Ecology and distribution of freshwater mussels (Bivalvia: Unionidae) in the region.

Bataller1, J.V.; J. Hernández2; A. Pradillo1.

(1)Centro para el Estudio de los Ecosistemas Acuáticos (C.E.E.A.), Ap. 6050, 46080, Valencia, . (2) Servicio de Conservación de la Biodiversidad, Consellería de Territorio y Vivienda, Francisco Cubells 7, 46011 Valencia, Spain.

Introduction

The native freshwater bivalves are among the most endangered Iberian freshwater fauna. These large unionids, locally known as “petxinots” or “náyades”, were abundant in our rivers and lakes until a few decades ago (GASULL, 1971 & 1981). Nowadays all species that belong to this group have experienced a great decline due to the generalized degradation of their habitat (MARTÍEZ & ROBLES, 2003). At the Valencia region three species of native freshwater mussels (Bivalvia:Unionidae) exist (VIDAL & SUAREZ, 1985): Anodonta cygnea (Linnaeus, 1758), Potomida littoralis (Lamarck, 1801) and Unio elongatulus (Pfeiffer, 1825). Due to rarefaction of these species, two of them are included, with different categories, in the regional endangered fauna act (Decreto32/2004, de 27 de febrero, del Consell de la Generalitat).

Location of sampling stations and mussels found Materials & Methods SAMPING STATION LOCALITY PROVINCE UTM X UTM Y PT AN UN 1. - Materials Fig. 2 Emblase de l´Alcora l´Alcora Castellón 737019 4442727 - - - Barranco de la Foia l´Alcora Castellón 737870 4442429 - - - - Densities estimation: Depending on water visibility, current velocity and Desembocadura Mijares Burriana Castellón 754817 4422938 - - - Anodonta cygnea Potomida littoralis Unio elongatulus Acequias de Burriana Burriana Castellón 752038 4418545 - - - substrata type; location and counting of individuals was made by transects (50 Acequia La Llosa Castellón 740910 4405942 - X X Ac Moli La Llosa Castellón 740793 4405763 - X X m length) with favorable conditions; or with a sampling quadrate (0.25 m2) Ac Pouets La Llosa Castellón 741248 4405120 - - X BF BF BF when these were negative (DUNN, 2000) . YL YL YL Ac Racó Almenara Castellón 741347 4401154 - X X YK YK YK Río Turia Valencia 714862 4376936 - - X - Marking and biometry: Biometric measures were taken with a precision (0.01 Azud río Magro Real Valencia 708462 4355440 - - X mm) digital calliper. Plastic marks, with an individual 3 character alphanumeric Trasvase norte 1 Valencia 715690 4370920 - - X Trasvase norte 2 Aldaia Valencia 715224 4369925 - - X code (Fig. 6), were attached to shell with cyanoacrylate adhesive (ROSS ET BE CE BE CE BE CE Trasvase norte 3 Aldaia Valencia 711684 4347240 - - X ALL. 2001). Trasvase sur 1 Valencia 711685 4346841 - - X Trasvase sur 2 Carlet Valencia 711588 4347501 - - X XK XK XK - Abiotic parameters: Some easy to measure were recorded to define habitat Azud 1 Valencia 707947 4328664 X - X Azud 2 Antella Valencia 707947 4328664 X - X requirements. Temperature, both air and water, were registered with a digital Azud 3 Antella Valencia 707947 4328664 - X X thermometer with 0.1 ºC precision. Transparency was measured with Secchi YJ YJ YJ Azud 4 Antella Valencia 707996 4328719 X - X Azud 5 Antella Valencia 707987 4328733 - - - disk to the nearest centimetre. Water velocity was measured to the nearest Río Jucar Valencia 711787 4329601 X X X m/s with a mechanical flow meter (General Oceanic, model 2030). Acequia río Verde 1 Alberic Valencia 714056 4334995 X - - BD BD BD XJ XJ XJ Acequia río Verde 2 Alberic Valencia 714056 4334995 X - - BC BC BC Acequia río Verde 3 Alberic Valencia 714056 4334995 X - - 2. - Methodology Río Verde 4 Alberic Valencia 714068 4335004 X - - verde 5 Alberic Valencia 713639 4334910 X - X 2.1 Abundances and densities: The counting of individuals varied greatly verde 6 Alberic Valencia 713639 4334910 X - X Río de los Santos Alcud. Crespins Valencia 707358 4316847 - - - depending on the condition of the water body: Acequia de Benifurt Xativa Valencia 716614 4320015 X - X - Clear waters, small width (Fig. 8). The shoreline was walked (usually 50m) Ac Ratlla Valencia 724610 4356449 - X X XH YH XH YH XH YH XG YG XG YG XG YG Carrera Saler Valencia Valencia 729930 4361780 - - - and all observed mussels were collected with a hand net. This process was Ac Romani Sollana Valencia 725811 4353944 X X X repeated three times. Ac Dreta 1 Sollana Valencia 729105 4353251 - X - Ac Dreta 2 Sollana Valencia 728402 4350391 - X X - Clear water, wide width. All observed (with naked eye or with a view bucket) Ac Dreta 3 Sollana Valencia 728461 4349398 - X X Escorrentia de la Flota Sueca Valencia 732542 4351279 - - X mussels were collected by hand along a fixed distance (usually 50 m) walking Brazal Alteró Albalat Ribera Valencia 725645 4345184 X - - along the streambed (Fig. 5). If the waters were deep, transect was made 1. Acequia Mitjana Cullera Valencia 737548 433652 X X X Cullera 2. Acequia Mitjana Cullera Valencia 737265 4336363 - - X diving. Cullera 3. Acequia junto río Cullera Valencia 737414 4338103 - X X - Turbid waters. In this case sampling was only possible in wadeable waters. Acequia Cami Groguet 1 Tavernes Val Valencia 737002 433009 - X X Acequia Cami Groguet 2 Tavernes Val Valencia 738334 4331262 - X X Fifteen replicates with a 0.025 m2 quadrate (0.5 m side) were taken along a 50 Ac Tancadella Valencia 743618 4321165 X - - m reach. Les Aigües Valencia 751654 4305937 - - - Ac. Bovar Oliva Valencia 756511 4306841 - - - 2.2 Biometry and marking. Bivalves were measured with a precision (0.01 mm) Sant Pere Pego Alicante 754254 4307619 - - - Alberca 1 Ondara Alicante 240997 4301830 - - - digital calliper. The shell dimensions were measured as: length (distance between Alberca 2 Ondara Alicante 240818 4301663 - - - umbones), height (from anterior to posterior edge) and width (dorsal to ventral Alberca 3 Ondara Alicante 240997 4301830 - - - PT = Potomida littoralis. AN = Anodonta cygnea; UN = Unio elongatulus. X = present. - = Not detected. margins) BRAID (2000).

