To continue our learning on Project SPAT, Revive Our Gulf and Kelly Tarlton’s Marine Wildlife Trust have been undertaking further investigation into kūtai spat (baby kūtai) settlement on the two seaweed species in the Hauraki Gulf that were previously identified as the preferred seaweed for kūtai spat settlement. These seaweeds are Xiphophora chondrophylla (a brown seaweed) and Pterocladia sp. (a red seaweed). See further details about how we previously identified these preferred seaweeds here.
One of our current challenges in restoration projects is recruitment (i.e., juvenile kūtai joining the adult bed to increase the size of the bed and the number of kūtai). One hypothesis of why this might be happening is the lack of suitable structures, like seaweed, for the kūtai larvae to settle on.
Settling on seaweed and other structures in the larval phase is a critical part of the kūtai lifecycle. Kūtai settlement occurs in two phases. The first phase (termed “primary settlement”) is usually on seaweed, and the second phase (termed “secondary settlement”) is usually in an environment where there are already adult kūtai. One idea for restoration to support successful recruitment is to transplant seaweed covered in kūtai spat alongside our restored kūtai beds. When the kūtai are ready for their second settlement, they could then move off the seaweed and into the adult kūtai bed, helping to grow the beds.
The research
This research looked into how long kūtai spat stay on the seaweed after they first settle, and how they grow. This information is important to know if we choose to transplant seaweed with kūtai spat on it as it informs us of the timing of seaweed transplantation and how we can find the optimal conditions for enhancing kūtai recruitment.
Seaweed was collected from the inner Hauraki Gulf, and kūtai spat were provided by SpatNZ in Nelson. The experiments were undertaken between 29 May 2024 and 6 July 2024 in specially designed tanks at SEA LIFE Kelly Tarlton’s Aquarium. Although conducted in a controlled environment, which won’t exactly mimic the variations in the ocean, the set-up provided researchers with a valuable opportunity to observe the spat behaviours and preferences over a continuous five-week period.
Photos supplied by Kelly Tarlton’s Marine Wildlife Trust, showing the experimental setup.
Interesting results of this experiment and next steps
Part way through the experiment the spat were transferred on the seaweeds to tanks with fresh brown and red seaweed and rocks to test which the spat then preferred. It was observed that kūtai spat left the old seaweed and moved onto the fresher seaweed. Very few kūtai settled on the rocks. These results tell us that the type and quality of seaweed is likely important for kūtai spat health and growth.
The number of kūtai spat that settled on the seaweed was highest within the first week of the experiment, which also suggests that if we want to translocate seaweed this should be done soon after spat settlement.
We still have lots to learn about kūtai spat and their interactions with seaweed, but this information helps us think about future experiments with seaweeds and other settlement structures.