Abstract. A survey of the historical background of chemically boring bivalves and the proposed methods of boring, indications for biocorrosion, observations, and experimental results are provided. The regional impact to the ecosystem is discussed with examples from the N. Adriatic, Caribbean, and E. Pacific. The fossil record of the geologically oldest biocorroders extends back into the Mesozoic, i.e., U. Triassic for Lithophaga and Jurassic for gastrochaenids.
Abstract. In the northern Red Sea several genera of sclcractinian corals arc used as hosts by Pedum spondyloideum. High population densities lead to space competition. The bivalves use chemical means to interact with each other and with their host corals. Due to dorsal attachment and predominantly ventral growth ‐ to keep pace with coral growth ‐ biocorrosion is less obvious, than in Lilhophuga.
The depth of water and the inclination angle of the coast and, in particular, the kind of substratum determine the distribution and population density of date mussels. Oolitic limestones are twice to three times as highly populated as dolomites.The growth takes place in stages, between periods of rest. 10 to 20% ofLithophaga lithophaga having a length of about ∼30mm grew by 0.4 to 3.1 mm in the period of 12 weeks in the substratum. 1 to 2% of mussels with a size of 50 to 60 mm grew by 0.1 to 1 mm outside the substratum. Small mussels grew more frequently and to relatively greater extent than big ones. The first 10 mm of growth in length occurs in the first three years, the next 10 mm after 5 years, etc. so that the biggest mussels (80 mm) will be about 80 years old.The boring activity depends on the condition of the animal and, largely, on the kind of substratum. The boring rate on prepared stones in the open was 0.09 to 0.25 ml in 12 weeks forLithophaga lithophaga with a size of 30mm, that is 0.5 to 1 ml per year. In the laboratory, this amounted to only a third.The depth of the etching effect depends on the granule size in the substratum. The crystals released from the substrate are removed as pseudofeces via the ciliary epithelium. The amount of the fine sediment may be calculated roughly from the volume of the hole.Finally, an attempt is made to apply the experimental findings to the conditions prevailing in the sampling area. It is true that the destruction of the coast by date mussels is restricted to relatively small areas, but it may amount to more than 40 cm/m at a depth of 1 to 2 meters and continue for a period of 1000 years on the steep slope of oolitic limestones.
Abstract. In the northern Red Sea, the nestling and facultatively boring pectinid bivalve Pedum spondyloideum lives embedded in various scleractinian host corals of seven families, including the previously unrecorded hosts Astreopora, Leptastrea and Hydnophora. Pedum density varied according to host species, locality and depth. The bivalve‐occupied coral surface (OCS) was measured on samples and from close‐up photos taken in the field. Based on the 9 × 6 cm photo frames, Pedum density ranged from 1.9 – 18.6 · (100 cm2)– 1. In 14 Montipora, apparently the favourite host genus, mean density was 6.5 · (100 cm2)– 1 and mean OCS 3.4 %, but maximum OCS amounted to 12.5 %. In 19 × 13 cm frames, Pedum density ranged from 0.4 – 10.7 · (100 cm2)– 1. The maximum density occurred again in Montipora, followed by Porites [6.7 · (100 cm2)– 1] and Cyphastrea [6.0 · (100 cm2)– 1]. The OCS ranged from 0.2 – 7.0 %. The latter was found in Goniastrea, and 6.6 % OCS in Montipora. The mean density of Pedum in 13 Montipora was 3.6 · (100 cm2)– 1 and mean OCS 2.2 %.
Heavy infestation does not appear to impact the corals, except in growth form. Shell size and dwelling volume are highly correlated. From the opening length on the coral surface, the expected volume can be calculated using the regression y = 0.2127 x2.7447. A high Pedum density indicates a southerly reef site or near‐shore locality with ample suspended nutrients in the water. Successions of Pedum generations in the same host demonstrate that corals usually outlive their inhabitants by many years. The embedded traces are less distinct than in the coral‐associated mytilid Lithophaga. Compared with the latter, Pedum dwellings have a less regular shape and a much wider opening. Coral overgrowth partly fills and camouflages dwellings. Although no fossil record is known, Pedum traces have a fossilisation potential.
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