Temperature and prey density drive growth and otolith formation of the world's most valuable fish stock.

Peruvian anchovy (Engraulis ringens) represents the largest single-species fishery worldwide. Knowledge on how temperature and prey availability influences growth and age estimation during marine fish early life stages is critical for predicting bottom-up processes impacting stock productivity under changing environmental conditions. We reared Peruvian anchovy larvae at two temperatures (14.5 and 18.5 °C) and prey concentrations [high (HF), and low (LF)] from 6 to 30 days post-hatch (dph) to measure growth rate and examine daily deposition of otolith increments. Peruvian anchovy larvae grew faster at 18.5 °C compared to 14.5 °C. Larvae reared at low prey concentration (18.5-LF) and low temperature (14.5-HF) grew 61 and 35% slower, respectively, than those at high prey and warm temperature (18.5-HF). Age and growth rates of larvae were well depicted in the otolith microstructure of well-fed larvae at 18.5 °C. However, larvae reared at 18.5-LF or 14.5-HF, had only 55 and 49% of the expected number of daily otolith increments. Our results suggest caution when attempting to explore how ocean processes regulate small pelagic stocks, the productivity of which are largely driven by changes in the survival and growth of young larvae.

Attenuation of wind intensities exacerbates anoxic conditions leading to sulfur plume development off the coast of Peru.

The release of vast quantities of sulfide from the sediment into the water column, known as a sulfidic event, has detrimental consequences on fish catches, including downstream effects on other linked element cycles. Despite being frequent occurrences in marine upwelling regions, our understanding of the factors that moderate sulfidic event formation and termination are still rudimentary. Here, we examined the biogeochemical and hydrodynamic conditions that underpinned the formation/termination of one of the largest sulfur plumes to be reported in the Peruvian upwelling zone. Consistent with previous research, we find that the sulfur-rich plume arose during the austral summer when anoxic conditions (i.e., oxygen and nitrate depletion) prevailed in waters overlying the upper shelf. Furthermore, the shelf sediments were organically charged and characterized by low iron-bound sulfur concentrations, further enabling the diffusion of benthic-generated sulfide into the water column. While these biogeochemical conditions provided a predicate to sulfidic event formation, we highlight that attenuations in local wind intensity served as an event trigger. Namely, interruptions in local wind speed constrained upwelling intensity, causing increased stratification over the upper shelf. Moreover, disturbances in local wind patterns likely placed additional constraints on wind-driven mesoscale eddy propagation, with feedback effects on coastal elemental sulfur plume (ESP) formation. We suggest ESP development occurs as a result of a complex interaction of biogeochemistry with regional hydrodynamics.

Effect of low pH on growth and shell mechanical properties of the Peruvian scallop Argopecten purpuratus (Lamarck, 1819).

Dissolution of anthropogenic CO2 modifies seawater pH, leading to ocean acidification, which might affect calcifying organisms such as bivalve mollusks. Along the Peruvian coast, however, natural conditions of low pH (7.6-8.0) are encountered in the habitat of the Peruvian scallop (Argopecten purpuratus), as a consequence of the nearby coastal upwelling influence. To understand the effects of low pH in a species adapted to these environmental conditions, an experiment was performed to test its consequences on growth, calcification, dissolution, and shell mechanical properties in juvenile Peruvian scallops. During 28 days, scallops (initial mean height = 14 mm) were exposed to two contrasted pH conditions: a control with unmanipulated seawater presenting pH conditions similar to those found in situ (pHT = 7.8) and a treatment, in which CO2 was injected to reduce pH to 7.4. At the end of the experiment, shell height and weight, and growth and calcification rates were reduced about 6%, 20%, 9%, and 10% respectively in the low pH treatment. Mechanical properties, such as microhardness were positively affected in the low pH condition and crushing force did not show differences between pH treatments. Final soft tissue weights were not significantly affected by low pH. This study provides evidence of low pH change shell properties increasing the shell microhardness in Peruvian scallops, which implies protective functions. However, the mechanisms behind this response need to be studied in a global change context.

Tolerance of juvenile Peruvian rock seabass (Paralabrax humeralis Valenciennes, 1828) and Peruvian grunt (Anisotremus scapularis Tschudi, 1846) to low-oxygen conditions.

