Marta Moyano

Measuring respiration rates in marine fish larvae: challenges and advances.

Metabolic costs can be extremely high in marine fish larvae and gaining reliable estimates of the effects of intrinsic and extrinsic factors on those costs is important to understand environmental constraints on early growth and survival. This review provides an historical perspective of measurements of larval marine fish respiration (O2 consumption) including the methods (Winkler, manometric, polarographic, paramagnetic and optodes) and systems (closed system to intermittent-flow) used. This study compares and systematically reviews the results (metabolic rates, ontogenetic changes and taxonomic differences) obtained from 59 studies examining 53 species from 30 families. Standard (anaesthetized or darkness), routine and active respiration rates were reported in 14, 94 and 8% of the studies and much more work has been performed on larvae of temperate (88%) compared with tropical (9%) and polar (3%) species. More than 35% of the studies have been published since 2000 owing to both advances in oxygen sensors and the growing emphasis on understanding physiological effects of environmental change. Common protocols are needed to facilitate cross-taxa comparisons such as the effect of temperature (Q10 : 1·47-3·47), body mass (slope of allometric changes in O2 consumption rate from 0·5 to 1·3) and activity level on metabolic costs as measured via respiration rate. A set of recommendations is provided that will make it easier for researchers to design measurement systems, to judge the reliability of measurements and to make inter-comparisons among studies and species.

Thermal impacts on the growth, development and ontogeny of critical swimming speed in Atlantic herring larvae

Increases in swimming ability have a profound influence on larval fish growth and survival by increasing foraging success, predator avoidance and the ability to favorably influence transport. Understanding how development and environmental factors combine to influence swimming performance in aquatic organisms is particularly important during the transition from viscous to inertial environments. We measured the growth, development and ontogenetic changes in critical swimming speed (Ucrit) in Atlantic herring (Clupea harengus) larvae reared at three temperatures (7, 11, 15°C). Temperature had a significant effect on growth rates (from 0.21 at 7°C to 0.34mm·d(-1) at 15°C), and larval morphology-at-length (increased dry weight (DW), body height and developmental rate at warmer temperatures). Temperature-dependent differences in morphology influenced swimming performance (e.g. the exponential increase in Ucrit with increasing body size was faster at warmer temperatures). Larvae entered the transition to an inertial environment (Reynolds numbers ≥300) at body lengths between 15 (15°C) and 17mm (7°C). Inter-individual differences in Ucrit were not related to nutritional condition (RNA·DNA(-1) or DNA·DW(-1)), but were negatively correlated to length-at-age, suggesting a trade-off between growth rate and locomotor activity. The Ucrit data from this and previously published studies suggest that Atlantic herring pass through four activity phases: 1) yolk-sac (<0.6cm·s(-1)), 2) pre-flexion (0.6-3.0cm·s(-1), temperature effect changes with body size), 3) post-flexion (up to 6-8cm·s(-1), Q10~1.8-2.0), 4) juvenile-adult period (20-170cm·s(-1)).

Short-term molecular and physiological responses to heat stress in neritic copepods Acartia tonsa and Eurytemora affinis

Invertebrates inhabiting shallow water habitats represent particularly appropriate organisms for studying the acclimation potential to environmental stress, since they naturally experience large fluctuations in key abiotic factors such as temperature and salinity. We quantified the biochemical- (mRNA transcripts of 78-kDa glucose-regulated protein (grp78), 70-kDa heat shock protein (hsp70), 90-kDa heat shock protein (hsp90), protein synthesis of HSP70) and organismal- (oxygen consumption rates) level responses to acute heat stress on two neritic copepods (Acartia tonsa and Eurytemora affinis) with special emphasis on the role of short-term acclimation. Transcripts of hsp increased with increasing acute temperature exposure and protein quantities (HSP70) were detectable for 30h. In A. tonsa, HSP70 synthesis was also associated with handling stress. In E. affinis, heat-dependent responses were detected in hsp90, grp78 (mRNA) and HSP70 (protein) expression. Acclimation to a warmer temperature significantly decreased the heat stress response in both species. In A. tonsa, short-term acclimation to heat was not detected at the organismal level via metabolic rate. This study reveals interspecific differences in both the gene expression of stress molecules (e.g. hsp90) as well as the stress factors needed to evoke a stress response (heat vs. handling). We demonstrate that cellular stress markers can be useful measures of short-term thermal acclimation in copepods, which may remain undetected by organismal-level measures.

