Egg masses were photographed attached to Macrocystis pyrifera at five locations in the Strait of Magellan, one location in Almirantazgo Sound, and one location in Beagle Channel (Fig. 1, Table 1). Twenty-one egg capsules from one egg mass in the Strait of Magellan at Punta Santa Ana (53°37,7′S; 70°54,8′W) were collected and transported to the Laboratory of Antarctic and Sub-Antarctic macroalgae of the Universidad de Magallanes. Eggs were kept in 80-L aquaria with nearly constant air flow, salinity of 31, temperature of 8±1°C and a 12:12 photoperiod. To identify the egg masses, we randomly selected seven of the capsules and made the following measurements, in accordance with Barón (2003) for Doryteuthis spp.: capsule length and weight, number of eggs in each capsule, egg diameter (mm) and number of dark chromatophores in the cheek patch area—two oval areas located at the posterior half of the ventral surface of the head (Vecchione & Lipinski 1995). Paralarvae were photographed using an Olympus SZ61 stereomicroscope (Tokyo, Japan) attached to Moticam 200 camera (Motic, Hong Kong, China). Measurements were made using Micrometrics SE Premium software.

Seven egg masses (one at each location) were observed attached to Macrocystis pyrifera (Fig. 2). Egg capsules from the egg mass at Punta Santa Ana had an average length of 61±1.9 mm and an average weight of 5.6±0.6 g (n=7) (Fig. 3), and contained an average of 56±7 eggs (n=7), with an average egg diameter of 2.5±0.2 mm. Arkhipkin et al. (2000) reported very similar measurements for this species with an average egg capsule length of 54.93±8.87 mm, an average number of 73±22.85 eggs and an average egg diameter of 2.0–2.5 mm. Most paralarvae had three to four chromatophores in each cheek patch. These measurements are similar to those reported for Doryteuthis gahi (Arkhipkin et al. 2000; Barón 2003), suggesting that the egg masses we observed were spawned by D. gahi.

This is the first report of D. gahi egg masses attached to M. pyrifera in the Magellanic channels of the sub-Antarctic ecoregion. Macrocystis pyrifera is a characteristic component of benthic ecosystems in this region (Mansilla & Ávila 2011). Charles Darwin observed these submarine forests during the Beagle expedition and noted their importance for the associated fauna (Darwin 1839). In this context, we highlight two aspects about the importance of M. pyrifera forests for the sub-Antarctic channel ecosystem: (a) their structural complexity could affect local conditions, such as currents and light intensity in the water column, resulting in increased biodiversity (Stachowicz 2001); (b) they provide a spawning substrate for invertebrates such as D. gahi that migrate into the calm waters in the interior of the channels to spawn.

Around the Falkland Islands, egg masses are found attached to stipes of both Lessonia spp. and M. pyrifera, but more often to Lessonia spp. (Arkhipkin et al. 2000; Brown et al. 2010). In our study, although M. pyrifera and Lessonia spp. were present at all locations, egg masses were found attached only to M. pyrifera. The congener Doryteuthis opalescens (Berry 1911) spawns in coastal water off California, where M. pyrifera is also present (Graham et al. 2007), but attaches its eggs to sandy substrate (Young et al. 2011). Doryteuthis gahi could be one of the few squid species that attaches its egg masses to kelp.

With diverse industrial uses, including providing phycocolloids in the form of alginate (Mansilla & Ávila 2011), M. pyrifera is a potentially important economic resource in the study region. Information is available about the biological basis for the sustainable exploitation of M. pyrifera (Mansilla et al. 2009), but caution is needed given that this kelp serves not only as a habitat for many animals but also as a spawning substrate for some benthic (e.g., gastropods) and pelagic (e.g., squid) species. This increases the ecological importance of conserving M. pyrifera forests.