Filling biodiversity knowledge gaps: Sponges (Porifera: 2 Demospongiae) recorded off San Jorge Gulf (Argentina), SW Atlantic Ocean

: The invertebrate by-catch of the Argentinean squid Illex argentinus collected by bottom trawls off San Jorge Gulf during an expedition performed in December 2020 was employed to characterize the bottom assemblages of the area, with special emphasis on sponges. According to the results, sponges were conspicuous and abundant components in these benthic communities, representing up to 40% of the total invertebrate bycatch (average: ~130 kg.nm 2 per site). Tedania (T.) mucosa was the dominant species. Other recorded species were T. (T.) charcoti, T. (T.) murcochi , Isodictya verrucosa, Iophon proximum, Clathria (C.) microxa, C. (C.) discreta, Haliclona bilamellata, Si-17 phonochalina fortis and Myxilla (M.) mollis . The results of this study contribute to fill in the gaps on the distribution records of the sponges in the continental shelf of Argentina in a previously poor-19 ly-studied area.


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In Argentina, knowledge on the biodiversity of marine Porifera is closely related to 24 the concentration of the sampling effort. Coastal areas such as Buenos Aires and Tierra 25 del Fuego have several records, while the majority of the continental shelf have few or no 26 records at all [1]. Pioneering studies, such as those developed after the "Challenger" and 27 "Discovery" expeditions, attempt to determine and identify the sponge species inhabit-28 ing the Argentinian waters [2-10]. Later, several authors contributed to the study of 29 sponges in specific areas [11][12][13][14][15][16][17][18][19][20]. The revision made by López Gappa and Landoni [1] 30 provided the first checklist of marine sponges in Argentina and highlighted noticeable 31 differences in records and sponge richness among different areas. In the past 15 years, 32 there were new contributions to the study of sponges and also new species were de-33 scribed. The shelf break sponge-fauna was studied by Schejter et al. [21,22] and Bertolino 34 et al. [24], while interesting contributions were performed for Burdwood bank region by 35 Schejter et al. [25,26,27] and for Bahía San Antonio by Gastaldi et al. [28]. However, 36 according to our knowledge, there are no specific records of sponge species in the area 37 located off San Jorge Gulf, Patagonia, only sparse mentions as a general group in tech-38 nical guides or reports (i.e. [29]). 39 Considering the former background, the aim of the present contribution was to 40 provide information on sponge richness and abundance from this scarcely studied area 41 (off San Jorge Gulf, Patagonia) taking advantage of the bottom by-catch collected during 42 a stock assessment expedition of the Argentinean squid Illex argentinus. Complementary, 43

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In December 2020, the RV "Victor Angelescu" performed a regular stock assessment 47 expedition in order to evaluate the population of the Argentinean squid Illex argentinus 48 off San Jorge Gulf, between 44-46°S and isobaths 80m-120m depth. Sampling was de-49 veloped using bottom trawls. At 23 random sites (Table 1), the invertebrate by-catch was 50 preserved frozen and transported to the Benthos Laboratory of the INIDEP. Sorting of the 51 species was performed at the laboratory and sponge morphospecies were separated and 52 weighted (wet weight) using an Ohause balance (precision 0.002kg). By-catch species 53 were identified using local guides [29,30], while sponge species were identified using the 54 literature mentioned in the Introduction section. Biomass values (as densities) were cal-55 culated for each taxa, using the swept area for each sampling site, and it was expressed in 56 kilograms per square nautical miles (kg.nm -2 ).

Results
Our results showed that the benthic assemblage was composed by 42 taxa. Sponges 61 were conspicuous and abundant components in the benthic communities off San Jorge 62 Gulf, Argentina. They represented 40% of the total invertebrate by-catch in the area (av-63 erage of 124.61 kg.nm -2 per station, maximum value of 656.5 kg.nm -2 at station 11, mini-64 mum value of 4.04 kg.nm -2 at station 1) (Table 1). However, tunicates were the most im-65 portant group in terms biomass (45%, average of 140.3 kg.nm -2 ), and the solitary ascidian 66 Paramolgula sp. accounted for an average of 128.4 kg.nm -2 per station. An unidentified 67 colonial tunicate accounted for an average of 11.36 kg.nm -2 . Other conspicuous, but less 68 important groups in terms of biomass in this benthic community were crustaceans (6%), 69 being the spider crab Libidoclaea granaria the most important one in terms of biomass, 70 reaching in average 11.67 kg.nm -2 . Polychaetes represented 5% of the benthic assemblage 71 and the most conspicuous taxa was Chaetopterus variopedatus (average 15.61 kg.nm -2 ). 72 Echinoderms only contributed in 2,3% to the benthic assemblage. It is worth to mention 73 that egg cases of the catshark Schroederichthys bivius were recorded at stations 13, 18 and 74 21, always attached to the sponge Tedania (Tedaniopsis) mucosa ( Figure 1A).  Figure 1A) were massive, beige to red-brown in 84 color, with a smooth surface and an evident ectosomal skeleton made of tornota arranged 85 in palisade. This species was recorded in all the sampled sites, except at station 4. At sta-86 tions 13, 18 and 21, egg cases of the catshark Schroederichthys bivius were found strongly 87 attached to the sponges, as described in [31]. Spicules are smooth styles of 230-255 by 10 88 µm; mucronate tornota of 190-220 by 5-7.5 µm and two categories of onichaete of 140-200 89 µm and 70-85 µm. 90 -Tedania (Tedaniopsis) charcoti specimens ( Figure 1K) were massive, but fragile and 91 friable in the dried state. The surface is uneven and looks porous, with no conspicuous 92 ectosome. This species was recorded at stations 4, 5, 6, 11, 15, 17, 18 and 20. Spicules are 93 styles of 245-380 by 5-10 µm; tornota of 180-250 by 5-7.5 µm and two categories of oni-94 chaete of 230-270 µm and 65-105 µm. Tedania (T.) charcoti accounted for 14.72 kg.nm -2 in 95 average in the studied area. This is a common species in Argentina [21], and our speci-96 mens fit very well with the previous records, although spicule dimensions in the holo-97 type and Antarctic specimens are usually bigger. 98 -Tedania (Tedania) murdochi specimens ( Figure 1H) were massive and rigid, beige in 99 color, with some evident oscula. It was recorded at stations 10 and 17. Spicule dimensions 100 are smaller than the other two recorded species: styles are 235-270 by 10-15 µm; tornota, 101 180-210 by 5-7.5 µm and onichaete are 155-205 µm.

