DISTRIBUTION OF LIOCARCINUS DEPURATOR ALONG THE WESTERN MEDITERRANEAN COAST By Marta M. Rufino A thesis submitted to the University of Wales, Bangor. School of Ocean Sciences for the degree of Doctor in Philosophy This thesis is dedicated to my mum, without whom none would have been possible Summary The distribution of L. depurator has been analysed through classical statistics, linear models and geostatistics. Density was obtained from a ten-year time series of bottom, otter trawl surveys in eight areas along the Mediterranean coast of Spain. Two peaks of L. depura- tor occurrence were observed. The first (80% occurrence) between 51 and 150 m, and the other (66% occurrence) between 301 and 400 m. Below 500 m, crab occurrence was negligi- ble (<8%) and densities fell sharply. The pattern shown by crab densities closely shadows that of occurrence, although a second abundance peak was barely evident, and was located at 201- 300 m. From 200-400 m, crab abundance appeared fairly evenly distributed but showing lower densities than in shallower waters. Analysis through linear modelling showed that L. depurator density decreased signifi- cantly with depth and year, but no effect of sample location was evident. The decrease of L. depurator density was most pronounced at shallower depths (depths < 150 m, declining at ~8±1 % per annum), than in deeper waters (depths > 150 m, declining at ~4±1 % per annum). Geostatistical analysis of L. depurator densities showed that the crabs distributions ex- hibited varying degrees of spatial structure with patch sizes varying between 19 and 75 km among the sampled years. When average densities were low, crabs were most abundant in Ebro River Delta area and Western Alborán Sea, areas showing permanent high-density popu- lations. The virtues and drawbacks of each approach are discussed. On a smaller scale, off the Ebro Delta L. depurator distribution (numbers and biomass) was related to sediment characteristics using geostatistics. Smaller crabs were found preferen- tially in shallower water, whereas larger crabs, in deeper ones. Given the presence of at least two distinctive aggregations (possible populations) of L. depurator on the Spanish coast, a series of morphometric studies were undertaken. A combi- nation of traditional dimension analysis and geometric morphometry (whole shape analysis) was used to compare crab morphology. Differences in carapace shape were identified between genders and geographic location that largely appeared to involve the abdomen width. 1 of 213 Table of contents Summary ................................................................................................................................................. 1 Table of contents ..................................................................................................................................... 2 List of Figures.......................................................................................................................................... 5 List of Tables......................................................................................................................................... 10 Acknowledgements ............................................................................................................................... 12 I. General introduction ...................................................................................................................... 14 I-1. The distribution of Liocarcinus depurator ...................................................................... 14 I-2. Geographic distribution ................................................................................................... 14 I- 2.1. Geographic variation in crab abundances...................................................................... 15 I-3. Bathymetric distribution .................................................................................................. 18 I-4. Liocarcinus depurator spatial structure........................................................................... 21 I-5. Distribution in relation to habitat..................................................................................... 21 I-6. Inter-specific relationships in distribution ....................................................................... 23 I-7. Effects of fishing..............................................................................................................26 I-8. Objectives of the thesis.................................................................................................... 30 I- 8.1. Part I: Distribution of Liocarcinus depurator in the western Mediterranean coast of Spain: small and large scale approaches................................................................................... 30 I- 8.2. Part II: On the application of geometric morphometrics to the Liocarcinus depurator carapace.................................................................................................................................... 32 PART I. Distribution of Liocarcinus depurator in the western Mediterranean coast of Spain: small and large scale approaches. .......................................................................................................................... 35 II. Introduction to the surveys and characteristics of the Mediterranean coast of Spain................... 36 II-1. GEODELTA survey ........................................................................................................ 36 II- 1.1. Aims and protocol ........................................................................................................ 36 II- 1.2. Sediment variable measurements ................................................................................. 37 II-2. MEDITS: Mediterranean bottom trawl surveys .............................................................. 38 II- 2.1. Aims and protocol ........................................................................................................ 38 II- 2.2. MEDITS-es: Details of the Spanish survey.................................................................. 39 II-3. Characteristics of the sampled areas: the Mediterranean coast of Spain ......................... 47 III. Geographical, bathymetric, and inter-annual variability in distribution of Liocarcinus depurator (Brachyura: Portunidae) along a western Mediterranean coast......................................................... 56 III-1. Abstract............................................................................................................................ 56 III-2. Introduction...................................................................................................................... 56 III-3. Materials and methods..................................................................................................... 57 III- 3.1. Survey details.............................................................................................................. 57 III-4. Results ............................................................................................................................. 59 III-5. Occurrences .....................................................................................................................59 Geographical variability........................................................................................... 61 Interannual variability.............................................................................................. 61 III- 5.1. Density ........................................................................................................................ 64 Geographical variability........................................................................................... 65 Interannual variability.............................................................................................. 66 III- 5.2. Linear model of the densities ...................................................................................... 69 III-6. Discussion........................................................................................................................ 72 IV. Geostatistics ................................................................................................................................ 75 2 of 213 IV-1. Short introduction to geostatistics ....................................................................................75 IV- 1.1. Why perform a geostatistical analysis .........................................................................75 IV- 1.2. Variogram analysis......................................................................................................76 Experimental variogram ...........................................................................................76 IV- 1.3. Spatial covariance model parameters ..........................................................................78 IV- 1.4. Spatial covariance model function...............................................................................80 IV- 1.5. Fitting method..............................................................................................................81 IV- 1.6. Kriging interpolation ...................................................................................................83 IV-2. Geostatistical analysis applied to crustaceans ..................................................................84 IV- 2.1. Historical perspective ..................................................................................................84