A dedication to my Australian colleagues and their small Ecklonia radiata. Thomas, a challenge from Eric: what is the social significance of your kelp ‘forests?’
Last week Friday we went diving off the tip of the Cape of Good Hope. It was a dive we had been planning for months, only generally being accessible when the ocean swell is completely down. It was the perfect day: False Bay was flat as a pond, and after the deeper dive off the Point (~14 m) we spent the rest of the day in the Bay doing various bits of kelp research.
But the point of this piece is to talk about the giant specimen of Ecklonia maxima that the divers (Thomas Wernberg, Robert Schlegel and Eric van Onselen) found. In a previous post I mentioned that there were unconfirmed reports of E. maxima specimens of up to 15 m in length – I don’t know where from. As far as I was concerned these were legendary – almost mythical – kelps as I don’t know anyone who has ever actually seen one, of if they think they did, really measured one.
We measured them. Thirteen of them. The maximum length is 16.91 m, and the average is 13.41 m. There are some interesting morphometric relationships between these kelps and those from other populations, but more of this in forthcoming publications.
We also sampled Laminaria pallida from the same deep site, and these are equally impressive. Generally Laminaria is a smaller kelp in stature. On average they are around 2.38 m in length, but the average length of the population at the deep site is 3.53 m. Interestingly, Stegenga, Bolton and Anderson’s 1997 red book mentions specimens to 10 m long in the northern portion of South Africa and into Namibia. I am not convinced, but we will certainly search for them.
Yesterday saw the start of Project Robokelp, which will shed light onto the the role of dense kelps beds of Ecklonia maxima in influencing the hydrodynamics of the nearshore waters around the Cape Peninsula, and hopefully further afield.
Electronic loggers capable of measuring acceleration in three dimensions, temperature, and light intensity were installed as part of a pilot project onto two kelps in waters of around 5-6 m deep. The data will allow us to understand how kelps modify the hydrodynamics in and around kelps, and if kelps are able to facilitate the warming of surface waters around the beds. Data will not only benefit the Kelps and Climate Change Programme, but also enhance our understanding of the finer scale nuances of the thermal regime of seawater along our coastline. Sam Bolton and Robert Schlegel will process the data as part of their MSc and PhD degrees, respectively.
Last weekend a group of us went to the De Hoop Nature Reserve, about 70 km east of the Southern-most tip of the African continent, Cape Agulhas. The intention was to install more temperature recorders there to form part of the South African Coastal Temperature Network, and to explore some of the kelp beds there. Sadly, neither of the objectives could be achieved due to permitting issues and undiveable sea conditions (although Eric did snorkel in some sheltered areas). A temperature recorder already exists around Koppie Alleen, but we also wanted to place one at Noetsie further to the east.
The region around Koppie Alleen is the subject of our scrutiny, as a recent paper (Bolton et al., 2012) has shown that kelp (Ecklonia maxima) has only recently established itself there, after historically being limited to a region about 73 km to the west. Certainly the kelps look quite different from their counterparts elsewhere in the Western Cape: for one, they are much smaller in stature. Also, there are questions about whether or not they are hybrids of E. maxima and the smaller E. radiata, which is abundant along the south coast.
Our existing data (AJ Smit, unpublished) show that the region is cooling, as we have hypothesised in the Bolton et al. (2012) paper. See the second figure here.
Bolton, J. J., Anderson, R. J., Smit, A. J., & Rothman, M. D. (2012). South African kelp moving eastwards: the discovery of Ecklonia maxima (Osbeck) Papenfuss at De Hoop Nature Reserve on the south coast of South Africa. African Journal of Marine Science, 34(1), 147–151.
Ecklonia maxima is known to occur along the coast of mainland South Africa and Namibia, the island of St Helena (Atlantic Ocean), St Paul Island (Indian Ocean), the Falkland Islands and Islas Malvinas near South America, and the Auckland Islands near Australia and New Zealand. Except for South Africa and Namibia, very little is known about the biology of the kelp in these regions. Even in South Africa, little is known about the population size frequency distribution. Considering the maximum length of the species, an early report by George Papenfuss (1942) states that “plants may attain a length of seven meters or more from base of stipe to tips of longest pinnae” and more recently Stegenga, Bolton, and Anderson (1997) state that it attains lengths of up to 15 m.
