Regional assessment of status and trends in imposex (VDS) in whelks

Overview

The 2024 OSPAR CEMP assessment of contaminant and biological effects data includes an assessment of the status and trends of imposex (VDS) in whelks at monitoring stations throughout the OSPAR area. Assessments are made for a large number of time series, each of VDS measurements in a single species at a single monitoring station. This document synthesises the results of the individual time series to assess the status and trends of VDS at the MIME regional level. For simplicity, the term ‘region’ is used throughout to describe MIME regions. OSPAR regions are always referred to as such.

The regional status assessments presented in this document are integrated with regional status assessments for contaminants using the CHASE approach. Details can be found here.

The following sections:

• summarise the individual time series results
• describe the methods used to combine the individual time series results to estimate regional status and trends
• present the estimates of regional trends
• present the estimates of regional status

Summary of individual time series results

A time series of VDS measurements is assessed for status if:

• there is at least one year with data in the period 2017 to 2022
• there are at least three years of data over the whole time series

A time series is also assessed for trends if:

• there are at least three years of data with individual measurements or four years of data with pooled measurements

Note that time series from Ireland with data from 2023 are also included in the assessment.

The first tab below shows all the monitoring stations where there are individual time series assessments of trend or status for VDS. The purple circles are stations where there is a trend assessment and the light blue cirles are stations where there is only a status assessment,

The next set of tabs show the trend and status assessments for VDS. The colours have the following meaning:

• blue: the mean VDS is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
• green: the mean VDS is significantly (p < 0.05) below the Environmental Assessment Criterion (EAC)
• red: the mean VDS is not signficantly below the EAC
• black: there are no assessment criteria available

And the shapes have the following meaning:

• downward triangle: the mean VDS is significantly decreasing (p < 0.05)
• circle: there is no significant change in mean VDS (p > 0.05) or there are too few years to test for trends
• upward triangle: the mean VDS is significantly increasing (p < 0.05)

The final set of tabs give:

• the number of time series with upwards, downwards or no trend in each MIME and OSPAR region
• the same information presented as proportions
• the number of time series with blue, green or red status in each MIME and OSPAR region
• the same information presented as proportions

Stations

VDS

Trend summary (numbers)

Number of time series with upwards, downwards or no trend by MIME and OSPAR region

OSPAR region	MIME region	status	VDS
1	Barents Sea	upward trend	0
		no trend	0
		downward trend	2
	total	upward trend	0
		no trend	0
		downward trend	2
2	Norwegian Trench	upward trend	0
		no trend	0
		downward trend	3
	Northern North Sea	upward trend	0
		no trend	11
		downward trend	18
	Skagerrak and Kattegat	upward trend	1
		no trend	2
		downward trend	14
	Southern North Sea	upward trend	0
		no trend	4
		downward trend	5
	Channel	upward trend	0
		no trend	30
		downward trend	2
	total	upward trend	1
		no trend	47
		downward trend	42
3	Irish and Scottish West Coast	upward trend	0
		no trend	4
		downward trend	7
	Irish Sea	upward trend	0
		no trend	6
		downward trend	13
	Celtic Sea	upward trend	0
		no trend	16
		downward trend	12
	total	upward trend	0
		no trend	26
		downward trend	32
4	Northern Bay of Biscay	upward trend	0
		no trend	10
		downward trend	2
	Iberian Coast	upward trend	0
		no trend	11
		downward trend	6
	total	upward trend	0
		no trend	21
		downward trend	8

Trend summary (proportions)

Proportion of time series with upwards, downwards or no trend by MIME and OSPAR region

