WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2016 55 FIGURE 1. A juvenile red abalone affected by burrowing worms. Note the open channel over the shell. The soft body was easily detached from the shell. the hole and to avoid damage to its soft tissue. Specialized cells in the mantle called amebocytes migrate to the affected area and produce a chitinous protein called conchiolin to repair damage to the shell and cover up the hole. This reaction results in an inner, soft, dark, chitinous blister. Over time soft blisters are covered by layers of calcite and once again the mollusk produces a hard shell surface. This phenomenon constantly takes place in nature and, as a result of this relationship, on some occasions half pearls are produced by this kind of shell repair. If the number of mud worms per shell is high or if the shell is thin, the damage can be considerable and can surpass the capacity of host cells to repair the damage. The shell becomes fragile and more vulnerable to predators. Furthermore, open holes allow the mud worm to contact the soft tissues that are then mechanically disrupted, resulting in an injury that can become infected by microorganisms such as opportunistic bacteria that are abundant in the organic material and detritus that accumulates in the blisters. If the damage caused by the worm affects the muscle that supports the shell, the muscle can be easily detached, condemning the mollusk to death. Burrowing worms are a group of spionid polychaetes that may settle on the shell of bivalve mollusks and gastropods such as abalone. The species that cause the greatest damage to their host belong to the genera Polydora and Boccardia. These worms are commonly referred to as mud worms from the great quantity of organic material and detritus that accumulates in the holes carved in the shell of their mollusk hosts. The worms settle on the shell as larvae or crawl in as juveniles and start to burrow into the shell to create a living space. Additionally, some species build a chimney with organic matter and detritus that protrudes from the shell that the worm uses to emerge and feed by capturing microorganisms, microalgae and organic matter in the water surrounding the mollusk shell. Mud worms are not considered true parasites because they do not feed on tissues of their host, but are considered epibionts, which means that they are in a type of biological relationship in which one animal lives over the other with no or minor negative effects. In general, this relationship can be beneficial for the epibiont because it acquires a place to live without harming the host. However, under certain circumstances this relationship can be life threatening for the host. When a worm reaches the inner surface of the mollusk shell and comes in contact with soft tissues such as the mantle or muscle, the host reacts immediately to try to cover Identification of Burrowing Worms and Bacteria Associated with Shell Injuries on Red Abalone Cultured in Baja California, Mexico Jorge Cáceres-Martínez, Yessica Hernández-Mercado, Roberto Cruz-Flores, Montserrat Muñoz-Flores and Rebeca Vásquez-Yeomans (CONTINUED ON PAGE 56) If the number of mud worms per shell is high or if the shell is thin, the damage can be considerable and can surpass the capacity of host cells to repair the damage. The shell becomes fragile and more vulnerable to predators. If the damage caused by the worm affects the muscle that supports the shell, the muscle can be easily detached, condemning the mollusk to death.
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