Disparate response of decapods to low pH: A meta-analysis of life history, physiology and behavior traits across life stages and environments.

We employed a meta-analysis to determine if the presumed resilience of decapods to ocean acidification extends to all biological aspects, environments, and life stages. Most response categories appeared unaffected by acidification. However, certain fitness-related traits (growth, survival, and, to some extent, calcification) were impacted. Acid-base balance and stress response scaled positively with reductions in pH, which maintains homeostasis, possibly at the cost of other processes. Juveniles were the only stage impacted by acidification, which is believed to reduce recruitment. We observed few differences in responses to acidification among decapods inhabiting contrasting environments. Our meta-analysis shows decapods as a group slightly to moderately sensitive to low pH, with impacts on some biological aspects rather than on all specific life stages or habitats. Although extreme pH scenarios may not occur in the open ocean, coastal and estuarine areas might experience lower pH levels in the near to medium future, posing potential challenges for decapods.

Decapod egg membranes: powerful barriers or regulatory structures?

Osmoregulatory abilities and mechanisms of adults and larvae of decapod crustaceans have been extensively investigated. However, how embryos carried by their mothers can deal with changing or extreme salinities is less understood. The egg membranes are believed to isolate embryos from a challenging environment, although osmoregulatory ability has been demonstrated in early developing embryos (naupliar stage) of two crabs. To establish whether embryos are isolated by their membranes and/or are able to osmoregulate, we measured the survival and volume change over 48 h of oocytes and embryos in different stages of three carideans (Betaeus lilianae, Palaemon macrodactylus and P. argentinus) and the brachyuran Neohelice granulata, subjected to different salinities. In addition, we recorded osmolality changes in homogenates of the same stages in P. argentinus and N. granulata after 2 h of exposure and mapped the presence of putative sites of ions exchange in the membrane of all species. High mortality, when it occurred, was associated with low salinity and mortality variation with the stage of development depended on the species. All species precipitated silver salts in or under the egg envelope, with a different pattern between carideans and the brachyuran. Changes in osmolality and egg volume after hypo- or hyper-osmotic salinity challenges indicate that eggs are not fully isolated by their membranes, and that some osmoregulatory mechanisms are in play to maintain developmental homeostasis. We suggest that egg membranes can participate in osmoregulation by selectively transporting ions to an intramembrane space, with differences between carideans and brachyurans.

Chemically induced plasticity in early life history of Palaemon argentinus: are chemical alarm cues conserved within palaemonid shrimps?

Most aquatic animals use infochemicals from both conspecifics and heterospecifics to assess local predation risks and enhance predator detection. Released substances from injured conspecifics and other species (chemical alarm cues) are reliable cues to indicate an imminent danger in a specific habitat and often mediate the development of inducible defenses. Amphibian and fish embryos have been shown to acquire this information while at the embryonic stage of development, in relation to the developing nervous system and sensory development. With the exception of Daphnia, there is no information on chemically mediated responses to alarm cues in embryos of any crustacean groups. Therefore, we tested whether embryo exposure to chemical cues simulating predation on conspecifics or heterospecifics (closely related, non-coexisting species), or a mixture of both, alters embryonic developmental time, size and morphology of the first larval instar in Palaemon argentinus (Crustacea: Decapoda). Embryonic exposure to chemical alarm cues from conspecifics shortened the embryonic developmental time and elicited larger larvae with a longer rostrum. Rostrum length of the first larval instar changed independently of their size, thus elongated rostra can be considered a defensive feature. Embryonic developmental time was not altered by chemical alarm cues from either heterospecifics or the mixed cues treatment; however, exposure to these cues resulted in larger larvae compared with the control group. Chemically induced morphological plasticity in larvae in response to alarm cues from con- and heterospecifics suggests that such cues are conserved in palaemonids shrimps, providing embryos with an innate recognition of heterospecific alarm cues as predicted by the phylogenetic relatedness hypothesis.