OSPAR region	MIME region	status	VDS
1	Barents Sea	upward trend	0
		no trend	0
		downward trend	100
	total	upward trend	0
		no trend	0
		downward trend	100
2	Norwegian Trench	upward trend	0
		no trend	0
		downward trend	100
	Northern North Sea	upward trend	0
		no trend	38
		downward trend	62
	Skagerrak and Kattegat	upward trend	6
		no trend	12
		downward trend	82
	Southern North Sea	upward trend	0
		no trend	44
		downward trend	56
	Channel	upward trend	0
		no trend	94
		downward trend	6
	total	upward trend	1
		no trend	52
		downward trend	47
3	Irish and Scottish West Coast	upward trend	0
		no trend	36
		downward trend	64
	Irish Sea	upward trend	0
		no trend	32
		downward trend	68
	Celtic Sea	upward trend	0
		no trend	57
		downward trend	43
	total	upward trend	0
		no trend	45
		downward trend	55
4	Northern Bay of Biscay	upward trend	0
		no trend	83
		downward trend	17
	Iberian Coast	upward trend	0
		no trend	65
		downward trend	35
	total	upward trend	0
		no trend	72
		downward trend	28

Status summary (numbers)

Number of time series with each status by MIME and OSPAR region

OSPAR region	MIME region	status	VDS
1	Barents Sea	blue	2
		green	0
		red	0
	total	blue	2
		green	0
		red	0
2	Norwegian Trench	blue	2
		green	1
		red	0
	Northern North Sea	blue	4
		green	23
		red	2
	Skagerrak and Kattegat	blue	3
		green	4
		red	11
	Southern North Sea	blue	3
		green	5
		red	1
	Channel	blue	11
		green	17
		red	4
	total	blue	23
		green	50
		red	18
3	Irish and Scottish West Coast	blue	6
		green	2
		red	3
	Irish Sea	blue	4
		green	12
		red	3
	Celtic Sea	blue	5
		green	21
		red	2
	total	blue	15
		green	35
		red	8
4	Northern Bay of Biscay	blue	2
		green	7
		red	0
	Iberian Coast	blue	0
		green	15
		red	13
	total	blue	2
		green	22
		red	13

Status summary (proportions)

Proportion of time series with each status by MIME and OSPAR region

OSPAR region	MIME region	status	VDS
1	Barents Sea	blue	100
		green	0
		red	0
	total	blue	100
		green	0
		red	0
2	Norwegian Trench	blue	67
		green	33
		red	0
	Northern North Sea	blue	14
		green	79
		red	7
	Skagerrak and Kattegat	blue	17
		green	22
		red	61
	Southern North Sea	blue	33
		green	56
		red	11
	Channel	blue	34
		green	53
		red	13
	total	blue	25
		green	55
		red	20
3	Irish and Scottish West Coast	blue	55
		green	18
		red	27
	Irish Sea	blue	21
		green	63
		red	16
	Celtic Sea	blue	18
		green	75
		red	7
	total	blue	26
		green	60
		red	14
4	Northern Bay of Biscay	blue	22
		green	78
		red	0
	Iberian Coast	blue	0
		green	54
		red	46
	total	blue	5
		green	60
		red	35

Regional assessment - methods

Tabulating the number of time series with each status category by region provides a quick summary of the individual time series results. However, it does not provide an objective regional assessment of status. Similarly, tabulating the number of time series with an upward or downward trend does not provide an objective regional assessment of trend. This section describes how the individual time series results can by synthesised in a meta-analysis to assess both status and trend at the regional level.

Trends

For a regional trend assessment, the trend in each time series is summarised by the estimated odds ratio of the VDS of an individual whelk being above the EAC in one year relative to the previous year. Values of 1 indicate no trend; i.e. the odds of an individual being above the EAC in one year are the same as in the year before. Values < 1 indicate that the odds of being above the EAC in one year are lower than in the year before, so there is a decline in the level of imposex. Conversely, values > 1 indicate an increase in the level of imposex. Regional trends are then estimated by fitting the following linear mixed model by restricted maximum likelihood:

• response: trend (odds ratio)
• fixed model: region
• random model: trend estimation variation + residual variation

The fixed model means that a trend is estimated for each region. The random model has two terms:

