Temporal variability of phytoplankton biomass and primary production off Magdalena Bay, Baja California Sur, Mexico

Abstract

Sixteen monthly cruises were carried out at a station 6.5 km to the NW of the mouth of Magdalena Bay (Mexico) to study the temporal variability of phytoplankton biomass and primary production rates, and the response of phytoplankton to the prevailing hydrographic characteristics. During each cruise, temperature and salinity were measured in the water column, and discrete samples were collected to measure inorganic nutrient concentrations (nitrate, phosphate, and silicate) and chlorophyll a content (as a proxy for phytoplankton biomass); in addition, in situ incubations were performed to estimate primary production (PP) rates using the 14 C technique. During spring and early summer (March-July), the water column at the study site was cold (14.4 ºC at 80 m depth and 17.7 ºC at the surface) and well mixed, with high nutrient concentrations (nitrate = 6.39 μM, phosphate = 0.91 μM, and silicate = 11.87 μM) at the surface, typical of intense upwelling systems. On the contrary, from August to February the water column was stratified (23.5 ± 3.2 ºC above the thermocline and 17.0 ± 1.7 ºC at 80 m depth) and had low nutrient concentrations (nitrate = 3.90 μM, phosphate = 0.47 μM, and silicate = 10.30 μM) at the surface. Phytoplankton abundance, chlorophyll a concentration, and PP rates in the euphotic zone were higher during the upwelling season, with maximum cell density of 1.7 × 10 6 cells•L-1 (nanoplankton fraction), integrated chlorophyll a content of 231 mg•m-2 , and integrated PP rates of 553 mg C•m-2 •h-1). Abundance of cells <20 μm, as determined by flow cytometry, revealed the importance of the nanoplankton and picoplankton fractions in this region. This study showed the seasonal variability of phytoplankton communities (biomass and productivity) in waters off Magdalena Bay and the coupling of phytoplankton to environmental variability. Seasonal variability was similar to that observed for other typical coastal upwelling regions, that is, higher phytoplankton abundances and PP rates in spring and summer and lower values in autumn and winter.

Growth of catarina scallop ( Argopecten ventricosus , Sowerby II, 1842) larvae from broodstock collected at different seasons

“…This result suggests that broodstock had poorer reproductive condition than those collected in March, which may be explained by the lowest food availability values in the wild. In a previous study, Cervantes‐Duarte et al (2018) reported lower values of primary productivity in Magdalena Bay from August to February. In addition, higher temperatures in autumn may be inadequate to induce higher reproductive condition.…”

“…ventricosus . Moreover, in Magdalena Bay, higher primary productivity and food quality for marine bivalves have been reported during spring when water temperature is colder (Félix‐Pico, 2006; Cervantes‐Duarte et al, 2018). Luna‐González et al, (2000) reported higher influence of food availability rather than temperature for A .…”

“…Although temperature is the main trigger of gametogenesis events in marine bivalves (Barber & Blake, 2016) food availability and diet composition are responsible of modulating reproductive condition and gamete quality of broodstock (Chávez‐Villalba et al, 2002; Chávez‐Villalba et al, 2003; Angel‐Dapa et al, 2015; Barber and Blake, 2016) which in turn regulate overall performance of developing larvae including metamorphosis and settlement (Wilson et al, 1996; Gómez‐Robles et al, 2013). Hypothetically, ripe scallops collected during late winter–spring peak —when primary productivity and food availability increase in Magdalena Bay— (Félix‐Pico, 2006; Cervantes‐Duarte et al, 2018) favour larval performance better than those collected during the summer–autumn peak when primary productivity decreases (Cervantes‐Duarte et al, 2018).…”

“…Greater larval growth obtained from spring broodstock was in accordance with gonadic histological reports by previous authors (Baqueiro-Cárdenas and Aldana Aranda 2000; Félix-Pico, 2006) confirming this season as the best natural reproductive peak of A. ventricosus. Moreover, in Magdalena Bay, higher primary productivity and food quality for marine bivalves have been reported during spring when water temperature is colder (Félix-Pico, 2006;Cervantes-Duarte et al, 2018). Luna-González et al, (2000) reported higher influence of food availability rather than temperature for A. ventricosus gonad maturity.…”

“…Hypothetically, ripe scallops collected during late winter-spring peak -when primary productivity and food availability increase in Magdalena Bay- (Félix-Pico, 2006;Cervantes-Duarte et al, 2018) favour larval performance better than those collected during the summer-autumn peak when primary productivity decreases (Cervantes-Duarte et al, 2018).…”