Distribution and abundance of rafts of Macrocystis pyrifera in the argentine sea and its role in the long distance dispersal of coastal benthic species

NAHUEL EMILIANO FARIAS; RAMIRO BAGNATO; MAXIMILIANO MANUEL HERNANDEZ; SOFIA PEREZ SALLES; GISELE QUESADA; JUAN ROMANELLI; JULIAN WEBB

Mar del Plata

Congreso; XVIII Congreso Latinoamericano de Ciencias del Mar-COLACMAR 2019; 2019

Asociación Latinoamericana de Investigadores en Ciencias del Mar-ALICMAR

The vast distribution and high connectivity typical of marine populations is traditionally explained by the passive transport of their planktonic phases. However, the accidental transport of juveniles or adults associated with floating objects carried by currents is a more efficient mechanism to explain dispersal over long distances. The macroalgae mats that detach from the bottom and drift, constitute small communities of coastal organisms that disperse for periods that greatly exceed the longest larval developments and are transported by hundreds to thousands of kilometers. This study is based on the recording of macroalgae rafts carried out by observers during a series of seismic surveys carried out between November 2017 and September 2019, on the Argentine platform and slope up to a depth of 3500 meters. The abundance and distribution of rafts was estimated from a spatially-referenced distance sampling to which a surface density model (DSM) was applied for detectability-adjusted counts. All the rafts registered were constituted by the "cachiyuyo", Macrocystis pyrifera. Some rafts could be obtained opportunistically during the same campaigns, which allowed to study the composition of associated species, dominating two oceanic organisms: the bivalve Gaimardia sp.and the goose barnacle Lepas australis in the leaves; and several coastal species associated mainly to the holdfasts: two crabs, the brachyuraPilumnoides hassleri and the anomura Pachycheles sp, the brittle star Ophioplocus januarii, at least five species of bryozoans and many unidentified polychaetes and epiphytic algae. Our results show that the M. pyrifera rafts are concentrated on the Malvinas current so there is an important south-north transport reaching the north to the Brazil-Malvinas oceanographic front. At least a fraction of these rafts are concentrated on the Buenos Aires platform, from where they can be carried to the coast by southerly winds reaching coasts in low latitudes (Batista et al. 2018). Our results suggest that this alternative transport mechanism is more important than previously thought and may be significant in determining the distribution patterns of some species and consequently the diversity of communities along the entire southwest Atlantic coast.