Fish larvae associations with cultivated giant kelp forests: First evidence from a large-scale farm in the Benguela upwelling systeM
Description
The dataset comprises ichthyoplankton (fish larvae) survey data collected between May 2024 and March 2025 from two coastal sampling sites off Lüderitz, Namibia: Shearwater Bay (SWB), a cultivated giant kelp (Macrocystis pyrifera) farm, and Far North Control (FNC), a nearby kelp-free control site. The raw data include sampling dates, sample identification numbers, site information, taxonomic identification of fish larvae (family, species, and common name where applicable), larval developmental stage, and the abundance of each taxon recorded per sample. The workbook also contains processed datasets summarising species richness and diversity, community composition, larval abundance, and correlations between biological and environmental variables. These data were collected to assess the role of cultivated kelp forests as potential nursery habitats by comparing the abundance, diversity, and composition of fish larvae between the cultivated kelp habitat and an adjacent control site.
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Steps to reproduce
Reproducible Fish Larvae Sampling Protocol 1. Define sampling sites Select sampling locations within: Cultivated kelp forest site (SWB): sampling transects positioned adjacent to cultivated kelp canopies within the kelp farm. Kelp-free control site (FNC): sampling transects positioned in an area lacking kelp habitat. Maintain consistent sampling conditions by using the same sampling design and gear at both sites. 2. Establish sampling schedule Conduct ichthyoplankton sampling during predetermined months when environmental conditions permit. Sampling was conducted during: July 2024 (two sampling events) August 2024 October 2024 March 2025 Record weather and sea-state conditions during each sampling event, as adverse conditions may restrict sampling frequency. 3. Prepare sampling equipment Use a WP2 zooplankton net with: Mesh size: 200 μm Mouth opening diameter: 100 cm Prepare: 250 ml polyethylene sample bottles 4% buffered formalin preservative Sample labels containing: Site name Date Transect number Replicate number 4. Deploy zooplankton net Deploy the WP2 net to an effective sampling depth of approximately 7 m. Calculate effective depth using: Sampling depth=wire length×cos(45 ∘ ) Tow the net along predetermined transects: Number of transects: six per site Transect length: 100 m Transects positioned adjacent to kelp habitat at SWB and equivalent locations at FNC. 5. Conduct plankton tows Tow the net at a constant vessel speed: Target speed: 1.5–3 knots Adjust speed according to sea-state conditions. Maintain consistent towing duration and direction where possible. Complete six replicate transects per site during each sampling month. 6. Sample collection and preservation Retrieve the net after completion of each tow. Transfer collected plankton material into labelled 250 ml polyethylene bottles. Immediately preserve samples using: 4% buffered formalin Store preserved samples until laboratory processing. Sampling effort achieved: Two sites (SWB and FNC) Six replicate transects per site per sampling month Five sampling months Total samples collected: 60 Laboratory Processing Protocol 7. Prepare samples for examination Examine preserved samples under a calibrated light microscope. Use an eyepiece micrometer calibrated for accurate measurements. 8. Measure and identify fish larvae For each fish larva: Measure: Total length (mm) Record morphological characteristics: Myotome counts Pigmentation patterns Jaw morphology Developmental characteristics Capture digital images using DinoCapture software. Produce standardized hand drawings of representative specimens to assist morphological comparisons. 9. Taxonomic identification Identify larvae using the following references: Two Oceans: A Guide to Marine Life of Southern Africa Guide to Ichthyoplankton of the Southeast Atlantic (Benguela Current Region) (Olivar & Fortuño, 1991) Standard protocols from the International Course on Ichthyoplankton