Maternal and cohort effects modulate offspring responses to multiple stressors

Impacts of artificial light at night on the early life history of two ecosystem engineers

Sessile marine invertebrates play a vital role as ecosystem engineers and in benthic-pelagic coupling. Most benthic fauna develop through larval stages and the importance of natural light cycles for larval biology and ecology is long-established. Natural light-dark cycles regulate two of the largest ocean-scale processes that are fundamental to larvae's life cycle: the timing of broadcast spawning for successful fertilization and diel vertical migration for foraging and predator avoidance. Given the reliance on light and the ecological role of larvae, surprisingly little is known about the impacts of artificial light at night (ALAN) on the early life history of habitat-forming species. We quantified ALAN impacts on larval performance (survival, growth, development) of two cosmopolitan ecosystem engineers in temperate marine ecosystems, the mussel Mytilus edulis and the barnacle Austrominius modestus. Higher ALAN irradiance reduced survival in both species (57% and 13%, respectively). ALAN effects on development and growth were small overall, and different between species, time-points and parentage. Our results show that ALAN adversely affects larval survival and reiterates the importance of paternal influence on offspring performance. ALAN impacts on the early life stages of ecosystem engineering species have implications not only for population viability but also the ecological communities that these species support. This article is part of the theme issue 'Light pollution in complex ecological systems'.

A common temperature dependence of nutritional demands in ectotherms

In light of ongoing climate change, it is increasingly important to know how nutritional requirements of ectotherms are affected by changing temperatures. Here, we analyse the wide thermal response of phosphorus (P) requirements via elemental gross growth efficiencies of Carbon (C) and P, and the Threshold Elemental Ratios in different aquatic invertebrate ectotherms: the freshwater model species Daphnia magna, the marine copepod Acartia tonsa, the marine heterotrophic dinoflagellate Oxyrrhis marina, and larvae of two populations of the marine crab Carcinus maenas. We show that they all share a non-linear cubic thermal response of nutrient requirements. Phosphorus requirements decrease from low to intermediate temperatures, increase at higher temperatures and decrease again when temperature is excessive. This common thermal response of nutrient requirements is of great importance if we aim to understand or even predict how ectotherm communities will react to global warming and nutrient-driven eutrophication.

Ontogeny of osmoregulation of the Asian shore crab Hemigrapsus sanguineus at an invaded site of Europe

We studied the ontogeny of osmoregulation of the Asian shore crab Hemigrapsus sanguineus at an invaded area in the North Sea. H. sanguineus is native to Japan and China but has successfully invaded the Atlantic coast of North America and Europe. In the invaded areas, H. sanguineus is becoming a keystone species as driver of community structure and the adults compete with the shore crab Carcinus maenas. Strong osmoregulatory abilities may confer the potential to use and invade coastal areas already earlier in the life cycle. We reared larvae and first juveniles at 24°C in seawater from hatching to intermoult of each developmental stage (zoea I-V, megalopa, crab I). We exposed each stage to a range of salinities (0-39 ppt) for 24 h, and then we quantified haemolymph osmolality, using nano-osmometry. In addition, we quantified osmolality in field-collected adults after acclimation to the test salinities for 6 days. Larvae of H. sanguineus were able to hyper-osmoregulate at low salinities (15 and 20 ppt) over the complete larval development, although the capacity was reduced at the zoeal stage V; at higher salinities (25-39 ppt), all larval stages were osmoconformers. The capacity to slightly hypo-regulate at high salinity appeared in the first juvenile. Adults were able to hyper-osmoregulate at low salinities and hypo-regulate at concentrated seawater (39 ppt). H. sanguineus showed a strong capacity to osmoregulate as compared to its native competitor C. maenas, which only hyper-regulates at the first and last larval stages and does not hypo-regulate at the juvenile-adult stages. The capacity of H. sanguineus to osmoregulate over most of the life cycle should underpin the potential to invade empty niches in the coastal zone (characterized by low salinity and high temperatures). Osmoregulation abilities over the whole life cycle also constitute a strong competitive advantage over C. maenas.

A state-space approach to understand responses of organisms, populations and communities to multiple environmental drivers

Understanding the response of biotic systems to multiple environmental drivers is one of the major concerns in ecology. The most common approach in multiple driver research includes the classification of interactive responses into categories (antagonistic, synergistic). However, there are situations where the use of classification schemes limits our understanding or cannot be applied. Here, we introduce and explore an approach that allows us to better appreciate variability in responses to multiple drivers. We then apply it to a case, comparing effects of heatwaves on performance of a cold-adapted species and a warm-adapted competitor. The heatwaves had a negative effect on the native (but not on the exotic) species and the approach highlighted that the exotic species was less responsive to multivariate environmental variation than the native species. Overall, we show how the proposed approach can enhance our understanding of variation in responses due to different driver intensities, species, genotypes, ontogeny, life-phases or among spatial scales at any level of biological organization.

