Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact
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1
University of Alicante, Department of Marine Sciences, Spain
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2
Department of Animal Biology, Faculty of Science, Malaga University, Spain
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3
Oceanographic Center of Málaga, Spanish Institute of Oceanography (IEO), Spain
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4
Oceanographic Center of Murcia, Spanish Institute of Oceanography, Spain
Abstract
The ascidiofauna of the MEDITS 2010 and 2017 cruises in the Iberian Mediterranean (from the Alboran Sea to NE-Iberian), has been studied, showing a high homogeneity with certain particularities according to the areas and fishing pressure. Murcia and Catalonia harbor a relatively high abundance and diversity, both in solitary and colonial species. While in Alboran and the Gulf of Valencia, diversity and abundance have been lower; as well as the colonial strategy. With regard to the bathymetric distribution, a progressive decrease in abundance and diversity is observed with the increase in depth, giving the highest values between 40 and 100m. Based on the results, the ascidians, with their strategies (solitary, colonial), can be good indicators of the state of the Mediterranean soft circalittoral bottoms impacted by trawling.
Introduction
The soft circalittoral and upper-bathyal bottoms (between 35 and 800 m depth) of the Mediterranean Sea are subject to heavy fishing pressure due to bottom trawling. Among its effects, the destruction of the habitat complexity and homogenization of the sediment with an increase in the fine fraction (Jones, 1992, Thursh et al., 1995, Gray et al., 2006). The sessile and filter-feeding epifauna (sponges, anthozoans, bryozoans, ascidians ...) is particularly vulnerable to this impact, representing an excellent indicator (de Juan et al., 2007). In this regard, the ascidians form aggregations in soft circalittoral bottoms known as "ascidian bottoms" (Costa, 1960, Pérès & Picard, 1964, Monniot, 1965, 1968, Pérès, 1985), creating a complex habitat and increasing biological diversity with new substrate (epi and endobionts), food and shelter. In addition, they present two types of organization (colonial and solitary) with a different response to sedimentation (Millar, 1971; Ramos & Ros, 1990).
In the present work, ascidiofauna is studied from the MEDITS 2010 and 2017 cruises (International Bottom Trawl Survey in the Mediterranean) in the Iberian Mediterranean, from Alborán to Catalonia and between 38 and 693m depths. The results show homogeneity of the ascidiofauna according to previous studies (Cornet & Ramos, 1980; Ramos, 1988; Turón, 1988), with certain biogeographical particularities. Also, the impact of trawling on the structure of taxocenosis is demonstrated, particularly in those areas with a wide continental shelf (in the case of the Gulf of Valencia).
Material and methods
The study area has been the Iberian Mediterranean, from the Alborán Sea to Catalonia, during the MEDITS 2010 and 2017 cruises aboard the B / O 'Miguel Oliver', at depths between 38 and 693m (Fig. 1). The epibenthic megafauna has been sampled using an experimental fishing trawl (GOC-73: 16-18m width, 2-3m height, 20mm cod end mesh). The presence of ascidians in the catch has been about 32% of the trawl samples. Two types of analysis have been carried out (PRIMER 5 program): i) structure of the ascidian community (specific richness, abundance, Shannon-Viewer diversity and Pielou equitability); and ii) multivariate analysis (Cluster, MDS), with species whose abundance has been> 3 (0.1% of the total abundance).
Figure 1. Studied zones with the number of samples (lances). Image from Google Earth
Results and discussion
Taxonomic study: A total of 3810 ascidians belonging to 39 spp. and 10 families have been determined (Table 1). The Styelidae family stand out (56.7% of the total abundance) with Polycarpa mamillaris, P. pomaria and P. gracilis; following by Pyuridae (14.4%) with Microcosmus vulgaris and Pyura microcosmus, Ascidiidae (9.8%) with Ascidia mentula, Molgulidae (8.7%) with Molgula appendiculata, and Didemnidae (6.8%) with Didemnum maculosum. Regarding the strategies, the solitary over the colonial dominates with 87.6%.
Table 1
Structure of the ascidiofauna. SE and NE-Iberian zones have presented the highest species richness (26 spp.), an average abundance per sample (81-83 ej.), and a diversity > 2.0 (Table 2). On the contrary, Alboran and Gulf of Valencia have presented 12 and 16 spp., an average abundance between 11 and 33 ind./sample, and a diversity <1.8. Regarding the range of depths, a progressive decrease of the species richness and the relative average abundance with the increase of the depth is observed. However, diversity has been slightly higher in the 100-199m range.
Table 2
Multivariate analysis: The MDS species/zone analysis discriminates 4 groups (Fig. 2). Group A encompasses the species that normally appear in soft circalittoral bottoms. In the remaining groups (B-D) appear the species that have only appeared in some of the sampled areas, or have been very abundant: (B) SE-Iberian; (C) NE-Iberian; (D) Gulf of Valencia and NE-Iberian.
Figure 2. Aggregation of ascidians/zone (MDS): (Aa) Ascidiella aspersa;(As) A. scabra;(Am) Ascidia mentula; (Ac) Aplidium conicum;(Ae) A. areolatum;(Br) Botryllus renieri; (Bs) B. schlosseri;(Cd) Cystodytes dellechiajei;(Dc) Didemnum coriaceum;(Dm) D. maculosum;(Dva) Distomus variolosus; (Dvi) Diazona violacea; (Hp) Halocynthia papillosa; (Ma) Molgula appendiculata;(Mp) Microcosmus polymorphus;(Ms) M. savignyi;(Msb) M. sabatieri;(Mv) M. vulgaris; (Pb) Polysyncraton bilobatum;(Pma) Phallusia mammillata (Pg) Polycarpa gracilis;(Pm) P. mamillaris;(Pp) P. pomaria; (Pmi) Pyura microcosmus;(Ps) P. squamulosa;(Rn) Rhopalaea neapolitana; (Sc) Styela canopus.
The observed ascidiofauna corroborates homogeneity in the soft circalittoral bottoms of the Iberian Mediterranean (Cornet & Ramos, 1980, Ramos, 1988, Turón, 1988, Díaz-Valdés, 2009). Large solitary ascidians have dominated (Costa, 1960, Monniot, 1965); while colonial species have been frequent in sheltered or protected areas (Alboran, Murcia, Catalonia), which are not accessible to trawling. On the contrary, in the Gulf of Valencia (Valencia, Castellón) they have been very rare. The ascidiofauna and its strategies (solitary and colonial) are good indicators of the state of the soft bottoms (Ramos & Ros, 1990), particularly the impact of trawling.
References
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Keywords:
ascidians,
circalittoral,
upper-bathyal,
Soft bottoms,
Mediterranean Sea,
Iberian Peninsula,
Bottom trawling impact
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Arroyo
E,
Urbano
EM,
Garcia-Ruiz
C,
Esteban
A and
Ramos-Esplá
AA
(2019). Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00075
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Received:
11 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Miss. Elisa Arroyo, University of Alicante, Department of Marine Sciences, San Vicente del Raspeig, Spain, elisa.arroyo.m@gmail.com