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Beyond annual metrics: Linking seasonal population dynamics to vertical oyster reef growth - PubMed

  • ️Mon Jan 01 2024

. 2024 Sep 17;14(9):e70238.

doi: 10.1002/ece3.70238. eCollection 2024 Sep.

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Beyond annual metrics: Linking seasonal population dynamics to vertical oyster reef growth

Kai Pfennings et al. Ecol Evol. 2024.

Abstract

Oysters are ecosystem engineering species building reef-like biogenic structures in temperate shallow water environments, serving as biodiversity hotspots. Recently, also their ecosystem services such as fish nursery, pollutants sink and self-sustaining coastal protection mechanisms came into a research focus. In light of accelerated sea level rise and increasing environmental dynamics, a determination of vertical growth rates of these biosedimentary structures is paramount in assessing their resilience. This study embarked on a comprehensive survey of seasonal vertical reef growth rates using terrestrial laser scanning and related population dynamics of two intertidal reefs built by the non-native oyster Magallana gigas in the Wadden Sea. We quantified median reef growth at 19.8 mm yr-1 for the Kaiserbalje reef and 17.5 mm yr-1 for the Nordland reef. Additionally, we tested the hypothesis that the seasonal variations in reef growth rates correspond to the local population dynamics, mainly the parameters of shell length and abundance which mirror delayed effects from previous spawning events. Shell growth rates were 0.03-0.06 mm d-1 in winter and 0.10-0.16 mm d-1 in summer, mean oyster abundance from autumn 2019 to spring 2022 was 627 ± 43 ind. m-2 and 338 ± 87 ind. m-2 at the Kaiserbalje and Nordland reefs respectively. Minor reef growth in the topmost reef area reflects an emerging equilibrium of the vertical reef position to actual sea level. Our findings are in accordance with growth of natural Crassostrea virginica reefs on the US East Coast, indicating potential resilience to actual and predicted sea level rise scenarios. Moreover, understanding local hydro-morphodynamic feedback linked to sea level rise will be vital in predicting the three-dimensional stability of these biosedimentary structures and habitats.

Keywords: Magallana gigas; Wadden Sea; biosedimentary structure; ecosystem engineering species; sea level rise; terrestrial laser scanning.

© 2024 The Author(s). Ecology and Evolution published by John Wiley & Sons Ltd.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1

(a) Location of the study sites (red triangles) in the central Wadden Sea (intertidal areas in dark grey (Federal Waterways Engineering and Research Institute (BAW), 2024)). (b) Drone image mosaic of oyster reef Nordland (NL) (53.6424960° N, 008.9411970° E). (c) Drone image mosaic oyster reef Kaiserbalje (KB) (53.6470116° N, 008.2664760° E). Drone image mosaic of KB was modified after Hoffmann et al. (2023), mosaic of NL was generated with the same method. Reef area is outlined in red (Nationalparkverwaltung Niedersächsisches Wattenmeer, 2021). Black triangles: Biological sampling locations, dashed squares: Terrestrial laser scanning area. Map created in QGIS version 3.32.2.

FIGURE 2
FIGURE 2

Analysis of elevation and vertical reef growth at the Kaiserbalje reef. Red scale bars indicating 10 × 1 × 1 m, y‐axis indicating north direction. (a) Elevation model of the Kaiserbalje ROI in March 2020. The detailed view displays reef internal sediment dynamics and reef internal drainage. (b) Visualization of M3C2 vertical distance between March 2020 and March 2022. Median vertical distance is added and centres the divergent colour scale.

FIGURE 3
FIGURE 3

Correlation of biotic and abiotic factors in oyster and reef growth rates, respectively, for the reefs Kaiserbalje (KB) and Nordland (NL). (a) Correlation of daily oyster growth rates with temperature (percentage of days above 10°C), based on the combined mean growth rate data from the 2018 and 2019 cohorts. (b) Correlation between daily vertical reef growth rates and daily oyster growth rates from seasonal samplings. Correlation of daily vertical reef growth rate with the product of daily oyster growth rate and square root transformed abundance of oysters (c) >25 mm, (d) >50 mm and (e) >75 mm.

