The effects of climate warming and heatwaves on in situ benthic marine community development

Understanding how, and predicting, the future impact of climate warming on biodiversity is one of the great challenges for environmental sciences, for ecologists and for society. Currently two main approaches exist to address this problem: 1. The matching of species and communities to current environments and predicting from models where those environments will be in future to assess likely new distributions; 2.

Assessing the performance of species in experimentally manipulated systems. Both have advantages and drawbacks. The former from unknowns, especially around ability to colonise and distances that can be covered, the importance of biodependencies between species and effects of environmental barriers.

The latter suffers from unrealistic rates of change compared to natural systems and a lack of ecological realism, because the vast majority of studies are laboratory based where conditions are held constant with the exception of the variable under investigation. On land experiments have included both laboratory and field based manipulations (e.g. Fordham 2015), and the latter has provided key information not available from lab based studies.

Field based experimental manipulations in the sea are more difficult to conduct, especially for temperature because of the large specific heat capacity of water and currents that rapidly remove heat from experimentally warmed areas. However, a method has recently been developed that allows the heating of surfaces of panels in situ in the sea. Biological communities develop on the heated surfaces and the 3-5 mm boundary layer of water over a panel such that for small species the whole life cycle from settlement to reproductive adult is in warmed conditions.

This method has great advantages because apart from heating all other ecological factors such as water currents, food supply, salinity, light regime, tides etc remain natural. The approach has been tested in Antarctica where 1C warming caused growth rates to double in some species and community composition was dramatically impacted (Ashton et al. 2017).

Further studies showed that species living on 2C warmed panels had failed to acclimatize to the higher temperature after 18 months (Clark et al. 2019) and that competitive interactions increased with 1C warming (Barnes et al. 2021).

The approach encourages small encrusting species to attach to panels, primarily spirorbid worms, bryozoan, sponges and ascidians, all members of the biofouling community. Biofouling of marine structures has serious economic consequences. For example, the blockage of pipes and equipment in the US power industry is estimated to cost around US$60 million per year, and the increased fuel costs for ships due to hull biofouling are suggested to be as high as US$150 billion annually (Selim et al. 2017).

In addition, biofouling of fish and shellfish cages is a serious problem for aquaculture, accounting for, 5-10% of production costs (Bannister et al. 2019). The aim of this project is to understand how biofouling in a temperate site will be affected under future climate warming for both constant warming and heatwaves. The project will also address how multiple generation exposure to warmed conditions affects biological performance.

Preliminary trials of these panels in the UK have also shown that even +1C can produce tipping points in some species in warm summers, and trials of similar panels currently running in New Zealand are showing very large differences of impacts on species performance and community effects in different seasons. So far no one has tested the effects of heatwaves or conducted multiple generation in situ manipulations.