Use of Continuous Plankton Recorder information in support of marine management: applications in fisheries, environmental protection, and in the study of ecosystem response to environmental change.
K. M. Brander a,* , R. R. Dickson b , M. Edwards c
aInternational Council for the Exploration of the Sea, Palaegade 2-4, Copenhagen, DK-1261, Denmark
b The Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, NR33 0HT, UK
c Sir Alister Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK
* Corresponding author. Tel.: 0045-33154225; fax: 0045-33934215
E-mail address: (K.M. Brander)
Abstract
The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research, designed to assist the fishing industry. Its survival and continuing vigour after seventy years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing Quality Status Reports (QSR); it has shown the distributions of fish stocks which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton.
The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.
Keywords: Continuous Plankton Reorder survey, climate change, marine management, fisheries change, eutrophication, biodiversity and long-term
Contents
1. Introduction
2. The growth of understanding
3. Support for fisheries
4. The issue of eutrophication
5. Biodiversity and global change
6. The role of the CPR within biological oceanography
1.Introduction
In the summer and autumn of 1921 and spring of 1922, an advanced multidisciplinary study in fisheries oceanography took place in the west-central North Sea. In three issues of the ICES Publications de Circonstance (Nos. 78, 79 and 80), published together in 1923, we read of a curiously modern attempt by Hardy (1923), Carruthers (1923) and Lumby (1923) to explain the relative failure of the English herring fishery in that year as the joint effect of abnormal conditions in the plankton, currents and hydrography. In the end, the attempt was almost bound to fail. As E.S. Russell notes in his Introductionto this paper:
“Conclusions as to the effects of hydrographic conditions in any one year can be drawn with complete confidence only when the extent of their departure from normal conditions can be determined; and the period over which regular observations have been made in the North Sea on a large scale is at present insufficient to furnish a norm”.
The inadequacies of the data set on which the 25 year-old Hardy was compelled to depend on that occasion - sparse tow-net hauls and no adequate baseline - do much to explain the applications for which the CPR was subsequently conceived and justified. And the CPR was plainly an applications-led development, designed from the start to provide improved scientific support for the fishing industry. First, in his earliest description of the ‘New Method of Plankton Research’, Hardy (1926) is concerned to resolve the highest time-space scales of plankton variability (‘patchiness’) which were obscuring his view of larger-scale and longer-term variability:
“For a long time I have felt the need of an instrument which by giving a continuous record, ….would enable one to study and compare the uniformity or irregularity of planktonic life in different areas, to measure the size, varying internal density and frequency of patches and to indicate…whether any correlation exists between different species”. Then, three years later, in his Civic Week lecture at the University College Hull, Hardy returns once more to the original aim of his 1921 study - the provision of interpretative and predictive support for the fishing industry on the scales important to them (Hardy, 1930):
“The experiment I want to make from this College consists of running a number of these instruments on definite steamship routes across the North Sea…. When these charts are examined and the results compared with the positions of herring shoals from year to year, we shall know whether or not we can forecast the position of the fish from the distribution of the plankton…. These varying movements of fish must have a definite ascertainable cause, and once ascertained, forecasting cannot be difficult”.
In seeking financial support from the Industry, Hardy was prudent enough not to promise results, yet confident enough to suggest that “If it fails to yield useful results, it will not be science that has failed; it will be because the experiment is not big enough, bold enough, for the problem concerned”. He got his money, though the enthusiasm of the Hull Fishing Vessel Owners Association was expressed no bolder than £100 per year, with £50 from the Fishmongers’ Company.
By the time the first of the familiar ‘Hull Bulletins’ began to appear in 1939, his focus was firmly and appropriately on the largest scales of variability, using the technique to develop a baseline against which anomalies in plankton distribution and abundance might be recognised and explained.
“The similarity of the methods to those of meteorology has already been stressed: we are aiming at producing, month by month, charts of the broad changes in the distribution of the more important plankton forms. It is then our aim to correlate these changes with the fluctuations in the fisheries, both the drift-net herring fisheries and the trawl fisheries, and also with hydrological and climatic changes. The correlation with the herring fisheries was one of the first economic results that was expected from such a survey ”. (Hardy,1939, p6)
Hardy was clearly far ahead of his time in realising the significance of spatial differences in the kinds and abundance of plankton and in devising the means to study them. As Platt and Stuart (1997) remind us: “Until the advent of satellite remote sensing, the CPR provided the only means of collecting plankton data at large spatial scales: it was the remote sensing of the day. Further, by recognising [from an overflight of the English Channel from Plymouth to the western mackerel grounds in the early 1920s] that colour differences in the ocean contained important biological information that could be surveyed rapidly with aircraft … he became a true pioneer of remotely-sensed ocean-colour science”.
