Scale-dependent patterns and processes of intertidal mussel recruitment around southern Africa

Abstract

Different processes shape ecological communities at different physical scales. Their relative importance is central to ecology, particularly in the case of foundational species like mussels. For 5 yr at 8 locations across 5 bioregions spanning 3200 km of the southern African coast, we monitored recruitment and adult populations of 4 intertidal mussel species. At most locations, mussel bed width and percent cover were surprisingly constant, but declines did occur at 3 locations. Recruitment rates displayed a strong geographic gradient: exceptionally high on the West Coast, low on the South Coast and intermediate on the East Coast. At a regional scale, significant positive relationships existed between the magnitude of annual recruitment maxima and (1) adult abundance, (2) intertidal primary productivity and (3) the magnitude of upwelling. Recruitment was highest at locations with large adult populations, high productivity and more upwelling. Within locations, recruitment varied inconsistently among sites, years and seasons. Sea temperature and recruitment were seasonal at all locations except in the southern Benguela, suggesting they are linked. At the medium scale (<1 km), at which local hydrology is believed to be important, relationships between recruitment and adult abundance were observed at only 2 locations, while at the smallest scale (<1 m), significant positive relationships were more common. Two of the 3 locations with lowest recruitment were recruitlimited. This has important management implications because low-recruitment and recruit-limited locations in southern Africa occur where human exploitation is most intense.

The role of recruitment and behaviour in the formation of mussel-dominated assemblages: an ontogenetic and taxonomic perspective

“…Log(X + 1) transformation achieved homogeneity for the Mytilus dataset, but not for the Perna dataset. Given that heterogeneous variances are not critical when the total degrees of freedom are as high (df = 48) as in this balanced analysis (Underwood 1997;Quinn and Keough 2002), all datasets were analysed following log (X + 1) transformation.…”

“…Both datasets were homogenous (Cochran's test) after logarithmic (X + 1) transformation. Student-Newman-Keuls post hoc comparisons were used to examine differences among means of groups in the event of significant effects (Underwood 1997;Quinn and Keough 2002).…”

“…Kostylev and Erlandsson 2001;Erlandsson et al 2005), have important repercussions for mussel bed ecosystems by altering recolonisation (Petrović and Guichard 2008), recruitment (Erlandsson and McQuaid 2004;Commito et al 2014), growth and survival (Petraitis 1995;Liu et al 2013) and resilience (Liu et al 2014) and could not be identified if interactions across the appropriate scales were not examined (Guichard et al 2003;Largaespada et al 2012). Rocky shore mussel beds in South Africa usually exhibit fractal patchy patterns (Erlandsson and McQuaid 2004;Erlandsson et al 2005), and on the south coast of South Africa, these patchy, smallscale patterns are context and density dependent and are probably driven by both local recruitment and behavioural processes (Erlandsson et al 2011;Reaugh-Flower et al 2011), resulting in patterns that influence local population dynamics.…”

Coastal Invasions: The South African Context

“…Also in contrast to M. galloprovincialis, which is virtually absent from the subtidal zone, S. algosus also occurs in large numbers in this habitat (Skein et al 2018a). It appears to owe much of its success and rapid rates of spread to an exceptionally high recruitment rate (Reaugh-Flower et al 2011;Zeeman et al 2018). Many of the impacts associated with S. algosus are similar to those of M. galloprovincialis, as both species dominate previously open rocky surfaces.…”

Variación estacional en la composición de ensambles sublitorales de macroalgas asociadas al alga roja Gigartina skottsbergii Setchell & Gardner, en el Estrecho de Magallanes, Chile

“…Un ejemplo es la heterogeneidad del substrato, Santa María se caracteriza por presentar un substrato de rodolitos, mientras que Santa Ana presenta un substrato de terrazas, en consecuencia algunos estudios han observado que ocurre un aumento de riqueza de macroalgas en superficies duras, y estables, aptas para su colonización, mientras que esta riqueza tiende a disminuir, o a estar influenciada por un substrato más suave, blando o inestable (Klöser et al 1996;Underwood, 2004;Wulff et al 2009), como es el caso de los rodolitos. Un factor biótico importante es la presencia del kelp (Kirikki, 1996), como M. pyrifera, en Santa Ana que forma un canopy, generando protección a otras especies de macroalgas, además de variaciones en la herbívora (Rilov & Schiel, 2011), y reclutamiento de algas (Reaugh-Flower et al 2011), el efecto de estas últimas variaciones, aún no han sido evaluadas en ambas praderas. Mientras que a macroescala, el fotoperiodo, la temperatura y la pluviosidad (Cruz-Motta et al 2010) pueden ser factores que afectan la riqueza espacial (Chappuis et al 2014).…”