ECOLOGICAL RESEARCH ON LOBSTERS



A tiny Phylosoma of the Mediterranean slipper lobster. It takes years for the lobster to grow from this floating stage to its adault form.

(Drawing: U. Fiedler)

Diana Barshaw, Kari Lavalli, and Ehud Spanier, together with research assistant Amir Yurman and dive officer Stephen Breitstein, continued a field research project begun last year on three species of lobsters which co-occur in parts of the Mediterranean Sea. The purpose of the project was to determine how effective the different morphologies (claws versus long, spined antennae; spined shells versus flattened, thickened shells; reduced size of appendages; and ability to cling to the substrate) of the lobsters are against attacking triggerfish (Balistes carolinesis), a predator that overlaps the range of all three species of lobsters.

Again we used the local species of slipper lobster, Scyllarides latus, which we obtained from a local Haifa fisherman, and imported 60 specimens of the two other species - the clawed lobster, Homarus gammarus and the spiny lobster (also known as "crawfish"), Palinurus elephas - from Ireland and the United Kingdom.

To test the effectiveness of the strategies particular to each species, we left one set of animals intact and manipulated another set: for clawed lobsters, we either left the claws intact or removed them; for spiny lobsters, we left the antennae intact or removed them; and for slipper lobsters, we bound their walking legs to prevent them from clinging, or left them untouched. Crustaceans are ideal for these kinds of manipulations, as they possess autonomy joints, meaning a limb can be removed with little blood loss due to the nature of the joint. We then tethered the lobsters at our experimental site near the artificial, tire-reefs established off the shores of Tel Shiqmona, Haifa, and assessed predation on the individuals after four and 24 hours. S. Breitstein invested considerable effort in order to obtain fantastic video footage of attack sequences on the lobsters, which we will use to analyze their behavior when under attack by the fish. This year our results have been much clearer: slipper lobsters, whether or not they possess the ability to cling to the substrate, have the highest survival rate of all three species; spiny lobsters possessing their antennae have the next greatest survival rate; intact clawed lobsters and spiny lobsters lacking their antennae rank third; and clawed lobsters lacking their claws never survive the attacks.

As a follow-up to these experiments, we conducted "punch" tests of the strength of the species' carapaces in collaboration with T. Weller, at the Materials Science Department of the Technion. Slipper lobsters possessed the thickest and strongest shells. Spiny lobsters and clawed lobsters had the same shell thickness but other properties of spiny lobster shells (pitting) made them 1.5 times stronger than clawed lobster shells. We have also constructed a lobster pot, which in France has been known to capture triggerfish, and are using this pot on the reef to obtain wild triggerfish which will afterwards be used in laboratory observations of handling time (subjugation, killing, and consumption). We anticipate that the slipper lobsters will require a much greater handling time for the fishes than the other species. We hope to be able to provide some theories about the distributions of these three species of lobster in the Mediterranean Sea, based on the abundance of these highly predatory fish.

As part of the scientific exchange program initiated last year together with our Italian colleagues, Marco Bianchini and Sergio Ragonese, we are sending legs from at least thirty slipper lobsters, packed in dry ice, to Italy for genetic analysis. This is in return for the eighteen spiny lobsters provided by them last year for our field experiments. The Italian laboratory will attempt to determine the genetic relationship between the western and eastern Mediterranean populations of slipper lobsters. Local fisherman Adam Kotzer is helping us in this project by allowing us to take the legs from the lobsters he captures for commercial purposes.

Additional projects planned for the fall, when water temperatures begin to drop enabling us once again to import lobsters, include: the continuation of the handling time observations with the triggerfish; an examination of group strategies against predation by the gregarious species (slipper and spiny lobsters); and an examination of the predatory capabilities of octopuses on these three species of lobster.

         Kari Lavalli


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