The percentage of bored valves in ? Ostrea ? patagonica was 98% (n=53), which is significantly higher (pO. puelchana (35%, n= 314) and ? O .? alvarezii (35%, n= 186).
In ? Ostrea ? patagonica 95% of right valves and 100% of left valves contained borings. On the other hand, in O. puelchana only 23% of right valves and 47% of left valves showed any borings. In ? Ostrea ? alvarezii the right valves with perforations were 18% while 51% of the left ones were bored. In ? Ostrea ? alvarezii and O. puelchana the percentage of borings in the left valve was significantly higher than in the right one (pOstrea puelchana and ? O .? Alvarezii showed no significant differences (p>0.05).
The studied valves of ? Ostrea ? patagonica record 1,169 borings of Lithophaga sp., with an average of 21 borings on the right valve and 25 on the left one. In Ostrea puelchana there was a total of 282 borings, averaging 1.7 for the right valve and 3 for the left one. In ? Ostrea ? alvarezii there were 168 borings with an average of 1.6 in the right valve and 3 in the left one.
Most of the bored valves of ? Ostrea ? patagonica showed between 1 and 30 borings, with a maximum of 75 (figure 4). In ? Ostrea ? alvarezii and O. Puelchana most bored valves showed between 1 and 2 borings (maximum 12) and 1 and 3 borings (maximum 21) respectively (figure 4).
Analysis of the contingency tables (tables 1, 2, 3) shows that only the left valve of ? Ostrea ? patagonica showed no preferential location for the borings (p>0.05). The right valve of ? Ostrea ? patagonica and both valves of ? O .? alvarezii and O . Puelchana showed preferential distribution of the borings (pOstrea ? patagonica were the anterior and posterior margins (figure 5). In the left valve of Ostrea puelchana , the platform and the apex carried the highest number of borings while on the right valve it was the apex (figure 6). In both valves of ? Ostrea ? alvarezii the sectors containing more borings were the apex and anterior margin (figure 7). In all species, the ventral margin showed a boring frequency lower than expected.