Abundance and spatial distribution of Polygordius (Polychaeta: Polygordiidae) neustonic exolarvae in estuaries from southern Chile

Abstract

Integration of meroplankton abundance and hydrographic data was employed to relate the Polygordius exolarvae spatial dynamics with different salinity gradients in order to define the factors that regulate the abundance and spatial distribution along the large estuarine system from southern Chile. The present study aims: i) record the abundance and spatial distribution of Polygordius neustonic exolarvae along of the estuaries with different gradients of salinity located between Guafo Channel, southern Chiloé Island (44º S) to Navarino Island (55º S), Chile; ii) connect this distributional pattern to oceanographic parameters to determine if members of this genus have adapted to euryhaline or stenohaline conditions, and iii) establish a comparison between the abundance of Polygordius and others meroplanktonic taxa collected during CIMAR Cruises 16, 18 and 20 Fjords. Neustonic samples were collected during three oceanographic cruises along southern Chilean fjord/channel systems (~ 1,700 km) with different freshwater supply regimes (CIMAR 16: October/November, 2010, 52º to 55º S; CIMAR 18: June/July, 2012, 44º to 47º S; CIMAR 20: October, 2014, 47º to 50º S), providing evidence to relate the influence of surface salinity on the Polygordius exolarvae spatial distribution of abundance. Polygordius exolarvae (average length=2.9 ± 0.8 mm), the most abundant meroplanktonic taxa within the neustonic community (54.04% of total abundance; 66,228 individuals; N Total =26 stations), was represented at 81% of stations sampled in CIMAR 16 (mean salinity=30.7 psu), showing higher abundance (1,518 ind. x 5 min of horizontal drag) than for other polychaete larvae (10 types) and other meroneustonic taxa; 60% of the abundance of exolarvae during CIMAR 16 was collected around Dawson Island, Magellan Strait. In CIMAR 18 cruise (mean salinity=24.28 psu), abundance of exolarvae was low (3 ind. x 5 min of horizontal drag) and were collected only at 5 stations along the Moraleda Channel (N Total =31 stations); no exolarvae were collected during CIMAR 20 (N total =39 stations) (mean salinity= 23.26 psu). Polygordius exolarvae have narrow haline/thermal requirements during their pelagic life, where sills and island mass effect could produce a restricted and aggregated spatial distribution in some areas of the study zone.

Importance of Remote Sensing for the Study of Spatial Dynamics of Estuarine Neuston From Southern Chile

“…In reference to the neuston and the existence of oceanographic process along Magellan Strait, we consider information recorded during CIMAR16 Fjord (C16F, spring 2010), where was reported a significant aggregation de the neuston in the northeastern end of Dawson Island, off Inútil Bay, Magellan Strait (Fig. 2) In this area, between 60 and 80% of the total abundance of three typical neustonic species was estimated: copepodites of pelagic harpacticoid copepod Microsetella rosea, larvae of the polychaete Polygordius sp and cyphonautes larvae of bryozoan Membranipora isabelleana (Cañete et al, 2016(Cañete et al, , 2019. Such spatial scale correspond to mesoscale (Mann, Lazier, 1991;Cañete et al, 2017).…”

“…Such spatial scale correspond to mesoscale (Mann, Lazier, 1991;Cañete et al, 2017). The neuston was collected with a net of 50 x 35 cm of mouth area, mesh net of 43 µm, which was dragged for 5 minutes with a velocity of 2 kn (horizontal drag = 500 m 2 ) (Cañete et al, 2016(Cañete et al, , 2019…”

“…Mesozooplankton living here are crucial to the sustenance and survival of important fisheries (Zaitsev, 2005). For these reasons, it would be very useful to understand how the neuston is influenced by environmental and oceanographic factors, including temperature, solar radiation, salinity, and acidification (Hardy, 1991;Zaitzev, 2005) and are important themes in oceanographic research that are associated with climatic warming and oceanographic change in sub-polar marine ecosystems (Zaitsev, 2005, Cañete et al, 2019.…”

Knots, spoons, and cloches: DNA barcoding unusual larval forms helps document the diversity of Neotropical marine annelids

“…In exolarvae the definitive worm body extends posterior to the episphere and hyposphere, whereas in endolarvae the body of the developing worm is tucked up inside the episphere and hyposphere (figured in Ramey‐Balci & Ambler, 2014). Exolarvae have been reported for Polygordius jouinae , Polygordius triestinus , and Polygordius neapolitanus , and endolarvae have been reported for Polygordius appendiculatus , Polygordius lacteus , and unidentified Polygordius from the east coast of North America (Ramey‐Balci & Ambler, 2014) and southern Chile (Cañete et al., 2019). The larval forms of the other species are so far unknown.…”