Secondary production by siphon regeneration in a tidal flat population of Macoma balthica

Abstract

The share of cropped siphon tips in the secondary production of the bivalve Macoma balthica (L.) was estimated in a tidal flat area in the westernmost part of the Dutch Wadden Sea. Basic data were year-round measurements of siphon- and body weights in the field and regeneration rates of siphons in the laboratory. The completeness of the inhalant siphon was expressed as the Siphon Condition: SC = siphon weight divided by the square root of the body weight. In field populations the SC values showed a seasonal pattern, viz. low in summer and high in winter. Regeneration of the siphons was rapid under simulated tidal flat conditions, hardly depended on temperature and season and was faster as siphons were lighter. Siphon growth stopped when a SC value of 0.36 was reached. In tidal flat animals, SC values between 0.03 and 0.36 were observed. The estimated amounts of Macoma siphon tissue lost during 1975 at 4 tidal flat transects varied from 0.31 to 1.66 g ADW·m −2·a −1, i.e. nearly half of the annual mean biomass of the soft parts and hardly different from elimination in the form of whole Macoma. Only about 13% of the siphon tip biomass lost was consumed by flatfish. Other epibenthic predators, like gobies, shrimps and shore crabs will have cropped the rest. Individual Macoma will have lost an average of several siphon tips per day. The loss and subsequent regeneration of siphon tips must be an important factor in the ecology of Macoma, affecting feeding behaviour, burying depth and body weight. In tidal flat ecosystems, regeneration of siphon tips and other cropped body parts will significantly contribute to benthic secondary production.