In the last post, Kathryn talked about how fungid corals move surprisingly far. Lizzie talked about how she's going to find out how far fish move within the course of their lifetime. And now, Joey and Michelle are asking about fish movement over evolutionary time - how closely related are different populations of fishes, how does geography influence their populations, and how do unique species form? While we humans are remarkably mobile thanks to air travel, fish movement is a bit more of a mystery. Trying to re-trace history is a tricky task-- especially here in the Red Sea.
Dr. Joseph DiBattista is a postdoc in the Bowen Lab at the University of Hawaii, who is here with HIMB graduate student Michelle Gaither. Joey did his bachelors, masters, and PhD degrees at McGill University in Canada before moving to more tropical climes.
I'll let him tell you his impressions of the Red Sea, firsthand.
Guest Post From Joey DiBattista:
Sniff, sniff ... I love the smell of rotting guts in the morning. The sights and sounds are infectious as the Jeddah fish market gets into full swing. Vendors shouting, the floor slick with a layer of piscivorous slime, colors abound.
Entrance to the Jeddah Fish Market (Photo: J. DiBattista)
Today's visit is a nice break after three days of diving outside of Thuwal in the Red Sea, although that is not to say our time spent on the boat hasn't been fantastic. Our primary goal is to collect small bits of tissue from fish species and invertebrates, for a genetics study, that we might not normally see during regular collections on SCUBA. Deepwater snappers, big groupers, and lobsters come to mind. And it seems that we are in luck, these appear to be abundant at most market stalls, each fisherman pushing his product with a wry grin.
Panulirus versicolor lobsters in the Jeddah Fish Market (Photo: J. DiBattista)The inability to take pictures due to local customs will make identification of the more obscure fauna a bit difficult, but otherwise this place is a gold mine.
We've actually come down to the Red Sea as part of a large phylogeographic project in hopes of expansion. Indeed, over the past 5 years we have collected samples from reef fish and some invertebrate species at a number of sites in the Indo-Pacific; genetic methods have allowed us to assess the level of connectivity (and dispersal) between islands, archipelagos, and coastlines. Given that our home base is the Hawaii Institute of Marine Biology (not bad at all!!), the survey was initially focused on addressing some interesting historical questions quite close to home.
For example, Hawaii is known for the highest level of endemic (indigenous and exclusive) reef fish fauna in the world, and yet we still don't know where they came from or when they got there. The two competing hypotheses are that reef fish colonized from the west Pacific via an offshoot of the warm water Kuroshio current somewhere near the coast of Japan, or they otherwise made their way up the southern line island chain, perhaps using Johnston Atoll as a stepping stone for colonization into Hawaii. These ideas are based on the overlap of fish fauna between these regions, as well as some models that simulated larval trajectories between such sites. Sequencing DNA at mitochondrial genes (i.e., Cyt b, COI) have allowed us to address theses competing hypotheses by assigning approximate dates to population splitting or colonization events, although the verdict is still out.
The push to get into the Red Sea was spurred by the fact that this body of water is similarly renowned for a high degree of endemic fish fauna (~17% overall). That is, ~17% of the reef fish in the Red Sea are found only in the Red Sea. In fact, endemism is as high as 50% for some charsimatic taxa like the butterflyfishes.
Chaetodon semilarvatus (L) and C. larvatus (R) are both butterflyfish species found ONLY in the Red Sea (Photos: R. Rotjan)
What can explain such isolation? Well, several barriers to dispersal from the Red Sea region have been proposed. First, the narrow (18 km wide) and shallow (100 meters deep) nature of its only connection with the Indian Ocean, the Straight of Bab-el-Mandab, presumably restricts movement of planktonic larvae in and out. This is particularly true during low sea-level stands as recently as 10,000 years ago that decreased the exchange of water masses through this narrow straight and may have led to massive extinction of fish fauna.
Another potential barrier exists just outside of the Red Sea in the Gulf of Aden and Indian Ocean. Indeed, a lack of suitable reef habitat from Somalia to India or Kenya, due in part to the cold water upwelling found off most of this coastline, may greatly restrict the dispersal of reef fish larvae and thus act to reinforce endemic species. Genetic tools provide a means to test these ideas. So, it's now back to the lab to process all of these samples! Balancing the taxonomic books is not simple... but here in the Red Sea, hopefully we'll come out in the black.