FIGURE 4
FIGURE 4

Analysis of elevation and vertical reef growth at the Nordland reef. Red scale bars indicating 10 × 1 × 1 m, y‐axis indicating north direction. (a) Elevation model of the Nordland ROI in September 2020 (a). The detailed view displays dynamics at the reef edge. (b) Visualization of M3C2 vertical distance between September 2020 and April 2022. Median vertical distance is added and centres the divergent colour scale.

FIGURE 5
FIGURE 5

Analysis of oyster reef growth across elevation and aerial exposure gradients for (a) Kaiserbalje (KB) and (b) Nordland (NL). The median vertical growth for 20‐mm elevation bins is represented by red dots, with whiskers denoting the 95% confidence interval. The colour gradient illustrates the combined density for each 20‐mm elevation bin and a 2‐mm vertical reef growth bin. Aerial exposure time is given in per cent in relation to data from nearby tide gauges as measured exposure time (MET) and using mean low water to mean high water level (MTR).

FIGURE 6
FIGURE 6

Live wet weight (a) and abundance >25 mm shell length (SL) (b) per square metre, and the condition index (ci) (c) of M. gigas for Kaiserbalje (KB) (green) and Nordland (NL) (blue) from autumn 2019 (a) to spring 2022 (S), with data from prior reef monitoring 2006–2013. The box plots illustrate the median as the horizontal line inside the box, the mean indicated by the dot within the box, the 25th and 75th percentiles defined by the box boundaries, the 10th and 90th percentiles denoted by the whiskers, and outliers shown as grey dots.

FIGURE 7
FIGURE 7

Length frequency distribution of M. gigas from autumn 2019 to spring 2022 at the oyster reef locations: Kaiserbalje (KB) (a) and Nordland (NL) (b). The live oyster abundance depicts the mean abundance of individuals per square metre, categorized in 5‐mm length bins. Colour gradients indicate the live wet weight of each corresponding 5 mm bin.

FIGURE 8
FIGURE 8

Daily mean water temperature in the Kaiserbalje area from 2006 to April 2022. The red line indicates temperatures exceeding 19.5°C, while the blue line represents temperatures below 5°C. Years marked by highest consecutive days (n > 28) exceeding 19.5°C are 2006 (n = 39), 2010 (n = 29), 2014 (n = 35), 2018 (n = 40) and 2021 (n = 34).

FIGURE A1
FIGURE A1

Point cloud perspective view of the terrestrial laser scanning area at the Kaiserbalje oyster reef. Intensity values are coloured and show the higher backscattered laser intensity on the oyster reef. Overview map in the left corner shows the viewpoint. Red scaling quadrat measures 1 × 1 × 1 m.

FIGURE A2
FIGURE A2

Median vertical oyster reef growth across elevation gradients for Kaiserbalje (a) and Nordland (b). Median vertical oyster reef growth across aerial exposure gradients for Kaiserbalje (c) and Nordland (d). Aerial exposure time is given in per cent in relation to seasonal data from nearby tide gauges as measured exposure time (MET). The median vertical growth for each 20 mm elevation bin is represented by symbols, with whiskers denoting the 95% confidence interval.

FIGURE A3
FIGURE A3

Mean oyster size over the study period by cohorts. Circles indicate the 2018 cohorts for Kaiserbalje (KB) and Nordland (NL), while triangles indicate the 2019 cohorts. Whiskers indicate ±1 SD.

FIGURE A4
FIGURE A4

Relationship between M. gigas shell length (SL) (mm), mean live oyster abundance m−2 and individual live wet weight (LWW) (g) at the Kaiserbalje oyster reef. The dashed green line and triangles represent the trimmed mean oyster abundance m−2 for size classes from 2006 to 2022, with the highest and lowest 10% of mean values excluded. The scale for mean live oyster abundance is displayed logarithmically. The relationship between individual live wet weight and shell length (SL) is depicted by the solid black logistic regression line. Individual measurements of live wet weight are represented as grey dots.

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