Population structure and maturity stages of Fritillaria borealis (Appendicularia, Tunicata): seasonal cycle in Ushuaia Bay (Beagle Channel)

Abstract

Fritillaria borealis is a cosmopolitan species, very frequent in sub-antarctic and antarctic waters. The objective of this paper was to analyze its size structure and maturity stages at two sites in Ushuaia Bay: a coastal site exposed to anthropogenic pressure (E1) and a reference site (E2) located in the external zone of the bay. Zooplankton was collected during the 2012 seasonal cycle. The sampling method involved the use of a 67 µm-mesh net. Appendicularians were classified in four maturity stages: I) undifferentiated gonads, II) testis and ovary differentiated, III) expanded testis, IV) discharged testis, expanded ovary. Our results showed that the highest densities of F. borealisoccurred in spring and summer at both sites; coinciding with high values of chlorophyll-a. The percentage of juveniles (I and II) exhibited a spatial and temporal pattern similar to that observed for chlorophyll-a values. During spring-summer, juveniles and mature specimens (III and IV) showed a greater gonadal development than those individuals found in autumn-winter. In conclusion, the mismatching in the population structure and the pattern of densities of F. borealis between coastal and external zones would suggest the existence of two sub-populations susceptible to the influence of the anthropogenic impact in the bay.

Spring abundance, biomass and sizes of appendicularians between open sea MPA Namuncurá/ Burdwood Bank and the adjacent coastal area, Southwest Atlantic Ocean: Are they a key link in the trophic web?

“…Their longitudinal distribution along the inshore-offshore gradient of the study area is consistent with their known habits. F. borealis was mainly concentrated in the inshore waters of SI, which is coherent with its typical coastal distribution in this subarctic region (Aguirre et al 2012;Presta et al 2015). Kalarus and Panasiuk (2021) also found the greatest abundances of F. borealis near the coasts of Tierra del Fuego and the Antarctic Peninsula but, interestingly, they also recorded this species offshore in the Drake Passage.…”

“…Despite the ecological importance of these small tunicates, most of the studies carried out so far in the Argentinean Continental Shelf are rather coastal (eg. Spinelli et al 2009Spinelli et al , 2012Presta et al 2015;Capitanio et al 2018). 2020) described the rst registration of zooplankton in the BB during a spring study.…”

Appendicularians and copepods from Scotia Bay (Laurie island, South Orkney, Antarctica): fluctuations in community structure and diversity in two contrasting, consecutive summers

“…Developmental stages (adults, copepodites I-III and IV-V) and sex (male/female) were identified for Oithona similis. Stages of Fritillaria borealis (mature or juvenile) were identified according to Presta et al (2015). Measures of the length of the trunk (appendicularians) and cephalothorax (nauplii, calanoids, and cyclopoids) were taken for size and structure analysis purposes (n = 30-50 for each group per sample).…”

An improved cultivation device for appendicularians with notes on the biology ofFritillariasp. collected in Sagami Bay, Japan

“…Fritillarid species are common in appendicularian assemblages and sometimes occur in high densities (Tokioka, 1955; Shiga, 1985; Presta et al ., 2015), however, laboratory investigations of their life cycles are limited. Paffenhöfer (1976) determined the generation time of Fritillaria borealis Lohmann, 1896 by conducting rearing experiments with his unique cultivation apparatus.…”

“…Fritillarid species are common in appendicularian assemblages and sometimes occur in high densities (Tokioka, 1955;Shiga, 1985;Presta et al, 2015), however, laboratory investigations of their life cycles are limited. Paffenhöfer (1976) Bückmann, 1926(Sato, 2000 and Appendicularia sicula Fol, 1874 (Sato et al, 1999) through several life cycles to examine their generation time.…”