Publication Date:
2024-06-01
Description:
Shallow-water rhodolith beds are rare in the Mediterranean Sea and generally poorly
known. The Punta de la Mona rhodolith bed extends for 16,000 square meters in shallow
and oligotrophic waters at the southern coast of Spain, off Almuñecar in the Alborán Sea.
We present a detailed analysis of the structure (rhodolith cover and density, rhodolith size
and shape, sediment granulometry) and morphospecies composition of the bed along a
depth gradient. A stratified sampling was carried out at six depths (9, 12, 15, 18, 21, and
24 m), estimating rhodolith cover and abundance; rhodoliths were collected from one 30
by 30 cm quadrat for each transect, resulting in 18 samples and a total of 656 rhodoliths.
The collected rhodoliths were measured and the coralline algal components identified
morphoanatomically through a stereomicroscope and SEM. Sediment on the seafloor
mainly consisted of pebbles and cobbles; the highest rhodolith cover occurred between 15
and 18 m, and the lowest at the shallowest and deepest transects (9 and 24 m). Mean
Rhodolith size was similar throughout the depth range (23–35 mm) with a slight increase at
24 m, although the largest rhodoliths occurred at 21 m. In monospecific rhodoliths, size
depended more on the forming species than on depth. We found 25 non-geniculate
coralline morphospecies, nearly all rhodolith-forming morphospecies reported in the
Mediterranean Sea in recent accounts. The highest morphospecies richness (18–19)
and proportional abundance were found at intermediate depths (15–18 m), where
rhodolith cover is also highest. Lithophyllum incrustans and Lithophyllum dentatum
dominated at shallow depths (9–12 m), whereas Lithothamnion valens was the
dominant species at intermediate and greater depths. Overall, the latter species was
the most common in the rhodolith bed. The shallow-water rhodolith bed in Punta de la
Mona is probably the most diverse in the Mediterranean Sea. This highlights the
importance of the conservation of this habitat and, in general, emphasizes the role of
the Alborán Sea as a diversity center of coralline algae. The Punta de la Mona example
contradicts the common assumption in the geological literature that rhodolith beds are
indicative of oligophotic environments with high nutrients levels.
Keywords:
coralline red algae
;
depth-gradient patterns
;
rhodolith cover and size
;
rhodolith diversity
;
Alboran sea
Repository Name:
National Museum of Natural History, Netherlands
Type:
info:eu-repo/semantics/article
Format:
application/pdf
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