Sensing the sea Silke Kro ¨ ger 1 and Robin J. Law 2 1 Centre for Environment, Fisheries and Aquaculture Science (CEFAS) Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK 2 Centre for Environment, Fisheries and Aquaculture Science (CEFAS) Burnham Laboratory, Remembrance Avenue, Burnham-on-Crouch, Essex, CM0 8HA, UK The development of the ‘ecosystem approach’ to the management of marine systems is leading to a require- ment for data to be collected with greater frequency and spatial resolution than has been necessary in the past. This is being met both by the analysis of more samples (to better describe variability and temporal change) and by the deployment of instrumented platforms that gather data over long time periods. To meet these requirements in the hostile conditions at sea, a range of sensors based on physical, chemical and biological responses is being developed. These sensors have applications in laboratory analysis of collected samples, during field studies and directly in situ at remote sites for real-time observations of environmental trends. Here, we consider the role that biosensors could have in future marine monitoring programmes. Introduction Biosensors are analytical devices that closely couple the sensitivity and selectivity of biological, biologically derived or biomimetic sensing elements with the versati- lity of a range of different transducers, most commonly electrochemical, optical, thermometric, piezoelectric, micromechanical or magnetic. Biosensors have been realized in various formats, from dipsticks to large laboratory flow-injection analysis systems, and for a wide range of applications, from single chemical quanti- fications to biological effect measurements. The sensing elements or receptors employed can make use of affinity interactions, as is the case with antibodies, cell receptors, nucleic acids or imprinted polymers, or catalytic reactions as would be carried out by whole organisms, tissue samples, cells, organelles or enzymes [1]. To date, the majority of applications have focused on medical diagnostics, process control, pharmaceutical products, food analysis and defence applications, although numerous environmental biosensors have also been developed [2]. The number of biosensors designed specifi- cally for marine applications is still relatively small, although many of the systems described for other applications are potentially applicable to marine measure- ments. Here, we outline the case for the use of biosensors in making marine measurements – that is, what are the drivers of research in the area, what are relevant analytes and what do we think biosensors will contribute to future marine monitoring programmes. Marine management is evolving rapidly from compart- mentalised programmes around specific activities to a more holistic view encompassed by the phrase ‘ecosystem approach’, and with this change in emphasis comes a change in data requirements. Biosensors offer advantages over traditional analytical methods in terms of cost, measurement frequency, use in decentralised locations and ecological relevance of measurements, but clearly they will be challenged by the requirements posed by the marine environment, for example regarding robustness. An overview of drivers, current and future measurement strategies and relevant biosensors will be provided together with a forecast of future needs and opportunities in the area. Why ‘sensing the sea’? There are many reasons for measurements to be made at sea, including scientific exploration, commercial exploita- tion, compliance with legislation or in support of over- arching initiatives aimed at understanding and protecting the marine environment. Some of these drivers are summarised in Box 1. Oceans are complex systems consisting of different ecosystem compartments and with a variety of inter- actions between them, as shown in Figure 1. Measure- ments are carried out to describe the state of each of these compartments, to quantify fluxes between them and to elucidate impacts resulting from natural variations (for example in climatic conditions) and from human activities. The ability to distinguish between natural variability and anthropogenic change is an important issue and requires exact observations to be made over long time-spans with high temporal and spatial resolution. In addition, a range of chemical and physical measurements must be made simultaneously. Depending on the information requirement addressed, the measurements can vary from fish stock surveys to single chemical analyses, from measurements of processes such as denitrification to the taxonomy of toxic algae or the detection of pathogens. Pollutants can enter the marine system from known or unknown point sources as well as through diffuse inputs, for example via the atmosphere, and concentrations can be studied to identify sources, environmental pathways, persistence or uptake into biota and degradation or biotransformation. In some cases, the need is for an early warning system, in others it Corresponding authors: Kro ¨ger, S. (s.kroeger@cefas.co.uk), Law, R.J. (r.j.law@cefas.co.uk). Available online 2 April 2005 Review TRENDS in Biotechnology Vol.23 No.5 May 2005 www.sciencedirect.com 0167-7799/$ - see front matter Crown Copyright Q 2005 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.tibtech.2005.03.004