The distribution, abundance and seasonality of pelagic marine invertebrate larvae in the maritime Antarctic

Abstract

A survey of pelagic larvae was undertaken between November 1992 and February 1995 at Signy Island, Antarctica (60843' S, 45836' W). A diver-towed net and hand-held plankton pump were used at ¢ve sites of varying depths (6^30 m) and benthic substrata, in a combination of monthly and fortnightly samples. Overall larval ecological diversity was much higher than expected, with 131 morphologically distinct larval forms collected, apparently representing most of the benthic phyla present. The species richness observed is comparable with levels recorded at temperate latitudes, and higher than Arctic data and the implications for Thorson's rule (the inferred cline of reduced pelagic larval diversity towards high latitudes) is discussed. Larval abundances were low (mean 2.6 individuals per m 3 ), which were two to six orders of magnitude lower than peaks in comparable data from temperate and tropical zones. We suggest that the low abundances recorded are a re£ection of both slow developmental rates and a high dilution of larvae, reducing synchrony and spreading larvae over larger distances. Three seasonal periods, during which di¡erent larval types occur, have been identi¢ed. Summer, late summer and winter spawning strategies were discernible, and in some groups larvae occurred throughout the year.

On the origin of Antarctic marine benthic community structure

“…With increasing observations of pelagic larval stages in polar regions, especially in shallow-water benthic organisms [10,[14][15][16], numerous reasons to dismiss Thorson's rule have been proposed (Box 1). Here, we present an interdisciplinary view of the factors involved in determining Antarctic benthic community structure during glacial-interglacial cycles.…”

“…He distinguished between planktotrophic (pelagic) and lecithotrophic larvae, which he considered to be benthic living only [8]. We now know of various intermediate larval feeding modes and drifting stages [7,60], but the total number of larval morphotypes known from Antarctic waters is still !250 [15,16]. Increasing records of pelagic larvae in Antarctic waters have frequently been used to challenge this idea [10,[14][15][16]58,59], but even allowing for missing species identification and unknown energetic conditions in most larval records [15,16], the lack of planktonic larvae is striking compared with the benthic diversity of Antarctic waters [61,62].…”

Brooding and Species Diversity in the Southern Ocean: Selection for Brooders or Speciation within Brooding Clades?

“…Similarly, Thatje et al (2005b) argue that the predominance of developmental lecithotrophy in the Antarctic is the consequence of the near-complete extinction of benthic communities during glacial maxima and recolonization from deeper waters where species had undergone an "evolutionary temperature adaptation" that led to lecithotrophy. However, no evidence supports the idea that either nonpelagic development or lecithotrophy is an adaptation to low temperature, and the fact that a wide variety of both planktotrophic and lecithotrophic pelagic larvae have been found in both Antarctic and Arctic waters (e.g., Thorson, 1936;Stanwell-Smith et al, 1999;Sewell, 2005;Palma et al, 2007;Vázquez, 2007;Fetzer and Arntz, 2008) persuasively indicates that marine invertebrate larvae are able to survive and grow at freezing temperatureseven under high pressures found in the deep sea (Tyler et al, 2000), where many species have pelagic, planktotrophic larvae (Gage and Tyler, 1991;however, see below).…”

“…This notion was persuasively reinforced by Thorson (1936Thorson ( , 1950, who focused on gastropods in the Northern Hemisphere, and Mileikovsky (1971), who termed it "Thorson's rule." Both Thorson (1936) and Mileikovsky (1971), however, recognized many exceptions, and subsequently, with more information and reanalyses of earlier data, the generality of Thorson's rule weakened substantially (Pearse et al, 1991;Clarke, 1992;Hain and Arnaud, 1992;Pearse, 1994;Young, 1994;Stanwell-Smith et al, 1999;Arntz and Gili, 2001;Schluter and Rachor, 2001;Absher et al, 2003;Sewell, 2005;Vázquez et al, 2007;Fetzer and Arntz, 2008). We now know that many of the most abundant species in Antarctic waters, especially those in shallow water, have pelagic larvae as in other areas of the world.…”

Desalination plants as plankton sampling devices in temporal studies: proof‐of‐concept and suggestions for the future

“…data). This suggests that in environments such as Antarctica, where meroplankton abundance is low (Stanwell-Smith et al 1999;Sewell 2005;Sewell et al 2006), the PF of a desalination plant may provide an efficient, cost-effective method for sampling meroplankton biodiversity.…”