Certainly we know that very longer plants exist, for example the 10.41 m and 9.90 m individuals recently collected at Betty’s Bay, and the somewhat shorter 8.73 m long plant from just off Baboon Rock in False Bay. Local divers speak of very tall plants off the tip of the Cape Peninsula, with unconfirmed reports of 12 to 15 m specimens in the vicinity of Southwestern Reefs, Anvil Rock and Bellows.
Over the course of the next few weeks we will undertake mini-expeditions to these reefs to assess the population structure of Ecklonia there. Not only will we gain new insight into the biology of the plants, but also about the structure and composition of the communities associated with these kelp forests.
GPS coordinates: Syy.yyyyy° Exx.xxxxx°
Divers visited this site on 10 April 2015, and the dive for kelp collections was from 10:23 to 10:33 (Robert S, Robert W, Sam; Eric as surface swimmer). The rocks around the lighthouse come up to the surface. The rocky outcropping from which these kelp were sampled came up to 3 m below the surface with gullies going down to 7 m before the entire rock dropped to 16 m rapidly. Only Laminaria was collected as Ecklonia was not present. The bottom topography is a round rock dome covered with thick old growths of redbait. Some almost a metre long. Nothing else grew on the top of the rocks other than these ascidians. The Laminaria grew on the edges of the rock dome at a depth of 5.5 to ~8 m on the hard rock outcroppings. The kelp were only sampled between 5.5 – 6.5 m. No sand was present but anemones and urchins could be found in the gullys. The rocky outcroppings on which the healthiest and largest Laminaria could be found had a more diverse assemblage of life.
GPS coordinates: Syy.yyyyy° Exx.xxxxx°
Divers visited this site on 10 April 2015, and the dive for kelp collections was from 10:45 to 11:05 (Robert S, Robert W, Sam; Eric as surface swimmer). The kelp bed behind the well known dive site A-Frame was sampled. The rocky outcropping from which these kelp were sampled came up to 1 m below the surface with the largest boulder sitting well above the surface. Laminaria and Ecklonia were sampled from similar depths (6 m?). The bottom topography is a few large boulders forming a reef. Ecklonia grow at the shallowest 1 m depth on top down to ~6 m, with the sand in between the boulder reef systems starting at 7 m. Sparse Laminaria forming a border around the denser Ecklonia beds were sampled from ~6 m. Reefs were not heavily populated by grazers or other organisms. Saw a few small shy sharks.
GPS coordinates: Syy.yyyyy° Exx.xxxxx°
Divers visited this site on 10 April 2015, and the dive for kelp collections was from 11:53 to 12:16 (Robert S, Sam; Robert W and Eric as surface swimmers). The Ecklonia were harvested at 6 m while the sparse Laminaria could only be found below 10 m and were sampled between 10 – 12 m. The bottom topography where the Ecklonia was sampled was a smooth reef sloping down with some larger boulders. The reef was populated with other large algal species, crustose corallines, sponges, anemones, rock lobsters, crabs and other reef goers. Several small shy sharks and a few large pyjama cat sharks were seen, too. This has been the most species rich site thus far. The reef ended at ~12 m in sand and this lower portion had many smaller rocks from which Ecklonia and Laminaria were found. The Ecklonia were still far more prevalent than the Laminaria, though the later were in very good condition. The kelp became denser the deeper the reef went. We had seals playing with us while sampling the Laminaria.
Three sites were scouted on 9 April 2015 via snorkel at Muizenberg but no kelps were sampled and only Ecklonia was seen.
GPS coordinates site 1: Syy.yyyyy° Exx.xxxxx°
Swam out from Bailey’s Cottage along flat rock shelf. Ecklonia found as sparse individuals growing on the flat shelf at a depth of ~ 1-2 m. Snorkel from ~9:00 – 9:20 (Robert S, Robert W and Eric surface swimmers).
