Phenotypic plasticity promotes persistence following severe events: physiological and morphological responses of seagrass to flooding

Abstract

Summary 1.Severe events such as floods or cyclones can have large ecological effects on the structure and functioning of ecosystems. The capacity of an ecosystem to adapt to, or absorb, the effects of a severe event depends on the severity and longevity of the event and the tolerance of the species present.2. Seagrasses exhibit phenotypic plasticity at the plant to meadow scale through a variety of physiological and morphological acclimations to light stress to enhance photosynthetic capacity. These acclimations provide early warning of the possible risk of larger scale seagrass loss and can therefore be used in predicting how ecosystems might respond to severe events. 3.The physiological and morphological responses of 12 seagrass (Zostera muelleri) meadows to a severe flood were examined to test two main hypotheses: (i) that the physiological and morphological characteristics of seagrass would differ between meadows along the established chronic water quality gradient, in a pattern consistent with prior acclimations which have been shown to enhance photosynthetic capacity and (ii) that physiological and morphological responses to the flood would differ between meadows in a manner consistent with their position along the water quality gradient. 4.Meadows had different physiological and morphological characteristics across the water quality gradient, with meadows subject to chronically poorer water quality exhibiting characteristics consistent with those that maximize photosynthetic capacity. Despite a large discrepancy in impact among meadows, all meadows sampled responded consistently to the flood, exhibiting only physiological changes with no significant reduction in biomass. This suggests that photoacclimation to chronically poor conditions can enable seagrasses to withstand the effects of severe events, such as floods. 5.Synthesis. Phenotypic plasticity in habitat-forming species can result in a large variation in their responses to severe events, such as floods or cyclones. Acclimation to prior poor environmental conditions can promote persistence in habitat-forming species, such as seagrasses, following severe events. The measurement of phenotypic characteristics along an impact gradient can therefore provide an indication of the response of habitat-forming species to severe events.

Characterization of a resilient seagrass meadow during a decline period

“…These areas may function as seed sources and allow the recovery of lost areas (Calleja et al 2017). When considering seagrass resistance and recovery, it is generally agreed that the greater the trait variability, the more likely the system is to survive periods of stress (Maxwell et al 2014). A main aspect of such studies is to understand how local factors are compromising and, in some cases, contributing to the resilience of seagrass ecosystems (Unsworth et al 2015).…”

“…A main aspect of such studies is to understand how local factors are compromising and, in some cases, contributing to the resilience of seagrass ecosystems (Unsworth et al 2015). Although this study does not focus on analysing the causes, there is evidence in the literature suggesting that exposure to certain environmental stresses may enable individuals or communities to adapt to drivers and improve their resistance (Maxwell et al 2014, Calleja et al 2017.…”

Rapid monitoring of seagrass biomass using a simple linear modelling approach, in the field and from space

“…A coincident benthic photo was acquired before each core harvest; these photos were geo-referenced and analysed for seagrass percentage cover and species composition as per the method in the following section. Whilst above and below-ground biomass are reasonably well correlated, exploratory work suggested that predicting below-ground biomass from above-ground estimates would not be appropriate using the same simple linear modelling approach, which is expected given demonstrated variability in seagrass phenology in Moreton Bay (Maxwell et al 2014). Thus we modelled above-ground biomass only, and all references to biomass refer to above-ground biomass.…”

“…Seagrass in Moreton Bay displays high phenotypic plasticity (Maxwell et al 2014), with morpho -9 Fig. 4.…”

“…This would be a step towards a more automated monitoring approach, enabling biomass estimation in new study sites without the need for in situ sampling. Future work should also aim to increase model complexity and introduce environmental covariate data to reconcile the non-linear relationship with changing species morphology, as discussed above; the data sets already exist in Moreton Bay , Maxwell et al 2014.…”