Abstract
The first record of the amphioxus Branchiostoma californiense on seagrass patches of Halodule wrightii in the Gulf of California is reported. Sixty individuals (19 males, 18 females, and 23 undifferentiated) were collected in May 2017 at Bahía Balandra, Gulf of California, from subtidal seagrass patches at a depth of 0.5 m at low tide. The length and weight ranged from 15.88–28.44 mm and from 0.01–0.11 g for females and 11.7–27.9 mm and 0.01–0.09 g for males, respectively. The minimum size of sexually mature individuals was 11.70 mm for males and 15.88 mm for females; 62% of the specimens were sexually mature. Analysis of the total length-weight relationship suggested an allometric growth pattern among females, males and undifferentiated individuals, whereas an analysis of the entire sample suggested an isometric growth pattern. Typical and additional morphological characters were used to identify the amphioxi. High morphological variability between individuals was found, suggesting the presence of several morphotypes. Branchiostoma californiense had been previously reported as exclusively associated with bare sandy areas, but our study shows that this species can also be found in seagrass patches, using them as breeding and feeding grounds. Thus, seagrass patches are evidenced as suitable habitats for amphioxus.
Highlights
Amphioxi are Cephalochordata often used as a model for studying the phylogeny and evolution of vertebrates (Stokes and Holland 1998, Bertrand and Escriva 2011, Vergara et al 2012)
Amphioxus abundance decreased with the distance from seagrass patches: 10 m away from a sampled patch, only a few individuals were found; 50 m or farther away from a sampled patch, no amphioxi were found in bare sediments
Since 1932, B. californiense has been reported from 68 localities in the Baja California Peninsula, 31 of those in the Gulf of California and 37 along the Pacific coast (Poss and Boschung 1996, GBIF 2018), but no study had previously recorded the occurrence of amphioxus in a seagrass habitat
Summary
Amphioxi are Cephalochordata often used as a model for studying the phylogeny and evolution of vertebrates (Stokes and Holland 1998, Bertrand and Escriva 2011, Vergara et al 2012). Amphioxi are marine organisms inhabiting shallow waters near the coast, such as estuaries, coastal lagoons, open coasts, and even river deltas, in temperate and tropical waters (Laudien et al 2007, Meerhoff et al 2016) They are benthic, obligate filter feeders that play a key role in the transfer of microbial and phytoplanktonic production to higher trophic levels, including fishes (Ruppert et al 2000, Vargas and Dean 2010). In Mexico, it is distributed from the northwestern coast of the Baja California Peninsula to the coast of Oaxaca, including the Gulf of California; some records from Central America have been reported (Poss and Boschung 1996, Vargas and Dean 2010, Del Moral-Flores et al 2016). We aim to highlight seagrass as a novel and likely suitable habitat for B. californiense during breeding in the southern part of the Gulf of California, as well as to add to the knowledge of its taxonomy and biology
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