DOI: 10.15493/dea.mims.13912023
title: Long-term monitoring of inshore temperatures in Elands Bay to support physiological research

description: Long-term monitoring of inshore temperatures in Elands Bay to support physiological research.
description: To better understand the physiological effects of climate change and ocean acidification on marine organisms, information on the environmental conditions experienced in their natural habitats is required. Data from long-term monitoring studies capture in situ variability of environmental parameters that are used to relate experimental findings with field conditions. Elands Bay on the west coast of South Africa is a key location for such research and monitoring. It is a popular location for West Coast rock lobster (Jasus lalandii) fishing and therefore an important sentinel site for a commercial fishery species and the benthic communities upon which it depends. Low pH conditions exist along the west coast due to effects of upwelling, while cold-bottom waters in Elands Bay often result in low oxygen events responsible for mass walkouts of rock lobster. Additional exposure to extreme stressors associated with climate change can exacerbate impacts on their physiological processes. For example, acute thermal stress experienced during a marine heatwave may cause a rapid deterioration of cellular processes and performances beyond tolerance limits, affecting survival, growth and development. In South Africa, occurrences of marine heatwaves are increasing all along the coastline, and occur on average at least once a year. Data on temperature extremes are therefore important to design experiments and calculate thermal windows. We initiated long-term monitoring of inshore environmental parameters in Elands Bay by deploying temperature loggers in representative habitat types: intertidal rock pools varying in surface area, volume and position along the shore, sun-exposed habitats, and subtidal habitats. Five rockpools situated at least 5m apart were chosen, and in each rockpool, two HOBO TidbiT temperature loggers set to record temperature measurements every five minutes are deployed at different positions (always North facing) using two methods - (i) attached via a cable tie to an iBOLT drilled into the rock (usually at a shallow position), (ii) inside a plastic housing embedded in a cement mooring block (usually at a deeper position). The mooring block is held in place by a chain secured to a rock. Significantly different temperature readings between the two deployment methods are recorded, with iBOLT loggers usually yielding higher temperatures. Temperature loggers attached to iBOLT are however more conspicuous and therefore subject to theft, with loss of data. The subtidal logger is positioned at an overhang in the same vicinity of the rockpools and housed in a mooring block. Data for the subtidal are available from 5 June 2023 onwards. The sun-exposed logger is situated at the nearby Fisheries Research office where it is attached underneath the gutter close to the top of the roof (facing the sun but shaded). Here we present both raw and clean temperature data from rockpools, the subtidal and exposed environment. This is an ongoing project with data collected every three to four months.
description: The details of each pool are captured in the 'README' file. The Hobo-tidbit temperature loggers were set to record temperature every 5 minutes. In each rockpool, two temperature loggers are deployed at different positions (always North facing) using two methods - (i) attached via a cable tie to an ibolt drilled into the rock (usually at a shallow position), (ii) inside a plastic housing embedded in a cement mooring block (usually at a deeper position). The mooring block is held in place by a chain secured to a rock. Data were extracted from the loggers using Hoboware Pro software and exported into excel files. Times are GMT+2. The data available are the raw files (all temperatures even outside of the rockpools) and 'clean' files where only the temperatures recorded once loggers were placed into the rockpools are provided. Clean data are presented here for each pool (x2 loggers per pool) although gaps do exist where ibolt loggers are missing or loggers failed to record. To avoid the inclusion of any 'handling' temperatures in the clean datasets, the temperatures extracted are from ten minutes once loggers are deployed, and 10 minutes before they are removed to download data.