Variation in the depth and morphology of burrows of the mud crab Helice crassa among different types of intertidal sediment in New Zealand

Abstract

Crabs are among the larger and more active burrowers in intertidal sedin~ents in New Zealand, as in many other parts of the world. Abundances of mud crabs Helice crassa and their burrows were compared among sites differing in the nature of the11 sediments. Differences in burrow archltecture among sites were quantified using casts of burrows made in situ. The effects of bioturbation on sediment geochemistry were also determined with respect to redox potential and the concentrations of 2 chemical phases, acid volatile sulphides (AVS) and iron pyrites (FeS,), that influence the bioavailability of heavy metals. The objective of this study was to identify effects of differences in the extent and nature of burrowing activity of the crab H. crassa among different sediment types on sediment geochemistry, particularly with respect to the bioavailability of heavy metals. Burrows were more abundant at muddy sites (average 22 to 59 burrows 20 cm diameter core-') than at sandy sites (average 12 burrows core-'). Although not necessarily deeper at muddy sites, burrows were more complex in structure. Average volumes of casts were larger at muddy than sandy sites by a factor of up to 14.8 and at the most densely-burrowed site, burrows represented 14,?? of the volume of the surrounding sediment. The architecture of the burrows of H. crassa is discussed in the context of published models of burrow structure and function for other crustacea. Patterns of differences in chemical variables among sites were not clear cut. Redox profiles generally showed decreases with depth in the sediment and, among the muddy sites, potentials were hlghest and most variable at the site with greatest burrowing activity. Concentrations of AVS and FeS, were lower in sandy sediments than in muddy ones. Among muddy sites, the concentration of AVS was lowest at the site with the greatest amount of burrowing, consistent with introduction of oxygen to the sediment and the consequent oxidation of AVS. Concentrations of FeSz showed a pattern that suggested that burrowing introduces FeS2 from deeper layers, where concentrations are higher, into shallower, bioturbated layers of the sediment, offsetting effects of oxidation due to burrowing activity. Concentrations of FeS, were highest at the site with most burrowing activity KEY WORDS: Crab .

Smothering of estuarine sandflats by terrigenous clay: the role of wind-wave disturbance and bioturbation in site-dependent macrofaunal recovery

“…The small (1 to 2 cm carapace width) mud crab Helice crassa is an important bioturbator on many New Zealand mudflats and is most abundant in muddy fine sediments, where they can maintain their burrows (Nye 1977, Morrisey et al 1999. Thus, the deposited clays provided a suitable habitat extension in areas dominated by more sandy sediments.…”

Mangrove habitat partitioning by Ucides cordatus (Ucididae): effects of the degree of tidal flooding and tree-species composition during its life cycle

“…However, the influences of certain abiotic and biotic parameters on the population biology of these brachyurans are comparatively well known, especially the effects of temperature (Kelemec 1979), salinity (Frusher et al 1994), tides (Reinsel 2004;Turra et al 2005), species composition of mangrove trees (Icely and Jones 1978), and sediment granulometry (Mouton and Felder 1996;Morrisey et al 1999;Ribeiro et al 2005).…”

Seasonal Burrow Distribution of the Ghost Crab, <i>Ocypode ceratophthalmus</i> (Pallas, 1772), on Sandy Shores of Gujarat, India

“…The distribution of the burrows and their morphological features can affect the physical and biochemical properties of the sediment (Mermillod-Blondin et al, 2004;Kristensen, 2008;Katrak et al, 2008). Burrow patterns and morphology are mostly species specific; however, species can modify their burrowing activity and burrow morphology in different sediment types and according to changes in environmental conditions (Bertness and Miller, 1984;Takeda and Kurihara, 1987;Morrisey et al, 1999;Lim and Diong, 2003;Chan et al, 2006). Burrow morphology and density of Ocypode crabs have, for example, been shown to vary with distance from the water line, more complex structure of burrows with low density of crabs were observed on the upper part while simple burrow structure with high density of crabs were observed on the lower part of sandy shore (Strachan et al, 1999;Chan et al, 2006).…”