Mass mortality of pen shell Atrina maura (Bivalvia: Pinnidae) due to abrupt population increase of tunicate (Distaplia sp.) in a subtropical bay, Mexico

Taxonomic identity of Distaplia stylifera (Tunicata, Ascidiacea), a new arrival to the eastern Pacific displaying invasive behavior in the Gulf of California, Mexico

“…The taxonomy of the genus Distaplia is mainly based on characters such as colony shape, arrangement of zooids in systems, presence or not of gonadal sac, stigmata per row, stomach shape and external surface, and muscle arrangement (Van Name 1945;Kott 1990;Monniot and Monniot 2001). According to these morphological characters, the specimens collected at Ensenada de La Paz between 2015 and 2017 reported in Moreno-Dávila et al (2021) and in the present study match well with the detailed descriptions of D. stylifera given by Van Name (1945), Monniot (1988), and Monniot and Monniot (2001). The original description of Kowalevsky (1874) as Didemnium styliferum lacks some key characters, as is often the case with old descriptions: the presence of parastigmatic vessels was not mentioned, and the holotype specimen was likely juvenile, with under-developed gonads.…”

“…Colonies of the three different color morphs (white, orange, and purple) of Distaplia cf. stylifera were collected with autonomous diving, using a spatula to extract the colonies from the substrate in four sampling sites of Ensenada de La Paz BCS ( 24°8'01"N, 110°23'26"W ; 24°7'29"N, 110°22'25"W ; 24°8'41"N, 110°21'52"W ; 24°9'31"N, 110°20'16"W ) during December 2017, June 2021, and October 2021, to investigate the identity of the species that caused the mass mortality event of pen shells Atrina maura ( Moreno-Dávila et al 2021 ). The specimens were relaxed with menthol crystals for taxonomic examination.…”

“…A rapid population growth of an ascidian, preliminarily identified as Distaplia cf. stylifera , was detected in Ensenada de La Paz starting in June 2015 and causing one year later (June 2016) a mass mortality event on Atrina maura (Sowerby, 1835), a bivalve whose natural populations are harvested and represents an economically relevant income for regional fishermen ( NOS 2015 ; Moreno-Dávila et al 2021 ). The abrupt and rapid colonization of the ascidian was facilitated by the abundant substrate provided by the pen shell, which reached mean densities in the area of more than 47 indvs/250 m 2 ( Moreno-Dávila et al 2021 ).…”

“… stylifera , was detected in Ensenada de La Paz starting in June 2015 and causing one year later (June 2016) a mass mortality event on Atrina maura (Sowerby, 1835), a bivalve whose natural populations are harvested and represents an economically relevant income for regional fishermen ( NOS 2015 ; Moreno-Dávila et al 2021 ). The abrupt and rapid colonization of the ascidian was facilitated by the abundant substrate provided by the pen shell, which reached mean densities in the area of more than 47 indvs/250 m 2 ( Moreno-Dávila et al 2021 ). The pen shell fishery was closed since 2013 to allow the population to recover after years of over-exploitation, thus the rapid tunicate colonization was linked to the success in the recovery of the pen shell population, while other environmental variables (sea surface temperature, sea surface Chlorophyll- a concentration, and dissolved oxygen concentration) did not have a significant ecological influence ( Moreno-Dávila et al 2021 ).…”

“…The abrupt and rapid colonization of the ascidian was facilitated by the abundant substrate provided by the pen shell, which reached mean densities in the area of more than 47 indvs/250 m 2 ( Moreno-Dávila et al 2021 ). The pen shell fishery was closed since 2013 to allow the population to recover after years of over-exploitation, thus the rapid tunicate colonization was linked to the success in the recovery of the pen shell population, while other environmental variables (sea surface temperature, sea surface Chlorophyll- a concentration, and dissolved oxygen concentration) did not have a significant ecological influence ( Moreno-Dávila et al 2021 ). Results of a biofouling experiment carried out in Bahía de La Paz reported that Distaplia cf.…”