FEEDING AND REPRODUCTIVE ACTIVITY OF THE COPEPODS Drepanopus forcipatus AND Calanus australis DURING LATE SUMMER ON THE SOUTHERN PATAGONIAN SHELF (ARGENTINA, 47°-55°S)

Abstract

Drepanopus forcipatus and Calanus australis are key planktonic copepods on the southern Patagonian shelf. Their feeding and reproductive patterns and population status were investigated during late summer, when environmental conditions may be critical. The presence of food in the gut and food-pellet length were recorded in adult females and the most abundant copepodite stages. Diet composition was also studied in adult females. Female reproductive status was evaluated by gonad staging. Despite generally low feeding conditions and decreasing seasonal temperature, both copepods fed to some degree. The most numerous copepodites and adult females of both species showed similarly low feeding activity. About half of the adult females of the two species and C5s of C. australis contained food in their guts, but the proportion of fed C4-females of D. forcipatus was much lower. All copepods were generally feeding at low or intermediate levels. Gonad stage distribution and population structure showed low but still ongoing reproduction in both species. Gut content findings suggest a preference for smaller nanoplanktonic particles, especially dinoflagellates by D. forcipatus, and for autotrophic prey, particularly large diatoms by C. australis. The feeding and reproduction patterns of the two copepods were likely influenced by the distributions of potential food resources and temperature. RESUMODrepanopus forcipatus e Calanus australis são copépodos planctônicos relevantes na plataforma da Patagônia Austral. Seus padrões de alimentação, reprodução e status populacional foram investigados durante o fim do verão, quando as condições ambientais podem ser críticas. A presença de alimento no abdomen e o tamanho das pelotas alimentares foram registados em fêmeas adultas e nos estágios mais abundantes de copepodito. A composição da dieta também foi estudada em fêmeas adultas. O status reprodutivo das fêmeas foi avaliado através do estágio gonadal. De modo geral, apesar das baixas condições alimentares e diminuição sazonal da temperatura, ambos os copépodos se alimentaram. Os copepoditos mais numerosos e as fêmeas adultas de ambas espécies mostraram baixa atividade alimentar. Cerca de metade das fêmeas adultas das duas espécies e C5s de C. australis apresentaram alimento em seu intestino, porém a proporção de fêmeas D. forcipatus C4 alimentadas foi consideravelmente menor. De modo geral, todos os copépodos se alimentaram entre níveis baixo e intermediário. A distribuição do estágio gonadal e a estrutura populacional apresentaram reprodução baixa, mas contínua para ambas as espécies. Os alimentos encontrados no intestino sugerem uma preferência por partículas nanoplanctônicas, especialmente dinoflagelatos em D. forcipatus, e por presas autotróficas, particularmente grandes diatomáceas em C. australis. Os padrões de alimentação e reprodução dos dois copépodos foram provavelmente influenciados pela distribuição de recursos alimentares e temperatura.

Domoic acid in a marine pelagic food web: Exposure of southern right whales Eubalaena australis to domoic acid on the Península Valdés calving ground, Argentina

“…and low DA levels found in the phytoplankton samples from both gulfs (except in GN during October) rather to the in ability of copepods to act as DA vectors. It should be noted that more numerically important copepod species recorded in the present study (Paracalanus parvus, Ctenocalanus vanus, Calanus australis and Calanoides carinatus) have been defined as herbivorous or omnivorous (Boltovskoy, 1981;1999;Lombard et al, 2010;D'Agostino, 2013;Antacli et al, 2014). These copepod species therefore, can also act as effective DA vectors either by direct consumption of DA producing species or by ingestion of lower trophic level organisms contaminated with this toxin.…”

Phytoplankton and protozooplankton on the southern Patagonian shelf (Argentina, 47°–55°S) in late summer: Potentially toxic species and community assemblage structure linked to environmental features

“…A triangular trophic web has been described for the SPS ecosystem (Ciancio et al, 2008(Ciancio et al, , 2010, with commercially important fish and squid species near the top (Hansen et al, 2004;Sánchez and Bezzi, 2004). Phyto-and protozooplankton are at the base and, as they constitute the main food resource for larger plankton, they are essential trophic components (Antacli et al, 2014a(Antacli et al, , 2014b. Hydrographically, the SPS shows a unique combination of characteristics: high tidal amplitudes, prevalent westerly winds, large freshwater inflows, and advection from the bordering Malvinas Current (Palma et al, 2008;Matano et al, 2010;Palma and Matano, 2012).…”

“…Studies of the phytoplankton communities and of chlorophyll-a variability largely encompassing the southern Patagonian shelf have been based on the analysis of remote sensing data (Rivas et al, 2006;Romero et al, 2006;Gonzalez-Silvera et al, 2006;Signorini et al, 2006;D'Ovidio et al, 2010;Dogliotti et al, 2014), and other studies have focused on the phyto-and protozooplankton communities with in situ sampling for composition analysis (Garcia et al, 2008;Painter et al, 2010;Santoferrara and Alder, 2009a, 2009bSantoferrara et al, 2011;De Souza et al, 2012;Sabatini et al, 2012;Segura et al, 2013;Balch et al, 2014;Gonçalves-Araujo et al, 2016;Antacli et al, 2014b). These show seasonal variation of phytoplankton in the SPS, which has been related to light intensity, nutrient supply, mixed layer depth, stratification and/or the thermohaline structure of the water column.…”

“…In a previous study, the 2-200 μm phytoplankton and protozooplankton communities were broadly assessed in the SPS during late summer 2004, but focusing on their potential trophic availability for copepods (Antacli et al, 2014b). Based on the same pool of data, the present work aims to make the first comprehensive assessment of the 2-200 μm phyto-and protozooplankton communities of the SPS in late summer in terms of taxonomy, biodiversity, presence of potentially toxic species, spatial structure (including vertical distribution through depth strata), and their linkage to hydrographic conditions.…”

Occurrence of Toxigenic Microalgal Species and Phycotoxin Accumulation in Mesozooplankton in Northern Patagonian Gulfs, Argentina

“…In Golfo San José the highest levels of domoic acid were recorded in the plankton samples during January 2015, May 2015, and January 2016 when C. australis , C. carinatus , and Acartia tonsa were the most abundant species, respectively. These copepod species have been defined as herbivores or omnivores (Boltovskoy , ; Lombard et al ; D'Agostino ; Antacli et al and references therein); therefore they could act as effective phycotoxin vectors, either by the direct consumption of domoic acid–producing species or by ingestion of organisms of lower trophic levels contaminated with toxins. Consequently, vectorial intoxication of pelagic food webs could occur either by the grazing of copepods on toxic microalgae and also by predation of organisms contaminated with domoic acid.…”