Introduction
Infaunal organisms inhabiting marine sediments serve as valuable ecological indicators, offering insights for the influence of key environmental factors in such habitats. Ecosystem health for these habitats subjected to wave storm events with different magnitude in frequency or intensity is reflected in several aspects like species composition, biodiversity, pollution tolerance, or resilience to physical disturbance among others. High-energy environments like wave storms may compromise survival and ecophysiology of inhabitants with potential to disrupt trophic interactions within the benthic food web. Here, we proposed to investigate the impact of high-energy environments on infaunal organisms, monitoring mortality events but also the importance of sublethal effects that may threat or imbalance metabolism, energetics and surviving bivalve´s health. The clam Polititapes rhomboides was the target species, creating different physical disturbance environments (short- and long-term scenarios) followed by an additive abiotic stressor (seawater warming, +3ºC). Altogether, behavioral, ecophysiological, and stress-related immune responses were monitored, resembling natural drivers impact on historic mortality events of this infaunal population.
Results and Discussion
Mortality events of the clam´s populations subjected to sediment mobilization was noted for 16 and 24 days of perturbation (but not for 8 days), representing 14% and 24% of the population, respectively. In all cases, mortality was accelerated with temperature increase reaching 41% for the worst scenario, temperature increase after 24 days of sediment disturbance. In any case, mortality was not linked to rickettsias proliferation or abundance as experimental colony densities remained extremely low and far below the >160 colonies/mm2 recorded during natural peak mortality episodes (Darriba et al., 2012; Villacieros-Robineau et al. 2022). As a general pattern, valve opening behaviour declined significantly (15-25%) during sediment mobilization with minor differences among perturbation exposure time (8, 16 and 24 days). Temperature increase at the end of these high-energy exposure periods did not suppose any significant detrimental effect for clam´s valve behaviour. Interestingly, primary valve opening behaviour which precedes the rest of the vital functions showed a significant correlation with feeding patterns that have not been observed in other bivalves (Comeau et al. 2018). It is plausible to speculate on such biological correlation for another trophic niche (e.g. infaunal disposition with siphons fully extended along sediment surface).
Physical perturbation of individuals caused a significant decrease in feeding and metabolic rates (approximately half of calm scenario) although posterior seawater warming activated also time-specific responses (increase) in both physiological parameters based on optimal food availability set-up selected. Projected energetic status showed a significant degree of vulnerability for disturbed populations based on scope for growth decreased (SFG index; Figure 1B). The cessation of such physical disturbance, together with seawater warming, led to a relatively short‑term increase in feeding rates—supported by the availability of optimal food resources—to restore energetic status, although still far from the undisturbed scenario. Combined sediment mobilization and seawater warming significantly increased nitric oxide production after each perturbation cycle (8, 16, or 24 days), with stronger effects following the longest disturbance. Clams under calm conditions did not show nitric oxide increase, even at high temperature, indicating disturbance as the main stressor. A comprehensive scheme of behavioural, physiological and immune-system shifts that infaunal populations experience when subjected to key abiotic stressors responsible of mortality events in the natural environment is discussed. Such knowledge is necessary not only for maintaining biodiversity in our coastlines but also relevant for the socioeconomic sector associated as well as understanding the set of ecosystem services being supported by this and other infaunal species.
AB
Figure 1. Cumulative mortality (%;A) and Scope For Growth (SFG; B) of the clams subjected to short- and long-term physical disturbance and seawater warming.
Acknowledgment
This work was supported by Project PID2019-106008RB-C21 (STRAUSS) financed by MCIN/ AEI/10.13039/501100011033 (Ministry of Science and Innovation, Goverment of Spain). We acknowledge Jorge Alfaya for clams collection through Cofradía de Pescadores de Vigo and, Lourdes Nieto Leiros for technical assistance in the laboratory.
References
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