Abstract
Diatom community composition and abundances on different thallus parts of adult and juvenile specimens of Eckloniamaxima and Laminariapallida were examined in False Bay, South Africa, using light and scanning electron microscopy. Altogether, 288 thallus portions were analysed. Diatom abundances ranged from 0 to 404 cells mm−2 and were generally higher on E. maxima and juvenile thalli than L. pallida and adult specimens. Moreover, diatom abundances differed between the various thallus parts, being highest on the upper blade and lowest on the primary blade. A total of 48 diatom taxa belonging to 28 genera were found. Gomphoseptatum Medlin, Nagumoea Witkowski and Kociolek, Cocconeis Ehrenberg, and Navicula Bory were the most frequently occurring genera, being present in 84%, 65%, 62.5%, and 45% of the analysed samples, respectively. Among these, Cocconeis and Gomphoseptatum were the most abundant, contributing 50% and 27% of total diatom cells counted collectively across all samples. Permutational multivariate analysis of variance (PERMANOVA) revealed that all investigated main factors (kelp species and age and thallus part), as well as their two- and three-way interactions, except for the interaction between the host species and age, were significant. The high residual variance (72%) indicated that the sum of other unexamined factors contributed the largest component of the variation observed in the kelp-associated diatom communities, and grazing and possible defence strategies utilised by kelps are proposed as processes playing an important role in the structuring of epiphytic diatom communities. Possible endophytism of tissue-boring diatoms colonizing both kelp species is briefly discussed.
Highlights
Kelp forests thrive along most rocky shorelines in temperate and polar waters across the globe [1].These dynamic biogenic habitats host large biodiversity of flora and fauna, forming the basis of complex marine food webs and providing, directly and indirectly, numerous valuable ecosystem services to humans, including food provision, the supply of raw materials for industry, atmospheric gas balance and climate regulation, disturbance prevention, and nutrient cycling [1,2]
The scanning electron microscope (SEM) analyses revealed that epiphytic diatoms were unevenly distributed across the various thallus parts and subsamples (Figures 3 and 4)
Based on the SEM analysis of the kelp surface, we infer that both grazing kelp response to grazer-caused damage and biofouling by epiphytes, as well as specific life strategies and the kelp response to grazer-caused damage and biofouling by epiphytes, as well as specific life employed by kelp-associated diatoms, may be responsible for a large portion of the unexplained strategies employed by kelp-associated diatoms, may be responsible for a large portion of the variation
Summary
Kelp forests thrive along most rocky shorelines in temperate and polar waters across the globe [1] These dynamic biogenic habitats host large biodiversity of flora and fauna, forming the basis of complex marine food webs and providing, directly and indirectly, numerous valuable ecosystem services to humans, including food provision, the supply of raw materials for industry, atmospheric gas balance and climate regulation, disturbance prevention (flood buffering and storm protection), and nutrient cycling [1,2]. Macroalgae may interact with epiphytes on their surfaces by either enhancing or deterring their growth [5,10] Those effects may be species-specific [10,11,12,13], may be related to the host morphology [6,7,10,14] or the thallus part [10,11,15], and may change throughout the host organism life cycle [16]. The level of epiphytic colonisation in Ecklonia radiata (C.Agardh) J.Agardh was positively correlated with the exposure time of the various thallus parts to the marine environment, and was related to the thallus age [17]
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