Wood-boring Isopod Research Articles

Sphaeroma terebrans : A Threat to the Mangroves of Southwestern Florida

Sphaeroma terebrans, a wood-boring isopod, is destroying the prop roots of red mangroves along the southwestern coast of Florida to such an extent that the Ten Thousand Islands and mangrove fringes of the mainland are steadily shrinking. Mangroves of the Florida Keys apparently are free of this wood borer.

Experimental interbreeding between geographically separated populations of the marine wood-boring isopod Limnoria tripunctata with preliminary indications of hybrid vigor

Populations of the marine wood-boring isopod Limnoria tripunctata Menzies were cultivated and interbred in the laboratory in order to determine whether geographically separated populations would interbreed. Two series of interbreeding studies were conducted. In the first, field populations from 11 Atlantic and Caribbean sites and 3 Pacific sites were interbred with a North Western Atlantic population from Beaufort, North Carolina (USA). Viable crossings, to at least F 1, occurred in all but one case—that of a BeaufortxChatham (Massachusetts, USA) cross. In the second series of experiments, field populations from 9 Atlantic and Caribbean sites were crossed with populations from St. Teresa, Florida, Gulf of Mexico. In this case also, all crosses except one produced viable offspring, not only to the F 1, but to the F 2 generations as well. The St. Teresa x Chatham cross was not successful. Geographic distance was not a factor in the success of crossbreeding between disjunct populations. Chatham populations (mainly) are now believed to represent a valid but previously obscure species, Limnoria tuberculata Sowinski, and not a variant of L. tripunctata Menzies. Enhanced viality or vigor, as determined from rate of wood destruction, population growth rate and survival, was indicated in several crossings, but this was not necessarily correlated with distance between populations. Observations were made on the manner in which the species has achieved a worldwide distribution, and a hypothesis is put forward to explain the evolution of species related to L. tripunctata.

The Effects of Temperature on the Development of Limnoria Eggs (Isopoda: Crustacea)

The study of the reproduction of marine invertebrates in relation to temperature has acquired an added interest in recent years because of the increasing number of electrical generating stations and other industrial plants that are being built on the shores of estuaries. The biological significance of these installations lies in the use of large volumes of sea water in their cooling systems. The water is heated in the process and discharged back into the sea at temperatures as much as 200 C above ambient. The effects of warm water effluents on marine life have been reviewed by Naylor (1965) who gives examples of the amounts of heat produced. Increased temperature may be expected to influence the reproductive processes and this paper is concerned with the effects of temperature changes on one reproductive aspect-egg development-of the gribble (Limnoria), a marine, wood-boring isopod. In view of the destructive habits of Limnoria, the matter is of some economic importance. There are three species of Limnoria in British watersL. (L.) lignorum (Rathke), L. (L.) quadripunctata Holthuis and L. (L.) tripunctata Menzies. Their distributions are given by Jones (1963). It has been found that warm water effluents can increase Limnoria damage in a number of ways. In the first place, the rise in temperature may stimulate the general boring activity and cause it to be continued into the normally quiescent winter months (Beckman & Menzies 1960; Eltringham 1965). Secondly, it may accelerate the onset of the breeding season in the spring and prolong its duration into the autumn and winter (Hockley 1963). Finally, it may shorten the developmental period of the young stages and thus permit the production of a larger number of broods each breeding season. Not much is known about this aspect. S0mme (1941) found that under conditions rising from 11 to 160 C, the eggs of L. lignorum took from 33 to 42 days to reach the stage at which the young forms leave the pouch. (The eggs develop within a brood pouch which is formed from the expanded epipodites (obstegites) of the second to fifth pair of pereiopods.) The only other published study appears to be that of Kampf (1957) who found that in L. tripunctata the total developmental time was 17 days at 200 C, 15 days at 220 C, 13 days at 260 C and 11 days at 300 C. Although the developmental time was accelerated by increased temperature, the percentage of eggs that reached the 'hatching' stage was reduced, e.g. .85%0 completed development at 200 C but only 51%0 at 300 C. Although these results are of great interest, it was clear that much remained to be learnt about the development of eggs in relation to temperature. One of the most important aspects, about which nothing is known, is the values of the limiting temperatures, both upper and lower, for successful development. Nor have the durations of the separate *stages through which the embryos pass been fully investigated, although Somme (1941) recorded those of a few eggs which had been extruded from the pouch by the movements of the female. The work to be described was carried out with eggs removed from the brood pouch and reared under constant temperature conditions in natural sea water of 33%, salinity.

The effects of varied dissolved oxygen concentrations and temperature on the wood-boring isopod genus Limnoria

Three species of the marine wood-boring genus Limnoria were subjected to low dissolved oxygen concentrations at different temperatures under laboratory conditions. 28-day median tolerance limits (TLm) were 1.0 mg/l of dissolved oxygen at 15° to 16°C and 19° to 20°C for L. lignorum, 0.75 and 0.60 mg/l at 15° to 16°C and 22° to 25°C, respectively, for L. quadripunctata, and 1.0 and 1.18 mg/l at 15° to 16°C and 22° to 25°C, respectively, for L. tripunctata. The amount of burrowing activity, as measured by the egestion rate, was directly related to the amount of dissolved oxygen. A daily egestion rate of 0.116 mg per day in L. tripunctata at 22° to 25°C was the highest figure measured. The daily egestion rate was sharply reduced at dissolved oxygen concentrations below 3.0 mg/l.

The geographical and vertical distribution of British Limnoria [Crustacea: Isopoda

There are three British species of the wood-boring isopod Limnoria. The boreal L. lignorum is found around all coasts, but is least common on the south and west coasts, where the temperate L. quadripunctata is dominant. The latter also occurs in the Isle of Man, Ireland and the Channel Isles, but has not been found on the east coast. The warm-water L. tripunctata is found only on the central south coast and in South Wales. Each species can survive at levels equivalent to 60-65 % exposure, but in mixed populations L. tripunctata dominates the upper level of Limnoria attack, L. quadripunctata dominates the middle zone and L. lignorum is found at the base of exposed piling or sublittorally.

Coexistence of Three Species of the Wood-boring Isopod Limnoria in Southampton Water

THREE species of Limnoria, L. lignorum (Rathke), L. quadripunctata Holthuis and L. tripunctata Menzies, have been found living together in piling and test blocks taken from Southampton Water. This is the first European record for L. tripunctata, which previously has been reported only from Central and North America1. This species has since been found with L. quadripunctata in piling taken from Cowes, Isle of Wight, and from Swansea, South Wales, where it was the only species present in the samples examined.

Aggregation by the Marine Wood-Boring Isopod, Limnoria

Aggregation by the Marine Wood-Boring Isopod, Limnoria

Occurrence of cellulose in Limnoria.

SINCE the report by Yonge1 on the absence of cellulase in the marine wood-boring isopod Limnoria, the nutrition of this destructive organism has remained a perplexing problem. A re-examination of the question has resulted in findings different from those of Yonge, and, in view of the commercial and biological importance of the borer problem, publication of a preliminary note at this time seems warranted.