Settlement and post-larvae behaviour of Mytitus galtoprovincialis: field and laboratory experiments

Abstract

Field sampling carried out in the Rfa de Vigo (NW Spain) from 1991 to 1993 showed that Mytdus galloprovincialis settle directly from the plankton onto substrates exposed to various environmental conditions: exposed rocky shore; protected rocky shore; exposed, raft mussel-culture area; and protected, raft mussel-culture area. For direct settlement, competent larvae may use a wide variety of substrates: filamentous nylon ropes; the byssus and intricately arranged material in the bottom of mussel beds; filamentous, thallus and membranous algae; and rugosities on adult mussel shells. The peak of settlement occurred from spring to early autumn and differences in the settlement abundance among localities were influenced by currents. After this peak, the settlement of larger post-larvae continued, associated with the increase in storms during autumn that detach them from their original substrates. This dispersion phase allows for the possibility of colonising, or recruiting on other areas, even during the post-spawning season when the presence of small post-larvae is at its minlmum. Laboratory experiments carried out with post-larval stages from 0.250 to 2.000 mm showed that under static water conditions they crawl and form clumps, but do not search for a specific substrate. If they are not disturbed, they may remain in their original place of settlement. Conversely, under moving water conditions they attach to a wide variety of substrates, particularly to byssal filaments and thalli of red algae Ceramium rubrum. The contact and attachment to substrates is carried out with a long mucous thread that also aids in forming clumps. The use of this mucus to settle results in a 'preference' for natural filamentous substrates but also in settlement on rugous hard surfaces. An alternative hypothesis to the primary and secondary settlement pattern previously described in the literature for Mytilus edulis is suggested.

Interacting effects of wave exposure, tidal height and substratum on spatial variation in densities of mussel Perna perna plantigrades

“…However, mussel spat are more abundant in finelybranched than coarsely-branched substrata, both natural and artificial (Alfaro & Jeffs 2002), and it has been argued that hydrodynamic processes alone can explain recruitment patterns on scales of > 3 cm (Bourget & Harvey 1998). Cáceres-Martínez et al (1994) suggest that settlement of Mytilus galloprovincialis is a passive process. Contact mucus threads produced by late pediveligers and post-larvae are more likely to snag filamentous surfaces so that algae trap settlers more efficiently than byssus threads, resulting in higher settlement on algae than on adult mussel beds (Lane et al 1985).…”

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

“…Most studies of patterns of settlement or recruitment of musse1.s have monitored artificial substrata (usually filamentous) and have found no evidence of colonization by mussels > 5 mm (e.g. De Rlok & Geelen 1958, King et al 1990, Caceres-Martinez et al 1994). In contrast, Paine (1974) observed that large Mytilus californianus (>3 cm) colonized plots of the natural substratum which had been cleared of mussels.…”

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“…Caceres-Martinez et al, 1994;Dobretsov & Railkin, 1996). The observation that blue mussel spat 'preference' for filaments is more conspicuous in moving water than in the absence of currents seems to support this view (Eyster & Pechenik, 1987).…”

“…In some cases, however, larvae seem to directly settle into blue mussel beds (McGrath et al, 1988). Due to a secreted mucus thread, the larvae may be trapped by these filaments rather than actively 'choosing' them (Caceres-Martinez et al, 1994;Bourget & Harvey, 1998). A strong physical (passive) component in the process of primary settlement would explain why rates of settlement are enhanced by water movement (Eyster & Pechenik, 1987).…”