Hypoxia is currently one of the greatest threats to coastal ecosystems worldwide, generating massive mortality of marine organisms, loss of benthic ecosystems and a decrease in fishery production. We evaluated and compared the tolerance to hypoxia of two species from different habitats of the Peruvian coast, the Peruvian rock seabass Paralabrax humeralis and the Peruvian grunt Anisotremus scapularis. The effect of hypoxia was measured as a function of the exposure time (progressive and chronic) on the behavioural and physiological responses of the two species, as well as on the enzymatic activity associated with the oxidative stress response of lactate dehydrogenase (LDH), superoxide dismutase (SOD) and alkaline phosphatase (AKP). The ventilatory frequency was measured at two different temperatures (16 and 22°C) under progressive hypoxia conditions to determine the ventilatory critical point (Vcp). A. scapularis showed a higher Vcp than P. humeralis, which was positively affected by temperature. The median lethal time of A. scapularis was 36 min at 60% of oxygen saturation, while P. humeralis showed no mortality after 31 days of exposure at 5% oxygen saturation. Different enzymatic activity (P < 0.05) between species under hypoxia was recorded, in SOD (gill and muscle) and AKP (blood). A general tendency, under hypoxia, to slightly increase LDH activity (except for blood in A. scapularis, P < 0.05) and SOD activity (mainly in muscle of A. scapularis, P < 0.05), and decrease AKP activity (mainly in liver of P. humeralis, P < 0.05) was observed. The response of P. humeralis to hypoxia goes through a reduction in activity and metabolism, so this species can be considered hypoxia-tolerant, allowing it to face hypoxia events during prolonged periods. On the other hand, A. scapularis response to hypoxia prioritizes avoidance mechanisms and, together with other adaptations, makes it especially vulnerable to hypoxia and able to be considered hypoxia-intolerant.

Paralytic shellfish toxins in Peruvian scallops associated with blooms of Alexandrium ostenfeldii (Paulsen) Balech & Tangen in Paracas Bay, Peru.

In recent years, dense Alexandrium ostenfeldii blooms have been reported in different coastal areas. In this study, we report for the first time the occurrence of A. ostenfeldii blooms associated with the detection of paralytic shellfish toxins (PSTs) in the Peruvian scallop (Argopecten purpuratus) from Paracas Bay. Alexandrium ostenfeldii blooms occurred at the end of summer and early fall, after the increase of riverine input and under stratified conditions following a decrease in wind velocity. The highest abundances occurred during warm sea surface temperatures (18-27 °C). High PST concentrations that exceed the maximum permissible level (800 µg STX eq. kg-1) occurred even under low A. ostenfeldii abundances (20 × 103 cells l-1). Our results contribute to a better understanding of the dynamics of A. ostenfeldii in coastal systems influenced by riverine inputs and upwelling and can be used to improve monitoring programs and allow the implementation of mitigation measures along the Peruvian coast.

Embryonic development and effect of temperature on larval growth of the Peruvian anchovy Engraulis ringens.

Understanding aspects of the biology of early life stages of marine fish is critical if one hopes to reveal the factors and processes that impact the survival and recruitment (year class) strength. The Peruvian anchovy (Engraulis ringens) is a key species in the Humboldt current system, and the present study provides the first description of the embryonic and larval development of this species reared in captivity. Embryonic and early exogenous feeding stages of larvae were illustrated in detail at 18.5°C. Hatching was completed within 42 and 48 h post-fertilization at 18.5 and 14.5°C, respectively. Mean ± 95% C.I. standard length (LS ) at hatch (3.40 ± 0.10 mm at 18.5°C and 2.76 ± 0.34 mm at 14.5°C) was significantly different between the two temperatures. Larval behaviour was assessed at 18.5°C; at the onset of exogenous feeding [3 days post-hatch (dph)], larvae were fed small, motile dinoflagellates, Akashiwo sanguinea. At 7 dph, larvae started to feed almost exclusively on zooplankton (rotifers and Artemia nauplii). Larval activity increased with age, and the first sign of schooling was noted at 31 dph (18.56 mm LS ) at 18.5°C. Temperature had a significant effect on size-at-age, but not on body shape (depth to LS ratio). The size-at-age data for larvae (this study) was used to parameterize a temperature-corrected von Bertalanffy growth function for Peruvian anchovy, the accuracy of which was assessed for juveniles and adults (literature values).