• trend estimation variation is the variance of the trend estimates from the individual time series analysis, assumed known and fixed
• residual variation is the variation that cannot be explained by any of the fixed effects or the other random effects

The meta-analysis is restricted to time series from monitoring stations that are classified as ‘representative’ or ‘impacted’ (close to a point source). ‘Baseline’ stations (near pristine conditions or only subject to very diffuse inputs) are omitted because any trends there will likely be caused by different processes to those at representative or impacted stations. Note that the inclusion of impacted stations differs from the approach used for contaminants (where they are excluded). Many imposex monitoring stations were chosen because they were close to harbours (i.e. impacted). However, the ban of TBT (which causes imposex) will have been the major driver of trends in imposex throughout the OSPAR area, so it seems plausible that trends in VDS might be similar (on the logistic scale) at both impacted and representative stations.

The meta-analysis is further restricted to regions with at least three trend stations with good geographic spread. Three stations is considered the minimum required to provide some sort of evidence base at the regional level.

Status

For a regional status assessment, the status of each time series is summarised by the ratio between the estimated mean VDS in the final monitoring year and the assessment critrion. This ensures that status is always measured on the same scale, even though the assessment criterion might vary between time series (because VDS is measured in a different species). The ratio is transformed to the square root scale (to better satisfy modelling distributional assumptions) and essentially the same linear mixed model as for trends is then fitted:

• response: status (sqrt(mean VDS / assessment criterion))
• fixed model: region
• random model: status estimation variation + residual variation

where status estimation variation is the variation in the status estimates from the individual time series analysis, assumed known and fixed.

There are no restrictions on the time series used in the status meta-analysis based on the classification of the monitoring station; time series from baseline, representative and impacted stations are all included.

Again, the meta-analysis is restricted to regions with at least three status stations with good geographic spread.

Presentation

The results of the status regional assessment are back-transformed for presentation. A value of 1 indicates that the regional mean VDS is equal to the assessment criterion; a value of 0.5 indicates that it is half the assessment criterion; and a value of 2 indicates that it is twice the assessment criterion. There is no need to back-transform the estimated regional trend, which is on the odds ratio scale.

Regional assessment - availability of time series

This section provides more detail on the number and geographic spread of the time series available for the meta-analyses. The tabs show the stations with parametric trend and status assessments for each OSPAR region in turn, having excluded trend assessments at baseline stations. The purple circles are stations where there is a trend assessment and the light blue cirles are stations where there is only a status assessment,

The following regions have an insufficient number of time series or spread of stations and are excluded from the regional assessment:

• trend: Barents Sea, Norwegian Trench
• status: Barents Sea, Norwegian Trench

OSPAR region 1

OSPAR region 2

OSPAR region 3

OSPAR region 4

Regional trends

The first 2 tabs show:

• Regional trends: estimates of the regional trend for VDS with pointwise 95% confidence intervals
• Individual time series: the trend estimates from the individual time series on which the regional assessment is based. The estimates for regions with insufficient geographic spread (and excluded from the meta-analysis) are also shown.

The symbols in all these plots have the following interpretation:

• downward triangle: the mean VDS is significantly decreasing (p < 0.05)
• circle: there is no significant change in mean VDS (p > 0.05)
• upward triangle: the mean VDS is significantly increasing (p < 0.05)

The final tab shows the estimates of the regional trend in VDS.

