While molluscs, echinoderms and corals have been the focus of climate change research other invertebrates such as crustaceans and polychaetes have received less attention. Building resilience in marine ecosystems against climate change, will depend on functional diversity and a variety of other features including modularity, openness, reserves, feedbacks, nestedness which requires monitoring, leadership and trust (Carpenter et al., 2012). This presentation will summarise what is known about the phenotypic plasticity and adaptation of polychaetes and crustaceans which have been around since the Cambrian and occupy all marine and estuarine habitats from deep sea soft bottom communities to the intertidal. They may have the capacity to adapt, how quickly they can do this is unknown. While crustaceans appear to have resilience, there have been very few studies on the adaptive capacity of polychaetes. Changes in polychaete species composition and abundance will almost certainly have flow on effects on food chains, the breakdown of organic matter especially for species which feed on polychaetes in the benthos and in the water column. A whole of ecosystem approach is needed, with attention polychaetes and crustaceans as key food sources for higher trophic leves, to accurately forecast the impact of climate change on marine systems.