Interaction Between Red Grouper and Caribbean Spiny Lobster throughout Lobster Ontogeny

In this article, Ellis’ investigates the phenomena in which Caribbean spiny lobster seek shelter and cohabitate in solution holes that are also occupied by red grouper, a common predator of spiny lobster. In detail, Ellis tries to find if in fact the presence of red grouper alters the shelter seeking behavior of spiny lobster, and in particular, juvenile spiny lobster. An additional goal of the experiment was to determine the size of spiny lobster grouper are more likely to consume. Ellis elaborates on the importance of this study by explaining that a farther understanding of this grouper and lobster interaction can help determine population growth and health for the species, as well as providing information for legislation concerning the harvest and protection of both species. To begin his experiment, Ellis located four sites in Florida Bay which had solution holes, potholes in the seafloor carved out by limestone erosion, that were occupied by both Caribbean spiny lobster and red grouper.

Of these test sites, he deemed three of the four sites observation only. The remaining site, Wilkerson Bank, was selected as the experiment site, where he would place his data collection devices and further conduct his research. However, at the three observation sites, Ellis’ team made repeated dives to record and observe the abundance, size and, presence of both red grouper and spiny lobster in solution holes. To do this, divers located solution holes and then proceeded to use flashlights to identify red grouper inside of the holes and estimate a size, as for the lobsters, divers were given a plastic measuring stick in which they would place beside the lobster to observe a measurement (Ellis 2015). Ellis’ then explained the procedure he used at the experiment site specifically to assess the effect of red grouper presence on spiny lobster behavior. For this, Ellis constructed four “casitas” where he used concrete paving stones affixed to a PVC or rebar framework to provide size selective shelter for the spiny lobsters.

He proceeded to place cages on top of two of the casitas, then placed a red grouper inside one of the cages, in hopes to simulate predator presence near a spiny lobster habitat (Ellis 2015). Another method Ellis’ used in his experiment was the use of lobster tethering. In this method, Ellis tethered lobsters of variable sizes near solution holes where red grouper were present. Ellis would then return at twelve and twenty-four hour intervals to assess the predation or presence of the lobster (Ellis 2015). The results of this method would help to assert what size lobster the grouper primarily fed on. In this study, Ellis built off of an extensive base of previous experiments and findings to gather his methods and form a hypothesis for these tests.

In particular, the methods of data collection by the use of casitas and lobster tethering had both been used before and deemed a sound method of determining predation and behavior for spiny lobsters (Behringer et al. 2015). In his discussion, Ellis elaborated on his hypothesis to suggest a connection between red grouper interaction with solution holes and lobster predation. He goes on to say when red grouper excavate solution holes, they indirectly attract more lobster as deeper solution holes were found to have slightly higher abundance of lobster present within them. Ellis then suggests that since there is a higher volume of lobster frequenting the solution hole, there would be more prey sized juvenile lobster nearby for the grouper to feed upon (Ellis 2015).

As for my evaluation of his evidence, the fact that lobsters in a post algal stage are indeed affected by conspecifcs in terms of gregarious behavior (Childress and Hernkind, 1996) supports the claim that the deepening of solution holes by grouper would attract lobster, whose presence would then attract more lobster. However, Ellis’ deployment of casitas is questionable due to the size of lobster that is commonly attracted to them. When casitas are deployed in areas of about ten meters depth, they tend to attract more subadult and adult lobsters than casitas deployed in depths more common in nursery habitats.

In my evaluation of this study, I found a few improvements that could be made in the data collection methods during the experiment. These concerns were primarily around measurement of both the red grouper and spiny lobster. First off the measurements of red grouper came only from the grouper that were being relocated off of solution holes that were being kept vacant and not actually the grouper that were being used in the tethering test. The second measuring error I noticed was in measurements taken at the three observation sites. Here, the measurements of the grouper had to be done by the diver using an eyeball method as the fish would tend to reside deep in cover. An additional aspect I would’ve liked to have seen in this study would be the presence of red grouper near a natural habitat instead of a casita. Finally, the placement of casitas could have been varied across water depths to ensure that casita placement was not too deep or shallow for a thorough mix of lobster sizes.