Cannibalism as a feeding strategy for mantis shrimp Oratosquilla oratoria (De Haan, 1844) in the Tianjin coastal zone of Bohai Bay

A representative semi-enclosed bay of China, Bohai Bay has experienced severe interference in recent decades and is under threat from rapid human development. Although the mantis shrimp Oratosquilla oratoria plays an important role in the ecosystem and fishery, its feeding ecology and the impact of habitat changes on its feeding habits are poorly known. In this study, we sought to identify the prey consumed by O. oratoria through the separation of stomach contents and to describe its trophic ecology during maturation, from March to July, in the Tianjin coastal zone of Bohai Bay. A total of 594 specimens were collected and 347 (58.59%) stomachs were found to have food remains. More than half of the O. oratoria individuals had poor feeding activity, and the degree of feeding activity of females was higher than that of males, but there was no significant difference in the visual fullness index and the fullness weight index (FWI) between sexes for each month. And the feeding activities of O. oratoria were consistent over the study months. A total of 207 prey items yielded 231 readable sequences and 24 different taxa were identified. Prey detected in O. oratoria consisted mainly of crustaceans, which accounted for 71.86 % of the clones detected; 16.02% corresponded to fishes, 8.23% corresponded to mollusks and the remaining 3.90% corresponded to other marine organisms. Cannibalism (occured frequently, 69.08%) in this study was noticeably higher than that seen in previous studies and confirmed that cannibalism may be a significant feeding strategy in the mantis shrimp O. oratoria in the Tianjin coastal zone of Bohai Bay. The ecological environment in Bohai Bay has been affected by anthropogenic activities and the macrofaunal biodiversity and abundance have noticeably declined, which might make the food scarce for the mantis shrimp O. oratoria. Then, the starvation obviously increased cannibalistic tendencies.


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The mantis shrimp, Oratosquilla oratoria (De Haan, 1844) (order Stomatopoda) 44 is well known as a ferocious predator with its large and powerful raptorial appendages. 45 It is a benthic, neritic and burrowing shrimp that is found on muddy bottoms in the 46 coastal waters of Siberia, Korea, China, Japan, Vietnam, and Australia [1,2]. It has 47 become a commercially important species in these regions. 48 In Bohai Bay, the mantis shrimp is heavily caught by bottom-trawl and trammel 49 nets, whose annual catches account for more than one-third of the crustacean catches 50 in the past ten years [3]. A substantial decrease in the stock size of large female 51 shrimps has been apparent since the fishing industry catch, in which larger individuals 52 are overexploited, and the season of spawning fastigium is delayed to mid-to-latter of 53 May, while some female shrimps also spawn into September [1,[4][5][6]. The abundance 54 of mantis shrimp pseudozoea is low before July [4,6].  China. As one of the most important marine fisheries and natural resource reserves in 65 China, the ecological environment of Bohai Sea has always been of wide concern [11,  Artificial breeding of mantis shrimp has been explored, and the promotion of 80 gonadal development has become a knotty technical problem in artificial cultures [17].

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In the absence of available formulated bait, the discovery of the feeding ecology 82 during gonad maturation will provide a reference for aquaculture and artificial 83 breeding of this commercially important species.

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Because of the importance of this species to the ecosystem and for fisheries, we 85 sought to identify the prey consumed by O. oratoria through the separation of 86 stomach contents, and to describe its trophic ecology during maturation in the Bohai 87 Bay using the DNA barcoding method. 90 Tianjin city is situated in the western part of Bohai Bay in China, and the study area 91 was the Tianjin coastal zone (Fig 1). All the analyses have been carried out using   Table 1.

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Feeding intensity during the study months was determined based on the degree of 117 fullness of the stomach. A visual stomach fullness index was assigned to 5 levels: 0= 118 empty, 1= scarce remains, 2= half full, 3= almost full, and 4= completely full [19].

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The mantis shrimp with stomachs at level 2 to 4 were considered to have been 120 actively feeding, while stomach at 0 and 1 levels were considered to indicate poor 121 feeding activity, and the percentages of shrimps with actively feeding (AF) and poor  Biosystems) automatic sequencer. Obtained sequence producing mixed peak indicated 154 that more than one prey species were present. Those PCR products were cloned using  the AF proportions of females were larger than those of males except in June (Fig 2). From March to July, most FWI values for the females ranged from 1.54 to 7.52 (Fig   206   3a) which were larger than those for males, from 1.49 to 4.83 (Fig 3b), but no 207 difference was found in the FWI between sexes for each month or between months for 208 each sex, after comparison with the transformed data (P>0.05).  (Table 2). Of the 21 clones, only one clone showed more than a 95% similarity 224 to reference sequences, while the remainder showed similarities between 82 and 91%.

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A total of 24 different taxa were identified. The representative sequences were 226 submitted to GenBank (submission ID is: 2250197) and also submitted as Supporting 227 information (S1 File).  and three matched to Varunidae (Fig 4). The cumulative prey curve shows that 207 stomachs were adequate to describe the 263 diet of this species. The slopes of the saturation curves rapidly approached the 264 asymptotes, indicating that sufficient sequencing reads were generated to capture 265 major prey items and trends towards capturing full taxon richness (Fig 6).  cannibalism decreased with an increase in diet species (Fig 7).  The survey data of the macrobenthic community were obtained as closely as possible 370 to the times when the mantis shrimps were sampled in previous studies, as listed in 371