Predator Oncaea mediterranea (Copepoda: Oncaeidae) attacking SD complex paralarvae in the Gulf of California

Presenting Author: Raymundo Avendaño-Ibarra

Authors: Raymundo Avendaño-Ibarra, Roxana De Silva-Dávila, Ricardo Palomares-García

Instituto Politécnico Nacional, CICIMAR – IPN, Av. IPN s/n. Col. Playa Palo de Sta. Rita. CP 23096. La Paz, BCS, México.

Studies on cephalopod paralarval abundance in Mexican Pacific waters, indicates that the SD complex (paralarvae ≤3.0 – 4.0 mm of mantle length of Sthenoteuthis oualaniensis and Dosidicus gigas) is the most abundant taxa in the cephalopod community. Attacks of zooplanktonic predators upon these ommastrephid paralarvae have been registered in samples collected in the mouth of the Gulf of California. Predation results were obtained from two out of 10 oceanographic cruises. These were made in November 2004 and 2006 on board of the SSV Robert C. Seamans and along 2014 – 2017 in one coastal station at Cabo Pulmo National Park (CPNP). Zooplankton samples were taken with a CalCOFI net towed obliquely (200 m depth, 19 samples) and with Neuston net (1 m wide x 0.5 m height, 335 μm, 15 samples) tows. The copepod Oncaea mediterranea was the only predator observed attacking paralarvae of the SD complex. During 2004 predation was recorded in two oceanic stations (10% of the total samples), in 2006 in 46% of the samples, and sporadically in the CPNP. In 2006, predation was observed in the same region that during 2004 but also in front of Bahía de La Paz where it was higher. Most attacks were associated with high abundance of paralarvae collected in surface, and occurred in organisms averaging 1.2 mm of mantle length.
Relative importance of Oncaea mediterranea predatory activity by station (1 to 30%), support the hypothesis that this copepod species account for mortality of recently hatched paralarvae to a high degree.

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