Monitoring seaweed at Waipu Cove

Background

Over the past years, the Waipu Cove beach in Northland has experienced stranding of large amounts of filamentous algae that have a negative impact on the tourism activities and the ecology of the area. As part of their ongoing work to improve the knowledge of the extent, seasonality, and the potential causes of the issue, the Waipu Cove Reserve Trust Board (WCRTB) commissioned Cawthron Institute (Cawthron) to design a medium to long-term (2–5 years) monitoring programme of algae on the shore and in the water column in the area.

For this purpose, a survey was designed to record the occurrence and spatial extent (area and percentage cover) of algal blooms at Waipu Cove. The goal of the survey is to compile a medium-term (2–5 years) algal dataset that can be used to identify spatial and temporal patterns in algal stranding events. An additional aim is that the collected dataset can later be used in conjunction with Northland Regional Council (NRC) water quality data to identify potential environmental drivers and to develop a predictive models of algal stranding events.

The online survey

A simple online survey was created using the Survey123 platform and can be found at this link. The survey has nine questions that are designed to be answered by non-professional volunteers, ensuring easy and sufficient implementation that will allow the collation of an extensive and representative dataset. In this context, we encourage WCRTB to promote the survey among their community members to engage volunteers in a “citizen science” approach that will allow creating scientific knowledge, awareness, and adequate data for the purpose of the project. The online survey can be shared using the web link or the QR code in Figure 1.

Figure 1: QR code for the Waipu Cove macroalgae online survey. Scan the QR code to open the survey on a device.

The online survey can be used in the field through any web browser on a smart phone or tablet. Ideally, surveys would be carried out at least once every month in each of the study sites. Details of the survey questions are as follow:

  1. Date and time: this field is automatically populated by the system, so users do not need to enter any information. This ensures there are no data entry errors and that the time and date format are consistent.

  2. Sampling location: the online survey provides a map where the user can show where the record is from. The online survey can automatically use the location of the device, or the user can press on the map to either search or drag a marker to a particular location. We recommend using the location provided by the mobile device, as it less prone to errors and provides sufficient accuracy for the purpose of the survey.

  3. Sample type: choose from:

  • Beach

  • Floating (water column)

  1. Area of the algal patch: record the approximate spatial extent of the algal patch or stranding in square metres. Five categorical options are provided:

  • No seaweed

  • Small (less than 1 m2)

  • Medium (between 1 and 100 m2)

  • Large (between 100 and 10,000 m2)

  • Extensive (more than 10,000 m2)

Some references of areas are provided as:

1 m2 = 1 x 1 m is like the area of a square of one-by-one steps.

100 m2 = 10 x 10 m is like the area of half a tennis court (ten-by-ten steps).

10,000 m2 = 100 x 100 m is like the area of a rugby field.

  1. Percentage cover: users are asked to use a 1 x 1 m quadrat frame to estimate the percentage covered by the seaweed. See this link for instructions on how to make a quadrat. If users do not have a quadrat, they can mark a 1 m2 square area (approximately one adult step for each of the four sides) in the sand or seaweed. Place the quadrat randomly, for example by closing your eyes and throwing the quadrat onto the study area. Record the data for quadrat 1 by checking the appropriate category:

  • 0% (no seaweed)

  • <1% (present but very sparse)

  • 2-10% (small amounts)

  • 10-50% (large amounts)

  • >50% (more than half of the quadrat)

If the algae are in the water, the recorder can estimate cover from the shore if necessary and report this in the notes section (see 8 below).

  1. Weight (optional): collect all algae in a 0.25 x 0.25 m quadrat and put into a lightweight container such as a supermarket carrier bag or mesh grocery bag. Weigh using a digital balance and record the weight for quadrat 1.

  2. Algae species identification (optional): users are asked to identify the species of seaweed(s) present in the quadrat, if possible. Two predefined options are provided (Figure 2):

  • Spyridia filamentosa

  • Plocamium species

(a) Spyridia filamentosa

(b) Plocamium species

Figure 2: Photos of two algae species commonly found stranded and floating at the Waipu Cove area. From botanicamarina.wordpress.com and inaturalist.nz.

  1. Notes: add any additional information.

  2. Photos: users are asked to add a photo of the algae or quadrat if needed for identification. Photos are saved in the Survey123 server, linked to the record, which can be used for future identification or further clarification of dubious records.

  3. Submit: press the submit button to save the data. Repeat steps 1–10 (above) for at least 10 quadrats.

Northland Regional Council water quality data

NRC has recently launched an online environmental data hub where relevant data are readily accessible by the public at Environmental data hub. NRC collect water quality data each month at five sites relevant to the algal stranding at Waipu Cove; the sites from north to south include:

  1. Lower Whangarei Harbour a2913, b265 at Mair Bank Outer Marker Pile (code 100190)

  2. Ruakaka Estuary at Princess Road (code 315710)

  3. Waipu Estuary at Johnston Point Road (code 315712)

  4. Waipu Estuary at Hamon Road (code 315711)

  5. Waipu Cove at Beach (code 322923).

Figure 3: Map of the study area showing the location of Northland Regional Council monitoring sites (red dots) relevant to the seaweed stranding events at Waipu Cove.

Environmental variables collected at these sites include a range of physico-chemical water quality parameters that are known drivers of algal blooms, including temperature, nutrients, dissolved oxygen, salinity, among others.

It is recommended that algae sampling is conducted at least monthly at each of the sites shown in Figure 3. Because of the proximity of site 3 and 4 (i.e., the two sites at Waipu Estuary), these two sites could be combined, resulting in a total of four sites sampled monthly. Any additional sampling at different sites within the study area shown in Figure 3, or conducted more frequently than monthly, will be beneficial for the dataset and any future analysis. It is also important to note that data on the absence of seaweed (i.e., zero cover) it is as important as the data on the presence of seaweed and must be accounted for in the dataset.

We plan to review the data after a period of six month to check the quality and completeness of the data. The algal abundance data collected using the online app will be a first and significant step toward understanding stranding events of excessive amounts of drift algae on beaches in the Waipu Cove region and provide a solid footing on which future work can be developed.