The rate of secretion and number of byssal threads by which blue mussels (Mytilus edulis L.) reattach were measured in circulating seawater and with the mussels exposed to currents between 10 and 20 cm/s. In circulating water, larger mussels secrete more byssal threads than small mussels and appear to do so more rapidly. If detached blue mussels are exposed to currents, this pattern is reversed; when exposed to high currents, small mussels reattach more rapidly than large mussels.

Dimensions of crab burrows were compared in two sympatric populations of fiddler crabs, Uca vocans and U. annulipes, to determine interspecies variation. Nine dimensions of burrow architecture were defined from 62 complete burrow casts of U. vocans: burrow diameter, BD; burrow volume, BV; total burrow depth, TBD; burrow neck height, BNH; curved burrow length, CBL; horizontal length, HL; chamber diameter, CD; angle between descending neck of burrow and the substrate surface, β; angle between the bend in the burrow and the perpendicular, θ . None of the nine dimensions of burrow architecture showed any difference between sexes. Six out of seven linear burrow dimensions differed significantly among crabs in the three size classes recognized; BNH did not differ among small, medium, and large-sized crabs. Regardless of species, larger-sized crabs dug larger entrances and resided in more voluminous burrows. The architecture of the burrows in the two sympatric populations is rather similar: the only significant difference is that Uca vocans had wider BDs than U. annulipes. This could be due to the difference in carapace proportions of the two species: adult specimens of U. vocans have significantly larger carapace length to width ratios than those of U. annulipes. Comparisons of β between the two species showed that the descent slopes of the burrows were similar, indicating that there is no evidence to suggest that burrows of fiddler crabs in sandy habitats have steeper descent slopes than those in muddy habitats. The mean volume of sediment excavated by U. vocans per m 2 , though not significantly greater than that of U. annulipes, suggests that U. vocans is potentially a more active agent of sediment re-working than its sympatric species in this lagoon. RÉSUMÉLes dimensions des terriers de crabes ont été comparées chez deux populations sympatriques de crabes violonistes, Uca vocans et U. annulipes, afin de déterminer la variation interspécifique. Neuf mesures de l'architecture du terrier ont été définies à partir de 62 moulages de terriers complets de 1 ) e-mail: slim@nie.edu.sg © Koninklijke Brill NV, Leiden, 2006 Crustaceana 79 (5): 525-540 Also available online: www.brill.nl 526 SHIRLEY S. L. LIM U. vocans : diamètre du terrier, BD ; volume du terrier, BV ; profondeur totale du terrier, TBD ; hauteur du conduit d'entrée du terrier, BNH ; longueur de la partie courbe du terrier, CBL ; longueur horizontale, HL ; diamètre de la chambre, CD ; angle entre la partie descendante du terrier et la surface du substrat, β; angle entre la courbure du terrier et la perpendiculaire, θ. Aucune de ces neuf mesures de l'architecture du terrier n'a montré de différences entre les sexes. Six des sept dimensions linéaires du terrier différaient significativement parmi les crabes, dans les trois classes de taille reconnues ; BNH ne différait pas, que les crabes soient de petite, moyenne ou grande taille. Par rapport à l'espèce, les grands crabes creusaient des entrées plus grandes et demeuraient dans des terriers de plus grand volume...

At ebb tide Macoma balthica makes crawling tracks on the intertidal sand flats near Churchill, Manitoba, on Hudson Bay. Clams from two tidal levels, mean low water and 1.0 m above mean low water, were sampled to compare the parasite load and growth rate of crawling versus buried Macoma. For each clam the number of trematode metacercariae present were counted and the growth rate was determined by the measurement of annual growth rings. Clams were infected by more metacercariae at the higher than at the lower tidal level, larger clams more than smaller ones and crawling clams more than buried ones. Increased exposure of the clams at the higher tidal level to shorebirds, the final host of the trematodes, is proposed as the reason for the difference in parasite load between the tide levels. High-tide clams (more parasitized) grew faster than low-tide ones (less parasitized), and crawlers (more parasitized) grew faster than the buried (less parasitized) clams. Enhanced somatic growth as a result of parasitic castration is proposed to be the most logical explanation to account for the faster growth of the parasitized clams.

Nine burrow-morphological characters (burrow diameter, BD; burrow volume, BV; total burrow depth, TBD; burrow neck height, BNH; curved burrow length, CBL; horizontal length, HL; chamber diameter, CD; angle between descending neck of burrow and the substrate surface,¯; angle between the bend in the burrow and the perpendicular, µ / were de ned from a study of 127 complete burrow casts of the ddler crab, Uca annulipes. Crabs in 14 one-m 2 quadrats randomly sited in low, mid, and high shore levels on a lagoonal beach were sexed and categorized into small, medium, and large size-classes. Sediment type in each quadrat was assessed as anoxic or non-anoxic. Density was estimated at 12.8 crabs m ¡2 I mean sex ratio was 2.75 ? : 1/. Five burrow-morphological characters (BV, TBD, BNH, CBL, and CD) differed signi cantly between sexes, being larger in male than in female crab burrows (p < 0:05). Differences in these burrow characters were indicative that males excavated larger burrows than females. Burrow mid-angle was signi cantly more obtuse in female crab burrows (p < 0:05), indicative of a more gradual turn in the descent of the burrows made by males. We attributed this to the poorer manoeuvrability of the males in the burrows due to their large chelipeds. Burrows of larger-sized crabs had greater BD, larger BV, and bigger CD than burrows of small-and medium-sized crabs. Signi cantly deeper burrows were dug at the high shore level than at both mid-and lower shore regions. We hypothesize that digging deeper burrows in the high intertidal is one way in which the ddler crab can maintain lower burrow temperatures when the tide recedes. Burrows in anoxic sediments had signi cantly shorter TBD, BNH, and CBL than burrows in nonanoxic sediments. We postulate that shorter burrows in anoxic sediments may help improve the aeration of the burrows as opposed to longer burrows that accumulate a greater amount of stagnant air. RÉSUMÉNeuf caractères morphologiques des terriers (diamètre, BD; la chambre, CD; angle entre le col descendant et la surface du substrat,¯; angle entre la courbe du terrier et la perpendiculaire, µ / ont été dé nis pour l'étude de 127 terriers du crabe violoniste, Uca annulipes. Les crabes, situés dans 14 quadrats de 1 m 2 , pris au hasard, à différents niveaux, bas, moyen et haut d'une plage de lagon ont été examinés pour déterminer leur sexe et les répartir par classe de taille, petite, moyenne et grande. Le sédiment de chaque quadrat a été caractérisé comme anoxique ou non-anoxique. La densité de population a été estimée à 12,8 crabes au m 2 et la sex-ratio moyenne à 2.75 ? : 1/. Cinq caractères morphologiques de terriers (BV, TBD, BNH, CBL et CD) diffèraient signi cativement suivant le sexe, étant plus grands pour le terrier des mâles (p < 0,05). Les différences observées sur ces caractères de terrier indiquaient que les mâles creusent des terriers plus grands que les femelles. L'angle médian des terriers était signi cativement plus obtus dans les terriers de femelles (p < 0,05), indiquant une courbure plus g...

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