Standard metabolism and growth dynamics of laboratory‐reared larvae of Sardina pilchardus

This study provides the first measurements of the standard respiration rate (R(S)) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between RS (µl O(2) individual(-1)  h(-1)) and larval dry mass (M(D), µg) was equal to: R(S) = 0·0057(±0·0007, ± s.e.)·M(D) (0·8835(±0·0268)), (8-11% M(D) day(-1)). Interindividual differences in RS were not related to interindividual differences in growth rate or somatic (Fultons condition factor) or biochemical-based condition (RNA:DNA).

Effects of warming rate, acclimation temperature and ontogeny on the critical thermal maximum of temperate marine fish larvae

Most of the thermal tolerance studies on fish have been performed on juveniles and adults, whereas limited information is available for larvae, a stage which may have a particularly narrow range in tolerable temperatures. Moreover, previous studies on thermal limits for marine and freshwater fish larvae (53 studies reviewed here) applied a wide range of methodologies (e.g. the static or dynamic method, different exposure times), making it challenging to compare across taxa. We measured the Critical Thermal Maximum (CTmax) of Atlantic herring (Clupea harengus) and European seabass (Dicentrarchus labrax) larvae using the dynamic method (ramping assay) and assessed the effect of warming rate (0.5 to 9°C h-1) and acclimation temperature. The larvae of herring had a lower CTmax (lowest and highest values among 222 individual larvae, 13.1–27.0°C) than seabass (lowest and highest values among 90 individual larvae, 24.2–34.3°C). At faster rates of warming, larval CTmax significantly increased in herring, whereas no effect was observed in seabass. Higher acclimation temperatures led to higher CTmax in herring larvae (2.7 ± 0.9°C increase) with increases more pronounced at lower warming rates. Pre-trials testing the effects of warming rate are recommended. Our results for these two temperate marine fishes suggest using a warming rate of 3–6°C h-1: CTmax is highest in trials of relatively short duration, as has been suggested for larger fish. Additionally, time-dependent thermal tolerance was observed in herring larvae, where a difference of up to 8°C was observed in the upper thermal limit between a 0.5- or 24-h exposure to temperatures >18°C. The present study constitutes a first step towards a standard protocol for measuring thermal tolerance in larval fish.

Exploring the microzooplankton–ichthyoplankton link: a combined field and modeling study of Atlantic herring (Clupea harengus) in the Irish Sea

The microzooplankton–ichthyoplankton link remains poorly resolved in field studies due to a lack of simultaneous sampling of these predators and potential prey. This study compared the abundance, distribution and growth of larval Atlantic herring (Clupea harengus) and the abundance, biomass and composition of micro- and small mesozooplankton throughout the Irish Sea in November 2012 and 2013. In contrast to warmer months, microzooplankton biomass was highest in eastern areas, in the vicinity of the main spawning grounds of herring. Although the protozoan composition differed somewhat between years, dinoflagellates (e.g. Gymnodinium spp., Protoperidinium spp., Ceratium furca) dominated in abundance and/or biomass, similar to other temperate shelf seas in autumn/winter. Spatial differences in the protozoan community were strongly related to hydrographic characteristics (temperature, salinity). Significant relationships between the abundance of larval herring and dinoflagellates (positive) and copepodites (negative) suggested that complex grazing dynamics existed among lower trophic levels. When different, in situ size fractions of zooplankton were used as prey in a larval herring individual-based model, simulations that omitted protozooplankton under-predicted observed (biochemically-based) growth of 8–18 mm larvae. This study suggests that small planktonic organisms (20–300 µm) should be routinely surveyed to better understand factors affecting larval fish feeding, growth and survival.