Flat rock mostly bare with some crustose coralline algae. Sparse boulders populated with anemones and some other organisms. Wave action was too large to be able to clearly identify the population structure.
GPS coordinates site 2: Syy.yyyyy° Exx.xxxxx°
Swam out from coast ~100 m South from site 1. Sandy beach with boulders in intertidal range. Ecklonia found in small but dense groups growing on or next to boulders at a depth of ~ 1-2 m. These plants looked very sad. Snorkel from ~9:30 – 9:50 (Robert S, Robert W and Eric surface swimmers).
Bare sandy bottom with sparse boulders populated with crustose coralline and some other organisms. Wave action was too large to be able to clearly identify the population structure.
GPS coordinates site 3: Syy.yyyyy° Exx.xxxxx°
Swam out from coast ~100m North from site 1. Ecklonia found as sparse groups growing on the flat rock shelf and around boulders at a depth of ~ 1 m. Snorkel from from ~10:00 – 10:20 (Robert S and Robert W surface swimmers).
Shallow intertidal pool with large boulders protruding from water. Area around boulders mostly covered in sand. Boulders and smaller rocks covered in many different types of algae.
Two beds directly next to each other were sampled in Kalk Bay:
GPS coordinates: Syy.yyyyy° Exx.xxxxx°
Divers visited this site on 9 April 2015, and the dive for kelp collections was from 11:13 to 11:24 (Robert S, Robert W: Eric as surface swimmer). The two reefs visited are situated at a depth of 6.5 and 5.5 m. Only Ecklonia was collected as Laminaria were not present. The bottom topography is a flat rock shelf slowly sloping down with protruding reefs covered in biomass. The reefs have sparse beds of Ecklonia (~20 individuals per bed). The deeper reef was covered in anemones and red bait and had very little to no grazers. The health of the kelp at this reef was poor. Twenty metres closer to shore, the shallower reef was covered with urchins and smaller algae with little to no red bait or anemones. The health of the kelp at this reef was markedly better. Dense populations of brittle stars could be found between reefs.
Two beds were sampled in Betty’s:
GPS coordinates, Site 1: Syy.yyyyy° Exx.xxxxx°
Divers visited this site on 31 May 2015, and the dive for kelp collections was from 10:25 to 10:55. This site is situated at a depth of 8 m and Laminaria and Ecklonia were collected (Laminaria does not occur at shallower depths here). The bottom topography is rocky with large boulders. The boulders have dense beds of Ecklonia on top and on the sides with no Laminaria occurring within these beds. Laminaria occur either at the fringes of these beds or as their own small clumps on smaller boulders and rocks. There is sand between the boulders and rocks.
GPS coordinates, Site 2: Syy.yyyyy° Exx.xxxxx°
The next day (1 April 2015), the site was visited again and a reef at 6 m was chosen for the collection of Ecklonia only – this was done to ensure that the depth was commensurate with the collections in False Bay, which are all at a depth of 6 m. The bottom is relatively flat, for a kelp reef, with very few large boulders. The rocky bottom is mostly covered with crusting coralline, sponges or light folios algae. Sandy gullies occur between the rocky kelp beds and tend to be 1 or 2 metres deeper. The overall depth gradually increases away from shore.
The Betty’s Bay collections on 31 May and 1 April 2015 coincided with Ross Coppin’s set-up and sampling of the kelp beds for his MSc.
GPS coordinates: S34.25522° E18.47825°
Kelp collection on 25 March 2015. Ecklonia and Laminaria taken from granite boulders at a depth of ~ 5.5 m. Dive from 12:03 – 12:43 (Robert S and Robert W; Ross and Sam as surface swimmers). The boulders are situated on sand at a depth of approx. 7 m.
Ecklonia occupy the tops of the boulders, while the Laminaria seems to be positioned sparsely and haphazardly in-between as individual plants, usually 1 m lower than Ecklonia. No Laminaria were found within dense beds of Ecklonia.