Scallop-Holothurian Relationship in the Middle-Deep (100m) Argentinian Shelf (Zygochlamys patagonica and Psolus patagonicus)

PENCHASZADEH, P. E.; GIMÉNEZ, J.

St. Petersburg, FL

Workshop; 14th International Pectinid Workshop; 2003

Psolus patagonicus (Ekman 1925) is an abundant holothuroid, living only on the top shell of liveZygochlamys patagonica (King and Broderip 1832), in depths of 100-110m offthe Province ofBuenos Aires, Argentina, among other invertebrates such as Foraminifera, Sponges, Anthozoans,Bryozoans, Ophiurans. Polychaets, Cirripedians, bised Bivalvia and Gastropoda.Characteristically the family Psolidae have a flattened sole they utilize to attach to hard substrataand an armored dorsum of large calcareous plates.McEuen (1986) and McEuen and Chia (1991) have summarized most published information onthe biology and particularly the reproduction and development ofmembers ofthe family. Oftheapproximately 85 species contained in the Psolidae (pawson 1982) there now exists at leastpartial information on the development of 15 species, and 11 species ofthe 15 are believed to bebrooders, but only three are properly documented (McEuen & Chia 1991). There are severaltypes ofbrooding described in Psolidae: coelomic, in dorsal depressions, in folds of sole, underthe sole, in 5 interradial pouches, in chambers underneath dorsal plates, in interradial pouchessurrounding the tentacular crown.Psolus patagonicus incubates the eggs and embryos under the body, between the sole and theZygochlamys shell; the complete development process takes seven months. The smallestrecorded incubating female was 17 mm in length and the maximum size recorded was 23 mm.The setting ofthe eggs under the sole is realized in the months ofFebruary - March (uncleavedegg diameter of887.72 ± SD26.71 um), with a number of eggs per brooding female of 147 ±SD20, the embryos develop reaching a size of 1972.57 ± 158.221lm in September, with numberper female of82 ± SD14. Independent life is achieved in October (2220 ± SD210 um).The most important banks of Zygochlamys patagonica are located along the 100m isobath wherevariation ofbottom temperature is within 1 °C range, mean of 6.5°C.(Campodónico et al. 2001).The longer spawning period coincides with the beginning of the water column verticalstratification (2-3 °C, termocline development) which occurs between October-November(Baldoni et al. 2000). These conditions would produce a phytoplankton sedimentation processtowards the bottom allowing availability offood at deeper waters. This could also explain thereproductive timing ofPsolus patagonicus in this extrem environment. When the juveniles arereleased from their mother sole, as they are suspension feeders, they would find a source of foodin the water in contact with the bottom.Each 40-65 mm in shell high Zygochlamys is hosting a mean of about 2 and a maximum of 4Psolus. The dispersion ofthe young Psolus in the Zygochlamys bank Is done actively crawlingby the holothurian, wich lacks a free swimming stage. For this reason, we found a biggerabundance ofPsolus in very dense Zygochlamys banks.