Biology, distribution and geographic variation of loliginid squids (Mollusca: Cephalopoda) off southwestern Atlantic

Rodrigo Silvestre Martins,Marcelo Juanicó

doi:10.3897/zoologia.35.e23176

Abstract

The biology and ecology of southwestern Atlantic loliginid squids have been intensively researched in the last few decades, mostly off the Brazilian southern coast. However, information gathered by scientific research cruisers, either past or recent, is limited. Three species of loliginid squids – the warm-tempered Doryteuthissanpaulensis (Brakoniecki, 1984), plus the tropical D.pleii (Blainville, 1823) and Lolligunculabrevis (Blainville, 1823) – were sampled along 16 degrees of latitude on the southwestern Atlantic (22–38°S). The samples were obtained mostly from oceanographic surveys, but also included squids caught by commercial fisheries, and a few specimens from museum collections. Squid response to abiotic variables, morphological variation and circadian behaviour were surveyed in detail. Doryteuthissanpaulensis can be divided into at least six distinguishable geographical groups, which do not form a cline. In contrast, D.pleii can be divided into only two morphological groups that are very similar. Doryteuthis spp. were heterogeneously distributed on the shelf, whereas L.brevis was confined nearshore. Our data extended the southernmost distribution range of D.pleii by at least nine degrees of latitude, owing to specimens obtained at ~38°S (Mar del Plata, Argentina). Small, immature D.sanpaulensis were sampled inside the Patos Lagoon estuary (~32°S). The morphologically similar Doryteuthis spp. apparently avoid direct competition by concentrating at different depths, displaying different thermal preferences, and inverse circadian levels of activity. The information reported herein may be regarded as a “snapshot” of the ecology of sympatric squids in a marine environment that has not been deeply affected by climate change.

Highlights

Loliginid squids are typical inhabitants of coastal and shelf waters (Jereb et al 2010)
Loliginid squids display noticeable variations in body proportions, some of which result in cryptic speciation, or distinct population groups that are clearly discernible based on their morphology, (Jackson and Moltschaniwskyj 2001, Herke and Foltz 2002, Sales et al 2013, 2014, 2017, van der Vyver et al 2016)
A discriminant morphological analysis identified a latitudinal phenotypic variability for D. sanpaulensis and D. pleii, more remarkable in the first species. This survey may be regarded as a framework for all subsequent studies on loliginid squid biology and ecology off the southern Brazilian coast (e.g., Perez and Zaleski 2013, Vidal et al 2013, Arkhipkin et al 2015)

Summary

Introduction

Loliginid squids are typical inhabitants of coastal and shelf waters (Jereb et al 2010). Loliginid squids display noticeable variations in body proportions, some of which result in cryptic speciation, or distinct population groups that are clearly discernible based on their morphology, (Jackson and Moltschaniwskyj 2001, Herke and Foltz 2002, Sales et al 2013, 2014, 2017, van der Vyver et al 2016). Those groups may differ in body proportions, and in other biological aspects, such as body condition, adult size, fecundity, reproductive cycle and lifespan (Pelc and Jackson 2008). A recent genetic analysis of L. brevis has confirmed cryptic speciation within

Methods

Discussion

Conclusion