Size at sexual maturity of the crab Halicarcinus planatus (Brachyura: Hymenosomatidae) in both extremes of its geographical distribution

MARIANO J. DIEZ; GUSTAVO A. LOVRICH; EDUARDO D. SPIVAK

Coquimbo, Chile

Congreso; The Crustacean Society Mid-Year Meeting; 2007

The Crustacean Society

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The brachyuran crab Halicarcinus planatus is the only Hymenosomatidae that occurs in the southern tip of South America. On the Atlantic coast, it is present along the Patagonian coast, from the Cape Horn (56º S) to Mar del Plata, Argentina (38º S), in the intertidal rocky shores and kelp holdfasts. Here, we compare the size at sexual maturity of H. planatus in the northern and southern limits of its geographical distribution in the Atlantic Ocean: Mar del Plata (37º 59´S 57º 32´W; minimum seawater temperature 10ºC, MDP) and the Beagle Channel (54º 51´S 68º 33´ W; maximum seawater temperature 11ºC, BC), respectively. The routine Mature was used to estimate the size of 50% of sexual maturity (SSM50) from crab morphometric data. Abdomen width and right chela length were regressed on caparace width (CW) in females and males, respectively. Eggs attached to the pleopods and the occurrence of spermatophores the vas deferens defined the physiological maturity in females and males, respectively. The CW value corresponding to 50% maturity from respective logistic equations provided the size at physiological maturity (SPM). In the BC, average sizes were 8.47±2.09 and 7.69±2.71 mm CW for females and males, and in MDP average sizes were 3.18±1.18 and 2.84±1.19 mm CW for females and males respectively. On average, females were always significantly bigger that males. In males, SSM50 was 9.01±0.24 and 3.89 mm CW in BC and MDP, respectively. In both populations the male SSM50 was higher than SPM. In females, SPM was 4.3 and 9.8 mm CW in MDP and BC, respectively. We hypothesize that these differences in sizes are related to a higher molt frequency and a lower molt increment in MDP than in CB, due to higher temperature regime. This presentation partially fulfills the requeriments for the PhD degree of MJD at the Universidad Nacional de Mar del Plata, Argentina.