MEPS 232:197-211 (2002)  -  doi:10.3354/meps232197

ABSTRACT: Ecosystems are fundamentally structured in space and time. The identification and quantification of scales of variability has occupied a central place in ecology for several decades. This paper examines spatial changes in the diversity of calanoid copepods and its regional dependence in the North Atlantic Ocean at diel, seasonal and interannual scales. Point cumulative semi-variograms, initially proposed for geological purposes, are described and intensively used to understand the relationships between diversity and its spatial scales of variability. A map of the mean spatial dependence in calanoid diversity is then proposed and diel and seasonal changes examined. This shows that diversity changes at small spatial scales over the European shelf seas. In oceanic areas, diversity changes at large spatial scales in both the subarctic and the northern boundary of the subtropical gyres. Low spatial scales of variability are detected in the Gulf Stream extension, in the path of the North Atlantic Current and west of Europe. A negative relationship between diversity and its spatial dependence is found in almost all the oceanic regions. This relationship is constant at all temporal scales. At an annual scale, relationships between diversity, spatial dependence and climatic indices have been investigated. Some links have been detected but both the intensity and the sign of these relationships vary greatly in space. The regime shift that took place in the North Sea after 1988 involved a sharp change in the diversity of calanoid copepods and a significant strengthening in the contrast between the neritic and oceanic spatial dependence.

KEY WORDS: Spatial scale of variability · Point cumulative semi-variograms · Calanoid copepods · Pelagic diversity · Continuous Plankton Recorder (CPR) survey