Effects of global warming on reproduction and potential dispersal of Mediterranean Cnidarians

Abstract

Water temperature directly affects life cycles, reproductive periods, and metabolism of organisms living the oceans, especially in the surface zones. Due to the ocean warming, changes in water stratification and primary productivity are affecting trophic chains in sensitive world areas, such as the Mediterranean Sea. Benthic and pelagic cnidarians exhibit complex responses to climatic conditions. For example, the structure and phenology of the Mediterranean hydrozoan community displayed marked changes in species composition, bathymetric distribution, and reproductive timing over the last decades. The regional species pool remained stable in terms of species numbers but not in terms of species identity. When the Scyphozoa group is considered, we observe that Pelagia noctiluca (among the most abundant jellyfish in the Mediterranean Sea and eastern Atlantic waters) has increasingly frequent massive outbreaks associated to warmer winters. Variations in metabolic activities, such as respiration and excretion, are strongly temperature-dependent, with direct increment of energetic costs with jellyfish size and temperature, leading to growth rate reduction. Water temperature affects sexual reproduction through changes in the energy storage and gonad development cycles. Anthozoan life cycles depend also on primary productivity and temperature: gonadal production and spawning are tightly related in shallow populations (0-30 m depth) with the spring-summer temperature trends and autumn food availability. Overall, the energy transferred from the mother colonies to the offspring may decrease, negatively affecting their potential to settle, metamorphose and feed during the first months of their lives, eventually impairing the dominance of long-living cnidarian suspension feeders in shallow benthic habitats. In this review, we describe the already ongoing effects of sea warming on several features of cnidarian reproduction, trying to elucidate how reproductive traits and potential dispersion will be affected by the cascade effects of increasing temperature in the Mediterranean Sea.

Settlement dynamics and recruitment responses of Mediterranean gorgonians larvae to different crustose coralline algae species

“…The frequency of climate change-related disturbances affecting Mediterranean gorgonian populations has been increasing in the last 20 years and for some species, such as C. rubrum, mass mortalities are coupled with harvesting pressure (Bramanti et al, 2009;Rossi et al, 2019). Larval settlement is a key bottleneck to the recovery of damaged populations, and it depends, in part on the capacity of larvae to select the optimal substrate (Harrington et al, 2004;Fabricius, 2011).…”

“…For example, in shallow areas of the Mediterranean Sea (10-30 m depth), in the last decades, several gorgonian populations have been hit by mass mortalities linked to acute thermal anomalies (Cerrano et al, 2000;Garrabou et al, 2009;Bramanti et al, 2005;Linares et al, 2008aLinares et al, , 2008bTuricchia et al, 2018). For some gorgonian species, recruitment may be impacted by prolonged high temperature (Rossi et al, 2019); nevertheless, some gorgonian populations have been able to recover, probably due to the increased recruitment after disturbance (Cupido et al, 2008(Cupido et al, , 2012Padrón et al, 2018). Understanding the processes driving settlement and recruitment is thus fundamental to shed light on recovery potential of gorgonian populations and help developing proper management and conservation plan at local level (Whalan et al, 2012).…”

Changes of energy fluxes in marine animal forests of the Anthropocene: factors shaping the future seascape

“…Phenology of the species (i.e. the timing of key seasonal events) will also affect the viability of new generations (Rossi et al, 2019). In fact, >60% of studied species in aquatic systems have responded to ocean warming by advancing their reproductive phenology (Greve et al, 2005;Poloczanska et al, 2016).…”

“…In fact, >60% of studied species in aquatic systems have responded to ocean warming by advancing their reproductive phenology (Greve et al, 2005;Poloczanska et al, 2016). Since reproductive events have evolved to occur at optimal times of food availability to maximize the survival of the next generation (Forrest and Miller-Rushing, 2010;Rossi et al, 2019), these phenological shifts can reduce reproductive success of species and affect their population in the long-term (Schaper et al, 2012). As an example, spawning and release of larvae in summer implies that lecithotrophic larvae of anthozoans in the Mediterranean Sea settle and metamorphose a few weeks before phytoplankton concentration rises in the early fall (Rossi and Gili, 2009), supplying moderate to high amounts of food.…”

“…Within the context of global change (see the previous considerations), there is a risk that the period of trophic crisis (Rossi et al, 2006) might be significantly prolonged to the point that the capacity of the energy reserves in lecithotrophic larvae would not last until the arrival of favourable feeding conditions in the early autumn. This situation could be even worse if the spawning of these species would be triggered earlier by the increase in temperature (Rossi et al, 2019). Despite the potential severe consequences of the undermining of reproductive success for the long-term persistence of species populations, little is known of the importance of prey phenology to population persistence.…”