Population dynamics of the amphioxus Branchiostoma elongatum from northern Chile

Abstract

Amphioxi represent the evolutionary link between vertebrates and invertebrates. For this reason, research dealing with these animals has been focused mainly on embryological and anatomical studies. Out of 30 described species, only one, Branchiostoma elongatum, is known to inhabit shallow sandy bottoms along the Humboldt Current System (HCS) of Chile and Peru. The population dynamics of B. elongatum from northern Chile was studied between February 2008 and January 2009, and the results were compared with other species within the genus Branchiostoma inhabiting distinct ecosystems. Mean abundance of B. elongatum was low (158.6 ind m 22 ) in comparison with the abundance of other species within Branchiostoma. Although the gametogenic activity was continuous, a clear spawning event was observed between August and October, which seemingly produced a recruitment pulse during the summer and consequently a simultaneous increase in population density and decrease of mean length during that period. Growth of B. elongatum was best fitted to the seasonalized von Bertalanffy growth function (K ¼ 0.45 year 21 and L 1 ¼ 64.6 mm), with faster growth during summer -autumn. Growth performance (V ′ ¼ 3.273) was high in comparison with other species within the genus. Mortality of B. elongatum (Z ¼ 1.075 year 21 ) was well fitted to the single exponential model (r 2 ¼ 0.92). The annual total production of B. elongatum reached 0.68 g ash-free dry mass (AFDM) m 22 and the annual mean biomass was 0.56 g AFDM m 22 , which determined a production to biomass ratio of 1.22. The huge productivity of the HCS was not reflected in a high abundance and biomass of B. elongatum. However, this species displayed a high growth efficiency and P/B ratio that are comparable to those of other Branchiostoma inhabiting highly productive ecosystems.

Effects of patch size and position above the substratum during early succession of subtidal soft-bottom communities

“…Sizes of juveniles (<19 mm body length) and adults (>20 mm body length) were obtained from length-frequency distribution presented in Vergara et al (2011) T. dombeii Distance from the anterior end to the posterior end. Measurements were made using a digital caliper…”

Taxonomic composition and distribution of cephalochordates (Cephalochordata: Amphioxiformes) from Mexico

“…Al ser verificada su georreferencia de recolecta se encontró que ésta corresponde a la parte baja de California, USA. La identidad de estos organismos debe ser verificada, debido a que B. elongatum sólo está registrada en las costas de Perú y Chile, incluyendo a las islas Galápagos (Vergara et al, 2012).…”

Molecular taxonomy confirms that the northeastern Atlantic and Mediterranean Sea harbor a single lancelet, Branchiostoma lanceolatum (Pallas, 1774) (Cephalochordata: Leptocardii: Branchiostomatidae)

“…The family Branchiostomatidae Bonaparte, 1846 (subphylum Cephalochordata) comprises about thirty species, known as lancelets or amphioxus [1][2][3][4]. They inhabit the soft bottoms of various sublittoral and coastal habitats (estuaries, coastal lagoons, river deltas, and open coasts) from temperate to tropical regions [5][6][7] and some species grow up to 10 cm in length. Lancelets are generally benthic, living half-buried and only exposing the rostral end to the water.…”

“…They filter plankton through the gill-bars by generating a ciliary water current, entering from the mouth through the buccal cirri. Food particles are embedded in mucus, collected in the pharynx and then passed into the intestine [6][7][8][9][10].…”