in dense sites. These differences between sites are very interesting in themselves. But what is even more interesting is that these results are the complete opposite of what was concluded after this same study was conducted last summer. Therefore, there must be some factor(s) that changed between these two studies. We’re not exactly sure what these factors are, but nonetheless, this highlights the importance of long term studies, as well as the importance of continuing this study to see how these trends in biodiversity change and pan out in the long run. I think a very interesting takeaway from this project is that invasive species, like G. vermiculohylla, can potentially provide benefits and sustain biodiversity in ecosystems here in Charleston and throughout the world.


Special thanks to Tony Harold and Mary Ann Taylor for their guidance in this research project. This project is funded by the National Science Foundation and is supported by the Fort Johnson REU Program, NSF DBI-1757899.

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Gracilaria: What are you hiding?

Nick Partington, St. Olaf College

Screen Shot 2018-07-03 at 10.37.44 AMThe approach: In my previous post, I discussed how we will primarily be researching differences in abundance and diversity of fish and fish species that utilize Gracilaria vermiculophylla as habitat in the Charleston harbor. In order to do so, we have been collecting several samples of fish from the two habitat types this summer. We then sort and identify fish from each sample to determine the number of individuals per species found in each habitat type, and will later carry out statistical analyses to determine if any significant differences exist between the two habitat types. Each of these steps, from collecting to identifying to analyzing, consists of techniques that must be replicated for each sample in order to ensure consistency.

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Sampling in a “sparse” patch of G. vermiculophylla

The first step is to collect the samples. We do this at Grice Cove, just a few minutes’ walk from Grice Marine Lab. On site, we have identified a section where about 20% or less of the beach is covered by G. vermiculophylla. These are the “sparse” patches. The “dense” patches are further down the beach, where about 80% or more of the beach is covered by the algae. At each site, we pull a fifteen foot seine net through about 1-2 feet of water for a distance of 15 meters. We then sort through the net, saving all of the fish and discarding plant matter and invertebrates such as crabs and shrimp. The next step is to sort and identify the specimens that we collected.

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An early stage of sample sorting. This sample includes a flounder (upper right), pipefish (upper left), and several anchovies (middle).

 

 

After being fixed in preservatives for about a week, we sort through our samples, grouping identical fish and identifying specimens to the lowest classification possible (hopefully to the species level). After the sorting and identifications are complete, the numbers of fish of each species for each sample are recorded. Later, after we have collected all of our data, we will perform statistical analyses on the data to discern any significant differences in diversity and abundance of fish that might exist between dense and sparse patches of G. vermiculophylla. Stay tuned to hear about our findings!


Special thanks to Dr. Tony Harold for his guidance in this research project. This project is funded by the National Science Foundation and is supported by the Fort Johnson REU Program, NSF DBI-1757899.

Gracilaria: A Weedy Invader

Nick Partington, St. Olaf College

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The problem: Invasive species come in many different shapes and sizes, with a great variety of effects on the environment. For example, some invasive species infiltrate and destroy native trees, while some are introduced into lakes where they may displace native species and absorb nutrients. Whether aquatic or terrestrial (or perhaps even extraterrestrial), invasive species have been shown to have considerable effects on the environments they invade, and have been proven to play a major role in affecting global change (Vitousek, 1996). Gracilaria vermiculophylla is an invasive seaweed that has been introduced to many regions throughout the world, including the east coast of the United States (Thomsen, 2006, 2007, 2009). It takes the form of a thin, brownish red algae and originated off the coasts of Japan, from which it has dispersed throughout the world by hitching a ride in the ballasts of commercial ships (Krueger-Hadfield, 2017). In South Carolina, it can be observed in dark patches on beaches when the tide recedes.

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A patch of Gracilaria vermiculophylla on Grice Beach, where we will be collecting samples this summer.

Many small fishes use G. vermiculophylla as habitat; it provides them with food, as well as shelter from predators (Byers, 2012). Many of these fishes serve as prey to larger fishes, and eventually the energy they contain travels up the food web to commercially and recreationally important fishes across the world, including within the Charleston harbor area. That is, G. vermiculophylla provides habitat to fishes, which in turn serve as food for larger fishes that are consumed by humans. Having a good understanding of how these fishes use G. vermiculophylla as habitat can aid the conservation and fishing industries in understanding this low-level component of the food web.

My research project this summer is aimed at improving this understanding. We will be replicating the design of a study implemented in the summer of 2017 by studying fish communities occurring in patches of Gracilaria vermiculophylla. Particularly, we will be exploring differences in the abundance and diversity of fishes utilizing dense patches of G. vermiculophylla as compared to sparse patches. We are also interested in any differences that might exist between dense and sparse patches concerning habitation patterns among different developmental stages of these fish species. Our findings may support that which was discovered last summer, or they might reveal a completely new piece of information. I am excited to see what we will find!


