Biological characteristics of parasitic Nepinnotheres novaezelandiae within a Perna canaliculus farm

Abstract

Pea crabs are commercially significant parasites in the aquaculture production of bivalves in many parts of the world. However, there is scant information available on the biology of these important parasites in aquaculture. The population structure, sex ratio, and breeding status were determined for the pea crab Nepinnotheres novaezelandiae residing in a typical greenlipped mussel Perna canaliculus farm in New Zealand. Of the 324 crabs randomly sampled, there were significantly more female (82.4%) than male (17.6%) crabs found. The vast majority of crabs (87.0%) were sexually mature and of these, females comprised 86.4% and males 13.6%. However, the sex ratio of immature crabs was relatively even, suggesting that male crabs may have higher mortality while searching for mates. Crab size was highly variable, indicating that recruitment to mussels in the farm was continuous. Carapace width ranged from 4.00 to 11.5 mm, with males tending to be smaller with a mean (± SE) carapace width of 6.31 ± 0.16 mm versus females with a carapace width of 8.03 ± 0.06 mm. The crabs did not show any preference for parasitizing mussels of different sexes. Despite the fact that the mussels were only 10 mo old, most female crabs were sexually mature (Stage V) and 89.3% were gravid. The mean (± SE) clutch size was 2592 ± 579 and clutch size was directly associated with female carapace width. The mussel farm pea crab population was estimated at 126 390 ± 14 144 individuals, including 93 000 gravid females carrying a total of over 241 million eggs. Overall, the results show that pea crabs rapidly colonize farmed mussels and mature quickly to establish a significant breeding population within the mussel farm, with larval output capable of infecting nearby mussel farms as well as wild populations of bivalves.KEY WORDS: Pea crab · Green-lipped mussel · Greenshell™ · Parasite · Mussel farm · Brachyura Resale or republication not permitted without written consent of the publisherDis Aquat Org 101: 61-68, 2012 62 that pea crab infection was responsible for a loss in production across the nation's mussel aquaculture industry of US $2.16 million annually (Trottier et al. 2012).Infection levels in wild mussel populations by Nepinnotheres novaezelandiae vary widely and have been reported to range from 4 to 70% (Jones 1977a, Hickman 1978, Baxter 1981, Bierbaum & Ferson 1986). Within green-lipped mussel aquaculture an infection level of 5.3% has been reported, although higher levels are suggested to occur (Trottier et al. 2012).The life history of Nepinnotheres novaezelandiae has been partially described, with most larval stages inferred from related species (Bennett 1964, Jones 1977b, Wear & Fielder 1985. After hatching from eggs, the larval development begins with an unknown number of zoeal stages which are presumably followed by a megalopal stage that has never been observed (Wear & Fielder 1985). The first crab instar is thought to be the invasive stage and is followed by a series of soft carapace stages for both sexes (Jones 197...

Association between the Crab, Nepinnotheres pinnotheres (Linnaeus, 1758), and the Endangered Species Fan Mussel, Pinna nobilis (Linnaeus, 1758), from the Aegean Sea, Turkey

“…In Campania and Sicily, large scale mortality of P. nobilis population was noticed pen shella of all sizes because of mycobacterial diseases (Carella et al, 2019). Trottier (2012) indicated that pea crab Nepinnotheres novaezelandiae (Filhol, 1885) caused a significant loss of production on aquaculture in New Zealand green-lipped mussels, Perna canaliculus. Pea crabs lead to a variety of negative effects such as gill damage, shell distortion, nodule formation, and decrease in condition index to their host (Trottier, 2014).…”

Mate locating and access behaviour of the parasitic pea crab,Nepinnotheres novaezelandiae, an important parasite of the musselPerna canaliculus

“…These results support the theory of a chemical cue although the use of a visual or acoustic cue, or combination of cues, would need to be verified further before definitively associating the mate attraction of this species. However, the ability of female crabs to remotely attract mates may be particularly important in this species in which the proportion of mature male crabs in a population can be relatively low (17.6%) and the number of mussels hosting a female is low (typically <10%) both of which would otherwise limit the successful location of mates by males [ 46 ].…”

“…Establishment and growth of N. novaezelandiae in newly seeded mussel farms from larval settlement is swift as the species appears capable of rapid infection and tremendous reproductive output [ 49 ]. For example, a 10-month-old population of farmed green-lipped mussels contained a crab population in which 86.4% were mature females carrying with a mean brood size of 2592 (±579 SE ) and totalling an estimated 241 million eggs for the farm [ 46 ].…”

“…Locating and accessing mates provides a potentially dangerous set of circumstances for male N. novaezelandiae . Mature male crabs must squeeze out of the gaping valves of their host mussel without being crushed in order to search for female mates [ 6 , 46 ]. Males of the oyster pea crab, Pinnotheres ostreum , were observed to be routinely crushed when attempting to enter or exit an oyster host and although 70% of males were able to make entry into a host, 13% of them were crushed in the process [ 44 ].…”

“…One of the potential ways male N. novaezelandiae may facilitate the location of mates is through the use of pheromones [ 46 ], a method used by many crustaceans and which has been observed in some Pinnotherids [ 3 , 20 , 21 , 40 ]. Indeed chemoreception has been highlighted in Pinnotherid species by Ambrosio and Brooks [ 2 ] for host recognition [ 17 , 42 ], habitat selection [ 5 , 24 , 43 ], predator avoidance [ 11 , 16 ] and conspecific signalling [ 4 , 28 ].…”