Climate and Marine Biodiversity
Climate Impacts on Biodiversity and Ecosystem Indicators
Recent changes in marine climate, most notably rising sea temperature, have been linked to changes in the distribution, abundance and phenology of marine species across the OSPAR Maritime Area. Climate change is an important factor in driving changes in distribution, abundance and seasonality of marine biota across the OSPAR Maritime Area. The NOSCCA report (Brander et al., 2016) described the biotic effects of a changing marine climate in terms of: “the physiology, reproduction, growth, survival, behaviour and transport of individuals; the distribution, dynamics and evolution of populations; and the trophic structure and coupling (e.g. benthic-pelagic coupling) of ecosystems”. The report nevertheless noted that such responses were not always direct and simple to associate with single climate parameters.
This section focuses on how the marine climate is identified within the IA 2017 indicator assessments. The links to climate noted within the assessments are repeated in Tables 3 and 4 to give an initial overview of potential issues. This initial analysis will also help indicate where future assessments could start to address some of the links between climate change and ocean acidification and the indicator in question.
For top predators (marine mammals, seabirds), direct impacts from climate change are not well established and effects are primarily seen through impacts on habitats and prey species. For example, the impacts of changing environmental conditions on forage species (e.g. sand eels, sprat), along with historical fishing pressure, are probably limiting the breeding success of some seabird species (e.g. black legged-kittiwake). Some marine mammal species are highlighted in the assessments as being sensitive to temperature, notably the observed preference of striped dolphin for warm conditions (21–24°C). Sightings of short-beaked common dolphin in the Greater North Sea, are thought to be associated with the North Atlantic Oscillation and warmer waters in the northern North Sea.
At the base of the food web, the changing environmental conditions are affecting the abundance and distribution of phytoplankton species. Phytoplankton is highly sensitive to changes in physical and chemical conditions (temperature, salinity, available light, nutrients, pH, storminess, currents), as well as oxygen and CO2 availability. Changes in key aspects of ecosystem function are indicated, with consequent effects higher up the food web.
Changes are evident across the Arctic (AMAP, 2017). The decline in sea ice thickness and extent, along with changes in the timing of ice melt, are affecting marine ecosystems and biodiversity; changing the ranges of Arctic species; increasing the occurrence of algal blooms; leading to changes in diet among marine mammals; and altering predator-prey relationships, habitat use, and migration patterns.
Some reports have highlighted the potential for an ice-free Arctic to enable the spread of non-indigenous species into the North-East Atlantic, but in general, marine climate drivers are not responsible for the direct introduction of non-indigenous species per se. However, warming could make environmental conditions more favourable for introduced species to become established and spread.
For benthic habitats, the importance of cumulative effects from a range of pressures is noted, as is the difficulty of teasing the effects of these different pressures apart. This challenge is further compounded by the impacts of climate change and its effects on species abundance, substrate and water properties and pressures (e.g. from storm disturbance).
In the QSR 2010, OSPAR identified the key threat posed by ocean acidification to marine biodiversity and ecosystems in the OSPAR Maritime Area. However, ocean acidification is still not identified in any of the assessments as a strong element of the changes in current status of the common indicators. In the wider scientific literature, complex responses to changing ocean pH have been found and are expected. The SGOA reported that changes in aragonite saturation (see section on pH) in deep water habitats in the OSPAR Maritime Area could “lead to irreversible damage, including habitat loss, to the detriment of important ecological function and services provided by these ecosystems”.
Biological Diversity and Ecosystems: Species State and Distribution
Table 3 highlights how and where marine climate has been identified within the IA 2017 common indicator assessments for biodiversity and ecosystems as assessed through species state and distribution in the OSPAR Maritime Area. The third column identifies some of the potential implications of climate change associated with these indicator assessments.
Biological Diversity and Ecosystems: Habitats and Food webs
Table 4 highlights how and where marine climate has been identified within the IA 2017 common indicator assessments for biodiversity and ecosystems as assessed through habitats and food webs in the OSPAR Maritime Area. The third column identifies some of the potential implications of climate change associated with these indicator assessments.