Special thanks to Dr. Tony Harold for his guidance in this research project. This project is funded by the National Science Foundation and is supported by the Fort Johnson REU Program, NSF DBI-1757899.


References:

Byers, J. E., P. E. Gribben, C. Yeager, and E. E. Sotka. 2012. Impacts of an abundant introduced ecosystem engineer within mudflats of the southeastern US coast. Biological Invasions 14:2587-2600.

Krueger-Hadfield, S. A., N. M. Kollars, A. E. Strand, J. E. Byers, S. J. Shainker, R. Terada, T. W. Greig, M. Hammann, D. C. Murray, F. Weinberger, and E. E. Sotka. 2017. Genetic identification of source and likely vector of a widespread marine invader. Ecology and Evolution 7:4432-4447.

Thomsen, M. S., K. J. McGlathery, and A. C. Tyler. 2006. Macroalgal distribution patterns in a shallow, soft-bottom lagoon, with emphasis on the nonnative Gracilaria vermiculophylla and Coldium fragile. Estuaries and Coasts 29:465-473.

Thomsen, M. S., K. J. McGlathery, A. Schwarzschild, and B. R. Silliman. 2009. Distribution and ecological role of the non-native macroalga Gracilaria vermiculophylla in Virginia salt marshes. Biological Invasions 11:2303-2316.

Thomsen, M. S., T. Wernberg, P. Staehr, D. Krause-Jensen, N. Risgaard-Petersen, and B. R. Silliman. 2007. Alien macroalgae in Denmark – a broad-scale national perspective. Marine Biology Research 3:61-72.

Vitousek, P. M., C. M. D Antonio, L. L. Loope, and R. Westbrooks. 1996. Biological invasions as global environmental change. American Scientist 84:218-228.

 

One Fish, Two Fish, Red Fish, Killifish

Melanie Herrera, U. of Maryland, College Park

After 9 sampling days, 18 collections, and over 3000 fish, we’ve discovered fishes’ habitat preferences are much more complex than we thought. To recap, our hypothesis predicted fish would prefer dense sites of the invasive seaweed, Gracilaria vermiculophylla, over sites with more open water (thus, less Gracilaria).  We also predicted that dense site would have greater diversity by attracting various types of fish due to its branches that conceal fish from predators.

Our belief that Gracilaria would fulfill the refuge effect, attracting more fish and more diverse species, was supported through the copious amounts of fish found in Gracilaria. Despite more abundance in the dense sites of Gracilaria, more diversity was shown in sparse sites (Figure 1). Among both the dense and sparse sites Atlantic Silversides and Bay Anchovies, Pipefish, and Striped Killifish were the most abundant and common species. While similar species occurred in both habitats, the sparse site had more occurrences of species that were considered rare in dense sites. For example, sparse sites had more occurrences of Spade fish and Florida Pompanos than dense sites. Additionally, sparse sites had species of fish such as leatherjackets and lizardfish that never occurred in dense sites.

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Figure 1: Rank abundance patterns of fish in dense sites (represented by triangles) and sparse sites (represented by circles) of G. vermiculophylla at Grice Cove. The number of fishes were calculated as a logarithm as a measure of relative abundance of fish at each site. Species are ranked from most abundant (1) to least abundant (8-10). Slopes show differences in species evenness amongst sites. Steeper slopes exhibit less species evenness.

 

Supporting our hypothesis, dense sites did demonstrate more abundance. In total, 2944 fish were collected from the dense sites while 361 fish were caught in the sparse sites. It is predicted that smaller-bodied fish used Gracilaria more as a refuge because of their increased vulnerability to threats as small animals. Lack of abundance in sparse sites could be explained by increased exposure to predators and environmental threats.

Increased use of the dense sites shows Gracilaria does contribute towards housing all types of fish, most importantly economically important fishes. According to the National Marine Fisheries Service’s report on fisheries economic in 2011, the seafood industry alone brings in a minimum of $88 million dollars annually. In order to support this important industry, commercial fisheries can use our research to establish sustainable fisheries by understanding the various habitats that help rear economically important fishes. Our identification of the invasive seaweed’s role on housing fish can be used as a protective measure for these fish in future sustainable management.

 

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Figure 2: Two of the top three most abundant species collected from dense sites of Gracilaria. (Left: Striped Kilifish; Right: Atlantic Silversides).

 

Thank you so much to my mentors Dr. Tony Harold and Mary Ann McBrayer for their advice and guidance. This research is funded through the National Science Foundation and College of Charleston’s Grice Marine Lab.

 

Invasive Species: Friend or Foe

Melanie Herrera,  University of Maryland – College Park

Invasive species…. Haunting, domineering, and downright evil. Or are they? Unlike the infamous Zebra Mussels, dominating the Great Lakes, or Fire Ants, constantly wreaking havoc, Gracilaria Vermiculophylla, are giving invasive species a good name. Don’t get me wrong, invasive species infuriate me just as much as the next guy; but Dr. Tony Harold and I are here to draw out the benefits of this invasive sea grass to baby fish.

