The distribution of the wood boring isopod Limnoria in Texas estuaries and bays in relation to environmental factors.




Lum, J.A.S.

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Texas A&M University.


The gribble Limnoria tripunctata and other members of the family Limnoriidae annually cause millions of dollars of damage to wooden structures in the marine environment. Thus it is of considerable economic importance to understand the factors which control the distribution of gribbles. The objectives of this study were: 1. to determine the geographic distribution of gribbles in Texas bays, 2. to determine tolerances of L. tripunctata to temperature and salinity in the laboratory, and 3. to correlate field distribution, laboratory tolerances, and hydrographic conditions of the study area. Wood samples were collected from pilings at 33 stations located in Galveston, Matagorda, San Antonio, Aransas, Corpus Cristi, and Baffin Bay systems and the Laguna Madre. Limnoria tripuncata, the only gribble species collected, was presented in samples from Bolivar ferry landing, Texas City Dike, West Bay, Christmas Bay, Freeport, Port O'Connor, Port Aransas, Corpus Christi, Kennedy Causeway, Port Mansfield, Port Isabel, and Brownsville. This species has previously been reported from Galveston, Freport, Port Aransus, Corpus Christi, and Port Isabel. Salinity and water circulation appeared to be the most important factors governing the local distribution of gribbles. Mean salinity (from Texas Parks and Wildlife Department Coastal Fisheries Projects Reports, 1963-1975) was greater than 19% at stations where Limnoria was found and less than 22% at negative stations. Most positive stations are near passes and are affected by tidal exchange between the gulf of mexico and the bay system. Limnoria tripunctata for the laboratory tolerance study were collected in winter and summer at the Texas City Dike in Galveston Bay. The animals were maintained on filter paper at a series of water salinity-temperature combinations. Experimental salinity range was 10-15% and temperature range was 5-35 C. Maximum survival occured at 30% salinity and at a temperature of 10 C in winter and 20 C in summer. The results suggest that seasonal temperature acclimation increases chances for survival at prevailing water temperatures. Animals acquire cold resistance in winter without loss of heat resistance and are able to tolerate the wide temperature fluctuations which occur on the Texas coast in winter. Animals are exposed to less temperature variation in summer but must tolerate higher temperatures. Warm acclimation reduces cold resistance and raises the upper temperature limit. The presence of L. tripunctata from Galveston to Brownsville indicates that environmental conditions favorable for this species occur along the entire Texas coast. Temperature conditions are favorable throughout the year, although laboratory studies suggest that highest summer (>30 C) and lowest winter (<10 C) temperatures are stressful. Results of the field and laboratory studies suggest 20-40% as the salinity range for successful establishment of L. tripunctata in Texas bays.


133 p., Dissertation


marine crustaceans, isopods, Limnoria tripunctata, boring organisms, ecological distribution, geographical distribution, hydrographic surveys, biological damage, gribbles, salinity tolerance, temperature tolerance