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University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES School of Ocean and Earth Sciences The Autecology of Tapes philippinarum (Adams and Reeve, 1850) in Southampton Water, UK by Wanwiwa Tumnoi Thesis for the degree of Doctor of Philosophy November 2012 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES School of Ocean and Earth Sciences Doctor of Philosophy THE AUTECOLOGY OF TAPES PHILIPPINARUM (ADAMS AND REEVE, 1850) IN SOUTHAMPTON WATER, UK By Wanwiwa Tumnoi The non-indigenous venerupid clam Tapes philippinarum (Manila clam) was probably introduced to the Solent and Southampton Water in 2005. Since then clams have been intensively harvested by the local fishermen because of high economic value. Two current measures are in force to regulate the commercial exploitation, (i) the EU minimum landing size regulation (35 mm shell length) and (ii) the district byelaw prohibiting boats from over 12 m fishing within SIFCA district. This thesis presents an investigation the autecology of T. philippinarum in Southampton Water. The knowledge obtained would not only to provide base-line information for the species in the Solent system but also to establish the appropriate fishery management for the sustainability of local stock. Histology revealed that the sex ratio of T. philippinarum was approximately 1:1. Gametogenesis started in February and the gonads matured from May onwards. Spawning was observed between May and September with a single peak from June to August. T. philippinarum in Southampton Water seems to have adapted to the lower water temperature (compared to its native range) of the UK because the gonad was active when the seawater temperature was much lower (4.8 oC) than the minimum temperature reported elsewhere to initiate gonadal activity (10 oC). The day degree rate required for successful spawning was more rapid (64.27 D o) than reported in the literature. Two peaks of bivalve larval density in June and August possibly indicated the successful spawning and development into larvae of the clam. The minimum size at sexual maturity of the clam was about 20 mm shell length, only clams larger than 25 mm showed a high percentage of the maturity (87.50%-100%). In addition, the oocyte diameter of the clams significant related to the shell length and time. Therefore, recent suggestions that the current 35 mm MLS could be reduced to say, 20 mm are not supported by this study. On the contrary, these results indicate that the MLS should not drop below 34 mm. The majority of the T. philippinarum population was within the 30-35 and 35-40 mm shell length size classes. The low proportion of the larger size i class (> 40 mm) might reflect the use of fishing gear developed during the period when the EU MLS was 40 mm. The environmental conditions in Southampton Water seem to provide T. philippinarum with a favourable habitat as indicated by its annual growth rate (2.93+1.23 mm in shell length) and normal immunocompetence. Winter and the spawning period were the stressors for T. philippinarum revealed by the lower haemocyte count, the thining of digestive epithelial thickness, and the increase in mean luminal radius/mean epithelial thickness. However, the immunocompetence was stabilised by the consistency of phagocytosis. An examination of the synergistic effect of temperature and reproductive development under food deficiency revealed that the winter food levels combined with temperature of ‘warm’ winter could result in a negative energy balance in T. philippinarum due to insufficient energy input to meet the energy demand for gonad development. The normal growth, good health status and completion of life history indicated that T. philippinarum has successfully naturalised in Southampton Water. Additionally, this bivalve species has great potential to extend its temperature tolerance below published observations. ii List of contents Chapter 1 General Introduction ............................................................................................ 1 1.1 Nomenclature and Taxonomy .................................................................................... 2 1.2 Morphology .................................................................................................................. 3 1.3 Geographic distribution and Introduction to the UK ................................................ 5 1.4 Risks associated with the introduction of Tapes philippinarum .............................. 9 1.5 Life history ................................................................................................................. 10 1.5.1 Reproduction ....................................................................................................... 10 1.5.2 Eggs and Fecundity ............................................................................................. 12 1.5.3 Larval development ............................................................................................ 12 1.6 Ecology ....................................................................................................................... 14 1.7 Growth ........................................................................................................................ 15 1.8 Population structure .................................................................................................. 17 1.9 Evaluation of health status in Tapes philippinarum ............................................... 18 1.9.1 Using immunological parameters as indicators of health status .................... 18 1.9.2 Haemocyte ........................................................................................................... 21 1.9.3 Phagocytosis ....................................................................................................... 23 1.9.4 Digestive Tubule ................................................................................................. 26 1.10 Spring mortality in Tapes philippinarum ............................................................... 28 1.11 Bioenergetics in Tapes philippinarum ................................................................... 30 1.11.1 Effect of temperature ....................................................................................... 30 1.11.2 Effect of food availability ................................................................................. 32 1.11.3 Synergistic effect of temperature and food availability ................................. 33 1.11.4 Effect of reproductive development ................................................................ 35 1.12 Southampton Water ................................................................................................. 36 Chapter 2 Materials and Methods ...................................................................................... 39 2.1 Study site: Bird Pile, Southampton ........................................................................... 39 2.2 Environmental parameters ........................................................................................ 40 2.3 Population structure .................................................................................................. 40 2.4 Growth rate ................................................................................................................ 40 2.5 Gonad histology and oocyte measurement ............................................................. 41 2.5.1 Gonad examination ............................................................................................ 41 2.5.2 Oocyte measurement.......................................................................................... 48 2.6 Immunological parameters ....................................................................................... 48 2.6.1 Haemocytes ......................................................................................................... 48 2.6.2 Phagocytosis ....................................................................................................... 49 2.6.3 Digestive tubule .................................................................................................. 49 2.6.4 Statistical analyses .............................................................................................. 49 iii 2.7 Bivalve larvae abundance .......................................................................................... 50 2.8 Spring mortality laboratory experiment .................................................................. 50 2.8.1 Collection and maintenance of animals ............................................................ 50 2.8.2