Results Conclusions

Considering the total number of sampling sites with one or more The main threats for freshwater mussels detected along this study are mussel species, Potomida littoralis was present in 44% of all sites, Unio principally four: canalization, dredging, desiccation and pollution. elongatulus in 80% and Anodonta cygnea in 48%. Sixty percent of all Complete canalization of streams means the loss of the whole population. sampling stations contained more than unionid species, that is, 40% were Works for cementation and coating of canals and irrigation ditches are common, for monospecific (Fig. 1). instance in the natural park of the Albufera, and represent a great loss in the Concerning the possible species associations, 12% of the sample Fig. 3 Fig. 4 populations. sites contained all three species, in 32% we found U. elongatulus together Dredging of canals and ditches is a common activity (Fig. 3), required for with A .cygnea, and in 16% U. elongatulus occurred together with P. the correct function of the irrigation network; but unfortunately, how nowadays this littoralis. Remarkable is the absence of the association A. cygnea with P. work is made, means a great loss in the populations of unionids that live in them. littoralis reasons for which are not yet well understood. Better practices are required to reduce the impact as much as possible. Distribution of the three unionid species in the Valencia region is Desiccation of streams (Fig. 8), if for a short period of time (3 to 5 days, restricted to the and nearby areas of Castellón and depending on environment temperature and humidity) produces the death of the Alicante (Fig. 2). younger individuals. Longer periods mean the death of a great percentage of the Canals and irrigation ditches (Fig. 4) are the main waterbodies population. inhabited by A. cygnea; although P. littoralis is also present in irrigation Finally, we can’t forget an indirect threat related with the singular unionid ditches, it is mainly found at the middle reach of rivers (Fig. 7). The most reproduction cycle. Larvae of unionids (known as glochidia) are obligate parasites ubiquitous species in Valencia Region is, with no doubt, Unio elongatulus; on the gills and fins of fish, and use them for their dispersion. And even it is still yet its optimum seems to be waterbodies with clean and shallow waters and not well known which the main host fishes are, the decline of host fish obviously slow current. Fig. 5 Fig. 6 will affect on the abundance of bivalves.

Different associations of Unionids Conservation actions species. U+P Sólo A SPECIES N % 16% 4% Sólo U 20% Sólo A 1 4 Regional environment agency (Consellería de Territorio y Vivienda) has SPECIES N % Sólo U 5 20 made several action plans in order to preserve the three species of unionid A 12 48 Sólo P 4 16 mussels: U 20 80 A+U+P 3 12 A+U Sólo P P 11 44 A+U 8 32 - Dredging control. 32% 16% A+U+P U+P 4 16 - Local distribution studies. 12% Total 25 100 - Artificial rearing experiences. Fig. 1 A = Anodonta cygnea, P = Potomida littoralis, U = Unio elongatulus. N = Fig. 7 Fig. 8 Total localities. % = Percentage among total. - Reintroductions by means of host fish infestation with glochidia. - Creation of sanctuaries.

References

BRAID, M.S. (2000). Life history of the spectaclecase, cumberlandia monodonta Say, 1829 (Bivalvia, Unionoidea, Margaritiferidae). M.S. Thesis. Southwest Missouri State University. 119 pp. DUNN, H.L. (2000) Development of strategies for sampling freshwater mussels (Bivalvia: Unionidae). Proceedings of the first freshwater mollusc conservation society symposium. Ohio Biological Survey: 161-67. GASULL, L. (1971) Fauna malacológica de las aguas continentales dulces y salobres del sudeste ibérico. Bol. Soc. Hist. Nat. Baleares, 16:23-82. GASULL, L. (1981) Fauna malacológica terrestre y de agua dulce de la provincia de Castellón de la Plana. Boll. Soc. Hist. Nat. Balears, 25: 55-102. MARTÍNEZ, A; Y F. ROBLES (2003) Moluscos continentales de la Comunidad Valenciana. Generalitat Valenciana. 261 pp. ROSS, K.A; J.P. THORPE; A. NORTON & A.R. BRAND (2001) An assessment of some methods for tagging the great scallop, Pecten maximus. J. Mar. Biol. Assoc., 81: 975-977. VIDAL ABARCA, C. Y M.L. SUAREZ (1985) Lista faunística y bibliográfica de los moluscos (Gastrópodos y Bivalvia) de las aguas continentales de la Península Ibérica e Islas Baleares. Asociación Española de Limnología. Madrid. 190 pp.