Regional trends

Individual time series

Estimates by region

This table shows the estimates of the regional trend:

• trend: the estimated mean odds ratio of the VDS of an individual whelk being above the EAC in one year relative to the previous year
• se: the corresponding standard error
• lower, upper: the corresponding pointwise 95% confidence limits

MIME region	trend	se	lower	upper
Northern North Sea	0.74	0.04	0.66	0.82
Skagerrak and Kattegat	0.79	0.05	0.68	0.89
Southern North Sea	0.48	0.07	0.34	0.62
Channel	0.78	0.05	0.69	0.88
Irish and Scottish West Coast	0.57	0.07	0.43	0.71
Irish Sea	0.66	0.05	0.56	0.76
Celtic Sea	0.63	0.05	0.54	0.73
Northern Bay of Biscay	0.68	0.10	0.49	0.87
Iberian Coast	0.80	0.06	0.69	0.90

Regional status compared to the Environmental Assessment Criterion (EAC)

The first 2 tabs show:

• Regional status: estimates of the regional status for VDS with pointwise upper one-sided 95% confidence intervals
• Individual time series: the status estimates from the individual time series on which the regional assessment is based. The estimates for regions with insufficient geographic spread (and excluded from the meta-analysis) are also shown.

The symbols in all the plots have the following interpretation:

• blue: the mean VDS is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
• green: the mean VDS is significantly (p < 0.05) below the EAC
• red: the mean VDS is not significantly below the EAC

Note that to see why some points might be coloured blue, it is necessary to look ahead to the next section, where status is compared to the BAC. Unfortunately, it isn’t easy to present the assessment of status relative to the EAC with the assessment of status relative to the BAC because the ratio of the BAC to the EAC can vary between species.

The final tab shows the estimates of the regional status in VDS.

Regional status

Individual time series

Estimates by region

This table shows the estimates of the regional status:

• status: the estimated mean sqrt (VDS / EAC)
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• VDS: the estimated mean VDS relative to the EAC
• VDS upper: the corresponding pointwise upper one-sided 95% confidence limit

MIME region	status	se	upper	VDS	VDS upper
Northern North Sea	0.40	0.08	0.53	0.16	0.29
Skagerrak and Kattegat	0.81	0.10	0.98	0.66	0.97
Southern North Sea	0.10	0.15	0.35	0.01	0.12
Channel	0.33	0.08	0.45	0.11	0.21
Irish and Scottish West Coast	0.29	0.13	0.51	0.08	0.26
Irish Sea	0.28	0.11	0.46	0.08	0.21
Celtic Sea	0.41	0.08	0.55	0.17	0.30
Northern Bay of Biscay	0.21	0.15	0.45	0.04	0.20
Iberian Coast	1.06	0.09	1.21	1.12	1.46

Regional status compared to the Background Assessment Concentration (BAC)

The first 2 tabs show:

• Regional status: estimates of the regional status for VDS with pointwise upper one-sided 95% confidence intervals
• Individual time series: the status estimates from the individual time series on which the regional assessment is based. The estimates for regions with insufficient geographic spread (and excluded from the meta-analysis) are also shown.

The symbols in all the plots have the following interpretation:

• blue: the mean VDS is significantly (p < 0.05) below the BAC
• green: the mean VDS is significantly (p < 0.05) below the Environmental Assessment Criterion (EAC)
• red: the mean VDS is not significantly below the EAC

The final tab shows the estimates of the regional status in VDS.

Regional status

Individual time series

Estimates by region

This table shows the estimates of the regional status:

• status: the estimated mean sqrt (VDS / BAC)
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• VDS: the estimated mean VDS relative to the BAC
• VDS upper: the corresponding pointwise upper one-sided 95% confidence limit

MIME region	status	se	upper	VDS	VDS upper
Northern North Sea	1.05	0.13	1.27	1.11	1.62
Skagerrak and Kattegat	0.10	0.34	0.65	0.01	0.43
Southern North Sea	0.18	0.33	0.72	0.03	0.52
Channel	0.82	0.12	1.01	0.67	1.02
Irish and Scottish West Coast	0.71	0.20	1.04	0.50	1.08
Irish Sea	0.67	0.18	0.96	0.45	0.92
Celtic Sea	1.05	0.13	1.26	1.09	1.59
Northern Bay of Biscay	0.54	0.23	0.93	0.29	0.86
Iberian Coast	1.62	0.17	1.90	2.61	3.62