ecotraj: Ecological Trajectory Analysis

#' North Sea zooplankton dataset
#' 
#' A multi-annual (1958-2021), monthly resolved dataset of zooplankton community composition in the
#' Northern and Southern North Sea used to illustrate Cyclical Ecological Trajectory Analysis (CETA)
#' 
#' The data describes the zooplankton community in the North Sea sampled 
#' by the [Continuous Plankton Recorder (CPR)](https://www.cprsurvey.org/) survey.
#' The CPR survey operates through towing of CPR samplers across commercial routes of merchant ships
#' (plankton silk mesh = 270 microm, sampling depth = 5-10 m). 
#' When brought back to the laboratory, plankton is counted and identified taxonomically following standardized protocols.
#' The raw data provided by the survey (\doi{10.17031/66f12be296d70}). 
#' was reformated into two monthly-resolved time series of the commonest zooplankton taxa in the Northern North Sea
#' (\code{"NNS"}) and the Southern North Sea (\code{"SNS"}). During data processing, a smoothing was performed 
#' by taking a rolling average (for each month, 5 values were averaged: a 3 months window + the corresponding month of the previous and next years). 
#' The abundances were finally Hellinger-transformed, making them amenable to ecological diversity study.
#' 
#' @encoding UTF-8
#' @format northseaZoo is an object of class \code{\link{list}} composed of 3 objects:
#' 
#' \describe{
#'  \item{Hellinger}{a \code{\link{data.frame}} containing Hellinger-transformed zooplankton taxa abundances.}
#'  \item{times}{a vector indicating the date (in year) associated to each line in \code{Hellinger}.}
#'  \item{sites}{a vector indicating the site (\code{"NNS"} = Northern North Sea, \code{"SNS"} = Southern North Sea) associated to each line in \code{Hellinger}.}
#' }
#' 
#' @name northseaZoo
#' @aliases northseaZoo 
#' @docType data
#' @author Nicolas Djeghri, \enc{Université}{Universite} de Bretagne Occidentale, France
#' @author Pierre \enc{Hélaouët}{Helaouet} and CPR survey staff, Marine Biological Association, United Kingdom
#' @keywords data
#' 
#' @seealso \code{\link{trajectoryCyclical}}
#' 
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