Filling gaps: closing the life cycle of the endangered Mediterranean limpet Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae)

Abstract

Several reproductive issues and the larval development of the ferruginous limpet, Patella ferruginea Gmelin, 1791, an endangered species endemic from the western Mediterranean Sea, were studied to fill gaps in the knowledge of its life cycle.Average diameter of mature oocytes was 141.83 μm and mean oocyte density in the ovary was 283,800 oocytes/gram. No significant correlations were found between both oocyte diameter or density and female shell length. Female fecundity (number of oocytes per gonad) was significantly correlated with shell length and varied between 189,200 oocytes in a 40.0 mm female and 5,019,200 oocytes in an 86.4 mm female. However, there was considerable variability, in particular for largest females.Spawning induction was not achieved using usual molluscan aquaculture methods. Thus, oocytes obtained after dissection of females were used for fertilizations trials. Alkalinization treatments of seawater were used to test improvement in oocyte maturation and later fertilization rates. Treatment at pH 9 during 2 h produced the highest increase in the percentage of mature oocytes and in the fertilization rate; but these results showed high variability and were mainly significant when the initial degree of maturation was low. Sperm concentration experiments determined that best in vitro fertilization were performed at 105 and 5×105 spermatozoids/ml. The sequence and timing of the complete larval development of Patella ferruginea in laboratory conditions is described and illustrated here for the first time. At 20 °C, larvae became competent for metamorphosis 3 days after fertilization, but some crawling pediveliger larvae with a still well developed velum were found even 7 days after fertilization. Recruits 1-2 mm in length were achieved in low numbers from two of the last assays and were first detected between 131-141 days after fertilization. The resulting juveniles were monitored during two years and sex determination of five survivors at the end of this period showed that two were mature males, two mature females and one indeterminate.Our results show that the main reproductive traits or larval development of P. ferruginea hardly differ from those of other non-endangered Mediterranean or NE Atlantic limpet species. Therefore, its decline cannot be mainly attributed to some constraints of these traits as was previously suggested, but to human impact.On the other hand, it is feasible to complete the life cycle of this species in laboratory conditions, from fertilized eggs to mature individuals. However, an important part of the process like spawning induction was not achieved as gonads needed to be dissected fatally from females, although sperm could be obtained from males through non-lethal biopsies. At present, large-scale aquaculture production for reintroduction, restocking or stock enhancement purposes is neither possible nor an advisable conservation tool yet. Further study is required and meanwhile, an appropriate design of a network of effectively protected marine areas that ensures connectivity among extant populations is necessary.

Effects of ocean warming on larval development of Patella ordinaria from the Canary Islands

“…The early stages of larval development in Patella ordinaria appear in this study to be very similar to other related limpet species such as P. ferruginea (Espinosa et al, 2010;Guallart et al, 2020) or P. vulgata (Dodd, 1957;Wanninger et al, 1999) and slightly faster than those recorded in P. caerulea (Wanninger et al, 1999). In both cases, development times did not exceed 48 h, making these species very vulnerable to any environmental alteration to which they are subjected (Morgan, 1995;Guallart and Templado, 2012;Parker et al, 2009).…”

Artificial maturation and larval production of the limpet Patella aspera Röding, 1798 (Patellogastropoda, Mollusca): Enhancing fertilization success of oocytes using NaOH‐alkalinized seawater

“…This suggests that the activation is a time‐dependent process in which the pH influence requires a given time to be effective. For P. aspera , the optimal AT was between 3 and 4 h, which is a long AT since few studies reported activation times longer than one hour (Aquino De Souza et al., 2009; Guallart et al., 2020; Pérez et al., 2019), and usually no more than 10 min (Damen & Dictus, 1994; González‐Novoa, 2014; Hodgson et al., 2007; Pabst‐Fernández, 2015; Pérez et al., 2019; Wanninger et al., 1999). RAO decreases at pH 10 or higher, as reported in other limpet species (Aquino De Souza et al., 2009), probably due to the degradation of the cellular membranes (Aquino De Souza et al., 2009) and the damage of the oocytes (González‐Novoa, 2014).…”

“…Controlled production of the species in aquaculture facilities provides a sustainable alternative to the exploitation of the natural resources and could be applied for restocking purposes. The aquaculture of limpets is a recent research field, so few bibliographical and methodological resources are available (Ferranti et al., 2018; Guallart, 2010; Guallart et al., 2020; Mau & Jha, 2018a), and zootechnical requirements are mostly unknown (Mau & Jha, 2018a). Most efforts on limpets aquaculture research have been focused on the acclimation of adult stocks (Hua & Ako, 2020), design of artificial diets (Hua & Ako, 2016; Mau & Jha, 2018b), reproduction in captivity (Aquino De Souza et al., 2009; Ferranti et al., 2018; Hodgson et al., 2007; Hua & Ako, 2020; Kay & Emlet, 2002; Mau et al., 2018), larviculture and settlement induction (Ferranti et al., 2018; Hua & Ako, 2020).…”

“…The alternative method implies the dissection of mature specimens to extract the gonads and release the gametes (Guallart, 2010; Guallart et al., 2020). However, only 5% of these oocytes could be suitable for fertilization (Dodd, 1957).…”

“…NaOH and NH 4 OH were the most common alkalinizing agents used for the activation in several limpet species (see Table 1 for details). The success of the activation is determined by the pH and duration of the bath (Aquino De Souza et al., 2009; González‐Novoa, 2014; Guallart et al., 2020; Pérez et al., 2016; Pérez et al, 2019). Regarding the sperm activation, in limpets it only requires to dilute the sperm in seawater during a given time (Hodgson et al., 2007; Pabst‐Fernández, 2015; Pérez et al., 2019).…”