Seasonal trends of the polyp expansion and nutritional condition of Alcyonium acaule (Octocorallia, Alcyonacea)

Abstract

The ecological physiology of anthozoans, as well as their resistance to stressors, are strongly influenced by environmental factors and the availability of resources. The energy budget of anthozoans can vary seasonally in order to find an equilibrium between the available resources and respiration, polyp activity, growth, and reproduction processes. The variation in the biochemical composition of the animal tissues in these organisms results from a combination of the productivity processes of the water column coupled with the reproductive effort and potential starvation periods of the anthozoans. Here, the seasonal variation in the polyp activity of a slow-growing passive suspension feeder, the octocoral Alcyonium acaule, as well as their carbohydrate, protein and lipid contents, was investigated in a warm temperate environment using in-situ observations and biochemical analyses. Polyp activity exhibited a significant variability that was moderately dependent on season, while an aestivation phenomenon in A. acaule (i.e., a resting period in which the anthozoan is not capable of any polyp activity) during the warmer months is clearly observed. Carbohydrate concentrations in the coral species showed a significant increase in the late winter and spring seasons, and the lipid content increased during the spring. A higher abundance of lipids and carbohydrates coincided with a higher primary productivity in the water column, as well as with the octocoral reproduction period. In late autumn, there was a depletion of these biomolecules, with protein levels exhibiting great variability across sampling times. Complex alterations driven by climate change could affect the energy fluxes that depend on the dead or alive particles that are intercepted by marine animal forests. The obtained findings show a food shortage in late summer and autumn of the benthic suspension feeder A. acaule through the integrative descriptors of the ecophysiology of these anthozoans. This research contributes to the knowledge of energy storage capabilities in benthic suspension feeders in general, highlighting the importance of understanding the limits of resistance to starvation periods through these indicators.

Phenology in the deep sea: seasonal and tidal feeding rhythms in a keystone octocoral

“…Similar seasonal patterns in feeding activity have been documented for shallow-water benthic suspension feeders, and corals in particular, in temperate seas [3]. Periods of metabolic dormancy (low feeding and respiration rates) have been linked to low food availability during the oligotrophic season (winter or summer depending on geographic location [3,30,36]).…”

“…For instance, polyp expansion facilitates respiration by increasing the surface available for gas exchange [63]. In shallow temperate habitats, decreased polyp activity at high temperatures has been associated with reduced respiration [36,37,63]. While a similar negative correlation between temperature and polyp expansion has been identified in our study, temperatures were much lower and less variable (between 2.9 and 3.7°C) than in the aforementioned studies and the detected correlation may be an indirect consequence of tidal currents.…”

“…However, to date, little information exists on the trophic ecology and phenology of most deep-sea coral species. In shallow water, studies have demonstrated an influence of seasonal and tidal cycles on coral feeding strategy through changes in currents, temperature, food quantity and quality [35][36][37]. Similarly, aquarium experiments and in situ observations of deep-sea corals (at depths of approximately 200 m) have demonstrated that their feeding behaviour varies diurnally and seasonally and is influenced by tidal currents (speed and direction) [12,38,39].…”