Recruitment of the brown mussel Perna perna onto natural substrata: a refutation of the primary/secondary settlement hypothesis

Abstract

Recruitment of the brown mussel Perna perna onto natural substrata: a refutation of the primary1 secondary settlement hypothesis T. A. Lasiak, T. C . E. BarnardDepartment of Zoology, University of Transkei, Private Bag XI, UNITRA. Umtata 5100, South Africa ABSTRACT: The pattern of recruitment of the brown mussel Perna perna on an exposed rocky shore on the southeast coast of South Africa between March 1991 and March 1992 is reported. The densities and population size structures of plantigrades associated with 2 natural substrata, filamentous algae and established mussel clumps, are contrasted. Mussels of c500 pm shell length were present throughout the study period, but peaked in abundance dunng the winter months (June to September). Although the density of these early plantigrades vaned with both samphng date and site, type of substratum had no effect. Late plantigrades, mussels of >0.5 to 3.5 mm shell length, reached peak abundance amidst mussel clumps in winter as opposed to spring/early summer on algal turf. Sampling date, site and type of substratum all influenced the dens~ty of late plantigrades. The size distributions of the recruits found in association with the 2 substrata dlffered s~gn~ficantly on 4 of the 11 sampling dates. The recruitment pattern of P perna does not, therefore, conform with the generally accepted primary/secondary settlement hypothesis. The observed pattern lndlcates direct settlement of larvae from the plankton onto adult beds in addition to temporary attachment on filamentous algae. The relatively low intensities of recruitment observed, compared with those of other mytilids, may explain such anomalous attributes of P. perna as its lack of competitive dominance and low resilience to disturbance.

Re-colonisation rate differs between co-existing indigenous and invasive intertidal mussels following major disturbance

“…The higher re-colonisation rate and recovery of Mytilus galloprovincialis in the mid-zone following disturbance can be explained by its r-selected traits of higher fecundity, recruitment and growth rates (van Erkom Schurink & Griffiths 1991, 1993, Lasiak & Barnard 1995, Harris et al 1998, Steffani & Branch 2003a, Branch & Steffani 2004. Settlement rates (in our definition, settlement does not encompass postsettlement mortality while recruitment does) in the Plettenberg Bay area are also generally lower and more inconsistent for Perna perna than for M. galloprovincialis (Bownes 2005), which can explain the differences in re-colonisation rates after the storms.…”

“…1000 km along the south coast of South Africa since 1990 (McQuaid & Phillips 2000, Robinson et al 2005). There it is a threat to the indigenous brown mussel Perna perna (Linnaeus, 1758), the dominant mussel on the south and east coasts, which has generally lower fecundity, recruitment and growth rates than other mytilid mussels (Lasiak & Barnard 1995, Harris et al 1998. While P. perna is infested by many different trematodes, M. galloprovincialis is free of these parasites both in one of its native regions (north of Spain) and in South Africa (Calvo-Ugarteburu & McQuaid 1998a).…”

Limited wind-driven dispersal of intertidal mussel larvae: in situ evidence from the plankton and the spread of the invasive species Mytilus galloprovincialis in South Africa

“…Sigurdsson et al 1976, Lane et al 1985. Nevertheless, the great majority of larvae were well below the size at which we would expect them to settle (Bayne 1964, Dare 1976, Sprung 1984, CaceresMartinez et al 1993, Lasiak & Barnard 1995. (3) We assume that we 'tracked' coherent, moving clouds across a sampling grid.…”

Population dynamics of the nonindigenous brown mussel Perna perna in the Gulf of Mexico compared to other world-wide populations

“…Removal of entire mussel clumps and their separation in a 1 mm sieve retained all but the smallest post-larval recruits, avoiding errors in length-frequency analysis associated with gear size selectivity and under-sampling of juveniles. P. perna has a short juvenile phase (15 to 20 d) and pediveligers settle directly into adult mussel beds (Lasiak & Barnard 1995). Thus, initial appearance of juveniles < 5 mm SL in samples marked recruitment events.…”

“…Population and reproductive dynamics have been described for Perna perna in South Africa (Berry 1978, Crawford & Bower 1983, Lasiak 1986, Lasiak & Dye 1989, van Erkom Schurink & Griffiths 1991, Lasiak & Barnard 1995, Tomalin 1995, northern Africa (AbadaBoudjema et al 1984, Shafee 1989, 1992, Abada-Boudjema & Dauvin 1995, India and Sri Lanka (Appukuttan et al 1989, Indrasena & Wanninayake 1994, Brazil (Lunetta 1969, Marques et al 1991 and Venezuela (Vélez & Martinez 1967, Carvajal 1969, Vélez 1971, Acuña 1977. The highly variable growth rates, life spans and spawning periodicities among different populations of P. perna (Vélez 1971, Berry 1978, Lasiak & Dye 1989, Indrasena & Wanninayake 1994, Tomalin 1995 makes the potential invasive success of this species in North America difficult to assess.…”