Gracilaria: A dynamic habitat

Nick Partington, St. Olaf College

Screen Shot 2018-07-03 at 10.37.44 AM

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

IMG_5742

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.

Screen Shot 2018-08-09 at 11.11.32 AM

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.

Advertisements

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.

Screen Shot 2017-08-07 at 6.29.24 PM

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.

 

Screen Shot 2017-08-07 at 6.30.34 PM

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.