However, although enthusiasm, optimism and foresight can initiate concepts, they can rarely sustain them. Duarte, Cebrian & Marba (1992) show that: “long-term monitoring programs are, paradoxically, among the shortest projects in marine science: many are initiated but few survive a decade”. As Grove (1992) concludes in his review of the ‘Origins of Western Environmentalism’, survival comes with utility: “If a single lesson can be drawn from the early history of conservation, it is that states will act to prevent environmental degradation only when their economic interests are shown to be directly threatened. Philosophical ideas, indigenous knowledge and people and species are, unfortunately, not enough to precipitate such decisions”.
The implication is clear: that to survive for seven decades, the CPR data set must have had some continuing utility for marine resource management or policy. In the remainder of this chapter we aim to describe both our increasing understanding of variability in the marine ecosystem with time as the CPR record has lengthened and the changing preoccupations that have justified its continued survival. Four main applications develop with time: the issues of Fisheries, Eutrophication, Biodiversity and Global Change.
2.The growth of understanding
It is increasingly difficult to fund long period measurements. The quotation above from Duarte et al. (1992) still applies. One reason for this may be the mistaken perception of ‘diminishing returns’ from long-term monitoring and it is worth making the case that there is in fact an increasingly valuable and complex scientific return with time.
When the major papers based on the CPR record are classified by type and date (arrowed in Fig. 1), we find that the elaboration of our understanding of the Atlantic plankton and its ecosystem grows steadily with time. Initially, these papers provide description. Then the samples become adequate to contribute to the systematics of the plankton; then successively to comment on variability at increasing time scales, from seasonal change through seasonal dynamics to interannual change and lastly to ecosystem change, involving a complex of variability across decades and trophic levels. Papers anticipating the planktonic signature of global change have begun to appear. Thus, over seven decades, the value of the time series has grown in terms of the breadth of understanding that we can mine from it.
It is as well that it is so. As Fig. 2 also shows, the management issues supported by these data have also become more elaborate and complex with time as a range of actual or potential anthropogenic impacts begin to affect our thinking. In each case, the requirement has been - in advance of their onset - to anticipate the likely chain of responses that will arise through the marine environment and its ecosystem, to deploy unambiguous and practical means of detecting these impacts, and to develop appropriate policies for managing them. To develop such criteria and policies in ignorance of the ‘natural’ envelope of variability in both the ecosystem and its environment is to risk implementing measures that are costly and do not work.
The longest time series give us access to the broadest spectrum of ocean variability. That, in short, is why a 70-year record of the planktonic ecosystem is of importance and why its value has increased with time. The following sections are intended to illustrate this point.
3.Support for fisheries
Hardy's aim in setting up the CPR survey was to provide a service, similar to that provided by meteorologists for the atmosphere, which would enable fishermen to locate their target species and eventually have some predictive capability. He was a realist and he recognised that this would be a long haul:
“It must take many years before we have enough knowledge of this changing plankton to establish what may be considered the normal state of distribution for any one time of year; only when this has been done can we see in which particular ways the different years have been abnormal. Not until then can we safely think of trying to predict the effects of such changes on a fishery.”
The aim of providing fishermen with operational information from the CPR to locate target species and improve their catches has not been realised in the way in which Hardy intended, or rather it has not been attempted for several reasons. For one thing the time-lag between sampling by the CPR and the availability of the information makes short-term application impossible. For another, new technologies, particularly acoustics, proved to be highly effective for real-time location and tracking of herring shoals. These techniques have made fishing operations for pelagic species, such as herring, so efficient, that there is far more concern now about how to restrain catches than enhance them.
The CPR has however proved useful in locating significant fishery resources, e.g. blue whiting, which have subsequently been explored and developed. The CPR showed the location of the blue whiting stock west of the British Isles (Fig. 3) at a time when only Spain recorded any landings of blue whiting and these were from areas south of 52oN (average 13,500 tonnes from 1958-1966). After 1967 the international fishery increased to over one million tonnes in 1979-80 (average 465,400 tonnes from 1967-1998). Another example is the redfish stocks in the Irminger Sea (Henderson, 1964b).
