How does nearshore biodiversity differ across the Aleutian archipelago?
Does nearshore biodiversity differ between kelp forests and urchin barrens?
In order to address these research questions SCUBA divers surveyed kelp forests, transition zones (an ecosystem that has kelp but also a high abundance of sea urchins, it may be in the process of being converted to an urchin barren), and urchin barrens. In each habitat, SCUBA divers conducted swath surveys, where they counted large invertebrates along a transect and scraping surveys, where they scraped smaller invertebrates and kelp within quadrats so we could count and weigh these organisms in the lab, before returning them back to the ocean.
Preliminary data prepared by Jacob Metzger, University of Alaska Fairbanks
Figure 1 is a non-metric Multidimensional Scaling plot (nMDS) that shows spatial relationships between different organisms across three habitat types: urchin barrens – red triangles, transition areas– blue inverted triangles, and kelp forests – green squares. In nMDS plots, points closer together represent a more similar community, while those further apart are more dissimilar. Data on this plot represents abundances of organisms from scrape surveys conducted in each habitat. On the plot, kelp habitats have little to no overlap with barren or transition habitats, indicating that they have distinct communities. In contrast, transition and barren habitats regularly overlap, indicating that communities are not distinctly different from each other. These interpretations are supported by formal statistical testing (PERMANOVA using PRIMER-R) that support the independence of Aleutian Archipelago kelp forest communities from communities within transition and urchin barren habitats.
Figure 2 is a slightly different nMDS plots, where the vector lines represent how the presence of certain species move the data-points. The overlaid species names indicate that those species contributed to differences between the habitats. Barren habitats have distinctly different kelp communities than transition or kelp communities, which makes sense because urchin barrens are characterized as having minimal kelp in them. However, the transition and barren habitats are more similar and are characterized by containing Eularia fistolosa, or the canopy forming dragon kelp and the understory algae species, Agarum clathratum and Thelassiophyllum clatimus.
Figure 3: We saw that mot species had distinct biogeographic limits, for example the under story kelp, Laminaria sp, and Musculus niger are more abundant in the East region than in the Western region. Some species, like the sunflower star Pycnopodia helianthoides, were completely absent from the Western region of the Aleutians. On the other hand, the sea star, Leptasterias dispar, was present in the western region but absent form the eastern region.