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-Isodictya verrucosa specimens ( Figure 1B) have the typical morphology of the genus, 103 yellow-beige in color, with a plumoreticulate skeleton. This species was recorded at sta-104 tions 12 and 13. Spicules are oxeas of 310-400 by 15 µm and small isochelae of 25-30 µm. 105 As noted by [21], megascleres are shorter than in the holotype and Antarctic specimens, 106 but the morphology of the spicules very much agree with the description of the species. 107 This is the second mention of the species for the SW Atlantic Ocean, after Schejter et al. 108 [21]. 109 -Iophon proximum specimens ( Figure 1D) are massive and variable in shape, porous 110 and became dark brown in color after preservation. It was found also associated (at-111 tached) with other sponge species. It was recorded at stations 2, 5, 7, 10, 14, 20 and 21. 112 This is a common and highly variable species and an extended description and revision 113 could be found at Desqueyroux-Faundez and van Soest [32].  Figure 1C) is bushy and was found growing 121 attached to a dead Flabellum coral. It was recorded at station 5. Spicules are two types of 122 styles, 370-440 by 15-20 m and 320-445 by 5-10m, acanthostyles of 100-115 by 5m, 123 toxas 230-460m and microxeas of 45m. This is the third mention of the species for the 124 SW Atlantic Ocean, after Schejter et al. [21,22]. 125 -Clathria (C.) discreta specimen ( Figure 1E) was found at station 14. This is a com-126 mon, well-registered species in Argentina and detailed information could be found at 127 Burton [8,10] and Schejter et al. [21]. 128 -Siphonochalina fortis specimen ( Figure 1I) was found at station 17, and it is charac-129 terized by their ramose morphology, highly compressible, with a skeleton conformed by 130 quadrangular meshes of fibres with embedded oxeas of 55-60 by 3.5-5 µm. It is a common 131 species in Argentina. 132 -Myxilla (Myxilla) mollis specimen ( Figure 1G) was recorded at station 7 and it is a 133 very common species in Argentina. A detailed description could be found at Bertolino et 134 al. [24]. 135 -Haliclona bilamellata specimen ( Figure 1J) has a massive to tubular morphology, soft 136 and sticky, and was recorded at station 17. It has oxeas of 160-185 by 10 µm, and also 137 some smaller and thinner of 140 by 5 µm. Our specimen agrees with the descriptions 138 provided in Burton [8] and Sará [12].
-Several unidentified specimens belonging to the Family Suberitidae ( Figure 1L) 140 were found at stations 17, 18, 21 and 22, and two fragments belonging to the order Hap-141 losclerida ( Figure 1F) were found at station 11. These specimens will require more studies 142 to get a proper identification at a species level. 143

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The results of this study contribute to better explore the benthic assemblage off San 145 Jorge Gulf, Patagonia and fill in the gaps on the records and distribution of the sponges in 146 this particular unknown region. Among the 42 registered taxa, 12 sponge species were 147 recorded in this area. Although all these species were previously recorded in other sec-148 tors of the Argentinian waters, this new evidence contribute to build the distribution 149 pattern of sponge species in Argentina. Additionally, it is worth to mention that the 150 studied area presented an unusually high abundance of sponges and tunicates in the 151 benthic communities that may reach up to 40% and 45% in wet weight, respectively, of 152 the total by-catch. This is probably an indication that this area was relatively preserved 153 from intense bottom fishing (i.e. [33]) and may constitute a potential refugee for juveniles 154 of species of commercial and non-commercial interest, as suggested for some regions of 155 the San Jorge Gulf [34]. It must be noted that Argentinean hake (Merluccius hubbsi) fishing 156 (developed using bottom trawlers) is banned at the studied area, but the Argentine red 157 shrimp (Pleoticus muelleri) fishing (developed also by a trawler fleet) is allowed. Finally, 158 and considering the finding of egg cases of the catshark S. bivius, this area may also have 159 interesting characteristics for oviparous chondrictian species and should be better ex-160 plored in order to understand if it should be managed in order to preserve target species 161 from anthropogenic impacts.