The utility of surveying plankton was based not only on what it was expected to reveal about the distributions of zooplankton and their fish predators, but also on the insight it would give into the dynamics of lower levels of the food chain leading to fish, with the expectation that changes in plankton production must have consequences for the higher trophic levels. Hardy's investigations resulted in a very detailed and complex food web for herring (Fig. 4) and now, with a sixty-year time series of variability in both the herring stock and their major prey items, we can see remarkable correlations between them (Reid, Battle, Batten & Brander, 2000). The rich detail of processes and interactions between all the components of the food chain and the influence of physical and biological factors at many stages make it difficult to distinguish between possible and actual causal relationships that give rise to the observed correlations between fish and plankton. Even the basic question of whether correlations between predators and prey demonstrate top-down or bottom-up control cannot be resolved unequivocally (Reid et al., 2000) and both types of control probably occur at different times and ecosystem states.
The CPR has provided immensely valuable information concerning the scale and nature of the processes affecting fish stocks. One of the first attempts to analyse the large-scale impact of environmental change on seasonal and interannual patterns of biological variability in the North Atlantic (Garrod & Colebrook, 1978) concluded:
"Convincing as these are, the mechanisms of the link between climatic/hydrographic changes and their biological effects has, in most cases, yet to be established. This paper does not come any closer to defining such links but shows that similar variation in plankton and fish communities are contemporary and on a geographic scale which suggests a common origin in pan-Atlantic environmental effects rather than in strictly localized phenomena.”
Subsequent analysis of the spatial scales of variability in cod (e.g. Myers, Mertz & Barrowman, 1995) confirms the importance of this work and many recent studies (e.g. Corten, 1998; Fogarty, Myers & Bowen, 2001; Ottersen, Plangue, Belgrano, Post, Reid & Stenseth, 2001; Brander in press) have confirmed the conclusion concerning large-scale geographic pattern. We continue to study the processes and to develop tools for making use of the information about large scale variability in relation to fisheries management.
CPR data have been applied in many specific studies of recruitment variability, with results which are tantalising, encouraging, but so far incomplete. For example Cushing (1984) tested the match-mismatch hypothesis on North Sea cod, using data on Calanus in the NE North Sea from the CPR survey to show both the interannual variability in abundance and also in the timing of spring production. He obtained a significant correlation between number of cod recruits and Calanus timing and abundance, but the relationship did not hold up in a later analysis (Brander, 1992) using more years and more information on Calanus. The relationship being modelled here may be fundamentally correct, but it depicts only a part of the dynamics needed for adequate representation of Calanus variability. Other case studies have shown both positive and negative relationships between zooplankton abundance from the CPR and recruitment of cod, haddock and herring (Drinkwater, Frank & Petrie, 2000; Reid et al., 2000). Thus empirical analyses and biological reasoning give us good grounds for expecting that the information from the CPR will become useful in understanding and assessing variability in fish stocks, but it is not clear whether the utility will derive mainly from the long-term, large-scale overview of ecological "regime shifts" which it provides, or from direct operational application at short time scales for improved year-to-year forecasting (Brander, in press).
Fisheries management has become more concerned about the impact of fishing on the marine ecosystem as a whole and this is now articulated in the FAO Code of Conduct for Responsible Fisheries and in numerous Ministerial declarations about future fisheries policy. Turning this general concern into an operational process, with measurable indicators, against which progress towards ecological objectives and compliance with statutory instruments can be measured, is by no means simple. It is evident that plankton is a key part of the marine ecosystem in this respect, since trophic calculations show that the fish removed by fisheries consume a very significant proportion of the production of phytoplankton and zooplankton (Pauly & Christensen, 1995) and that fisheries therefore have a major impact on plankton (Reid et al., 2000). Quantifying this effect, providing observational evidence, evaluating whether the effects are deleterious and designing procedures for mitigating such effects are in their infancy. Here the CPR has a special role to play, not least because it provides a unique example of the problems and pay-offs which such a spatially, temporally and taxonomically detailed time series gives rise to. The rationale, history and operation of the CPR over 70 years provides many useful lessons for the design of any future monitoring which is intended to provide ecosystem indicators.