Long-term, high frequency in situ measurements of intertidal mussel bed temperatures using biomimetic sensors

At a proximal level, the physiological impacts of global climate change on ectothermic organisms are manifest as changes in body temperatures. Especially for plants and animals exposed to direct solar radiation, body temperatures can be substantially different from air temperatures. We deployed biomimetic sensors that approximate the thermal characteristics of intertidal mussels at 71 sites worldwide, from 1998-present. Loggers recorded temperatures at 10-30 min intervals nearly continuously at multiple intertidal elevations. Comparisons against direct measurements of mussel tissue temperature indicated errors of similar to 2.0-2.5 degrees C, during daily fluctuations that often exceeded 15 degrees-20 degrees C. Geographic patterns in thermal stress based on biomimetic logger measurements were generally far more complex than anticipated based only on 'habitat-level' measurements of air or sea surface temperature. This unique data set provides an opportunity to link physiological measurements with spatially-and temporally-explicit field observations of body temperature

Evidence for rangewide panmixia despite multiple barriers to dispersal in a marine mussel

Oceanographic features shape the distributional and genetic patterns of marine species by interrupting or promoting connections among populations. Although general patterns commonly arise, distributional ranges and genetic structure are species-specific and do not always comply with the expected trends. By applying a multimarker genetic approach combined with Lagrangian particle simulations (LPS) we tested the hypothesis that oceanographic features along northeastern Atlantic and Mediterranean shores influence dispersal potential and genetic structure of the intertidal mussel Perna perna. Additionally, by performing environmental niche modelling we assessed the potential and realized niche of P. perna along its entire native distributional range and the environmental factors that best explain its realized distribution. Perna perna showed evidence of panmixia across > 4,000 km despite several oceanographic breaking points detected by LPS. This is probably the result of a combination of life history traits, continuous habitat availability and stepping-stone dynamics. Moreover, the niche modelling framework depicted minimum sea surface temperatures (SST) as the major factor shaping P. perna distributional range limits along its native areas. Forthcoming warming SST is expected to further change these limits and allow the species to expand its range polewards though this may be accompanied by retreat from warmer areas.Fundacao para a Ciencia e Tecnologia (FCT-MEC, Portugal) [UID/Multi/04326/2013, IF/01413/2014/CP1217/CT0004]; South African Research Chairs Initiative (SARChI) of the Department of Science and Technology; National Research Foundation; South African National Research Foundation (NRF); Portuguese Fundacao para a Ciencia e Tecnologia (FCT) [SFRH/BPD/85040/2012, SFRH/BPD/111003/2015]info:eu-repo/semantics/publishedVersio

Low temperature trumps high food availability to determine the distribution of intertidal mussels Perna Perna in South Africa

Explanations of species distributions often assume that the absence of a species is due to its inability to tolerate an environmental variable. Recent modelling techniques based on the dynamic energy budget (DEB) theory offer an effective way of identifying how interacting environmental parameters influence distributions through non-lethal effects on growth and development. The mussel Perna perna is an abundant ecosystem engineer around the coasts of Africa, South America and the Arabian peninsula, with an unexplained 1500 km lacuna in its distribution on the west coast of South Africa. We used a DEB approach to explain its distribution in southern Africa and test the hypothesis that this lacuna is caused by sublethal effects of low temperatures on its metabolism. We parameterized a standard DEB model for P. perna using eco-physiological parameters measured in the laboratory, validated by comparison with the body size and reproductive effort of animals from the field throughout South Africa. The model highlighted the importance of reproductive failure under the cold water conditions of the west coast, despite particularly high food availability there, and the surprisingly good performance of P. perna under the warm, highly oligotrophic conditions of the east coast. The results suggest that P. perna is well adapted to low food conditions, but is reproductively vulnerable to low temperatures. DEB models accurately described and explained the anomalous biogeography of this intertidal mussel, allowing us to disentangle the interaction of antagonistic stressors and reveal the critical importance of sublethal temperature effects on reproduction to the species' distribution

Zooplankton metabolism in South African estuaries: does habitat type influence ecological strategies?

Zooplankton community composition, biomass and metabolism can vary drastically over space and time in subtropical estuaries. Changing environmental conditions can affect communities differently, depending on the characteristics of the species involved. In the present study, we compared the rates of oxygen consumption of the dominant zooplankton taxa living in permanently open and in temporally open/closed estuaries. The metabolic response was tested at four temperatures experienced by the animals in their natural environment. Zooplankton from the temporally open/closed estuary showed low activation energies and low rate of metabolism at the highest temperature tested. Animals from the permanently open estuary had higher respiration rates at increased temperatures than those from the open/closed counterpart, with one taxon showing a particularly strong response to temperature increase. Results suggest that the metabolism of zooplankton in subtropical estuaries can be influenced by the environmental conditions experienced and those characteristics need to be accounted for in the development of bioenergetics budgets of species and ecosystems

Predicting the performance of cosmopolitan species: dynamic energy budget model skill drops across large spatial scales

Individual-based models are increasingly used by marine ecologists to predict species responses to environmental change on a mechanistic basis. Dynamic Energy Budget (DEB) models allow the simulation of physiological processes (maintenance, growth, reproduction) in response to variability in environmental drivers. High levels of computational capacity and remote-sensing technologies provide an opportunity to apply existing DEB models across global spatial scales. To do so, however, we must first test the assumption of stationarity, i.e., that parameter values estimated for populations in one location/time are valid for populations elsewhere. Using a validated DEB model parameterized for the cosmopolitan intertidal mussel Mytilus galloprovincialis, we ran growth simulations for native, Mediterranean Sea, populations and non-native, South African populations. The model performed well for native populations, but overestimated growth for non-native ones. Overestimations suggest that: (1) unaccounted variables may keep the physiological performance of non-native M. galloprovincialis in check, and/or (2) phenotypic plasticity or local adaptation could modulate responses under different environmental conditions. The study shows that stationary mechanistic models that aim to describe dynamics in complex physiological processes should be treated carefully when implemented across large spatial scales. Instead, we suggest placing the necessary effort into identifying the nuances that result in non-stationarity and explicitly accounting for them in geographic-scale mechanistic models