It is well-studied that predators have a significant effect on their prey both on the land and in the sea, termed top-down control. However, characterizing the geographic variation in the strength of predation, scaling from different habitats to different latitudes, has been difficult to do, particularly in the ocean.
MarineGEO has pioneered a well-vetted, simple assay to assist in building a map of feeding intensity around the world using the “squidpop”. A squidpop is a piece of dried squid tethered to a stake, deployed in a large array, and sampled for presence/absence after 24 hours to quantify the rate of consumption at a site.
In Florida, led by Dean Janiak and with the help of two summer interns, Madison Wheeler (Stetson University) and Ben Johnson (Florida A&M), we are trying to advance this simple technique by asking a variety of new questions that focus on the particular prey being used. Tunicates, commonly called sea squirts, are a marine fouling species found throughout the ocean attaching themselves to a variety of different structures. Tunicates also form a large majority of the non-native species, found aggregating on mostly on artificial structures (e.g. docks, seawalls, pilings).
Within the Indian River Lagoon, Florida, we are starting to see a well-established, non-native tunicate, Styela plicata, in relatively high densities in seagrass beds. This summer we are running several trials using what we call “tuni-pops” in conjunction with squidpops to test prey preference of fish in seagrass beds. Tuni-pops utilize the same technique as a squidpop assay and the morphology of a tunicate is quite comparable to dried squid.
Within the Indian River Lagoon, we have over 30 species of tunicates, many being non-native, and consequently have an endless supply of prey to utilize. Many of these species have a cosmopolitan distribution and therefore simple experiments deployed in different habitats or even throughout world can easily be done to test how particular fish species or diversity of fish can provide a means of biotic resistance (i.e. the ability of a native community to prevent non-natives from becoming established). For example, non-native species are more prevalent on artificial structures but is this because in general, fewer fish are found under docks? Non-native species are a major threat to ecosystems around the world and it is important to not only study their effects on native communities but also what, in particular, makes them such good invaders.
Results from our preliminary trials are indicative that at least for Stylea plicata, fish appear to have no interest in consuming this species compared to squid, potentially leading to its high densities in the seagrass beds in Florida.