Unlike the native, simpler sea grass previously occupying Charleston Harbor, Gracilaria is characterized by coarse branching structures that appeal to many species of fish as protective homes. We are particularly interested in fishes in the larval and juvenile stages (the young ones) that associate with these complex habitats. Having access to more protective sea grass, such as this invasive, in these vulnerable life stages can help determine how many of these little guys make it into adulthood. Similar macro-algae to Gracilaria, such as seaweeds, have been known to be preferable hideouts for larvae and juveniles, reducing the pressures of predation. Since Gracilaria is on the rise in our local estuary, the Charleston Harbor, it’s important to find out the role they play in keeping our fish alive and well.

Our project is designed to better understand the level of association of local fish such as Gobies, Atlantic Menhaden, Atlantic Silversides, and other estuary-occupying fishes, with Gracilaria. We will compare abundance and distribution of young fish in dense patches of Gracilaria to sparse patches. Maybe these young fishes prefer the familiarity that native sea grass and open water brings. Or maybe Gracilaria’s “new and improved” design is too advantageous to resist. After we figure this out, we can go on sustainably managing local fish critical to commercial and recreational use and condemning the rest of the invasive species.

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An example of a collection site characterized as a “dense” habitat of Graclaria vermiculophylla.  Photo Credit: Melanie Herrera

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An example of a collection site characterized as a “sparse” habitat of Gracilaria vermiculophylla. Photo Credit: Melanie Herrera

 

Thank you so much to my mentor Dr. Tony Harold and his lab for his advice and guidance. Thank you to Mary Ann McBrayer for helping me facilitate this project. This research is funded through the National Science Foundation and College of Charleston’s Grice Marine Lab.

 

Works Cited

Munari, N. Bocchi & M. Mistri (2015) Epifauna associated to the introduced Gracilaria vermiculophylla (Rhodophyta; Florideophyceae: Gracilariales) and comparison with the native Ulva rigida (Chlorophyta; Ulvophyceae: Ulvales) in an Adriatic lagoon, Italian Journal of Zoology, 82:3, 436-445, DOI: 10.1080/11250003.2015.1020349

 

Grac Attack!

Aaron Baumgardner, The University of Akron

The only thing more pervasive than the constant thoughts of, conversations about, and stress from Gracilaria vermiculophylla in Dr. Erik Sotka’s lab is the invasion of this red alga that is occurring along the coasts of North America and Europe (Sotka, et al. 2013). After only a few short weeks in Charleston, I have seen how prevalent and successful this seaweed is. The success of G. vermiculophylla along the southeastern coasts of the United States is due in part to the established mutualism between it and the decorator worm Diapatra cuprea. This mutualism provides a secure site for the seaweed to grow (Kollars, Byers, and Sotka unpublished manuscript), but it does not explain the success of G. vermiculophylla to thrive in environmental conditions that differ from its native Japanese range.

G. vermiculophylla colonizes a mudflat in Charleston Harbor by clinging to tube-building decorator worms. Credit, Erik Sotka

G. vermiculophylla colonizes a mudflat in Charleston Harbor by clinging to tube-building decorator worms. Credit, Erik Sotka.

Researching G. vermiculophylla can help us understand how aquatic invasions occur. Do introduced populations evolve novel characteristics or do they simply benefit from the phenotypic plasticity of their source populations? To answer this question, it is necessary to test plasticity in response to varying environmental conditions on native and non-native populations (Huang, et al. 2015). Since G. vermiculophylla has spread outside its latitudinal range and into high salinity environments (Kollars, et al. 2015), I will be testing the plasticity of native and non-native G. vermiculophylla populations to a range of temperatures and salinities. Photosynthetic efficiency will be measured using a PAM fluorometer to provide a more objective way to quantify stress (Rasher and Hay 2010).

I would like to thank the College of Charleston for this internship opportunity, Dr. Erik Sotka for mentoring me on my project, and the National Science Foundation for funding REU programs.

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References:

Huang, Q. Q., et al. (2015). Stress relief may promote the evolution of greater phenotypic plasticity in exotic invasive species: a hypothesis. Ecology and Evolution 5(6), 1169-1177.

Kollars, N. M., Byers, J. E.,  & Sotka, E. E. (unpublished manuscript). Invasive décor: a native decorator worms forms a novel mutualism with a non-native seaweed.

Kollars, N. M., et al. (2015, in review). Development and characterization of microsatellite loci for the haploid-diploid red seaweed Gracilaria vermiculophylla. PeerJ.

Rasher, D. B., & Hay, M. E. (2010). Chemically rich seaweeds poison corals when not controlled by herbivores. PNAS 107(21), 9683-9688.

Sotka, E. E., et al. (2013). Detecting genetic adaptation during marine invasions. Grant proposal to the National Science Foundation.