Spatial and temporal variability of patterns of colonization by mussels (Mytilus trossulus, M. edulis) on a wave-exposed rocky shore

Abstract

Colonization rates of mussels (Mytilus trossulus and M. edulis) were measured on natural substrata in tidepools and on emergent rock in recently ice-scoured and non-scoured regions of a rocky shore near Halifax, Nova Scotia, Canada. The relative importance of initial settlement/colonization, compared to subsequent dispersal and mortality, in determining the distribution and abundance of mussels was examined by comparing patterns and rates of mussel colonization at sampling intervals of days to months over a 17 mo period. Lrss than 4 ":, of mussels which colonized the quadrats sampled at short (2 to 7 d) intervals were settling larvae (<O.5 mm shell length), indicating the importance of poslsettlement dispersal of mussels on this shore. Most colonists were >2 mm, too large to be dispersed by byssal drifting, suggesting they \Yere redistributed by wave dislodgment and deposition. At both short (2 to 7 d) and long (5 to 16 mo) sarnpllng ~ntervdls, colon~sts were most abundant in ice-scoured tidepools and least abundant on ice-scoured emergent rock, probably reflecting d~fferences In the macrobenthic assemblaqe. the sllhc;tratl~m fnr co!oniza!ic~. 1 :: addi:ion, thr-luny L~I I I I dbunaance oi colonists was linearly related to the cumulativct short term abundance during all but one of the intervals. Therefore, our results ~ndicate that, over time scales up to 16 mo, patterns of initial colonization by settlers and larger post-larval mussels were inore important than post-colonizati.on mortality and dispersal in determining pattt=rns of distribution and abundance of n~ussels on this shore

Spatio-temporal variability of larval abundance and settlement of Perna perna: differential delivery of mussels

“…For sedentary marine species with planktonic larvae, settlement is a major process, regulating the dynamics and structure of benthic populations (Hunt & Scheibling 1998, Balch & Scheibling 2000 and acting as a bridge between dispersal and recruitment. In fact, intertidal community structure and population dynamics are strongly affected by the arrival of larvae on the shore, as settlement rates may determine the final spatial variation of adults .…”

Scales of Mytilus spp. population dynamics: importance of adult displacement and aggregation

“…Among all marked individuals, many remained within the confines of the 50 × 50 cm sites -at most, displaced 5 to 15 cm from the transplant. Active crawling behaviour (Schneider et al 2005) generally takes place within a few centimetres and usually occurs on a time scale of months, and wave disturbance is also a source of passive movement on a scale of 10s of centimetres (Hunt & Scheibling 1998). Similar displacement of tagged mussels (5 to 25 mm shell length) was also documented on a temperate shore, most of which moved < 5 cm and 6 individuals which moved 10 to 49 cm (Hunt & Scheibling 2002).…”

“…Hunt & Scheibling (1996) documented the settlement of post-larval mussels on natural substrata in a temperate system in which only 20 to 31% of colonizers measured 5 to 12 mm. In another study, most colonizers were either recruits (0.5 to 1.9 mm) or small juveniles (2 to 4.9 mm; Hunt & Scheibling 1998). An experiment using mussel transplants revealed that most colonizers were recruits < 2 mm shell length, while individuals measuring 2 to 10 mm only contributed to <15-20% of colonization (Hunt & Scheibling 2001).…”

“…Of these sites, 45 were then randomly selected and cleared of all benthic organisms. Each selected site also included a 10 cm cleared buffer zone, hence excluding any contribution of active mussel movement to colonization into experimental sites (Hunt & Scheibling 1998); 15 sites were kept as controls (no mussel transplant), 15 sites received a low-density transplant (50 mussels), and 15 sites received a high-density transplant (175 mussels; Fig. 2).…”

“…Passive migration of adult mussels by wave dislodgement has been documented (Hunt & Scheibling 1998, 2001, 2002, but the contribution of adult displacement to population dynamics across spatial scales and body sizes has not been resolved. Mussel movement at very small body size or spatial scales have been shown to contribute to mussel distribution and growth.…”