DAO 24:215-226 (1996)  -  doi:10.3354/dao024215

The echinoid Strongylocentrotus droebachiensis in the Vestfjorden area of northern Norway is infected by the epizootic nematode endoparasite Echinomermella matsi. The incidence of E. matsi was 68.8% in a sample taken from Godøystraumen, and 16.4% in a sample from Værøy Island. The high-incidence sample was collected in late February prior to the annual spawning season, when the echinoids have sexually mature gonads, and the low-incidence sample was collected in late August, when the echinoids have sexually immature gonads. Infected echinoids in both samples had smaller gonads than non-infected echinoids. The parasite-related reduction in gonad size for adult echinoids >=35 mm in test diameter was approximately 75% in the high-incidence sample, and approximately 63% in the low-incidence sample. Most S. droebachiensis in the high-incidence sample were infected before they reached a size of 20 mm test diameter. The infected individuals had parasite loads ranging from approximately 0.01 to >5 g. However, lightly infected individuals with loads <0.1 g were most common, comprising 52% of the infected individuals in the high-incidence sample, and 72% of the infected individuals in the low-incidence sample. The abundance of heavily infected echinoids with parasite loads >=0.1 g peaked in the [30, 35> mm size group, but dropped abruptly in the next interval of the size-frequency distribution. Although the peak abundance of heavily infected echinoids coincided with the onset of sexual maturity for non-infected echinoids, the majority of the infected echinoids in this size group were still classified as virtual castrates of unknown sex. These results suggest that a large proportion of infected echinoids never reproduce, but are effectively castrated as juveniles and succumb to parasite-related mortality before they reach a size of 35 to 40 mm.

Sea urchin . Disease outbreak dynamics