Giménez et al. explore a “state-space” approach (SSEA) to examine variation in effects of multiple environmental drivers on biological systems. They illustrate the SSEA with a case study where larvae of an exotic crab were less responsive to an experimental heatwave than those of a native species.

The cascade of effects caused by emersion during early ontogeny in porcelain crabs of the Southeast Pacific coast: Biochemical responses of offspring

Petrolisthes crabs inhabit a wide range of coastal environments, from the upper intertidal to the subtidal, experiencing regular changes in pH, salinity, and temperature. Hence, such subtidal and intertidal invertebrates are likely to show physiological and biochemical adaptive responses in order to successfully develop during early ontogenetic stages and thus reach reproduction. We herein evaluated the biochemical responses to contrasting environmental conditions of the early ontogenetic stages of two coastal crabs from the Southeast Pacific coast: Petrolisthes laevigatus and Allopetrolisthes punctatus. For this purpose, stage I embryos of both species were subjected to two treatments: (1) emersion (i.e., a daily 3 h aerial exposure until the zoeas hatched) and (2) immersion (i.e., uninterrupted underwater submersion until the zoeas hatched); the total contents of glucose, proteins, lipids, and fatty acids of the organisms were measured in stage I embryos and recently hatched zoeas in order to assess the biochemical constitution of the two species. Both species showed changes in their energetic reserves when treatments within species were compared. Our results found that A. punctatus was negatively affected by stressful periods of emersion, while P. laevigatus showed the opposite tendency and was affected by periods of immersion. The sensitivity of the response and the contrasting outcomes for these two crabs underpin the fact that changes in environmental conditions along the Chilean coast due to climate change (e.g., increased anoxic coastal waters) may have significantly negative consequences on the populations of these ecologically important species and the associated taxa within their ecosystems.

Physiological basis of interactive responses to temperature and salinity in coastal marine invertebrate: Implications for responses to warming

Developing physiological mechanistic models to predict species' responses to climate-driven environmental variables remains a key endeavor in ecology. Such approaches are challenging, because they require linking physiological processes with fitness and contraction or expansion in species' distributions. We explore those links for coastal marine species, occurring in regions of freshwater influence (ROFIs) and exposed to changes in temperature and salinity. First, we evaluated the effect of temperature on hemolymph osmolality and on the expression of genes relevant for osmoregulation in larvae of the shore crab Carcinus maenas. We then discuss and develop a hypothetical model linking osmoregulation, fitness, and species expansion/contraction toward or away from ROFIs. In C. maenas, high temperature led to a threefold increase in the capacity to osmoregulate in the first and last larval stages (i.e., those more likely to experience low salinities). This result matched the known pattern of survival for larval stages where the negative effect of low salinity on survival is mitigated at high temperatures (abbreviated as TMLS). Because gene expression levels did not change at low salinity nor at high temperatures, we hypothesize that the increase in osmoregulatory capacity (OC) at high temperature should involve post-translational processes. Further analysis of data suggested that TMLS occurs in C. maenas larvae due to the combination of increased osmoregulation (a physiological mechanism) and a reduced developmental period (a phenological mechanisms) when exposed to high temperatures. Based on information from the literature, we propose a model for C. maenas and other coastal species showing the contribution of osmoregulation and phenological mechanisms toward changes in range distribution under coastal warming. In species where the OC increases with temperature (e.g., C. maenas larvae), osmoregulation should contribute toward expansion if temperature increases; by contrast in those species where osmoregulation is weaker at high temperature, the contribution should be toward range contraction.

Maternal and cohort effects modulate offspring responses to multiple stressors

Current concerns about climate change have led to intensive research attempting to understand how climate-driven stressors affect the performance of organisms, in particular the offspring of many invertebrates and fishes. Although stressors are likely to act on several stages of the life cycle, little is known about their action across life phases, for instance how multiple stressors experienced simultaneously in the maternal environment can modulate the responses to the same stressors operating in the offspring environment. Here, we study how performance of offspring of a marine invertebrate (shore crab Carcinus maenas) changes in response to two stressors (temperature and salinity) experienced during embryogenesis in brooding mothers from different seasons. On average, offspring responses were antagonistic: high temperature mitigated the negative effects of low salinity on survival. However, the magnitude of the response was modulated by the temperature and salinity conditions experienced by egg-carrying mothers. Performance also varied among cohorts, perhaps reflecting genetic variation, and/or maternal conditions prior to embryogenesis. This study contributes towards the understanding of how anthropogenic modification of the maternal environment drives offspring performance in brooders.