Dataset for the "Seasonal dynamics and environmental regulation of sessile invertebrate assemblages in natural and farmed kelp habitats" Manuscript
Description
The study tested the hypothesis that seasonal and environmental variability influences the composition and relative abundance of sessile invertebrate assemblages, and that these patterns differ between habitats inside a kelp farm and natural reference sites. The study had two objectives: (i) to assess whether marine environmental conditions, including temperature, salinity, and total dissolved solids, influence the spatio-temporal patterns of sessile invertebrates at shearwater Bay kelp farm and Diaz Point native kelp forest; and (ii) to investigate seasonal dynamics in the composition and abundance of these assemblages, providing insights into their ecological roles in natural and farmed kelp systems. Two complementary datasets were collected. The quarterly survey (QS), conducted at Diaz Point and Shearwater Bay, recorded abundance of sessile invertebrates on structures alongside environmental parameters. Counts and percentage cover were normalized to calculate relative abundances, and Redundancy Analysis (RDA) was used to assess correlations between environmental variables and assemblage composition. These data show that environmental factors, particularly temperature, salinity, and total dissolved solids, are correlated with relative abundances of key taxa, indicating their influence on community structure. The experimental survey (ES), conducted at Shearwater Bay inside and outside the kelp farm, monitored specific quadrats (10 x 10cm) on structures (float tops, rope sides with tags, and block surfaces). Due to dense red algae growth, a semi- and later full-destructive approach was employed to accurately assess percent cover and visibility of sessile taxa. Temporal patterns in assemblage composition were analyzed using the Friedman test, revealing clear seasonal variability across sites and structure components. These datasets provide detailed records of species identity, abundance, percent cover, environmental parameters, and structure-specific observations. They can be used to explore seasonal dynamics, environmental drivers, and habitat-specific assemblage patterns. Researchers can reproduce the surveys by deploying similar structures, applying fixed quadrats, recording environmental variables, and using comparable statistical approaches. Percent cover, visibility scores, and normalized abundances allow interpretation of community composition and ecological responses to environmental variability in natural and farmed kelp systems.
Files
Steps to reproduce
The data were collected to examine seasonal variability in sessile invertebrate assemblages and the influence of environmental factors on their relative abundance across two surveys. The quarterly survey (QS) was conducted at Diaz Point and Shearwater Bay, focusing on the abundance of sessile invertebrates and the environmental drivers affecting their relative abundance. While diversity indices were calculated for a separate study, this manuscript only considers environmental correlations. During the QS, sessile invertebrates were recorded using two metrics, individual counts and percentage cover, on deployed structures, and environmental parameters, including temperature, salinity, dissolved oxygen, and pH, were measured using handheld multiparameter sonde. Counts were normalized to calculate relative abundances, and statistical analysis was conducted using Redundancy Analysis (RDA) in R to evaluate the relationship between environmental factors and assemblage composition. The experimental survey (ES) was conducted exclusively at Shearwater Bay, both inside the kelp farm and outside the farm. This survey targeted seasonal changes in the assemblages on experimental structures using 10 x 10cm quadrats placed on the top of the float, the sides of the rope with tags, and both sides of the block. Initially, a semi-destructive approach was used to remove obstructing red algae and sediment from quadrats, and as algal growth increased, a full-destructive method was applied to one structure per site per month to expose sessile organisms fully. Percent cover and visibility scores of sessile taxa were recorded at each sampling event. Temporal changes in the quadrat data were analyzed using the Friedman test to assess seasonal variability across structure sections and sites in SPSS. Datasets include site, structure, species names, abundance or percent cover, and environmental measurements. The methods described allow other researchers to reproduce the surveys, apply similar destructive or semi-destructive monitoring approaches, and analyze environmental influences on sessile invertebrate assemblages in comparable marine habitats.
Institutions
- University of Namibia Faculty of Agriculture and Natural Resources